Identification of coliform genera recovered from water using different technologies

Methods for the detection of coliforms in water have changed significantly in recent years with procedures incorporating substrates for the detection of beta-d-galactosidase becoming more widely used. This study was undertaken to determine the range of coliform genera detected with methods that rely on lactose fermentation and compare them to those recovered using methods based upon beta-d-galactosidase.

Coliform isolates were recovered from sewage-polluted water using m-endo, membrane lauryl sulfate broth, tergitol TTC agar, Colilert-18, ChromoCult and ColiScan for primary isolation. Organisms were grouped according to whether they had been isolated based upon lactose fermentation or beta-d-galactosidase production.

A wide range of coliform genera were detected using both types of methods. There was considerable overlap between the two groups, and whilst differences were seen between the genera isolated with the two method types, no clear pattern emerged. Substantial numbers of 'new' coliforms (e.g. Raoutella spp.) were recovered using both types of methods.

The results presented here confirm that both methods based on lactose fermentation or detection of beta-d-galactosidase activity recover a range of coliform organisms. Any suggestion that only methods which are based upon fermentation of lactose recover organisms of public health or regulatory significance cannot be substantiated. Furthermore, the higher recovery of coliform organisms from sewage-polluted water using methods utilizing beta-d-galactosidase-based methods does not appear to be because of the recovery of substantially more 'new' coliforms.