Isolation of Vero cytotoxin-producing Escherichia coli O157 from wild birds


Dr Joanne S. Wallace Department of Life Sciences, University of East London, Romford Road, London E15 4LZ, UK.


In a survey of wild birds (mainly gulls), 0·9% of the bacterial isolates from faecal samples at an urban landfill site and 2·9% of bacterial isolates from faecal samples on intertidal sediments in Morecambe Bay were Vero cytotoxin-producing Escherichia coli O157. Isolation procedures employing commonly used cultural methods were hindered by the selection of a large number of false positives. The only procedure which resulted in the isolation of E. coli O157 from bird faecal samples was : enrichment (18 h) in a selective tryptone soya broth followed by filtration using hydrophobic grid membranes and growth on Chromagar®O157. The majority of isolates selected as potential E. coli O157 by characteristic growth on Chromagar®O157 could be eliminated by subsequent growth on CT-SMAC or CR-SMAC. This second identification (characterization) stage reduced the number of potential E. coli O157 requiring further confirmation by typing methods (serotype and Vero cytotoxin) by more than 70%.