Longitudinal investigation of Salmonella spp. from farm to fork in the pig industry in Reunion Island

Salmonella is, after Campylobacter, the most reported zoonotic pathogen in Europe. Pork meat is frequently incriminated in salmonellosis. However, asymptomatic carrying of Salmonella by pigs makes its detection difficult. Despite its tropical situation, pig industry of Reunion Island is also concerned by this public health burden. Our epidemiological study aims to identify the pathways of contamination along the pig chain industry. Three Salmonella positive farms were followed from the farrowing to the pork cuts. At farm level, Salmonella excretion was detected by individual samples of feces at birth, farrowing, post-weaning and fattening. During slaughtering, samples were taken from pigs entering and from carcasses after polishing, splitting and chilling. Caeca and pork cuts were also collected. Environmental samples of water, food and environment at farm and at different stages before slaughtering and cutting of the day were taken. Among the 900 analysed samples, 229 isolates were collected and divided into 42 pulsotypes and 12 serotypes. S. monovariant 4,[5],12:i:-, S. Rissen, S. Typhimurium and S. Livingstone were predominant. Three different infection profiles were observed. At the nursing stage, piglets were Salmonella free. Infection occurred either after post-weaning (2/3) or during the fattening period (1/3). Truck and lairage are cross-contamination stages (100% are positive before pig loading). On the contrary, slaughterhouse is a decreasing contamination stage (equipment and pork cuts are Salmonella free). Farm surroundings play a major role in the reinfection of pigs like other animal productions. This original investigation, made for the first time until now, give an accurate photography of Salmonella spreading along the chain. Introduction Salmonella is one of the main zoonotic pathogens in Europe. Pork meat is frequently incriminated in salmonellosis. Despite being highly studied in poultry production, epidemiological data are missing concerning Salmonella contamination of pork meat in Reunion Island. Limiting Salmonella contamination is dependent on identifying the source and ways of dissemination of Salmonella transmission at each stage during production and during slaughtering. The aim of this study was to identify the pathways of contamination all along the chain industry of Reunion Island, from the farm to pork cuts. Material and Methods Three farrow-to-finish farms, previously detected Salmonella positive, were selected for this project. Farms were selected from different geographical locations in Reunion Island and with different environmental characteristics and different general husbandry practices. They were monitored from farrowing to the pork cuts. Three sows and 5 piglets by sow were selected from one batch per farm. At farm level, Salmonella excretion was detected by individual samples of feces, after farrowing and throughout each growing stage. At slaughterhouse level, gauze swabs from pigs entering and from carcasses after polishing, splitting and chilling, caecal contents and pork cuts were sampled. Environmental samples were collected at both farm and slaughterhouse levels. They were collected at each visit in farms and all along the slaughtering and cutting process at the beginning of the day, before the slaughter of the followed pig batch. Environmental and feces samples were pre-enriched in buffered peptone water (BPW) in 1:10 sample/broth ratio. Disinfectant neutralizer was added in BPW broth (1:10) for samples collected after cleaning and disinfection. Environmental swabs and socks were pre-enriched with 150 and 300 ml of BPW respectively. After incubation at 37°C for 18h ± 2h, one ml and 3 Safepork 2013 Procedings • 107 drops of BPW broth were inoculated respectively to 10 ml of Müller–Kauffmann Tetrathionate-Novobiocin broth (MKTTn) and on Modified Semisolid Rappaport Vassiliadis agar (MSRV) plate. Both were incubated respectively at 37°C for 24 h and 41.5°C for 24-48h. Samples of feed were analysed as described previously. However, selective enrichment was done with MKTTn and Rappaport Vassiliadis Broth (RVB), incubated respectively at 37°C and 41.5°C for 24h. A loopful of selective enrichment in MKTTn or RVB was then streaked on Xylose-Lysine-Desoxycholate Agar (XLD) and Rambach Agar. MSRV plates with characteristic halo of migration were streaked onto XLD and Rambach agar. After 24h at 37°C, four typical colonies per sample (one per way if possible) were biochemically confirmed as Salmonella and serotyped according to the Kauffman-White scheme.