Listeria monocytogenes en queso amarillo madurado tipo Edam y su resistencia al pH y salinidad

Cheeses, high demand dairy products, have been recently involved in cases of food poisoning and infections caused, overwhelmingly, by microbial agents such as Listeria monocytogenes , due to factors such as their wide distribution in nature, pH resistance, salinity and temperature. We analyzed 48 samples of mature cheddar cheese Edam type, obtained from two commercial supplies in the Maracaibo and San Francisco municipality, Zulia state, Venezuela using Palcam and Oxford Agar. Strength tests were made at pH values of 4, 5, 6, 6.5 and 7 and salinity of 1, 2, 3, 4 and 5% (w / v). Of the 48 samples of cheese, 7 (15%) were positive for the genus Listeria spp. Preliminary tests (microscopic and biochemical) confirmed 11 colonies (C1 to C11) with characteristics of the genus Listeria . Out of the eleven colonies, five were identified: L. welshimeri (46%), three L. grayi (27%), two L. innocua (18%) 4, and one strain was identified as L. monocytogenes (9%), which was resistant to pH≥ 4 and gradually affected the concentrations of salt. The presence of this organism in a high consumption of food like cheese is a warning as to the safety management systems carried out in such foods.