[Development and application of a method for isolating Escherichia coli O157:H7 in the city of Gualeguaychú]. / Desarrollo y aplicación de una metodología de aislamiento de Escherichia coli O157:H7 en el Municipio de Gualeguaychú.

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.

Desarrollo y aplicación de una metodología de aislamiento de Escherichia coli O157:H7 en el Municipio de Gualeguaychú / [Development and application of a method for isolating Escherichia coli O157:H7 in the city of Gualeguaychú]

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.

Isolation and characterization of Escherichia coli O157:H7 from retail meats in Argentina.

Between February and May 2000, 279 meat samples were collected from 136 retail stores in Gualeguaychú City, Argentina. Samples were assayed for Escherichia coli O157:H7 by selective enrichment in modified EC broth containing novobiocin, followed by immunomagnetic separation (IMS) and plating onto both sorbitol MacConkey agar supplemented with cefixime and potassium tellurite and a chromogenic medium. Eleven E. coli O157:H7 isolates were detected in 6 (3.8%) of 160 ground beef samples, in 4 (4.8%) of 83 fresh sausages, and in 1 (3.3%) of 30 dry sausages. E. coli O157:H7 was not isolated from five hamburger patties or one barbecue-type fresh sausage assayed. The isolates were tested for virulence-related genes. Ten additional Shiga toxin-producing E. coli (STEC) O157:H7 isolates of food origin, recovered from different locations in Argentina, were included for comparison purposes. All 21 isolates harbored both eae and EHEC-hlyA genes, and 12 (57.1%) encoded stx2/stx2vh-a. The isolates were of phage types 87 (seven strains), 14 (four strains), 4 (three strains), and 26 (one strain). Six strains were nontypable by phage typing. Pulsed-field gel electrophoresis (PFGE) revealed 19 XbaI-PFGE profiles. Fifteen (71%) strains were grouped in four clusters, which shared more than 80% of DNA restriction fragments. The enrichment culture method with IMS was a sensitive procedure to detect E. coli O157:H7 strains in retail meats. Some of the isolates from different stores presented a high clonal relatedness, as determined by XhaI-PFGE and phage typing, and harbored the virulence factors associated with human illness.

Salmonella: comparación de dos métodos para su detección en alimentos para aves / Comparison of two methods for detection of Salmonella in broiler feed

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

[Salmonella: comparison of methods for its detection in bird feed]. / Salmonella: comparación de dos métodos para su detección en alimentos para aves.

The Gene Trak colorimetric hybridization method (GENE TRAK Systems, 31 New York Avenue, Framingham, M.A.) was compared with conventional methodology proposed by International Commission for Microbiological Standard Foods (ICMSF) for the detection of Salmonella in samples of broiler feed and raw materials of vegetal and animal origin used in its formulation. In this study 249 samples which included inoculated samples and 9 uninoculated samples were studied. On 240 uninoculated samples, 62.9% resulted free of Salmonella, 27.9% were positive for both methods and 9.2% were positive by Gene Trak but it couldn't be confirmed by conventional methodology after five determinations. This methodology is presented as an interesting method of screening with important advantages in comparison to conventional methodology: facility for processing a big number of samples with few material expenses, less time to get results and high sensibility.