Studies on detection methods for Legionella species from environmental water

Abstract

We investigated selective cultivation media and previous treatments of samples suitable for detection of Legionella species from environmental water and for elimination of co-existing microbes which gave rise to an interference with the evaluation of Legionella sp. growth. Twenty thousand U of polymyxin B (PL-B)/ml and 100 micrograms of oxytetracycline (OTC)/ml seem to be useful as additives to MWY selective agar medium. Both antibiotics markedly inhibited the growth of co-existing microbes with almost no influence on the growth of Legionella sp. In the studies on the resistance of 8 strains of Legionella sp., 24 strains of co-existing microbes and 2 standard strains of Staphylococcus aureus and Escherichia coli to acid treatment (0.2 M HCl-KCl, pH 2.2, 25 degrees C, 4 minutes) and heating (50 degrees C, 20 minutes), acid treatment or heating alone showed no inhibition on the growth of almost all strains examined. However, combination with acid treatment after heating resulted in an apparent extinction of almost all microbes except for Legionella sp., Seven strains from co-existing microbes showed an apparent growth inhibition against 8 strains of Legionella sp. with different serotypes and were all identified as Pseudomonas aeurginosa, which were all eliminated by means of the combination with acid treatment after heating. From these results, it was concluded that the combined pre-treatment of water samples with acid after heating and the addition of PL-B and OTC into the selective cultivation medium is an useful method for detection of Legionella sp. from environmental water.