Medical Bacteriology and Entomology Exam 2018/2019 MCQs

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

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

Accepted Answer

P. 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 3

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 4

Staphylococcal scalded skin syndrome is caused by exotoxin produced by

Accepted Answer

Propionibacterium acnes — 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 5

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 6

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 7

Which disease is best diagnosed by serologic means?

Accepted Answer

Gonorrhea — 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 8

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

Accepted Answer

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

Question 9

Mycobacterial survival after macrophage ingestion is attributed to

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 10

The molecular basis for cholera toxin's effect on duodenal cells is

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 11

Bacterial capsules function as virulence factors by interfering with

Accepted Answer

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

Question 12

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

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 13

Snails are both first and second intermediate hosts of

Accepted Answer

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

Question 14

How can millipedes cause medical problems?

Accepted Answer

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

Question 15

Holometabolous insects have

Accepted Answer

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

Question 16

Rift Valley fever is mainly transmitted by

Accepted Answer

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

Question 17

Autogenous insects

Accepted Answer

Lay eggs without mating — Autogenous insects can produce their first batch of eggs without taking a blood meal, using stored nutrients from their larval development. ---

Question 18

Parthenogenesis is a type of

Accepted Answer

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

Question 19

The best mode of malaria control is

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 20

Which insects are included in order Blattaria?

Accepted Answer

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

Question 21

Which insects are included in order Diptera?

Accepted Answer

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

Question 22

Which insects transmit cholera pathogens?

Accepted Answer

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

Question 23

Arboviruses are mainly transmitted by

Accepted Answer

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

Question 24

Anthropophilic insects prefer

Accepted Answer

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

Question 25

Exophagic insects prefer

Accepted Answer

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

Question 26

Presence of Chrysops in the environment could lead to

Accepted Answer

Conjunctivitis — 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 27

Which stage of filarial nematodes is found in the chest muscles of vectors?

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 MCQs

Questions, Answers & Explanations