Medical Bacteriology and Entomology — Notes OmpathStudy

Question 1 A 22-year-old woman who works in a plant nursery presents with a history of fever and cough for 2 months. Over this period she has lost 5 kg. Chest radiography shows bilateral upper lobe infiltrates with cavities. A stain of her sputum shows acid-fast bacilli. The likely means by which the patient acquired her infection is A. Ingesting the microorganisms in her food B. Holding onto contaminated hand rails when she takes public transportation C. Handling potting soil D. Breathing aerosolized droplets containing the microorganism E. Primarily an incidental laboratory finding Answer: D. Breathing aerosolized droplets containing the microorganism Explanation: The clinical presentation (chronic cough, weight loss, bilateral upper lobe cavities, acid-fast bacilli in sputum) is classic for pulmonary tuberculosis caused by Mycobacterium tuberculosis. TB is primarily transmitted through airborne droplets when infected individuals cough or sneeze. --- Question 2 During a pandemic, 175 airline passengers flew from Lima, Peru, to Los Angeles. Lunch included crab salad eaten by two-thirds of passengers. Two passengers who stayed in Los Angeles developed severe watery diarrhea. The likely cause of the diarrhea is A. Vibrio cholerae type O139 B. Shigella dysenteriae type 1 C. Campylobacter jejuni D. Entamoeba histolytica E. Usually mediated by non-specific mechanisms Answer: A. Vibrio cholerae type O139 Explanation: The severe watery diarrhea following consumption of seafood (crab salad) from Peru during a pandemic outbreak is characteristic of cholera. Vibrio cholerae is commonly associated with contaminated seafood and causes profuse watery diarrhea. --- Question 3 A 65-year-old woman with a long-term central venous catheter develops fever and multiple blood cultures positive for Staphylococcus epidermidis. A biofilm is thought to be present on the catheter. Which statement about such an infection is correct? A. Production of extracellular polysaccharide inhibits growth of S B. The S. epidermidis in the biofilm are more susceptible to antim C. The quorum-sensing ability results in increased susceptibility D. Biofilms E. Mostly unchanged in early disease Answer: D. Biofilms Explanation: Biofilms are notoriously difficult to treat with antibiotics because the extracellular matrix protects bacteria and reduces antibiotic penetration. Catheter removal is often necessary for cure. --- Question 4 The first microorganism to satisfy Koch's postulates (in the late 19th century) was A. Stenotrophomonas maltophilia B. Mycobacterium leprae C. Bacillus anthracis D. Neisseria gonorrhoeae E. Reduced by routine feedback control Answer: C. Bacillus anthracis Explanation: Robert Koch first demonstrated his postulates using Bacillus anthracis as the causative agent of anthrax in the 1870s, establishing the germ theory of disease. --- Question 5 Which of the following statements about lipopolysaccharide is correct? A. The toxic component is the O side chain B. It forms holes in red blood cell membranes yielding hemolysis C. It causes hypothermia D. It causes paralysis E. Occurs only after chronic exposure Answer: A. The toxic component is the O side chain Explanation: LPS (endotoxin) from gram-negative bacteria binds to Toll-like receptor 4 on macrophages and monocytes, triggering cytokine release (TNF-α, IL-1, IL-6) that causes fever and septic shock. The toxic component is lipid A, not the O side chain. --- Question 6 A 27-year-old man had rhinoplasty with nasal tampon placement. Eight hours later, he developed headache, muscle aches, abdominal cramps with diarrhea, and an erythematous rash resembling sunburn over his body including palms and soles. His blood pressure is 80/50 mm Hg. This illness was likely caused by A. Peptidoglycan B. This presentation C. A toxin that has A and B subunits D. Lecithinase (alpha toxin) E. Limited to a single tissue compartment Answer: B. This presentation Explanation: This presentation is classic for Toxic Shock Syndrome (TSS). The superantigen toxin (TSST-1) causes massive T-cell activation and cytokine release, leading to the characteristic rash, hypotension, and multi-organ involvement. --- Question 7 The organism most likely responsible for the patient's disease (Question 6) is A. Corynebacterium diphtheriae B. Clostridium perfringens C. Neisseria meningitidis D. Staphylococcus aureus E. Primarily an incidental laboratory finding Answer: D. Staphylococcus aureus Explanation: Staphylococcus aureus produces TSST-1, the superantigen toxin responsible for Toxic Shock Syndrome, particularly associated with tampon use and wound packing. --- Question 8 Which of the following is most likely to be associated with bacterial biofilm formation? A. Urinary tract infection with Escherichia coli B. Meningitis with Neisseria meningitidis C. Tetanus D. Impetigo caused by Staphylococcus aureus E. Usually mediated by non-specific mechanisms Answer: A. Urinary tract infection with Escherichia coli Explanation