Enteropathogenic Providencia alcalifaciens : A Subgroup of P. alcalifaciens That Causes Diarrhea

Despite being considered a normal flora, can cause diarrhea. In a previous study, strain 2939/90, obtained from a diarrheal patient, caused invasion and actin condensation in mammalian cells, and diarrhea in a rabbit model. Four Tn mutants of 2939/90 produced negligible invasion and actin condensation in mammalian cells. Now, the parent strain and the mutants have been sequenced to locate Tn insertion sites and determine the effect on virulence. A Tn insertion was detected in the type three secretion system (T3SS) locus on a large plasmid and not in a T3SS locus on the chromosome. In 52 genomes of surveyed, the chromosomal T3SS locus was present in all strains, including both genomic clades, which we classified as group A and group B. Plasmid T3SS was present in 21 of 52 genomes, mostly in group A genomes, which included isolates from an outbreak of hemorrhagic diarrhea in dogs. The Tn insertion only in the plasmid T3SS locus affected the invasion phenotype, suggested that this locus is critical for causation of diarrhea. We conclude that a subgroup of that possesses this plasmid-mediated T3SS is an enteric pathogen that can cause diarrheal disease.