Screening of lactic acid bacteria for bacteriocins by microbiological and PCR methods.

We describe a practical laboratory designed for third-year undergraduate students of Biotechnology as part of a Microbial Physiology and Genetics course. It comprises a five-session laboratory module to screen foods for lactic acid bacteria (LAB)1 and to test isolated LAB for the presence of bacteriocins. Traditional Thai fermented foods are first screened for bacteriocin-producing LAB using microbiological methods. This is followed by a simple and rapid DNA extraction and by a multiplex polymerase chain reaction (PCR) using three pairs of specific primers to test for the presence or absence of various bacteriocin genes in the isolated LAB. PCR amplicons of 332, 412, and 608 bp indicate the presence of pediocin, enterocin, and nisin genes, respectively, whereas no amplicon band indicates the absence of these bacteriocins. The laboratory provides the students with experience in the use of microbiological and multiplex PCR methods and shows how the molecular biology techniques can be related to their daily lives. The module could easily be adapted to the study of fermented foods from other countries.