[Detection of Listeria monocytogenes in white cheese by polymerase chain reaction (PCR)]

The polymerase chain reaction, known as PCR, is a method to replicate thousands of times within a few hours and in vitro, small amounts of DNA. The application of rapid and sensitive methods to detect Listeria monocytogenes in cheese samples, allow a better microbiological control of the production process. PCR was applied to 30 samples of of white cheese, from Valencia, Carabobo State. It was detected PCR specificity and sensitivity by using the control strain Listeria monocytogenes 446. DNA extraction according to the methodology described by Torres et al., Molecular weight marker 100 base pairs. Were used: four primers hlyA gene of listeriolysin O; L1/U1 primers for 938 bp band and LF/LR 750 bp band hlyA gene. Epilnfo Statistical V6 to match observations in gels, by Kappa coefficient (K).

8 out of 30 cheese samples analyzed showed presumptive growth of Listeria spp in PALCAM Agar. Two of the samples not belonged to the genus Listeria, in the 6 remaining sample confirmation tests showed that: 2 were L. monocytogenes, 3 L. ivanovii and 1 L. seeligeri. In PCR 2 samples were positive for L. monocytogenes by amplify the 938 bp band for Listeria and 750 bp band for the species monocytogenes. We concluded that PCR was highly specific and sensitive to L. monocytogenes, taking advantage of PALCAM agar to detect the presence of the pathogen specifies a relatively short time.