Normal flora — MCQs

A hospital implements a bundle to reduce catheter-associated bloodstream infections. Components include: chlorhexidine bathing, antibiotic-impregnated catheters, antiseptic catheter site dressings, and daily line necessity assessment. After implementation, bloodstream infections with coagulase-negative staphylococci decrease by 60%, but Candida bloodstream infections increase by 40%. Evaluate the microbiological mechanisms underlying these divergent outcomes and synthesize an optimal prevention strategy.

A 68-year-old man develops Clostridioides difficile infection after hospitalization for pneumonia. He is treated with oral vancomycin with resolution of diarrhea. Two weeks later, he has recurrent C. difficile infection. After a second vancomycin course, he has a third recurrence. His physician must choose between extended vancomycin taper, fidaxomicin, or fecal microbiota transplantation (FMT). Synthesize the microbiological rationale for selecting FMT over continued antibiotic therapy in recurrent C. difficile infection.

A research team is designing a probiotic intervention to prevent Clostridioides difficile infection in patients receiving antibiotics. They must choose between: (1) single-strain Lactobacillus; (2) multi-strain bacterial cocktail; (3) fecal microbiota transplantation; (4) prebiotic fiber supplementation. Evaluate which approach best applies principles of colonization resistance and normal flora restoration for PRIMARY prevention during antibiotic therapy.

A 32-year-old woman presents with malodorous vaginal discharge and vaginal pH of 5.5. Microscopy shows clue cells and a paucity of lactobacilli. She has been sexually active with a new partner for 2 months. Metronidazole treatment resolves her symptoms. Three months later, she returns with recurrent symptoms. Her partner is asymptomatic. Analyze the microbiological basis for treatment failure and the role of normal vaginal flora in this condition.

A 55-year-old man with cirrhosis and ascites undergoes diagnostic paracentesis. Fluid analysis shows 380 neutrophils/μL and culture grows Escherichia coli (single organism). He denies abdominal pain or fever. His primary care physician treated him with ciprofloxacin for a UTI one week ago. Analyze the most likely pathogenesis of this finding considering the role of normal flora and his recent antibiotic use.