In vitro invasion capacity of Salmonella Typhimurium DT9 isolates sourced from humans and layer hen environments

In Australia, Salmonella Typhimurium definitive type 9 is frequently isolated during foodborne outbreaks of salmonellosis. Multiple-locus variable number tandem repeat analysis (MLVA) trace back investigations frequently identify isolate distribution patterns that may be epidemiologically linked to disease outbreaks. In this study, the in vitro virulence potential of S. Typhimurium DT9 isolates possessing different MLVA patterns (03 15 07 11 550, 03 24 11 10 523, 03 15 08 11 550 and 03 14 08 11 550) isolated from either humans or layer hens was assessed using a human colon carcinoma cell line. Four strains per MLVA from each host for a total of 32 isolates were included in these experiments. Bacteria were grown to stationary phase and added to cells at a multiplicity of infection of 100. Across all isolates, mean percent recovery ranged from 7.1 ± 1.1 to 33.3 ± 7.1%. The layer hen isolate, KC900 (MLVA profile 03 15 08 11 550), exhibited the greatest invasion with a mean percent recovery of 33.3 ± 7.1%. Overall, layer hen isolates of S. Typhimurium DT9 had significantly higher invasion into Caco2 cells than human isolates (p = .0021). RAPD and enterobacterial repetitive intergenic consensus genomic fingerprinting was also performed. Irrespective of source, the SalmonellaDT9 isolates included in this study exhibited similar fingerprint patterns.