Sequence-based classification scheme for the genus Legionella targeting the mip gene

Abstract

The identification and speciation of strains of Legionella is often difficult, and even the more successful chromatographic classification techniques have struggled to discriminate newly described species. A sequence-based genotypic classification scheme is reported, targeting approximately 700 nucleotide bases of the mip gene and utilizing gene amplification and direct amplicon sequencing. With the exception of Legionella geestiana, for which an amplicon was not produced, the scheme clearly and unambiguously discriminated among the remaining 39 Legionella species and correctly grouped 26 additional serogroup and reference strains within those species. Additionally, the genotypic classification of approximately 150 wild strains from several continents was consistent with their phenotypic classification, with the exception of a few strains where serological cross-reactivity was complex, potentially confusing the latter classification. Strains thought to represent currently uncharacterized species were also found to be genotypically unique. The scheme is technically simple for a laboratory with even basic molecular capabilities and equipment, if access to a sequencing laboratory is available.

FIG. 1

UPGMA phylogenetic dendrogram of sequence similarities found among type strains and wild strains of Legionella. The vertical bar joining two isolates or clusters indicates the level of similarity. sg, serogroup; ^a, Wadsworth 130b, Benidom 030 E, and Bellingham-1 strains; ^b, Knoxville-1 and Allentown strains; ^c, Philadelphia-1, Camperdown-1, Heysham 1, OLDA, and Oxford 4032 E strains.