INTERNALIZATION OF PROTEUS-MIRABILIS BY HUMAN RENAL EPITHELIAL-CELLS

Proteus mirabilis, a common agent of bacteriuria in humans, causes acu te pyelonephritis and bacteremia. Renal epithelium provides a barrier between luminal organisms and the renal interstitium. We have hypothes ized that P. mirabilis may be internalized into renal epithelium. To t est this hypothesis, we added suspensions of three P. mirabilis strain s (10(8) CFU) to confluent monolayers of primary cultures of human ren al proximal tubular epithelial cells (HRPTEC) and, after 3 h, found th e bacteria internalized within membrane-bound vacuoles by light and el ectron microscopy. Internalization of bacteria by HRPTEC was corrobora ted by using the gentamicin protection assay. Cytolysis of HRPTEC by t he HpmA hemolysin, however, was a confounding factor in this assay, an d therefore a hemolysin-negative hpmA mutant was used in subsequent ex periments. The nonhemolytic mutant WPM111 did not disrupt the monolaye r and was recovered in numbers that were 10- to 100-fold higher than t hose of the hemolytic parent BA6163. Cytochalasin D (20 mu g/ml) inhib ited internalization of Salmonella typhimurium but not that of P. mira bilis, suggesting that the latter species enters HRPTEC by a mechanism that is not dependent on actin polymerization. We suggest that HpmA h emolysin-mediated cytotoxicity and internalization of bacteria by HRPT EC may play a role in the development of Proteus pyelonephritis.