Micro Final

Which of the following patients is at highest risk for invasive aspergillosis, that is, invasion of Aspergillus hyphae into tissue and blood vessels and potential dissemination to other organs? a. A 16-year-old girl that has been neutropenic for one month during induction chemotherapy for acute myelogenous leukemia b. A 33-year-old man with asthma and a history of allergic bronchopulmonary aspergillosis c. A 60-year-old woman that was treated for tuberculosis as a child and developed a pulmonary cavity that is now superinfected with an aspergillus fungal ball (aspergilloma) d. A 70-year-old man that lives in a mold-ridden cinderblock house since the Katrina hurricane destroyed most of his neighborhood e. A new born baby discovered in the morning after being abandoned on a mulch pile (?!?)

a. A 16-year-old girl that has been neutropenic for one month during induction chemotherapy for acute myelogenous leukemia

Another of your patients, a 60-year-old man with colon cancer has undergone a colectomy and has a central line in place. He develops low grade fevers and is started on broad spectrum antibiotics with vancomycin and ceftazidime. Two-days later, three separate blood cultures begin to grow a yeast. A day after that, the yeast is identified as Candida glabrata. He is otherwise well appearing with normal vital signs. In addition to starting antifungal medication, your team decides that the central line should be removed because: a. Candida forms biofilms that are more resistant to antifungals and will cause the infection to relapse after treatment b. Antifungal medication is not compatible with central catheters because of the proximity to the heart could cause QT elongation and arrhythmia. It should only be given through peripheral intravenous lines c. Candida is a skin colonizer, so the best treatment will be topical and not intravenous. The central line is not needed d. Antibiotics and antifungals should not be delivered through the same intravenous line. He will need multiple peripheral lines instead e. He is well appearing with normal vital signs and a central line will just increase his risk of further infections. You will treat him with oral antifungal medications

a. Candida forms biofilms that are more resistant to antifungals and will cause the infection to relapse after treatment

You are counseling a patient that was diagnosed with HIV. She is in the clinically latent phase of the infection and has no symptoms. She has never taken medications for more than a day or two. The regimen involves taking several pills every day. You need to convince her that starting a drug regimen involving multiple antiretroviral medications is important. Which of the following arguments would be best to use? a. Combining several medications prevents the virus from becoming resistant to the treatment b. One of the medications is for inhibiting virus replication but an equally important one is to stimulate the differentiation of CD4 T-cells in the bone marrow c. Taking all the medications as prescribed will likely eliminate the HIV virus and cure the infection d. One medication is not sufficient because each targets a different part of the virus, but taking a different one each day is OK e. All the medications should be taken together since some prevent side effects from the others such as nausea

a. Combining several medications prevents the virus from becoming resistant to the treatment

A child in the local elementary school developed fever and a persistent cough three weeks after traveling to Disneyland by car across the California San Joaquin valley. Her astute pediatrician considered coccidiodomycosis and tuberculosis based on the exposure history and epidemiology and obtained a chest radiograph that revealed a focal infiltrate. Tests for tuberculosis are negative, while serologic tests for antibodies against Coccidioides immitis confirmed the diagnosis. You are asked by her elementary school teacher, whether the child can return to class or whether there is a risk of contagion to other students? You explain that: a. Endemic fungi are not transmitted person-to-person and are acquired only from environmental sources. There is no danger of transmission to other children. b. You will start her on high dose oral Fluconazole and thus the risk of transmission to others will be minimal. c. She will not be able to attend school in the near future because there are no oral formulations to treat this infection and she would be putting others at high risk if she attends school while untreated. d. Pulmonary coccidioidomycosis is a sentinel infection suggesting severe immunosuppression like AIDS, thus she will be at risk of acquiring other infections if she attends school. e. She can attend school but should wear an N-95 protective mask for the first month until you repeat a chest radiograph to make sure the fungal pneumonia is treated.

a. Endemic fungi are not transmitted person-to-person and are acquired only from environmental sources. There is no danger of transmission to other children.

Your patient's son is a healthy-appearing 24-year-old man, without a history of cough, fevers or weight loss. Since he has been exposed to his father with active pulmonary TB, you decide to test him and see if he has been infected himself. You find out that he was also born in India and received BCG at birth. You therefore choose to obtain an IGRA instead of placing a TST. The IGRA test is more specific than the TST because: a. IGRAs utilize Mtb peptide antigens lost in the BCG vaccine strain during attenuation b. IGRAs measure interferon gamma, which is a more specific cytokine response to TB than the multiple cellular responses measured by the TST c. IGRAs cannot detect reactivity to antigens in any nontuberculous mycobacterial species d. Antigens used for IGRAs are not found in M. bovis which is more closely related to M. avium than to Mtb e. PPD is a mixture of antigens from the BCG vaccine

a. IGRAs utilize Mtb peptide antigens lost in the BCG vaccine strain during attenuation

The bacterial cell envelope of Gram-negative bacteria differs from that of Gram-positive bacteria in that, a. It has two membranes surrounding the peptidoglycan b. Its lipooligosaccharides are modified so that lysozyme cannot degrade them c. The inner membrane contain porins that can actively pump antibiotics out of the periplasmic space d. The cell wall is much thicker thus making it difficult for beta-lactam antibiotics to penetrate e. It is impervious to antimicrobial peptides

a. It has two membranes surrounding the peptidoglycan

You are the resident taking care of a 19-year-old adolescent young man with acute myelocytic leukemia (AML) who is experiencing prolonged neutropenia during an attempted hematopoietic stem cell transplantation. He develops fevers and a chest radiograph shows new pulmonary nodular infiltrates surrounded by "ground glass" opacity. You are concerned about an infection due to Aspergillus fumigatus. Which of the following established microbiological tests is most consistent with this diagnosis? a. Positive blood test for galactomannan b. Positive blood test for polysaccharide capsule antigen c. Positive blood test for ergosterol d. Blood cultures growing a yeast-like fungus e. Positive urine antigen test for Aspergillus

a. Positive blood test for galactomannan

Several thermally dimorphic fungi can be serious pathogens in immunocompetent hosts. These fungi are characterized by having a different morphology in the environment vs inside the mammalian host. These fungi grow as a. Yeasts within tissues at mammalian body temperature but as molds at room temperature b. Molds at mammalian body temperatures from where they form conidia to disperse and are found as mucoid yeast biofilms in the soil c. Pseudohyphae on the skin but as highly branching septate hyphae when they invade deeper tissues at higher body temperature d. Invasive mycelia when they are in the high temperature and high oxygen content of the lung, but as small budding yeasts between keratinocytes in the skin e. Large yeasts with a thick glucoronic acid capsule in the tissue which prevents phagocytosis, and as small yeasts covered in a thin layer of glycoprotein that serves to help extract nutrients from the soil in the environment

a. Yeasts within tissues at mammalian body temperature but as molds at room temperature

Jock itch, ringworm, and athlete's foot all share which of the following? a. are conditions caused by filamentous fungi with the ability to digest, metabolize and survive on keratin b. are diseases caused by fungal spores from soil that germinate in the humid environment of public bathrooms and locker rooms c. typically become superinfected with bacteria and thus require both antifungal and antibiotics for treatment d. are rare and difficult to diagnose requiring a biopsy for accurate determination of etiology e. when they cause symptoms of itching and pain they involve deep dermal structures of the skin

a. are conditions caused by filamentous fungi with the ability to digest, metabolize and survive on keratin

Penicillin-binding-proteins or PBPs are: a. enzymes that crosslink the stem-peptides in the nascent peptidoglycan chains b. bound and inactivated by vancomycin which is the reason this antibiotic is very broad spectrum c. only found in gram-positive bacteria and thus gram negatives are resistant to penicillins d. secreted proteins that bind to penicillin and inactivate it thus making the bacteria resistant e. proteins made by fungi that have a high affinity for penicillins and thus can be used to purify the antibiotics in large quantities

a. enzymes that crosslink the stem-peptides in the nascent peptidoglycan chains

The relative capacity of a microorganism to cause damage to the host is called "virulence". This is a property that: a. is dictated by both pathogen characteristics and the immune responses of the host b. Is strongly correlated with the infectivity of a microorganism c. Is most highly apparent in the preferred host species d. Is inherent in the genetic sequences of virulence genes in the pathogen e. Is equivalent amongst different strains of a microorganism and thus can serve as a way of differentiating microbial species

a. is dictated by both pathogen characteristics and the immune responses of the host

Once inside the host, pathogens hide from the host immune system in order to persist and replicate. One important way some bacteria avoid phagocytosis is: a. to produce polysaccharide capsules that can block phagocyte receptors from detecting bacterial surfaces and inhibit complement b. to secrete endotoxin which inhibits the phagocytic machinery of macrophages c. to produce superantigens to overwhelm host immune responses and allow unchecked replication in the bloodstream d. to make neurotoxins, like botulinum toxin, which cause respiratory arrest thus completely disarming the immune response e. to avoid phagolysosome fusion in order to persist inside host cell vacuoles

a. to produce polysaccharide capsules that can block phagocyte receptors from detecting bacterial surfaces and inhibit complement

You are a star Medical Student that has discovered a new gram-negative bacterium, and isolated several of its virulence factors. Now you want to make a vaccine to prevent disease with this microbe. Of the following components you might add to your vaccine which do you think would make it most specific and effective in preventing infection without affecting the commensal microbiota or injuring the host: a. An active exotoxin that acts as a neurotoxin by blocking synaptic transmission b. A purified pilus tip protein involved in initial attachment to the host epithelium via a cell surface receptor c. Purified endotoxin from the outer membrane of your pathogen d. A plasmid from your pathogen containing its antibiotic resistance cassette e. A bacterial ribosomal subunit responsible for protein production in the pathogen

b. A purified pilus tip protein involved in initial attachment to the host epithelium via a cell surface receptor

Which of the following molecules is a lipid component of the fungal membrane and an important target of some antifungals? a. Chitin b. Ergosterol c. Beta-glucans d. Galactomannan e. Lipomannan

b. Ergosterol

After mosquitos deliver Plasmodium falciparum sporozoites into the bloodstream, the first cells to be invaded by the parasites are: a. Keratinocytes in the skin b. Hepatocytes in the liver c. Dendritic cells in the dermis d. Red blood cells in the peripheral circulation e. Macrophages in the bone marrow

b. Hepatocytes in the liver

Patients with HIV/AIDS are at risk for serious sequelae from Toxoplasma gondii infection because: a. HIV infection of cells harboring Toxoplasma gondii undergo apoptosis forcing the parasites to exit, reinvade and multiply the number of infected cells b. Latent Toxoplasma gondii bradyzoites in the tissue can reactivate when immune responses are deficient c. Antiretroviral medication stimulates replication of Toxoplasma gondii d. Ingested oocytes are much more likely to migrate to the brain in patients with HIV because of a defective blood-brain barrier e. Persons with HIV/AIDS harbor highly infectious forms of Toxoplasma gondii spreading the infection within their community

b. Latent Toxoplasma gondii bradyzoites in the tissue can reactivate when immune responses are deficient

You are taking care of a 6-year-old girl with a fever, sore throat and exudative tonsillitis. The rapid strep test was negative but the microbiology lab now says her throat culture is growing Gram-positive cocci. These bacteria could represent a pathogen causing her pharyngitis or a number of commensal bacteria that reside in the throat. Which of the following descriptions would be consistent with Streptococcus pyogenes? a. The Gram stain shows Gram-positive cocci in groups. The blood agar plate shows no hemolysis around the colonies. b. The Gram stain shows Gram-positive cocci in short chains. The blood agar plate shows a zone of clear hemolysis around the colonies. c. The Gram stain shows Gram-positive cocci in short chains. The blood agar plate shows no hemolysis around the colonies. d. The Gram stain shows Gram-positive cocci in long chains. The blood agar plate shows a zone of greenish hemolysis around the colonies. e. The Gram stain shows Gram-positive cocci in groups. The blood agar plate shows a zone of greenish hemolysis around the colonies.

b. The Gram stain shows Gram-positive cocci in short chains. The blood agar plate shows a zone of clear hemolysis around the colonies.

Which of the following statements is true about the 23-valent pneumococcal vaccine? a. This vaccine is recommended for all patients on an annual basis due to antigenic drift. b. The polysaccharide antigens included in this vaccine are normally present in the capsule of this microorganism. c. The vaccine covers all known serotypes of Streptococcus pneumoniae d. This vaccine induces immunity to surface bacterial antigens normally hidden from immune recognition. e. This vaccine induces immunity to surface protein antigens common to most penicillin-sensitive strains of Streptococcus pneumoniae.

b. The polysaccharide antigens included in this vaccine are normally present in the capsule of this microorganism.

One reason many Gram-negative bacteria are resistant to penicillin is that: a. The inner membrane porins have evolved mutations making them impermeable to penicillin b. Their outer membrane restricts penetration of the antibiotic and many make beta-lactamases that concentrate in the periplasm c. Most Gram-negative bacteria have acquired a gene for the production of penicillin efflux pumps that rapidly secrete the antibiotic out of the bacterial cell cytoplasm d. The target of beta-lactam antibiotics is not essential in Gram-negative bacteria because they do not need to cross-link their thin peptidoglycan e. They have acquired mutations in the genes for LPS which no longer binds to penicillin

b. Their outer membrane restricts penetration of the antibiotic and many make beta-lactamases that concentrate in the periplasm

Vincent is a 61-year-old man with a history of smoking one pack of cigarettes a day for the last 30 years. He also drinks a couple of glasses of whiskey each evening. He comes to your clinic with a high fever of 41°C and shortness of breath. His exam reveals crackles and decreased breath sounds in the right lower chest. A chest radiograph shows a lobar pneumonia. His sputum has many short Gram-negative bacilli as well as neutrophils. Which of the following is the most common mechanism that explains his clinical condition: a. Fungal spores of Aspergillus niger are commonly found in tobacco. Because Vincent rolls his own cigarettes and they lack a filter, he inhaled the spores and bypassed the glottis. The spores germinated in the alveoli and produced hyphae which were too large to be engulfed by the resident macrophages. Hyphal obstruction of the airways and local inflammation produced his symptoms and radiographic picture. b. While sleeping, Vincent had episodes of microaspiration that brought resident bacteria from the nasopharynx into the lower airways. Cigarette smoke had injured his respiratory cilia and caused ectasia of small airways trapping and impairing the clearance of the bacteria. An encapsulated type of Haemophilus influenzae avoided phagocytosis by neutrophils and alveolar macrophages and began to grow in the alveoli, eliciting a strong neutrophilic response. c. Mycoplasma pneumoniae resident in Vincent's upper airway avoided clearance thanks to the toxic effects of cigarette smoke on the respiratory epithelium. These bacteria invaded the epithelium intracellularly and expanded, making their way into the lower airways where they initiated a pneumonia. d. Vincent drank too much whiskey one night, which lead to nausea, retching and vomiting. His airway protection was impaired by alcohol allowing gastric juices contaminated with bacteria to reach the alveoli of his right lower lobe. E. coli, resident in the stomach, initiated an infection in the lung aided by the tissue destruction caused by the caustic gastric acid. e. Because of the effects of cigarette smoke on the eustachian tube, Vincent developed a purulent otitis media due to infection with Streptococcus pneumoniae. The bacterial IgA protease prevented opsonization and clearance by neutrophils, and Vincent became bacteremic. Bacteria from the bloodstream seeded the pulmonary vasculature initiating the pneumonia and causing his symptoms and clinical picture.

b. While sleeping, Vincent had episodes of microaspiration that brought resident bacteria from the nasopharynx into the lower airways. Cigarette smoke had injured his respiratory cilia and caused ectasia of small airways trapping and impairing the clearance of the bacteria. An encapsulated type of Haemophilus influenzae avoided phagocytosis by neutrophils and alveolar macrophages and began to grow in the alveoli, eliciting a strong neutrophilic response.

Your patient with Candida glabrata bloodstream infection was started on Caspofungin, an echinocandin. Your colleague is concerned that the antifungal agent that you have recommended might have excessive toxicity due to inhibition of both the fungal protein targeted by this medication as well as the analogous human enzyme. Which is the most appropriate response? a. You acknowledge that folic acid synthesis is a common process in both fungi and humans, and you review the patient's medication list to ensure that there are no other medications inhibiting this process. b. You indicate that beta-glucan synthesis is a fungal-specific process, and that there is no analogous mammalian enzyme. c. You indicate that ergosterol biosynthesis is a fungal-specific process, and that there is no analogous mammalian enzyme. d. You choose an alternative antifungal agent since caspofungin has no activity against pathogenic yeasts. e. You explain that the isoform of the human enzyme targeted by caspofungin is only present in certain ethnic populations that do not include your patient.

b. You indicate that beta-glucan synthesis is a fungal-specific process, and that there is no analogous mammalian enzyme.

Many pathogenic microbes attach to host cells via specific adhesins to avoid host mechanisms of mechanical clearance, establish colonization, deliver toxins or invade. Several forms of bacterial adhesion have been described. Pili or fimbriae, for example are often involved in initial adhesion of pathogenic bacteria. These structures: a.wrap around epithelial cilia to avoid being cleared by mucociliary action b. are polymerized protein tubes that have unique tips to bind to host cell glycoprotein or glycolipid receptors c. inject toxins directly into host cells to modify the host cell cytoskeleton under attached bacteria d. are only found in pathogenic forms of a microbe e. function like spears, impaling the cell surface for both adhesion and release of cytosolic nutrients

b. are polymerized protein tubes that have unique tips to bind to host cell glycoprotein or glycolipid receptors

Influenza virus can change quickly because it has a segmented RNA genome. The mechanism by which its genome undergoes major changes (antigenic shift) and gives rise to most pandemic strains is: a. by rapid mutation due to the fact that its RNA polymerase has no proof reading mechanism b. by shuffling of RNA segments when a single cell is infected by multiple different viruses thus giving rise to reassortants. c. by breaking the genome into smaller segments, shuffling the fragments and creating new genes at each replication cycle d. by being themselves infected by bacteriophages that can add new pathogenic determinants e. by multiple viruses fusing with each other and creating multicopy virions that acquire new properties

b. by shuffling of RNA segments when a single cell is infected by multiple different viruses thus giving rise to reassortants.

The definitive host for Plasmodium falciparum is: a. humans b. mosquitoes c. monkeys d. snails e. rodents

b. mosquitoes

When you obtain a history, you find out that the man's mother died of pulmonary tuberculosis when he was a child in India. He was eight years old when she died. He helped take care of her until the end, and never became ill himself. However, he does remember that her symptoms are similar to the ones he has now. A likely reason he did not develop tuberculosis as a child is that: a. he received the BCG vaccine as an infant which prevented him from becoming infected by his mother b. most people with a normal immune system infected with Mtb can control Mtb infection and keep it in an asymptomatic state throughout their lives c. most people infected with Mtb will clear the infection once their T-cell mediated immunity is established d. most infected people shed and transmit tuberculosis asymptomatically thus never experiencing disease e. it is rare for family members to transmit TB to each other because the constant exposure to small doses of Mtb induces protective immunity

b. most people with a normal immune system infected with Mtb can control Mtb infection and keep it in an asymptomatic state throughout their lives

The result of his IGRA is positive, consistent with prior infection by Mtb. To make sure he has only LTBI and not active TB disease, you perform a full physical exam and order a chest radiograph. The film shows a calcified nodule in the right middle lobe. This means: a. you have now been exposed to TB and you have better get an IGRA test on yourself in the next week or two b. the calcified granuloma is consistent with LTBI and you should reassure him that he is not contagious or diseased c. he may have lung cancer and you should consider a biopsy of the lesion d. he is likely immunocompromised and you should also test for HIV e. he has had a very recent infection less than 9 weeks since exposure

b. the calcified granuloma is consistent with LTBI and you should reassure him that he is not contagious or diseased

You are volunteering your services as a doctor for low income families. You visit a household of Indian immigrants and are asked to see a 73-year-old man who has become cachectic and has been coughing for several months. He sometimes coughs blood-tinged sputum. Tuberculosis is on your differential diagnosis. Before entering his small room, you put on an N-95 mask. If he has active TB, the Mtb bacilli will circulate in the closed space and remain viable for several hours. Mtb are resistant to desiccation and survive being airborne in microscopic respiratory nuclei because: a. mycobacterial metabolism uses beta-oxidation to split long chain fatty acids into acetyl CoA and water thus maintaining hydration b. the cell envelope mycolic acids form a hydrophobic barrier that protects them from drying c. the mycobacterial thick peptidoglycan layer absorbs water molecules in its lattice d. mycobacterial porins are regulated by osmosis and close if the mycobacteria become dehydrated e. mycobacteria naturally thrive in environments with low water content like dessert soils

b. the cell envelope mycolic acids form a hydrophobic barrier that protects them from drying

A 70-year-old woman is critically ill with respiratory failure from pneumonia and is intubated in the intensive care unit of your hospital. She requires frequent suctioning of the endotracheal tube to clear thick pulmonary secretions. Your resident is concerned that the patient's ventilatory status is worsening despite empiric treatment with broad spectrum antibiotics, and decides to use a sterile cotton-tip applicator to collect some of endotracheal tube secretions for culture. The swab is sent to the microbiology lab, with the hope of identifying a possible pathogen. Growth of which of the following is likely to represent a contaminant from the normal oropharyngeal microbiota rather than the cause of the pneumonia, a. Coccidiodes immitis b. Aspergillus fumigatus c. Candida albicans d. Mucor indicus e. Sporothrix schenckii

c. Candida albicans

The microbiology lab calls to tell you that the his sputum smears do show AFB-positive bacilli. Perhaps the cavitary lesion has tuberculous caseum irritating the airways. Caseum is made from: a. T-cell cytokines causing loss of blood vessels in the granuloma and thus making the avascular structure appear white in the microscope b. Macrophages binding to each other and forming epithelioid structures that resemble crumbling cheese at autopsy c. Cellular and tissue necrosis formed by cell-mediated immune responses to Mtb d. Dying Mtb bacilli which agglutinate into waxy cheese like aggregates e. The metabolism of Mtb inside the granulomas which ferments membranes in a similar process to cheese fermentation

c. Cellular and tissue necrosis formed by cell-mediated immune responses to Mtb

Once inside red blood cells Plasmodium parasites depend on hemoglobin as an amino acid resource. Large quantities of hemoglobin are brought into a food vacuole where it is metabolized. Heme becomes a waste product that is detoxified by the formation of hemozoin crystals. How are some antimalarial drugs able to interfere with merozoite growth inside red blood cells: a. Primaquine changes the pH of the parasite vacuole causing heme to precipitate and form crystals inside the growing parasites b. Atovaquone binds hemoglobin, stabilizing the molecule and preventing Plasmodium from utilizing it as a nutrient source c. Chloroquine and its derivatives bind hemozoin molecules and interfere with hemozoin crystal formation thus generating buildup of toxic heme products that kill the parasites d. Artemisinins induce covalent cross-linking of heme to the hemoglobin blocking digestion of this molecule by the parasite e. Mefloquine triggers the breakdown of heme into hemosiderin thus starving the parasites of iron

c. Chloroquine and its derivatives bind hemozoin molecules and interfere with hemozoin crystal formation thus generating buildup of toxic heme products that kill the parasites

More than 100,000 fungal species are known and many secrete powerful enzymes that can digest plant and animal tissues. It is surprising that only a few dozen species can cause invasive disease in humans with normal immune systems. One major reason the number of fungal pathogens infecting humans is small is: a. Very few fungi can digest the tough keratinized layers that cover our epithelial surfaces b. Human tissues are rich in iron, which is a toxic chemical for most fungi c. Human body temperature is higher than the temperature at which most fungi thrive d. Most fungi require cellulose as part of their nutrition and this is a component of plants, not animals e. Most fungi derive their energy from photosynthesis, only those that have lost this capacity are human pathogens

c. Human body temperature is higher than the temperature at which most fungi thrive

A two-year-old little girl is seen in the emergency room. Her parents are concerned that she is having trouble breathing and you hear an inspiratory stridor and prominent cough. You suspect that her symptoms are due to: a. Laryngitis due to human metapneumovirus b. Pneumonia from adenovirus infection c. Laryngotracheobronchitis due to parainfluenza virus d. Acute otitis media and rhinitis due to rhinovirus e. Bronchiolitis due to respiratory syncytial virus (RSV)

c. Laryngotracheobronchitis due to parainfluenza virus

You examine the patient, draw blood to be sent for an Interferon Gamma Release Assay (IGRA), obtain sputum for AFB smears and culture, and also ask the family to bring him to the hospital for a chest radiograph and further evaluation. The next day you review the chest radiograph and find that he has a cavitary lesion in the right lung. If the cavitary lesion is due to tuberculosis: a. Mtb bacilli will be in a non-replicating state in the caseum of the cavity because of its acidic and avascular nature b. this explains why he only has low grade fever, since the liquefying caseum has anti-inflammatory metabolites c. Mtb will thrive in the aerobic extracellular environment of the caseum and grow to high numbers d. the only option is to surgically remove the affected lung tissue since anti-tuberculous drugs will not penetrate the cavity e. transmission of TB will not occur unless the cavity erodes into a blood vessel causing hemoptysis

c. Mtb will thrive in the aerobic extracellular environment of the caseum and grow to high numbers

A 15-year-old adolescent comes to the emergency department complaining of worsening sore throat and fever. He looks unwell and speaks with a muffled voice. He whispers that it is painful to open his mouth. When you examine his throat you notice that the left tonsillar area is swollen and that his uvula is deviated to the right. You suspect a peritonsillar abscess and admit him to the ENT service. They place him on IV vancomycin and piperacillin/tazobactam perform an incision and drainage procedure in the operating room that drains pus. The Gram stain of the pus has gram-positive cocci in chains. The next morning he is afebrile and the culture is growing Streptococcus pyogenes. In terms of his antibiotic management you should: a. Stay on vancomycin and piperacillin/tazobactam since this treatment is already working and you don't want to breed resistance to a different drug b. Stop antibiotics since his symptoms have now resolved c. Narrow your treatment to penicillin d. Add an antibiotic with a broader spectrum of activity because you want to make sure to cover any possible microbe that was present in the throat e. Wait until sensitivities are available for the Streptococcus pyogenes strain that grew from your patient and choose the antibiotic with the lowest MIC.

c. Narrow your treatment to penicillin

You have a patient with signs and symptoms consistent with atypical community acquired pneumonia. If his condition is due to Mycoplasma pneumoniae a. Penicillin would be a good treatment choice because of the high peptidoglycan content in its cell wall. b. She will likely develop a lobar pneumonia because Mycoplasma produce pneumolysin which damages the epithelium and causes localized vascular leak c. One choice for treatment would be azithromycin which inhibits protein synthesis. d. This organism cannot be cultured on artificial growth medium because it is an obligate intracellular pathogen that cannot grow without the host cell. e. Antibiotics, such as fluoroquinolones, that inhibit DNA topoisomerases have no activity against this bacterial species

c. One choice for treatment would be azithromycin which inhibits protein synthesis.

A normal function of the spleen is to remove abnormal erythrocytes such as those containing infectious inclusions. P. falciparum-infected red blood cells (RBCs) are not efficiently phagocytosed and cleared in the spleen because: a. parasitized RBCs retain their compliance and elasticity and are not recognized by phagocytic cells in the spleen b. parasitized RBCs are coated with a capsular polysaccharide which prevents phagocytosis c. P. falciparum expresses adhesins on parasitized RBCs that cause the RBCs to adhere to vascular endothelium in the peripheral vessels d. P. falciparum produces a pore-forming toxin that kills macrophages in the spleen e. parasitized RBCs express an antiphagocytic transmembrane protein similar to M-protein from Streptococcus pyogenes

c. P. falciparum expresses adhesins on parasitized RBCs that cause the RBCs to adhere to vascular endothelium in the peripheral vessels

A 25-year-old young man presents with a headache and change in vision. On exam he has unilateral left-sided proptosis, ptosis and cannot move his left eye laterally. The rest of his exam is unremarkable. What is the likely source of microbes in this infection? a. The eye muscles became infected with a myotropic virus through the bloodstream b. The middle ear became infected with bacteria which extended through the ethmoid sinus into the orbit c. The ethmoid sinus became infected and bacteria eroded into the medial wall of the orbit d. The lacrimal duct became congested and superinfected by nasal bacterial colonizers e. The conjunctiva became infected with a virus and then superinfected with skin bacteria

c. The ethmoid sinus became infected and bacteria eroded into the medial wall of the orbit

You have been studying the life cycle of a new virus that spreads rapidly and kills 40% of those infected. You need to quickly choose a target to develop antivirals before the infection reaches epidemic proportions. Which of the following parts of the life cycle would be the most reasonable to target: a. The virus uses clathrin-dependent endocytosis to become internalized into the host. You decide to use a clathrin inhibitor to block endocytosis of the virus. b. The virus enters the cell by binding to a growth factor receptor that is essential for viability of alveolar cells. You decide to make a monoclonal antibody that will bind to this receptor and cause its internalization thus removing the ability of the virus to enter. c. The virus codes for its own RNA-dependent RNA-polymerase. You decide to target the RNA polymerase enzyme with a drug that will bind covalently at the catalytic site. d. The virus uses microtubules to transport its newly synthesized capsid proteins for self assembly. You will test a drug that is a powerful microtubule depolymerizer to block virus assembly. e. The virus RNA is transcribed by the host cell ribosomes. You decide to use a drug that inhibits protein synthesis by binding to the ribosomes and thus prevent virus replication.

c. The virus codes for its own RNA-dependent RNA-polymerase. You decide to target the RNA polymerase enzyme with a drug that will bind covalently at the catalytic site.

How would you characterize the pathogenic bacteria that cause infections in the spaces of the head and neck: a. Most of the pathogenic bacteria in the nasopharynx are zoonotic that is are acquired from animals and displace the normal human commensal counterparts b. They enter when another ill person sneezes or coughs on you, rapidly cause inflammation and disease and are cleared from the nasopharynx once the infection resolves c. They are mostly commensals or normal flora living on the mucosal surfaces in the nasopharynx and cause disease when there is an environmental change associated with inflammation like a viral respiratory infection d. The pathogenic bacteria are not detected by the immune system, thus one cannot make vaccines against them. e. The pathogenic bacteria are almost never found in asymptomatic individuals

c. They are mostly commensals or normal flora living on the mucosal surfaces in the nasopharynx and cause disease when there is an environmental change associated with inflammation like a viral respiratory infection

Viruses are called infectious particles rather than organisms because they cannot replicate on their own without invading a host cell. In their simplest form viruses are composed of: a. a protein coat surrounding mRNA and ribosomes b. an outermembrane envelope studded with host derived glycoproteins surrounding a segmented RNA genome c. a nucleic acid genome surrounded by a protein capsid d. a fragment of a bacterial cell e. a pleomorphic cell membrane surrounding a small amount of cytosol and a circular plasmid

c. a nucleic acid genome surrounded by a protein capsid

Viruses sometimes persist in reservoir hosts in which they cause minimal or no disease. Influenza A virus has a preferred animal host in which it persists and from which it can evolve into strains that can infect other animals and humans. This main reservoir animal host is: a. dogs b. bats c. aquatic birds d. humans e. mosquitoes

c. aquatic birds

A 50-year-old man develops shingles in the the lower abdomen. He has a new girlfriend that does not believe in vaccines. If he transmits the infection to his girlfriend who has never been immunized or had natural infection, you would expect that she will: a. develop shingles in the same abdominal dermatome in the opposite side of the body b. develop shingles in multiple dermatomes c. develop a generalized vesicular rash throughout her body d. develop fever and splenomegaly without a rash e. develop painful mouth ulcers

c. develop a generalized vesicular rash throughout her body

The outer membrane of gram-negative bacteria has an outer leaflet with specialized sugar-decorated lipid termed lipopolysaccharide (LPS). Our innate immune system can recognize the lipid portion of LPS at nanomolar amounts and this sometimes leads to: a. non-specific activation of T-cell signaling via crosslinking of the T-cell receptor with MCH molecules b. production of large amounts of antimicrobial peptides which can injure not just bacteria but also the epithelium c. hypotension, capillary leak and fever d. severe constipation that can lead to intussusception e. severe pain at the site of infection

c. hypotension, capillary leak and fever

You are working in a local ED and are called by a family physician who just saw a 6-month-old ex-premature baby that tested positive by nasopharyngeal swab for RSV infection. He is sending the patient to you for evaluation. The main symptoms you would be concerned about include: a. ear pain due to swelling of the eustachian tube and fluid accumulation in the middle ear cavity b. stridor due to inflammation of the laryngeal mucosa c. tachypnea, subcostal retractions and wheezing due to inflammation of the bronchioles d. tachypnea, and snoring due to mucus plugging of the mainstem bronchi e. copious nasal secretions due to inflammation of the nasopharynx

c. tachypnea, subcostal retractions and wheezing due to inflammation of the bronchioles

You are evaluating a 5-year-old boy with cough, runny nose, fever, conjunctivitis and a sore throat. It is July and you wonder whether his symptoms are due to a seasonal allergy vs a viral infection. Of the following respiratory viruses, which is most likely to explain your patient symptoms: a. Parainfluenza virus b. Influenza virus c. Respiratory syncytial virus (RSV) d. Adenovirus e. Rhinovirus

d. Adenovirus

Despite the varied shapes, sizes, structural and genomic organization found in viruses they all share one common feature that makes them distinct from living cells: a. All viruses can be organized into a phylogenetic tree with a common ancestor that gave rise to all viral families b. All viruses need host cell DNA polymerases to make the first copies of the viral genome c. All viruses have incomplete transcription machineries that need to be complemented by host derived transcription initiation factors d. All viruses lack a protein synthesis machinery and therefore need to generate mRNA that can be translated into proteins by host ribosomes. e. All viruses protect their core by enclosing themselves in a lipid envelope derived from the host cell plasma membrane

d. All viruses lack a protein synthesis machinery and therefore need to generate mRNA that can be translated into proteins by host ribosomes.

A 14-year old male teenager that you saw last week in your primary care clinic for a skateboard injury told you that he has had multiple sexual partners this past year. You decide to test him for sexually transmitted infections and include a test for HIV. Which of the following HIV tests would be used for screening an asymptomatic teenager? a. A skin test that detects the presence of T-cells reactive to HIV antigens b. A western blot that detects antibodies to specific HIV proteins in the person's blood c. A flow cytometry test to measure the CD4 and CD8 T-cell counts in his blood d. An antigen detection test that looks for the presence of HIV capsid protein combined with a test that looks for the presence of antibodies against the virus e. An enzymatic test that detects the presence of reverse transcriptase by measuring the capacity of his serum to convert RNA into DNA

d. An antigen detection test that looks for the presence of HIV capsid protein combined with a test that looks for the presence of antibodies against the virus

A 23-year-old woman develops the sudden onset of fevers, productive cough, and chest pain. Her physician notes focal consolidation at the left lung base, and a likely pathogen is identified by Gram stain and routine bacterial culture of sputum. Etiologies of this "typical" bacterial pneumonia syndrome include which of the following? a. Legionella pneumophila b. Pneumocystis jirovecii c. Mycoplasma pneumoniae d. Haemophilus influenzae e. Chlamydophila pneumoniae

d. Haemophilus influenzae

(About the same Sara with taenia solium) The most likely mechanism by which Sara developed seizures is: a. The newly acquired larval cyst secreted neuroactive peptides that triggered excitatory synapses resulting in seizures b. The growing cyst stole blood flow from the surrounding brain tissue causing local ischemia c. Sara is likely immunocompromised, perhaps due to undiagnosed HIV, which allowed the cysticercal cysts to grow displacing brain tissue. d. Her immune system responded to dying larval cysts which lead to inflammatory damage e. She had larval cysticerci migrating through her brain tissue, thus disrupting normal electrical activity

d. Her immune system responded to dying larval cysts which lead to inflammatory damage

Which of the following best describes the pathogenesis of otitis media: a. Viruses infect commensal bacteria in the middle ear and deliver DNA that codes for virulence factors allowing the bacteria to cause inflammation b. Commensal bacteria of the middle ear become pathogenic and secrete toxins when the host restricts iron c. Bacteria colonizing the mastoid air cells travel to the middle ear via the mastoid antrum where they can initiate an infection. d. Inflammation induced by a viral infection results in dysfunction and swelling of the eustachian tube allowing bacteria to avoid mucociliary clearance, become trapped and grow in the middle ear space. e. Pathogenic bacteria colonizing the ear canal translocate into the middle ear across the tympanic membrane

d. Inflammation induced by a viral infection results in dysfunction and swelling of the eustachian tube allowing bacteria to avoid mucociliary clearance, become trapped and grow in the middle ear space.

Most immunocompetent human hosts infected by Toxoplasma gondii will develop: a. Hydrocephalus b. Chorioretinitis c. Seizures d. No symptoms or signs of disease e.Anemia

d. No symptoms or signs of disease

A 40-year-old woman had an upper respiratory tract infection with cough and copious rhinorrhea but no fever two weeks ago. She recovered, however, 3 days later she began to have worsening nasal congestion, and developed low-grade fevers. It has been 12 days since these new symptoms began and she is worsening. She now has headache most of the day, fevers up to 38.5°C, and feels pressure and pain over her cheekbones when she bends forward. The most likely explanation for her symptoms is that: a. A viral infection triggered an inflammatory reaction that then resulted in a localized autoimmune response against commensal bacteria. b. She first had a minor viral or bacterial infection. However this allowed spores from an environmental mold to germinate in her nasal passages. She likely has has minimally invasive fungal sinusitis. c. A viral infection caused an inflammatory response that induced commensal bacteria to produce toxins. These affected the sensory end of the trigeminal nerve and now she has a facial neuritis d. She had viral rhinitis that caused inflammation and swelling of the nasal passages, and disruption of the local bacterial commensal flora. This resulted in trapping of both commensals and potential pathogens in her maxillary sinuses e. She acquired a contagious bacterial pathogen from some other infected human. This infection has a biphasic course first resembling a viral infection during colonization, then producing virulence factors that rapidly increase inflammatory responses and local swelling

d. She had viral rhinitis that caused inflammation and swelling of the nasal passages, and disruption of the local bacterial commensal flora. This resulted in trapping of both commensals and potential pathogens in her maxillary sinuses

You decide to treat her with empiric antimicrobials that will cover the following microbes: a. Neisseria meningitidis, Corynebacterium diphtheriae, and Mycoplasma pneumonia b. Aspergillus fumigatus and Coccidioides immitis c. Pseudomonas aeruginosa, Klebsiella pneumoniae, and Escherichia coli d. Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis e. Fusobacterium nucleatum, Arcanobacterium haemolyticum and Streptococcus pyogenes

d. Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis

Many microbes have the capacity to cause disease but don't do so often. Thus we can think of infectious diseases as a spectrum of outcomes of the host-microbe interaction. Which of the following patients is most likely to have a severe infection: a. Your patient is colonized in the throat by a microbe that can produce a thick capsule b. Your patient is colonized in the oral cavity by a microbe that can form biofilms c. Your patient is infected with a microbe that can persist in the body for years d. Your patient recently received a bone marrow transplant e. Your patient is colonized in the intestine by a bacterium carrying a plasmid for multi-drug resistance

d. Your patient recently received a bone marrow transplant

When he became asymptomatically infected by Mtb, he formed some granulomas. Tuberculous granulomas: a. rapidly trap and kill Mtb. Only those bacilli that avoid granulomas are able to survive to cause disease b. do not contain Mtb bacilli, rather they are follicular compartments with large numbers of Mtb-specific B-cells that produce opsonizing antibodies c. are made up of large numbers of granulocytes, white blood cells characterized by cytoplasms full of granules. d. are composed of multiple cell types including lymphocytes, neutrophils, dendritic cells and even macrophages that resemble epithelial cells e. are made up of calcium and have the same density as bones on X-ray films

d. are composed of multiple cell types including lymphocytes, neutrophils, dendritic cells and even macrophages that resemble epithelial cells

A five-year-old girl is brought in with symptoms and signs of fever, tachypnea, crackles, and hypoxia. You suspect she may have pneumonia and obtain a chest radiograph. A finding in her radiograph that should make you suspect a bacterial over a viral pneumonia is: a. diffuse interstitial patchy opacification of both lungs b. loss of visualization of the heart border c. a steeple sign of the trachea due to subglottic edema d. localized consolidation of a lobe of the lung parenchyma e. hyperinflation of the lungs visualized as flattening of the diaphragms

d. localized consolidation of a lobe of the lung parenchyma

Most viruses cannot infect many cell types and have specific tropism of a particular tissue. This determines what kind of clinical manifestations can occur. An important determinant of viral tissue tropism is: a. the type of endosomal transport that a cell possesses such as microtubule vs microfilament based transport b. the type of internalization that a cell is capable of i.e. clathrin-mediated endocytosis vs caveolin-mediated endocytosis c. the type of host cell ribosome that can transcribe viral mRNA d. the site and abundance of host receptors that bind specifically to viral adhesion proteins prior to internalization e. the blood flow to a particular organ carrying the viral particle to those cells

d. the site and abundance of host receptors that bind specifically to viral adhesion proteins prior to internalization

Toxoplasma gondii has a very broad range of intermediate hosts that even includes marine mammals. In California, scientists have found an increase in sea otter deaths due to Toxoplasma gondii Which of the following is a likely mechanism by which Toxoplasma gondii is being transmitted to these endangered sea otters? a. T. gondii tachyzoites are a normal part of the coastal zooplankton and thus are ingested by otters from the sea water b. Otters are eating birds infected with T. gondii tissue cysts c. Human sewage is contaminating the bay water with T. gondii oocyst released by infected humans d. Otters kept as pets and fed animal meat have become infected with T. gondii tissue cysts and when released into the wild transmit the disease to their mates and offspring e. Freshwater runoff containing cat feces is contaminating the bay costal water with T. gondii oocyst

e. Freshwater runoff containing cat feces is contaminating the bay costal water with T. gondii oocyst

Invasive bacterial pathogens evade the immune system using many strategies. One strategy is to avoid being engulfed by phagocytes. One prominent mechanism used by Streptococcus pyogenes to avoid phagocytosis is: a. It secretes a pore forming toxin, alpha-leukocidin, which kills phagocytes b. The presence of white blood cells induces the production of flagella which allow the bacteria to move out of range of the phagocytes c. It induces autoantibodies through M-protein that bind to phagocytes causing white blood cells to engulf each other rather than the microbes d. It secretes a coagulase enzyme that encases the bacteria in thrombi thus making them inaccessible to phagocytes e. It produces a hyaluronic acid capsule that mimics human connective tissue and hides surface antigens from opsonizing antibodies

e. It produces a hyaluronic acid capsule that mimics human connective tissue and hides surface antigens from opsonizing antibodies

A 12-month-old baby boy contracted RSV infection in December. He required a brief hospitalization and resolved his infection without sequelae. A year later, at the end of January he comes to your office with similar symptoms of tachypnea and fever and is confirmed to have RSV infection again by PCR testing. The parents ask you, his primary pediatrician, why he is re-infected again. You explain that children can be re-infected with RSV because: a. Use of the monoclonal antibody palimuzimab (which is only directed against one epitope of the F-fusion protein), selects for escape mutants that can re-infect children b. he antiviral he received last winter suppressed viral replication but also reduced the immune response to RSV, thus allowing reinfection c. RSV has multiple serotypes that circulate simultaneously in the Winter and year-round, so an immune response to one serotype is not enough to protect against infection with another serotype. d. Many people refuse the RSV vaccine for fear of autism, so heard immunity is low e. RSV has evolved several strategies to evade immune responses, so RSV protective immunity is incomplete, although it helps reduce severity.

e. RSV has evolved several strategies to evade immune responses, so RSV protective immunity is incomplete, although it helps reduce severity.

Sara is a 35-year-old woman from El Salvador who was healthy, working as a baby sitter in the Bay Area for ten years. A few weeks ago, she suddenly developed new onset generalized seizures. An MRI of her head showed a nodular lesion with surrounding edema in the subarachnoid space of the temporal lobe. She underwent a craniotomy for a diagnostic excisional biopsy. Below you can see pictures from her MRI and craniotomy. She recovered promptly from the surgery, and fortunately the pathologists did not report a brain tumor, but instead found evidence of degenerating juvenile worm scolex. Sara was infected with Taenia solium, a cestode helminth that can form tissue cysts in the brain and other tissues. Ova and parasite examinations of her stool did not find evidence that she is infected with Taenia in her gastrointestinal tract. Which of the following would be the most likely source of Sara's infection: a. Sara was bitten by a sand fly in the coastal region of La Palma in El Salvador where these parasites are endemic b. Sara ate food contaminated with pork feces in Mexico during the trip she took to enter the United States c. Sara ate poorly cooked beef at the local Church during a Sunday community barbecue d. Sara ate poorly cooked pork meat on a recent trip to El Salvador to visit her family e. Sara ingested food contaminated with human feces when she was living in El Salvador

e. Sara ingested food contaminated with human feces when she was living in El Salvador

How does the formation of brain cysts in Sara's brain benefit Taenia solium? a. T. solium becomes latent in the human brain in order to reactivate later when the immune system weakens b. T. solium brain cysts changes human behavior to make us less likely to undertake hygienic practices that curtail transmission c. The weak immune response in the brain allows T. solium to replicate to high numbers in the brain tissue d. T. solium evolved at a time where infected humans were not properly buried and their carcasses contaminated the soil with Taenia cysts e. T. solium does not benefit from causing brain cysts in humans but it evolved to do so in pork to enhance its transmission into the human intestine

e. T. solium does not benefit from causing brain cysts in humans but it evolved to do so in pork to enhance its transmission into the human intestine

A 3 month-old infant boy, born 12 weeks prematurely, presents with respiratory distress and fever. The pediatrician does a PCR test on the nasal secretions and tells the family that the child has been infected with the most common cause for bronchiolitis. What is the mechanism of pathogenesis of this clinical disease? a. Viral Infection of the vascular endothelial cells of the capillary bed for the small airways releases an exotoxin that results in loss of endothelial tight junctions and extravasation of capillary fluid, edema and constriction of the airways b. Viral infection of respiratory epithelial cells resulting in formation of multinucleated giant cells, necrosis, and obstruction of small airways c. Infection of the respiratory dendritic cells results in increased antigen presentation and recruitment of natural killer T-cells with subsequent sloughing of the epithelium and blockage of the airway d. Viral infection of the smooth muscle cells of the respiratory airways causes smooth muscle cell contraction and spasm of the airway walls resulting in narrowed air passages e. Viral infection of the respiratory epithelial cells elicits cytokine and chemokines that recruit inflammatory cells resulting in increased mucus and edema and swelling of the walls of the respiratory tract.

e. Viral infection of the respiratory epithelial cells elicits cytokine and chemokines that recruit inflammatory cells resulting in increased mucus and edema and swelling of the walls of the respiratory tract.

Biofilms are a form of inter-bacterial adhesion important in medicine because: a. biofilm polysaccharides are a good target for lysozyme-like antibiotics b. biofilms allow intracellular bacteria to find each other in the cytosol of the host cell forming large aggregates that cannot be recognized by innate immune sensors c. biofilms form nets that trap neutrophils preventing them from reaching the site of infection d. biofilms allow the bacteria to survive on autoclaved surgical instruments and cause most surgical site infections e. biofilms allow some bacteria to form aggregates and colonize foreign bodies like intravenous catheters

e. biofilms allow some bacteria to form aggregates and colonize foreign bodies like intravenous catheters

One of the first steps in identifying the cause of a bacterial infection may be an analysis of a Gram-stain from a patient sample. This study will describe not just the result of the Gram-stain reaction (positive or negative), but also the shape (cocci, rods, spiral, etc) and the organization of the bacteria (groups, chains). Bacteria can have many shapes which can be an important clue to their identity. Which of the following components of bacterial structure is most important in determining cell shape: a. glycolipids of the outer membrane b. capsular polysacharides c. biofilm exopolysacharides d. flagellar motors e. peptidoglycan

e. peptidoglycan

Given that he is not sick with active tuberculosis, he may have benefited from BCG vaccination, which is given in many countries in which TB is endemic. BCG is most effective at: a. reducing the amount of time required to treat an infected person with antibiotics b. preventing adults from progressing from LTBI to active TB disease c. reducing the number of people that become infected with Mtb after exposure d. preventing disease from M. bovis since it is an attenuated form of this mycobacterium e. preventing infants from developing miliary tuberculosis

e. preventing infants from developing miliary tuberculosis

One way Mtb bacilli survive attack by professional phagocytes like macrophages is to: a. secrete bioactive surface lipids that paralyze the cytoskeleton of phagocytes preventing engulfment b. produce a thick waxy capsule that is anti-phagocytic because the macrophages cannot bind to it c. produce a decoy molecule that structurally resembles the TNF-alpha receptor, thus reducing signaling and macrophage activation via this pathway d. Secrete IgA proteases that cleave the Fc portion of anti-mycobacterial antibodies and thus avoid opsonization e. use bioactive cell envelope lipids to block fusion of the phagosome with lysosomes and prevent acidification

e. use bioactive cell envelope lipids to block fusion of the phagosome with lysosomes and prevent acidification