Strategies for recovering of planktonic and sessile cells of Escherichia coli O157:H7 from freshwater environment.

The experiments were performed with Escherichia coli O157:H7 EDL 933 in freshwater microcosms at 12 °C. At 35, 45, and 70 days, samples were taken and filtered through 0.45 µm membrane filters. The following alternatives were tested to evaluate the recovery percentage of injured cells: (1) selective media CHROMagar(™)O157 and chromID(™)O157:H7 agar, at 37 °C for 24 h; (2) tryptic soy agar supplemented with yeast extract (TSAE), incubated at 25 °C for 2 or 4 h, then transferred to CHROMagar(™)O157 or chromID(™)O157:H7 agar at 37 °C (TSAE2h-CHROM, TSAE4h-CHROM and TSAE2h-ID, TSAE4h-ID); (3) thin agar layer (TAL) method, TSAE was overlaid on CHROMagar(™)O157 or chromID(™)O157:H7 agar (TALCHROM and TALID, respectively) and incubated at 37 °C for 24 h; and (4) TALCHROM at 25 °C for 4 h, then continued up to complete 24 h at 37 °C (TALCHROM4h). Furthermore, the recovery of E. coli O157:H7 cells adhering to glass coverslips were evaluated to mimic biofilm conditions. The recovery percentages obtained from each alternative were calculated relative to TSAE counts. After 70 days, TSAE4h-CHROM and TALCHROM4h showed the highest recovery percentage (>90 %) from water microcosms. Despite the improved recovery of cell adhering to glass surfaces, the percentages obtained with TSAE4h-CHROM were low. Further studies for the recovery of biofilm-forming E. coli O157:H7 are required. Pre-incubation on TSAE at 25 °C for 4 h, combined with CHROMagar(™)O157, or by thin agar layer method (TALCHROM) enhanced significantly the recovery of viable cells of E. coli O157:H7 after prolonged stay in water microcosms.

The occurrence of Shiga toxin-producing Escherichia coli in bathing water of the Sierra de la Ventana region, Buenos Aires Province, Argentina.

The region of Sierra de la Ventana is located in the southwest of Buenos Aires Province, Argentina. Traditionally, this area has been devoted to livestock and agriculture, but tourism has had a significant development in recent years. In the region, there are many rivers and streams that are used for swimming and bathing. A survey of the occurrence of Shiga toxin-producing Escherichia coli (STEC) in these waters was conducted, and the microbiological quality of rivers and streams was investigated. No E. coli O157 was recovered by immunomagnetic separation. Nevertheless, the Shiga toxin gene, exclusively stx2 genotype, was detected in four non-O157 E. coli strains. Two STEC strains carried eae factor, but none of them harbored the EHEC-hlyA gene. Three of the STEC isolates belonged to samples obtained in the warm months, and one to the winter sampling. In the sample sites where STEC strains were isolated the counts of E. coli/100 ml exceeded or were close to the limit recommended by the United States Environmental Protection Agency for bathing water. The relationship observed between the rainy season and E. coli counts suggests that among the main causes for the hygienic indicator increase is the runoff of manure deposited on soils that may also induce the entrance of pathogens into the aquatic environment. This research, the first reporting STEC isolation from recreational waters in this area, revealed that streams and rivers from a beef-producing area of Argentina are a reservoir of STEC strains.