Abstract:
Staphylococcus aureus and Listeria monocytogenes are widely-known food pathogens which are common causes for various infections. The increasing resistance of these pathogens to common antibiotics has drawn much attention in seeking probable alternative inhibitors, such as the lactic acid bacteria and their bacteriocins. In this study, eight bacteriocinogenic lactic acid bacteria comprised of Lactococcus lactis K3A2-2, Pediococcus acidilactici K2A2-5, P. acidilatici K2A2-1 and P. pentosaceous K2A2-3, isolated from a local carabao’s intestine, and P. acidilatici S3, P. acidilatici 1069, Lactobacillus plantarum BS and lastly, P. acidilatici AA-5a, isolated from other sources, were tested for their inhibitory effects against Stapthylococcus aureus strains, 1972, 1975, 1976, 1981, and 1982, and also Listeria sp. strains 0210, 031a, CM904, FB206, including LM3, a strain of Listeria monocytogenes. It was conducted through direct assay and ‘spot-on-lawn’ assay, using actively growing cells and both cell-free culture supernatants and semi-purified bacteriocin extracts, respectively. All test organisms were inhibited by the eight lactic acid bacteria through direct assay. However, in the ‘spot-on- lawn’ assay, Pediococcus acidilactici 1069 was able to inhibit only L. monocytogenes LM3 and had no effect on the S. aureus strains. Moreover, only S', aureus 1976 was inhibited through ‘spot-on-lawn’ assay of the seven cell-free culture supernatants while Listeria sp. CM904 remained resistant to all. Bacteriocin activity was assessed through the observation of inhibition zones. The Analysis of Variance (ANOVA) using Randomized Complete Block Design (RCBD) and the Tukey HSD test determined the significant differences in the actual trials of the antimicrobial inhibitory activity in both direct and ‘spot-on-lawn’ assay. Only the cell-free culture supernatant from P. acidilactici K2A2-1 was semi-purified through the adsorption/desorption method. Bacteriocin activity was lost upon treatment with pronase and decreased slightly upon treatment with amylase, rendering it proteinaceous with hints of glyco moiety. The semipurified bacteriocin was still found to have an activity at 100’C for 5, 30, and 60 min, although not at autoclave conditions (121“C for 15 min). Optimum pH range included slightly acidic to neutral pH (pH 5-7). In the Integrated MIC Matrix, an increase in bacteriocin effectiveness, as seen in fewer colony counts, was observed as the bacteriocin was diluted with distilled water.
