Serological versus sequence-based methods for Legionella identification.

The genus Legionella comprises 48 species and 70 different serogroups, and approximately half of them have been associated with human disease. Serological methods have been widely used for species and serogroup identification, but the progressive characterization of new species has established that antigen cross-reactivity limits specificity and restricts their use to a few frequently isolated species. Serological and sequence-based methods were used by the authors in a study for comparing Legionella identification with 93 Legionella strains including clinical and environmental ones, L. pneumophila, and other species. The aims of the study were to determine the correlation between serological and sequence-based methods and to establish a better strategy to increase the number of species of Legionella that can be identified. Comparing serological methods, 90 of 93 (96.7%) strains presented agreeing results with the three methods used. Comparing gene sequencing methods, 85 of 93 (96.7%) strains presented agreeing results with both genes. The percentage of similarity for species allocation was 99 to 100% with the mip gene and 97 to 100% with the 16S rRNA gene. Serological methods have been the most frequently used for Legionella identification, but the number of species that could be identified is limited. Sequencing methods allow the identification of any strain, detecting all species described and new ones. In this study all strains were identified with both genes, but disagreements were detected when both gene results were compared.