Normal flora — MCQs

A 28-year-old woman delivers a healthy baby vaginally. During passage through the birth canal, the neonate is exposed to maternal vaginal flora. Two days later, the infant develops conjunctivitis with purulent discharge. Gram stain of the discharge shows gram-negative diplococci within neutrophils. Application of which principle regarding normal flora could have prevented this infection?

A 35-year-old woman with recurrent urinary tract infections presents to the clinic. Urine culture grows Escherichia coli sensitive to multiple antibiotics. She reports that she has had five UTIs in the past year, all caused by E. coli. She asks why she keeps getting infections with the same bacteria. Which characteristic of normal flora best explains the pathogenesis of her recurrent infections?