Rapid detection of Escherichia coli in water using a hand-held fluorescence detector

The quantification of pathogenic bacteria in an environmental or clinical sample commonly involves laboratory-based techniques and results are not obtained for 24–72 h after sampling. Enzymatic analysis of microbial activity in water and other environmental samples using fluorescent synthetic substrates are well-established and highly sensitive methods in addition to providing a measure of specificity towards indicative bacteria. The enzyme b-D-glucuronidase (GUD) is a specific marker for Escherichia coli and 4-methylumbelliferone-b-D-glucuronide (MUG) a sensitive substrate for determining the presence of E. coli in a sample. However, currently used procedures are laboratory-based and require bench-top fluorimeters for the measurement of fluorescence resulting from the enzyme–substrate reaction. Recent developments in electronic engineering have led to the miniaturisation of fluorescence detectors. We describe the use of a novel hand-held fluorimeter to directly analyse samples obtained from the River Thames for the presence of E. coli. The results obtained by the hand-held detector were compared with those obtained with an established fluorescent substrate assay and by quantifying microbial growth on a chromogenic medium. Both reference methods utilised filtration of water samples. The miniaturised fluorescence detector was used and incubation times reduced to 30 min making the detection system portable and rapid. The developed hand-held system reliably detected E. coli as low as 7 cfu/mL river water sample. Our study demonstrates that new handheld fluorescence measurement technology can be applied to the rapid and convenient detection of bacteria in environmental samples. This enables rapid monitoring to be carried out on-site. The technique described is generic and it may, therefore, be used in conjunction with different fluorescent substrates which allows the assessment of various target microorganisms in biological samples.