Microbiology

SHiNES SKiS:

Encapsulated Organism: *S*treptococcus pneumoniae *H*aemophilus Influenzae type b *N*eisseria meningitidis *E*scherichia coli P*S*eudomonas aeruginosa *S*almonella spp. *K*lebsiella pneumoniae Group B *S*treptococci

Erysipelas

Erysipelas is an infection involving the dermis and superficial lymphatics, usually from Streptococcus pyogenes infection.

Induration ≥ 15 mm:

Healthy person with no risk factors

Granulomatosis Infantiseptica

Intrauterine or cervical infections can occur when pregnant women develop listeriosis. Neonates may suffer from granulomatosis intantiseptica, which are pyogenic granulomas distributed all over the body.

Pasteurella multocida

Is a common cause of cellulitis following a dog or cat bite.

Scarlet fever

Is a febrile illness caused by infection with S. pyogenes and characterized by fever, pharyngitis, and an erythematous rash. Streptococcal pyrogenic exotoxin (SPE) causes a delayed type IV hypersensitivity reaction, leading to the formation of the rash.

Staphylococcus aureus

Is the most common organism causing endocarditis in intravenous drug abusers. Is the most common cause of salivary gland infections in sialadenitis. Endocarditis in intravenous drug abuse most commonly infects the *tricuspid valve* of the heart. is a gram positive coccus that can cause styes, an infection of the follicles or glands of the upper eyelid. Is the most common cause of *osteomyelitis*. Is the most common cause of *furunculosis* in diabetics. Is stained *purple* by gram staining.

Tetanospasmin

Is the toxin responsible for the characteristic spastic paralysis of tetanus. Works by cleaving SNARE, a set of proteins required for neurotransmitter release via vesicular fusion. Released by Clostridium tetani prevents release of (stimulatory/inhibitory) inhibitory neurotransmitters from Renshaw cells in the spinal cord.

Woolsorter's Disease

Occurs in the textile industry, when spores are inhaled from contaminated wool of livestock.

Plasmodium malariae

One of the protozoans causing malaria, is associated with travel to sub-Saharan Africa, Southeast Asia, and South America.

IL-17 is produced by?

Produced by TH17 cells, is necessary for appropriate neutrophil chemotaxis.

Salmonella Subspecies other than typhi (S. enteritidis, S. typhimurium)

Salmonella Subspecies other than typhi (S. enteritidis, S. typhimurium) *Distinguishing Features* • Facultative gram-negative rods, non-lactose-fermenting on EMB, MacConkey medium • Produces H2S, motile (unlike Shigella) • Speciated with biochemical reactions and serotyped with O, H, and Vi antigens *Reservoir:* enteric tracts of humans and domestic animals, e.g., chickens and turtles *Transmission:* raw chicken and eggs in kitchen; food-borne outbreaks (peanut butter, produce, eggs); reptile pets (snakes, turtles)

Fluoroquinolones

Should not be taken simultaneously with *antacid* medications because they contain *metal cations* that impair absorption of the antibiotic.

Sydenham chorea

Sydenham chorea is the most common cause of chorea in children. It typically manifests a few months following a group A streptococcal infection and is characterized by involuntary movements of the face and extremities.

Bartonella henselae

The cause of *cat scratch* disease and bacillary angiomatosis, is associated with feline contact.

The production of an amine odor when mixing a 10% potassium hydroxide solution with a sample of vaginal discharge, more commonly known as a positive whiff test, is indicative of an infection caused by ____________________.

The production of an amine odor when mixing a 10% potassium hydroxide solution with a sample of vaginal discharge, more commonly known as a positive whiff test, is indicative of an infection caused by Gardnerella vaginalis.

Capnocytophaga canimorsus

*Characteristics* Gram negative filamentous *Reservoir:* Dog oropharynx/ *dog bites wounds* *Disease:* Cellulitis, splenectomy leads to overwhelming sepsis *Treatment:* Third-generation cephalosporins; fluoroquinolones resistant to aminoglycosides

Bartonella henselae Details

*Characteristics* Gram negative rods *Reservoir:* Cats and dogs/bites, scratches, fleas *Disease:* Cat scratch fever; *bacillary angiomatosis (AIDS* *Treatment:* Azithromycin; doxycycline

Streptococcus pyogenes (Group Enterococcus Streptococcus; GAS)

*Distinguishing Features* • β hemolytic • Bacitracin sensitive • Pyrrolidonyl arylamidase (PYR) positive Reservoir: human throat; skin Transmission: direct contact; respiratory droplets Pathogenesis* *• Hyaluronic acid: is non-immunogenic • M-protein: antiphagocytic, associated with acute glomerulonephritis, rheumatic fever • Streptolysin O: immunogenic, hemolysin/cytolysin • Streptolysin S: not immunogenic, hemolysin/cytolysin *Spreading Factors* • Streptokinase: breaks down fibrin clot • Streptococcal DNAse: liquefies pus, extension of lesion • Hyaluronidase: hydrolyzes the ground substances of the connective tissues • Exotoxins A-C (pyrogenic or erythrogenic exotoxins) - Phage-coded (i.e., the cells are lysogenized by a phage) - Cause fever and rash of scarlet fever: superantigens *Diseases* *Acute Suppurative Group A Streptococcal Infections* Pharyngitis- Abrupt onset of sore throat, fever, malaise, and headache; tonsillar abscesses and tender anterior cervical lymph nodes Scarlet fever-Above followed by a blanching "sandpaper" rash (palms and soles are usually spared), circumoral pallor, strawberry tongue, and nausea/vomiting Pyoderma/impetigo-Pyogenic skin infection (honey-crusted lesions) *Nonsuppurative Sequelae to Group A Streptococcal Infections* Rheumatic fever-Sequelae of Pharyngitis with group A strep- Antibodies to heart tissue/2 weeks post pharyngitis, fever, joint inflammation, carditis, erythema marginatum (chorea later)type II hypersensitivity Acute glomerulonephritis (AGN)-Sequelae of Pharyngitis or skin infection- Immune complexes bound to glomeruli/pulmonary edema and hypertension, "smoky" urine (type III hypersensitivity) *Laboratory Diagnosis* • Rapid strep test (ELISA-based) misses approximately 25% of infections. Culture all negatives. • Antibodies to streptolysin O (ASO) titer of >200 is significant for rheumatic fever. • Anti-DNAse B and antihyaluronidase titers for AGN *Treatment:* beta lactam drugs, macrolides in the case of penicillin allergy *Prevention:* possible prophylactic antibiotics for at least 5 years post-acute rheumatic fever; beta lactams and macrolides

Extreme Forms of Leprosy Tuberculoid Lepromatous

*Tuberculoid* Strong CMI(Th1) Lepromin test + *Lepromatous* Weak CMI (Th2) Lepromin test -

The most common bacterial causes of acute otitis media

Are Streptococcus pneumoniae and Haemophlius influenzae, with Moraxella in third. In adults, M catarrhalis may contribute to COPD exacerbations and is a rare cause of pneumonia.

Streptococcus pneumoniae, Klebsiella, and Staphylococcus spp.

Are bacteria known to cause *pneumonia* in *alcoholics* and/or *intravenous drug* users.

Bacterial vaginosis

Bacterial vaginosis is characterized by a thin, gray-white discharge that often has a "fishy" odor. Exposure to potassium hydroxide accentuates this odor. On microscopy, the pathognomonic finding is the clue cell, which is a vaginal epithelial cell surrounded by adherent coccobacilli.

Histoplasmosis

Can cause erythema nodosum, a skin disease presenting with painful inflammatory lesions on the anterior shins. Disseminated histoplasmosis is treated with amphotericin B (drug), like all other systemic mycoses. Calcifications can be seen in the hilar region on the chest x-ray of a patient with histoplasmosis. Does not show person-to-person transmission. May mimic tuberculosis in presentation.

Anaerobes Can't Breathe Fresh Air!

Clostridium, Bacteroides, Fusobacterium, Actinomyces

Granulocytes

are a category of white blood cells characterized by the presence of granules in their cytoplasm. They are also called polymorphonuclear leukocytes (PMN, PML, or PMNL) because of the varying shapes of the nucleus, which is usually lobed into three segments. This distinguishes them from the mononuclear agranulocytes. In common parlance, the term polymorphonuclear leukocyte often refers specifically to neutrophil granulocytes, the most abundant of the granulocytes; the other types (eosinophils, basophils, and mast cells) have lower numbers. Granulocytes are produced via granulopoiesis in the bone marrow.

Corynebacterium diphtheriae forms ______________(colored) colonies on __________________ agar.

forms black (colored) colonies on cysteine-tellurite agar.

Pontiac Fever

is a disease caused by Legionella that presents as a mild flu-like illness.

Brudzinski's sign

is one of the physically demonstrable symptoms of meningitis. Severe neck stiffness causes a patient's hips and knees to flex when the neck is flexed.

Moxifloxacin

is the least potent fluoroquinolone for use against Pseudomonas aeruginosa.

Pneumolysin

is the virulence factor from Streptococcus pneumoniae that acts as a cytotoxic agent and activates complement.

Nocardia infection

leads to caseous necrosis in tissues. Is weakly acid-fast.

Vaginal candidiasis usually occurs when the vaginal pH is decreased/normal _______________.

normal

Ecthyma gangrenosum

rapidly progressive, necrotic cutaneous lesion B caused by Pseudomonas bacteremia. Typically seen in immunocompromised patients.

Two common bacterial causes of Guillain-Barre syndrome are:

Two common bacterial causes of Guillain-Barre syndrome are Campylobacter jejuni and Mycoplasma pneumoniae.

Viridans group streptococci

Viridans group streptococci live in the mouth because they are not afraid of-the-chin (optochin resistant)

Induration ≥10 mm:

1. Travel to country with high prevalence of TB within the past 5 years 2. Injection drug user 3. Resident or employee of high-risk setting (hospitals, prisons, homeless shelter, mycobacteriology lab) 4. Children <4 years old 5. Children exposed to adults with high-risk exposure

Which 3 anti-plasmodial drugs are contraindicated in a patient with a G6PD Deficiency?

Which 3 anti-plasmodial drugs are contraindicated in a patient with a G6PD Deficiency? Chloroquine, Primaquine, Quinine.

Clindamycin and penicillin

are the antibiotics of choice for Clostridium perfringens infection.

GABA and glycine

are the major two inhibitory neurotransmitters, the release of which is blocked in tetanus.

Botulinum toxin

can be used as treatment for hyperhidrosis, achalasia, and focal dystonia.

Trachoma

caused by Chlamydia trachomatis serotypes A-C, is the leading infectious cause of preventable blindness worldwide. Trachoma is characterized by mild itching and irritation of the eyes and eyelids. Untreated or repeat infections leads to scarring around the eyelids, eyelashes turning inwards, and development of corneal ulcers and blindness.

Corynebacterium diphtheriae

is a bacterium that causes pharyngitis with characteristic pseudomembrane formation. Tests (positive/negative) positive for the Elek test.

Yersinia enterocolitica

is a gram-negative bacteria that causes a mesenteric adenitis that can mimic Crohn disease or appendicitis in presentation. is a gram-negative bacteria that is associated with day care outbreaks and pseudoappendicitis.

Pseudomonas aeruginosa

is a gram-negative nosocomial bacterium, infection from which is particularly associated with the use of mechanical ventilation.

Eikenella corrodens

*Characteristics* Gram negative rods "corrodes" agar; bleach-like odor *Reservoir:* Human oropharynx *human bites or fist fight injuries* *Disease:* Cellulitis *Treatment:* Third-generation cephalosporins; fluoroquinolones

Mycobacterium marinum

*Disease:* -Soft tissue infections -"Fish tank granuloma" *Transmission:* -Abrasions *Clinical Presentation:* -Cutaneous granulomas in tropical fish enthusiasts *Treatment* -Isoniazid -Rifampin or ethambutol

Mycobacterium leprae

*Distinguishing Features* • Acid fast rods (seen in punch biopsy) • Obligate intracellular parasite (cannot be cultured in vitro) • Optimal growth at less than body temperature *Reservoir:* human mucosa, skin, and nerves are only significant reservoirs; some infected armadillos in *Texas* and *Louisiana* *Transmission:* nasal discharge from untreated lepromatous leprosy patients *Pathogenesis:* obligate intracellular parasite; cooler parts of body, e.g., skin, mucous membranes, and peripheral nerves *Disease(s):* leprosy: a continuum of disease, which usually starts out with an indeterminate stage called "borderline" *Diagnosis* • Punch biopsy or nasal scrapings; acid fast stain • Lepromin skin test is positive in the tuberculoid but not in the lepromatous form • No cultures *Treatment:* multiple-drug therapy with dapsone and rifampin, with clofazimine added for lepromatous *Prevention:* dapsone for close family contacts

Mycobacterium tuberculosis

*Distinguishing Features* • Auramine-rhodamine staining bacilli (fluorescent apple green); no antibody involved (sensitive but not specific) • Acid fast • Aerobic, slow growing on Lowenstein-Jensen medium; new culture systems (broths with palmitic acid) faster • Produces niacin • Produces a heat-sensitive catalase: catalase-negative at 68.0°C (154.4 F) (standard catalase test); catalase active at body temperature *Reservoir:* human lungs *Transmission:* respiratory droplets *Pathogenesis* • Facultative intracellular organism (most important) • Sulfatides (sulfolipids in cell envelope): inhibit phagosome-lysosome fusion, allowing intracellular survival (if fusion occurs, waxy nature of cell envelope reduces killing effect) • Cord factor (trehalose dimycolate): causes serpentine growth in vitro; inhibits leukocyte migration; disrupts mitochondrial respiration and oxidative phosphorylation • Tuberculin (surface protein) along with mycolic acid → delayed hypersensitivity and cell-mediated immunity (CMI): granulomas and caseation mediated by CMI; no exotoxins or endotoxin; damage done by immune system *Disease(s)* • Primary pulmonary TB - Symptoms can include fever, dry cough - Organisms replicate in naive alveolar macrophages, killing the macrophages until CMI is set up (Ghon focus) - Macrophages transport the bacilli to the regional lymph node (Ghon complex) and most people heal without disease - Organisms that are walled off within the Ghon complex remain viable unless treated • Reactivational TB - Symptoms can include fever, hemoptysis, night sweats, weight loss - Erosion of granulomas into airways (high oxygen) later in life under conditions of reduced T-cell immunity can lead to mycobacterial replication and disease symptoms - Complex disease with the potential of infecting any organ system - May disseminate (miliary TB): kidneys, GI tract, brain, spine (Pott disease) *Diagnosis* • Microscopy of sputum: screen with auramine-rhodamine stain (fluorescent apple-green); no antibody involved; very sensitive; if positive, confirm with • acid fast stain • PPD skin test (Mantoux): measure zone of induration at 48-72 hours; positive if: - ≥5 mm in HIV+ or anyone with recent TB exposure; AIDS patients have reduced ability to mount skin test. - ≥10 mm in high-risk population: IV drug abusers, people living in poverty, or immigrants from high TB area - ≥15 mm in low-risk population • Positive skin test indicates only exposure but not necessarily active disease. • Quantiferon-TB Gold Test: measures interferon-gamma production when leukocytes exposed to TB antigens • Slow-growing (3-6 weeks) colonies on Lowenstein-Jensen medium (faster new systems) • Organisms produce niacin and are catalase-negative (68°C). • No serodiagnosis *Treatment* • Multiple drugs critical to treat infection • Standard observed short-term therapy for uncomplicated pulmonary TB (rate where acquired resistance <4%): - First 2 months: rifampin + isoniazid + pyrazinamide + ethambutol (RIPE) - Next 4 months: rifampin and isoniazid • Streptomycin added for possible drug-resistant cases until susceptibility tests are back (if area acquired has >4% drug-resistant mycobacteria) • For MDR TB, use 3−5 previously unused drugs: aminoglycosides, fluoroquinolones, thioamide, cycloserine, bedaquiline *Prevention* • Isoniazid taken for 9 months can prevent TB in persons with infection but no clinical symptoms • Bacille Calmette-Guérin (BCG) vaccine containing live, attenuated organisms may prevent disseminated disease; not used in U.S. • UV light or HEPA filter used to treat potentially contaminated air

Blastomycosis

a systemic mycosis, verrucous skin lesions can appear very similar to squamous cell carcinoma. Itraconazole (except in the central nervous system) is the drug of choice.

Ehrlichia

Por lo regular tienes co infection with borrelia burgdorferi pq el tick que las trasmite es el mismo, puedes distinguir que tienen coinfection ya que la fiebre va a ser mas alta

Shigella enterocolitis/shigellosis (most severe form is dysentery)

Fever (generally >38.3 C [101.0 F]); lower abdominal cramps; tenesmus; diarrhea first watery, then bloody; invasive but rarely causes septicemia; shallow ulcers

____________________ can be given to immunocompromised patients to prophylactically suppress cryptococcal meningitis.

Fluconazole

Side Effects of Macrolides: MACRO:

Gastrointestinal *M*otility issues, *A*rrhythmia caused by prolonged QT interval, acute *C*holestatic hepatitis, *R*ash, e*O*sinophilia. Increases serum concentration of theophylline, oral anticoagulants. Clarithromycin and erythromycin inhibit cytochrome P-450.

Chlamydia trachomatis

*Distinguishing Features* • Obligate intracellular bacterium; cannot make ATP • Found in cells as metabolically active, replicating reticulate bodies • Infective form: inactive, extracellular elementary body • Not seen on Gram stain; peptidoglycan layer lacks muramic acid *Reservoir:* human genital tract and eyes Transmission: sexual contact and at birth; trachoma is transmitted by handto-eye contact and flies. Pathogenesis: infection of nonciliated columnar or cuboidal epithelial cells of mucosal surfaces leads to granulomatous response and damage *Diseases* *• STDs in U.S*. - Serotypes D-K (most common bacterial STD in U.S., though overall herpes and HPV are more common in prevalence) - Nongonococcal urethritis, cervicitis, PID, and major portion of infertility (no resistance to reinfection) - Inclusion conjunctivitis in adults (with NGU and reactive arthritis) - Inclusion conjunctivitis and/or pneumonia in neonates/infants (staccato cough) with eosinophilic infiltrate *• Lymphogranuloma venereum* - Serotypes L1, 2, 3 (prevalent in Africa, Asia, South America); painless ulcer at site of contact; swollen lymph nodes (buboes) around inguinal ligament (groove sign); tertiary includes ulcers, fistulas, genital elephantiasis *• Trachoma* - Leading cause of preventable infectious blindness: serotypes A, B, Ba, and C - Follicular conjunctivitis leading to conjunctival scarring, and inturned eyelashes leading to corneal scarring and blindness

Ureaplasma urealyticum

*Distinguishing Features:* member of family *Mycoplasmataceae Pathogenesis:* urease positive *Diseases:* urethritis, prostatitis, renal calculi *Diagnosis:* non-Gram-staining, urease(+) *Treatment:* erythromycin or tetracycline Esta bacteria tiende a ser parte de la normal flora cuando una persona comienza a estar sexually active, si encuentras esto en un infante se entiende que es *sexual abuse* ya que esto no es parte de la flora normal hasta que la persona comienza a estar activo sexualmente. Ejemplo una mujer sexually active en la vagina va a ser positivo para esta bacteria, una nina que de positivo en la vagina a esta bacteria se entiende que es sexual abuse

GENUS: STAPHYLOCOCCUS Staphylococcus aureus

*Genus Features* • Gram-positive cocci in clusters • Catalase positive (streptococci are catalase negative) *Species of Medical Importance* • S. aureus • S. epidermidis • S. saprophyticus *Distinguishing Features* • Small, yellow Staphylococcus aureuscolonies on blood agar • β-hemolytic • Coagulase positive (all other Staphylococcus species are negative) • Ferments mannitol on mannitol salt agar *Reservoir* • Normal flora - Nasal mucosa (25% of population are carriers) - Skin *Transmission* • Hands • Sneezing • Surgical wounds • Contaminated food - Custard pastries - Potato salad - Canned meats *Predisposing Factors for Infection* • Surgery/wounds • Foreign body (tampons, surgical packing, sutures) • Severe neutropenia (<500/µL) • Intravenous drug abuse • Chronic granulomatous disease • Cystic fibrosis *Pathogenesis* • Protein A binds Fc component of IgG, inhibits phagocytosis • Enterotoxins: fast acting, heat stable • Toxic shock syndrome toxin-1 (TSST-1): superantigen (see Chapter 6 of Immunology for further explanation of a superantigen) • Coagulase: converts fibrinogen to fibrin clot • Cytolytic toxin (α toxin): pore-forming toxin, Panton-Valentine leukocidin (PVL), forms pores in infected cells and is acquired by bacteriophage; associated with increased virulence, MRSA strains • Exfoliatins: skin-exfoliating toxins (involved in scalded skin syndrome [SSS]) and bullous impetigo *Treatment* • Gastroenteritis is self-limiting. • Nafcillin/oxacillin are drugs of choice because of widespread penicillinase-producing stains. • Mupirocin for topical treatment. • For methicillin-resistant Staphylococcus aureus (MRSA): vancomycin • For vancomycin-resistant Staphylococcus aureus (VRSA) or vancomycin-intermediate S. aureus (VISA): quinupristin/dalfopristin

Clostridium difficile

*Key Vignette Clues* Clostridium difficile • Hospitalized patient on antibiotics • Develops colitis, diarrhea *Reservoir:* human colon/gastrointestinal tract *Transmission:* endogenous *Pathogenesis* • Toxin A: enterotoxin damaging mucosa leading to fluid increase; granulocyte attractant • Toxin B: cytotoxin: cytopathic *Disease(s):* antibiotic-associated (clindamycin, cephalosporins, amoxicillin, ampicillin) diarrhea, colitis, or pseudomembranous colitis (yellow plaques on colon) *Diagnosis:* culture is not diagnostic because organism is part of normal flora; stool exam for toxin production *Treatment* • Metronidazole for severe disease; vancomycin only when no other drug is available to avoid selecting for vancomycin-resistant normal flora • Fecal transplant for chronic infections • Discontinuation of other antibiotic therapy for mild disease *Prevention:* use caution in overprescribing broad-spectrum antibiotics (consider limited-spectrum drugs first); in nursing home setting, isolate patients who are symptomatic; use autoclave bed pans (treatment kills spores)

Pasteurella multocida Details

*Reservoir:* Mouths of many animals, especially cats and dogs *Transmission:* Animals bites; particularly from cat bites *Pathogenesis:* Endotoxin capsule; spreads *rapidly* within skin, no exotoxins known *Disease:* *Cellulitis with lymphadenitis* wound infections, rapidly spreading Frequently polymicrobial infections *Treatment:* Amoxicillin/clavulanate

Salmonella enterica typhi

*Transmission:* fecal-oral route from human carriers (gall bladder); decreased stomach acid or impairment of mononuclear cells as in sickle cell disease predisposes to Salmonella infection *Pathogenesis and Disease:* typhoid fever (enteric fever), S. typhi (milder form: paratyphoid fever; S. paratyphi) • Infection begins in ileocecal region; constipation common • Host cell membranes "ruffle" from Salmonella contact. • Salmonella reach basolateral side of M cells, then mesenteric lymph nodes and blood (transient 19 septicemia) • At 1 week: patients have 80% positive blood cultures; 25% have rose spots (trunk/abdomen), signs of septicemia (mainly fever) • S. typhi survives intracellularly and replicates in macrophages; resistant to macrophage killing because of decreased fusion of lysosomes with phagosomes and defensins (proteins) allow it to withstand oxygen-dependent and oxygen-independent killing • By week 3: 85% of stool cultures are positive • *Symptoms:* fever, headache, abdominal pain, *constipation more common than diarrhea* • Complications if untreated: necrosis of Peyer patches with perforation (local endotoxin triggered damage), thrombophlebitis, cholecystitis, pneumonia, abscess formation, etc. *Treatment:* fluoroquinolones or third-generation cephalosporins *Prevention:* sanitation; 3 vaccines (attenuated oral vaccine of S. typhi strain 21 (Ty21a), parenteral heat-killed S. typhi (no longer used in U.S.), and parenteral ViCPS polysaccharide capsular vaccine)

Atypical "Walking pneumonia"

-Mycoplasma Pneumoniae -Chlamydophilia Pneumoniae C. pneumoniae: atypical pneumonia: sputum with intracytoplasmic inclusions

Induration ≥5 mm:

1. HIV patients 2. Immunocompromised patients 3. Person with recent contact with someone with active TB 4. Person with fibrocystic changes on chest x-ray consistent with old TB

Group B Streptococcus (S. agalactiae, GBS)

Group B Streptococcus (S. agalactiae, GBS) are the most common cause of bacterial meningitis in patients < 1 year of age.

Atypical pneumonia caused by Legionella pneumophila (can/cannot) ____________ be spread from person to person.

Atypical pneumonia caused by Legionella pneumophila (can/cannot) cannot be spread from person to person.

Clostridium tetani

Causes a disease of spastic paralysis that presents with risus sardonicus and trismus.

Congenital infection with syphilis, CMV, toxoplasmosis, or parvovirus B19 can result in stillbirth through hydrops fetalis.

Congenital infection with syphilis, CMV, toxoplasmosis, or parvovirus B19 can result in stillbirth through hydrops fetalis.

Peritonsillar abscess

Is characterized by odynophagia, trismus, unilateral referred ear pain and/or uvula deviation away from the infected tonsil. If the abscess gets large enough it may cause airway obstruction.

Dimorphism

Is the ability of a fungus to change from yeast to a mold and back. The mnemonic "mold = cold, yeast = heat" is reversed with Candida albicans because the mold/hyphae form grows at 37°C while the yeast/pseudohyphae form predominates at 20°C.

India ink stain

Is a microbiology laboratory test useful to confirm the morphology of Cryptococcus neoformans, an encapsulated yeast with a narrow-based budding organism that grows in Sabouraud agar and is responsible for causing fungal meningitis in immunocompromised patients.

Brucella melitensis (B. melitensus)

Is a small, intracellular gram-negative coccobacillus which, like Nocardia, stains with a modified acid-fast stain. It is endemic to the Mediterranean basin, the Arabian peninsula, and India, as well as Mexico and Central and South America, making this patient's recent travel to Greece a likely setting for transmission. Enters the body after the ingestion of *contaminated milk products* or *direct contact with contaminated livestock*, and spreads via the lymphatics to the reticuloendothelial system (liver and spleen). *Clinical manifestations* of brucellosis include those seen in this patient: *undulating fever*, *weakness*, and *loss of appetite*. Pertinent exam findings include generalized lymphadenopathy, hepatosplenomegaly, and a characteristic moldy body odor. Anti-LPS antibody titers are the most effective method of diagnosis. Blood cultures may also be used. Brucellosis can be treated with *doxycycline*, with the addition of *rifampin* in cases of relapse.

Borrelia recurrentis

Is a spirochete which can also cause a *relapsing fever*, but is also associated with signs of hepatic injury (for example, jaundice.)

Mucor indicus

Is a thermotolerant, dimorphic fungus and a member of zygomycetes fungi. It is commonly found in soil, digestive system, and plant surfaces. It is responsible for causing necrotizing infections called zygomycosis. M. indicus causes mucormycosis, a type of zygomycosis. These infections are treated by *amphotericin B*. Is one of the members of the zygomycetes fungi which causes necrotizing infections known as zygomycosis. This case describes a classic presentation of mucormycosis which is characterized by facial pain, nasal congestion that progresses to black discharge, fever, unilateral headache, and eye swelling. The disease is characterized by hyphae growing in and around blood vessels. The CT scan shows signs of invasive fungal sinusitis. The histologic section shows multiple, broad, non-septate hyphae which provides conclusive proof of a fungal infection. Mucormycosis is is usually treated by amphotericin B. In most cases the prognosis of the disease is poor and patients with AIDS usually have a mortality rate of 100%.

Listeria monocytogenes

Is also associated with *unpasteurized dairy*, but would cause a *diarrheal illness* rather than a cyclic fever.

A 55-year-old man comes to the clinic because of cough, shortness of breath, and nausea since the past two days. He denies chills, abdominal pain, vomiting, diarrhea, or rhinorrhea. He recently returned from an extended business trip and has stayed in several hotels. He has not been ill or exposed to any sick person recently but has been feeling 'hot'. He did not take his temperature. Medical history is significant for chronic obstructive pulmonary disorder treated with an ipratropium inhaler. Vital signs show BP 134/95 mm Hg, 89 beats/min, 19 breaths/min, 39 C. General examination shows a thin man quietly breathing through his mouth without using accessory muscles. Physical examination is unremarkable, except for rales on auscultation. Pulse oximetry shows 98% on room air. Chest X Ray reveals diffuse bilateral interstitial opacities. Which of the following is the most appropriate diagnostic step? A. Echocardiogram B.Urine antigen C. Sputum stain and culture D. Stool antigen E. Electrocardiogram

Major Takeaway Urine antigen is the best diagnostic step for Legionnaire disease as it is fast and very specific. Legionella infection can be acquired through aerosolized water found in ill-maintained plumbing and is associated with fountains, air conditioners, hotels, and cruise cabins. Main Explanation This patient likely has Legionnaire disease. Legionella pneumophila infection can be acquired through aerosolized water found in ill-maintained plumbing and is associated with fountains, air conditioners, hotels, and cruise cabins. Legionella tends to affect immunocompromised individuals and adults aged 50+ who have some history of smoking, lung, and liver disease. Infection presents as an atypical pneumonia typically with fevers of 39C or more. Gastrointestinal symptoms such as vomiting and diarrhea are common. The most common neurological sign is confusion, associated with hyponatremia. The best diagnostic test for legionella is urine antigen and bronchoalveolar lavage with culture on cysteine yeast extract (with the addition of polymyxin, anisomycin, and other agents to help legionella grow). Urine antigen is faster and maintains positivity even after starting antibiotics while culture is very difficult and takes longer to obtain. However, urine antigen is specific for legionella serotype 1 only but this the most common cause of community acquired pneumonia due to legionella.

A 26-year-old man comes to your clinic because of a persistent cough. He has episodes on and off for the past 7 years. The cough is usually non-productive, but he has seen blood a few times. He has also noticed his sheets are sometimes wet in the mornings. He works as a dentist in the Southeastern US, but it considering moving out West because dry air improves his symptoms. His mother also had a long-standing cough and passed away when he was fifteen. His temperature is 37.8°C (100.2°F), pulse is 85/min, respirations are 16/min, and blood pressure is 118/70 mm Hg. His BMI is 23 kg/m2. Physical examination shows a thin, young male in no acute distress. Regular rate and rhythm are heard on auscultation of the heart. The lungs are clear to auscultation. Which of the following histological findings are most closely associated with his underlying disease? A. Acid-fast & aerobic B. Acid-fast & anaerobic C. Gram-negative &anaerobic D. Keratin pearls and intercellular bridges E. Macrophages with intracellular inclusions

Major Takeaway Mycobacterium tuberculosis is a strictly aerobic bacillus with a waxy cell wall that makes them acid-fast, or resistant to acid decolorization techniques. Main Explanation The clinical picture of a thin man with low grade fever, chronic cough, hemoptysis and history of a possible exposure is suspicious for tuberculosis. Mycobacterium tuberculosis is an aerobic bacillus that is visible with the acid-fast stain. The most common test for acid-fast bacteria is the Zichl-Neelsen stain which will cause mycobacterium to appear bright red. This vignette describes John Henry "Doc" Holliday (1851-1887), a gambler, gunfighter, and dentist in the American West known for his involvement at the shooting at the OK Corral and friendship with Wyatt Earp. Diagnosed with tuberculosis in his twenties, he moved to the west hoping the drier climate would prolong his life. He may have contracted the disease from his mother or one of his dental patients. His constant coughing is thought to have made business unprofitable, and may have turned him towards illegal activities.

Bordatella pertussis

Major Takeaway is a Gram-negative cocci that causes whooping cough, a disease now more common in adolescents and adults than in children. A cough lasting longer than 2 weeks accompanied by paroxysms of coughing, inspiratory whoop, or posttussive emesis should raise suspicion for pertussis. Main Explanation Bordatella pertussis is a Gram-negative, encapsulated coccobacillus that is the causative agent of pertussis. Since the pertussis vaccine became part of the childhood vaccination schedule, the epidemiological pattern of the disease has changed; more than half of new cases now occur in adolescents and adults rather than in children. For this reason, a Tdap booster vaccination is recommended between ages 11 to 18, and then again between ages 19 to 64. It is especially important for individuals working with young children, since B. pertussis is highly infectious. The patient describes an initial phase of her illness that presented with malaise, rhinorrhea, and a mild cough. This corresponds to the catarrhal phase. She now has a residual, vigorous cough suggesting she is now in the paroxysmal phase. The cough, which occurs during expiration, is followed by a characteristic deep inspiration with a distinctive "whooping" sound. Culture and PCR are sensitive diagnostic tools for up to two and four weeks, respectively. Without treatment, the paroxysmal phase lasts up to three months, then transitions into a convalescent phase. Macrolide such as azithromycin and clarithromycin are effective treatments.

Major encapsulated organisms: Some Killers Have Pretty Nice Capsules

Major encapsulated organisms Some Killers Have Pretty Nice Capsules: Strep pneumoniae Klebsiella pneumoniae Haemophilus influenzae Type b (a-d) Pseudomonas aeruginosa Neisseria meningitidis Cryptococcus neoformans (the yeast) (Not a complete list, just the big ones

Thyphoid Mary

Mary Mallon was born in 1869 in Ireland and emigrated to the US in 1884. She had worked in a variety of domestic positions for wealthy families prior to settling into her career as a cook. As a healthy carrier of Salmonella typhi her nickname of "Typhoid Mary" had become synonymous with the spread of disease, as many were infected due to her denial of being ill. She was forced into quarantine on two separate occasions on North Brother Island for a total of 26 years and died alone without friends, having evidently found consolation in her religion to which she gave her faith and loyalty.

Clostridium perfringens

May cause *food poisoning* if ingested. If exposed to an open wound, it may cause *gas gangrene.* The *alpha toxin* of the Clostridium perfringens bacterium is a phospholipase, lecithinase, that breaks down cell membranes.

Pseudomonas aeruginosa

Pseudomonas aeruginosa, a gram negative rod, is classically associated with hot tub folliculitis, an inflammation of the hair follicles that appears like a rash on the skin. Main Explanation The patient in this question most likely has hot tub folliculitis secondary to infection by Pseudomonas aeruginosa, a gram negative rod that is ubiquitous in the environment. It can cause infections associated with hot tubs, contaminated contact lenses, and has an affinity for immunocompromised patients, including burn patients and patients with cystic fibrosis. It is the second most common cause of nosocomial pneumonia, and it is also associated with a variety of infections. P. aeruginosa has a characteristic grape-like odor, is oxidase positive, and can appear green in color. Exotoxin A is responsible for P. aeruginosa pathology, and this exotoxin acts by inhibiting protein synthesis via ADP ribosylation of Elongation Factor 2. Diagnostic tools include complete blood count, blood cultures, and other cultures depending on the site of infection. Once confirmed, treatment is with a combination of antipseudomonal drugs such as a β-lactam with an aminoglycoside, or carbapenems with antipseudomonal quinolones and aminoglycosides, since P. aeruginosa has a variety of mechanisms for drug resistance. Pseudomonas folliculitis however is self limiting and so no treatment is necessary.

An 11-year-old girl comes to the office because of sore throat. She has had a fever greater than 37.8°C (100°F) for the past few days and has not been able to attend school. Physical examination shows an erythematous pharynx with pain on swallowing and coughing. Following results of a throat culture, the patient is prescribed penicillin. Which of the following psychiatric conditions are often associated with this particular infection? A. Anorexia nervosa B. Attention-deficit hyperactivity disorder C. Depression D. General anxiety disorder E. Obsessive-compulsive disorder

Streptococcal pharyngitis is caused by group A Streptococcus, a gram-positive, beta-hemolytic, bacitracin-sensitive cocci. Streptococcal infection is associated with *obsessive-compulsive disorder* and *Tourette syndrome.* Streptococcal pharyngitis, or strep throat, is an infection caused by group A Streptococcus (GAS). GAS is a gram-positive, beta-hemolytic, bacitracin-sensitive cocci. GAS pharyngitis is characterized by an exudative pharyngitis with additional symptoms including headache, fever, vomiting, cervical lymphadenopathy, palatal petichiae, and scarlatiniform rash. It can be treated with oral penicillin. GAS infection has been associated with onset or exacerbation of obsessive-compulsive disorder (OCD). The cause is believed to be an immune reaction to GAS that damages the basal ganglia. This association is termed pediatric autoimmune neuropsychiatric disorder associated with streptococcal infections (PANDAS). Tourette syndrome has also been associated with streptococcal infection. PANDAS is still debated in the literature and a causal link between GAS infection and resulting neuropsychiatric disease has not yet been shown.

Legionnaires' disease

Suspect Legionnaires' disease in patients who present with respiratory and gastrointestinal symptoms. These patients should receive a respiratory culture and a urinary antigen test. Main Explanation Since its identification in 1976, during an outbreak at an American Legion Convention in Philadelphia, Legionella species have been identified as a relatively common cause of community acquired pneumonia (CAP) and hospital-acquired pneumonia (HCAP). Clinicians should suspect Legionnaires' disease in any patient with respiratory and gastrointestinal symptoms. The chest X-ray can look very consolidated, although the clinical respiratory symptoms may not be as significant. When Legionnaires' disease is suspected, both a urinary antigen test and Legionella pneumophila. culture of a respiratory specimen should be ordered. The urinary antigen tests have sensitivities of approximately 80% and a specificity of approximately 97%-100%. It should be noted that the urine antigen test only detects L. pneumophila serogroup 1 which accounts for 70%-80% of cases.

Coccidioidomycosis

This organism resides in the soil, and the spores are swept into the air when the soil is disrupted, such as during construction, farming, or after earthquakes. Earthquakes are especially associated with tremendous increases in case rates of Coccidiomycoses. The spherules measure 20-60 um and contain endospores within that measure slightly larger than a RBC. C.immitis can spread to the CNS and cause meningitis with granulomatous lesions. Fungi disseminate to the skin and (organ) bone after causing initial pneumonia or meningitis. Initially manifests as pneumonia or meningitis, and is found in the Southwestern United States, specifically in (US states) Arizona and California. Silver stain is used to diagnose Coccidioidomycosis by visualizing the Coccidioides fungi, since gram staining does not stain them very well.

Coxiella Burnetii

Transmission: This organism is common in cattle, sheep, and goats and can be acquired via inhalation of spores from contaminated birthing products like cattle placenta. Due to this mode of transmissions, at risk occupations include veterinary personnel, farmers, and shearers. Unlike the other Rickettsial infections, Coxiella *does not cause rash* *Q fever is the disease caused by Coxiella burnetii and commonly manifest as flu-like symptoms with fever, malaise, myalgia, nausea, vomiting, and diarrhea. During the course of disease, it can progress to a pneumonia, which can result in life-threatening acute respiratory distress syndrome.

Empyema

is a pleural cavity bacterial infection predominantly caused as a complication of pneumonia that results in the accumulation and collection of pus. The mainstay therapy is to treat the underlying infection and pleural drainage of the collection. Main Explanation This patient's presentation with fever, pleuritic pain, and chest wall swelling, in addition to an encapsulated fluid collection with a yellowish pleural drainage is consistent with pleural empyema. Pleural empyema (also known as, pyothorax or purulent pleuritis) is predominantly caused by bacterial infection of fluid within the pre-existing anatomical space between the visceral and parietal pleura. The most common bacterial causes are anaerobic (Bacteroides, Fusobacterium, etc), though other causes of pneumonia such as Klebsiella pneumoniae, Streptococcus, etc may also cause empyema. The pathogenesis arises from an infection within the lung often associated with complicated parapneumonic effusions. Complicated parapneumonic effusion results when bacteria invade the pleural space with a resultant formation of an empyema. Thus, empyema is most commonly caused as a complication of pneumonia. However, it can also arise from penetrating chest trauma, esophageal rupture, a complication from lung surgery, or inoculation of the pleural cavity after thoracentesis or chest tube placement. Morphologically, pleural empyemas are usually unilateral, markedly asymmetric, and tend to form an obtuse angle with the chest wall (biconvex in shape). CT scan characteristically reveals the "split pleura" sign, which is characterized by an enhancing thickened pleura.

Weil disease

is a severe form of leptospirosis that presents with jaundice and azotemia from liver and renal dysfunction.

Leptospirosis

is a zoonotic disease transmitted to humans from animal urine in contaminated water or soil, particularly in the tropics. Although subclinical disease is common, jaundice, hepatosplenoegaly, renal failure, and pulmonary hemorrhage are possible serious clinical manifestations.

Pontiac fever

is an acute, nonfatal respiratory disease caused by Legionella pneumophila, which is an aerobic, flagellated, nonspore-forming, Gram-negative bacteria. Most cases of Pontiac fever are contracted from inhalation of aerosolized potting soil or water droplets containing Legionella pneumophila. Main Explanation Legionella pneumophila is an aerobic, flagellated, nonspore-forming, gram-negative bacteria. It is the causative agent of both Legionnaires disease and Pontiac fever. Pontiac fever is a legionellosis that resembles acute influenza. It typically resolves spontaneously and often goes undiagnosed and unreported. Outbreaks tend to be travel related, and thus geographically removed from the source of outbreak at the time symptoms begin. It is more common in the warmer months due to increased use of air conditioning units which can spread the bacteria, as well as pool filtration units. The main difference between Legionnaires disease and Pontiac fever is that Legionnaires disease includes pneumonia. It can be much more serious and requires antibiotic therapy. Most cases of Pontiac fever are contracted from inhalation of aerosolized water droplets containing Legionella pneumophila. It does not spread from person to person. Incubation period for Pontiac fever is 1 to 3 days. Age, gender, and smoking do not increase risk for disease.

Cryptococcal encephalitis, which may occur in AIDS patients, has a classic ___________________________ appearance on brain MRI.

soap bubble

Pertussis has three major phases:

the catarrhal phase (like the common cold), the paroxysmal phase (bouts of coughing), and the convalescent phase (resolution). Treatment is largely supportive, but antibiotics can reduce the duration of symptoms.

Candidal endocarditis in IV drug users most commonly affects the __________________ valve.

tricuspid

Mycoplasma pneumoniae

• Young adult with atypical pneumonia • Mulberry-shaped colonies on media containing sterols • Positive cold agglutinin test *Treatment:* erythromycin, azithromycin, clarithromycin; *no* cephalosporin or penicillin