Injured coliforms in swimming pools : How big a threat?

Background: A swimming pool is an important leisure facility, but it can harbor injured cells creating potential health hazards. Disinfection of swimming pools can cause bacterial injury, when cells are exposed to a suboptimal concentration of disinfectants. Possible pathogenic bacteria can enter into an injured state, for example, Escherichia coli, Klebsiella spp, and Enterococcus faecalis. Injured bacteria can retain their pathogenicity and virulence and they may recover causing diseases.
Aim: To assess the presence of injured coliforms in swimming pools based on differential plating media.
Materials and Methods: This study compared the difference in recovery of coliforms between two differential media, one designed for recovery of injured coliforms (HiCrome ECC selective agar and the other is CHROMagar ECC). A total of 120 samples were collected from 10 semi-public swimming pools with sporadic distribution around Alexandria, Egypt, and included in this study. Five pools were used for swim training, 4 were used for both training and recreational swimming and one was used for children only.
Results: The recovery medium (HiCrome ECC selective agar) detected 1.47 and 2.54 times total coliforms and E. coli, respectively, as CHROMagar ECC. The compliance of samples per fresh water swimming pool Egyptian standard in total coliforms and E. coli fell from 54.10% when examined by CHROMagar ECC medium to 35% by HiCrome ECC selective medium.
Conclusion: The current findings may not be universal to all swimming pools but may be applicable to ones where the physicochemical properties of their water induce coliform injury. Results suggest that the use of media that detect injured yet viable coliforms will give a more sensitive and representative guidance about the quality of examined water and will assist in the treatment and decontamination of swimming pools.