Characteristics of Legionella pneumophila serogroup 2 strains by colony morphology.

The isolation rate of Legionella pneumophila serogroup 2 from clinical samples is low. In 2007, we encountered the second case known to occur in Japan. As the L. pneumophila serogroup 2 type strain, the Kobe strain isolated in 1988, and the Okinawa strain isolated from the present patient could not be differentiated using the usual biochemical and serological tests, we tried to achieve differentiation by observing colony morphology. In Oxoid BCYEalpha medium, colonies of the Kobe strain developed multiple protuberances on the surface, but these did not develop on the other two strains. In Becton-Dickinson BCYEalpha medium, colonies of the Okinawa strain had several outgrowths from the margin, but the type strain and the Kobe strain did not have any outgrowths. The Okinawa strain isolated from the present case showed intermediate characteristics between the type strain and the Kobe strain in the appearance of colony morphology. It may be useful to conduct an investigation of this rare serogroup.