Prediction of Salmonella in seawater by total and faecal coliforms and enterococci

Microbial quality of marine bathing water in terms of public health has been concern for the general public for years. There as several directives for different countries to follow in order to monitor the microbial quality bathing water. The main directives include the European Union (EU) Framework Directive (2000) and the US Environmental Protection Agency (USEPA) Water Quality Guidelines. Indicator organisms are currently used to detect microorganism in bathing water rather than the direct detection of waterborne pathogens as this proved to be too expensive and time-consuming. The microorganisms used presently as faecal indicators include Enterococci and Escherichia coli. Enterococci have been found by major epidemiological studies to relate best to adverse health effects to bathers.

A large proportion of gastrointestinal symptoms occurring in the general population after contact with contaminated bathing water are due to Salmonella infection. However it has been found that faecal indicators in marine water have a low predictive capability for the presence of Enteroviruses, for example Salmonella.

This study looks at the ability of enterococci to predict the presence of Salmonella spp. better than total or faecal coliforms and that indicator bacteria limits set by the USEPA and the EU are satisfactory in excluding Salmonella from marine bathing water.

Samples were obtained, over a 24 month period, from 9 sites along the coast south of Athens, Greece. Three sampling sites were affected by sewage outlets and the other 6 were close to the mouth of a polluted small river. Total coliforms, faecal coliforms and Enterococci were enumerated by membrane. Total coliforms were then enumerated on Membrane Lauryl Sulphate Agar, mFC Broth Base plus agar was used for faecal coliforms. Finally enterococci were measured on Slanetz and Bartley medium. Salmonella detection was qualitative according to the World Health Organisation method (I can give you more details if you are interested).

The results show that 33 out of 240 samples were positive for Salmonella. Total coliforms were isolated from 209 samples, faecal coliforms from 192 and enterococci from 234. A statistical increase in frequency of Salmonella isolation was observed in an increase in densities of each of the 3 indicator bacteria. The percentage of Salmonella isolations depended on statistically significant increase on each indicator organism separately. The statistics used showed when TC or FC were used for Salmonella prediction in logistic regression, the addition of another indicator did not have a statistically significant effect. When enterococci were used for prediction, then the addition of one or two other indicators led to a statistically significant improvement.

Overall, this study shows that the presence of Salmonella can be predicted using total or faecal coliforms alone. Also Enterococci can be used to discriminate between the presence and absence of Salmonella. This can be statistically significantly improved by also looking at total or faecal coliforms.  The US EPA Water Quality Guidelines and the EU Framework Directive are suitable to find out if Salmonella is present in bathing water. If Salmonella is found to be present then total or faecal coliforms could be used to identify it more accurately. I think that this paper is significant as it backs up previous studies that have looked at the capability of faecal indicators to predict the presence of Salmonella. Salmonella can be a big health threat and so this study is important to the health of the general public.

Maria A. Efstratiou, Athena Mavridou, Clive Richardson. Marine Pollution Bulletin. Volume 58, Issue 2, February 2009, Pages 201–205.

http://www.sciencedirect.com/science/article/pii/S0025326X08004906