Medical Bacteriology and Entomology Exam 2018/2019 | MCQ Quiz | OmpathStudy Kenya

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

Nose — S. aureus is commonly carried asymptomatically in the anterior nares (nose) of 20-40% of healthy individuals. Healthcare workers' nasal carriage is often the source of nosocomial outbreaks in nurseries. ---

Question 2

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

Accepted Answer

Ribosome — Ribosomes are internal cellular structures not exposed on the bacterial surface, making them poor targets for serological identification. Capsule, cell wall, and flagella are surface-exposed and highly antigenic. ---

Question 3

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

Accepted Answer

*Pasteurella bettyae* — P. bettyae is associated with human genital tract infections and can cause neonatal infections. P. multocida typically causes wound infections after animal bites. ---

Question 4

Each statement about streptococci classification is correct except

Accepted Answer

Viridans streptococci are identified by Lancefield grouping based on C carbohydrate — Viridans streptococci typically lack the C carbohydrate antigen and are not classified by Lancefield grouping. They are identified by biochemical tests and alpha-hemolysis pattern. ---

Question 5

Staphylococcal scalded skin syndrome is caused by exotoxin produced by: A) Streptococcus pyogenes

Accepted Answer

** *Staphylococcus aureus*** — Staphylococcal scalded skin syndrome is caused by exfoliative toxins (exfoliatins A and B) produced by certain strains of S. aureus . These toxins cause separation of the epidermis. ---

Question 6

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

Accepted Answer

The mother's previous treatment for syphilis was effective — Non-reactive RPR with reactive treponemal test indicates past treated syphilis. The treponemal test remains positive for life, while non-treponemal tests become negative after successful treatment. ---

Question 7

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

Accepted Answer

*Shigella sonnei * — Shigella species have extremely low infectious doses (10-100 organisms), making them highly contagious. Salmonella and V. cholerae require much higher doses (10⁴-10⁶ organisms). ---

Question 8

Which disease is best diagnosed by serologic means?

Accepted Answer

Typhoid fever — Typhoid fever is often diagnosed serologically using the Widal test (though blood culture is gold standard). The others are better diagnosed by direct methods: TB (sputum AFB), gonorrhea (culture/PCR), actinomycosis (direct examination). ---

Question 9

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

Accepted Answer

*Streptococcus pyogenes * — S. pyogenes causes pharyngitis, cellulitis, and invasive infections but not gastroenteritis. The others are established causes of diarrhea. ---

Question 10

A woman develops gonococcal PID. What is the most common sequela? A) Cancer of the cervix

Accepted Answer

** Infertility** — Gonococcal PID commonly causes fallopian tube scarring and adhesions, leading to infertility and increased risk of ectopic pregnancy. ---

Question 11

Mycobacterial survival after macrophage ingestion is attributed to: A) Inhibition of complement activation

Accepted Answer

** Inhibition of phagosome formation and endosomal acidification** — Mycobacteria prevent phagosome-lysosome fusion and inhibit acidification of the phagosome, allowing survival within macrophages. ---

Question 12

The molecular basis for cholera toxin's effect on duodenal cells is: A) Inactivation of Gi protein

Accepted Answer

** Ribosylation of GTP-binding protein — Cholera toxin ADP-ribosylates the Gs protein, preventing GTPase activity and leading to continuous adenylyl cyclase activation and cAMP production. ---

Question 13

Bacterial capsules function as virulence factors by interfering with: A) Antibiotic penetration

Accepted Answer

** Phagocytosis — Bacterial capsules are antiphagocytic, making it difficult for neutrophils and macrophages to engulf and destroy encapsulated bacteria. ---

Question 14

Which is NOT a major cause of acute bacterial meningitis?

Accepted Answer

*Streptococcus pyogenes * — S. pyogenes rarely causes meningitis. The classic triad of bacterial meningitis pathogens includes S. pneumoniae , N. meningitidis , and H. influenzae . ---

Question 15

A woman with UTI has gram-negative, lactose-fermenting, indole-positive bacilli. The organism's effectiveness in causing UTI is associated with: A) Exotoxins

Accepted Answer

** P fimbriae** — This describes E. coli . P fimbriae allow adherence to uroepithelial cells with P blood group antigens, facilitating ascending UTI and pyelonephritis. ---

Question 16

The coagulase test differentiates

Accepted Answer

*S. aureus* from *S. epidermidis * — The coagulase test distinguishes coagulase-positive S. aureus from coagulase-negative staphylococci like S. epidermidis . ---

Question 17

Snails are both first and second intermediate hosts of: A) Echinostoma ilocanum

Accepted Answer

** *Fasciola hepatica*** — E. ilocanum uses the same snail species as both first and second intermediate hosts, unlike other flukes that use different intermediate hosts. ---

Question 18

How can millipedes cause medical problems? A) Stinging

Accepted Answer

** Spraying defensive secretions** — Millipedes secrete defensive chemicals (hydrogen cyanide, quinones, phenols) that can cause skin burns, eye irritation, and respiratory problems. ---

Question 19

Holometabolous insects have: A) 2 life stages

Accepted Answer

** 4 life stages** — Holometabolous insects undergo complete metamorphosis with four stages: egg → larva → pupa → adult. Examples include flies, beetles, and butterflies. ---

Question 20

Rift Valley fever is mainly transmitted by: A) Culex species

Accepted Answer

** *Aedes* species** — Rift Valley fever is primarily transmitted by Aedes mosquitoes, especially flood-water Aedes species in endemic areas of Africa. ---

Question 21

Autogenous insects: A) Lay eggs without mating

Accepted Answer

** Mate but do not lay eggs** — Autogenous insects can produce their first batch of eggs without taking a blood meal, using stored nutrients from their larval development. ---

Question 22

Parthenogenesis is a type of: A) Asexual reproduction with offspring from unfertilized eggs

Accepted Answer

** Asexual reproduction with offspring from fertilized eggs** — Parthenogenesis is asexual reproduction where embryos develop from unfertilized eggs, producing genetic clones of the parent. ---

Question 23

The best mode of malaria control is: A) Elimination of insect eggs

Accepted Answer

** Integrated vector management** — IVM combines multiple approaches (bed nets, treatment, environmental management, surveillance) for sustainable malaria control, more effective than single interventions. ---

Question 24

Which insects are included in order Blattaria? A) Cockroaches

Accepted Answer

** Lice** — Order Blattaria (now Blattodea) includes cockroaches and termites. Lice belong to Phthiraptera, flies to Diptera, and beetles to Coleoptera. ---

Question 25

Which insects are included in order Diptera? A) Cockroaches

Accepted Answer

** True flies** — Order Diptera includes all true flies (two wings). Cockroaches are Blattodea, lice are Phthiraptera, and fleas are Siphonaptera. ---

Question 26

Which insects transmit cholera pathogens? A) True flies

Accepted Answer

** *Haematogogus*** — House flies and other true flies mechanically transmit Vibrio cholerae by contaminating food and water after contact with infected feces. ---

Question 27

Arboviruses are mainly transmitted by: A) Aedes species

Accepted Answer

** All of the above — Different arboviruses are transmitted by various arthropods: Aedes (dengue, yellow fever), Culex (West Nile), and Culicoides (bluetongue). Cimex can potentially transmit some viruses. ---

Question 28

Anthropophilic insects prefer: A) Animal hosts

Accepted Answer

** Human hosts** — Anthropophilic means "human-loving." These insects preferentially feed on humans rather than other animals (e.g., Aedes aegypti ). ---

Question 29

Exophagic insects prefer: A) Resting indoors

Accepted Answer

** Feeding outdoors** — Exophagic insects prefer to feed outdoors, as opposed to endophagic insects that feed indoors. This affects vector control strategies. ---

Question 30

Presence of Chrysops in the environment could lead to: A) River blindness

Accepted Answer

** Pink eye disease** — Chrysops species (deer flies) transmit Loa loa (African eye worm), which can cause transient conjunctivitis and the characteristic migration of adult worms across the conjunctiva. ---

Question 31

Which stage of filarial nematodes is found in the chest muscles of vectors? A) Larval stage 1

Accepted Answer

** Larval stage 3** — In filarial development within vectors, L3 larvae (infective stage) develop in the flight muscles and then migrate to the mouthparts for transmission during the next blood meal.

Medical Bacteriology and Entomology Exam 2018/2019 | MCQ Quiz | OmpathStudy Kenya

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