Weekly Year 2: Microbiology Exam - April 17, 2026 (Section A

Question 1

A paroxysm is a and is characteristic of .

Accepted Answer

Sudden attack or recurrence of symptoms; Pertussis — A paroxysm is a sudden attack or increase of symptoms, such as the coughing fits seen in the paroxysmal stage of Bordetella pertussis (Whooping cough).

Question 2

To treat patients who have ingested botulism toxin, large doses of must be administered.

Accepted Answer

Specific antitoxin — Since the symptoms of botulism are caused by the pre-formed neurotoxin, neutralization with an antitoxin is the primary treatment.

Question 3

The organism Clostridium perfringens multiplies in foods only under conditions.

Accepted Answer

Anaerobic — Clostridium perfringens is an obligate anaerobe; it requires an environment devoid of oxygen to multiply.

Question 4

Woolsorter disease applies to the form of .

Accepted Answer

Inhalation; Anthrax — Woolsorter's disease is the historical name for inhalation anthrax, contracted by workers handling contaminated animal hides or wool.

Question 5

Ophthalmia neonatorum is associated with what two STDs?

Accepted Answer

Gonorrhea and Chlamydia — Neisseria gonorrhoeae and Chlamydia trachomatis are the leading causes of neonatal conjunctivitis (ophthalmia neonatorum) transmitted during childbirth.

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 causal relationship between a microbe and a disease using Bacillus anthracis in 1876.

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 — Corynebacterium diphtheriae produces an A-B toxin that inhibits Elongation Factor 2 (EF-2), halting protein synthesis in host cells.

Question 8

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

Accepted Answer

Ribosomes — Ribosomes are internal structures and are highly conserved/less accessible for standard surface-based serological typing compared to flagella (H-antigens) or capsules (K-antigens).

Question 9

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

Accepted Answer

P. bettyae — Pasteurella bettyae is unique among the genus for its association with the human urogenital tract and neonatal infections.

Question 10

Which of the following diseases is best diagnosed by serologic means (antibody detection) rather than culture?

Accepted Answer

Syphilis — Treponema pallidum cannot be cultured on artificial media; diagnosis relies on serology (RPR/VDRL and FTA-ABS).

Question 11

Which of the following is NOT one of the most common causes of acute bacterial meningitis?

Accepted Answer

Bacillus anthracis — While B. anthracis can cause meningitis, it is not a common epidemiological cause like 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 slime/biofilms on indwelling medical devices like prosthetic valves and catheters.

Question 13

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

Accepted Answer

Increases intracellular cAMP — LT increases cAMP by activating adenylate cyclase, while the heat-stable toxin (ST) increases cGMP.

Question 14

Which of the following statements regarding Pseudomonas aeruginosa is correct?

Accepted Answer

It produces a blue-green pigment called pyocyanin — Pseudomonas aeruginosa produces pyocyanin and fluorescein, giving it a characteristic blue-green appearance.

Question 15

Long-term carriage and chronic shedding are most likely after gastrointestinal infection with:

Accepted Answer

Salmonella Typhi — S. Typhi can persist in the gallbladder for years, leading to chronic asymptomatic shedding in stool.

Question 16

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

Accepted Answer

Vibrio cholerae — Cholera is rare in non-endemic areas without specific exposures; the other options are common causes of sudden-onset diarrhea/vomiting globally.

Question 17

A 19-year-old man has urethral discharge. Culture shows Neisseria gonorrhoeae that is β-lactamase positive. Which statement is correct?

Accepted Answer

The organism possesses a plasmid-encoded penicillinase — β-lactamase positive strains produce penicillinase, usually via a plasmid, making them resistant to penicillin.

Question 18

Which Neisseria gonorrhoeae structure mediates attachment to host epithelial cells?

Accepted Answer

Pili — Pili (fimbriae) are essential for the attachment of the gonococcus to the mucosal surfaces.

Question 19

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

Accepted Answer

Chemoprophylaxis with Rifampin — Rifampin (or Ciprofloxacin/Ceftriaxone) is used for chemoprophylaxis of close contacts to eliminate nasopharyngeal carriage.

Question 20

A common long-term complication of gonococcal pelvic inflammatory disease (PID) is:

Accepted Answer

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

Question 21

Which statement best describes the pathogenesis of Clostridium botulinum?

Accepted Answer

Toxin is absorbed and blocks the release of acetylcholine — Botulinum toxin prevents 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 on light exposure. The organism is:

Accepted Answer

Mycobacterium kansasii — M. kansasii is a photochromogen (produces pigment only when exposed to light).

Question 23

A patient has fever, weight loss, and granulomas with acid-fast bacilli in liver and bone marrow. Chest X-ray is normal. Most likely organism:

Accepted Answer

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

Question 24

A major concern for a patient with TB-like disease is infection with a strain that is MDR. MDR stands for resistance to:

Accepted Answer

Isoniazid and Rifampin — Multi-drug-resistant TB (MDR-TB) is defined as being resistant to at least Isoniazid and Rifampin.

Question 25

Fish are second intermediate hosts of?

Accepted Answer

Clonorchis sinensis — The Chinese liver fluke (Clonorchis sinensis) uses freshwater fish as its second intermediate host.

Question 26

Which of the following secretes defensive secretions to cause irritation on human skin?

Accepted Answer

Paederus beetles — Paederus beetles (Rove beetles) contain pederin, which causes severe dermatitis when the beetle is crushed against the skin.

Question 27

Holometabolous insects have:

Accepted Answer

Complete metamorphosis (egg, larva, pupa, adult) — Holometabolous refers to insects that undergo a complete four-stage transformation.

Question 28

Which of the following transmits parasites causing river blindness (Onchocerciasis)?

Accepted Answer

Black fly (Simulium) — Onchocerca volvulus is transmitted by the bite of infected Black flies (genus Simulium).

Question 29

Which insecticide targets GABA receptors in its action?

Accepted Answer

Fipronil — Fipronil and certain cyclodienes act as GABA-gated chloride channel blockers.

Question 30

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

Accepted Answer

Chagas disease — Triatomine bugs transmit Trypanosoma cruzi, the causative agent of Chagas disease.

Question 31

People living in forested areas are at a specific risk of which vector-borne disease often carried by deer flies?

Accepted Answer

Loiasis — Loa loa (African eye worm) is transmitted by Chrysops (deer flies) in forest environments.

Question 32

Which of the following insects are commonly found in Latin America and transmit Chagas disease?

Accepted Answer

Triatoma — Triatoma bugs are the primary vectors of T. cruzi in Latin America.

Question 33

Pruritus (itching) is a hallmark symptom for the diagnosis of:

Accepted Answer

Scabies — Sarcoptes scabiei (scabies) mites burrowing into the skin cause intense allergic pruritus.

Question 34

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

Accepted Answer

Pediculus humanus corporis — Body lice (Pediculus humanus corporis) lay their eggs (nits) in the seams of clothing, whereas head lice lay them on hair shafts.

Question 35

Which of the following is the 'odd one out' in terms of transmission (non-insect vector)?

Accepted Answer

Schistosomiasis — Malaria, Dengue, and Zika are mosquito-borne; Schistosomiasis is transmitted via water contact with snail-released cercariae.

Question 36

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

Accepted Answer

Tsetse fly — The Tsetse fly (Glossina) is unusual because it gives birth to a single fully developed larva (larviparity).

Question 37

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

Accepted Answer

Rheumatic fever — Rheumatic fever and Glomerulonephritis are immune-mediated (non-suppurative) complications of Strep throat.

Question 38

The presence of a thick, gray pseudomembrane in the throat is characteristic of:

Accepted Answer

Diphtheria — Corynebacterium diphtheriae produces a toxin that causes tissue necrosis, forming a characteristic pseudomembrane.

Question 39

The Mantoux test is used to identify:

Accepted Answer

TB exposure and cell-mediated immunity — The Mantoux skin test (PPD) detects delayed-type hypersensitivity resulting from exposure to M. tuberculosis.

Question 40

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

Accepted Answer

Streptococcus pneumoniae — Streptococcus pneumoniae (the pneumococcus) is the #1 cause of lobar, typical pneumonia.

Question 41

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

Accepted Answer

Bacillus cereus — Bacillus cereus causes two types of food poisoning: the emetic type (often linked to rice) and the diarrheal type (linked to meats/sauces).

Question 42

Which one of the following describes the mode of action of tetanospasmin?

Accepted Answer

It inhibits the release of glycine and GABA — Tetanospasmin prevents the release of inhibitory neurotransmitters, leading to spastic paralysis (lockjaw).

Question 43

Salpingitis is inflammation of the fallopian tubes often associated with and can lead to :

Accepted Answer

Chlamydia; infertility — Salpingitis is a key component of PID, commonly caused by Chlamydia or Gonorrhea, leading to tubal scarring and infertility.

Question 44

The term 'Staphylococcus' is derived from Greek meaning:

Accepted Answer

Grape-like cluster — Staphyle means 'bunch of grapes' and kokkos means 'berry/grain' in Greek.

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 haloduric; they can grow in salt concentrations up to , which is used in selection media:

Accepted Answer

15% — Mannitol Salt Agar (MSA) uses 7.5% NaCl to select for Staphylococci.

Question 47

The primary test used to clinically classify staphylococci into 'virulent' vs 'less virulent' (opportunistic) groups is:

Accepted Answer

Coagulase — The coagulase test separates S. aureus (positive) from coagulase-negative staphylococci (CoNS) like S. epidermidis.

Question 48

Protein A, found in the cell wall of S. aureus, has a high affinity for:

Accepted Answer

The Fc portion of IgG — Protein A binds the Fc region 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) cause the separation of the epidermis at the desmosomes.

Question 50

Staphylococcal food poisoning is caused by:

Accepted Answer

Ingestion of pre-formed heat-stable enterotoxins — S. aureus grows in food and produces heat-stable enterotoxins; the toxin, not the bacteria, causes the rapid onset of illness.

Weekly Year 2: Microbiology Exam - April 17, 2026 (Section A

Questions, Answers & Explanations