The occurrence of E-coli O157 : H7 in South African water sources intendedfor direct and indirect human consumption

The occurrence of Escherichia coli O157:H7 in selected water samples in Sou th Africa was investigated. The chromogenic Rainbow(TM) agar O157 medium de signed for the rapid identification of E. coli O157:H7 was used for the det ection of these organisms in various river-water samples in the Vaal Barrag e Reservoir drainage basin of South Africa. A total of 204 samples were obt ained from 15 sites where water was used for direct and indirect human cons umption. Samples were filtered through Gelman filter-units and incubated on Rainbow(TM) agar O157 which produced different colours according to the ba cterial chromogenic properties. Six hundred and sixty-three suspected E. co li O157:H7 colonies, with colours ranging between dark blue, grey and black , were subcultured onto sorbitol-MacConkey agar and screened for different virulence factors specific for E. coli O157:H7 and agglutination with anti- E. coh O157 antiserum. The results indicated that none of the suspected col onies contained all of the virulence factors necessary to classify them as E. coli O157:H7. None of these organisms agglutinated with antisera against E. coli O157. The probability of being infected with E. coli O157:H7 from direct or indirect consumption of these river water sources is therefore lo w. Some samples did, however, contain enterohaemorrhagic E. coli virulence properties, such as Stx1, Stx2 and enterohaemolysin, which might impose a h ealth risk if ingested. (C) 2001 Elsevier Science Ltd. All rights reserved.