Sequence-Based Typing of Legionella pneumophila Serogroup 1 Offers the Potential for True Portability in Legionellosis Outbreak Investigation

Abstract

Seven gene loci of Legionella pneumophila serogroup 1 were analyzed as potential epidemiological typing markers to aid in the investigation of legionella outbreaks. The genes chosen included four likely to be selectively neutral ( acn , groES , groEL , and recA ) and three likely to be under selective pressure ( flaA , mompS , and proA ). Oligonucleotide primers were designed to amplify 279- to 763-bp fragments from each gene. Initial sequence analysis of the seven loci from 10 well-characterized isolates of L. pneumophila serogroup 1 gave excellent reproducibility ( R ) and epidemiological concordance ( E ) values ( R = 1.00; E = 1.00). The three loci showing greatest discrimination and nucleotide variation, flaA , mompS , and proA , were chosen for further study. Indices of discrimination ( D ) were calculated using a panel of 79 unrelated isolates. Single loci gave D values ranging from 0.767 to 0.857, and a combination of all three loci resulted in a D value of 0.924. When all three loci were combined with monoclonal antibody subgrouping, the D value was 0.971. Sequence-based typing of L. pneumophila serogroup 1 using only three loci is epidemiologically concordant and highly discriminatory and has the potential to become the new “gold standard” for the epidemiological typing of L. pneumophila .