Identification of Legionella pneumophila in various specimens by the polymerase chain reaction

Amplification of the mip sequence with polymerase chain reaction (PCR) proved to be specific for Legionella pneumophila. With nested PCR, the sensitivity of the test was markedly increased. The lower limit of detection for nested PCR in the aqueous medium for live and heat-inactivated dead L. pneumophilia was approximately 1-10 bacteria/ml. The sensitivity of the method, however, was reduced by a factor of 10 to 100 when the bacteria were added to homogenised pulmonary tissue. Fixing the bacteria in aqueous suspension or in tissue homogenate with buffered 4% formalin (pH 7.3) reduced the sensitivity of the PCR by a factor of about 100. After intravenous injection of heat-inactivated bacteria in mice L. pneumophila was detected in deep-frozen samples of plasma and various tissues. The molecular biological technique of nested PCR is proposed as an additional method for the diagnosis of legionella.