Evaluation of a novel autonomous detector for microbial water quality monitoring

Heather L Saffert, University of Rhode Island


Rapid testing methods are needed for monitoring waters for fecal contamination to identify associated health hazards. Today, standard methods quantify the amount of indicator bacteria, E. coli and enterococci, using culture-based techniques that require incubation periods from 18 to 48 hours. For recreational waters, this time lag delays the closure of waters when a potential health hazard exists and prolongs closures after contamination has dissipated. ^ A remotely deployable, autonomous sampler capable of rapid automated data analysis and reporting of fecal contamination would provide a more effective warning system for both managers and the public. An in situ instrument may also prove useful in locating pollution sources for remediation. As part of this dissertation, enzyme-substrate methods were found to be feasible with some limitations, supporting the development of a new instrument, the SubBio Analyzer (SubChem Systems Inc.). Bench-top prototypes were tested and evaluated in the laboratory. A portable field prototype that could be used on-site at a dock or a beach facility with a 120-v power supply has undergone preliminary testing. ^ Two commercial media test kits were used for analyses and assessed. Colilert-18, which tests for E. coli and total coliforms, is not practical because it requires that E. coli be positive for two enzymes, one of which (β-D-galactosidase) was found to be induced upon starvation. The enzyme-substrate targeting E. coli (β-D-glucuronidase), however, may be effective if used in a different, more selective media that minimizes interference by other organisms with β-D-glucuronidase activity. Enterolert, which tests for enterococci, has high background fluorescence that saturated the prototype instrument's optical detectors. To remove some of the fluorescent components prior to analysis, Enterolert was clarified with a solid phase extraction column. This process also removed some of the selective agents within the media, as false positives were evident in environmental and sewage samples. While supplementing the clarified Enterolert with antibiotics is possible, reformulating the media will provide a better long term solution. ^ Using the field prototype and clarified Enterolert to analyze cultured Enterococcus faecalis, the time to detection was decreased and exponentially correlated with the initial concentration of bacteria, with 106/ml E. faecalis detected < 1 hr and ∼2/ml in 12 hrs. While faster than traditional methods, the time to detection still takes > 6 hours for concentrations < 10,000 E. faecalis/100 ml. In the current configuration, the instrument could serve as a same-day warning system of very high enterococci levels. Concentrating a sample with a filter to increase the initial numbers of cells and reduce the detection is possible and beneficial; however, more research is needed to ensure that filtration does not affect the accuracy and precision of the test. ^

Subject Area

Biology, Microbiology|Biology, Oceanography|Environmental Sciences

Recommended Citation

Heather L Saffert, "Evaluation of a novel autonomous detector for microbial water quality monitoring" (2008). Dissertations and Master's Theses (Campus Access). Paper AAI3314448.