Medical Bacteriology and Entomology Exam 2020/2021 MCQs

Question 1

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

Accepted Answer

Vibrio cholerae — Vibrio cholerae, Entamoeba histolytica, and Rotavirus are all transmitted through the fecal-oral route (contaminated water/food). Thelazia species (eyeworms) are transmitted by flies that feed on lacrimal secretions, making it the odd one out. ---

Question 2

Which one of the following is larviparous?

Accepted Answer

Glossina species — Larviparous insects give birth to live larvae rather than laying eggs. Tsetse flies (Glossina species) are larviparous, producing one larva at a time that pupates immediately after birth. ---

Question 3

Argasid ticks have

Accepted Answer

Multiple hosts — Argasid (soft) ticks are multi-host ticks that can feed on different hosts throughout their life cycle and can take multiple blood meals at each life stage. ---

Question 4

Ixodid ticks have how many nymphal stages?

Accepted Answer

One — Ixodid (hard) ticks have a single nymphal stage in their life cycle: egg → larva → nymph → adult. ---

Question 5

Traps for Aedes mosquitoes are composed of

Accepted Answer

Aedes mosquitoes — Aedes mosquitoes are attracted to contrasting black and white patterns. Ovitrap designs often use black containers with white interiors or black and white striped patterns. ---

Question 6

Traps for Glossina species are composed of

Accepted Answer

Black and blue colors — Tsetse flies (Glossina species) are attracted to blue and black colors. Standard tsetse traps use blue cloth with black panels to attract the flies effectively. ---

Question 7

Blackwater fever is due to presence of which species in the environment?

Accepted Answer

Blackwater fever — Blackwater fever is a severe complication of falciparum malaria characterized by massive hemolysis and dark urine. It's associated with Plasmodium falciparum infection transmitted by Anopheles mosquitoes. ---

Question 8

Hepatitis B virus has been associated with

Accepted Answer

Cimex species — While not definitively proven, bed bugs (Cimex species) have been investigated as potential mechanical vectors for Hepatitis B virus, though human-to-human transmission remains the primary route. ---

Question 9

Snails are both first and second intermediate hosts of

Accepted Answer

Echinostoma ilocanum — Echinostoma ilocanum uses snails as both first and second intermediate hosts in its complex life cycle, unlike other flukes that use different intermediate hosts. ---

Question 10

How can millipedes cause medical problems?

Accepted Answer

Spraying defensive secretions — Millipedes defend themselves by secreting toxic chemicals (hydrogen cyanide, quinones) that can cause skin irritation, burns, and eye damage in humans. ---

Question 11

Holometabolous insects have

Accepted Answer

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

Question 12

Rift Valley fever is mainly transmitted by

Accepted Answer

Rift Valley fever virus — Rift Valley fever virus is primarily transmitted by Aedes mosquitoes, particularly Aedes mcintoshi and Aedes ochraceus in flood-water breeding sites. ---

Question 13

Autogenous insects

Accepted Answer

Lay eggs without mating — Autogenous insects can develop their first batch of eggs without taking a blood meal, using nutrient reserves from their larval stage. This is different from anautogenous insects that require blood meals. ---

Question 14

Parthenogenesis is a type of

Accepted Answer

Parthenogenesis — Parthenogenesis is a form of asexual reproduction where offspring develop from unfertilized eggs, essentially creating genetic clones of the parent. ---

Question 15

Which insects are included in order Blattaria?

Accepted Answer

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

Question 16

The best mode of malaria control is

Accepted Answer

Integrated vector management — Integrated vector management combines multiple control strategies (bed nets, treatment, environmental management, etc.) and is considered the most effective approach for sustainable malaria control. ---

Question 17

A 70-year-old man with diverticulosis experiences sudden severe left lower quadrant pain and fever. Surgery reveals a ruptured diverticulum with an abscess. The most likely bacteria to be found in the abscess are

Accepted Answer

Mixed normal gastrointestinal flora — Diverticular abscesses typically contain mixed anaerobic and aerobic bacteria from normal colonic flora, including Bacteroides, E. coli, Enterococcus, and other enteric bacteria. ---

Question 18

Antimicrobial therapy can allow proliferation of resistant colonic bacteria. Which species can proliferate and produce a toxin causing diarrhea?

Accepted Answer

difficile — C. difficile is relatively resistant to many antibiotics and can overgrow when normal flora is suppressed. It produces toxins A and B that cause antibiotic-associated colitis. ---

Question 19

Which microorganism can be part of normal vaginal flora and cause meningitis in newborns?

Accepted Answer

Group B streptococci — Streptococcus agalactiae (Group B Strep) is normal vaginal flora in ~25% of women but can cause serious infections in newborns, including meningitis, pneumonia, and sepsis. ---

Question 20

Dental plaque and periodontal disease represent what type of physiological process?

Accepted Answer

Biofilm formation — Dental plaque is a classic example of biofilm formation where bacteria adhere to tooth surfaces and produce extracellular matrix, leading to periodontal disease. ---

Question 21

Which microorganism is closely associated with dental caries?

Accepted Answer

S. mutans — S. mutans is the primary causative agent of dental caries. It produces acids from sugar metabolism that demineralize tooth enamel and produces sticky glucans that help it adhere to teeth. ---

Question 22

Streptococcus pneumoniae can be normal flora in 5-40% of people. At what anatomic site?

Accepted Answer

Nasopharynx — S. pneumoniae commonly colonizes the nasopharynx asymptomatically. Colonization rates are highest in children and can lead to invasive disease under certain conditions. ---

Question 23

Resident flora is commonly found in the

Accepted Answer

Urethra — The distal urethra contains resident flora, primarily Staphylococcus epidermidis and other coagulase-negative staphylococci. The other sites listed are normally sterile. ---

Question 24

Resident flora is absent from the

Accepted Answer

Lungs — Synovial fluid in healthy joints is sterile. The other sites normally contain resident flora, though the lungs have minimal flora in healthy individuals. ---

Question 25

A 65-year-old woman post-surgery with central line becomes febrile. Blood and line tip cultures grow gram-positive organisms that are ovoid and reproduce by budding. The most likely organism is

Accepted Answer

Candida albicans — The description of ovoid organisms reproducing by budding describes yeast. Candida albicans commonly causes catheter-related bloodstream infections, especially in patients on broad-spectrum antibiotics. ---

Question 26

The most likely portal of entry for the organism in Question 25 is

Accepted Answer

During placement of the central line — Central line-associated bloodstream infections typically occur through contamination during insertion or through the catheter hub during maintenance. ---

Question 27

A housewife develops double vision, difficulty talking, dry mouth, and descending paralysis after eating home-canned green beans. The diagnosis is

Accepted Answer

Botulism — Classic botulism presentation: descending flaccid paralysis starting with cranial nerves, associated with home-canned foods. Botulinum toxin blocks acetylcholine release. ---

Question 28

Which is an important virulence factor of Bacillus anthracis?

Accepted Answer

Protective antigen — Protective antigen is a component of anthrax toxin that binds to host cells and facilitates entry of lethal factor and edema factor, the toxic components. ---

Question 29

A motorcyclist with leg trauma develops fever, swollen leg with crepitus, hemolysis, and pale, shining skin. The most likely organism is

Accepted Answer

Clostridium perfringens — This describes gas gangrene: crepitus (gas in tissues), hemolysis, and characteristic pale, shining skin. C. perfringens is the most common cause. ---

Question 30

For the patient in Question 29, what is responsible for the hemolysis?

Accepted Answer

Lecithinase — C. perfringens alpha toxin (lecithinase) is a phospholipase that breaks down cell membrane phospholipids, causing massive hemolysis and tissue necrosis. ---

Question 31

The incubation period for inhalational anthrax can be up to

Accepted Answer

6 weeks — Inhalational anthrax has a variable incubation period that can extend to 6 weeks or more, depending on spore dose and host factors. Most cases occur within 1-7 days. ---

Question 32

A food commonly associated with Bacillus cereus food poisoning is

Accepted Answer

Fried rice — B. cereus food poisoning is classically associated with fried rice that has been kept warm for extended periods, allowing spore germination and toxin production. ---

Question 33

Tetanus toxin blocks the release of

Accepted Answer

Inhibitory glycine and γ-aminobutyric acid — Tetanospasmin blocks release of inhibitory neurotransmitters (glycine and GABA) from Renshaw cells, causing unopposed muscle contraction and spastic paralysis. ---

Question 34

A man with a puncture wound develops jaw spasms and generalized muscle spasms triggered by noise. The diagnosis is

Accepted Answer

Tetanus — Classic tetanus: puncture wound, trismus (lockjaw), generalized muscle spasms triggered by stimuli, and opisthotonus (arching of back). Patient remains alert and conscious. ---

Question 35

Culex species are major vectors of which disease?

Accepted Answer

Lymphatic filariasis — Culex mosquitoes, particularly Culex quinquefasciatus, are the primary vectors for Wuchereria bancrofti, the most common cause of lymphatic filariasis. These mosquitoes become infected when taking blood meals from infected humans and transmit microfilariae through subsequent feeding. ---

Question 36

Onchocerca volvulus is mainly transmitted by

Accepted Answer

Anopheles mosquitoes — Simulium species (blackflies) are the exclusive vectors of Onchocerca volvulus, causing onchocerciasis (river blindness). These flies breed in fast-flowing, well-oxygenated water bodies, explaining why the disease is associated with river systems in endemic areas. ---

Question 37

Fresh water snails serve as intermediate hosts for

Accepted Answer

Freshwater snails — Freshwater snails are obligatory intermediate hosts for Schistosoma blood flukes. Different snail genera host specific Schistosoma species: Biomphalaria (S. mansoni), Bulinus (S. haematobium), and Oncomelania (S. japonicum). The parasites undergo crucial developmental stages within these snails. ---

Question 38

The primary mechanism of tetanus toxin action involves

Accepted Answer

Blocking acetylcholine release — Tetanus toxin (tetanospasmin) cleaves synaptobrevin, preventing the release of inhibitory neurotransmitters GABA and glycine from Renshaw cells. This results in uncontrolled muscle contractions and spastic paralysis characteristic of tetanus.

Medical Bacteriology and Entomology Exam 2020/2021 MCQs

Questions, Answers & Explanations