Escherichia coli in marine water: Comparison of methods for the assessment of recreational bathing water samples

•477 seawater samples were examined for E. coli presence using reference method and six alternative methods•The temperature modified ISO 9308-1 (44 °C) seems to be a suitable method for marine bathing water quality assessment•Previously used TSA/TBA media possibly overestimate the E. coli count•Colilert-18 in marine water results inconclusive, hence need exists to expand research to diverse geographical locations•In order to improve health protection, application of rapid method is required

Bathing Water Directive (2006/7/EC) specifies two reference methods for Escherichia coli detection: ISO 9308-1 and 9308-3. The revised ISO 9308-1 is recommended only for waters with a low bacterial background flora. Considering the extended time needed for analysis and, generally, the lack of experience in using ISO 9308-3 in the Mediterranean, the suitability of ISO 9308-1 for the examination of E. coli in bathing water was evaluated. The present study was aimed at a comparison of data obtained by the reference method in seawater samples (110 beaches, N = 477) with data received from six alternative methods. Results show that recently used TSA/TBA method may overestimate E. coli numbers in marine waters. The temperature modified ISO 9308-1 (44 °C) did not significantly alter the results, but outperformed the antibiotic supplemented agar at reducing non-E. coli bacteria on the plates, allowing the use of the respective method for monitoring coastal water.