title: The Polymyxin Ceftazidime Oxford Medium as an alternative selective and differential medium for isolation of Listeria monocytogenes from raw or unpasteurized food.
abstract: The Polymyxin Ceftazidime Oxford Medium (PCOM) was developed to recover Listeria monocytogenes from raw or unpasteurized foods. It contains esculin-ferric ammonium citrate as indicator system for Listeria growth, and ceftazidime and polymyxin B as selective agents, which are available in several Latin American countries. Comparison of PCOM, Modified Oxford Medium (MOX) and Tryptic Soy agar with 0.6% yeast extract (TSAYE) indicated that both selective media were equally effective at recovering four individual strains of L. monocytogenes (Scott A, V7, California and broccoli), and a mixture of these strains (LMM) (P > 0.05). The ability of PCOM, MOX, TSAYE and TSAYE supplemented with 4% NaCl to recover heat, acid and freeze-damaged LMM was similar for all media (P > 0.05). The PCOM proved to be effective at isolating colonies of LMM from inoculated raw beef chunks, unpasteurized orange juice, cabbage, and Mexican-style cheese by direct plating and by the US Department of Agriculture's Food Safety and Inspection Service enrichment method. Differentiation of L. monocytogenes colonies was easier on PCOM than on MOX for foods with high levels of background microbiota. Based on the evaluations performed on foods naturally contaminated with L. monocytogenes, PCOM was a more economical alternative than MOX for selective and differential isolation of Listeria from raw or unpasteurized foods.
authors.affiliation: Departamento de Farmacobiología, Universidad de Guadalajara, Boulevard Marcelino García Barragán 1451, Guadalajara, Jalisco 44430, Mexico.
authors.forename: N E
authors.initials: NE
authors.lastname: Martínez-Gonzáles
authors.forename: L
authors.initials: L
authors.lastname: Martínez-Chávez
authors.forename: C
authors.initials: C
authors.lastname: Martínez-Cárdenas
authors.forename: E
authors.initials: E
authors.lastname: Cabrera-Díaz
authors.forename: A
authors.initials: A
authors.lastname: Castillo
mesh_terms: D000818:Animals; D001937:Brassica / Q000382:microbiology; D002417:Cattle; D002442:Ceftazidime / Q000494:pharmacology; D002611:Cheese / Q000382:microbiology; D015169:Colony Count, Microbial / Q000295:instrumentation / Q000379:methods*; D003470:Culture Media / Q000737:chemistry / Q000378:metabolism*; D005516:Food Microbiology; D008089:Listeria monocytogenes / Q000187:drug effects / Q000254:growth & development / Q000302:isolation & purification* / Q000378:metabolism; D008892:Milk / Q000382:microbiology
chemical_list: D003470:Culture Media; D002442:Ceftazidime
keywords: Isolation media; Listeria monocytogenes; Raw food; Unpasteurized food