Weekly Year 2: Microbiology Exam - April 21, 2026 (Section A

Question 1

A paroxysm is a sudden attack or increase in symptoms and is characteristic of which respiratory disease?

Accepted Answer

Pertussis — Paroxysms are the characteristic bursts of coughing seen in the second stage of Pertussis (Whooping Cough).

Question 2

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

Accepted Answer

Type-specific antitoxin — Ingestion of botulism toxin (foodborne botulism) requires passive immunization with antitoxin to neutralize circulating toxin.

Question 3

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

Accepted Answer

Anaerobic — Clostridia are obligate anaerobes and require an environment without oxygen to multiply.

Question 4

Woolsorter disease applies to the form of .

Accepted Answer

Inhalation; Anthrax — Inhalation anthrax is known as Woolsorter disease because it was historically contracted by workers processing wool containing B. anthracis spores.

Question 5

Neonatal ophthalmia (conjunctivitis) is most commonly associated with which two STDs?

Accepted Answer

Chlamydia and Gonorrhea — Neisseria gonorrhoeae and Chlamydia trachomatis are the primary causes of neonatal conjunctivitis.

Question 6

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

Accepted Answer

Bacillus anthracis — Robert Koch first proved the causative role of Bacillus anthracis in anthrax.

Question 7

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

Accepted Answer

Inhibition of protein synthesis by ADP-ribosylation of EF-2 — Diphtheria toxin inhibits protein synthesis by ADP-ribosylating elongation factor 2 (EF-2).

Question 8

Which bacterial component is least likely to contain useful antigens for serological identification?

Accepted Answer

Cytoplasmic phospholipids — Surface structures like the cell wall, flagella (H-antigen), and capsule (K-antigen) are highly antigenic, whereas internal lipids are less useful for serotyping.

Question 9

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

Accepted Answer

P. bettyae — Pasteurella bettyae is a rare species associated with urogenital and neonatal infections.

Question 10

Which of the following diseases is best diagnosed by serologic means (detecting antibodies)?

Accepted Answer

Secondary Syphilis — Syphilis (Treponema pallidum) cannot be easily cultured and is primarily diagnosed via serology (e.g., VDRL, RPR, FTA-ABS).

Question 11

Which of the following is NOT among the three most important causes of acute bacterial meningitis?

Accepted Answer

Staphylococcus aureus — The classic trio for acute bacterial meningitis comprises S. pneumoniae, N. meningitidis, and H. influenzae.

Question 12

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

Accepted Answer

Staphylococcus epidermidis on a prosthetic valve — S. epidermidis is well known for producing biofilms on indwelling medical devices.

Question 13

The heat-labile toxin (LT) of ETEC acts through which mechanism?

Accepted Answer

Increasing cAMP — LT (Heat-labile toxin) increases cAMP, similar to Cholera toxin, leading to secretory diarrhea.

Question 14

Which of the following statements regarding Pseudomonas aeruginosa is correct?

Accepted Answer

It produces a blue-green pigment called pyocyanin — P. aeruginosa is a Gram-negative aerobe known for producing pyocyanin and pyoverdine.

Question 15

Long-term carriage and chronic shedding in the gallbladder are most likely after infection with:

Accepted Answer

Salmonella Typhi — S. Typhi can establish chronic carriage in the gallbladder, leading to continued shedding in feces.

Question 16

A patient presents with acute non-bloody diarrhea for 12 hours. Which organism is LEAST likely to cause this in a non-endemic area without travel?

Accepted Answer

Vibrio cholerae — Vibrio cholerae is typically associated with endemic regions or travel; others are common causes of food poisoning or viral gastroenteritis locally.

Question 17

Regarding a 19-year-old man with N. gonorrhoeae that is beta-lactamase positive and tetracycline resistant, which is correct?

Accepted Answer

The resistance is plasmid-mediated — Beta-lactamase production in N. gonorrhoeae is usually carried on plasmids.

Question 18

Which Neisseria gonorrhoeae structure mediates attachment to host epithelial cells?

Accepted Answer

Pili — Pili (fimbriae) are the primary mechanism for Neisseria attachment to mucosal surfaces.

Question 19

A 6-year-old boy has meningitis (serogroup B). What is recommended for household contacts?

Accepted Answer

Chemoprophylaxis with Rifampin or Ciprofloxacin — Close contacts of meningococcal meningitis patients require chemoprophylaxis to eradicate nasopharyngeal carriage.

Question 20

A common long-term complication of gonococcal Pelvic Inflammatory Disease (PID) is:

Accepted Answer

Infertility — Scarring of the fallopian tubes following PID often leads to ectopic pregnancy or infertility.

Question 21

Which statement best describes the pathogenesis of Clostridium botulinum?

Accepted Answer

Preformed toxin blocks acetylcholine release — Botulism toxin blocks excitatory acetylcholine release at the neuromuscular junction, causing flaccid paralysis.

Question 22

A patient with cavitary lung disease grows an acid-fast bacillus that produces orange pigment only on light exposure. It is:

Accepted Answer

Mycobacterium kansasii — M. kansasii is a photochromogen (produces pigment in light).

Question 23

A patient has fever, weight loss, and granulomas with AFB in liver and bone marrow, but normal CXR. Likely organism:

Accepted Answer

M. avium-intracellulare — Disseminated MAC (Mycobacterium avium complex) is common in immunocompromised patients and involves the reticuloendothelial system.

Question 24

A major concern for the treatment of M. tuberculosis is an infection with a strain that is:

Accepted Answer

Multidrug-resistant (MDR) — MDR-TB (resistant to isoniazid and rifampin) is a major global public health concern.

Question 25

Fish are the second intermediate hosts for which parasite?

Accepted Answer

Diphyllobothrium latum — The broad fish tapeworm, D. latum, uses freshwater fish as its second intermediate host.

Question 26

Which of the following insects secretes defensive secretions (cantharidin) to cause irritation on human skin?

Accepted Answer

Blister beetles — Blister beetles (family Meloidae) release cantharidin, which causes skin blistering.

Question 27

Holometabolous insects have which of the following life cycle stages?

Accepted Answer

Egg, Larva, Pupa, Adult — Holometabolous development refers to complete metamorphosis (egg, larva, pupa, adult).

Question 28

Which of the following transmits the parasites responsible for River Blindness (Onchocerciasis)?

Accepted Answer

Blackfly (Simulium) — Onchocerca volvulus is transmitted by the bite of the Simulium blackfly.

Question 29

Which insecticide targets GABA receptors in its mechanism of action?

Accepted Answer

Fipronil — Fipronil blocks GABA-gated chloride channels in insects.

Question 30

Presence of triatomine bugs (Kissing bugs) could predispose a population to:

Accepted Answer

Chagas disease — Triatomine bugs are the vectors for Trypanosoma cruzi, the cause of Chagas disease.

Question 31

People living in forested areas are at specific risk of which vector-borne disease?

Accepted Answer

Loiasis — Loiasis (African eye worm) is transmitted by deer flies (Chrysops) which inhabit rainforests.

Question 32

Which of the following insects is commonly found in Latin America as a vector for Chagas disease?

Accepted Answer

Triatoma infestans — Triatoma infestans is a key vector for Chagas disease in Latin America.

Question 33

Severe pruritus (itching), particularly at night, is most diagnostic for:

Accepted Answer

Scabies — Nocturnal pruritus is a hallmark symptom of Sarcoptes scabiei infestation.

Question 34

If you found lice eggs (nits) in someone's clothing rather than their hair, they are most likely from:

Accepted Answer

Pediculus humanus corporis — Body lice (P. humanus corporis) live and lay eggs in the seams of clothing.

Question 35

Which of the following is the 'odd one out' in terms of being a biological vector?

Accepted Answer

Housefly — Houseflies are typically mechanical vectors, whereas the others are biological vectors.

Question 36

Which one of the following flies is larviparous (deposits larvae instead of eggs)?

Accepted Answer

Glossina (Tsetse fly) — Tsetse flies (Glossina) are unusual because the female retains the larva and nourishes it until it is ready to pupate.

Question 37

Which one of the following is a potential non-suppurative complication of Streptococcus pyogenes pharyngitis?

Accepted Answer

Rheumatic fever — Acute Rheumatic Fever is a post-streptococcal sequela following untreated pharyngitis.

Question 38

The presence of a thick, grey pseudomembrane in the throat is a hallmark result of:

Accepted Answer

Diphtheria — Corynebacterium diphtheriae produces a toxin that causes cell death, creating a grey pseudomembrane.

Question 39

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

Accepted Answer

M. tuberculosis — The Mantoux test (PPD) is the standard skin test for tuberculosis screening.

Question 40

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

Accepted Answer

Streptococcus pneumoniae — S. pneumoniae (Pneumococcus) remains the leading cause of typical lobar pneumonia.

Question 41

A spore-forming, motile Gram-positive rod that causes foodborne illness in a diarrheal or emetic form is:

Accepted Answer

Bacillus cereus — B. cereus is known for two types of food poisoning: emetic (heat-stable toxin) and diarrheal (heat-labile toxin).

Question 42

Which one of the following describes the mode of action of tetanospasmin (Tetanus toxin)?

Accepted Answer

Blocking release of inhibitory neurotransmitters (GABA/Glycine) — Tetanospasmin blocks inhibitory signals, leading to spastic paralysis (uncontrolled contraction).

Question 43

Salpingitis (inflammation of fallopian tubes) is most commonly caused by Chlamydia or Gonorrhea and can lead to:

Accepted Answer

Ectopic pregnancy — Salpingitis causes tubal scarring, a leading risk for ectopic pregnancy.

Question 44

The term 'Staphylococcus' is derived from Greek meaning:

Accepted Answer

Bunch of grapes — Staphyle (grapes) and kokkos (berry/kernel).

Question 45

Which test is most useful for distinguishing staphylococci from streptococci?

Accepted Answer

Catalase test — Staphylococci are catalase-positive, while streptococci are catalase-negative.

Question 46

Staphylococci are halotolerant and can grow in salt concentrations up to:

Accepted Answer

10% — Staphylococci uniquely tolerate high salt (up to 10%), utilized in Mannitol Salt Agar.

Question 47

The primary test used to clinically classify staphylococci into 'virulent' or 'less virulent' groups is:

Accepted Answer

Coagulase — The coagulase test divides S. aureus (positive) from CNS (Coagulase-Negative Staphylococci).

Question 48

Protein A in the S. aureus cell wall has a high affinity for which part of the immunoglobulin molecule?

Accepted Answer

Fc region — Protein A binds the Fc portion of IgG, preventing opsonization and phagocytosis.

Question 49

Which toxin is responsible for Staphylococcal Scalded Skin Syndrome (SSSS)?

Accepted Answer

Exfoliative toxin — Exfoliative toxins A and B break down desmoglein-1 in the epidermis.

Question 50

Staphylococcal food poisoning is typically caused by the ingestion of:

Accepted Answer

Preformed enterotoxin — Symptoms occur rapidly (1-6 hours) because the toxin is already present in the food.

Weekly Year 2: Microbiology Exam - April 21, 2026 (Section A

Questions, Answers & Explanations