Host defence mechanisms in the bladder. I. Role of mechanical factors.

This study evaluated the contribution of host defence mechanisms to bacterial clearance from the urinary bladder using an animal model in which rats were infected with Escherichia coli. Factors studied included the effect of hydration status, induced ultrastructural changes to the surface of the bladder mucosa, and the relevance of bacterial replication. Clearance was divided into two phases, primary (0-4 h), and secondary (4-24 h). Ninety-nine per cent of Escherichia coli 075 was cleared during the primary phase from normal, dehydrated and polyuric animals and 93% from anuric animals. Clearance was shown to be dependent on the presence of viable tissue. Bacterial numbers continued to decrease during the secondary phase in normal and dehydrated animals but increased in polyuric and anuric groups. No such rise occurred when rats were inoculated with Escherichia coli E/2/64, a non-replicating mutant. Evidence of ultrastructural changes to the bladder associated with impaired antibacterial properties was found in polyuric and anuric animals. Clearance of particulate matter (killed Candida albicans) however was unaffected by mucus disruption. The study has shown that the clearance of microorganisms from the bladder was unrelated to the voided volume, but is closely associated with the antibacterial activity of the mucosal surface.