Longitudinal study of Salmonella 1,4,[5],12:i:- shedding in five Australian pig herds

The shedding patterns of Salmonella spp. and MLVA profiles of Salmonella enterica subspecies enterica (I) serotype 1,4,[5],12:i:- were monitored in a 12-month longitudinal observational study of five pig herds to inform management; provide indications of potential hazard load at slaughter; and assist evaluation of MLVA for use by animal and public health practitioners. Twenty pooled faecal samples, stratified by age group, were collected quarterly. When Salmonella was cultured, multiple colonies were characterized by serotyping and where S. Typhimurium-like serovars were confirmed, isolates were further characterized by phage typing and multiple locus variable number tandem repeat analysis (MLVA). Salmonella was detected in 43% of samples. Salmonella 1,4,[5],12:i- was one of several serovars that persisted within the herds and was found among colonies from each production stage. Virtually all Salmonella 1,4,[5],12:i:- isolates were phage type 193, but exhibited 12 different, closely-related MLVA profiles. Salmonella 1,4,[5],12:i:- diversity within herds was low and MLVA profiles were stable indicating colonization throughout the herds and suggesting each farm had an endemic strain. High prevalence of S. 1,4,[5],12:i:- specific shedding among terminal animals indicated high hazard load at slaughter, suggesting that primary production may be an important pathway of S. 1,4,[5],12:i:- into the human food chain, this has implications for on-farm management and the application and targeting control measures and further evidence of the need for effective process control procedures to be in place during slaughter and in pork boning rooms. These findings have implications for animal health and food safety risk mitigation and risk management.