Rapid enumeration ofEscherichia coliin marine bathing waters: potential interference of nontarget bacteria

Abstract

Aims: To compare the Escherichia coli quantification given by the ‘Coliplage®’ assay, based on the direct measurement of the β‐d‐glucuronidase (GLUase) activity and the reference Most Probable Number (MPN) method from seawater sites and investigate the possible interference of non‐E. coli strains in the GLUase activity measurement. Methods and Results: Comparison performed from 69 French coastal bathing sites (1401 samples) showed nonconcordance between both methods, only for 8% of samples. Non‐E. coli 4‐methylumbelliferyl‐β‐d‐glucuronide (MUG+) were isolated from nonconcordant samples. Phylogenetic analysis showed that Gammaproteobacteria were dominants and mainly represented by Vibrio species, which displayed GLUase activities on the same order of magnitude and sometimes much higher as E. coli reference strains. Conclusions: The‘Coliplage®’ assay is a rapid method for the quantification of E. coli showed few discordances with the standard MPN method. Some Vibrio species could interfere on the direct GLUase activity measurement of E. coli. Significance and Impact of the Study: Data present the first qualitative investigation on disagreement between Coliplage® and the MPN results. If the interference of Vibrio species is confirmed in situ, appropriate treatments should be developed to remove the interfering signal.

ColiSense, today's sample today: A rapid on-site detection of β-d-Glucuronidase activity in surface water as a surrogate for E. coli

“…β-D-Galactosidase (GAL) and β-D-Glucuronidase (GUS) have been used as marker enzymes in assays for E. coli [7][8][9][10][11][12][13] while Glucosidase has been used in assays for Enterococci. Of these target enzymes GUS is the most specific, being present in 94-97% of E. coli strains tested [9,14].…”

“…However certain species e.g, A. viridans, Bacillus spp [22] and Vibrio harveyi (particularly in the marine environment) [8] are highly GUS positive and may interfere with an assay if present at similar numbers to the target bacteria. Further interferences can occur from chemicals in the water matrix [23].…”

“…As a consequence 4-MethylUmbelliferyl-β-D-Glucuronide (4-MUG) has been used extensively in discontinuous assays. Its fluorophore 4-Methyl-Umbellierone (4-MU) has a pKa of 7.8 and is highly fluorescent at pH values over 9 [8,9,13]. Recent work in our research group [24] demonstrates the use of 6-Chloro-4-Methyl-Umbelliferyl-β-D-Glucuronide (6CMUG) for continuous GUS assays with greatly reduced sample handling.…”

“…Instrumental detection of hydrolysis products of assays has commonly been conducted using standard laboratory bench fluorimeters [8,16]. There have been a few attempts to conduct analysis on-site with portable fluorimeters [26,27], but there remains a need for a rapid, sensitive on-site test for FI bacteria.…”

Monitoring of β-d-Galactosidase Activity as a Surrogate Parameter for Rapid Detection of Sewage Contamination in Urban Recreational Water

“…Several studies have shown quite a good correlation between GAL activity or GLU activity and fecal indicator bacteria in water samples, but some studies have shown no or low correlation, in particular at low levels of fecal contamination [11,12,[23][24][25][26]. The present study also indicated a low correlation between GAL activity and E. coli in coastal water at levels <1000 E. coli per 100 mL, but too few samples were included to determine a potential relationship.…”