Prevalence and genetic diversity of Salmonella in organic and conventional pig productions in France

The objectives of this study were 1) to assess the occurrence of Salmonella in organic and conventional pig productions, 2) to evaluate the genetic diversity of strains isolated from these two productions, and 3) to estimate the cross-contamination on slaughter line between conventional pigs and organic pigs. 26 organic herds and 31 conventional herds were considered in one slaughterhouse. Two pigs per herds were sampled. For each pig, Salmonella detection was realized on colon content and swabs of carcass. Two isolates per positive samples were serotyped and genotyped by PFGE using XbaI enzyme. Prevalence of Salmonella in colon content was higher for organic pigs, 37,9% IC95%[25.5-51.6] than for conventional pigs, 32.7% IC95%[19.5-44.5] but it was not significantly different. Salmonella prevalence was lowest on carcasses and very close between the two productions; 10.7% IC95%[4.0-21.8] for organic carcasses and 10.3 IC95%[3.9-21.2]) for conventional carcasses. The 104 isolates were distributed in 7 serovars: Derby (46), , Brandenburg (18), Typhimurium (13), 2 types of monophasic variant of serovar Typhimurium 4,12:i:- (11) and 4,5,12:i:- (10), Infantis (2) and Mbandaka (2). Sixteen PFGE profiles were obtained: 1 per serovar for Mbandaka, Infantis, and Brandenbrug, 2 for monophasic variant 4,5,12:i:-, 3 for Derby, 4 for Typhimurium and 4 for monophasic variant 4,12:i:-. Seven PFGE profiles (84% of the strains) were common between organic and conventional pigs. A major profile gathered 79% of the S. Derby strains. S. Brandenburg strains presented only one PFGE profile which was detected in 5 different herds. It has not been possible to show with certainty Salmonella cross-contamination between organic and conventional pigs during the process. Indeed, only one S. Typhimurium PFGE profile was evidenced for organic and conventional carcasses during the same sampling day. This study gives for the first time data on Salmonella in organic pig production in France