Medical Microbiology Q&A Guide | MCQ Quiz | OmpathStudy Kenya

Question 1

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

Accepted Answer

** American roaches** — Athens, with its Mediterranean climate and urban environment, supports multiple cockroach species including German roaches (most common indoor species), American roaches (prefer warm, moist areas), and Smokey brown roaches (outdoor species that enter buildings). ---

Question 2

What is the main advantage of using larval control against mosquitoes? A) Control will supplement natural control

Accepted Answer

** Larvae are restricted to confined aquatic habitats that can be treated** — Larval control is advantageous because mosquito larvae are confined to specific aquatic breeding sites (pools, containers, marshes) making them easier to target with larvicides or environmental management compared to flying adult mosquitoes that are widely dispersed. ---

Question 3

If you found lice eggs (nits) in someone's clothing, what species would they most likely be from? A) Crab lice (Pthirus pubis)

Accepted Answer

** Head lice (Pediculus capitis)** — Body lice (Pediculus humanus corporis) are the only lice species that lay their eggs (nits) on clothing fibers, particularly along seams of garments. Head lice attach nits to hair shafts, while crab lice attach to coarse body hair. ---

Question 4

What are effective non-pesticide ways to control problems from cockroaches? A) Store food in plastic containers

Accepted Answer

** Clean your kitchen counter tops nightly** — Integrated pest management for cockroaches includes removing food sources (sealed containers), eliminating food residues (cleaning), and blocking entry points (sealing cracks). All these methods work together to make environments less suitable for cockroach survival and reproduction. ---

Question 5

The pupal stage is found in: A) Incomplete metamorphosis

Accepted Answer

** Complete metamorphosis** — The pupal stage only occurs in complete metamorphosis (holometabolism) where insects go through egg → larva → pupa → adult stages. Incomplete metamorphosis (hemimetabolism) has only egg → nymph → adult stages with no pupal stage. ---

Question 6

How does insecticide resistance develop? A) By using Integrated Pest Management practices

Accepted Answer

** By using low doses of insecticides** — Insecticide resistance develops through both low doses (sub-lethal doses allow resistant individuals to survive and reproduce) and high/prolonged doses (intense selection pressure favors resistant genotypes). IPM actually helps prevent resistance by reducing selection pressure. ---

Question 7

Ceratopogonidae larvae are found in: A) Freshwater marshes

Accepted Answer

** Salt marshes** — Ceratopogonidae (biting midges/no-see-ums) larvae are semi-aquatic and found in various moist environments including freshwater marshes, salt marshes, and muddy areas around water sources. Different species adapt to different salinity and moisture conditions. ---

Question 8

Integrated Pest Management: A) Relies solely on pesticides

Accepted Answer

** Relies solely on biological and natural control** — IPM is a comprehensive approach that considers pest biology, ecology, and behavior to develop sustainable control strategies. It integrates multiple control methods (biological, cultural, chemical, mechanical) rather than relying solely on any single approach. ---

Question 9

Epidemic typhus and Chagas disease can both be vectored via: A) Saliva of a vector

Accepted Answer

** Feces (frass) of a vector** — Both epidemic typhus (Rickettsia prowazekii via body lice) and Chagas disease (Trypanosoma cruzi via triatomine bugs) are transmitted through contaminated vector feces rubbed into bite wounds or mucous membranes, not through vector saliva. ---

Question 10

Which of the following groups of Glossina species is insignificant in the transmission of Trypanosoma brucei rhodesiense? A) Palpalis group

Accepted Answer

** Morsitans group** — The Palpalis group of tsetse flies primarily transmits T. b. gambiense (West African sleeping sickness), while the Morsitans and Fusca groups are the main vectors for T. b. rhodesiense (East African sleeping sickness). ---

Question 11

Which of these habitats would be likely places for mosquito larvae to live? A) Clogged drainage ditch

Accepted Answer

** Fast flowing stream** — Different mosquito species have adapted to various aquatic habitats. Culex breeds in polluted water (drainage ditches), some Anopheles species in clean flowing water, and many species utilize large water bodies like lakes and reservoirs for breeding. ---

Question 12

Which of the above does NOT attract host seeking mosquitoes? A) Carbon dioxide

Accepted Answer

** Host odors** — Mosquitoes are attracted to CO₂ and host odors (lactic acid, ammonia, etc.) but are generally repelled by light colors like white. They are more attracted to dark colors (black, navy, red) which retain heat and provide visual contrast. ---

Question 13

Glossina species are easily controlled by traps impregnated with which colors? A) Red and blue

Accepted Answer

** Red and white** — Tsetse flies are strongly attracted to blue and black colors. This attraction is exploited in tsetse control programs using blue-black cloth traps or targets, often impregnated with insecticides for effective population control. ---

Question 14

Which of the following organisms have the characteristics to be an effective mechanical vector of human disease? A) Simulium

Accepted Answer

** Culicine** — All can serve as mechanical vectors: Simulium (blackflies) can carry pathogens on mouthparts, Culicine mosquitoes can mechanically transfer pathogens between hosts, and Blattella (cockroaches) carry pathogens on their bodies and legs from contaminated areas to food/surfaces. ---

Question 15

Where might you look if you suspected bedbugs have infested your house? A) Behind the headboard of the bed

Accepted Answer

** Between the mattress and the box spring** — Bedbugs hide in cracks and crevices near sleeping areas during the day. Common hiding places include behind headboards, mattress seams, box spring crevices, bed frame joints, and other furniture cracks within 8 feet of the bed. ---

Question 16

Which of the following structure is part of the bacterial cell envelope? A) Peptidoglycan

Accepted Answer

** Lipopolysaccharide** — The bacterial cell envelope consists of the cell membrane, peptidoglycan layer, and outer membrane (in gram-negatives). While LPS is part of the outer membrane and capsules surround some bacteria, peptidoglycan is the fundamental structural component of the cell wall in the envelope. ---

Question 17

Microbial resistance to drugs is acquired through: A) Conjugation

Accepted Answer

** Transformation** — Bacteria acquire antibiotic resistance genes through all three horizontal gene transfer mechanisms: conjugation (direct cell-to-cell transfer via pili), transformation (uptake of free DNA), and transduction (bacteriophage-mediated transfer). ---

Question 18

The single most important method for classification and speciating Streptococci is: A) Agglutination using antisera against the cell wall group-specific substance

Accepted Answer

** Biochemical testing** — The Lancefield grouping system using antisera against group-specific C carbohydrate antigens (A, B, C, etc.) is the primary method for classifying beta-hemolytic streptococci. This serological typing is more definitive than hemolysis patterns alone. ---

Question 19

The specific action of haemolysin is: A) To damage white blood cells

Accepted Answer

** Cause fever** — Hemolysins are bacterial toxins that specifically lyse red blood cells by creating pores in their membranes. This is their primary and specific action, though secondary effects may include fever due to released cellular contents. ---

Question 20

Which of the following is not a symptom of septicemia? A) Fever

Accepted Answer

** Respiratory alkalosis** — Septicemia typically causes hypotension (low blood pressure) due to vasodilation and capillary leak, not hypertension. Fever, respiratory alkalosis (from hyperventilation), and shaking chills are characteristic symptoms of septicemia. ---

Question 21

Certain microorganisms can never be considered to be members of the normal flora. They are always considered to be pathogens. Which of the following is true? A) Commensals

Accepted Answer

** Opportunistic pathogens** — True (obligate) pathogens like Mycobacterium tuberculosis, Yersinia pestis, and Plasmodium species always cause disease when they infect humans and are never part of normal flora, unlike opportunistic pathogens that can exist as commensals. ---

Question 22

Which of the following conditions are associated with Streptococcus pyogenes? A) Pharyngitis

Accepted Answer

** Scarlet fever** — Streptococcus pyogenes (Group A Strep) causes pharyngitis (strep throat), scarlet fever (when infected with erythrogenic toxin-producing strains), and post-infectious complications including rheumatic fever due to molecular mimicry. ---

Question 23

Which of the following organisms is closely associated with dental caries? A) Streptococcus mutans

Accepted Answer

** Candida albicans** — Streptococcus mutans is the primary etiologic agent of dental caries. It adheres strongly to tooth surfaces, produces acids from dietary sugars that demineralize tooth enamel, and forms biofilms (dental plaque). ---

Question 24

The microbial factor responsible for cholera diarrhea is a toxin that: A) Blocks EF-2

Accepted Answer

** Cleaves AMP** — Cholera toxin ADP-ribosylates the Gs protein, permanently activating adenylyl cyclase, leading to massive cAMP accumulation in intestinal epithelial cells. This causes massive secretion of chloride, sodium, and water into the intestinal lumen. ---

Question 25

A 20-year old university student complains of dysuria, frequency and urgency on urination for 24 hours. She has become sexually active. Urinalysis shows many polymorphonuclear cells, the most likely organism responsible for the signs and symptoms is: A) Staphylococcus aureus

Accepted Answer

** Streptococcus agalactiae** — E. coli causes 80-90% of uncomplicated urinary tract infections in young, sexually active women. The classic presentation includes dysuria, frequency, urgency, and pyuria (PMNs in urine). Sexual activity increases risk by introducing bacteria into the urinary tract. ---

Question 26

A/an is passive animal transporter of pathogens: A) Zoonosis

Accepted Answer

** Biological vector** — A mechanical vector passively transports pathogens on its body surface without the pathogen undergoing development or multiplication within the vector. Examples include houseflies carrying bacteria on their feet from feces to food. ---

Question 27

Which of the following bacteria would be most accurate indicator of fecal contamination? A) Enterobacter

Accepted Answer

** Escherichia** — Escherichia coli is the gold standard indicator of fecal contamination because it's abundant in human and animal intestines, doesn't multiply in water environments, and survives similarly to enteric pathogens. Its presence indicates recent fecal contamination and potential health risks. ---

Question 28

What is simulotoxicosis? A) A form of pesticide poisoning

Accepted Answer

** A negative reaction to the saliva of black flies** — Simulotoxicosis is a toxic reaction caused by the saliva of Simulium blackflies during mass attacks. The toxic compounds in their saliva can cause systemic reactions including respiratory distress, especially in livestock and occasionally in humans. ---

Question 29

What is the pathogen that causes river blindness? A) Simulium damnosum

Accepted Answer

** Borrelia recurrentis** — Onchocerca volvulus is the filarial nematode that causes river blindness (onchocerciasis). Simulium damnosum is the vector (blackfly) that transmits the parasite, not the pathogen itself. ---

Question 30

The stage of Leishmania that develops in the sand fly and is transmitted to humans is the: A) Gametocyte

Accepted Answer

** Promastigote** — The promastigote is the motile, flagellated form of Leishmania that develops in the sandfly vector's gut. When the infected sandfly feeds, promastigotes are injected into human skin where they transform into amastigotes within macrophages. ---

Question 31

Which of these sub-families is not in the family Culicidae? A) Culicinae

Accepted Answer

** Anophelinae** — Phlebotominae is a subfamily of Psychodidae (sandfly family), not Culicidae (mosquito family). Culicidae contains three subfamilies: Anophelinae, Culicinae, and Toxorhynchitinae. ---

Question 32

Malaria infected patients experience cycles of extreme fever followed by chills then a brief period of recovery. These cycles occur because: A) Merozoites are synchronously emerging from red blood cells, briefly stimulating immune reaction

Accepted Answer

** Merozoites alter surface protein expression in cycles** — Malarial fever cycles correspond to the synchronous rupture of infected erythrocytes releasing merozoites, toxins, and cellular debris. This mass release triggers cytokine cascades causing the characteristic fever-chill-recovery pattern every 48-72 hours depending on the Plasmodium species. ---

Question 33

Secondary metabolites of microbes are formed during the growth phase: A) Exponential

Accepted Answer

** Stationary** — Secondary metabolites (like antibiotics, toxins, pigments) are produced during the idiophase, which typically coincides with the stationary phase of bacterial growth when primary metabolic processes slow down and cells redirect metabolism toward secondary compound production. ---

Question 34

Which of the following microorganisms can be part of normal vaginal flora and can cause meningitis in newborns? A) Candida albicans

Accepted Answer

** Corynebacterium species** — Group B Streptococcus (Streptococcus agalactiae) colonizes the vagina in 15-40% of healthy women asymptomatically but can cause severe neonatal infections including meningitis, sepsis, and pneumonia during delivery or early neonatal period. ---

Question 35

This sporeformer contaminates meats and vegetables and is the causative agent of gas gangrene: A) Bacillus cereus

Accepted Answer

** Clostridium perfringens** — Clostridium perfringens is an anaerobic spore-forming bacterium that causes gas gangrene (clostridial myonecrosis) and is commonly found contaminating meat and vegetables. Its spores survive cooking and germinate under anaerobic conditions. --- ## SECTION B: SHORT ANSWER QUESTIONS

Question 36

Describe the pathogenesis of Streptococcus pyogenes. Answer: Initial Colonization: - Adheres to pharyngeal epithelium via M protein and lipoteichoic acid - Survives on skin through resistance to fatty acids and defensins Invasion Mechanisms: - Hyaluronidase breaks down connective tissue matrix - Streptokinase dissolves blood clots facilitating spread - DNases degrade neutrophil DNA traps Tissue Damage: - Streptolysin O and S cause cell membrane damage - Erythrogenic toxins cause scarlet fever rash - C5a peptidase inhibits neutrophil recruitment Immune Evasion: - M protein prevents complement activation and phagocytosis - Molecular mimicry leads to autoimmune complications - Capsule (hyaluronic acid) resembles human connective tissue Systemic Effects: - Pyrogenic exotoxins cause fever and toxic shock - Post-infectious sequelae: rheumatic fever, glomerulonephritis --- ## SECTION C: ESSAY QUESTIONS ### Essay Question 1 Discuss the medical importance of fleas. Vector-Borne Disease Transmission: Bubonic Plague (Yersinia pestis) - Primary vector: Xenopsylla cheopis (oriental rat flea) - Mechanism: Flea becomes "blocked" when bacteria multiply in proventriculus - Transmission: Regurgitation of bacteria during feeding attempts - Epidemiology: Maintains sylvatic plague cycles in rodent populations - Historical significance: Caused medieval Black Death pandemic - Modern relevance: Endemic in western United States, Madagascar, Central Asia Murine Typhus (Rickettsia typhi) - Vector: Xenopsylla cheopis, Ctenocephalides felis - Reservoir hosts: Rats, opossums, cats - Transmission: Flea feces contamination of bite wounds - Clinical presentation: Fever, headache, myalgia, rash - Global distribution: Tropical and subtropical regions Other Rickettsial Diseases - R. felis transmitted by cat fleas (Ctenocephalides felis) - Causes flea-borne spotted fever - Emerging pathogen with global distribution Parasitic Disease Transmission: Hymenolepiasis - Hymenolepis diminuta (rat tapeworm) transmitted by rat fleas - Accidental human infections through ingestion of infected fleas - More common in children with poor hygiene Direct Pathogenic Effects: Flea Allergy Dermatitis - Hypersensitivity reactions to flea saliva - Common in pet owners and areas with heavy flea infestations - Presents as papular urticaria, intense pruritus - Secondary bacterial infections from scratching Tungiasis (Sand Flea Disease) - Caused by Tunga penetrans (jigger flea) - Female fleas penetrate skin, typically feet - Causes painful nodular lesions, secondary infections - Endemic in tropical Africa, Central and South America Public Health Significance: Urban Pest Problems - Cat fleas (Ctenocephalides felis) most common in homes - Reproduction in carpets, pet bedding, cracks - Economic impact through pest control costs - Quality of life issues in infested homes Occupational Exposure - Veterinarians, animal handlers at higher risk - Researchers working with rodent colonies - Pest control professionals Control Strategies: Environmental Management - Regular vacuuming removes eggs and larvae - Humidity control (below 50%) prevents development - Pet bedding management and washing Chemical Control - Insecticides for adult fleas on pets - Growth regulators targeting immature stages - Premise treatment for environmental control Biological Control - Nematodes (Steinernema carpocapsae) attack larvae - Diatomaceous earth as desiccant Integrated Pest Management - Combination of multiple control approaches - Pet treatment with veterinary products - Environmental modification and chemical control Surveillance and Monitoring: Plague Surveillance - Monitoring flea indices in endemic areas - Flea testing for Y. pestis in plague foci - Early warning systems for epizootics Resistance Monitoring - Tracking insecticide resistance in flea populations - Rotation of control products to prevent resistance Research Applications: Disease Transmission Studies - Laboratory models for vector-pathogen interactions - Vaccine development and testing - Understanding plague transmission dynamics Evolutionary Biology - Host-parasite coevolution studies - Adaptation mechanisms in ectoparasites --- ### Essay Question 2 Discuss how intestinal tract infections are caused by Escherichia coli. Pathogenic

Accepted Answer

coli Categories: Enterotoxigenic

Medical Microbiology Q&amp;A Guide | MCQ Quiz | OmpathStudy Kenya

Questions, Answers & Explanations

Medical Microbiology Q&A Guide | MCQ Quiz | OmpathStudy Kenya