OLIVERA nelda Lila
congresos y reuniones científicas
Occurrence of Shiga toxin-producing Escherichia coli in recreational waters of Sierra de la Ventana, Buenos Aires, Argentina.
Buenos Aires, Argentina
Simposio; 7th International Symposium on Shiga Toxin (Verocytotoxim)- Producing Escherichia coli Infections; 2009
Institución organizadora:
Asociación Argentina de Microbiología
Enterohemorrhagic Escherichia coli has emerged as a serious gastrointestinal pathogen. Although the predominant mode of transmission to humans is via contaminated meat or meat products, waterborne outbreaks associated with drinking water and recreational bathing waters contaminated with faeces have both been reported. Pathogenicity of Shiga toxin-producing Escherichia coli (STEC) is associated with various virulence factors. The ability of STEC strains to cause several diseases is related principally to the production of one or more Shiga toxins (Stx1, Stx2, and variants of Stx2), encoded by lysogenic bacteriophages. Sierra de la Ventana is a tourist and rural region 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. The region has many rivers and streams which are used for recreational purposes, especially bathing. The aim of this study was to investigate the occurrence of STEC strains in recreational waters of Sierra de la Ventana. Surface water samples were collected from 5 sites allocated by the authorities to recreational use: Parque Norte, Balneario Villa Ventana, La Hoya, El Dique and San Bernardo. The sampling activities were extended during 2007 and early 2008 to obtain samples under different seasonal conditions. Two hundred millilitres of each sample were filtered through 0.45 ¥ìm pore size sterile cellulose filter. In order to recover the injured cells, filters were put onto a plate with Plate Count Agar at 25¨¬C for 1 h. Then, two different protocols were performed to isolate E. coli O157:H7 and non O157. In the first protocol, the filters were incubated into 20 mL of modified EC broth amended with novobiocine at 41¨¬C for 18 h, thereafter Immunomagnetic separation (IMS) techniques with beds anti-E. coli were applied. The isolations were carried out on CHROMagarTM. In the second protocol, the enrichments were done in EC broth incubated at 44¨¬C for 18 h. The isolations were carried out on Mac Conkey Agar and Eosin Methylene-blue Lactose Sucrose Agar. The presumptive positive colonies were confirmed as E. coli by biochemical tests. The isolates characterized as E. coli, were subjected to DNA extraction and PCR amplification of stx1/stx2 genes. E. coli strains EDL933 (stx1, stx2) and E coli ATCC 25922 were used as positive and negative controls, respectively. No E. coli O157:H7 was detected by IMS. None of the E. coli isolates considered as non O157 amplified stx1 gene, while stx2 gene was detected in 3 strains. Such strains came from El Dique, Parque Norte and Villa Ventana, which have a high attendance of public in summer. These preliminary results emphasize the importance to continue investigating the occurrence of STEC strains and the risks of their presence in these environments. Further studies are being conducted to detect other virulence factors and to maintain a monitor programme in the region.