Screening of antimicrobial-producing lactic acid bacteria isolated from traditional fish fermentation against pathogenic bacteria

Abstract

Abstract This study aims to obtain lactic acid bacteria (LAB) which have probiotic properties and inhibitory effects against pathogens. Peda fish fermented in 20% salt solution used as samples. Antimicrobial properties of LAB isolates against gram-positive and gram-negative pathogens (Salmonella typhi BPE 127.1.MC, Salmonella typhi BPE 122.4.CCA, Salmonella typhi NCTC 786, Salmonella typhimurium FNCC 0050, Pseudomonas putida FNCC 0071, Bacillus subtilis ATCC 6633 and Staphylococcus aureus ATCC 25923) were tested using agar well diffusion method. To exclude acid production, the cell-free culture supernatant (CFCS) solution was neutralized using 1 N NaOH before antimicrobial activity was tested. Likewise with bacteriocin tests, CFCS solutions that have been neutralized, were treated first by heating at 100ºC for 10 minutes in order to enzyme inactivation. A total of 26 out of 50 LAB isolates showed clear zones in the MRS-CaCO3 agar medium, gram positive, and negative catalase as the main characteristics of LAB. Sixteen of the 26 LAB isolates were known to be tolerant to pH 2 and 1% of bile salts. In addition, 92.3% of LAB isolates (15 of 16 LAB isolates) were homofermentative. The antimicrobial test results found that two of 26 LAB isolates (i.e. LAB Pr.3.4L and Pi.5.8 isolates) were shown to have very strong inhibitory effects against gram-positive pathogens S. aureus ATCC 25923 compared to S. typhi BPE 122.4.CCA. Thus the two strains of LAB are indicated as bacteriocin-producing probiotic strains, and need to be pursued further for identification and optimization of production.