Selection of bacteriocin-producing lactic acid bacteria from Nham for inhibition of pathogenic bacteria

A total of 107 lactic acid bacteria (LAB) isolated from 20 samples of Thai sour pork (nham), were collected from Suddhiluck Innofood Co.,Ltd. Bacteriocin-producing LAB were screened using an agar spotted test and agar well diffusion method. Among those LAB, only 34 isolates could inhibit Staphylococcus aureus. The most inhibition on S. aureus of these isolates namely NSL13-2, NSL1-4 and NSL5-2 were selected and identified based on morphology and biochemical characteristics using API 50 CHL (BioMérieux, France) and 16S rDNA analysis. NSL13-2, NSL1-4 and NSL5-2 were identified as Pediococcus pentosaceus, Weissella cibaria and Enterococcus gilvus, respectively. Growth inhibition of pathogenic bacteria was investigated by co-culturing with selected LAB in MRS broth. The highest efficiency of inhibitory effect observed when 104 CFUml-1of pathogenic bacteria were co-cultured with 106 CFUml-1 of P. pentosaceus. Complete growth inhibition of S. aureus, Listeria monocytogenes and Salmonella Typhimurium were detected after 12 hours of incubation, while Bacillus cereus and Escherichia coli were observed after 8 and 16 hours, respectively. Maximal growth of P. pentosaceus was obtained by culturing in MRS broth pH 8.0 and incubated at 30°C for 24 hours. Whereas, the highest bacteriocin activity was obtained by culturing in MRS broth adding with 3% (w/v) NaCl. Temperature, pH and incubation time that more favourable for bacteriocin production were range from 25 to 37๐C, pH 6.0-9.5 and 12 or 24 hours. The application of 106 CFUg-1 of P. pentosaceus as starter culture for nham preparation was performed for study inhibitory efficiency in food model. No detection of S. aureus, B. cereus and S. Typhimurium in nham inoculated both of pathogenic bacteria and P. pentosaceus (NSP) after 120, 24 and 120 hours of fermentation time, respectively. Whereas, decrease in number of L. monocytogenes and E. coli were observed. The number of L. monocytogenes and E. coli in NSP decreased to 2.26 and 3.23 log CFU at the end of fermentation, respectively. Therefore, P. pentosaceus could be used as starter culture in nham preparation in order to prevent the harmless of pathogenic bacteria.