Growth, cellular differentiation and virulence factor expression by Proteus mirabilis in vitro and in vivo

A uropathogenic strain of Proteus mirabilis was grown in vitro in human and mouse urine and brain-heart infusion broth (BHIB) and in vivo in subcutaneous open chambers (SOC) in mice, intraperitoneal diffusion chambers (IPC) in rats and by ascending urinary tract infection in mice in order to compare growth pattern, cellular differentiation and expression of virulence factors. Although the growth rate was slower in vivo than in vitro, the extent of growth was similar after 24 h. P. mirabilis differentiated into filamentous swarmer cells in all in-vitro culture conditions, but no filamentous cells were observed in either of the in-vivo chamber models. Transurethrally infected mice showed a rapid release or loss of filamentous cells and these could not be seen in kidney or bladder homogenates 7 days after infection. Bacteria showed increasing haemagglutination titres for fresh and tanned red blood cells after subculturing in BHIB, but bacteria grown in vivo did not show haemagglutination. An increasing resistance to normal serum was found when bacteria were grown in vivo. Significant haemolytic activity was detected with bacteria grown in BHIB and IPC, but almost no activity was found when bacteria had grown in urine. These findings improve the understanding of the role of P. mirabilis uropathogenic virulence factors in vivo.