Biotyping as a method of screening for enterotoxigenic Escherichia coli

A scheme of biotyping described originally for E. coli isolated from urine was used to investigate enterotoxigenic (ETEC) and non-enterotoxigenic (non-ETEC) fecal E. coli. Primary biotype was determined by fermentation of raffinose, sorbose and dulcitol and decarboxylation of ornithine. Failure to ferment sorbose correlated best with enterotoxicity; 95.5% of ETEC and less than 40% of non-ETEC did not ferment sorbose. The sensitivity compares favourably with reported results of the use of polyvalent antisera for recognition of serotypes associated with ETEC, although specificity was lower using biotyping. Strains included in our study were mainly from Australia, New Zealand or Indonesia and we do not know if our observations apply to E. coli isolated elsewhere. If failure to ferment sorbose proved to be a characteristic of most ETEC, this reaction offers the possibility of developing selective media to increase the yield of ETEC from primary plates for laboratories in which gene probe techniques for recognition of ETEC are not available.