Aim: To determine the occurrence and characteristics of Shiga toxinproducing Escherichia coli (STEC) in drinking water supplies treated and untreated. Methods and Results: Drinking water samples (n = 1850) were collected from 41 municipalities in the north of Paran a State between February 2005 and January 2006. Escherichia coli isolates (n = 300) were recovered from water and investigated for the presence of virulence markers related to STEC by PCR. STEC isolates recovered were then characterized for both phenotypic and genotypic traits. A total of 12 isolates (11 from untreated water and one from treated water) were positive for stx, including five positive for both stx1 and stx2, two positive for stx1 and five positive for stx2. None of the STEC isolates contained eae, but other virulence genes were observed such as ehxA (100%), saa (100%), lpfA O113 (75%), iha (42%), subAB (25%) and cdtV (8%). Multidrug resistance was identified in 25% of the STEC isolates. The 12 STEC isolates belonged to seven distinct serotypes and pulsed-field gel electrophoresis typing revealed the presence of two clusters and two clones in this region. Conclusion: Drinking water, especially from untreated water supplies, can be source of STEC strains potentially pathogenic for humans. Significance and Impact of the Study: The investigation of the drinking water supplies for pathogenic E. coli, as STEC, may be useful to prevent waterborne outbreaks.

Aims:  The objective of the study was to determine the microbiological quality of samples of water and dialysate in a haemodialysis unit. Methods and Results:  Seventy‐two samples each of water and dialysate were collected during November 2003 to April 2004. The following microbiological analyses were performed: test for total and faecal coliforms, which produced negative results for all the samples; counts of total heterotrophic bacteria, where three samples of water and two of dialysate showed levels higher than those permitted by national standards; and endotoxin assay, which revealed high quantities only in samples of water that preceded reverse osmosis. Nonfermenting Gram‐negative bacteria were identified in 54 samples of dialysate and in 26 samples of water. The test for adhesion to an inert surface showed that various bacteria were capable of forming biofilms. Twenty‐seven per cent of the bacteria were resistant to sodium hypochlorite at 500 ppm for 10‐min contact time. Sixty per cent of the isolates were resistant to three or more antibiotics. Conclusions:  Water and dialysate can be a source of infection for patients who need haemodialysis. Significance and Impact of the Study:  An adequate system for water treatment, disinfection of the haemodialysis system and microbiological monitoring of the water and dialysate are necessary to reduce bacteraemia and pyrogenia outbreaks.