Strong antimicrobial activity ofLactobacillus rhamnosusGG againstSalmonella typhimuriumis due to accumulation of lactic acid

Abstract

Spent culture supernatant (SCS) of the probiotic Lactobacillus rhamnosus GG had been reported to exert antibacterial activity against Salmonella typhimurium. However, the chemical identity of the antimicrobial compound(s) responsible remained unknown. A survey of the antimicrobial compounds produced by L. rhamnosus GG was performed. Lactobacillus rhamnosus GG produced a low-molecular weight, heat-stable, non-proteinaceous bactericidal substance, active at acidic pH against a wide range of bacterial species. SCS of L. rhamnosus GG grown in MRS medium contained five compounds that could meet the above description, if present at the appropriate concentration. Based on different experimental approaches, it could be concluded that under the growth conditions tested, the strong antimicrobial activity of L. rhamnosus GG against Salmonella was mediated by lactic acid.

Probiotic Mechanisms of Action

“…Organic acids, in particular acetic acid and lactic acid, have a strong inhibitory effect against Gram-negative bacteria, and they have been considered the main antimicrobial compounds responsible for the inhibitory activity of probiotics against pathogens [106,107,108]. The undissociated form of the organic acid enters the bacterial cell and dissociates inside its cytoplasm.…”

Antimicrobial Activity of Lactobacillus Isolated From Kashk-e Zard and Tarkhineh, Two Iranian Traditional Fermented Foods

“…During fermentation, the growths of pathogens as well as other spoilage organisms are frequently inhibited through antimicrobial components produced by lactic acid bacteria (LAB) (5)(6)(7). Reports have shown that LAB-produced organic acids can work in combination to display a strong inhibitory activity against many foodborne pathogens such as Salmonella typhimurium, Escherichia coli, Bacillus cereus, Clostridium botulinum, C. perfringens, Listeria monocytogenes, and Staphylococcus aureus (8)(9)(10)(11)(12).…”

RaoN, a small RNA encoded within Salmonella pathogenicity island-11, confers resistance to macrophage-induced stress

“…We found that in S. enterica serovar Typhimurium hydrogen peroxide treatment induces the expression of ldhA (data not shown). However, S. enterica is known to be very sensitive to the antimicrobial activity of lactate (De Keersmaecker et al, 2006;Marianelli et al, 2010). Therefore, we can speculate that during conditions leading to excretion of lactate, Salmonella may have a feedback-inhibition system to prevent overexpression of LdhA.…”