Resumo

Diarrheagenic Escherichia coli remains an important cause of diarrheal disease worldwide. In terms of global public health, enteropathogenic E. coli (EPEC) and Shiga toxin-producing E. coli (STEC) are the most important categories of diarrheagenic E. coli. EPEC is one of the main causes of infantile diarrhea in developing countries, while STEC is an important causative agent of hemorrhagic colitis (HC) and hemolytic–uremic syndrome (HUS). Several water-associated outbreaks caused by these pathogens are reported in the world. The aim of this work was to detect the presence of EPEC and STEC in E. coli strains isolated from drinking water sources in the northern Paraná State. A total of 200 strains of E. coli were isolated from drinking water during the period of February 2006 to December 2007. Of these, 180 strains were obtained from untreated water and 20 from treated water. All E. coli strains were screened for the presence of virulence markers stx1, stx2, eae and bfp by PCR.  The isolates positive for these virulence determinants were further tested for additional virulence factors (hlyA, saa, lpf, astA, cnf-1 and cnf-2), cytotoxicity in Vero cells, adherence to HEp-2 cells, expression of enterohemolysin on washed sheep blood agar plates and sensitivity to antimicrobials by the disk diffusion method. Two of the E. coli isolates were found to be positive for one of the investigated virulence genes (1,0%): one isolate was positive for stx2 gene and one for eae gene. None of the 200 isolates contained the stx1 or bfp genes. Strains identified as stx2+ and eae+ were classified as STEC and atypical EPEC, respectively. STEC strain also possessed hlyA, saa and lpf sequences, while atypical EPEC strain was not positive for any of the additional virulence factors tested. Only STEC strain showed cytotoxic effect in Vero cells and enterohemolysis on blood agar plates. With respect to adhesion in Hep-2 cells, atypical EPEC and STEC strains showed localized adhesion-like and non-characteristic adhesion in 6-h, respectively. Both strains were sensitive to all antibiotics tested. Thus, we can conclude that the presence of pathogenic strains of E. coli in drinking water can be considered a direct risk to public health. Moreover, studies of virulence factors in strains of E. coli isolated from drinking water are important in preventing outbreaks of waterborne infections.