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

Abstract

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.

Microevolution of antimicrobial resistance and biofilm formation of Salmonella Typhimurium during persistence on pig farms

“…Based on the reported short-term substitution rate of 1–2 SNPs per genome per year for Salmonella Typhimurium 60,72,73 , the common ancestor for farm-specific clusters existed in the last 2–7 years. This is also consistent with previous studies that used subgenomic typing methods 15,74,75 .…”

Worldwide Epidemiology ofSalmonellaSerovars in Animal-Based Foods: a Meta-analysis

“…Studies have reported that multidrug-resistant (MDR) S. Typhimurium phage type U 288, DT 120, and DT 193 are the most prevalent in swine (39,(62)(63)(64)(65)(66)(67)(68)(69)(70)(71)(72) and DT 193 in both humans and pigs (62,72,73). Some researchers have suggested that the prevalence of phage type DT 193 has increased in humans over the past 10 years due to its association with the dominant clone of monophasic S. Typhimurium (39,(73)(74)(75)(76), although this clonal line is a heterogeneous phage type comprising different monophasic S. Typhimurium lineages (74). Similarly, DT 120 has been associated with the monophasic variant, although some DT 120 members have derived from DT 104 and are not monophasic (74).…”

pSTM6-275, a Conjugative IncHI2 Plasmid of Salmonella enterica That Confers Antibiotic and Heavy-Metal Resistance under Changing Physiological Conditions

“…Typhimurium (strain SO4698-09) carries a Salmonella genomic island (SGI) which contributes to enhanced resistance to copper sulfate, a common animal feed additive ( 3 ). We recently reported the genome sequence of S. enterica 1,4,[5],12:i:- strain TW-Stm6, an isolate recovered from pig feces which has the same antigenic formula, phage type, and sequence type as strain SO4698-09, and also carries the genomic island, SGI-4 ( 3 – 5 ). The assembled genome of TW-Stm6 comprised a 4,999,862-bp chromosome, a 4-kb MOB Q plasmid (pSTM6-4), and a 275.8-kb IncHI2 plasmid (pSTM6-275).…”