Weekly Year 2: Microbiology Exam - May 22, 2026 (Section A:

Question 1

A paroxysm is a sudden, violent recurrence or intensification of symptoms, and is characteristic of which disease?

Accepted Answer

Pertussis — A paroxysm, particularly a paroxysmal cough, is a hallmark symptom of Pertussis (whooping cough), caused by Bordetella pertussis.

Question 2

To treat patients who have ingested botulism toxin, large doses of which of the following must be administered?

Accepted Answer

Antitoxin — Botulism is caused by a toxin, not the bacteria directly causing infection, so antitoxin is critical to neutralize circulating toxin. Antibiotics are generally not effective for the toxin itself.

Question 3

The organism Clostridium perfringens multiplies in foods only under which of the following conditions?

Accepted Answer

Strictly anaerobic — Clostridium perfringens is an obligate anaerobe, meaning it can only multiply in the absence of oxygen. This is why it's commonly associated with food poisoning in poorly cooked or reheated meats.

Question 4

Woolsorter's disease applies to the form of anthrax that affects which organ system?

Accepted Answer

Inhalation — Woolsorter's disease is another name for inhalation anthrax, which primarily affects the respiratory system and is acquired by inhaling spores from contaminated animal products like wool.

Question 5

Ophthalmia neonatorum (conjunctivitis in newborns) is most commonly associated with which two sexually transmitted infections (STIs)?

Accepted Answer

Chlamydia and Gonorrhea — Neisseria gonorrhoeae and Chlamydia trachomatis are the most common bacterial causes of ophthalmia neonatorum, transmitted from an infected mother during birth.

Question 6

The first microorganism to satisfy Koch's postulates in the late 19th century was:

Accepted Answer

Bacillus anthracis — Robert Koch first applied his postulates to Bacillus anthracis in 1876, establishing it as the causative agent of anthrax.

Question 7

Which of the following best describes the mechanism of action of diphtheria toxin?

Accepted Answer

Inhibits protein synthesis by inactivating elongation factor-2 (EF-2) — Diphtheria toxin is an A-B toxin that inhibits protein synthesis in eukaryotic cells by ADP-ribosylating and inactivating elongation factor-2 (EF-2).

Question 8

The identification of bacteria by serological tests is based on the presence of specific antigens. Which of the following bacterial components is least likely to contain useful antigens for routine serological identification?

Accepted Answer

Ribosomes — While ribosomes are present in bacteria, they are generally internal structures and their antigens are less accessible and less variable for routine serological classification compared to surface structures like capsules, cell walls (O antigens), and flagella (H antigens).

Question 9

Which of the following Pasteurella species has been associated with infection of the female genital tract and newborn?

Accepted Answer

Pasteurella pneumotropica — Pasteurella pneumotropica has been reported in rare cases of female genital tract infections and neonatal sepsis, often associated with exposure to animal reservoirs.

Question 10

Which of the following diseases is best diagnosed by serologic means due to the difficulty in culturing the causative agent?

Accepted Answer

Syphilis — Treponema pallidum, the causative agent of syphilis, cannot be cultured on artificial media, making serological tests (e.g., VDRL, RPR, TPPA, FTA-ABS) the primary diagnostic method.

Question 11

Which of the following is NOT a most important cause of acute bacterial meningitis in adults?

Accepted Answer

Haemophilus influenzae type b — Haemophilus influenzae type b (Hib) was a major cause of meningitis in children but is now rare in developed countries due to vaccination. Neisseria meningitidis and Streptococcus pneumoniae remain leading causes in adults, with Listeria monocytogenes being important in immunocompromised individuals and the elderly.

Question 12

Which of the following is most likely to be associated with the formation of a bacterial biofilm?

Accepted Answer

Catheter-associated urinary tract infection — Bacterial biofilms are frequently associated with medical devices like catheters, leading to persistent infections that are difficult to treat, such as catheter-associated UTIs.

Question 13

Which one of the following is a potential complication of untreated Streptococcus pyogenes pharyngitis?

Accepted Answer

Rheumatic fever — Rheumatic fever is a serious non-suppurative complication that can develop after an untreated or inadequately treated Group A Streptococcus (GAS) pharyngitis.

Question 14

The presence of a pseudomembrane, typically found in the throat, is a characteristic result of infection by:

Accepted Answer

Corynebacterium diphtheriae — Corynebacterium diphtheriae produces a potent exotoxin that causes local tissue necrosis, leading to the formation of a tough, grayish pseudomembrane in the throat or tonsils.

Question 15

The Mantoux test is used to identify exposure to which pathogen?

Accepted Answer

Mycobacterium tuberculosis — The Mantoux tuberculin skin test (TST) assesses for latent tuberculosis infection by injecting purified protein derivative (PPD) and checking for a delayed-type hypersensitivity reaction.

Question 16

This bacterial species is the most common cause of 'typical' community-acquired pneumonia:

Accepted Answer

Streptococcus pneumoniae — Streptococcus pneumoniae (Pneumococcus) is the leading cause of community-acquired bacterial pneumonia.

Question 17

A spore-forming, motile rod that can cause foodborne illness in a diarrheal or emetic form is:

Accepted Answer

Bacillus cereus — Bacillus cereus is a common cause of food poisoning, presenting with either a diarrheal syndrome (long incubation, heat-labile toxin) or an emetic syndrome (short incubation, heat-stable toxin).

Question 18

Which one of the following describes the mode of action of tetanospasmin, the toxin produced by Clostridium tetani?

Accepted Answer

It causes spastic paralysis by inhibiting the release of inhibitory neurotransmitters (GABA and glycine) from Renshaw cells. — Tetanospasmin is a neurotoxin that acts by cleaving synaptobrevin, a SNARE protein, thereby preventing the release of inhibitory neurotransmitters (GABA and glycine) in the spinal cord, leading to uncontrolled muscle spasms and spastic paralysis.

Question 19

Salpingitis, inflammation of the fallopian tubes, is commonly associated with which STIs and can lead to which serious complication?

Accepted Answer

Chlamydia and Gonorrhea; pelvic inflammatory disease (PID) — Chlamydia trachomatis and Neisseria gonorrhoeae are major causes of salpingitis, which can progress to pelvic inflammatory disease (PID), a significant cause of infertility and ectopic pregnancy.

Question 20

Which of the following transmits the parasitic nematodes responsible for river blindness (onchocerciasis)?

Accepted Answer

Blackfly — River blindness is caused by the parasite Onchocerca volvulus, which is transmitted by the bite of infected blackflies (Simulium species).

Question 21

The presence of triatomine bugs (kissing bugs) in a population could predispose them to which disease?

Accepted Answer

Chagas disease — Triatomine bugs are the vectors for Trypanosoma cruzi, the parasite that causes Chagas disease, endemic in Latin America.

Question 22

If you found lice eggs (nits) predominantly in someone's clothing seams and bedding, what species would they most likely be from?

Accepted Answer

Pediculus humanus humanus (body louse) — Body lice (Pediculus humanus humanus) typically live and lay their nits in clothing seams rather than directly on the body, except for feeding.

Question 23

Which one of the following antibiotics is likely to be the most effective agent in the treatment of an infection due to enterococci if used in conjunction with penicillin G for synergistic effect?

Accepted Answer

Gentamicin — Aminoglycosides like gentamicin exhibit synergistic bactericidal activity when combined with cell-wall active agents (like penicillin G or vancomycin) against enterococci, especially in serious infections like endocarditis.

Question 24

Regarding the antibacterial action of gentamicin, which one of the following statements is the MOST accurate?

Accepted Answer

It binds to the 30S ribosomal subunit, inhibiting protein synthesis. — Gentamicin is an aminoglycoside antibiotic that primarily exerts its bactericidal effect by irreversibly binding to the bacterial 30S ribosomal subunit, leading to misreading of mRNA and inhibition of protein synthesis.

Question 25

A 24-year-old woman is diagnosed with genital herpes simplex virus infection. Which agent is indicated for use in this diagnosis?

Accepted Answer

Acyclovir — Acyclovir is a nucleoside analog that inhibits viral DNA replication and is a first-line antiviral agent for the treatment of herpes simplex virus infections, including genital herpes.

Question 26

A 72-year-old man is admitted to the hospital from a nursing home with severe pneumonia. He was discharged from the hospital 1 week ago after open heart surgery. The patient has no known allergies. Which of the following regimens is most appropriate for empiric coverage of methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa in this patient with hospital-acquired pneumonia?

Accepted Answer

Piperacillin-tazobactam + Vancomycin — This patient has risk factors for hospital-acquired pneumonia, including recent hospitalization and nursing home residence. Empiric coverage for MRSA (Vancomycin) and Pseudomonas aeruginosa (Piperacillin-tazobactam is an antipseudomonal beta-lactam) is appropriate for severe cases.

Question 27

Superinfections, such as Clostridium difficile-associated diarrhea or candidiasis, are more common with which type of antimicrobial therapy?

Accepted Answer

Broad-spectrum antibiotics — Broad-spectrum antibiotics disrupt a wider range of normal microbiota, allowing for overgrowth of resistant organisms or opportunistic pathogens, leading to superinfections.

Question 28

Which one of the following drugs is most likely to be effective against multi-drug-resistant (MDR) strains of M. tuberculosis, including those resistant to streptomycin?

Accepted Answer

Bedaquiline — Bedaquiline is a newer antitubercular agent specifically approved for the treatment of MDR-TB. Isoniazid, Rifampin, and Ethambutol are first-line drugs, but resistance to them defines MDR-TB.

Question 29

A 77-year-old woman was started on antibiotics for pneumonia treatment. After 3 days of antibiotic therapy, the serum creatinine doubled. Which of the following antibiotics is most likely responsible for this increase in serum creatinine?

Accepted Answer

Gentamicin — Aminoglycosides like gentamicin are well-known for their nephrotoxic potential, particularly in elderly patients or those with pre-existing renal impairment, often causing an acute increase in serum creatinine.

Question 30

The persistent suppression of bacterial growth that may occur following limited exposure to some antimicrobial drugs, even after drug concentrations have fallen below the minimum inhibitory concentration (MIC), is called:

Accepted Answer

Post-antibiotic effect (PAE) — The post-antibiotic effect (PAE) describes the continued suppression of bacterial growth after antibiotic levels have dropped below the MIC. It's an important pharmacokinetic/pharmacodynamic parameter for antibiotic dosing.

Question 31

Select the antibiotic whose dose must be reduced in patients with renal insufficiency:

Accepted Answer

Vancomycin — Vancomycin is primarily eliminated by the kidneys, and its dosage must be carefully adjusted in patients with renal insufficiency to prevent accumulation and toxicity (e.g., nephrotoxicity, ototoxicity).

Question 32

Isoniazid is a primary antitubercular agent that:

Accepted Answer

Inhibits mycobacterial cell wall mycolic acid synthesis. — Isoniazid is a prodrug that, once activated, inhibits the synthesis of mycolic acid, a crucial component of the mycobacterial cell wall, leading to its bactericidal effect against Mycobacterium tuberculosis.

Question 33

Linezolid would be a good choice for antibiotic treatment in which of the following patient scenarios?

Accepted Answer

A patient with severe MRSA pneumonia and vancomycin intolerance. — Linezolid is a synthetic oxazolidinone antibiotic primarily used for infections caused by multidrug-resistant Gram-positive bacteria, including MRSA and vancomycin-resistant enterococci (VRE), making it suitable for a patient with severe MRSA pneumonia and vancomycin intolerance.

Question 34

The term 'Staphylococcus' is derived from Greek words meaning:

Accepted Answer

Grape-like cluster of berries — Staphylococcus comes from 'staphyle' (grape) and 'kokkos' (berry), referring to their characteristic arrangement in grape-like clusters.

Question 35

Which test is most useful for distinguishing staphylococci from streptococci?

Accepted Answer

Catalase test — The catalase test distinguishes staphylococci (catalase-positive) from streptococci (catalase-negative). Staphylococci produce the enzyme catalase, which breaks down hydrogen peroxide into water and oxygen, producing bubbles.

Weekly Year 2: Microbiology Exam - May 22, 2026 (Section A:

Questions, Answers & Explanations