ABSTRACT
Culture media, reagents, and commercial kits were compared on artificially contaminated food samples. The objective was to find an isolation method for Escherichia coli O157:H7 sensitive, specific and accessible in terms of cost, requirements of equipments and qualification of the analyst. The adopted scheme consisted in a selective enrichment at 42 degrees C during 18 to 24 h, using an appropriate medium, in accordance with the nature of the sample, followed by a step of immunomagnetic separation and simultaneous isolation on a chromogenic agar and MacConkey sorbitol agar with potassium tellurite and cefixime, during 18-24 h at 37 degrees C. The presumptive colonies were confirmed as E. coli O157 by serological and biochemical tests. Secondly, this methodology was applied to food samples, water, bovine gastric content and manure. A total of 410 samples were studied: 279 from meat, 54 milk and dairy products, 6 from vegetables, 27 water samples and 44 bovine gastric content and manure. The frequency of isolation of E. coli O157:H7 was of 3.9
. The phenotypic and genotypic characterization of the isolates was performed. A simple isolation methodology for E. coli O157 was developed, which proved accessible to food laboratories of lower complexity. This methodology allowed the detection of this pathogen in food and environmental samples in Gualeguaychú City. The role of water as vehicle of infection was also established. The strains harbored the same virulence factors as those recovered from human disease.
ABSTRACT
El método de hibridación colorimétrico de Gene Traktm (GENE TRAK Systems, 31 New York Avenue, Framingham, M.A.) fue comparado con la metodología convencional propuesta por International Commission for Microbiological Standard Foods (ICMSF) en la detección de Salmonella en muestras de alimentos balanceados y materias primas de origen animal y vegetal utilizadas en la formulación de los mismos. Se procesaron 249 muestras que incluyen muestras inoculadas y 9 muestras no inoculadas. De un total de 240 muestras no inoculadas, 62,9 por ciento no acusaron presencia de Salmonella por ningún método, 27,9 por ciento fue positivo por ambos métodos y el 9,2 por ciento dio positivo por Gene Trak no pudiéndose confirmar después de cinco determinaciones por el método convencional. Esta metodología se presenta como un método interesante de detección con importantes ventajas frente al convencional: facilidad para procesar un gran número de muestras sin despliegue de gran cantidad de material, acortamiento del tiempo en obtener resultados y alta sensibilidad