DETECTION OF ENTEROCOCCI WITH RIBOSOMAL-RNA-TARGETED DNA PROBES AND THEIR USE FOR HYGIENIC DRINKING-WATER CONTROL

Enterococci are useful indicators of faecal contamination with their h igh abundance in faeces and long survival in the environment and the p ossibility of indicating the source of contamination by species identi fication has lead to discussion of whether enterococci would be more r eliable faecal indicators than E. coli. In an attempt to facilitate ra pid and accurate identification of enterococci, 16S rRNA targeted olig onucleotide probes were designed by computer-aided analysis of more th an 4,000 rRNA sequences. Probes were labelled non-isotopically with di goxigenin and fluorescent dyes. Conditions for specific hybridisation were optimised for dot blot hybridisation and whole cell hybridisation for all probes. With a combination of two probes, all hygienically im portant enterococci could be detected and 24 biochemically identified environmental isolates also hybridised with one of these probes. A qua ntitative detection method with a high sensitivity was developed based on filtration of water samples through polycarbonate filters, a short incubation on agar and microcolony filter hybridisation with fluoresc ently labelled probes followed by epifluorescence microscopy. Within 8 -20h sampling a specific identification of enterococcal microcolonies was possible. With this method 15/32 well- and tap-water sources from the Mainz area were identified as being of substandard quality. The pr oposed method detects faecal contamination significantly earlier than conventional methods and could be helpful in the hygienic monitoring o f drinking water. (C) 1997 IAWQ. Published by Elsevier Science Ltd.