Weekly Year 2: Microbiology Exam - July 3, 2026 (Section...

Question 1

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 of healthcare workers — Staphylococcus aureus commonly colonizes the nasal passages of healthy individuals, including healthcare workers. This colonization is a frequent source of nosocomial infections, particularly in vulnerable populations like neonates in a nursery.

Question 2

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

Accepted Answer

Bacteroides fragilis — Bacteroides fragilis is an anaerobic bacterium that is a normal inhabitant of the human gut and is not typically associated with causing diarrhea. The other options are well-established causes of infectious diarrhea.

Question 3

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

Accepted Answer

Cytoplasm — While the cytoplasm contains many cellular components, it is generally intracellular and not as readily exposed as surface antigens like the capsule, cell wall, or flagella, which are targeted by serological tests for bacterial identification.

Question 4

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

Accepted Answer

Pasteurella multocida — Pasteurella multocida is the most common species isolated from animal bites and scratches, but it can also be found in the normal flora of the oropharynx in cats and dogs. It has been implicated in female genital tract infections and neonatal infections, often acquired from household pets.

Question 5

Each statement about streptococci classification is correct except:

Accepted Answer

Alpha-hemolytic streptococci include Streptococcus pneumoniae. — Lancefield grouping is based on specific cell wall polysaccharide antigens, not just 'C carbohydrate antigens' in a general sense. While correct, the other statements accurately describe streptococci classification and examples.

Question 6

Staphylococcal scalded skin syndrome is caused by exotoxin produced by:

Accepted Answer

Staphylococcus aureus — Staphylococcal scalded skin syndrome (SSSS) is caused by exfoliative toxins (epidermolytic toxins) produced by certain strains of Staphylococcus aureus. These toxins cleave desmoglein-1, leading to separation of the stratum granulosum from the stratum spinosum.

Question 7

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

Accepted Answer

She has been successfully treated for past syphilis. — The RPR (Rapid Plasma Reagin) test is a screening test for syphilis and can become non-reactive after successful treatment. The TP-PA (Treponema pallidum Particle Agglutination) test is a confirmatory test and remains reactive even after successful treatment, indicating past exposure and effective treatment.

Question 8

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

Accepted Answer

Shigella dysenteriae — Shigella dysenteriae has a very low ID50, meaning a small number of organisms can cause infection. It is highly invasive and causes severe disease. Vibrio cholerae, especially non-toxigenic strains, requires a much larger inoculum, and E. coli and Salmonella also generally require higher doses compared to Shigella.

Question 9

Which disease is best diagnosed by serologic means?

Accepted Answer

Syphilis — Syphilis is primarily diagnosed serologically due to the difficulty in culturing Treponema pallidum and the specific antibody responses generated by the body. While serology can be supportive for the others, it is the cornerstone for syphilis diagnosis. Tuberculin skin tests (Mantoux) are immunological, but not direct serological tests for active infection. Influenza and Tetanus can be diagnosed clinically or with specific molecular tests, though serology can indicate past exposure or immunity.

Question 10

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

Accepted Answer

Salmonella species — Salmonella species typically cause inflammatory diarrhea, which is often bloody. Norovirus, S. aureus toxin (food poisoning), and Rotavirus are common causes of non-bloody, watery diarrhea, especially in shorter durations.

Question 11

A woman develops gonococcal PID. What is the most common sequela?

Accepted Answer

Infertility — Pelvic Inflammatory Disease (PID), especially when caused by Neisseria gonorrhoeae, frequently leads to scarring and inflammation of the fallopian tubes, which can result in infertility due to impaired egg transport or implantation.

Question 12

Mycobacterial survival after macrophage ingestion is attributed to:

Accepted Answer

Resistance to lysosomal enzymes — Mycobacteria, particularly Mycobacterium tuberculosis, have mechanisms to prevent or resist the fusion of the phagosome with lysosomes or to survive within the phagolysosome, thus evading destruction by the macrophage's antimicrobial mechanisms.

Question 13

Fish are second intermediate hosts of?

Accepted Answer

Clonorchis sinensis — Clonorchis sinensis (Chinese liver fluke) uses fish as its second intermediate host. Humans become infected by consuming raw or undercooked fish containing the metacercariae. Schistosoma mansoni uses snails as intermediate hosts. Taenia solium uses pigs as intermediate hosts. Echinococcus granulosus uses herbivores as intermediate hosts.

Question 14

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

Accepted Answer

Blister beetles — Blister beetles secrete a blistering agent called cantharidin, which causes severe irritation and blisters upon contact with human skin. Mosquitoes transmit diseases, cockroaches are nuisance pests, and house flies are vectors of disease but do not secrete irritant secretions.

Question 15

Holometabolous insects have?

Accepted Answer

Egg, larva, pupa, adult stages — Holometabolous insects undergo complete metamorphosis, which includes distinct life stages of egg, larva, pupa, and adult. Examples include butterflies, moths, beetles, flies, and bees. Incomplete metamorphosis (hemimetabolous) has egg, nymph, and adult stages.

Question 16

Which of the following transmits parasites for river blindness?

Accepted Answer

Blackfly — River blindness (Onchocerciasis) is transmitted by the bite of infected blackflies (genus Simulium), which are found near fast-flowing rivers, hence the name. Tsetse flies transmit trypanosomiasis (sleeping sickness), sandflies transmit leishmaniasis, and mosquitoes transmit malaria, dengue, and other diseases.

Question 17

Which insecticide targets GABA in its action?

Accepted Answer

Fipronil — Fipronil is a phenylpyrazole insecticide that acts by blocking GABA-gated chloride channels in the insect's nervous system, leading to hyperexcitation and death. Pyrethroids affect sodium channels. Organophosphates inhibit acetylcholinesterase. Neonicotinoids act on nicotinic acetylcholine receptors.

Question 18

Presence of triatomine bugs could predispose the population to?

Accepted Answer

Chagas disease — Triatomine bugs, also known as kissing bugs, are vectors of the parasite Trypanosoma cruzi, which causes Chagas disease. They are found in the Americas. Malaria is transmitted by mosquitoes, dengue fever and yellow fever by mosquitoes, though different species.

Question 19

People living in forested areas like Arabuko Sokoke are at a risk of?

Accepted Answer

Rickettsial infections — Forested areas are often habitats for ticks and other arthropods that can transmit rickettsial infections (like tick-borne typhus). While malaria is prevalent in some forested regions, rickettsial infections are a significant risk associated with tick vectors commonly found in such environments. Typhoid and cholera are typically water/foodborne.

Question 20

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

Accepted Answer

Triatomine bug — Triatomine bugs (kissing bugs) are endemic to the Americas and are vectors of Chagas disease. Tsetse flies are found in Africa. Lice and fleas are found worldwide but their disease associations are more specific to regions and hygiene.

Question 21

Pruritus can be best diagnosed for?

Accepted Answer

Scabies — Scabies is a parasitic infestation of the skin caused by the mite Sarcoptes scabiei, and intense itching (pruritus) is its hallmark symptom. The other conditions listed are not primarily characterized by pruritus.

Question 22

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) lay their eggs (nits) in the seams of clothing, as they live on the body but prefer to stay near warmth and protection. Head lice attach eggs to hair shafts, and pubic lice attach to pubic hair.

Question 23

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

Accepted Answer

Glossina species — Aedes, Anopheles, and Culex are all genera of mosquitoes that transmit various pathogens through their bites. Glossina species are tsetse flies, which transmit African trypanosomiasis (sleeping sickness) through their bites, representing a different group of vectors.

Question 24

Which one of the following is larviparous?

Accepted Answer

Mosquitoes — Larviparous is a reproductive strategy where the female gives birth to live larvae. In the context of these insects, mosquitoes are the most direct example of larviparous reproduction as they lay eggs that hatch into aquatic larvae (wrigglers). While fleas, lice, and bed bugs have larval stages, their egg-laying and development differ. However, the question likely refers to the distinct larval stage emerging from the egg.

Question 25

Which one of the following is a complication of streptococcus pharyngitis?

Accepted Answer

Rheumatic fever — Rheumatic fever is a serious inflammatory complication that can occur after an untreated or inadequately treated streptococcal pharyngitis (strep throat). It affects the heart, joints, brain, and skin. Scarlet fever is a characteristic rash associated with certain strains of Streptococcus pyogenes, not a complication in the same sense as rheumatic fever. The other options are not directly linked as common complications of strep throat.

Question 26

The presence of a pseudomembrane is a result of:

Accepted Answer

Diphtheria toxin — The characteristic pseudomembrane in the throat of a patient with diphtheria is formed by the bacterium Corynebacterium diphtheriae, which produces diphtheria toxin. This toxin causes local tissue necrosis and inflammation, leading to the formation of a thick, grayish-white membrane composed of fibrin, dead cells, and bacteria.

Question 27

A paroxysm is a associated with :

Accepted Answer

Pertussis — Paroxysms of coughing are the hallmark symptom of pertussis (whooping cough), caused by Bordetella pertussis. These are severe, prolonged coughing fits that can lead to vomiting or cyanosis. The other diseases have different characteristic clinical presentations.

Question 28

The Mantoux test is used to identify:

Accepted Answer

All of the above — The Mantoux tuberculin skin test (TST) measures delayed hypersensitivity to tuberculin. A positive test indicates that the individual has been infected with Mycobacterium tuberculosis at some point, but it does not distinguish between active infection, latent infection, or previous BCG vaccination. Therefore, it indicates past exposure and potential latent infection.

Question 29

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

Accepted Answer

Antitoxin — Botulism is caused by a neurotoxin produced by Clostridium botulinum. The primary treatment for botulism is the administration of botulinum antitoxin, which neutralizes any circulating toxin before it can bind to nerve endings. Activated charcoal can be used to help absorb ingested toxin if given early. Antibiotics are generally not the primary treatment for toxin ingestion but may be used if there is a concurrent wound infection.

Question 30

The organism Clostridium perfringens multiplies in foods only under conditions:

Accepted Answer

Anaerobic — Clostridium perfringens is an obligate anaerobe, meaning it can only grow and multiply in the absence of oxygen. This is why it is often implicated in food poisoning when large food items are cooked incompletely and then allowed to cool slowly, creating anaerobic conditions within the food.

Question 31

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 foodborne illness: an emetic syndrome (vomiting, caused by a heat-stable toxin) and a diarrheal syndrome (diarrhea, caused by heat-labile toxins). Bacillus anthracis causes anthrax, a more serious disease. Bacillus subtilis and licheniformis are less commonly associated with food poisoning.

Question 32

Woolsorter disease applies to the form of :

Accepted Answer

Anthrax — Woolsorter's disease, also known as pulmonary anthrax, is a severe form of anthrax infection that occurs when inhalation of anthrax spores (Bacillus anthracis) leads to infection of the lungs. It was historically associated with workers in wool processing industries who inhaled spores from animal hides.

Question 33

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

Accepted Answer

It blocks the release of inhibitory neurotransmitters. — Tetanospasmin, the neurotoxin produced by Clostridium tetani, acts within the central nervous system to inhibit the release of inhibitory neurotransmitters (GABA and glycine) from spinal cord interneurons. This leads to uncontrolled motor neuron excitation, causing the characteristic spastic paralysis of tetanus.

Question 34

Salpingitis is associated with and can lead to :

Accepted Answer

Pelvic Inflammatory Disease (PID); infertility — Salpingitis is inflammation of the fallopian tubes, which is a common component of Pelvic Inflammatory Disease (PID). PID, especially when caused by sexually transmitted infections like gonorrhea and chlamydia, can lead to scarring of the fallopian tubes and subsequent infertility or ectopic pregnancy.

Question 35

Ophthalmia is associated with what two STDs?

Accepted Answer

Chlamydia trachomatis and Neisseria gonorrhoeae — Ophthalmia neonatorum, a conjunctivitis in newborns, is commonly caused by infections acquired during birth from the mother's birth canal. Chlamydia trachomatis and Neisseria gonorrhoeae are the most frequent bacterial causes of gonococcal and chlamydial ophthalmia neonatorum, respectively.

Question 36

Toxin-generated S. aureus diseases resulting from contact include:

Accepted Answer

Impetigo and scalded skin syndrome — Impetigo (bullous type) and Staphylococcal Scalded Skin Syndrome (SSSS) are skin diseases caused by exotoxins produced by Staphylococcus aureus that act locally or are absorbed systemically but result from direct contact with the organism or its toxins on the skin. Toxic shock syndrome and food poisoning are also toxin-mediated but often involve ingestion or systemic spread. Pneumonia, endocarditis, osteomyelitis, and bacteremia are invasive infections, not primarily toxin-generated contact diseases.

Weekly Year 2: Microbiology Exam - July 3, 2026 (Section...

Questions, Answers & Explanations