Week 1: Formative quiz

Question 1

Antibiotic that is most commonly implicated for the adverse effects listed: Redman Syndrome

Answer 1

Vancomycin

Redman Syndrome is a reaction to infusion of vancomycin. It is not an allergic reaction but rather a flushing reaction associated with rapid infusion of intravenous vancomycin. It can be resolved by slowing down the infusion rate. (Antibiotics-adverse effects)

Question 2

antibiotic that is most commonly implicated for the adverse effects listed: Rash in patient with infectious mononucleosis

Answer 2

Ampicillin. When patients with EBV-associated infectious mononucleosis (Ebstein-Barr Virus) are prescribed an aminopenicillin, such as ampicillin or amoxicillin, many patients will develop a rash. This does not mean that the person has an allergy to the aminopenicillin. (Antibiotics-adverse effects)

Question 3

Antibiotic that is most commonly implicated for the adverse effects listed: Esophageal ulcer

Answer 3

Doxycycline

Tetracycline derivatives (minocycline and doxycycline) are associated with drug induced esophageal ulceration. Recumbent posture after drug ingestion is a predisposing factor. The most important measure to prevent this condition is to instruct patients to take drugs in the upright position with at least 100 ml of water. (Antibiotics-adverse effects)

Question 4

Choose the mechanism of action for the class of antibiotic: Clindamycin

Answer 4

Protein synthesis inhibitor

Protein synthesis inhibitor. Clindamycin is a lincosamide antibiotic that binds to the 50S subunit of the ribosome and is therefore a protein synthesis inhibitor (Antibiotics-mechanisms of action)

Question 5

Choose the mechanism of action for the class of antibiotic: Penicillins

Answer 5

Cell wall synthesis inhibitor

Cell wall synthesis inhibitor . Penicillins are β-lactam antibiotics. They bind to the transpeptidase (aka PBP or penicillin binding protein) and as such are cell wall synthesis inhibitors. (Antibiotics-mechanisms of action)

Question 6

A previously healthy 23-month-old girl presents with a fever, vomiting and flank pain. A urine is collected by in-and-out catheterization and the urine is sent for urinalysis (UA) and urine culture. The UA has pyuria (leukocytes in the urine) and many bacteria. She is admitted for intravenous antibiotics for presumptive pyelonephritis (kidney infection). A Gram-negative rod is isolated on the preliminary urine culture report. Which of the following is the MOST APPROPRIATE antibiotic to be prescribed empirically while waiting for culture results?

Answer 6

Gentamicin. Gentamicin is the only correct choice of those antibiotics that are listed because none of the others ever has activity against Gram-negative rods (Antibiotics-spectrum)

Question 7

Which of the following orally administered antibiotics is not appropriate for outpatient treatment of a severe systemic infection because it has negligible oral absorption?

Answer 7

Vancomycin. Negligible amounts are absorbed when taken orally. The other drugs are fairly well absorbed when taken orally (Antibiotics-route)

Question 8

An elderly patient in a nursing home is given a proton pump inhibitor (PPI) to prevent acid reflux. She develops shortness of breath with coughing. Her chest X-ray indicates she has developed pneumonia. What host defense barrier has been impaired that increased her susceptibility to infection?

Answer 8

Stomach acidity (low pH). The low pH in the stomach helps to kill potentially pathogenic organisms so interfering with this can increase risk of pneumonia. (Host-Pathogen Interaction)

Question 9

A college student goes to Student Health complaining of vomiting and diarrhea over the past few hours. The physician who sees her is not concerned and tells her that a virus is going around and she will be well in a day. Within 24 hours, she is no longer vomiting and the diarrhea has ended. What host defense factor was responsible for limiting the course of this infection?

Answer 9

Type 1 Interferon. (Host-Pathogen Interaction)

Question 10

A previously healthy 9 year-old boy presents in early December with a two day history of a sore throat. Several classmates have been sick the past 2 weeks with Strep throat so his mother brings him in to see you today to rule out Strep. In addition to the sore throat, he has had a runny nose and sneezing but no fever and no other symptoms. On examination his temperature is 37.0˚C and his other vital signs are normal. He is talkative, interactive and breathing comfortably. His neck is supple. He has shotty (minimal) anterior cervical lymphadenopathy bilaterally. His conjunctivae are normal with no erythema and no drainage. His tympanic membranes are pearly with good landmarks and good mobility. He has profuse serous rhinorrhea. His oral mucosa is moist. His tonsils are mildly enlarged with erythema but no exudates. He has no palatal petechiae. The remainder of his physical exam is normal. Which one of the following is the MOST LIKELY diagnosis?

Answer 10

Viral upper respiratory tract infection. It is unlikely to be Strep because he does not have fever and he DOES have rhinorrhea and sneezing. He does not have a history of seasonal allergies and it would be an unusual time of the year to have allergies. If he is fully immunized and has not traveled outside the U.S., would be very unlikely to have diphtheria and he should be more ill. Would expect fevers and significant lymphadenopathy for infectious mononucleosis. (ENT Infection - Differential Diagnosis)

Question 11

An adult with chronic liver disease is treated with azithromycin and ceftriaxone for community-acquired pneumonia. He improves and is ready to be discharged on oral medications. His sputum cultures are positive for Streptococcus pneumoniae. The isolate is resistant to azithromycin. What is the most likely mechanism for this pattern of resistance to azithromycin?

Answer 11

A gene associated with protection of the ribosomal target. (Antibiotic Resistance)

Question 12

Choose the most likely mechanism of genetic transfer between cells described below. This mechanism is the mating or quasi-sexual exchange of genetic material from one bacterium (the donor) to another bacterium (the recipient) and usually occurs between members of the same or related species.

Answer 12

Conjugation. Conjugation is transfer of plasmid from one bacteria to another related bacteria or transfer of genomic DNA from 1 to another bacteria. Transduction involves transfer of genetic material by way of a bacteriophage. Transformation is when there is cell lysis and naked DNA gets picked up by other bacteria. Transposons are not a mechanism of transfer but rather a genetic element that is transferred aka jumping genes. (Bacteriology, Antibiotic Resistance)

Question 13

For the definition below, choose the most likely genetic element it describes. These are small genetic elements that replicate independently of the bacterial chromosome. Most are circular, double-stranded DNA molecules. Some can integrate into the host chromosome.

Answer 13

Plasmids. Many bacteria share their DNA with other bacteria. The transferred DNA can be integrated into the recipient cell’s genomic chromosomal DNA or stably maintained as an extrachromosomal element – i.e., a plasmid. Bacteriophages are extrachromosomal genetic elements that can survive outside of a host cell because a protein coat (it is a bacterial virus) protects the nucleic acid genome. Transposons are mobile genetic elements that can transfer DNA within a cell, from one position to another in the genome, or between different molecules of DNA (ie plasmid to plasmid or plasmid to chromosome) aka jumping genes. (Bacteriology, Antibiotic Resistance)

Question 14

A 21-year-old male military recruit is seen in the Emergency Department with sudden onset severe headache, neck stiffness, and fever. He is hypotensive and has a bilateral lower extremity petechial rash. Cerebrospinal fluid is sent for culture. Growth of small transparent colonies is noted on chocolate agar. Gram stain reveals intracellular gram negative cocci in pairs. Which of the following stains is responsible for the color seen on Gram stain of this organism?

Answer 14

Safranin. Gram-negative organisms are decolorized by 95% alcohol and then take on a safranin counter-stain that dyes the organism red. Our patient has Neisseria meningitidis infection with meningitis and meningococcemia. (Laboratory Diagnosis of Bacterial Infection)

Question 15

Which of the following components is found in BOTH human cells and bacteria.

Answer 15

Phospholipid bilayer. Cholesterol is not found in bacteria. Some bacteria can form endospores. Ergosterol is found in fungi. LPS is found in Gram negative organisms. (Bacteriology)

Question 16

A 1-week-old infant is brought to the Emergency Department by his parents with a 2 day history of fever, vomiting, poor feeding, and irritability. Blood and cerebrospinal fluid are sent for culture. The next day, multiple bacterial colonies surrounded by a clear zone are seen on blood agar. A catalase test is performed and is negative. Which of the following organisms is the MOST LIKELY cause of this infant’s illness?

Answer 16

Streptococcus agalactiae. Streptococcus agalactiae / Group B Strep is β-hemolytic (clear zone on blood agar). Like all Strep, it is catalase negative. GBS is one of the top three causes of meningitis in infants younger than 3 months old. Streptococcus pneumoniae is alpha-hemolytic. Staph aureus is â-hemolytic but it is catalase positive. (Laboratory Diagnosis of Bacterial Infection)

Question 17

This bacterial external structure consists of polysaccharide. It allows the bacteria to firmly adhere to various structures including skin, heart valves, and indwelling catheters. It is found in certain strains of Pseudomonas aeruginosa and Staphylococcus epidermidis. Which external specialized structure does this describe?

Answer 17

Glycocalyx. A (capsule) is not correct. Although most bacterial capsules consist of polysaccharide, capsules are not seen in Staph epidermidis etc. Fimbriae are also known as pili and aid in adherence. Flagella help with movement / mobility of the bacteria. Spores are dormant forms that only certain Gram positive bacteria can become when under stressful environmental conditions. (Bacteriology)

Question 18

For the bacteria listed, choose the correct gram stain morphology. Staphylococcusepidermidis

Answer 18

Gram-positive cocci in clusters. (Laboratory Diagnosis of Bacterial Infection)

Question 19

A 16-year-old female gymnast was admitted with pyelonephritis (kidney infection). Her urine grew Escherichia coli that was susceptible to all antibiotics in the antibiotic susceptibility profile. She has no known drug allergies. Her fever, flank pain and vomiting have resolved, she is well hydrated and is ready for discharge home. You would like to switch her to cephalexin, an oral antibiotic to which her organism was susceptible. When switching from parenteral to enteral therapy, which of the following pharmacologic properties is the MOST IMPORTANT one to consider in this setting?

Answer 19

Bioavailability of the antibiotic. Lipid solubility would be important if she had a central nervous system infection – lipophilic drugs can penetrate the blood brain barrier better. She needs an antibiotic that is excreted in the kidneys and achieves good concentration in the urine. When switching from a parenteral to an enteral (oral antibiotic) already there is another factor introduced and that is oral absorption. A drug that is not well absorbed will have lower serum concentrations that one that is absorbed very well (ie bioavailability). (Antibiotic Overview)

Question 20

Which one of the following sites is sterile (i.e., no normal flora / microbiome)?

• Gingiva
• Large intestine
• Middle ear
• Nares
• Vagina

Answer 20

Middle ear. The middle ear is one of those sites that is always sterile in the normal host. Other sites include blood, brain, renal parenchyma, bladder, synovial fluid, peritoneal fluid, pleural fluid, etcetera. (Host-Pathogen Interaction, Bacteriology)

Question 21

These culture media support the growth of most organisms that do not have fastidious growth requirements. Examples of media in this category include blood agar and chocolate agar. What type of culture media does this best describe?

• Enriched, nonselective culture media
• Selective differential culture media
• Specialized culture media

Answer 21

Enriched, nonselective culture media. The first media that a sample (urine, wound, spinal fluid) is inoculated onto for incubation, and is one that will support the growth of most organisms.. Specialized culture media would be for isolation of fastidious organisms. Selective differential media are designed for the recovery of specific organisms that may be present in a mixture of other organism – e.g. trying to find Staph aureus from a nasal swab since the nose is colonized with many bacteria. Some commonly used enriched, nonselective culture media include blood agar, chocolate agar, Mueller-Hinton agar, Thioglycolate broth, Sabourand dextrose agar. (Laboratory Diagnosis of Bacterial Infection)

Question 22

Which of the following lab tests is used to differentiate Staphylococcus from Streptococcus?

Answer 22

Catalase. All Staphylococci are catalase positive while All Streptococci are catalase negative. Bacitracin is a test used to differentiate Streptococci. Group A streptococcus is sensitive to Bacitracin. Coagulase is a test used to differentiate Staph aureus from all other Staph. Oxidase and urease are tests used to differentiate Gram-negative bacilli. (Laboratory Diagnosis of Bacterial Infection)

Question 23

The medical technologist was performing a Gram stain on an isolate from a blood culture when she was interrupted by a phone call. When she returned to the Gram stain, she forgot the step that uses acetone / ethanol. If the organism that she was gram staining was Escherichia coli, what color would it appear on this incorrectly performed Gram stain?

Answer 23

Purple. The procedure for a gram stain begins with heat fixing the organism to a slide, then Step 1: Staining it with crystal violet. Step 2: Adding Gram’s iodine. The crystal violet is precipitated by the iodine and is trapped in the thick peptidoglycan layer of Gram-positive bacteria. Step 3: Acetone or ethanol is then used. It doesn’t affect the gram positives, but it decolorizes (washes away) the blue- purple stain – i.e. the crystal violet-Gram’s iodine complex – because Gram negatives that have a thin peptidoglycan layer. Step 4: Safranin – a counter stain – is then added. The safranin will not change the “Purple” color of the gram positives. For gram negatives, they would be colorless after the ethanol step if there was not a counter stain. The safranin imparts a pinkish / red color to the Gram negatives. So if the ethanol step was left out, the E coli would remain purple. Remember what Dr. Culbreath said: P = Peptidoglycan (thick), Positive (gram), and Purple. Also – due to degradation of the peptidoglycan, Gram stain is not a dependable test for bacteria that are starved (e.g. old cultures or stationary phase cultures) or for bacteria that have been treated with antibiotics (which can affect the gram stain and morphology). Bacteria that cannot be classified by Gram stain include mycobacteria, which have a waxy outer shell, and mycoplasma – which have no peptidoglycan, chlamydiae, which don’t pick up stain well, and treponemas, which are too small to see in light microscopy. (Laboratory Diagnosis of Bacterial Infection)

Question 24

A Gram positive coccus is isolated from a blood culture in a patient with a prosthetic heart valve. On Gram stain, this organism is arranged in pairs or short chains (see Gram stain below). The isolate is α-hemolytic on blood agar plate. It is catalase negative, resistant to bile, resistant to optochin, and positive for PYR (pyrrolidonyl arylamidase). Which of the following is the MOST LIKELY organism?

• Enterococcus faecium
• Leuconostoc
• Streptococcus agalactiae
• Streptococcus pneumoniae
• Streptococcus pyogenes

Answer 24

Enterococcus faecium. Enterococci will appear as elongated gram-positive cocci arranged in pairs and short chains. These bacteria cannot be distinguished from S. pneumoniae by Gram stain alone. Enterococci can be identified by the PYR test (positive test for the enzyme pyrolidonyl arylamidase). S. pneumoniae can be rapidly identified by exposing the cell to bile (or another detergent) which will dissolve the bacteria (“bile soluble”). the PYR test is negative. Leuconostoc is a catalase-negative gram positive coccus that is an opportunistic pathogen. It resembles streptococcus but it is inherently resistant to vancomycin, a trait that has not been seen in streptococci.Streptococcus agalactiae (Group B streptococcus) is negative for PYR, and is β-hemolytic, not α-hemolytic. Streptococcus pyogenes (Group A Streptococcus) is positive for pyrrolidonyl arylamidase, but it is β-hemolytic, not α-hemolytic.(Laboratory Diagnosis of Bacterial Infection)

Question 25

Your patient returns today with another soft tissue abscess. He has had several methicillin-resistant Staphylococcus aureus skin and soft tissue infections in the past 3 months. Assuming this is a Staph aureus infection, which of the following tests is the best way to diagnose a Staph infection? * Bacterial culture of an aspirate of the pus * Direct fluorescent antibody for Staph on a sample of the pus * Gram stain of the pus * Polymerase Chain Reaction of the pus * Serology for Staph aureus * Currently there is no PCR for Staph aureus that is commercially available. Serology is not useful either, because everyone has been exposed to Staph aureus (since it is normal flora) and would have antibodies so it would not differentiate past exposure from current infection. A Gram stain could be suggestive of Staph, but coagulase-negative Staph is universally present on the skin, so Gram positive cocci in clusters would not be diagnostic in this setting. There is no DFA for Staph either. DFA is used for viral infections like HSV & VZV. (Laboratory Diagnosis of Bacterial Infection)

Answer 25

Bacterial culture of an aspirate of the pus. Culture is the best method for diagnosing a Staph aureus infection. It also permits susceptibility testing so you can determine if it is MRSA or MSSA (methicillin-susceptible)

Question 26

A 3 day old term neonate presents with sepsis syndrome. Her CSF (cerebrospinal fluid) is culture negative but her blood is growing a β-hemolytic Gram positive coccus. Streptococcus agalactiae (Group B Streptococcus) can be tentatively identified and differentiated from Streptococcus pyogenes (Group A Streptococcus) by which of the following tests? * Bile solubility * CAMP test * Catalase * Coagulase * Optochin

Answer 26

CAMP test. Streptococcus agalactiae (Group B Strep) can be tentatively identified and differentiated from Group A strep by the following tests: negative catalase test, positive CAMP test and hydrolysis of hippurate. Group A strep are catalase negative too so that doesn't help differentiate them. Coagulase is a test used to differentiate species of Staph. Optochin and bile are used to diagnose Strep pneumoniae. (pneumococcus). Group B streptococci are identified definitively by the demonstration of the group-specific carbohydrate or the use of commercially prepared molecular probes. Group B streptococci produce a diffusible, heat-stable protein (CAMP factor) that enhances β hemolysis of Staphylococcus aureus. S. aureus (streaked from the top to the bottom of the agar plate) produces sphingomyelinase C, which can bind to erythrocyte membranes. When exposed to the group B CAMP factor, the cells undergo hemolysis (compare the two positive reactions of enhanced hemolysis to the immediate left of the vertical line) (Laboratory Diagnosis of Bacterial Infection)

Question 27

A 21-year-old sexually-active college student living in the dorms was seen by student health with a complaint of two days of a sore throat. Examination of the pharynx revealed patchy erythema and exudates on the tonsillar pillars. A throat swab was sent to the lab. Gram stain of the smear revealed gram-positive cocci in chains and gram-negative diplococci. What is the significance of Gram stain of the smear in his case? * It is not useful since diagnosis cannot be made by Gram stain alone. * It provides a rapid means of diagnosing the infection. * It is more specific than Streptococcal antigen testing. * It suggests pharyngitis caused by Neisseria gonorrheae. * It is evidence of infection with Group A Streptococcus and Neisseria.

Answer 27

It is not useful since diagnosis cannot be made by Gram stain alone. This is an important concept. Gram stains are most useful when performed on a specimen from a normally sterile site (i.e. cerebrospinal fluid, pleural fluid, peritoneal fluid, synovial fluid, middle ear fluid) OR from an abscess.Gram stains of body sites that are not sterile (e.g. throat, nose, stool, skin etc) do not give you much information – it confirms that there are bacteria present but doesn't tell you if it is a pathogen or a colonizer because the gram stain gives gram morphology only, not the culture results, and many bacteria may appear similar on Gram stain. Most gram stains offer only preliminary information not diagnostic information (i.e. a Gram-positive cocci in clusters seen on a Gram stain of synovial fluid is suggestive of Staph aureus). Most of the time most physicians will not / should not narrow their empiric therapy based on a gram stain but rather should wait for the culture results. However, sometimes results of a gram stain of a sterile site will lead someone to prescribe an additional therapeutic agent while waiting culture confirmation.One setting where a gram stain can be diagnostic is in detecting gonococcal infection in men with purulent urethritis. It is very sensitive (\>90%) and specific (98%). However its sensitivity in diagnosing infection in asymptomatic men is \< 60%. It is also relatively insensitive in detecting gonococcal cervicitis in both symptomatic and asymptomatic women. (Laboratory Diagnosis of Bacterial Infection, Tutorial 1)

Question 28

Genes are not expressed unless an active regulator initiates expression * Negative control * Positive control * Inducible genes * Repressible

Answer 28

Positive control. Bacterial Gene expression: Positive control: genes are not expressed unless an active regulator initiates expression. Negative control: genes are always expressed unless turned off by repressor protein. Inducible genes: Introduction of a substrate for activation. Repressible: an abundance of end-products marks the shut down of the pathway (Bacteriology)

Question 29

Choose the most common mechanism of resistance. What is the mechanism of resistance to penicillin seen in Streptococcus pneumoniae?

Answer 29

Altered penicillin binding protein. Correct Answer is A / altered penicillin binding protein (Antibiotic Resistance)

Question 30

Choose the most common mechanism of resistance. What is the mechanism of resistance to penicillin seen in methicillin-susceptible Staphylococcus aureus?

Answer 30

Penicillinase production. (Antibiotic Resistance)

Question 31

Pharmacokinetics is the study of: * Absorption, distribution, metabolism and excretion of drugs * Biological and therapeutic effects of drugs * Mechanisms of drug action * Methods of new drug development

Answer 31

Absorption, distribution, metabolism and excretion of drugs. Pharmacokinetics is the study of absorption, distribution, metabolism, and excretion of drugs. (Antibiotics Overview)

Question 32

What does the term bioavailability mean?

Answer 32

Fraction of a drug reaching the systemic circulation following any route of administration. Bioavailability is the fraction of a drug reaching the systemic circulation following any route of administration. (Antibiotics Overview)

Question 33

The volume of distribution (Vd) relates:

Answer 33

The amount of a drug in the body to the concentration of a drug in plasma. (Antibiotics Overview)

Question 34

Correct statements listing characteristics of a particular route of drug administration include all of the following EXCEPT: * Inhalation provides slow access to the general circulation * Intramuscular administration requires a sterile technique * Intravenous administration provides a rapid response * Subcutaneous administration may cause local irritation

Answer 34

Inhalation provides slow access to the general circulation. Inhalation of a drug allows for local administration to the brochial tree with minimal systemic absorption. This route may be used for antibiotic administration to biofilm-related infection (i.e. chronic bronchitis in patients with cystic fibrosis) where parenteral antibiotics may not adequately get to the area concerned or where systemic absorption is not desired due to the potential toxicity of the drug. The other options are true about the characteristics of a particular route of drug administration. (Antibiotics Overview)

Question 35

Bactericidal effect is:

Answer 35

Destruction of bacterial cells. Bactericidal effect is destruction/death of bacterial cells. (Antibiotics Overview)

Question 36

Bacteriostatic effect is:

Answer 36

Inhibition of bacterial cell division. Bacteriostatic effect is inhibition of bacterial cell division. (Antibiotics Overview)

Question 37

Pharmacodynamics involves the study of all of the following EXCEPT: * Absorption and distribution of drugs * Biological and therapeutic effects of drugs * Drug interactions * Mechanisms of drug action

Answer 37

Absorption and distribution of drugs. Pharmacodynamics involves the study of biological and therapeutic effects of drugs, drug-drug interactions, and mechanisms of drug action. Pharmacokinetics is the study of absorption, distribution, metabolism, and excretion of drugs. (Antibiotics Overview)

Question 38

All of following antibiotics are aminoglycosides, EXCEPT: * Amikacin * Clindamycin * Gentamicin * Streptomycin * Tobramycin

Answer 38

Clindamycin. Clindamycin is a Lincosamide. Both lincosamides (50S) and aminoglycosides (30S) are protein synthesis inhibitors. (Antibiotics-mechansim of action)

Question 39

Which of the following statements is correct? Antimicrobial resistance: * Can be facilitated by the practices of health professionals * Can only be acquired through plasmid transfer * Is a characteristic of the drug not the microbe * Means that one species of microbe is resistant to all antibiotics

Answer 39

Can be facilitated by the practices of health professionals. Antimicrobial resistance can be facilitated by the practices of health professionals like inappropriate prescribing. (Antibiotic Resistance)

Question 40

Which of the following is not a prerequisite for implementing a hospital-based Antimicrobial Stewardship Program? * Buy-in from prescribers * Collaboration among pharmacists, clinical microbiologists, and preventionists * Considerable financial resources * Support by hospital leadership

Answer 40

Considerable financial resources. Antimicrobial stewardship programs have been shown to save hospitals a considerable amount of money but in order for them to be successful, they must have buy-in from prescribers, support from hospital leadership, and collaboration among pharmacists, clinical micriobiologists, and preventionists. This will not be tested on the Summative exam as it was not included in the learning objectives. (Antibiotic Resistance)

Question 41

The agents trimethoprim and sulfamethoxazole act synergistically to diminish the folic acid cofactor required for thymidine synthesis. Resistance in gram-negative bacteria to trimethoprim often arises in long term care facilities and is commonly associated with the acquisition of a plasmid that encodes an altered target of trimethoprim. This resistant enzyme is likely to be: * Deoxyribonucleotide reductase. * Dihydropteroate synthetase. * Dihydrofolate reductase. * Sulfamethoxazole acetyltransferase. * Thymidylate synthetase.

Answer 41

Dihydrofolate reductase. Trimethoprim is a direct inhibitor of bacterial dihydrofolate reductase. The sulfonamides inhibit dihydropteroate reductase. The combination of sulfamethoxazole and trimethoprim thus inhibits sequential steps in the synthesis and reduction of folic acid and inhibits formation of reduced folic acid cofactor involved in the synthesis of dTMP from dUMP, resulting in loss of dTTP. Sulfamethoxazole acetyltranferase, an enzyme that can also be transferred by plasmid, inactivates sulfmethoxazole. Note that only specific mechanisms of resistance for Gram-positive cocci will be tested in Summative exam 1 but you will need to know resistance mechanisms for Gram-negative bacilli for Summative exam 4. (Antibiotic Resistance)

Question 42

ou decide to treat an aerobic gram-negative infection with gentamicin. The patient weighs 80 kg, and you determine the apparent volume of distribution to be 0.31 L/kg. You want to give an IM injection to obtain a peak concentration of 5 ug/ml. Assuming rapid absorption and distribution and complete availability, your estimate of the dose you give this patient is: * 62 mg * 124 mg * 188 mg * 287 mg * 615 mg

Answer 42

124 mg. The calculation makes use of the formula Css x Vd = 80 kg x 0.31 L/kg x 5 mg/L = 124 mg. Note that you will not be required to calculate dosing for any of the ID block Summative exams but may need to know how to do this for Step 1. (Antibiotic Overview)

Question 43

Considering the antibiotic Augmentin®, the combination of amoxicillin and clavulanic acid, what would be the effect of the addition of probenecid on the elimination of amoxicillin?

Answer 43

Blood levels of amoxicillin would increase because amoxicillin would be protected from degradation, which would be the direct cause of an increase in the rate constant of elimination (ke) for amoxicillin. Probenecid is an organic acid, thus it would be expected to compete with penicillin (or amoxicillin) for elimination by the renal organic acid secretory mechanisms that clear penicillin from the body. Thus the half-life of penicillin would be prolonged by competition for elimination sites, which means that probenecid would decrease the rate constant of elimination (ke) for amoxicillin, i.e., the t1/2 would be increased ( t1/2 is inversely related to ke by t1/2 = 0.693/ke). First-order elimination, t1/2 is independent of the amount of drug given as long as elimination sites are not saturated. This rarely occurs for the penicillins, i.e., it is difficult to exceed the tubular maximum secretion, meaning that elimination generally occurs via first pass renal elimination. Note that you will not be tested on this for any of the ID Summative exams but may need to know it for Step 1. (Antibiotic overview)

Question 44

Which of the following best describes the main mechanism of most drugs absorbed in the gastrointestinal tract? * Active transport (carrier-mediated diffusion) * Endocytosis and exocytosis * Filtration (aqueous diffusion) * Passive diffusion (lipid diffusion)

Answer 44

Passive diffusion (lipid diffusion). The main mechanism that drugs are absorbed in the GI system is by passive diffusion (lipid diffusion). (Antibiotic Overview)

Question 45

Which of the following is NOT a cause of exudative pharyngitis? * Adenovirus * Arcanobacterium haemolyticum * Epstein-Barr Virus * Neisseria meningitidis * Streptococcus pyogenes

Answer 45

Neisseria meningitidis. Exudative pharyngitis may be caused by adenovirus, Archanobacterium, EBV, CMV, Strep pyogenes, and Neisseria gonorrhea. Neisseria meningitides is the cause of acute bacterial meningitis. (ENT-differential diagnosis)

Question 46

Which of the following infections are NOT caused by Streptococcus pyogenes? * Cellulitis (skin infection) * Colitis (intestinal infection) * Osteomyelitis (bone infection) * Septic joint (joint infection) * Toxic shock syndrome

Answer 46

Colitis (intestinal infection). Streptococcus pyogenes may be the cause of skin & soft tissue infections including cellulitis, septic joint, osteomyeltitis, and toxic shock syndrome. It does not cause infection in the GI tract. (Bacteriology-clinical syndromes

Question 47

You are the provider in charge of laboratory services for your group practice. There are 3 different companies that make rapid screening tests for group A Streptococcus. You need to review the performance of each test and decide which you will purchase for the coming year. Assume all culture-negative patients do not have group A Streptococcus infection.

Answer 47

91%. Fill in the 4 Square table. Sensitivity = 194/(194+6)=97%; Specificity = 273/300=91% (Laboratory Diagnosis of Bacterial Infections)

Question 48

Choose the antibiotic that is most commonly implicated for each of the adverse effects listed: Photosensitive dermatitis

Answer 48

Doxycycline. Doxycyline, a tetracycline, can cause photosensitive dermatitis. (Antibiotics-adverse effects)

Question 49

Choose the mechanism of action for the class of antibiotic. Aminoglycosides

Answer 49

Protein synthesis inhibitor. Aminoglycosides act as protein synthesis inhibitors by binding to the bacterial 30S ribosomal unit. (Antibiotics-mechanism of action)

Question 50

Choose the mechanism of action for the class of antibiotic. Vancomycin

Answer 50

Cell wall synthesis inhibitor. Vancomycin is a cell wall synthesis inhibitor thus having bactericidal effect. (Antibiotics-mechanism of action)

Question 51

Which of the following statements is correct? Bacteria achieve resistance to antibiotics by: * Enzymatic modification of the chemical structure of the antibiotic * Mechanisms that actively pump the antibiotic out of the cell * Modification of the target of the antibiotic * Conjugal transfer of plasmids between cells * All of the above are correct

Answer 51

All of the above

Question 52

For the bacteria listed, choose the correct gram stain morphology: Staphylococcus aureus

Answer 52

Gram-positive cocci in clusters. Staphylococcus aureus is a GPC in clusters. Streptococcus and Enterococcus are GPC in chains. Strep pneumoniae is a GP diplococcus. Neisseria meningitides is a GN diplococcus. Listeria is a GPR(bacillus). Escherichia colis is a GNR(bacillus). (Bacteriology, Tutorial 1)

Question 53

For the bacteria listed, choose the correct gram stain morphology: Streptococcus pneumoniae

Answer 53

Gram-positive diplococci. Strep pneumoniae is a GP diplococcus. Neisseria meningitides is a GN diplococcus. Staphylococcus aureus is a GPC in clusters. Streptococcus and Enterococcus are GPC in chains. Listeria is a GPR(bacillus). Escherichia coli is a GNR(bacillus). (Bacteriology, Tutorial 1)

Question 54

For the bacteria listed, choose the correct gram stain morphology: Corynebacterium diphtheriae

Answer 54

Gram-positive bacillus. Corynebacterium is a GPR(bacillus). Strep pneumoniae is a GP diplococcus.

Question 55

You are seeing a previously healthy 15 year old male in your office with a presenting complaint of tea-colored urine that started 3 days ago. His review of systems is negative other than puffy eyes. His past medical history is essentially negative other than recurrent episodes of impetigo. His last episode of impetigo was 4 weeks ago. On exam he is afebrile. His blood pressure is elevated at 130 / 90 mm Hg, but all other vital signs are normal. He is alert and oriented, non-toxic. He has periorbital edema. He does not have any skin lesions. A urinalysis reveals a specific gravity of 1.030, 2+ protein, 2+ blood, and rbc casts. Which of the following is his MOST APPROPRIATE test result would confirm his likely diagnosis? * Elevated anti-DNAse B * Elevated C4 * Low ASO titer * Low C3

Answer 55

Elevated anti-DNAse B. An elevated anti-DNAse B is consistent with post-Strep glomerulonephritis.

Question 56

Which route of drug administration is MOST LIKELY to lead to the first-pass effect? * Intramuscular * Intravenous * Oral * Sublingual

Answer 56

Oral. An orally administered drug may lead to first-pass effect. (Antibiotic Overview)

Question 57

This antibiotic, a bacterial ribosomal 30S inhibitor, has a fixed positive charge at all physiological pHs, confining it primarily to extracellular fluids. It is cleared by renal filtration, but is taken up by the kidney, where it has a longer t1/2 than in blood. Another compartment with prolonged t1/2 of this drug is the fluid compartment bathing the hair cells of the vestibular and cochlear structures. This antibiotic is particularly prone to causing ototoxicity when used at the same time as a high ceiling diuretic, e.g., furosemide, or in those rare individuals harboring a mitochondrial mutation that makes their mitochondrial ribosomes more sensitive to the drug. The description above BEST DESCRIBES which of the following antibiotics? * Azithromycin * Gentamicin * Metronidazole * Sulfadiazine * Tetracycline * Aminoglocosides are protein synthesis inhibitors which act at the 30S ribosomal subunit. Tetracyclines also act at this site but do not commonly cause renal or otic complications. Azithromycin is a macrolide which acts at the 50S ribosomal subunit. Metronidazole is a free radical generator and sulfadiazine acts as an antimetabolite

Answer 57

Gentamicin. It is important to recognize the common agents in each antibiotic class, its mechanism of action, and toxicities. Aminoglycosides can lead to renal and otic complications

Question 58

This antibiotic acts by binding to and inhibiting the A (acceptor) site of the bacterial 30S ribosomal subunit and has a wide spectrum of activity. The drug is cleared by both the hepatic and renal systems, although renal elimination is the most prominent route. This drug can bind by chelation to calcium orthophosphate in growing teeth, causing discolored and fragile teeth with repeated or prolonged use in children. The description above BEST DESCRIBES which of the following antibiotics? * Clarithromycin * Metronidazole * Sulfadiazine * Tetracycline * Vancomycin

Answer 58

Tetracycline. Tetracyclines are protein synthesis inhibitors which act at the 30S ribosomal subunit and have the characteristics noted above. Clarithromycin is a macrolide which acts at the 50S ribosomal subunit. Vancomycin is a cell-wall active agent. Sulfadiazine is an antimetabolite.

Question 59

Which immune factor helps to control infection with encapsulated organisms like Streptococcus pneumonia? * CD8+ Lymphocytes * C-Reactive Protein * Eosinophils * IgG

Answer 59

IgG. IgG is particularly effective in assisting the immune system in clearing encapsulated organisms. IgG can coat the organism/opsonization, improving phagocytosis.

Question 60

Which host factor is responsible for clearance of viral infections? * CD8+ Lymphocytes * C-Reactive Protein * IgF * Neutrophils

Answer 60

CD8+ Lymphocytes. NK cells also kill virally infected cells. Immunoglobulin act to neutralize viruses. The humoral immune response results in antibody-dependent cell-mediated cytotoxicity.

Question 61

Which of the following cells is NOT an antigen-presenting cell? * Dendritic cell * Langerhans cell * Macrophage * Neutrophil

Answer 61

Neutrophil. Neutrophils are not antigen presenting cells. Dendritic cells, Langerhans cells, and macrophages are APCs.

Question 62

Which of the following choices is correct? * Antigenic peptide-MHC Class I complex is presented to macrophages * Antigenic peptide-MHC Class I complex is presented to B lymphocytes * Antigenic peptide-MHC Class II complex is presented to CD4+ T lymphocytes * Antigenic peptide-MHC Class II complex is presented to CD8+ T lymphocytes

Answer 62

Antigenic peptide-MHC Class II complex is presented to CD4+ T lymphocytes.

Question 63

Which of the following cells secretes IL-4 thus stimulating B cells to differentiate into antibody-secreting plasma cells? * CD4+ Th1 cells * CD4+ Th2 cells * CD8+ T cells * CD8+ B cells

Answer 63

CD4+ Th2 cells.

Question 64

Which route of drug administration is MOST LIKELY to lead to the first-pass effect? * Intramuscular * Intravenous * Oral * Sublingual

Answer 64

Oral. An orally administered drug may lead to first-pass effect. (Antibiotic Overview)

Question 65

You are seeing a previously healthy 15 year old male in your office with a presenting complaint of tea-colored urine that started 3 days ago. His review of systems is negative other than puffy eyes. His past medical history is essentially negative other than recurrent episodes of impetigo. His last episode of impetigo was 4 weeks ago. On exam he is afebrile. His blood pressure is elevated at 130 / 90 mm Hg, but all other vital signs are normal. He is alert and oriented, non-toxic. He has periorbital edema. He does not have any skin lesions. A urinalysis reveals a specific gravity of 1.030, 2+ protein, 2+ blood, and rbc casts. Which of the following is his MOST APPROPRIATE test result would confirm his likely diagnosis? * Elevated anti-DNAse B * Elevated C4 * Low ASO titer * Low C3

Answer 65

Elevated anti-DNAse B. An elevated anti-DNAse B is consistent with post-Strep glomerulonephritis.

Question 66

A 1-week-old infant is brought to the Emergency Department by his parents with a 2 day history of fever, vomiting, poor feeding, and irritability. Blood and cerebrospinal fluid are sent for culture. The next day, multiple bacterial colonies surrounded by a clear zone are seen on blood agar. A catalase test is performed and is negative. Which of the following organisms is the MOST LIKELY cause of this infant's illness? * Escherichia coli * Listeria monocytogenes * Staphylococcus aureus * Streptococcus agalactiae * Streptococcus pneumoniae

Answer 66

Streptococcus agalactiae. Streptococcus agalactiae / Group B Strep is β-hemolytic (clear zone on blood agar). Like all Strep, it is catalase negative. GBS is one of the top three causes of meningitis in infants younger than 3 months old. Streptococcus pneumoniae is alpha-hemolytic. Staph aureus is â-hemolytic but it is catalase positive. (Laboratory Diagnosis of Bacterial Infection)

Question 67

For the bacteria listed, choose the correct gram stain morphology. Staphylococcusepidermidis * Gram-negative bacilli * Gram-positive bacilli * Gram-positive cocci in chains * Gram-positive cocci in clusters * Gram-positive diplococci

Answer 67

Gram-positive cocci in clusters

Question 68

Expression of this type of gene requires introduction of a substrate * Negative control * Positive control * Inducible genes * Repressible

Answer 68

Inducible genes. Bacterial Gene expression: Inducible genes: Introduction of a substrate for activation. Negative control: genes are always expressed unless turned off by repressor protein. Positive control: genes are not expressed unless an active regulator initiates expression. Repressible: an abundance of end-products marks the shut down of the pathway. (Bacteriology)