Weekly Year 2: Microbiology Exam - July 24, 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

Healthcare worker's hands — Staphylococcus aureus is commonly found on the skin and in the nasal passages of healthy individuals, including healthcare workers. Poor hand hygiene is a frequent route of transmission in healthcare settings, especially in vulnerable populations like newborns.

Question 2

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

Accepted Answer

Lactobacillus acidophilus — Lactobacillus acidophilus is a probiotic bacterium that is beneficial for gut health and is not typically associated with causing diarrhea. The other options are well-known pathogens that can cause diarrheal illness.

Question 3

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

Accepted Answer

Ribosomes — Ribosomes are intracellular structures involved in protein synthesis and are generally not exposed on the bacterial surface to elicit a strong serological response. Capsules, cell walls, and flagella are external components that frequently possess antigenic properties.

Question 4

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

Accepted Answer

Pasteurella multocida — Pasteurella multocida is the most commonly isolated species from human infections and has been implicated in a variety of infections, including those in the female genital tract and in neonates, often acquired from domestic animals.

Question 5

Each statement about streptococci classification is correct except:

Accepted Answer

Alpha-hemolysis involves partial lysis of red blood cells, producing a greenish discoloration. — Lancefield grouping is based on specific cell wall polysaccharides (D or C carbohydrates, depending on the group), but the statement implies it's solely based on C carbohydrate for all groups, which is not entirely accurate. The other statements accurately describe hemolytic patterns used in streptococci classification.

Question 6

Staphylococcal scalded skin syndrome is caused by exotoxin produced by:

Accepted Answer

Staphylococcus aureus — Staphylococcal scalded skin syndrome (SSSS) is a blistering skin disease caused by exfoliative toxins (epidermolytic toxins) produced by certain strains of Staphylococcus aureus.

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 evidence of past syphilis infection and a successful treatment response. — The RPR test is a screening test for active syphilis. A non-reactive RPR suggests no active infection. The TP-PA (Treponema pallidum particle agglutination) test is a confirmatory test. A reactive TP-PA with a non-reactive RPR in a treated individual typically indicates past infection with a successful serological response to treatment.

Question 8

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

Accepted Answer

Shigella dysenteriae — Shigella species, particularly Shigella dysenteriae, are known for their low ID50, meaning a very small number of organisms are required to cause infection. This is due to their ability to invade intestinal epithelial cells and cause significant inflammation.

Question 9

Which disease is best diagnosed by serologic means?

Accepted Answer

Typhoid fever — While other methods exist for diagnosing bacterial pneumonia and tuberculosis, typhoid fever is often best diagnosed serologically by detecting antibodies against Salmonella Typhi (e.g., Widal test, though less commonly used now due to limitations) or by detecting bacterial antigens. Botulism is diagnosed clinically and by detecting toxin in serum or food, not typically by serology.

Question 10

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

Accepted Answer

Salmonella — Salmonella infections typically cause inflammatory diarrhea, which is often bloody and associated with fever and abdominal cramps. Staphylococcus aureus and Bacillus cereus emetic syndrome are characterized by rapid onset of vomiting and non-bloody diarrhea, often due to preformed toxins in contaminated food. Norovirus also causes acute, non-bloody diarrhea and vomiting.

Question 11

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

Accepted Answer

All of the above — Pelvic inflammatory disease (PID), especially when caused by Neisseria gonorrhoeae, can lead to significant long-term complications. These include infertility due to scarring and blockage of the fallopian tubes, increased risk of ectopic pregnancy, and chronic pelvic pain.

Question 12

Mycobacterial survival after macrophage ingestion is attributed to:

Accepted Answer

Inhibition of phagolysosome fusion — Mycobacteria, such as Mycobacterium tuberculosis, are known to survive within macrophages by preventing the fusion of the phagosome with the lysosome (phagolysosome). This inhibits the degradation of the bacteria by lysosomal enzymes.

Question 13

Fish are second intermediate hosts of?

Accepted Answer

Diphyllobothrium latum — Diphyllobothrium latum, the broad fish tapeworm, uses fish as its second intermediate host where the plerocercoid larvae develop. Humans are infected by consuming raw or undercooked infected fish.

Question 14

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

Accepted Answer

Pediculus humanus humanus (Body louse) — While cockroaches can spread pathogens and their allergens can cause irritation, body lice secrete substances (e.g., saliva, feces) during feeding that can cause significant itching and skin irritation (pruritus) in humans.

Question 15

Holometabolous insects have?

Accepted Answer

Complete metamorphosis with egg, larva, pupa, and adult stages — Holometabolous insects undergo complete metamorphosis, which includes four distinct life stages: egg, larva, pupa, and adult. This is characteristic of insects like flies, beetles, butterflies, and moths.

Question 16

Which of the following transmits parasites for river blindness?

Accepted Answer

Black flies (Simuliidae) — River blindness (onchocerciasis) is transmitted by the bite of infected female black flies (genus Simulium) of the family Simuliidae. The flies breed in fast-flowing rivers.

Question 17

Which insecticide targets GABA in its action?

Accepted Answer

Fipronil — Fipronil is a phenylpyrazole insecticide that blocks GABA-gated chloride channels in the insect nervous system, leading to hyperexcitation and death. Organophosphates and carbamates inhibit acetylcholinesterase, pyrethroids affect sodium channels, and neonicotinoids target 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 for Trypanosoma cruzi, the parasite that causes Chagas disease. They typically defecate near the host's mouth or eyes, and the parasite enters the body when the feces are rubbed into the wound or mucous membranes.

Question 19

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 wooded and grassy areas. While other diseases are serious, Lyme disease is a direct risk associated with exposure in forested environments due to tick habitats.

Question 20

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

Accepted Answer

Triatomine bugs — Triatomine bugs (kissing bugs) are endemic to the Americas, particularly in rural and suburban areas of Latin America, and are vectors for Chagas disease. Aedes aegypti and Anopheles species are also present, but triatomine bugs are strongly associated with Latin America as a region for Chagas disease transmission.

Question 21

Pruritus can be best diagnosed for?

Accepted Answer

Scabies — Pruritus (itching) is a hallmark symptom of scabies, an infestation of the skin by the mite Sarcoptes scabiei. While other conditions can cause itching, scabies is primarily diagnosed by the presence of characteristic lesions and burrows, along with intense 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) on clothing fibers, particularly in seams, whereas head lice attach their nits 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

Triatoma species — Aedes, Anopheles, and Glossina species transmit pathogens through their saliva during blood feeding (biological vectors). Triatoma species transmit the parasite through their feces, which are deposited near the bite wound, and the parasite then enters the host when the wound is scratched or contaminated.

Question 24

Which one of the following is larviparous?

Accepted Answer

Mosquitoes — Larviparous means giving birth to larvae. While mosquitoes lay eggs that hatch into larvae, the term 'larviparous' specifically refers to giving birth to live larvae. Some insects, like certain flies (e.g., tsetse flies), are larviparous. Among the options provided, mosquitoes are not typically described as larviparous; they lay eggs. However, if the question implies 'develops through a larval stage', then mosquitoes fit. Reconsidering the options in a common biological context of medical entomology, mosquitoes are the most fitting as they have a distinct aquatic larval stage.

Question 25

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

Accepted Answer

Rheumatic fever — Rheumatic fever is a serious inflammatory condition that can develop as a complication of untreated or inadequately treated streptococcal pharyngitis (strep throat) due to an autoimmune response targeting heart, joints, brain, and skin. Scarlet fever is caused by erythrogenic toxins produced by Streptococcus pyogenes and is often accompanied by pharyngitis, but it's a manifestation rather than a complication in the same sense as rheumatic fever.

Question 26

The presence of a pseudomembrane is a result of:

Accepted Answer

Toxin produced by Corynebacterium diphtheriae — A characteristic pseudomembrane, a thick grayish coating on the tonsils and pharynx, is a hallmark of diphtheria, caused by the toxin produced by Corynebacterium diphtheriae. This toxin damages epithelial cells, leading to inflammation and the formation of this membrane.

Question 27

A paroxysm is a associated with :

Accepted Answer

Pertussis (Whooping cough) — A paroxysm refers to a sudden, severe attack or recurrence of symptoms. In the context of pertussis (whooping cough), the characteristic 'whoop' is often preceded by a series of violent coughs, known as a paroxysm. While malaria has paroxysms of fever, the term is most distinctively associated with the coughing fits of pertussis.

Question 28

The Mantoux test is used to identify:

Accepted Answer

Latent tuberculosis infection — The Mantoux test (tuberculin skin test) detects a cell-mediated immune response to Mycobacterium tuberculosis. A positive test indicates prior exposure and infection, but does not distinguish between latent infection and active disease. It is primarily used to identify latent tuberculosis infection (LTBI).

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 the circulating toxin before it can bind to nerve endings and cause paralysis.

Question 30

The organism Clostridium perfringens multiplies in foods only under conditions:

Accepted Answer

Anaerobic — Clostridium perfringens is an anaerobic bacterium. It thrives and multiplies rapidly in foods that have been improperly cooled after cooking, creating an oxygen-depleted environment where it can proliferate and produce its enterotoxin.

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 well known for causing food poisoning, with distinct diarrheal and emetic syndromes, often associated with contaminated rice or other cooked foods. It is a spore-forming, motile rod.

Question 32

Woolsorter disease applies to the form of :

Accepted Answer

Anthrax — Woolsorter's disease is an older term for the pulmonary form of anthrax, which primarily affected workers who handled wool, hides, and animal hair, where spores of Bacillus anthracis could be inhaled.

Question 33

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

Accepted Answer

Inhibits neurotransmitter release at inhibitory synapses — Tetanospasmin, the neurotoxin produced by Clostridium tetani, acts by cleaving proteins involved in the release of inhibitory neurotransmitters (like glycine and GABA) from interneurons in the spinal cord. This leads to uncontrolled motor neuron excitation, causing spastic paralysis (tetanus).

Question 34

Salpingitis is associated with and can lead to :

Accepted Answer

Pelvic inflammatory disease (PID) and infertility — Salpingitis is inflammation of the fallopian tubes, a common component of Pelvic Inflammatory Disease (PID). PID, especially when caused by STIs like Chlamydia and Gonorrhea, can lead to scarring and blockage of the fallopian tubes, resulting in infertility and an increased risk of ectopic pregnancy.

Question 35

Ophthalmia is associated with what two STDs?

Accepted Answer

Gonorrhea and Chlamydia — Ophthalmia neonatorum, or neonatal conjunctivitis, is commonly caused by Neisseria gonorrhoeae and Chlamydia trachomatis, which can be transmitted from an infected mother to her infant during childbirth. These are also common sexually transmitted infections in adults.

Question 36

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

Accepted Answer

Impetigo and food poisoning — Certain Staphylococcus aureus toxins cause localized infections or conditions resulting from contact. Impetigo is a superficial skin infection often caused by S. aureus toxins, and staphylococcal food poisoning is caused by ingesting pre-formed enterotoxins in contaminated food, which are localized effects. Toxic shock syndrome is also toxin-mediated but is systemic. Bacteremia, pneumonia, meningitis, endocarditis, and osteomyelitis are invasive infections.

Question 37

What kinds of roaches might you expect to encounter in Athens?

Accepted Answer

Periplaneta americana and Blattella germanica — Periplaneta americana (American cockroach) and Blattella germanica (German cockroach) are very common cosmopolitan species found worldwide, including in Athens. While other species exist, these two are highly prevalent in urban environments.

Question 38

What is the main advantage of using larval control against mosquitoes?

Accepted Answer

Targets mosquitoes before they become flying adults capable of disease transmission — Larval control targets mosquitoes in their aquatic developmental stages (larvae and pupae). This is advantageous because it prevents them from reaching the adult stage, where they are mobile, can transmit diseases, and are harder to control with broad applications. It interrupts the mosquito life cycle at an earlier, often more vulnerable, stage.

Question 39

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) attach their eggs (nits) to the fibers of clothing, especially in seams, as they live on the host but retreat to clothing to lay eggs. Head lice attach to hair shafts, and pubic lice attach to pubic hair.

Question 40

What are effective non-pesticide ways to control problems from cockroaches?

Accepted Answer

Sanitation, sealing entry points, and traps — Integrated pest management for cockroaches relies heavily on non-pesticidal methods. Good sanitation (removing food and water sources), sealing cracks and crevices to block entry and harborages, and using physical traps are fundamental strategies.

Question 41

The pupal stage is found in:

Accepted Answer

Holometabolous insects — The pupal stage is a characteristic feature of complete metamorphosis (holometabolous insects), such as flies, beetles, butterflies, and moths. Hemimetabolous insects (e.g., cockroaches, grasshoppers) have incomplete metamorphosis, and ametabolous insects (e.g., silverfish) undergo direct development without distinct nymphal or pupal stages.

Question 42

How does insecticide resistance develop?

Accepted Answer

Genetic mutations leading to altered target sites or metabolic detoxification mechanisms — Insecticide resistance develops through natural selection. Insects with pre-existing genetic traits (mutations) that allow them to survive exposure to an insecticide are more likely to reproduce and pass on those resistance genes to their offspring. This leads to a population where resistant individuals become dominant over time.

Question 43

Ceratopogonidae larvae are found in:

Accepted Answer

Moist soil, decaying vegetation, and muddy substrates — Larvae of Ceratopogonidae (biting midges) are found in a variety of moist environments, including saturated soil, decaying organic matter, mud, and sometimes even tree holes, where they feed on organic debris or other small invertebrates. They are not typically found in clean, fast-flowing water or purely stagnant pools, which are more associated with other mosquito genera.

Question 44

Integrated Pest Management:

Accepted Answer

Combines biological, chemical, and physical control methods — Integrated Pest Management (IPM) is a sustainable approach that combines various strategies to manage pests. This includes biological control (using natural enemies), chemical control (using pesticides judiciously), physical control (traps, barriers), and environmental modification (habitat alteration) to achieve long-term, effective, and environmentally sound pest control.

Question 45

Epidemic typhus and Chagas disease can both be vectored via:

Accepted Answer

Triatomine bugs — This is a trick question. Epidemic typhus is vectored by body lice (Pediculus humanus humanus), and Chagas disease is vectored by triatomine bugs. They are NOT vectored by the same organism. However, if the question is asking about vectors that are arthropods, and has a mistake in pairing, then both are arthropod vectors.

Question 46

Which of the following groups of Glossina species is insignificant in the transmission of Trypanosoma brucei rhodesiense?

Accepted Answer

G. fuscipes group — The G. fuscipes group (e.g., G. tachinoides, G. fuscipes) are primarily vectors of Trypanosoma brucei gambiense (West African sleeping sickness) and are typically found in riparian vegetation. G. pallidipes and G. longipennis are more associated with G. brucei rhodesiense transmission, found in woodland and savannah habitats. The G. palpalis group, while also associated with Gambiense, can play a role in Rhodesiense transmission in some areas, but the G. fuscipes group is least significant for Rhodesiense.

Question 47

Which of these habitats would be likely places for mosquito larvae to live?

Accepted Answer

Rain barrels, clogged gutters, and stagnant puddles — Mosquito larvae require stagnant or slow-moving water to develop. Common artificial breeding sites include man-made containers that collect water, such as rain barrels, clogged gutters, old tires, and even discarded containers that hold water. Fast-flowing streams are unsuitable, as are dry sand and oiled surfaces which are not conducive to larval survival.

Question 48

Which of the above does NOT attract host seeking mosquitoes?

Accepted Answer

Strong perfumes — Mosquitoes are attracted to several cues from their hosts, including exhaled carbon dioxide (CO2), body heat, and certain chemical compounds like lactic acid found in sweat. Strong perfumes, while sometimes used to mask human scent, are not a primary attractant for host-seeking mosquitoes and may even deter them.

Question 49

A gram-positive coccus isolated from a wound shows golden-yellow colonies on blood agar but is coagulase negative. The most likely organism is

Accepted Answer

Staphylococcus epidermidis — Staphylococcus aureus typically produces golden-yellow colonies and is coagulase-positive. Staphylococcus epidermidis is a coagulase-negative staphylococcus that is often found on skin and can cause opportunistic infections. While it can form various colony colors, it is the most likely coagulase-negative cause of a wound infection among the options, especially if the 'golden-yellow' description is slightly atypical or referring to a variant.

Question 50

A patient with 'rice water' stool most likely has infection with

Accepted Answer

Vibrio cholerae — 'Rice water' stool is the classic description of the voluminous, watery diarrhea characteristic of cholera, caused by Vibrio cholerae. This is due to the toxin produced by the bacteria that stimulates massive fluid secretion in the intestines.

Weekly Year 2: Microbiology Exam - July 24, 2026 (Section...

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