Inhibition of Salmonella Typhimurium by medium-chain fatty acids in an in vitro simulation of the porcine cecum

Salmonella typhimurium was responsible for more than half of the reported cases of human salmonellosis in Belgium in 2007 and was the predominant serovar isolated from slaughter pig carcasses. To lower the Salmonella contamination of pork meat, measures can be taken at the primary production level, e.g. by reducing the shedding of Salmonella through the use of feed additives such as medium-chain fatty acids (MCFAs). An in vitro continuous culture system, simulating the porcine cecum, was developed for investigating the effect of MCFAs (sodium caproate, sodium caprylate and sodium caprinate) on the pig intestinal microbial community. The system was monitored by plating on selective media, PCR-DGGE and HPLC analysis of fermentation products. An inoculated S. typhimurium strain could be maintained by the system at a population size of about 5 log(10)cfu/mL. By the addition of 15 mM caprylate, significant reductions of coliforms and Salmonella counts by 4.69 log(10) units (95% confidence interval: 4.19-5.18) could be achieved, while other bacterial populations were clearly less affected. This concentration seems economically feasible in pig feed, provided that the substance can reach the cecum without being absorbed. Thus, caprylate, for example in the form of encapsulated beads or as triacylglycerol oil, might have potential as a Salmonella-reducing additive in pig feed.