Medical Bacteriology and Entomology

# Medical Bacteriology and Entomology Quiz ** --- ## 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) ** Sexual activity** B) ** Ingesting the microorganisms in her food** C) ** Holding onto contaminated hand rails when she takes public transportation** D) ** Handling potting soil** E)** Breathing aerosolized droplets containing the microorganism **Answer: E) 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) ** Escherichia coli O157:H7** B) ** Vibrio cholerae type O139** C) ** Shigella dysenteriae type 1** D) ** Campylobacter jejuni** E)** Entamoeba histolytica **Answer: B) 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) ** The biofilm containing S. epidermidis is likely to wash off the catheter** B) ** Production of extracellular polysaccharide inhibits growth of S. epidermidis** C) ** The S. epidermidis in the biofilm are more susceptible to antimicrobial therapy** D) ** The quorum-sensing ability results in increased susceptibility to antimicrobial therapy** E)** The complex molecular interactions within the biofilm make it difficult to provide effective antimicrobial therapy, and the catheter will likely need to be removed **Answer: E) The complex molecular interactions within the biofilm make it difficult to provide effective antimicrobial therapy, and the catheter will likely need to be removed** **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) ** Treponema pallidum** B) ** Stenotrophomonas maltophilia** C) ** Mycobacterium leprae** D) ** Bacillus anthracis** E)** Neisseria gonorrhoeae **Answer: D) 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) ** It interacts with macrophages and monocytes yielding release of cytokines** B) ** The toxic component is the O side chain** C) ** It forms holes in red blood cell membranes yielding hemolysis** D) ** It causes hypothermia** E)** It causes paralysis **Answer: A) It interacts with macrophages and monocytes yielding release of cytokines** **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) ** Lipopolysaccharide** B) ** Peptidoglycan** C) ** A toxin that is a superantigen** D) ** A toxin that has A and B subunits** E)** Lecithinase (alpha toxin) **Answer: C) A toxin that is a superantigen** **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 respo