Use of the indirect immunofluorescence method for detection and enumeration of Escherichia coli in seawater samples

Development of a fluorescent antibody method for the detection of Enterococcus faecium and its potential for coastal aquatic environment monitoring

A direct, microscopic fluorescent antibody method was developed to detect the occurrence of Enterococcus faecium in coastal aquatic environments and was compared with the conventional membrane filtering method. The "in situ" application of the antibody-based protocol in the analysis of water samples collected from coastal polyhaline habitats demonstrated good sensitivity and ease of implementation. Data obtained with the microscopic technique were in agreement with those obtained from culture counts. The fluorescent antibody method proved to be a rapid and reliable technique for the detection of E. faecium. The advantages and limitations intrinsic to the method are discussed, highlighting the potential of this new technique for monitoring coastal aquatic environments.

Combined fluorescent antibody assay and viability staining for the assessment of the physiological states of Escherichia coli in seawaters

AIMS

A comparison of methods that combine the use of immune sera with specific fluorescent probes for testing viability at single cell level was performed in order to estimate different living attributes of Escherichia coli in natural seawater samples.

METHODS AND RESULTS

Cell culturability was assayed by plate method, respiratory activity and membrane integrity were determined by an indirect fluorescent antibody assay, combined with 5-cyano-2, 3 ditolyl tetrazolium chloride and propidium iodide, respectively. Results showed the coexistence of different physiological states within the E. coli population, of which a large fraction (46%) of cells was actively respiring.

CONCLUSIONS

The methodological approach used offer interesting perspectives in water pollution monitoring, particularly when the differentiation between dead and living E. coli cells is required for a more precise assessment of the bacteriological quality of seawaters.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study suggests the importance of knowledge of the viability status of faecal bacteria in aquatic environments as a fundamental issue for the preservation of public health; the availability of rapid analytical procedures for this purpose may find significant applications in the evaluation of the sanitary risk consequent to water use.

Immunofluorescence detection of Escherichia coli in seawater: a comparison of various commercial antisera

Through a microscopical method, relying on the interaction between fluorescent antibodies and target antigen, it is possible to detect and enumerate Escherichia coli in seawaters. Various commercial monoclonal and polyclonal antisera have been tested in an indirect immunofluorescence (IIF) assay developed for microbiological monitoring of coastal waters. Prior to use, they have been titrated and screened for cross-reactions with a collection of clinical and environmental isolates. A comparison among counts obtained on field samples showed higher performance for microscopical than for plate methods, due to the ability of all antisera to label target cells specifically, regardless of their viability. Because of their different specificities, polyclonal antisera yielded better quantitative results than monoclonal antisera. The study further suggested the usefulness of the immunofluorescence assay as a rapid alternative analytical tool for the specific detection of bacterial pathogens in aquatic environments.

Development of an enzyme assay for rapid assessment of Escherichia coli in seawaters

AIMS

An analytical protocol has been developed and applied for the detection of glucuronidase activity in marine waters as a rapid alternative approach to assess the microbiological quality of seawaters.

METHODS AND RESULTS

The fluorogenic substrate 4-methylumbelliferyl-beta-D-glucuronide is cleaved to a fluorescent product, methylumbelliferone, by the enzyme beta-glucuronidase, specific to Escherichia coli and closely related enterobacterial species (Shigella). The results suggest that this test is related to E. coli numbers, as estimated by immunofluorescence, more significantly than to faecal coliform numbers, obtained from culture media.

CONCLUSIONS

The determination of the potential rate of glucuronidase activity may be used as a diagnostic tool for the indirect estimation of the presence of E. coli in seawaters.

SIGNIFICANCE AND IMPACT OF THE STUDY

The method may be particularly useful in the early warning of seawater pollution, allowing the screening of coastal areas with different contamination levels in reduced time.