Nosocomial Legionnaires' disease caused by Legionella pneumophila serogroup 6: implication of the sequence-based typing method (SBT)

Abstract

Sequence-based typing (SBT) was used to determine the allelic profiles of 3 sporadic clinical isolates as well as 7 environmental isolates of Legionella pneumophila serogroup 6, isolated at the Karolinska Hospital during 2004. The clinical isolates were cultured from patients with nosocomial Legionnaires' disease (LD), while the environmental isolates were cultured from potable water sources of the hospital wards in the close vicinity of the 3 patients being investigated. The genes sequenced for the construction of the SBT profile included flaA, pilE, asd, mip, mompS and proA, in this pre-determined order and the allelic profile of the 10 isolates was identical (3, 13, 1, 28, 14, 9). Furthermore, 2 of the isolates, 1 clinical and 1 environmental, were analysed using the amplified fragment length polymorphism analysis (AFLP). The AFLP genotype of both isolates was congruent. Eight of 9 control L. pneumophila serogroup 6 isolates had the same SBT profile as the study isolates. We conclude that the environmental strain isolated from our hospital's drinking water is indistinguishable genotypically from the 3 clinical isolates of Legionella. However, this genotype of L. pneumophila is geographically widespread. Thus, results of genotyping must be evaluated in conjunction with the clinical and epidemiological data.