Mitsuokella jalaludinii inhibits growth of Salmonella enterica serovar Typhimurium

Salmonella continues to be a significant human health threat, and the objective of this study was to identify microorganisms with the potential to improve porcine food-safety through their antagonism of Salmonella. Anaerobic culture supernatants of 973 bacterial isolates from the gastrointestinal tract and feces of swine were screened for their capacity to inhibit the growth of Salmonella enterica serovar Typhimurium. Growth inhibition of 1000-fold or greater was observed from 16 isolates, and 16S rRNA sequencing identified the isolates as members of the genera Mitsuokella, Escherichia/Shigella, Anaerovibrio, Selenomonas, and Streptococcus. Four isolates were identified as Mitsuokella jalaludinii, and the mechanism of Salmonella Typhimurium growth inhibition by M. jalaludinii was further investigated. M. jalaludinii stationary phase culture supernatants were observed to significantly inhibit growth, and featured the production of lactic, succinic, and acetic acids. Aerobic and anaerobic S. Typhimurium growth was restored when the pH of the culture supernatants (pH 4.6) was increased to pH 6.8. However, S. Typhimurium growth in fermentation acid-free media was the same at pH 4.6 and pH 6.8 – indicating a synergistic effect between fermentation acid production and low pH as the cause of S. Typhimurium growth inhibition. Furthermore, exposure of S. Typhimurium to M. jalaludinii culture supernatants inhibited Salmonella invasion of HEp-2 cells by 10-fold. The results identify M. jalaludinii as a possible inhibitor of Salmonella growth and invasion in swine, and thus a potential probiotic capable of improving food safety.