Medical Bacteriology & Entomology 2021/2022 Q&A | MCQ Quiz | OmpathStudy Kenya

Practice 29 MCQs on Medical Bacteriology & Entomology 2021/2022 Q&A with OmpathStudy. Built for Kenyan medical and health students to revise key conc...

Questions, Answers & Explanations

1. Q1. Which one of the following is a complication of streptococcus pharyngitis? A) Rheumatic fever

   • ** Pseudomembrane blockage**
   • ** Tubercle formation**
   • ** Meningococcemia**
   • ** Waterhouse-Friderichsen syndrome **Answer:** A) Rheumatic fever

   Answer: ** Pseudomembrane blockage**

   Explanation: Rheumatic fever is a post-infectious autoimmune complication of Group A Streptococcus (S. pyogenes) pharyngitis. It occurs 2-4 weeks after untreated strep throat due to molecular mimicry between streptococcal M protein and cardiac myosin, leading to carditis, arthritis, and other manifestations. ---

2. Q2. The presence of a pseudomembrane is a result of: A) Strep throat

   • ** Meningitis**
   • ** Scarlet fever**
   • ** Diphtheria**
   • ** Psittacosis **Answer:** D) Diphtheria

   Answer: ** Meningitis**

   Explanation: Diphtheria toxin produced by Corynebacterium diphtheriae causes local tissue necrosis and inflammation, leading to formation of a characteristic gray-white pseudomembrane in the throat that can obstruct airways. This fibrinous exudate is pathognomonic for diphtheria. ---

3. Q3. A paroxysm is a associated with : A) Fever; meningitis

   • ** Rapid-fire cough; meningitis**
   • ** Fever; pneumonia**
   • ** Headache; pertussis**
   • ** Rapid-fire cough; pertussis **Answer:** E) Rapid-fire cough; pertussis

   Answer: ** Rapid-fire cough; meningitis**

   Explanation: Paroxysmal cough is the hallmark of pertussis (whooping cough) caused by Bordetella pertussis. The characteristic paroxysm consists of rapid-fire coughing fits followed by a high-pitched "whoop" during inspiration, often accompanied by vomiting. ---

4. Q4. The Mantoux test is used to identify: A) TB exposure

   • ** Q fever**
   • ** Ornithosis**
   • ** Pertussis**
   • ** Meningitis **Answer:** A) TB exposure

   Answer: ** Q fever**

   Explanation: The Mantoux test (tuberculin skin test) uses purified protein derivative (PPD) injected intradermally to detect delayed-type hypersensitivity response indicating previous exposure to Mycobacterium tuberculosis or BCG vaccination. Induration ≥10mm in normal individuals suggests TB exposure. ---

5. Q5. This bacterial species is the most common cause of "typical" pneumonia: A) H. influenzae

   • ** S. pneumoniae**
   • ** M. pneumoniae**
   • ** L. pneumophila**
   • ** B. pertussis **Answer:** B) S. pneumoniae

   Answer: ** S. pneumoniae**

   Explanation: Streptococcus pneumoniae (pneumococcus) is the leading cause of community-acquired pneumonia in adults, causing classic "typical" pneumonia with sudden onset, high fever, productive cough with rusty sputum, and lobar consolidation on chest X-ray. ---

6. Q6. To treat patients who have ingested botulism toxin, large doses of must be administered: A) Antibiotic

   • ** Aspirin**
   • ** Pepto-Bismol**
   • ** Antitoxin**
   • ** Electrolytes **Answer:** D) Antitoxin

   Answer: ** Aspirin**

   Explanation: Botulism antitoxin (equine-derived antiserum) neutralizes circulating botulinum toxin and prevents progression of paralysis. It must be administered early as it cannot reverse existing nerve damage but prevents further toxin binding to nerve terminals. ---

7. Q7. The organism Clostridium perfringens multiplies in foods only under conditions: A) Aerobic

   • ** Freezing**
   • ** Anaerobic**
   • ** Saline**
   • ** Permissive **Answer:** C) Anaerobic

   Answer: ** Freezing**

   Explanation: Clostridium perfringens is an obligate anaerobe that multiplies rapidly in foods under anaerobic conditions. Its spores survive cooking and germinate when oxygen is excluded, leading to rapid multiplication in improperly stored cooked foods. ---

8. Q8. A spore-forming, motile rod that can cause foodborne illness in a diarrheal or emetic form is Bacillus: A) Anthracis

   • ** Abortus**
   • ** Enterocolitica**
   • ** Cereus**
   • ** Botulinum **Answer:** D) Cereus

   Answer: ** Abortus**

   Explanation: Bacillus cereus causes two forms of food poisoning: diarrheal syndrome (8-16 hours after ingestion, watery diarrhea) and emetic syndrome (1-6 hours, nausea and vomiting). It's commonly associated with rice dishes and forms heat-resistant spores. ---

9. Q9. Woolsorter disease applies to the form of : A) Inhalation; tularemia

   • ** Toxic; myonecrosis**
   • ** Intestinal; anthrax**
   • ** Inhalation; anthrax**
   • ** Ingested; leptospirosis **Answer:** D) Inhalation; anthrax

   Answer: ** Toxic; myonecrosis**

   Explanation: Woolsorter disease is pulmonary (inhalation) anthrax historically seen in workers processing contaminated wool, hair, or hides. Bacillus anthracis spores are inhaled, germinate in alveolar macrophages, and cause severe pneumonia with high mortality if untreated. ---

10. Q10. Which one of the following describes the mode of action of tetanospasmin? A) It inhibits muscle contraction

    • ** It damages and lyses red blood cells**
    • ** It disrupts cell tissues**
    • ** It inhibits muscle relaxation**
    • ** It lyses white blood cells **Answer:** D) It inhibits muscle relaxation

    Answer: ** It damages and lyses red blood cells**

    Explanation: Tetanospasmin cleaves synaptobrevin proteins in inhibitory neurons, preventing release of GABA and glycine neurotransmitters. This blocks muscle relaxation signals, resulting in sustained muscle contractions and spastic paralysis characteristic of tetanus. ---

11. Q11. Salpingitis is associated with and can lead to : A) Syphilis; gumma formation

    • ** Gonorrhea; sterility**
    • ** Chlamydia; ophthalmia**
    • ** Chancroid; soft chancre**
    • ** Gonorrhea; pharyngitis **Answer:** B) Gonorrhea; sterility

    Answer: ** Gonorrhea; sterility**

    Explanation: Salpingitis (fallopian tube inflammation) is commonly caused by ascending Neisseria gonorrhoeae infection. Chronic inflammation leads to scarring and tubal occlusion, resulting in infertility or increased risk of ectopic pregnancy. ---

12. Q12. Ophthalmia is associated with what two STDs? A) Syphilis and chlamydia

    • ** Gonorrhea and chlamydia**
    • ** Syphilis and chancroid**
    • ** Syphilis and gonorrhea**
    • ** Chlamydia and chancroid **Answer:** B) Gonorrhea and chlamydia

    Answer: ** Gonorrhea and chlamydia**

    Explanation: Neonatal ophthalmia (conjunctivitis) is primarily caused by Neisseria gonorrhoeae and Chlamydia trachomatis transmitted from infected mothers during delivery. Both can cause severe purulent conjunctivitis that may lead to blindness if untreated. ---

13. Q13. Toxin-generated S. aureus diseases resulting from contact include: A) Purpuric fever

    • ** Scalded skin syndrome**
    • ** Toxic shock syndrome**
    • ** Pseudomembranous colitis**
    • ** Both B and C are correct **Answer:** E) Both B and C are correct

    Answer: ** Scalded skin syndrome**

    Explanation: Staphylococcus aureus produces exfoliative toxins causing staphylococcal scalded skin syndrome (SSSS) and toxic shock syndrome toxin-1 (TSST-1) causing toxic shock syndrome. Both are toxin-mediated diseases that can result from skin contact or colonization. ---

14. Q14. A 22-year-old woman who works in a plant nursery presents with fever and cough for 2 months, 5 kg weight loss, bilateral upper lobe infiltrates with cavities, and acid-fast bacilli in sputum. The likely means of infection acquisition is: A) Sexual activity

    • ** Ingesting microorganisms in food**
    • ** Contaminated hand rails on public transportation**
    • ** Handling potting soil**
    • ** Breathing aerosolized droplets containing the microorganism **Answer:** E) Breathing aerosolized droplets containing the microorganism

    Answer: ** Ingesting microorganisms in food**

    Explanation: This presentation is classic for pulmonary tuberculosis caused by Mycobacterium tuberculosis. TB is transmitted via airborne droplet nuclei containing viable bacteria. The patient's occupation and clinical findings suggest respiratory transmission, not soil contact. ---

15. Q15. The first microorganism to satisfy Koch's postulates (in the late 19th century) was: A) Treponema pallidum

    • ** Stenotrophomonas maltophilia**
    • ** Mycobacterium leprae**
    • ** Bacillus anthracis**
    • ** Neisseria gonorrhoeae **Answer:** D) Bacillus anthracis

    Answer: ** Stenotrophomonas maltophilia**

    Explanation: Robert Koch first demonstrated his postulates using Bacillus anthracis in 1876, proving it was the causative agent of anthrax. This established the germ theory of disease and the scientific method for linking specific pathogens to specific diseases. ---

16. Q16. Which of the following statements about lipopolysaccharide is correct? A) It interacts with macrophages and monocytes yielding release of cytokines

    • ** The toxic component is the O side chain**
    • ** It forms holes in red blood cell membranes yielding hemolysis**
    • ** It causes hypothermia**
    • ** It causes paralysis **Answer:** A) It interacts with macrophages and monocytes yielding release of cytokines

    Answer: ** The toxic component is the O side chain**

    Explanation: Lipopolysaccharide (endotoxin) binds to CD14/TLR4 receptors on macrophages and monocytes, triggering release of inflammatory cytokines (TNF-α, IL-1, IL-6) that cause fever, hypotension, and other septic shock symptoms. The toxic component is lipid A, not the O antigen. ---

17. Q17. Which of the following statements is correct?

    • Lipopolysaccharide is part of the cell wall of Escherichia coli
    • Cholera toxin is attached to the flagella of Vibrio cholerae
    • The lecithinase of Clostridium perfringens causes diarrhea
    • Toxic shock syndrome is caused by Staphylococcus epidermidis
    • Lipopolysaccharide is part of the cell wall of Escherichia coli
    • coli. Cholera toxin is not attached to flagella, lecithinase causes tissue necrosis not diarrhea, and TSS is caused by S. aureus, not S. epidermidis. --

    Answer: Lipopolysaccharide is part of the cell wall of Escherichia coli

    Explanation: Lipopolysaccharide (LPS) is a major component of the outer membrane in gram-negative bacteria like E. coli. Cholera toxin is not attached to flagella, lecithinase causes tissue necrosis not diarrhea, and TSS is caused by S. aureus, not S. epidermidis. ---

18. Q18. Which of the following best describes the mechanism of action of diphtheria toxin? A) Forms pores in red blood cells causing hemolysis

    • ** Degrades lecithin in eukaryotic cell membranes**
    • ** Causes release of tumor necrosis factor**
    • ** Inhibits elongation factor 2**
    • ** Causes increased adenylate cyclase activity **Answer:** D) Inhibits elongation factor 2

    Answer: ** Degrades lecithin in eukaryotic cell membranes**

    Explanation: Diphtheria toxin ADP-ribosylates elongation factor 2 (eEF2), permanently inactivating it and halting protein synthesis in eukaryotic cells. This leads to cell death and the characteristic local tissue necrosis and systemic toxicity of diphtheria. ---

19. Q19. Certain microorganisms are never considered members of normal flora and are always considered pathogens. Which organism fits this category? A) Streptococcus pneumoniae

    • ** Escherichia coli**
    • ** Mycobacterium tuberculosis**
    • ** Staphylococcus aureus**
    • ** Neisseria meningitidis **Answer:** C) Mycobacterium tuberculosis

    Answer: ** Escherichia coli**

    Explanation: M. tuberculosis is a true (obligate) pathogen that always causes disease when it infects humans and is never part of normal flora. The other organisms can be found as normal flora in certain body sites and cause opportunistic infections. ---

20. Q20. Which one of the following genera is the ODD one out in terms of pathogen transmission? A) Fannia

    • ** Musca**
    • ** Blatta**
    • ** Bulinus**
    • ** None of the above **Answer:** D) Bulinus

    Answer: ** Musca**

    Explanation: Bulinus is a freshwater snail that serves as an intermediate host for Schistosoma haematobium (biological vector), while Fannia, Musca, and Blatta are arthropods that primarily serve as mechanical vectors of pathogens through contamination. ---

21. Q21. Which of the following diseases can be effectively controlled by the use of acaricides? A) Leishmaniasis

    • ** Amoebiasis**
    • ** Katayama fever**
    • ** Q-fever**
    • ** Sleeping sickness **Answer:** D) Q-fever

    Answer: ** Amoebiasis**

    Explanation: Q-fever is transmitted by ticks (Ixodes species), which are arachnids (mites and ticks) controlled by acaricides. Leishmaniasis is transmitted by sandflies, Katayama fever by snails, sleeping sickness by tsetse flies (all insects), and amoebiasis is not vector-borne. ---

22. Q22. Which one of the following genera is a biological vector of scrub typhus pathogens? A) Glossina

    • ** Blatta**
    • ** Simulium**
    • ** Leptotrombidium**
    • ** Dermacentor **Answer:** D) Leptotrombidium

    Answer: ** Blatta**

    Explanation: Leptotrombidium mites (chiggers) are the biological vectors of Orientia tsutsugamushi, the causative agent of scrub typhus. The mites serve as both vector and reservoir, with transovarial transmission maintaining the pathogen in mite populations. ---

23. Q23. Which of the following pathogens can be transovarially transmitted by its biological vector? A) Entamoeba histolytica

    • ** Onchocerca volvulus**
    • ** Loa loa**
    • ** Orientia tsutsugamushi**
    • ** Wuchereria bancrofti **Answer:** D) Orientia tsutsugamushi

    Answer: ** Onchocerca volvulus**

    Explanation: Orientia tsutsugamushi (scrub typhus) is maintained in Leptotrombidium mite populations through transovarial transmission from infected female mites to their offspring, making the mites both vector and reservoir host. ---

24. Q24. Which of the following is the BEST treatment for scabies? A) Metronidazole

    • ** Amphotericin B**
    • ** Sodium stibogluconate**
    • ** Benzyl benzoate**
    • ** Praziquantel **Answer:** D) Benzyl benzoate

    Answer: ** Amphotericin B**

    Explanation: Benzyl benzoate is a topical scabicide effective against Sarcoptes scabiei mites causing scabies. It kills adult mites and eggs when applied to the entire body. Other options treat different parasites: metronidazole for protozoa, amphotericin B for fungi, sodium stibogluconate for leishmaniasis, praziquantel for helminths. ---

25. Q25. Which of the following reagents can be used in the diagnosis of mites infection? A) Liquid iodine

    • ** Liquid crystal violet**
    • ** Liquid safranin**
    • ** Liquid tetracycline**
    • ** Blood agar **Answer:** A) Liquid iodine

    Answer: ** Liquid crystal violet**

    Explanation: Liquid iodine can be applied to skin suspected of scabies infection to visualize burrows created by Sarcoptes scabiei mites. The iodine stains the burrows dark brown, making them more visible for diagnosis. This is a simple diagnostic technique for scabies. ---

26. Q26. Indoor residual spraying is BEST effective against insect vectors of pathogens: A) Exophagic

    • ** Endophagic**
    • ** Exophilic**
    • ** Endophilic**
    • ** All of the above **Answer:** D) Endophilic

    Answer: ** Endophagic**

    Explanation: Indoor residual spraying (IRS) is most effective against endophilic vectors that rest indoors after blood feeding, where they contact insecticide-treated surfaces. Exophilic vectors rest outdoors and have minimal contact with indoor-applied insecticides. ---

27. Q27. Which one of the following genera belongs to the family Argasidae? A) Hyalomma

    • ** Amblyomma**
    • ** Rhipicephalus**
    • ** Ornithodoros**
    • ** Boophilus **Answer:** D) Ornithodoros

    Answer: ** Amblyomma**

    Explanation: Ornithodoros belongs to the family Argasidae (soft ticks), characterized by lack of a hard scutum and mouthparts not visible from above. The other genera belong to Ixodidae (hard ticks) with visible scutum and prominent mouthparts. ---

28. Q28. Which one of the following vectors utilizes one host in its life cycle and pathogen transmission? A) Haemaphysalis

    • ** Ornithodoros**
    • ** Amblyomma**
    • ** Boophilus**
    • ** Hyalomma **Answer:** D) Boophilus

    Answer: ** Ornithodoros**

    Explanation: Boophilus ticks are one-host ticks that complete their entire life cycle (larva, nymph, adult) on a single host animal. The other genera are either two-host or three-host ticks that drop off between life stages to molt before finding new hosts. ---

29. Q29. Which one of the following vectors of pathogens is BEST controlled by using boric acid powder (e.g., borax)? A) Pediculus humanus

    • ** Pthirus pubis**
    • ** Ixodes species**
    • ** Periplaneta species**
    • ** Tunga species **Answer:** D) Periplaneta species

    Answer: ** Pthirus pubis**

    Explanation: Periplaneta species (cockroaches) are effectively controlled using boric acid powder, which acts as a stomach poison when ingested during grooming. Boric acid damages the insect's digestive system and is a common cockroach control method in integrated pest management programs.