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.