Mbmm3311 – Medical Bacteriology

## 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 des