A novel subpopulation of Salmonella enterica serovar Infantis strains isolated from broiler chicken organs other than the gastrointestinal tract

Salmonella enterica subsp. enterica serovar Infantis strains were isolated from broiler chickens from six farms in Japan and the pathogenicity associated with the recently reported 280 kbp mega plasmid was examined by possession of the plasmid and histopathology of tissues from these chickens. S. Infantis strains were isolated from 10 of 24 chickens. Phylogenetic, network and Bayesian cluster analyses were used to determine whether these strains were in the previously defined Clusters 1-5. Phylogenetic analysis classified the strains isolated in this study in two groups (Groups A and B). Both groups contained strains from gastrointestional contents, but only Group A also contained strains from spleen, liver, and lymphoid tissues. Histopathology showed suppurative splenitis in a spleen from which Group A strains were isolated. Although network and Bayesian cluster analyses were unable to differentiate Group A and B strains from the previously defined Clusters 1-5, population genetic analysis indicated that Group A was a different population from Cluster 5, indicating that Group A would be a subpopulation of Cluster 5. The irp2 gene, which is in the mega plasmid carried by a pathogenic S. Infantis strain recently isolated in Israel, was found in both Groups A and B strains and in the previously reported Clusters 4 and 5 strains. These results suggested that Group A would be a novel subpopulation of the previously defined Cluster 5, and presence of the mega plasmid may not be related whether S. Infantis strains can infect certain organs.