29 Year 2: Microbiology exam questions on Medical Bacteriology & Entomology 2021/2022 Q&A for medical students. Includes MCQs, answers, explanations and
This MCQ set contains 29 questions on Medical Bacteriology & Entomology 2021/2022 Q&A in the Year 2: Microbiology unit. Each question includes the correct answer and a detailed explanation for active recall and exam preparation.
Correct answer: A – Pseudomembrane blockage
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. ---
Correct answer: A – Meningitis
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. ---
Correct answer: A – Rapid-fire cough; meningitis
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. ---
Correct answer: A – Q fever
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. ---
Correct answer: A – S. pneumoniae
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. ---
Correct answer: A – Aspirin
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. ---
Correct answer: A – Freezing
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. ---
Correct answer: A – Abortus
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. ---
Correct answer: A – Toxic; myonecrosis
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. ---
Correct answer: A – It damages and lyses red blood cells
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. ---
Correct answer: A – Gonorrhea; sterility
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. ---
Correct answer: A – Gonorrhea and chlamydia
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. ---
Correct answer: A – Scalded skin syndrome
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. ---
Correct answer: A – Ingesting microorganisms in food
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. ---
Correct answer: A – Extracellular polysaccharide production inhibits S. epidermidis growth
S. epidermidis biofilms on catheters are highly resistant to antimicrobials due to decreased metabolic activity, altered gene expression, and physical barrier effects of the extracellular matrix. Catheter removal is often necessary for cure. ---
Correct answer: A – Stenotrophomonas maltophilia
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. ---
Correct answer: A – The toxic component is the O side chain
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. ---
Correct answer: A – Degrades lecithin in eukaryotic cell membranes
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. ---
Correct answer: A – Escherichia coli
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. ---
Correct answer: A – Musca
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. ---
Correct answer: A – Amoebiasis
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. ---
Correct answer: A – Blatta
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. ---
Correct answer: A – Onchocerca volvulus
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. ---
Correct answer: A – Amphotericin B
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. ---
Correct answer: A – Liquid crystal violet
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. ---