Detection of Salmonella spp and Listeria monocytogenes in fresh and semi-cured cheeses that are sold on the street markets in Mexico City

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MARÍA SALUD RUBIO LOZANO
CLAUDIA DOLORES ALCAZAR MONTAÑEZ
ROGELIO ALONSO MORALES
JOSÉ FERNANDO NÚÑEZ ESPINOSA

Abstract

THE OBJECTIVE OF THIS STUDY WAS TO DETERMINE THE BACTERIOLOGICAL SAFETY OF FRESH AND SEMI-CURED CHEESES THAT ARE SOLD ON THE STREET MARKETS IN MEXICO CITY. THE POLIMERASE CHAIN REACTION (PCR) WAS USED TO SIMULTANEOUSLY DETECT SALMONELLA SPP AND LISTERIA MONOCYTOGENES. ALSO, TRADITIONAL MICROBIOLOGICAL METHODS WERE USED TO DETERMINE SALMONELLA SPP (NOM-114-SSA1-1994) AND L. MONOCYTOGENES (NOM-143-SSA1-1995) IN FOOD. A TOTAL OF 120 SAMPLE, RANDOMLY TAKEN FROM FOUR STREET MARKETS OF THE SOUTH OF THE CITY, WERE ANALYZED. THE METHODOLOGY FOR MULTIPLEX PCR WAS BASED ON THE SIMULTANEOUS AMPLIFICATION OF INVA AND IAP GENES FROM SALMONELLA SPP AND L. MONOCYTOGENES RESPECTIVELY. BACTERIAL DNA EXTRACTION FROM CHEESE SAMPLES WAS DEVELOPED IN ORDER TO ELIMINATE OR DIMINISH THE POSSIBLE INTERFERENCE OF INHIBITORS OF FOOD USING PREVIOUS CENTIFUGATION OF THE SAMPLES AND IT WAS CHECKED THAT THE AMPLIFICATION OF BOTH RESULTED POSITIVE, EVEN WHEN THE PATHOGENS ARE PRESENT IN THE SAMPLES AT A CONCENTRATION OF, AT LEAST, 30 UFC/G. PCR RESULTS INDICATED THAT ONLY 3 SAMPLES WERE POSITIVE TO SALMONELLA SPP AND NONE TO L. MONOCYTOGENES COMPARED TO THE BACTERIOLOGICAL METHOD RESULTS WHICH SHOWED NO POSITIVE RESULTS
Keywords:
CHEESES STREET VENDERS SALMONELLA SPP L MONOCYTOGENES BACTERIOLOGICAL PCR

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