Detection of viable but nonculturable Escherichia coli O157:H7 bacteria in drinking water and river water.

A sensitive method for specific detection of viable Escherichia coli O157:H7 cells, including viable but nonculturable (VBNC) cells, in water samples was developed. This method involved capture of the bacterial cells on a low-protein-binding membrane and direct extraction and purification of RNA followed by reverse transcription-PCR and electronic microarray detection of the rfbE and fliC genes of E. coli O157:H7. It detected as few as 1 CFU of E. coli O157:H7 in diluted cultures, 3 to 4 CFU/liter in tap water, 7 CFU/liter in river water, and 50 VBNC cells in 1 liter of river water, demonstrating the best limit of detection reported to date for VBNC cells in environmental water samples.