Isolation of potentially pathogenic bacteria from the sediment of recreational lakes

Public beaches on the Great Lakes and in the Toronto and Credit Valley Conservation Areas were sampled regularly during the months of May, June, July and Aug, 1973 and 1974. Surface water samples and lake bottom sediments were analysed for the presence of Salmonella spp, Pseudomonas aeruginosa and coagulase-positive Staphylococcus aureus. It was found that higher recovery yields of the organisms could be achieved from bottom sediments. The recovery rate of Sal.enteritidis ser Thompson and Sal.enteritidis ser Typhimurium from sediments e.g. was 3 times higher than from lake water. Of the 1972 samples of sediment and lake water taken, {approx} 70% of the Ps.aeruginosa organisms recovered were found in the bottom sediments. In 44 of the samples, the organisms were isolated from the sediment only. Coagulase-positive Staph.aureus were isolated on 28 separate occasions from sediment, but only 13 times from the surface water. This indicates that recovery yields of potential pathogens might be higher than usually reported for surface waters if lake bottom sediments were concomitantly sampled.