Weekly Year 2: Microbiology Exam - May 15, 2026 (Section A:

Question 1

Fish are second intermediate hosts for which group of parasites?

Accepted Answer

Trematodes (flukes) — Many trematodes, such as Clonorchis sinensis and Paragonimus spp., use fish as their second intermediate host where the metacercariae encyst.

Question 2

Which of the following organisms secretes defensive secretions that can cause irritation on human skin?

Accepted Answer

Certain species of beetles (e.g., Blister beetles) — Many insects, including certain beetles, secrete cantharidin or other irritant compounds as a defense mechanism. Contact with human skin can cause blistering and irritation.

Question 3

Holometabolous insects undergo which type of development?

Accepted Answer

Complete metamorphosis with egg, larva, pupa, and adult stages — Holometabolous insects, such as flies, beetles, and butterflies, have a life cycle characterized by complete metamorphosis, involving distinct larval and pupal stages.

Question 4

Which of the following arthropods is the primary vector for transmitting parasites that cause river blindness (onchocerciasis)?

Accepted Answer

Black fly (Simulium species) — Onchocerciasis is transmitted by the bite of infected female black flies (Simulium species), which breed in fast-flowing rivers and streams.

Question 5

Which common insecticide targets the GABA receptor complex in its mechanism of action?

Accepted Answer

Fipronil — Fipronil is a phenylpyrazole insecticide that acts by blocking GABA-gated chloride channels, disrupting the insect's central nervous system.

Question 6

The presence of triatomine bugs (kissing bugs) in a community could predispose the population to infection with:

Accepted Answer

Chagas disease (American trypanosomiasis) — Triatomine bugs are the vectors of Trypanosoma cruzi, the parasite that causes Chagas disease. They typically bite near the mouth of sleeping individuals and defecate, allowing the parasite to enter the host.

Question 7

People living in forested or wooded areas are at a higher risk of infection with which of the following pathogens?

Accepted Answer

Lyme disease (Borrelia burgdorferi) — Lyme disease is transmitted by the bite of infected Ixodes ticks, which are commonly found in wooded and grassy areas where deer and rodents, the primary hosts, reside.

Question 8

Which of the following insects are commonly found in Latin America and are vectors for important diseases?

Accepted Answer

Triatomine bugs — Triatomine bugs, also known as kissing bugs, are prevalent in Latin America and are the vectors of Chagas disease.

Question 9

Pruritus (itching) associated with insect bites or ectoparasitic infestations is best diagnosed by:

Accepted Answer

Skin scraping and microscopic examination — Direct examination of the skin, often with a skin scraping, is the most effective way to identify ectoparasites like mites (scabies) or lice, and their eggs (nits).

Question 10

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

Accepted Answer

Pediculus humanus humanus (body louse) — Body lice (Pediculus humanus humanus) are more likely to lay their eggs (nits) on clothing, particularly in seams, compared to head lice or pubic lice, which primarily infest hair.

Question 11

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

Accepted Answer

Leptospira interrogans — Plasmodium falciparum, Dengue virus, and Trypanosoma cruzi are all transmitted by arthropod vectors (mosquitoes and triatomine bugs, respectively). Leptospira interrogans is primarily transmitted through contact with contaminated water or soil, often via urine of infected animals.

Question 12

Which one of the following insects is considered larviparous?

Accepted Answer

Housefly (Musca domestica) — Larviparous means giving birth to living larvae. Some species of flies, including certain houseflies, are larviparous, meaning the eggs hatch inside the female and she gives birth to maggots.

Question 13

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

Accepted Answer

Activation of adenylate cyclase, leading to increased intracellular cAMP — The heat-labile toxin (LT) of ETEC is an enterotoxin that activates adenylate cyclase in intestinal epithelial cells, leading to increased cyclic AMP (cAMP) levels, which in turn causes fluid and electrolyte secretion.

Question 14

Which of the following statements regarding Pseudomonas aeruginosa is correct?

Accepted Answer

It is a common cause of opportunistic infections in immunocompromised individuals. — Pseudomonas aeruginosa is an opportunistic, Gram-negative rod that is ubiquitous in the environment. It frequently causes infections in patients with weakened immune systems, such as those with cystic fibrosis, burns, or prolonged hospitalization, often in healthcare settings.

Question 15

Long-term carriage and chronic shedding of an organism are most likely after a gastrointestinal infection with:

Accepted Answer

Salmonella Typhi — Salmonella Typhi is known for establishing a chronic carrier state in the gallbladder, leading to prolonged shedding of the bacteria in feces, even after resolution of acute illness.

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 a travel history?

Accepted Answer

Vibrio cholerae — Vibrio cholerae is endemic in certain regions and typically causes severe, watery diarrhea. While it can cause rapid onset illness, in a non-endemic area without a travel history, it is less likely than common foodborne pathogens like S. aureus or viruses like Norovirus, or even Salmonella.

Question 17

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

Accepted Answer

Ceftriaxone is the recommended first-line treatment. — Due to widespread resistance of Neisseria gonorrhoeae to many antibiotics, including β-lactams and tetracyclines, current guidelines recommend ceftriaxone as the first-line treatment. The information provided about β-lactamase positivity and tetracycline resistance highlights the need for appropriate antibiotic choices.

Question 18

Which Neisseria gonorrhoeae structure primarily mediates attachment to host epithelial cells?

Accepted Answer

Pili (fimbriae) — Pili (fimbriae) are hair-like appendages on the surface of Neisseria gonorrhoeae that play a crucial role in adherence to host epithelial cells in the genitourinary tract, facilitating colonization and infection.

Question 19

A 6-year-old boy has meningitis. CSF culture grows Neisseria meningitidis serogroup B. What is recommended for household contacts?

Accepted Answer

Antibiotic prophylaxis with rifampin. — For close contacts of a case of meningococcal meningitis, antibiotic prophylaxis is recommended to reduce secondary cases. Rifampin is a common choice for prophylaxis against serogroup B strains, although ciprofloxacin may also be used depending on local guidelines. The MenACWY vaccine does not cover serogroup B.

Question 20

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

Accepted Answer

Infertility — Pelvic inflammatory disease (PID), often caused by Neisseria gonorrhoeae or Chlamydia trachomatis, can lead to scarring and inflammation of the reproductive organs, resulting in chronic pelvic pain and infertility.

Question 21

Which statement best describes the pathogenesis of Clostridium botulinum?

Accepted Answer

The bacteria produce a potent neurotoxin that blocks acetylcholine release at neuromuscular junctions. — Clostridium botulinum produces an extremely potent neurotoxin (botulinum toxin) that inhibits the release of acetylcholine from presynaptic nerve terminals, leading to flaccid paralysis.

Question 22

A patient with cavitary lung disease grows a photochromogenic acid-fast bacillus (orange pigment on light exposure). The organism is:

Accepted Answer

Mycobacterium kansasii — Mycobacterium kansasii is a photochromogenic species of nontuberculous mycobacteria that produces a characteristic orange pigment when exposed to light. It can cause pulmonary disease resembling tuberculosis, often with cavitary lesions.

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 complex (MAC) — Disseminated infection with Mycobacterium avium complex (MAC) is common in individuals with advanced HIV/AIDS. It can present with fever, weight loss, lymphadenopathy, and involvement of organs like the liver and bone marrow, often with acid-fast bacilli seen on microscopy. Pulmonary involvement may be absent initially.

Question 24

A major concern for the patient above (with disseminated MAC infection) is infection with a strain that is:

Accepted Answer

Highly resistant to multiple antibiotics — Strains of Mycobacterium avium complex (MAC) are often inherently resistant to many standard anti-tuberculosis drugs, including isoniazid and rifampin. Treatment typically requires a combination of multiple drugs, and even then, eradication can be challenging.

Question 25

Which one of the following is a common complication of untreated streptococcal pharyngitis?

Accepted Answer

Rheumatic fever — Rheumatic fever is an inflammatory condition that can occur as a sequela of untreated or inadequately treated group A Streptococcus pharyngitis. It affects the heart, joints, brain, and skin.

Question 26

The presence of a pseudomembrane in the throat is a hallmark of:

Accepted Answer

Diphtheria (Corynebacterium diphtheriae) — Diphtheria is characterized by the formation of a grayish-white pseudomembrane composed of fibrin, leukocytes, erythrocytes, and Corynebacterium diphtheriae. This membrane adheres to the pharyngeal wall and can obstruct the airway.

Question 27

A paroxysm is a period of intensified symptoms, often associated with:

Accepted Answer

Severe coughing fits; pertussis — In pertussis (whooping cough), a paroxysm refers to a sudden, severe attack of coughing, typically followed by a characteristic 'whoop' sound as the patient inhales deeply.

Question 28

The Mantoux test is primarily used to identify:

Accepted Answer

Past exposure to Mycobacterium tuberculosis — The Mantoux tuberculin skin test (TST) measures a person's reaction to purified protein derivative (PPD) of Mycobacterium tuberculosis. A positive result indicates that the person has been infected with TB at some point, but it does not distinguish between latent infection and active disease.

Question 29

Which one of the following bacterial species is the most common cause of 'typical' bacterial pneumonia in adults?

Accepted Answer

Streptococcus pneumoniae — Streptococcus pneumoniae is historically considered the most common bacterial cause of typical community-acquired pneumonia in adults, characterized by sudden onset, fever, cough with purulent sputum, and lobar consolidation on chest X-ray.

Question 30

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

Accepted Answer

Antitoxin — Treatment for botulism focuses on neutralizing the circulating botulinum toxin before it binds to nerve endings. This is achieved by administering botulinum antitoxin.

Question 31

The organism Clostridium perfringens multiplies rapidly in foods only under conditions.

Accepted Answer

Anaerobic — Clostridium perfringens is an anaerobic bacterium. It proliferates in foods that have been improperly cooled, allowing it to grow in the absence of oxygen.

Question 32

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

Accepted Answer

Cereus — Bacillus cereus is a spore-forming, motile bacterium known to cause two types of food poisoning: an emetic (vomiting) form due to a preformed toxin in the food, and a diarrheal form caused by toxins produced after ingestion.

Question 33

Woolsorter's disease applies to the form of .

Accepted Answer

Cutaneous; anthrax — Woolsorter's disease is an old term for the severe, inhalational form of anthrax (Bacillus anthracis) that was historically seen in workers who processed animal wool and hides.

Question 34

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

Accepted Answer

It prevents the release of inhibitory neurotransmitters in the spinal cord. — Tetanospasmin, the toxin produced by Clostridium tetani, blocks the release of inhibitory neurotransmitters (like GABA and glycine) from interneurons in the spinal cord, leading to uncontrolled muscle spasms and rigidity (spastic paralysis).

Question 35

Salpingitis is inflammation of the fallopian tubes, most commonly associated with and can lead to .

Accepted Answer

Gonorrhea or Chlamydia; infertility — Salpingitis is a key component of Pelvic Inflammatory Disease (PID), which is frequently caused by Neisseria gonorrhoeae and Chlamydia trachomatis. Untreated PID can lead to scarring of the fallopian tubes, resulting in infertility and ectopic pregnancy.

Question 36

Ophthalmia neonatorum is a serious eye infection in newborns that can be caused by transmission of sexually transmitted diseases. Which two STDs are most commonly associated with ophthalmia neonatorum?

Accepted Answer

Gonorrhea and Chlamydia — Gonococcal ophthalmia neonatorum (caused by Neisseria gonorrhoeae) and chlamydial ophthalmia neonatorum (caused by Chlamydia trachomatis) are the most common and serious forms of conjunctivitis in newborns, acquired during passage through an infected birth canal.

Weekly Year 2: Microbiology Exam - May 15, 2026 (Section A:

Questions, Answers & Explanations