Studies of aquatic micro-organisms in domestic swimming pools

Abstract

Microbial attachment and proliferation on a surface leads to the formation of a structure known as a biofllm. In this thesis attention is directed towards the attachment of microorganisms to submerged surfaces in private swimming pools
Samples were taken from two private swimming pools located in West Lancashire, England. The planktonic phase of the water was sampled using a standard fluid grab technique and the submerged surfaces (e.g. the pool lining, the steps and the water recirculation trap) were sampled using swabs and a scalpel blade to scrape the surface.
Using these techniques, thirteen different bacteria (e.g. Pseudomonas spp. and Staphylococcus spp.) and one alga (Chlorella vulgaris) were isolated from the two private swimming poois.
In both cases the use of a swimming pool sanitiser (Baquacil, ICI Chemicals) showed excellent control of the planktonic population. Only algae were recovered from the fluid grab sample when incubated in appropriate media. Bacteria were found to be present only on plates incubated aerobically and from areas where swabbing/scraping had taken place. No anaerobic bacteria were isolated even after a long incubation period of 120 h.
On further investigation it was shown that two of the isolated species, Pseudomonas maltophilia and Ps.putida, were capable of producing extracellular polymeric substance (EPS). Production of this material has been implicated in the initial adhesion of bacteria, and further, it can act as a barrier against the diffusion of the sanitiser so that organisms exhibit higher levels of tolerance to the added swimming pooi sanitiser.
Laboratory studies demonstrated that planktonic populations of one of the isolates, Pseudomonas fluorescens, attached rapidly to the surface of PVC coupons from a planktonic population thereby mimicking the in vivo situation. The shortest time
investigated for attachment (3.5 h) demonstrated that up to 1x10 7 cells/cm2 were firmly adhered to the surface. Attacimient to the coupons wasalso shown to provide resistance to the swimming pool sanitiser below, at and above the recommended levels (Chapter 2), the greatest increase in resistance being two fold. Planktonic populations of bacteria were reduced to acceptable levels after incubation for only 3 hours in a dilute medium. It was also shown that the organism attached to the surface produced extracellular material.
On screening of Ps.fluorescens mutants (approximately 2000, induced by transposon mutagenesis, Chapter 4) for altered sanitiser resistance, it was found that 14 of these mutants had an increased resistance to the sanitiser above that shown by the wild type cells. Polyacrylamide gel electrophoresis of total cell protein extracts of thirteen of these mutants revealed that in 11 cases, a band with a molecular weight between 52,000 and 54,000 was induced or enhanced when biocide was added to the system.
If a swimming pool is not to become a potential source of infection to the bathers then attention must be paid to the submerged surface-attached population of microorganisms. Planktonic sampling will indicate that there is little microbial activity within the main body of the pool water but the techniques used only assess the quality of the bulk fluid phase of the system and not the submerged surfaces. The attachment of potentially pathogenic micro-organisms to submerged surfaces must be accepted as a nornrnl occurrence. In this state, the organisms often exhibit increased resistance to the
swimming pool sanitiser. Therefore, regular cleaning (i.e. scrubbing/vacuuming) of the submerged surfaces is suggested as a part of the recommended maintenance programme for domestic swimming pools of this type.