DETECTION OF LISTERIA MONOCYTOGENES BY THE POLYMERASE CHAIN REACTION (PCR) TECHNIQUE IN SAMPLES OF RAW BOVINE MILK

Abstract

Considering the possible incidence of Listeria monocytogenes in raw foods and their pathogenicity and health risk, this study aimed to compare techniques for extraction of bacterial DNA from milk samples and investigate the presence of L. monocytogenes by Polymerase Chain Reaction (PCR) in raw milk. We tested four different extraction protocols (generally identified: A, B, C, and D) for isolation of bacterial DNA directly from milk. In all of them was obtained identifying the product of 702 bp (base pairs) corresponding to the listeriolysin gene from L. monocytogenes. The protocol B containing proteinase K and phenol buffered, was chosen for the extraction of DNA from milk samples from eight dairy farms within the RS. The subsequent PCR amplification with DNA obtained by the protocol B allowed the identification of L. monocytogenes from 10³ CFU/mL. None of the samples was positive for the producer L. monocytogenes by PCR or by conventional microbiological analysis. With this study it is concluded that the tested protocols, the protocol B was more effective for the detection of L. monocytogenes by PCR. Moreover, for the samples of the producers, the result PCR technique was obtained in a shorter time than conventional analysis of L. monocytogenes, which may allow earlier treatment of infected animals and thus avoid losses to the producer.