Quiz 9 (Chapter 20 & 21)

** Part G ** Dr. Smith prescribes oral erythromycin for Scott. She also recommends that he consider using an over-the-counter gel or cream containing benzoyl peroxide. Although this regimen should be effective at treating Scott's acne, there are some possible side effects. Which of the following are possible side effects of Scott's treatment? Select all that apply. A) excessive drying of the skin B) immunosuppression due to prolonged use of oral antibiotics C) gastrointestinal problems resulting from a reduction/elimination of normal intestinal flora D) inflammatory bowel disease E) selection of antibiotic-resistant strains of bacteria

A) excessive drying of the skin C) gastrointestinal problems resulting from a reduction/elimination of normal intestinal flora Although the combined use of oral antibiotics and benzoyl peroxide has been shown to be effective in treating inflammatory acne, it is not without side effects. Even though the treatment may achieve the desired result, it is always important to recognize it can have side effects. Many times, these may be tolerable enough for the patient to continue the treatment.

* Part C - Interpret results. * You take a sample of pus from your patient's abscess for analysis. Results from Gram-staining are shown here: Picture of a Gram stain What does this result show? The Gram stain shows the presence of ______. A) gram-positive, spherical bacteria B) gram-negative rod bacteria C) gram-negative spherical bacteria D) gram-positive rod bacteria

A) gram-positive, spherical bacteria Yes! You observe spherical gram positive bacteria.

Figure 20.1 The antibiotic tetracycline binds to the 30S subunit of the ribosome, as shown by the dark black bar on the right portion of the diagram in the figure. The effect is to A) interfere with the attachment of the tRNA to mRNA-ribosome complex. B) prevent transcription. C) stop the ribosome from moving along the mRNA. D) prevent attachment of DNA. E) prevent peptide bond formation.

A) interfere with the attachment of the tRNA to mRNA-ribosome complex.

All of the following are transmitted via the respiratory route EXCEPT A) tinea. B) smallpox. C) chickenpox. D) measles. E) rubella.

A) tinea.

The greatest single cause of blindness in the world is A) trachoma. B) inclusion conjunctivitis. C) pinkeye. D) neonatal gonorrheal ophthalmia. E) keratoconjunctivitis.

A) trachoma.

*Staphylococcus aureus* is responsible for all of the following EXCEPT A) boils. B) acne. C) carbuncles. D) sties. E) pimples.

B) acne.

Scabies is a skin disease caused by a A) protozoan. B) mite. C) slow virus. D) prion. E) bacterium.

B) mite.

* Part K * Given the above results, is it safe to say your patient has a MRSA infection? A) yes B) no

B) no MRSA stands for methicillin-resistant *Staphylococcus aureus*. Your patient is infected with a strain of *S. aureus* that is resistant to penicillin, but still sensitive to methicillin.

Which of the following organisms would MOST likely be sensitive to natural penicillin? A) penicillinase-producing *Neisseria gonorrhoeae* B) helminths C) Penicillium D) Streptococcus pyogenes E) Mycoplasma

D) Streptococcus pyogenes

Most of the available antimicrobial agents are effective against A) fungi. B) protozoa. C) viruses. D) bacteria.

D) bacteria.

Part C - The Penicillins All penicillins, or "cillins," share several structural features but differ in others. This activity asks that you identify several features common to all "cillin" antibiotics. Drag the labels to the appropriate locations on the image.

TOP: Common nucleus LEFT: Side chain BOTTOM: β-lactum ring ^ Correct identification of the different parts of the "cillin" molecule. Any antibiotic that has this common nucleus is a type of penicillin. The β-lactam ring portion of the molecule is the target of β-lactamase enzymes (also known as penicillinase) that are made by some bacteria. These bacteria are able to break the β-lactam ring and inactivate the antibiotic.

Part A - Potential Targets of Antibacterial Drugs The activity asks you to identify potential targets of antimicrobial drugs by dragging labels to the target. Drag the following labels to the appropriate antimicrobial target in the diagram. ~ Some of the broader targets of antimicrobials (such as cell wall synthesis or protein synthesis) are made up of a series of steps or multiple separate components that are eventually assembled to form the final product. For example, think about the bacterial cell wall and the variety of substances that must be synthesized to form the wall. Cell wall synthesis presents multiple potential targets for antimicrobial activity. The same is true of protein synthesis.

ROW 1: Inhibition of cell wall synthesis 2: (in order from L->R) Interference with... DNA replication, transcription, translation 3: Inhibition of synthesis of essential metabolites 4: Injury to plasma membrane ^ Correctly identified major targets of antimicrobial drugs - These include inhibition of cell wall synthesis and interference with cell membrane permeability. Some antimicrobial drugs interfere with enzymes necessary for the synthesis of various metabolites. There are antimicrobials that interfere with DNA replication, as well as those that interfere with transcription (synthesis of RNA using the DNA template). Lastly, there are a number of antibiotics that interfere with some aspect of protein synthesis (translation).

The following results were obtained from a disk-diffusion test for microbial susceptibility to antibiotics. *Staphylococcus aureus* was the test organism. Antibiotic / Zone of Inhibition: A / 3 mm B / 7 mm C / 12 mm D / 10 mm In the table, the most effective antibiotic tested was a) B. b) A. c) C. d) D. e) The answer cannot be determined based on the information provided.

unsure if correct ; d) D (10mm) *NOT ANSWER CHOICE c)*

* MEDICAL HISTORY (Hx) * The patient is a male, age 9. He is from Reno, Nevada. He was admitted to the clinic with a deep, red, swollen abscess on the nape of his neck. The patient is a student at a local grade school. He is also in a scout troop that meets most weekends and after school. The patient's dad is a highschool teacher, and his mother is an engineer. The family has a history of heart disease (paternal) and diabetes (maternal). The boy owns a pet boa constrictor and a gopher snake. Ten days ago, he went on a four-day backpacking trip with his scout troop. On the second morning of the trip, he noticed a "spider bite" on his neck. Two of the other children on the trip had similar bites on their arms and face, respectively. The troop-leader applied a topical antibiotic ointment to the bites and administered each child an adhesive bandage. The next day, the boy noticed that the bandage had fallen off at some point during the morning hike. When the trip ended, two days later, the boy's parents noticed that the bite appeared red and somewhat swollen. Concerned, the boy's father swabbed the bite with alcohol and ointment and applied an adhesive bandage. The next day, the bite still appeared raised and inflamed. After a few days, it began to feel hard and hot to the touch, and the patient often complained of tiredness and headaches. He was febrile upon admission to the clinic. The abscess on his neck is roughly 2 inches in diameter, with a yellowish center and weeping, crusted tips. Access "Diseases in Focus" Tables 21.1, 21.2, and 21.3.

* Differential Diagnoses * Differential diagnosis is the process of identifying a disease from a list of possible diseases that fit the information derived from examining a patient. Your job will be to synthesize information from a patient whose main presenting symptoms are consistent with a microbial disease of the skin. Use the "Diseases in Focus" 21.1, 21.2, and 21.3 tables and your knowledge about microbial diseases of the skin and eyes to identify the patient's risk factors and symptoms, evaluate diagnostic evidence, formulate and test a diagnosis about the pathogen responsible for the patient's woes, and suggest a course of treatment.

* Diseases in Focus Chapter 21 - Male, age 9. *

* Part A-L *

Part G - Examples of Antibiotic Resistance There are numerous examples of microorganisms displaying each of the four major resistance mechanisms. In this activity, you are asked to identify the mechanism that each example best illustrates. Drag each item into the appropriate bin.

*Enzymatic inactivation of the antibiotic:* - Many strains of *Neisseria gonorrhoeae* are resistant to penicillin because of the production of β-lactamases. *Prevention of penetration to the target site within the microbe:* Resistance to tetracycline may result from modified pore proteins in the outer membrane that forms a porin too small for the tetracycline to pass through. *Alteration of the drug's target site*: - MRSA (*methicillin-resistant Staphylococcus aureus*) is resistant to all β-lactam drugs because of a mutation in its penicillin-binding protein (PBP). - Resistance to clindamycin develops when mutations in bacteria alter the ribosomal binding site to which clindamycin would normally bind. *Rapid efflux of the antibiotic:* - *Pseudomonas aeruginosa* has membrane pumps that export a number of different antibiotics from its cells.

Part B - How Do Antimicrobial Drugs Inhibit Bacterial Growth? In this activity, you will identify the general mechanism of inhibition for the antimicrobial actions listed. Drag each item into the appropriate bin. - Most people have heard of penicillin, the first major antibiotic discovered and developed. There are actually over 50 different antibiotics in the penicillin, or "cillin," group of antibiotics. All of the members of this group share a structural feature referred to as the common nucleus, within which is a chemical group referred to as the β-lactam ring. The "cillins" differ in the side chain attached to the common nucleus. The different side chains alter the spectrum as well as the stability of the antibiotic. All of the "cillins" interfere with the peptide cross-linking that stabilizes peptidoglycan cell walls. Note the four different "cillins" illustrated here.

*Inhibiting cell wall synthesis (4):* Inhibiting... - bonding of N-acetyl glucosamine to N-acetylmuramic acid - mycolic acid synthesis - synthesis of peptide cross-links - lipopolysaccharide synthesis *Injuring the plasma membrane (1):* Inhibiting fatty acid synthesis *Interfering with DNA replication (2):* - Inhibiting DNA gyrase - Interfering with DNA polymerase *Interfering with RNA synthesis (transcription) [1]:* Interfering with RNA polymerase *Interfering with protein synthesis (4):* Interfering with... - activity of 50S ribosomal unit - activity of 30S ribosomal unit - attachment of tRNA to mRNA - peptide bond formation, catalyzed by the ribosome ^ Correct association of each inhibitory mechanisms with their broader activity.

** Part D ** Scott's pimples result from the inflammatory response generated in his hair follicles. The statements below describe events that occur during this response. Place the following statements in the chronological order that best describes the sequence of events leading to the appearance of acne. 1. Immune cells such as neutrophils and phagocytes move into the follicle to try to eliminate P. acnes. 2. Overproduction of sebum leads to an accumulation in the follicle. 3. The blood vessels surrounding the follicle dilate and become more permeable. 4. P. acnes metabolizes glycerol in sebum, forming free fatty acids. 5. The buildup of dead cells, bacteria, and body fluids causes a raised pustule to appear on the skin surface. 6. Free fatty acids stimulate the release of proinflammatory cytokines within the follicle.

2, 4, 6, 3, 1, and 5 The overproduction of sebum resulting from the hormonal changes that Scott is experiencing is the initial event responsible for his acne. P. acnes is able to utilize the glycerol in sebum for fuel; in the process of doing so, it produces free fatty acids. These fatty acids lead to the production of inflammatory cytokines, which lead to vasodilation and increased vessel permeability. These changes allow for immune cells to move into the follicle. As the immune cells work to eliminate P. acnes, dead cells, bacterial waste, and pressure (from the massive influx of cells) will build. This ultimately distends the follicle. If great enough, this buildup will be visible on the skin as a pus-containing papule.

Use of antibiotics in animal feed leads to antibiotic-resistant bacteria because A) the antibiotics kill susceptible bacteria, but the few that are naturally resistant live and reproduce, and their progeny repopulate the host animal. B) bacteria from other animals replace those killed by the antibiotics. C) the few surviving bacteria that are affected by the antibiotics develop immunity to the antibiotics, which they pass on to their progeny. D) the antibiotics cause new mutations to occur in the surviving bacteria, which results in resistance to antibiotics. E) the antibiotics persist in soil and water.

A) the antibiotics kill susceptible bacteria, but the few that are naturally resistant live and reproduce, and their progeny repopulate the host animal.

** Part F ** Dr. Smith assures Scott that although inflammation may sound scary, there are several possible options for treating Scott's moderate acne. Which of the following would be the most appropriate for Scott's case? Select all that apply. A) topical treatment with a product containing benzoyl peroxide B) eliminating the intake of fatty foods C) topical application of salicylic acid D) a prescription for Accutane E) Clear Light, a nonchemical, light-based system F) an oral antibiotic such as erythromycin

A, E, F A) topical treatment with a product containing benzoyl peroxide E) Clear Light, a nonchemical, light-based system F) an oral antibiotic such as erythromycin - A variety of different approaches that have been successful in treating inflammatory acne. These treatments typically target the growth of the causative organism, P. acnes, and/or the clogged follicle.

More than half of our antibiotics are A) synthesized in laboratories. B) produced by bacteria. C) produced by Fleming. D) produced by fungi. E) produced by eukaryotic organisms.

B) produced by bacteria.

The antibiotic actinomycin D binds between adjacent G-C pairs, thus interfering with A) cellular respiration. B) transcription. C) translation. D) plasma membrane function. E) peptide bond formation.

B) transcription.

** Part C ** Acne is the result of the inflammatory response. In this case, the inflammation is resulting in acne that is very painful (physically and emotionally) for Scott. However, inflammation is a critical component of a normal immune response. What are the main functions of the inflammatory response? Select all that apply. A) producing antibodies, which can target and eliminate the invading organism B) destroying and eliminating the invading pathogen C) "walling off" the site of injury or infection D) generating an increase of body temperature to inhibit the growth of the invading organism E) repairing tissue damage resulting from inflammation

B, C, and E B) destroying and eliminating the invading pathogen C) "walling off" the site of injury or infection E) repairing tissue damage resulting from inflammation

* Part D - Refine your hypothesis. * The bacteria appear to be in clusters, as opposed to chains. This suggests that your patient has ______. A) an infection whose source cannot be determined B) a streptococcal infection C) a staphylococcal infection

C) a staphylococcal infection Yes! You believe your patient has a carbuncle resulting from a staphylococcal infection.

In the presence of penicillin, a cell dies because A) it lacks a cell wall. B) its contents leak out. C) it undergoes lysis. D) it plasmolyzes. E) it lacks a cell membrane.

C) it undergoes lysis.* * (osmotic lysis)

All of the following are characteristic of the Group A beta-hemolytic streptococci EXCEPT A) the ability to damage cell membranes. B) hyaluronidase production. C) methicillin resistance. D) M proteins. E) the ability to dissolve blood clots.

C) methicillin resistance.

** Part E ** Research has indicated that during the inflammatory response to P. acnes, both the classical and the alternative complement pathways are activated. Which of the following are outcomes of activating complement pathways? Select all that apply. A) generation of antibodies against P. acnes B) activation of T cytotoxic cells C) opsonization D) cytolysis E) inflammation

C) opsonization D) cytolysis E) inflammation Activation of the complement cascade has three major outcomes: inflammation, opsonization, and cytolysis. The increased opsonization enhances the ability of phagocytes to engulf and destroy P. acnes. In addition, the formation of membrane attack complexes enhances direct killing of P. acnes. Notice the membrane attack complexes in the figure—the extensive formation of pores in the membrane causes leakage of cell contents and ultimately cell death. The inflammation associated with Scott's acne is intended to bring cells to the site of infection. However, this inflammation is also significantly contributing to the symptoms associated with acne as it is occurs within the localized environment of the hair follicle.

Which of the following is NOT a fungal infection? A) jock itch B) thrush C) pediculosis D) ringworm

C) pediculosis ^ is not a fungal infection. This is a term which refers to an infection with lice.

Which of the following does NOT affect eukaryotic cells? A) antihelminthic drugs B) nucleotide analogs C) semisynthetic penicillins D) antifungal drugs E) antiprotozoan drugs

C) semisynthetic penicillins

Which of the following is NOT caused by HSV-1? A) herpes gladiatorum B) herpes whitlow C) cold sores D) canker sores E) herpes encephalitis

D) canker sores

* Part H * In the 1940s, penicillin began to be widely used to treat a variety of bacterial infections. At that time, penicillin-resistant strains of *S. aureus* were virtually unknown. Twenty years later, 80% of hospital-acquired *S. aureus* were penicillin-resistant, leading to the introduction of methicillin in 1961 to combat penicillin-resistant strains. Within one year, doctors began to encounter methicillin-resistant strains of *S. aureus*. Since the development of methicillin-resistance, strains of *S. aureus* have become resistant to beta-lactam drugs (including all the penicillins), as well as some cephalosporins, leaving vancomycin (typically a "drug of last resort") as the favored treatment for antibiotic-resistant *Staph* infection.In the late 1990s, vancomycin-resistant strains of *Staph* began to appear. Around that time, oxazolidinones also became available, and linezolid, also a drug of last resort, was introduced as a treatment for *S. aureus*. Linezolid-resistant strains of *Staph* were subsequently reported in 2003. The development of multi-drug resistance in *Staphylococcus aureus* is a classic example of ______. A) genetic engineering B) Koch's postulates C) drug-induced cytotoxic reactions D) evolution

D) evolution Yes! The development of multi-drug resistance in *Staphylococcus aureus* is a classic example of evolution.

Warts are caused by A) herpesvirus. B) poxvirus. C) parvovirus. D) papillomavirus. E) *Staphylococcus aureus*.

D) papillomavirus.

Exfoliative toxin is responsible for A) fever blisters. B) impetigo. C) otitis externa. D) scalded skin syndrome. E) thrush.

D) scalded skin syndrome.

Protozoan and helminthic diseases are difficult to treat because A) they do not have ribosomes. B) they do not reproduce. C) they replicate inside human cells. D) their cells are structurally and functionally similar to human cells. E) they have more genes than bacteria.

D) their cells are structurally and functionally similar to human cells.

Drug resistance occurs A) against antibiotics and not against synthetic chemotherapeutic agents. B) when antibiotics are taken after the symptoms disappear. C) because bacteria are normal microbiota. D) when antibiotics are used indiscriminately. E) All of the answers are correct.

D) when antibiotics are used indiscriminately.

* Part B - Review possible diagnoses. * Now that you have considered the evidence at hand, you should start to build a hypothesis about what disease your patient has. In the beginning of your diagnostic process you should try to think broadly and consider any and all reasonable possibilities. You can then narrow down these possibilities by performing diagnostics that can support or refute your hypothesis. Select all conditions that could reasonably apply to your patient. A) measles, rubella B) fifth disease, roseola C) candidiasis D) staphylococcal skin infection (folliculitis, impetigo, scalded skin syndrome, toxic shock syndrome) E) smallpox, monkeypox F) chickenpox, shingles G) herpes simplex H) streptococcal skin infection (necrotizing fasciitis, erysipelas) I) *Pseudomonas* dermatitis, otitis externa J) acne K) Buruli ulcer L) warts M) ringworm N) sporotrichosis O) scabies P) pediculosis

D, H, J D) staphylococcal skin infection (folliculitis, impetigo, scalded skin syndrome, toxic shock syndrome) H) streptococcal skin infection (necrotizing fasciitis, erysipelas) J) acne Yes! You suspect that your patient has nodular cystic acne, or a staphylococcal or streptococcal skin infection.

Newborns' eyes are treated with an antibiotic A) when *Neisseria gonorrhoeae* is isolated from the eyes. B) when the mother is blind. C) when the mother has genital herpes. D) when the mother has gonorrhea. E) as a routine precaution.

E) as a routine precaution.

Which of the following pairs is mismatched? A) otitis externa - *Pseudomonas* B) keratitis - *Acanthamoeba* C) Buruli ulcer - *Mycobacterium* D) conjunctivitis - *Chlamydia trachomatis* E) chickenpox - poxvirus

E) chickenpox - poxvirus

All of the following are protective factors of the skin and its secretions EXCEPT A) lysozyme production. B) tightly packed cells. C) salt. D) keratin. E) pyocyanin production.

E) pyocyanin production.

Foundation Figure 20.2: Major Action Modes of Antimicrobial Drugs & Foundation Figure 20.20: Bacterial Resistance to Antibiotics The goal of antimicrobial treatment is to kill or inhibit the growth of microbes without damaging the host. This is referred to as selective toxicity. To achieve selective toxicity, antimicrobial drugs generally target bacterial cell structures, enzymes, or processes that are unique to the microbe and not found in host cells. In seeking targets that are unique to the microbes, developers of antimicrobial drugs must consider the differences between prokaryotic and eukaryotic cells. Those structures that are exclusive to or distinctly different in prokaryotic cells are likely targets for antibacterial drugs.

Read through both Foundation Figures, and then complete the activity and questions of Part A-H.

Just below the Surface—A Case Study in Acne Part A-G

Scott is excited about starting college in about a month. He's looking forward to living on his own for the first time, meeting new friends, and taking college courses. However, he's also a little apprehensive about becoming part of this new community, full of new people who don't know him. He's particularly self-conscious about the acne on his face and neck. He always had a few pimples here and there, but over the last couple of months, his acne has gotten much more severe. He's been washing his face a lot, but still the acne just seems to be getting worse. Scott tells his mother that he's scared to start college looking this way. Although his mother assures him that it's not as bad as he thinks, she makes an appointment for Scott to see a dermatologist. At the doctor's office, Scott learns that he is not alone. Dr. Smith tells him that it is estimated that more than 80% of teenagers suffer from acne. Scott is happy to learn that although it may seem like a hopeless situation, there are several options available to help treat his acne. Dr. Smith explains to Scott that his acne is caused by a bacterium known as Propionibacterium acnes. It's the interaction between this bacterium and Scott's immune system that is leading to his acne.

Part F - Mechanisms of Antibiotic Resistance, Part 2 There are basically four mechanisms of microbial resistance. This activity asks that you drag the statement describing each mechanism to the appropriate area of the image that represents the mechanism. Drag each statement to the appropriate area of the diagram. - Antibiotic resistance has become a serious problem in health care that continues to worsen. Organisms such as MRSA (methicillin-resistant *Staphylococcus aureus*), VRE (vancomycin-resistant *Enterococcus*), and XDR-TB (extensively drug-resistant tuberculosis) are in the news almost every week as their frequency increases in both hospitals and the community. The names MRSA and VRE really don't tell the entire story. These two bacterial strains are resistant to more than methicillin (MRSA) or vancomycin (VRE); they exhibit resistance to numerous different classes of antibiotics, which greatly complicates treatment of infections.

TOP: Entry of antibiotic into the cell is blocked. BOTTOM: Efflux mechanism pumps antibiotic out of the cell. LEFT: Target site to which antibiotic binds is altered. RIGHT: Cellular enzyme inactivates an antibiotic. The figure illustrates the four basic mechanisms that enable microorganisms to resist the inhibitory or lethal effects of antibiotics. In the next part, you will identify examples of each of these mechanisms of antibiotic resistance.

Which statement regarding the skin is false? a) Sweat contains an enzyme called lysozyme, which breaks down the cell walls of some bacteria. b) The sweat glands produce a salty fluid that is a rich source of protective antibodies. c) The outer layer is composed of dead cells. d) It is waterproof.

b) The sweat glands produce a salty fluid that is a rich source of protective antibodies. ^ NOT TRUE Antibodies are not typically found in the perspiration.

Part E - Mechanisms of Antibiotic Resistance, Part 1 Consider the different mechanisms through which antibiotics inhibit microbial growth, and consider what changes in the microbe might enable it to resist the inhibitory effects of antibiotics. Select all of the statements that describe a mechanism that would enable a microorganism to resist the action of an antibiotic. a) An enzyme that destroys the antibiotic is produced. b) An altered target enhances the binding of antibiotic. c) A transport mechanism that rapidly transports antibiotic through the plasma membrane into the cytoplasm is developed. d) Altered porins in the cell wall block passage of antibiotic through the cell wall. e) Target site is modified, so that an antibiotic is unable to bind to its target. f) A microbe develops a transport mechanism in the plasma membrane that rapidly pumps antibiotic out of the bacterial cell.

a) An enzyme that destroys the antibiotic is produced. d) Altered porins in the cell wall block passage of antibiotic through the cell wall. e) Target site is modified, so that an antibiotic is unable to bind to its target. f) A microbe develops a transport mechanism in the plasma membrane that rapidly pumps antibiotic out of the bacterial cell. ^ Correctly identified several different antibiotic-resistance mechanisms. There are multiple examples of each of these resistance mechanisms illustrated by the array of resistant bacteria.

Which of the following is incorrectly matched? a) Pseudomonas - inclusion conjunctivitis b) Acanthamoeba - keratitis c) Haemophilus influenzae - pinkeye d) Chlamydia trachomatis - trachoma e) Neisseria gonorrhea - opthalmia neonatorum *Left side of answer choices before the dash mark (-) are italicized*

a) Pseudomonas - inclusion conjunctivitis ^ NOT CORRECT

Which statement regarding tests for microbial susceptibility to chemotherapeutic agents is FALSE? a) The Kirby-Bauer test is useful because it can differentiate bacteriostatic effects from bactericidal effects. b) During a disk-diffusion test, a clear zone around the test disk indicates that growth was inhibited. c) A broth dilution test is often used to determine MIC and MBC of an antimicrobial drug. d) During the Kirby-Bauer test, a Petri plate with agar medium is uniformly inoculated with a standardized amount of a test organism.

a) The Kirby-Bauer test is useful because it can differentiate bacteriostatic effects from bactericidal effects. ^ NOT TRUE

Which statement correctly describes the normal microbiota of the skin? a) The skin's normal microbiota are capable of growth at elevated salt concentrations. b) Most microorganisms that grow on the skin are sensitive to drying. c) Most of the normal microbiota on the skin are gram-negative. d) Vigorous washing will eliminate all skin bacteria.

a) The skin's normal microbiota are capable of growth at elevated salt concentrations.

Part D - Antibiotics That Inhibit Protein Synthesis There are a large number of antibiotics that inhibit protein synthesis at 70S ribosomes found in bacterial cells but do not interfere with protein synthesis at the 80S ribosomes found in eukaryotic cells. Some of these antibiotics bind to the smaller ribosomal subunit and interfere with the reading of the mRNA code, whereas others bind to the larger ribosomal subunit and inhibit the formation of peptide bonds. Unfortunately, some of the antibiotics that inhibit protein synthesis in bacteria exhibit some toxicity to the eukaryotic host cells as well. What is the most likely reason for this toxicity to the host cell? a) These antibiotics interfere with protein synthesis within eukaryotic mitochondria. b) These antibiotics interfere with DNA replication in eukaryotic cell nuclei. c) These antibiotics plug up the membrane transport mechanisms in eukaryotic cells. d) These antibiotics bond to eukaryotic tRNA. e) These antibiotics bind to eukaryotic cytoplasmic ribosomes. - A substantial amount of progress has been made in the development of antibacterial drugs. The search for new antibiotics is critical, however, as bacteria continue to develop resistance to currently used antibiotics. Resistance typically arises by mutation, and once microorganisms have become resistant, the continued use of antibiotics enables those that have developed resistance to survive at the expense of those that are susceptible. Over time, this selection of the resistant strains gives rise to their predominance in the bacterial population. Antibiotic resistance can spread among bacterial populations both vertically (by binary fission) and horizontally (via genetic transfer mechanisms).

a) These antibiotics interfere with protein synthesis within eukaryotic mitochondria. Eukaryotic mitochondria have 70S ribosomes, composed of 50S and 30S subunits, which are very similar to the ribosomes of bacterial cells. Some of the antibiotics that target bacterial ribosomes will cause some toxicity in eukaryotic cells because of their effects on the mitochondrial ribosomes.

* Part L - Treat the infection. * You carefully think over these results. You ultimately decide to drain the pus from the carbuncle and dress the wound. You instruct the boy and his family about proper wound care and decontamination to prevent the spread and recurrence of the infection. Why did you not prescribe antibiotics in this case? a) Using antibiotics can accelerate drug resistance in Staph. b) Antibiotics have side effects. c) Antibiotics will kill off beneficial bacteria. d) Antibiotics may increase opportunistic infections.

a, b, c, d (All answer choices are correct) Yes! With careful supervision, your patient's wound heals well. Many health professionals agree that if a Staph infection can be treated without the use of antibiotics, it should be! Unnecessary antibiotic use for staphylococcal infections can double the probability of developing future MRSA infection.You made responsible choices with the treatment you administered, and if these sort of smart choices continue, you may be able to fight drug-resistant bacteria more efficiently.

* Part A - Identify relevant information. * After reviewing your patient's medical history, you decide to list out the factors that you think will be most important to your diagnostic process. Review the following list and select the factors that you believe are most relevant to a diagnosis. a) the patient's symptoms b) the fact that the bite did not respond to treatment with antibiotic ointment c) the patient's pets d) the patient's activities before and during the infection e) the patient's parents' occupations f) the fact that more than one person had similar symptoms g) the patient's age h) the patient's location

a, b, d, f a) the patient's symptoms b) the fact that the bite did not respond to treatment with antibiotic ointment d) the patient's activities before and during the infection f) the fact that more than one person had similar symptoms

* Part J * Natural selection is a gradual, nonrandom process by which biological traits become more or less frequent within a population. Which of the following are necessary conditions for natural selection to occur within a population of *Staphylococcus aureus*? a) Individuals in the population vary from one another. b) Some individuals in the population reproduce more than others. c) Deleterious (harmful) genes are removed from the population. d) Traits are hereditary. e) Some individuals within the population are optimally adapted for survival. f) There is adaptation. g) Traits that permit an individual to survive at least until reproduction will increase in frequency over time. ~ Interpret evidence. Since you have considered how bacteria evolve antibiotic resistance, you want to be very careful about what medicine you treat your patient's infection with. Although there is a fairly good chance that if you treat your patient with linezolid (a powerful antibiotic of last resort), his infection will improve, you also know that unnecessary antibiotic use can perpetuate the evolution of drug resistance. You decide to use the Kirby-Bauer test to assess the sensitivity of the strain of *Staphylococcus aureus* affecting your patient. Your results are shown below: Picture of P= penicillin, M= methicillin, E= erythromycin, V= vancomycin, X = trimethoprim sulfamethoxazole

a, b, d, g a) Individuals in the population vary from one another. b) Some individuals in the population reproduce more than others. d) Traits are hereditary. g) Traits that permit an individual to survive at least until reproduction will increase in frequency over time. Yes! Because individuals in a population differ from one another and can pass these differences on, the genes of individuals that survive to reproduce will increase in the population over time.The length of time it takes for these genes to increase within a population of bacteria is relatively short. There are several reasons for this: bacteria have relatively large population sizes and short generation times; bacteria also can pass their genes on to others by either vertical (from parent to offspring) OR horizontal transfer (one bacterium can pass a plasmid to another). All of these factors influence the rate at which genetic variations can arise and be sustained in a population.

Which of the following does NOT constitute an advantage of using two antibiotics together? a) It allows treatment to be provided prior to diagnosis. b) Two are always twice as effective as one. c) It lessens the toxicity of individual drugs. d) It can prevent drug resistance. e) All of these are advantages of using two antibiotics together.

b) Two are always twice as effective as one.

Part H - How Do Microorganisms Acquire Antibiotic Resistance? Identify the statements below that accurately describe the mechanisms through which organisms acquire antibiotic resistance. Select all of the statements that accurately describe the origins and spread of antibiotic resistance. a) Antibiotic-resistance genes can be passed horizontally via bacterial conjugation. b) Antibiotics cause an increase in the rate of horizontal gene transfer. c) Antibiotic-resistance genes can be passed horizontally via transduction. d) Antibiotic resistance is readily transmitted to the next generation during binary fission. e) Mutations are the ultimate source of antibiotic-resistance genes. f) Antibiotics select for those microbes that have developed resistance, increasing their frequency in the bacterial population. g) Antibiotics cause mutations; heavy antibiotic use directly leads to mutations in microbes, giving rise to antibiotic resistance. h) Antibiotic-resistance genes can be passed from one bacterium to another by bacterial transformation.

a, c, d, e, f, h a) Antibiotic-resistance genes can be passed horizontally via bacterial conjugation. c) Antibiotic-resistance genes can be passed horizontally via transduction. d) Antibiotic resistance is readily transmitted to the next generation during binary fission. e) Mutations are the ultimate source of antibiotic-resistance genes. f) Antibiotics select for those microbes that have developed resistance, increasing their frequency in the bacterial population. h) Antibiotic-resistance genes can be passed from one bacterium to another by bacterial transformation. You have identified the statements that accurately describe the origins and spread of antibiotic resistance. It is important to understand that resistance typically originates through spontaneous mutations and then can spread horizontally through bacterial transformation, conjugation, and transduction and vertically through binary fission. Antibiotic use provides the selective pressure that reduces the number of antibiotic-susceptible bacteria, resulting in an increase in the number of antibiotic-resistant strains. Antibiotics don't cause the DNA changes that bring about the resistance, but rather provide a selective environment in which only those microbes that are resistant can proliferate.

Infants may acquire a serious form of conjunctivitis during birth if they are born to a mother infected with __________. a) *Haemophilus influenzae b) Neisseria gonorrhoeae c) Acanthamoeba* species d) Beta hemolytic streptococcus Group B

b) *Neisseria gonorrhoeae*

** Part A ** The name Propionibacterium is derived from the fact that the organism produces propionic acid during fermentative metabolism. Which of the following statements about fermentative metabolism is true? a) Fermentation does not yield any ATP for the cell. b) Fermentation produces significantly less ATP than aerobic respiration; however it generates NAD+, which can be used in glycolysis. c) Fermentation is unfavorable because the production of acidic end-products provides an unfavorable environment for the organism's growth. d) All fermentative organisms have the ability to perform ethanol fermentation. ~ Scott is a little concerned when Dr. Smith tells him that a bacterium is in part responsible for his acne. Dr. Smith explains that bacteria are a normal part of a healthy functioning immune system and that they actually have important roles in our normal physiology. The problem in Scott's case is that things are a little out of balance. Hormonal changes are causing Scott's body to produce more sebum than is needed.

b) Fermentation produces significantly less ATP than aerobic respiration; however it generates NAD+, which can be used in glycolysis. For fermentative organisms, ATP is typically generated only during glycolysis. Recall that glycolysis yields 2 ATP per glucose molecule for the organism. Although this may not seem significant compared to the amount of ATP that can be produced during oxidative phosphorylation, it is enough to meet the needs of the organism. Essential to this is the recycling of NADH that occurs during fermentation. As organisms convert pyruvate into other organic compounds such as propionic acid, they are able to oxidize NADH and regenerate NAD+ to be used in glycolysis. Without this ability, glycolysis (and ATP production) would cease.

Which of the following is NOT true of acne? a) Drugs that inhibit sebum formation are useful in treating inflammatory acne. b) It can be treated by eliminating fatty foods from the diet. c) It is often due to the action of *Propionibacterium*. d) Mild cases are treated with topical agents. e) Antibiotics may be prescribed for moderate cases.

b) It can be treated by eliminating fatty foods from the diet.

The patient has scaling skin on his fingers. Conidiospores are seen in microscopic examination of skin scrapings. The etiology is a) Candida. b) Microsporum. c) Pseudomonas aeruginosa. d) Staphylococcus aureus. e) Mycobacterium ulcerans. *All answer choices are italicized*

b) Microsporum.

* Part F - Diagnose the organism. * These results support the idea that your patient's infection was caused by ______. a) Staphylococcus saprophyticus b) Staphylococcus aureus c) Staphylococcus epidermis *All answer choices are italicized*

b) Staphylococcus aureus Yes! You believe that your patient is infected with *Staphylococcus aureus*. DNA tests confirm your diagnosis- your patient has a *Staph* infection!

Why is it more difficult to treat viral infections than it is to treat bacterial infections? a) Viruses are very similar to human cells. b) Viruses use the host cell's processes to carry out their own reproduction. c) Viruses are smaller than human cells. d) Viruses have cell walls.

b) Viruses use the host cell's processes to carry out their own reproduction.

** Part B ** Part of the reason for Scott's acne is the overproduction of sebum. Scott's initial instinct is that shutting down production of sebum would be the quickest route to eliminating his acne; however, sebum actually plays an important role in maintaining the skin as a first line of defense against pathogens. Which of the following best describes the role of sebum as a component of the first line of defense? Select all that apply. a) Sebum creates an anaerobic environment, thereby preventing the growth of pathogenic organisms. b) Sebum helps to keep the pH of the skin low, which inhibits the growth of microorganisms. c) Sebum forms a protective layer over the skin. d) Sebum contains enzymes that inhibit the growth of pathogens. ~ Dr. Smith continues to explain to Scott that the overproduction of sebum is just half of the equation. The excess sebum is not only clogging his pores, but also serving as a food source for P. acnes. This increases the growth of the bacteria, which in turn leads to inflammation. The acne on Scott's face and neck is a physical manifestation of this inflammation.

b) and c) b) Sebum helps to keep the pH of the skin low, which inhibits the growth of microorganisms. c) Sebum forms a protective layer over the skin. During adolescence, hormonal changes cause the production of sebum to increase above "normal" levels. As a result of this overproduction, the follicle can become clogged with sebum—setting the stage for P. acnes growth and subsequent acne. Sebum production is essential not only for normal immune function but also for overall skin health and function. Therefore, although completely eliminating sebum production would have an impact on acne, it would lead to other significant physiological impacts as well.

Several individuals who frequently swim at a local community pool have developed infections. Some have developed a skin rash and others have developed a painful infection of the outer ear canal. What is the most likely etiologic agent? a) Staphylcoccus aureus b) Candida albicans c) Pseudomonas aeruginosa d) Herpes simplex virus *All answer choices are italicized*

c) Pseudomonas aeruginosa These are two typical examples of infections caused by *Pseudomonas aeruginosa*. The ear infection is also known as otitis externa.

* Part E - Interpret results. * You would like to determine which species of Staphylococcus your patient is infected with. Which test will allow you to eliminate some possibilities? One of the most important phenotypic features that can be used to differentiate among Staph species is their ability to produce _________ , an enzyme that causes blood clot formation.

coagulase Yes! You perform a coagulase test. Your results are shown here: - Picture: Negative control (left), Isolate from patient (right)

Which of the following statements concerning necrotizing fasciitis is FALSE? a) Some cases require limb amputation. b) It may be caused by several different organisms, but Streptococcus pyogenes is the most common. c) It is often associated with streptococcal toxic shock syndrome. d) The tissue damage is mainly due to the production of endotoxin, which stimulates a severe immune response.

d) The tissue damage is mainly due to the production of endotoxin, which stimulates a severe immune response. ^ NOT TRUE Many cases of necrotizing fasciitis are caused by gram-positive bacteria which do not produce endotoxin.

A 45-year-old man has pus-filled vesicles distributed over his back in the upper right quadrant, over his right shoulder, and upper right quadrant of his chest. His symptoms are most likely due to a) Streptococcus pyogenes. b) herpes simplex virus. c) Candida albicans. d) varicella-zoster virus. e) Staphylococcus aureus. *All answer choices are italicized* except for b) and d)

d) varicella-zoster virus.

* Part G - Consider new evidence. * Before you can treat you patient, there is a very important factor you must consider. Selecting the best drug to treat *Staphylococcus aureus* infections can be difficult because some strains of the bacteria have developed ____ __________ .

drug resistance Yes! Some strains of *Staphylococcus aureus* have developed antibiotic resistance.

Thrush and vaginitis are caused by a) Chlamydia trachomatis. b) Streptococcus pyogenes. c) Staphylococcus aureus. d) herpesvirus. e) Candida albicans. *All answer choices are italicized* except d)

e) Candida albicans.

The following results were obtained from a disk-diffusion test for microbial susceptibility to antibiotics. *Staphylococcus aureus* was the test organism. Antibiotic / Zone of Inhibition: A / 3 mm B / 7 mm C / 0 mm D / 10 mm In the table, the antibiotic that exhibited bactericidal action was a) D. b) C. c) A. d) B. e) The answer cannot be determined based on the information provided.

e) The answer cannot be determined based on the information provided.

Which disease commonly leads to blindness in parts of the world but can be largely controlled through sanitary practices and health education? a) *Acanthomoeba* keratitis b) Herpetic keratitis c) Yaws d) Buruli ulcer e) Trachoma

e) Trachoma

* Part I * A driving force of this sort of evolution is _______ _________, which is sometimes colloquially referred to as the "survival of the fittest."

natural selection Yes! Natural selection is a driving force in the evolution of antibiotic resistance.