Isolation and detection of Listeria monocytogenes using polymerase chain reaction

The incidence of infection arising out of food poisoning is on the rise, especially in the developing countries. Cases of microbial contamination of milk have been reported and analyzed by scientists, worldwide. Listeria monocytogenes has been associated with such foods as raw milk, supposedly pasturized fluid milk, cheese (particularly soft - ripened varieties), ice cream, raw vegetables, fermented raw - meat, sausages, raw and cooked poultry, raw meats (all types) and raw and smoked fish. Its ability to grow at temperatures as low as 3°C permits multiplication in refrigerated foods. The methods for the analysis of food are complex and time - consuming. In this study a selective enrichment media isolated Listeria monocytogenes, a pathogenic, gram - positive bacterium from raw and packed milk. A protocol, that is economical, both in terms of cost and time is sought after the Listeria monocytogenes were confirmed by polymerase chain reaction. Primers specific to hly A gene which is characteristic only to Listeria monocytogenes were used to amplify the said gene. Agarose gel electrophoresis of the PCR products were finally performed which confirmed the presence of Listeria monocytogenes in some packed brands of milk and all the raw milk samples.