Abstract
We investigated the genetic characteristics of 161 Legionella pneumophila strains isolated over a period of 10 years from cooling towers in Japan. Minimum spanning tree analysis based on the sequence-based typing (SBT) of them identified three clonal complexes (CCs); CC1 (105/161, 65.2%), CC2 (22 /161, 13.7%), and CC3 (20/161, 12.4%). CC1 was formed by serogroup (SG) 1 and SG7, whereas CC2 was mainly formed by SG1. All of the CC3 isolates except two strains were SG13. The major sequence types (STs) in CC1 and CC2 were ST1 (88/105, 83.8%) and ST154 (15/22, 68.2%), respectively. These STs are known as typical types of L. pneumophila SG1 in Japanese cooling tower. Additionally, we identified 15 strains of ST2603 as the major type in CC3. This ST has not been reported in Japanese cooling tower. Whole genome sequencing (WGS) analysis of the representative strains in the three CCs, which were isolated from various cooling towers over the 10 years, elucidated high clonal population of L. pneumophila in Japanese cooling tower. Moreover, it revealed that the strains of CC2 are phylogenetically distant compared to those of CC1 and CC3, and belonged to L. pneumophila subsp. fraseri.
Highlights
Legionella pneumophila is a major pathogen causing Legionnaires’ disease, whose severity varies from a mild febrile illness to a serious and potentially fatal form of pneumonia [1,2]
Amemura-Maekawa et al elucidated the differences in the distribution of sequence types (STs) of L. pneumophila SG1 isolated from bathwater, cooling tower water, and soil in Japan [11]
SG13 isolates were contained in CC3. These results suggested that the specific genotypes in CC1, CC2, and CC3 are found in the cooling towers of Japan
Summary
Legionella pneumophila is a major pathogen causing Legionnaires’ disease, whose severity varies from a mild febrile illness to a serious and potentially fatal form of pneumonia [1,2]. In Japan, several outbreaks of Legionnaires ‘disease associated with public bath facilities have been reported. Public baths are known to be major sources of infection in Japan [4]. Cooling towers contaminated with Legionella have caused large community outbreaks in several countries [5,6,7,8,9]. Amemura-Maekawa et al elucidated the differences in the distribution of sequence types (STs) of L. pneumophila SG1 isolated from bathwater, cooling tower water, and soil in Japan [11]. There exists no surveillance system in cooling towers in Japan focusing on the population structure of L. pneumophila. We investigated the population structure and genetic characteristics of L. pneumophila in cooling towers water system over a period of 10 years, using sequence-based typing (SBT) methods. The detailed characteristics of the representative isolates from the major clonal groups were further identified by whole genome sequencing (WGS)
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