Aerobic and anaerobic urethral flora of healthy females in various physiological age groups and of females with urinary tract infections.

We characterized the aerobic and anaerobic urethral flora of healthy females in three physiological age groups (premenarcheal, reproductive, and postmenopausal) and of females with urinary tract infections. The mean number of species per sample was 6.5, 7.7, and 10.3 for each of the physiological age groups, respectively, and 6.5 for the urinary tract infection group. Marked quantitative changes were seen with age and disease. Aerobes accounted for 65.6 and 73.8% of the flora of the premenarcheal and reproductive age groups, respectively, whereas anaerobes were dominant in the postmenopausal age group, accounting for 65.5% of the flora. Aerobic gram-negative rods were not isolated from any of the premenarcheal or reproductive-age subjects. Of the 10 postmenopausal subjects, 5 carried aerobic gram-negative rods, but these organisms accounted for only 1% of the flora. In contrast, they constituted 95% of the urethral flora of the urinary tract infection group. Bacteroides melaninogeneicus was commonly isolated and was the dominant isolate in the postmenopausal age group. Bacteroides fragilis was recovered from 7 of the 10 postmenopausal subjects, but these organisms constituted only 3% of the total flora. The factors responsible for the changes in urethral flora with age remain to be determined.