Salmonella: The forgotten pathogen

Bathing water quality is an important indicator of environmental quality. Surface waters and reservoirs are vulnerable to pollution due to industrial, urban and agricultural effluents discharges which often contain a mixture of non-pathogenic and pathogenic bacteria that have been shown to be the cause of several human minor morbidity diseases. To comply with the 1976 European Bathing Water Directive, 80% of samples taken during the bathing season must meet the quality standards for the faecal indicators (which are given in the paper), and Salmonella must be absent in 1 litre and enterovirus absent from 10 litres.

Salmonella spp. is a common and expansively distributed pathogenic microorganism, and is often the recorded cause of gastroenteritis in humans; with some serotypes leading to worse illnesses such as typhoid and paratyphoid fevers.

The aim of the investigation was to assess any possible associations between the pervasiveness of Salmonella spp. and the levels of indicator microorganisms established by the new EU Directive, to assess the importance for public health of the analysis of this specific pathogen in bathing waters. The authors compared the conventional method of testing to a rapid and automated immunoassay; this detects Oxygen and Hydrogen antigens, using the Enzyme Linked Fluorescent Assay method, which is able to detect motile and non-motile strains in 45 minutes after pre-enrichment (a much cheaper and less time consuming detection of Salmonella).

Water samples for analysis were taken from 62 points: 45 coastal waters, three transitional waters and 14 inland waters in the north of Portugal; and 36 monitoring points: 26 coastal waters and 10 transitional and inland waters were analysed for the concentration of indicator microorganisms, during the bathing seasons 2005-2008.

The samples were collected from approximately 30cm below the water at chest level (typically around 1.2-1.5m) and processed within 4-6 hours of collection. A total of 540 samples were analysed.

The analysis for Salmonella spp. was qualitative. The methods are given in the paper, but briefly, the cultural pre-enrichment and enrichment protocol, plating on selective agars and preliminary confirmation.

A total of 125 out of the 540 samples tested positive for the presence of Salmonella spp.; 35 serotypes of Salmonella spp. were identified; 18 recovered from sea water, 23 from rivers and six from transitional waters. The most frequent serotype in rivers was S. enteritidis found in 20%, and the most common in marine waters was S. typhimurium found in 15.6%.

Despite the improved control over bathing water quality, the results given in the paper seem to suggest that two microbiological indicators are insufficient to protect the health of bathers, as there is no unambiguous relationship between the presence of these indicators and the presence of pathogenic microorganisms in the water.

This study emphasizes the importance of public health in the assessment of bathing water quality, suggesting routine sampling should be carefully applied, defining health hazard indicators and employing strategies on a beach-to-beach basis, that strengthen public health inspection systems and information, in order to enhance health prevention.

Mansilha, C. R., Coelho, C. A., Reinas, A., Moutinho, A., Ferreira, S., Pizarro, C., & Tavares, A., 2010. Salmonella: The forgotten pathogen: Health hazards of compliance with European Bathing Water Legislation. Marine Pollution Bulletin. 60 (6): 819-826.