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
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 responsible for the patient's disease (Question 6) is: A) Escherichia coli B) Corynebacterium diphtheriae C) Clostridium perfringens D) Neisseria meningitidis E) Staphylococcus aureus Answer: E) 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) Airway colonization in a cystic fibrosis patient with mucoid Pseudomonas aeruginosa B) Urinary tract infection with Escherichia coli C) Meningitis with Neisseria meningitidis D) Tetanus E) Impetigo caused by Staphylococcus aureus Answer: A) Airway colonization in a cystic fibrosis patient with mucoid Pseudomonas aeruginosa Explanation: Mucoid P. aeruginosa strains produce alginate, which forms biofilms in the airways of cystic fibrosis patients, making infections extremely difficult to eradicate. --- Question 9 Regarding bacterial type III secretion systems, which statement is correct? A) They are commonly found in gram-positive commensal bacteria B) They play an important role in the pathogenesis of diseases caused by Clostridium species C) They cause release of effectors into the extracellular environment D) They directly inject bacterial proteins into host cells across bacterial and host cell membranes E) Mutations that prevent functioning enhance pathogenesis Answer: D) They directly inject bacterial proteins into host cells across bacterial and host cell membranes Explanation: Type III secretion systems are molecular syringes that directly inject virulence factors into host cells, bypassing extracellular defenses. They're found in gram-negative pathogens like Salmonella , Shigella , and Yersinia . --- Question 10 Which of the following statements is correct? A) Lipopolysaccharide is part of the cell wall of Escherichia coli B) Cholera toxin is attached to the flagella of Vibrio cholerae C) The lecithinase of Clostridium perfringens causes diarrhea D) Toxic shock syndrome toxin-1 is produced by hemolytic strains of Staphylococcus epidermidis Answer: A) Lipopolysaccharide is part of the cell wall of Escherichia coli Explanation: LPS is a major component of the outer membrane of gram-negative bacteria like E. coli . Cholera toxin is not attached to flagella, lecithinase causes tissue necrosis (not diarrhea), and TSST-1 is produced by S. aureus , not S. epidermidis . --- Question 11 A 15-year-old girl develops severe watery diarrhea that looks like "rice water." It is voluminous ( 1L in 90 minutes). She has no fever and seems otherwise normal except for fluid/electrolyte loss effects. The most likely cause is: A) Clostridium difficile enterotoxin B) A toxin with A and B subunits C) Shigella dysenteriae type 1 that produces Shiga toxin D) Enterotoxigenic Escherichia coli that produces heat-labile and heat-stable toxins E) Staphylococcal enterotoxin F Answer: B) A toxin with A and B subunits Explanation: This classic presentation of "rice water" stools with massive fluid loss and no fever is pathognomonic for cholera. Cholera toxin has A and B subunits - the B subunit binds to GM1 ganglioside receptors, and the A subunit activates adenylyl cyclase. --- Question 12