Assessment of Antibacterial Activity of Lactic Acid Bacteria Isolated from Fermented Foods against Escherichia coli O157:H7 and Proteus penneri and Their Potential as Starter Cultures

Abstract

Fermented fish and vegetables produced by spontaneous fermentation are the most well-known traditional foods in Cambodia. Even though fermented foods provide health benefits related to nutrition, probiotics, and postbiotics, some of them are not safe due to the survival of bacteria harmful to humans. The purpose of this research is to examine in vitro the antibacterial activity of lactic acid bacteria (LAB) isolated from fermented fish and vegetables against E. coli O157:H7 and Proteus penneri, histamine forming LAB, and the survival of LAB in low pH levels and high salt concentration using pH and salt tolerance tests. LAB was isolated from 134 naturally fermented fish and vegetables from four different provinces and identified using the Biolog GEN III MicroStation semi-automated system. The antagonistic properties of these isolates against E. coli O157:H7, and Proteus penneri were examined using a co-culture method at 24, 48, and 72 hours of incubation times. As a result, 36 strains of LAB were identified from a total of 134 samples. Seven LAB species out of 36 strains can survive at pH 3 for 6 hours, while four of these seven LAB can tolerate pH 2. Lactobacillus plantarum, Lactococcus lactis, Lactobacillus gasseri, Leuconostoc lactis, and Leuconostoc gilidum have a significant capacity to inhibit E. coli O157:H7 and Proteus penneri growth when compared to control. These five LAB do not produce histamine and can tolerate up to a 10% salt concentration. All the results demonstrate that Lactobacillus plantarum, Lactobacillus lactis, Lactobacillus gasseri, Leuconostoc lactis, and Leuconostoc gilidum have great potential for use as starter cultures for suppressing pathogenic bacteria growth in fermented fish and vegetables.