Viable but nonculturable bacteria are present in mouse and human urine specimens

Abstract

The presence of viable but nonculturable bacteria in human clean-catch and mouse bladder-isolated urine specimens was investigated. Viable but nonculturable bacteria are alive but do not give rise to visible growth under nonselective growth conditions. Urine specimens obtained from human female volunteers with or without an active urinary tract infection were found to contain, on average, significantly more viable than culturable forms of bacteria. Additional support for the presence of viable but nonculturable cells in urine specimens considered sterile was obtained from examination of urine specimens obtained directly from the bladder of healthy mice. Because the viability assay used to study the viable but nonculturable condition is by necessity growth independent, and hence indirect, the accuracy of this assay that scores cells with intact cell membranes as being viable was studied. Greater than 95% of Escherichia coli cells exposed to lethal doses of UV irradiation were found to lose their membrane integrity within a day, a time frame similar to that used to examine urine specimens. These data suggest that viable but nonculturable cells can occur within regions of the urinary tract previously considered sterile.

FIG. 1.

Concentration and physiological status of bacteria found in human urine specimens. Urine was collected, as described in the text, from women who had never had a UTI (NN column), who had no current UTI but had had at least one previous UTI (NY columns), and who had a current UTI (YY column). Error bars indicate the positive standard error of the mean. * indicates a significant difference between this and the other two participant categories.

FIG. 2.

Time required to degrade the cell membrane of bacteria exposed to lethal doses of UV light. E. coli cells were examined after the indicated times following exposure to UV light for 25 min as described in the text. Cell concentration is given as a percentage of the starting concentration for live cells (striped columns), dead cells (gray columns), and lysed cells (black columns). Error bars represent the standard error of the mean.