Use of DNA Probes for the Diagnosis of Infections Caused by Mycoplasma Pneumoniae and Legionellae- A Review

Abstract

Specific DNA probes have been made for both M. pneumoniae and Legionella species. Dot blot methods have been used in research laboratories to test culture isolates of both organisms, and also to test animal tissues with a L. pneumophila-specific probe. Commercial kits are also available for direct specimen testing for these two organisms. The commercial kits are made by a single manufacturer, Gen-Probe, Inc. (San Diego, CA), and use a novel in-solution rapid hybridization assay, using ¹²⁵I-labeled cDNA to rRNAs of the organisms. The Gen-Probe M. pneumoniae probe appears to be 80% to 100% sensitive, and 97% to 100% specific, based on analysis of two clinical studies using positive culture as the diagnostic criterion. The Gen-Probe legionella probe appears to be 33% to 71% sensitive (mean 57%), and 98.9% to 99.7% specific (mean 99.7%), based on analysis of four prospective clinical studies, using positive culture as the definition of disease, with a total sample size of 3,243 patients, 49 of which were culture-positive. Both Gen-Probe direct tests appear to be clinically useful, although the poor performance of the legionella test in one major university laboratory, and the expense of performing these tests, mandate that thorough evaluations be carried out in each laboratory anticipating using the test. Culture must always be performed for legionella whether or not the DNA probe test is used. It is likely that the use of the M. pneumoniae kit would greatly speed diagnosis, but whether this would alter medical practice or result in lower morbidity and health care costs is unknown.