Monitoring faecal contamination of the Thames estuary using a semiautomated early warning system.

The Colifast Early Warning System, based on measuring beta-galactosidase activity (2 h method), was evaluated for monitoring the level of faecal contamination in the upper tidal Thames. Two trials were performed, one following heavy rain in November 2000, the next during a dry and sunny period in July 2001. In general the beta-galactosidase activity and the two coliform reference methods (recovery following membrane filtration with membrane lauryl sulphate broth (MLSB) and Colilert Quantitray) were comparable. However, in several samples in July the beta-galactosidase activity seemed to overestimate the number of culturable coliforms, suggesting that the rapid enzymatic method detected beta-galactosidase produced by other bacterial sources, such as Aeromonas spp. or Vibrio spp., or nonculturable coliforms. The later could be attributed to sunlight-induced injury. Nevertheless, the rapid method based on beta-galactosidase activity gave an estimate of the level of culturable coliforms, which did not differ from both coliform reference methods by more than one log. Monitoring of beta-galactosidase activity in river water samples using the Colifast Analyser may therefore be useful as an early warning indicator of faecal contamination.

Early warning of faecal contamination of water: a dual mode, automated system for high- (< 1 hour) and low-levels (6-11 hours).

There is a recognised need for methods that permit rapid estimation of the sanitary quality of water e.g. during raw water monitoring and emergencies involving water treatment failure or main breaks in a distribution network. In this study, two models for predicting the level of faecal contamination of water were studied. The first format, based on measurement of beta-galactosidase activity by the automated Colifast analyser, detected faecal contamination of high levels, corresponding to > 15 thermotolerant coliforms (FC)/5 mL, in 1-3 h, in a format that allowed for semi-quantification of results. By setting up a cut-off level, the system could be used as an operational tool identifying random increases in faecal contamination during routine raw water monitoring. A second Presence-Absence format was dependent upon the growth of low levels of FC with subsequent detection in the Colifast analyser. 95% of water samples containing 1-15 FC/sample volume showed positive detection after 11 h.

Effect of u.v. light irradiation, starvation and heat on Escherichia coli beta-D-galactosidase activity and other potential viability parameters.

The effect of u.v. light irradiation and two other types of stress (heat and starvation) on cellular functions of Escherichia coli have been studied. The severe reduction of the culturable cell number (cfu) and the direct viable count (DVC) after exposure to moderate u.v. light doses (48 mWs cm-2), was not reflected by the dehydrogenase activity (5-cyano-2,3-ditolyl tetrazolium chloride (CTC)-positive cells), the membrane integrity (SYTOX Green-negative cells), the membrane potential (bis-(1,3-dibutylbarbituric acid) trimethine oxonol (DiBAC4[3]) (OXONOL)-negative cells), and the beta-D-galactosidase activity. All parameters were affected by high u.v. light doses. Cellular activities (CTC, SYTOX, OXONOL, beta-D-galactosidase activity) were intact in non-culturable cells with presumably severe damage to DNA, and the activities seemed not to be appropriate for detection of viable E. coli after u.v. light irradiation. Heating for 20-30 min at 63 degrees C was required to cause a severe loss of the beta-D-galactosidase activity and the numbers of CTC-positive, SYTOX Green-negative or OXONOL-negative cells. A large portion (> or = 38%) of pre-irradiated (190 mWs cm-2) cells maintained their ability to reduce CTC and exclude SYTOX Green and OXONOL after 51 d of starvation (dark, 7 degrees C) in phosphate-buffered saline.

Effect of chlorination on beta-D-galactosidase activity of sewage bacteria and Escherichia coli.

The effect of chlorine on beta-D-galactosidase activity of sewage bacteria and Escherichia coli was studied. beta-D-galactosidase activity of sewage was more resistant to chlorine than faecal coliform cultivability. At low initial dosage (0.05 mg Cl2 l-1) neither cultivability (colony-forming units (cfu)), nor enzyme activity of E. coli suspensions were severely impaired. When initial chlorine concentration was increased to 0.1 mg Cl2 l-1, the cfu number decreased whereas enzyme activity remained high, i.e. the enzyme activity calculated cfu-1 increased. At higher chlorine doses both cfu and enzyme activity were reduced, but non-cultivable cells retained assayable activity after chlorination. Mean values of the enzyme activity calculated cfu-1 decreased when the chlorine dosage was increased from 0.1 to 0.5 mg Cl2 l-1, but were not significantly different (P > 0.05) for dosages of 0.2-0.7 mg Cl2 l-1. After chlorination, beta-D-galactosidase activity of E. coli was less reduced than cfu and direct viable count numbers, but more reduced than 5-cyano-2-3, ditolyl tetrazolium chloride and total cell counts, and the enzyme activity represented an alternative activity parameter of chlorinated samples.

Enzyme characteristics of beta-D-galactosidase- and beta-D-glucuronidase-positive bacteria and their interference in rapid methods for detection of waterborne coliforms and Escherichia coli.

Bacteria which were beta-D-galactosidase and beta-D-glucuronidase positive or expressed only one of these enzymes were isolated from environmental water samples. The enzymatic activity of these bacteria was measured in 25-min assays by using the fluorogenic substrates 4-methylumbelliferyl-beta-D-galactoside and 4-methylumbelliferyl-beta-D-glucuronide. The enzyme activity, enzyme induction, and enzyme temperature characteristics of target and nontarget bacteria in assays aimed at detecting coliform bacteria and Escherichia coli were investigated. The potential interference of false-positive bacteria was evaluated. Several of the beta-D-galactosidase-positive nontarget bacteria but none of the beta-D-glucuronidase-positive nontarget bacteria contained unstable enzyme at 44.5 degrees C. The activity of target bacteria was highly inducible. Nontarget bacteria were induced much less or were not induced by the inducers used. The results revealed large variations in the enzyme levels of different beta-D-galactosidase- and beta-D-glucuronidase-positive bacteria. The induced and noninduced beta-D-glucuronidase activities of Bacillus spp. and Aerococcus viridans were approximately the same as the activities of induced E. coli. Except for some isolates identified as Aeromonas spp., all of the induced and noninduced beta-D-galactosidase-positive, noncoliform isolates exhibited at least 2 log units less mean beta-D-galactosidase activity than induced E. coli. The noncoliform bacteria must be present in correspondingly higher concentrations than those of target bacteria to interfere in the rapid assay for detection of coliform bacteria.