Weekly Year 2: Microbiology Exam - September 25, 2026 (Se...

Question 1

A paroxysm is a severe coughing fit and is characteristic of which disease?

Accepted Answer

Pertussis — Paroxysms, characterized by severe and rapid coughing fits, are a hallmark symptom of pertussis (whooping cough).

Question 2

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

Accepted Answer

Antitoxin — Botulism toxin is neutralized by specific antitoxin, which binds to and inactivates the toxin before it can cause further damage.

Question 3

The organism Clostridium perfringens multiplies in foods only under what conditions?

Accepted Answer

Anaerobic — Clostridium perfringens is an obligate anaerobe, meaning it can only grow and multiply in the absence of oxygen.

Question 4

Woolsorter's disease applies to which form of anthrax?

Accepted Answer

Inhalational anthrax — Woolsorter's disease is an older term for inhalational anthrax, historically associated with workers who processed wool contaminated with Bacillus anthracis spores.

Question 5

Ophthalmia neonatorum, a form of conjunctivitis, is associated with which two sexually transmitted diseases?

Accepted Answer

Chlamydia trachomatis and Neisseria gonorrhoeae — Ophthalmia neonatorum in newborns is most commonly caused by infections with Chlamydia trachomatis and Neisseria gonorrhoeae, acquired during passage through the birth canal.

Question 6

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

Accepted Answer

Bacillus anthracis — Robert Koch first successfully applied his postulates to demonstrate that Bacillus anthracis was the causative agent of anthrax.

Question 7

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

Accepted Answer

It inhibits protein synthesis by ADP-ribosylating elongation factor 2 (EF-2). — Diphtheria toxin is an exotoxin that inhibits protein synthesis by irreversibly modifying and inactivating elongation factor 2 (EF-2), crucial for translation.

Question 8

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

Accepted Answer

Intracellular enzymes — Intracellular enzymes are typically not exposed on the bacterial surface and thus are not readily accessible for serological detection unless the bacterium is lysed.

Question 9

Which of the following diseases is best diagnosed by serologic means?

Accepted Answer

Syphilis — Syphilis is primarily diagnosed using serological tests (e.g., RPR, VDRL, FTA-ABS) that detect antibodies produced by the host in response to infection with Treponema pallidum.

Question 10

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

Accepted Answer

Haemophilus influenzae type b — While Haemophilus influenzae type b (Hib) is a significant cause of meningitis, it is more common in unvaccinated children. In adults, Streptococcus pneumoniae and Neisseria meningitidis are the most common bacterial causes of meningitis.

Question 11

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

Accepted Answer

Staphylococcus aureus — Staphylococcus species, particularly coagulase-negative staphylococci (e.g., S. epidermidis), are notorious for forming biofilms on medical devices like catheters and prosthetic joints, contributing to persistent infections.

Question 12

Fish are second intermediate hosts of?

Accepted Answer

Clonorchis sinensis — Clonorchis sinensis (Chinese liver fluke) requires freshwater snails as the first intermediate host and fish as the second intermediate host.

Question 13

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

Accepted Answer

Centipede — Centipedes possess venom glands and can inject irritating secretions through their forcipules, causing pain and inflammation upon contact with human skin.

Question 14

Holometabolous insects have?

Accepted Answer

Complete metamorphosis with larval, pupal, and adult stages — Holometabolous insects undergo complete metamorphosis, characterized by distinct larval, pupal, and adult stages, with significant transformation between stages (e.g., butterflies, beetles, flies).

Question 15

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

Accepted Answer

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

Question 16

Which insecticide targets GABA in its action?

Accepted Answer

Fipronil — Fipronil is a phenylpyrazole insecticide that acts by blocking GABA-gated chloride channels in insects, disrupting their central nervous system.

Question 17

Presence of triatomine bugs could predispose the population to?

Accepted Answer

Chagas disease — Triatomine bugs (kissing bugs) are vectors for the parasite Trypanosoma cruzi, which causes Chagas disease.

Question 18

People living in forested areas are at a risk of?

Accepted Answer

Lyme disease — Lyme disease is transmitted by ticks, which are commonly found in forested and grassy areas. The causative agent is Borrelia burgdorferi.

Question 19

Which of the following insects are commonly found in Latin America?

Accepted Answer

Triatomine bug — Triatomine bugs, the vectors for Chagas disease, are endemic to the Americas, particularly in rural and semi-rural areas of Latin America.

Question 20

Pruritus can be best diagnosed for?

Accepted Answer

Scabies infestation — Pruritus (itching) is a cardinal symptom of scabies infestation, caused by the mite Sarcoptes scabiei.

Question 21

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

Accepted Answer

Body louse (Pediculus humanus humanus) — Body lice (Pediculus humanus humanus) lay their eggs (nits) on clothing or bedding, whereas head lice attach nits to hair shafts and pubic lice to hairs in the genital area.

Question 22

Which of the following is odd one out in terms of transmission?

Accepted Answer

Typhoid fever — Malaria, Dengue fever, and Yellow fever are all transmitted by arthropod vectors (mosquitoes). Typhoid fever is primarily transmitted through contaminated food and water (fecal-oral route).

Question 23

Which one of the following is larviparous?

Accepted Answer

Mosquito — Mosquitoes are larviparous, meaning they lay eggs that hatch into larvae, which then develop through pupal stages before becoming adults.

Question 24

An outbreak of sepsis caused by Staphylococcus aureus has occurred in the newborn nursery. What is the most likely source of the organism?

Accepted Answer

Nasal carriage by healthcare workers — Staphylococcus aureus is a common colonizer of the nasal passages. Healthcare workers with nasal carriage can transmit the organism to vulnerable newborns, leading to sepsis.

Question 25

Each of the following agents is a recognized cause of diarrhea except:

Accepted Answer

Mycobacterium tuberculosis — Mycobacterium tuberculosis primarily causes tuberculosis, affecting the lungs. While it can cause gastrointestinal symptoms in disseminated TB, it is not a common cause of acute diarrhea compared to the other listed bacterial pathogens.

Question 26

Bacterial identification by serological tests is based on specific antigens. Which component is least likely to contain useful antigens?

Accepted Answer

Ribosomal proteins — Ribosomal proteins are intracellular components. Serological tests typically target surface antigens or extracellular products that elicit an immune response, making ribosomal proteins less likely to be useful for identification by this method.

Question 27

Which Pasteurella species has been associated with female genital tract and newborn infections?

Accepted Answer

Pasteurella multocida — Pasteurella multocida is frequently isolated from the female genital tract and can be transmitted to newborns during childbirth, causing various infections.

Question 28

Each statement about streptococci classification is correct except:

Accepted Answer

Gamma-hemolytic streptococci exhibit no hemolysis of red blood cells. — Beta-hemolytic streptococci are NOT further classified by their sensitivity to bacitracin; this is a characteristic used to differentiate Group A Streptococcus (Streptococcus pyogenes) from other beta-hemolytic streptococci. Bacitracin sensitivity is a key identifying feature of Group A Strep.

Question 29

Staphylococcal scalded skin syndrome is caused by exotoxin produced by:

Accepted Answer

Staphylococcus aureus — Staphylococcal scalded skin syndrome (SSSS) is caused by exfoliative toxins (ETA and ETB) produced by certain strains of Staphylococcus aureus.

Question 30

A pregnant woman with previous syphilis treatment shows: RPR non-reactive, TP-PA reactive. Which statement is most correct?

Accepted Answer

She has a past syphilis infection. — A non-reactive RPR (a screening test) and a reactive TP-PA (a confirmatory treponemal test) in a previously treated patient generally indicates a past infection that has been treated. The TP-PA can remain reactive long after treatment.

Question 31

Which bacteria has the lowest 50% infective dose (ID50)?

Accepted Answer

Shigella dysenteriae — Shigella species, particularly Shigella dysenteriae, are highly virulent and have a very low ID50, meaning a small number of organisms can cause infection, often fewer than 100 bacteria.

Question 32

Which disease is best diagnosed by serologic means?

Accepted Answer

Syphilis — Syphilis is primarily diagnosed using serological tests, which detect antibodies produced by the body in response to Treponema pallidum infection. Influenza and Tetanus can be diagnosed clinically or by specific antigen/PCR tests, and TB is usually diagnosed via PPD or IGRA tests and sputum microscopy/culture.

Question 33

A woman has non-bloody diarrhea for 14 hours. Which organism is least likely to cause this?

Accepted Answer

Shigella species — Shigella species typically cause dysentery, characterized by bloody diarrhea due to invasion of the colonic mucosa. The other options are more commonly associated with non-bloody diarrhea or vomiting.

Question 34

A woman develops gonococcal pelvic inflammatory disease (PID). What is the most common sequela?

Accepted Answer

All of the above — Gonococcal PID can lead to a range of serious long-term complications, including ectopic pregnancy, chronic pelvic pain, and infertility, due to scarring and inflammation of the reproductive organs.

Question 35

Mycobacterial survival after macrophage ingestion is attributed to:

Accepted Answer

Resistance to lysosomal enzymes and ability to prevent phagosome-lysosome fusion. — Mycobacteria, such as Mycobacterium tuberculosis, have evolved mechanisms to survive within macrophages by preventing the fusion of the phagosome with lysosomes and resisting the microbicidal activity of the phagolysosome.

Weekly Year 2: Microbiology Exam - September 25, 2026 (Se...

Questions, Answers & Explanations