ABSTRACT
Three diagnostic selective media used for the isolation of Legionella pneumophila were compared. These included BCYEAalpha (Oxoid, a reference medium), BCYEAalpha (Hi Media), and elective legionellosis medium (ELM) developed at the Rostov-on-Don Research Institute for Plague Control. The virulent L. pneumophila strain Philadelphia-1 (LD50 was 10(5) CFU for guinea-pigs) was used a test culture. The susceptibility of the media was determined, by culturing 10(-6) and 10(-7) dilutions of the suspension of the macerated Legionella-infected guinea-pig spleen, as well as the suspension of a culture of this strain (100 CFU) and 6 L. pneumophila cultures freshly isolated from water. The BCYEAalpha (Oxoid) and ELM media demonstrated the similar growth characteristics (chi2 < 0.7; p = 0.05) while the BCYEAalpha (Hi Media) medium showed a low susceptibility. The BCYEAalpha (Oxoid) and ELM media were first found to be successful in detecting Legionella in viable, but nonculturable state, induced by the following factors: 1) starvation in distilled water; 2) exposure to hydroquinone (oxidative shock, and 3) elevated temperature (56 degrees C). The BCYEAalpha (Oxoid) and EML media did not differ either in their ability to suppress extraneous microflora and to maintain stable initial pH under the conditions of incubation of culture plates, as well as in their Na+ concentration (15-19 mmol/l). However, the BCYEAalpha (Oxoid) medium exceeded the ELM one in the growth rate and diameter of Legionella colonies. Two L. pneumophila cultures were isolated in the BCYEAalpha (Oxoid) and EML media used in the field experiment studying 15 water samples from different hot water supply systems. Thus, the conclusion can be drawn that the EML medium is comparable with the reference BCYEAalpha (Oxoid) medium in its susceptibility and ability to detect Legionella in both vegetative and viable, but nonculturable states and is suitable for practical application.
