Explore Mbmm3311 Medical Bacteriology. Learn about pathogenic bacteria, their role in infectious diseases, diagnosis, and treatment. Essential for Year 2 microb
DEPARTMENT OF MEDICAL MICROBIOLOGY MBMM3311 – MEDICAL BACTERIOLOGY BACHELOR OF MEDICINE AND BACHELOR OF SURGERY (MBChB) YR:2021 INSTRUCTIONS: Answer all questions in Section A and Section B. Answer only ONE question in Section C. --- SECTION A – MULTIPLE CHOICE QUESTIONS (40 MARKS) 1. The heat-labile toxin of Enterotoxigenic Escherichia coli (ETEC) acts through which mechanism? A. Attachment and effacementB. Activation of adenylyl cyclaseC. Aggregative adherenceD. Ribosomal dysfunction Answer: B Explanation: The heat-labile toxin (LT) of ETEC functions similarly to cholera toxin by activating adenylyl cyclase, which increases intracellular cAMP levels, leading to secretion of water and electrolytes into the intestinal lumen and causing watery diarrhea. --- 2. Which of the following statements regarding Pseudomonas aeruginosa is correct? A. P. aeruginosa is typically susceptible to penicillin GB. P. aeruginosa grows readily in anaerobic blood culturesC. P. aeruginosa penetrates intact skin using the enzyme "invasin"D. P. aeruginosa seldom causes pneumoniaE. P. aeruginosa possesses fimbriae that promote attachment to epithelial cells Answer: E Explanation: P. aeruginosa has fimbriae (pili) that facilitate adherence to epithelial cells, which is crucial for colonization and infection. The organism is resistant to penicillin G, requires oxygen (obligate aerobe), does not penetrate intact skin, and is a common cause of hospital-acquired pneumonia. --- 3. Long-term carriage and chronic shedding are most likely after gastrointestinal infection with: A. Escherichia coli O157:H7B. Shigella dysenteriaeC. Vibrio choleraeD. Campylobacter jejuniE. Salmonella typhi Answer: E Explanation: Salmonella typhi can establish chronic carriage in the gallbladder, with persistent shedding in feces for months to years after acute infection. This is particularly important in typhoid fever transmission. The other organisms listed rarely cause chronic carriage. --- 4. A patient presents with acute non-bloody diarrhea for 12 hours. He lives in Thika and has not traveled recently. Which organism is least likely to cause his illness? A. Salmonella typhimuriumB. Campylobacter jejuniC. Shigella sonneiD. Vibrio cholerae Answer: D Explanation: Vibrio cholerae is endemic to specific regions with poor sanitation and contaminated water sources. In Kenya, cholera outbreaks occur sporadically but are not common causes of sporadic acute diarrhea in non-endemic areas like Thika without recent travel history. --- 5. A 19-year-old man has urethral discharge. Culture shows Neisseria gonorrhoeae that is β-lactamase positive and highly resistant to tetracycline. Which statement is correct? A. Both β-lactamase and tetracycline resistance genes are plasmid-mediatedB. β-lactamase is chromosomal, tetracycline resistance is plasmid-mediatedC. β-lactamase is plasmid-mediated, tetracycline resistance is chromosomalD. Both β-lactamase and tetracycline resistance genes are chromosomal Answer: C Explanation: In N. gonorrhoeae, β-lactamase production is typically encoded by plasmid-mediated genes (TEM-1 type), while high-level tetracycline resistance is usually due to chromosomal mutations in ribosomal protection proteins or efflux pumps. --- 6. Which Neisseria gonorrhoeae structure mediates attachment to host epithelial cells? A. LipooligosaccharideB. FimbriaeC. IgA1 proteaseD. Outer membrane porin proteinsE. Iron-binding proteins Answer: B Explanation: Fimbriae (pili) are the primary adhesion structures of N. gonorrhoeae that mediate initial attachment to mucosal epithelial cells. This is the critical first step in colonization and infection. --- 7. A 6-year-old boy develops fever, headache, and neck stiffness. CSF culture grows Neisseria meningitidis serogroup B. What should be recommended for household contacts? A. No prophylaxis neededB. Pilin vaccineC. Serogroup B polysaccharide capsule vaccineD. Rifampin prophylaxisE. Sulfonamide prophylaxis Answer: D Explanation: Close contacts of meningococcal meningitis cases should receive chemoprophylaxis with rifampin, ciprofloxacin, or ceftriaxone to eradicate nasopharyngeal carriage and prevent secondary cases. Serogroup B polysaccharide vaccine is poorly immunogenic, and sulfonamide resistance is common. --- 8. An 18-year-old woman with fever and pelvic pain is diagnosed with gonococcal pelvic inflammatory disease. A common long-term complication is: A. Cervical cancerB. Urethral strictureC. Uterine fibroidsD. InfertilityE. Vaginal–rectal fistula Answer: D Explanation: Pelvic inflammatory disease (PID) can lead to scarring and adhesions of the fallopian tubes, resulting in tubal infertility, ectopic pregnancy, and chronic pelvic pain. This is one of the most serious long-term complications of untreated or inadequately treated gonococcal infection. --- 9. Which statement best describes the pathogenesis of Clostridium botulinum? A. Toxin inhibits acetylcholine release at cholinergic synapsesB. Exotoxin is a lecithinase causing tissue necrosisC. Capsule inhibits phagocytosis and aids CNS invasionD. Toxin suppresses release of inhibitory neurotransmittersE. Produces leukotoxin leading to abscess formation Answer: A Explanation: Botulinum toxin blocks the release of acetylcholine at neuromuscular junctions by cleaving SNARE proteins required for vesicle fusion. This prevents muscle contraction, leading to flaccid paralysis characteristic of botulism. --- 10. A 47-year-old woman with cavitary lung disease grows a photochromogenic acid-fast bacillus (produces orange pigment on light exposure). The organism is: A. Mycobacterium tuberculosisB. Mycobacterium kansasiiC. Mycobacterium gordonaeD. Mycobacterium avium complexE. Mycobacterium fortuitum Answer: B Explanation: Mycobacterium kansasii is a photochromogenic (Runyon Group I) nontuberculous mycobacterium that produces yellow-orange pigment when exposed to light. It can cause pulmonary disease resembling tuberculosis, particularly in patients with underlying lung disease. --- 11. A 31-year-old Asian woman has fever, weight loss, and granulomas with acid-fast bacilli in liver and bone marrow. Chest X-ray is normal. Most likely organism: A. Mycobacterium lepraeB. Mycobacterium fortuitumC. Mycobacterium ulceransD. Mycobacterium gordonaeE. Mycobacterium tuberculosis Answer: E Explanation: This presentation is consistent with disseminated (miliary) tuberculosis, which can occur without prominent pulmonary findings on chest X-ray. M. tuberculosis commonly causes extrapulmonary disease involving liver, bone marrow, and other organs, especially in immunocompromised patients. --- 12. A concern for the patient above is infection with a strain that is: A. Susceptible only to isoniazidB. Resistant to streptomycinC. Resistant to clarithromycinD. Resistant to isoniazid and rifampinE. Enterotoxin-producing E. coli Answer: D Explanation: Multidrug-resistant tuberculosis (MDR-TB), defined as resistance to both isoniazid and rifampin, is a major concern as these are the two most effective first-line anti-TB drugs. MDR-TB requires prolonged treatment with second-line drugs and has worse outcomes. --- 13. A 10-week pregnant woman previously treated for syphilis has RPR non-reactive and TP-PA reactive. The most correct interpretation is: A. Previous treatment was effectiveB. Baby is at high risk for congenital syphilisC. Mother requires re-treatmentD. Mother needs lumbar puncture for neurosyphilis evaluationE. None of the above Answer: A Explanation: A non-reactive RPR (non-treponemal test) with a reactive TP-PA (treponemal test) indicates past treated syphilis. The treponemal test remains positive for life, while the non-treponemal test becomes negative after successful treatment. The baby is at low risk if treatment was adequate. --- 14. A 20-year-old woman has a 2-cm painless ulcer with raised border on the labia majora. The most likely pathogen is: A. Haemophilus ducreyiB. PapillomavirusC. Neisseria gonorrhoeaeD. Chlamydia tracho