Role of bacterial growth rates in the epidemiology and pathogenesis of urinary infections in women.

The mean minimum generation time in shake culture in urine of 6 urinary isolates of Escherichia coli (21.7 +/- 0.6 min) was significantly shorter (P = 0.0003) than that of 14 isolates of less common urinary pathogens (46.0 +/- 18.6 min). Mixed populations of approximately equal numbers of E. coli cells paired with other urinary, fecal, and urethral organisms were introduced into a laboratory model of the lower human urinary tract. This model used urine as a medium and reproduced some features of the balance between bacterial growth and the flushing effect of urine. After 24 h E. coli formed greater than or equal to 99% of the bacterial population in the bladder model for 16 our of 18 pairs of isolates examined. Relatively high oxygen tensions in urine sample from 18 healthy women (10.9 +/- 22. kPA) and 18 infected patients (8.0 +/- 4.3 kPa) may explain why anaerobic urinary infections are uncommon. The rapid growth rate of E. coli may be one explanation why it is the commonest cause of urinary infection even though it is relatively uncommon at the urethral meatus.