Salmonella in pig farming: excretion level, serovars and resistance to antibiotics
Résumé
Salmonella is the second foodborne pathogen responsible for gastroenteritis in the European Union and pork would be involved in 10 to 20% of human salmonellosis. Data on the level of Salmonella at farm are necessary for a better quantitative assessment of the risk at this first stage of the food chain. This project was setting up with two objectives: 1) acquire data on the level of Salmonella excretion by pigs on the farms 2) identify the serovar, genotypic and antibiotic resistance profiles of the Salmonella strains.
Four farrowing-fattening pig farms were visited three times. At each visit, individual faeces from 10 farrowing sows located in the same room of maternity and individual faeces from 20 finishing pigs belonging from the same band were collected for Salmonella detection and enumeration using an adapted method from NF U47-102 and ISO/TS 6579-2:2012. Isolates were typed by Pulsed-Field-Gel-Electrophoresis (PFGE) and their antibiotic resistance tested by Minimum Inhibitory Concentration (MIC). No sow was positive for Salmonella. For pigs, 52 of the 240 samples (21.6%) were positive, with a percentage in the bands varying from 0 to 75%. On the 52 positive samples, 44 were enumerable, of which 63.5% were below 10 MPN/g. Seven samples contained more than 100 MPN/g. Of the 97 Salmonella strains isolated, 89 trains were the monophasic variant of S. Typhimurium (mVST) and the others S. Derby (8 strains). All the S. Derby strains highlighted the same PFGE profile and the same resistance to 2 antibiotics (SuT). The mVSTs were divided into 6 PFGE profiles, 2 linked to penta-resistant strains (ACSuTTm) and 4 to strains resistant to 3 antibiotics (ASuT).
This explanory study allows to collect Salmonella data count for the first time in France in pigs under real-life conditions. These quantitative data are important for feeding risk assessment models and ultimately allowing better control of the risk associated with Salmonella contamination of food.