Immunomagnetic separation of Escherichia coli O157:H7 from environmental and wastewater in South Africa

Recreational and drinking water supplies polluted with sewage have become an important source of E. coli O157:H7 infection. Immunomagnetic separation (IMS) has been extensively used for the isolation of E. coli O157:H7 from food and stool samples but not for samples such as wastewater. In this study the IMS method was used in combination with the E. coli O157:H7 selective media, immunoassays, biochemical tests and FUR, to, assess the prevalence of E. coli O157:117 in selected sewage and environmental water in South Africa. Environmental and wastewater were seeded with E. coli O157:H7 to determine the sensitivity selectivity of the enrichment-IMS-selective agar method. Naturally occurring E coli O157:H7 organisms were recovered from selected samples by means of IMS. The IMS concentrates were plated on three selective E coli O157:117 media. E coli O157:147 was detected in seeded sewage and river, water samples with numbers as low as 1.2 cfu.ml(-1). The IMS procedure was used to investigate the prevalence of E coli O157:H7 in randomly selected sewage and river water samples in South Africa. A total of 91 sewage and 40 river water samples were tested and 17.6%,and 20% yielded,suspected E,coli O157:H7 colonies on CT-SMAC agar medium respectively. PCR was used to confirm the presence of gene s, coding for Shiga toxin-1 (Stx1), Shiga toxin-2 (Stx2), enterocyte attaching and effacing genes (eaeA) and enterohaemolysin( hly). Standard immunoassay kits specific for the O157 and H7 antigen and a biochemical indole test Were used for further E coli O157:H7 confirmation. Three colonies from one sewage samples (1.1% of all sewage samples) agglutinated with anti-E. coli O157 and H7,antiserum and contained the genes coding for Stx2, eaeA and hly. None of the colonies isolated from the,river water samples were positive for E. coli O157:H7. CT-SMAC proved :to have limited E coli O157:H7 selective capabilities from, samples such as sewage with high bacterial counts. Seeded sample experiments indicated that IMS is a suitable method for isolating E., coli O157:H7 from samples with high bacterial interference and low numbers of E coli O157:H7. Evidence has been presented that the enrichment-IMS-selective agar procedure substantially increased the sensitivity of E coli O157:H7 isolation, compared, to direct-plating of test samples onto selective agar generally practised in the past.