Antimicrobial activity of Lactobacillus cell free supernatant against Salmonella Enteritidis and Infantis

Cell-free supernatants (CFS) produced by lactic acid bacteria (LAB) have been characterized as natural antagonists of important pathogens, including Salmonella. Their bacteriostatic or bactericidal properties have been reported to serve as an alternative to antibiotics by minimizing problems related to antimicrobial resistance. This study aimed to evaluate the antimicrobial activity of CFS of 4 selected LAB strains belonging to Lacticaseibacillus paracasei (2 strain), Limosilactobacillus reuteri (1 strain), and Lacticaseibacillus rhamnosus (1 strain) species against Salmonella Enteritidis and Infantis serovars by the agar-well diffusion method. Cell-free culture media of lactic acid bacteria were used in either crude CFS (acidic) and neutralized form (NCFS) to also understand non-pH-dependent antimicrobial potential. All crude CFSs were found to exhibit antimicrobial activity against pathogens, ranging from moderate to strong. After pH neutralization, the crude CFS of L. paracasei (2 strains) lost their antimicrobial activity, except for the crude CFS produced by L. reuteri and L. rhamnosus. However, there was a significant decrease in the level of anti-Salmonella activity of L. rhamnosus NCFS. It was determined that L. reuteri NCFS continued to show antimicrobial activity at levels similar to the effects of crude CFS. It is thought that the antibacterial activity of L. reuteri and L. rhamnosus CFS determined in the research does not depend only on their acidity and that the chemical characterization of the postbiotics, which is the source of this antimicrobial activity, should be evaluated.