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Enteropathogenic Providencia alcalifaciens: A Subgroup of P. alcalifaciens That Causes Diarrhea
Dieter Bulach1,2, Glen P Carter3, M John Albert4
1Microbiological Diagnostic Unit Public Health Laboratory, Peter Doherty Institute for Infection and Immunity, The University of Melbourne, Melbourne, VIC 3000, Australia.
Abstract:
Despite being considered a normal flora, Providencia alcalifaciens 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 TnphoA 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 TnphoA insertion sites and determine the effect on virulence. A TnphoA 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 P. alcalifaciens surveyed, the chromosomal T3SS locus was present in all strains, including both P. alcalifaciens 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 TnphoA 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 P. alcalifaciens that possesses this plasmid-mediated T3SS is an enteric pathogen that can cause diarrheal disease.
Insights
Providencia alcalifaciens can cause diarrhea. A specific plasmid-mediated type III secretion system (T3SS) is crucial for this bacterium's invasion capabilities and diarrheal disease causation.
Area of Science:
- Microbiology
- Pathogenesis
- Genomics
Background:
- Providencia alcalifaciens, a common gut bacterium, can cause diarrhea.
- Previous studies showed a specific strain (2939/90) invades cells and causes diarrhea in rabbits.
Purpose of the Study:
- To identify the genetic basis of virulence in P. alcalifaciens.
- To investigate the role of the type III secretion system (T3SS) in P. alcalifaciens pathogenesis.
Main Methods:
- Whole-genome sequencing of P. alcalifaciens strain 2939/90 and its TnphoA mutants.
- Bioinformatic analysis of 52 P. alcalifaciens genomes to identify T3SS loci.
- Phenotypic analysis of bacterial invasion and actin condensation in mammalian cells.
Main Results:
- TnphoA insertion occurred in a plasmid-borne T3SS locus, not the chromosomal one.
- The plasmid T3SS was found in 21 of 52 genomes, predominantly in strains from a dog diarrhea outbreak.
- Disruption of the plasmid T3SS significantly reduced bacterial invasion of mammalian cells.
Conclusions:
- A specific subgroup of P. alcalifaciens carrying a plasmid-mediated T3SS is an enteric pathogen.
- The plasmid-mediated T3SS is essential for the invasive phenotype and diarrheal disease caused by P. alcalifaciens.
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