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.

The purposes of this study were to detect non-O157 Shiga toxin-producing Escherichia coli (STEC) in bovine rectums and water in a beef cattle farm in Argentina, and to determine the pathogenic potential of the circulating strains. During the study, 292 rectal swabs from healthy animals and 79 environmental water samples were collected. The rectal swabs and one loop of the Moore swabs, enriched in Escherichia coli broth for 24 h at 37°C, were streaked on MacConkey agar plates and incubated overnight at 37°C. The isolates were characterized by biochemical tests and serotyped. Nonmotile STEC strains were typed for their H-specific (fliC) antigens by polymerase chain reaction (PCR). Isolates were characterized by detection of stx1, stx2, and their variants, eae, ehxA, and saa genes. Macrorestriction fragment analysis by pulsed-field gel electrophoresis (PFGE) was performed using the PulseNet standardized protocol. From 371 samples analyzed, 36.6% of rectal swabs and 34.2% of water samples were non-O157 STEC-positive by PCR, and 110 strains from rectal swabs, but only three from water, were isolated. The strains were grouped into 24 different serotypes, from which, O103:[H2] (n = 12), O136:H12 (n = 8), O178:H19 (n = 8), and O103:NM (n = 5) were most prevalent, representing 29.2% of the isolates. Predominant genotypes were stx1/eae/ehxA (16.8%) and stx2/saa/ehxA (15.9%). PFGE analysis revealed 56 different patterns, with 65 strains grouped in 19 clusters of 100% similarity. Two STEC O124:H19 strains isolated from rectal swabs and water with a 5-month interval harbored the stx1/stx2/saa/ehxA genotype, and showed an indistinguishable PFGE profile. By comparison, some XbaI-PFGE patterns identified in the present study were identical to the profiles of strains isolated from human, food, and animal sources included in the Argentine PulseNet database. By PCR, similar non-O157 detection rates were found in rectal swabs and water. However, the methodology for water samples needs to be improved, since only three strains from the total number of positive samples were recovered.

Shiga toxin-producing Escherichia coli (STEC) is an important foodborne pathogen, and ruminants are recognized as the main natural reservoir. The purposes of this study were to detect E. coli O157 in bovine feces and surface water in a beef cattle farm of Gualeguaychú, Argentina; to characterize the isolates; and to establish the clonal relatedness by pulsed-field gel electrophoresis. Between September 2005 and November 2006, 288 samples of bovine feces and 79 samples of water troughs were studied. E. coli O157 was detected by immunomagnetic separation and polymerase chain reaction as screening techniques. The rfb(O157) gene was detected in 3.8% of the 288 fecal samples and in 17.7% of the 79 water samples. The stx gene was detected in all rfb(O157)-positive fecal samples and in 5.1% of water samples. Eleven E. coli O157 strains isolated from bovine fecal samples and eight from water samples were characterized. The most frequent stx genotype identified was stx(1) and stx(2c(vh-a)). Twelve (63.2%) strains harbored fliC(H7), eae, and ehxA genes. Using pulsed-field gel electrophoresis with the enzyme XbaI, a total of eight patterns with at least 72.1% similarity were identified among the 19 strains. The patterns of 15 strains were grouped into four clusters: two of them included only bovine strains and the other two only aquatic strains. No genetic correlation was established between the bovine and water STEC strains detected. The prevalence of STEC O157:H7 established in the herd studied was higher than that previously reported for Argentine grazed cattle.

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La carne de pescado es altamente perecedera y microbiológicamente sensible. Este trabajo tuvo como objetivo caracterizar la carne de boga (Leporinus obtusidens) y evaluar el efecto de impregnación a vacío con jugo de limón en sus características microbiológicas y fisicoquímicas. Se determinó humedad, proteínas, grasa, cenizas, pH y recuento de microorganismos indicadores en boga fresca. Los filetes fueron impregnados a vacío con jugo de limón durante 5, 10 y 15 minutos. Las muestras, fueron envasadas a vacío, almacenadas a 3 °C y se analizó variación de peso, pH, color superficial, índice de blancura (IB), nitrógeno básico volátil total (NBVT), recuentos de bacterias psicrótrofas y proteolíticas. La composición de la boga resultó similar a la informada por otros autores, los parámetros a* y b*, y el contenido de grasa fueron acordes a pescados grasos. Los recuentos de microorganismos indicadores resultaron aceptables, a excepción de las enterobacterias que se encontraron levemente aumentadas. La impregnación generó ganancia de peso, aumento de L* e IB, y disminución de pH y de bacterias psicrótrofas y proteolíticas. El NBVT disminuyó significativamente en la carne de boga impregnada por 15 minutos. Durante el almacenamiento, las muestras tratadas presentaron mayor pérdida de peso, en correspondencia con la ganancia generada por el tratamiento; se tornaron más claras; el NBVT se mantuvo constante y se redujeron las bacterias psicrótrofas y proteolíticas. La impregnación a vacío con jugo de limón resultó una tecnología viable para extender la vida útil de la carne de pescado refrigerada hasta cuatro días después del fileteado.

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