Occurrence of Listeria species in raw milk in farms on the outskirts of Mexico city |
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| Affiliation: | 1. Departmento de of Biotecnologı́a, División de Ciencias Biológicas y de la Salud, Universidad Autónoma Metropolitana, Michoacán y Purı́sima S/N, Col. Vicentina, C.P. 09340, Mexico;2. Departmento de Microbiologı́a, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, Carpio y Plan de Ayala S/N, Col. Santo Tomás, C.P. 11340, Mexico;1. School of Nutrition and Food Sciences, Louisiana State University AgCenter, Baton Rouge, LA 70803, USA;2. Department of Agricultural and Extension Education & Evaluation, Louisiana State University AgCenter, Baton Rouge, LA 70803, USA;3. Pennington Biomedical Research Center, Baton Rouge, LA 70808, USA;1. Food Technology Department, Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco (CIATEJ), Guadalajara, Jalisco, Mexico;2. Biotechnology Department, Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco (CIATEJ), Guadalajara, Jalisco, Mexico;1. Instituto Superior Tecnológico de Acayucan, Costera del Golfo Km 216.4, Acayucan, Veracruz, 96100, Mexico;2. Universidade Católica Portuguesa, Rua de Diogo Botelho, 1327, Porto, 4169-005, Portugal;3. University of Reading, Whiteknights, Reading, RG6 6AH, United Kingdom;1. Departamento de Biotecnología, División de Ciencias Biológicas y de la Salud, Universidad Autónoma Metropolitana-Iztapalapa, Av. San Rafael Atlixco 186, Col. Vicentina, CP 09340, Iztapalapa, Ciudad de México, Mexico;2. Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Hidalgo, Carretera Pachuca-Tulancingo km 4.5 Col. Carboneras, C.P. 42184, Mineral de la Reforma, Hidalgo, Mexico |
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| Abstract: | Listerosis may be transmitted by direct contact with infected animals or by consumption of contaminated vegetables or meat and milk products. In Mexico, raw milk is widely consumed and the incidence of milkborne disease is unknown. A total of 1300 raw milk samples were obtained from 20 l bulk tanks at four different dairy farms in southeast of Mexico City from June 1998 to June 1999. The samples were enriched for 48 h at 30°C and plated onto McBride's Modified Agar (MMA). Suspect colonies were biochemically tested to confirm identity. Overall, 23% of all raw milk samples examined tested positive forListeria species; 13% were positive for L. monocytogenes (45·6% were serotype-4b and 54·4% were serotype 1); 6% for L. ivanovii; 4% for L. seeligeri and 1% forL. innocua. L. monocytogenes contamination was more frequent during the spring and summer months as isolation rates were 12·2% from June to October 1998 and 17% from March to June 1999. Serotype-4b isolates were not pathogenic for the mouse, while for serotype-1, strains DL50ranged from 1·8×106to 4×107CFU ml−1. Additional studies are needed to assess the public health impact of contaminated milk in Mexico. |
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