Science Inventory

Categorical performance characteristics of method ISO 7899-2 and indicator value of intestinal enterococci for bathing water quality monitoring

Citation:

Tiwari, A., A. Hokajärvi, J. Santodomingo, A. Kauppinen, M. Elk, H. Ryu, J. Balamuralikrishna, AND T. Pitkänen. Categorical performance characteristics of method ISO 7899-2 and indicator value of intestinal enterococci for bathing water quality monitoring. JOURNAL OF WATER AND HEALTH. IWA Publishing, London, Uk, 16(5):711-723, (2018). https://doi.org/10.2166/wh.2018.293

Impact/Purpose:

In this study a method was evaluated for the ability to isolate enterococci and other fecal bacteria from environmental samples. The identity of the presumptive enterococci isolates was assessed using DNA sequencing

Description:

Intestinal enterococci are enumerated from bathing water in the European Union Member States by using the standard method ISO 7899-2 (2000). The objective of the study was to evaluate the performance characteristics of the ISO 7899-2 method with 21 water samples collected from three inland and two coastal bathing areas in Finland and to confirm the identity of cultured isolates. Additionally, we identified potential sources of fecal pollution and sought the presence human pathogens. The national water quality standards for a single sample were exceeded in five coastal bathing water samples for intestinal enterococci and in three samples for E. coli. A total of 341 bacterial isolates grown on Slanetz and Bartley (S&B) medium were selected for further analysis, and 63.6 % of the isolates were confirmed as intestinal enterococci on bile aesculin agar (BEA). The phylogenetic analysis of the partial 16S rRNA gene sequences showed that the clades of Enterococcus faecium and E. faecalis accounted for 93.1% of the confirmed isolates. Based on the sequence analysis, the range of the false positive and false negative rate of the ISO 7899-2 method was 0.0-18.5% and 5.6-57.1%, respectively, being affected by the presumptive colony count on the membrane. Our observations show that the actual intestinal enterococci count can be overestimated when the colony count is less than 10 colony forming units per membrane and underestimated when the presumptive colony count exceeds 100 colony forming units per membrane. The gull-specific sources were detected in all studied bathing areas while human-specific sources were detected in the two inland areas. Adenoviruses were present in all inland sites and Campylobacter spp. was detected in 83% of the studied samples. Based on our results, the analysis of multiple sample volumes is proposed to reach 10-100 colonies per membrane when 47mm diameter membranes are used. However, the intestinal enterococci count alone proved to be insufficient for water quality assessments as the presence of fecal pathogens was observed in some inland samples when intestinal enterococci counts were low.