TnphoA mutants of Providencia alcalifaciens with altered invasiveness of HEp-2 cells

Recent studies have shown that Providencia alcalifaciens is a diarrhoeal pathogen. It may cause diarrhoea by an invasive mechanism, as it invades cultured mammalian cells in vitro and intestinal epithelial cells of experimentally inoculated rabbits in vivo. To locate the gene(s) involved in invasion, TnphoA mutants of a diarrhoeal isolate of P. alcalifaciens were generated. Compared with the parent strain, these mutants exhibited negligible invasion and actin condensation in HEp-2 cells. TnphoA insertion was located in fragments of 4.9 kb and 11.1 kb of the bacterial chromosome by Southern blot. These mutants did not secrete a 28-kDa protein, which may be involved in invasion. It should be possible now to study the gene(s) involved in invasion of P. alcalifaciens with these mutants. This investigation is another example of the usefulness of TnphoA mutagenesis in the study of bacterial virulence genes.