Abstract
Approximately 85% of cases of Legionnaires' disease are caused by Legionella pneumophila serogroup 1. In this study, we analyzed the distribution of lag-1 alleles, ORF 7 and ORF 8 genes of lipopolysaccharide (LPS) and sequence-based types of 616 L. pneumophila serogroup 1 strains isolated in Japan (206 clinical, 225 environmental) and China (13 clinical and 172 environmental). The lag-1 gene was harbored by significantly more of the clinical isolates compared with the environmental isolates (90.3 vs. 19.1% and 61.6 vs. 3.0%, respectively; both P < 0.001). ORF 7 genes were detected in 51.0% of Japanese clinical and 36.0% of Japanese environmental (P = 0.001) isolates, as well as 15.3% of Chinese clinical and 9.9% of Chinese environmental isolates (P = 0.544). ORF 8 genes were detected in 12.1% of Japanese clinical and 5.8% of Japanese environmental (P = 0.017) isolates, as well as 7.7% of Chinese clinical and 3.4% of Chinese environmental isolates (P = 0.388). The Japanese and Chinese isolates were assigned to 203 and 36 different sequence-types (ST), respectively. ST1 was predominant. Most isolates with the same ST also had the same lag-1, ORF 7, and ORF 8 gene subgroups. In conclusion, the lag-1 was present in most of the clinical isolates, but was absent from most of the environmental isolates from both China and Japan, regardless of the water source and SBT type. PCR-based serotyping and subgrouping methods can be used to define a hierarchy of virulence genotypes that require stringent surveillance to prevent human disease.
Highlights
Legionella, the causative agent of Legionnaires’ disease, is a facultative intracellular Gram-negative bacteria that is ubiquitous in natural and man-made water systems (Rowbotham, 1980)
Among the Chinese isolates, 61.6% of the clinical isolates and 3.0% of the environmental isolates harbored the lag1 gene (P < 0.001 based on χ 2 test on proportions) (Tables 3, 4, Figures 1C,D). These results demonstrated that the lag-1 was present in most of the clinical isolates but absent from most of the environmental isolates for both the Chinese and Japanese isolates
The lag 1 gene was harbored by significantly more of the L. pneumophila sg1 clinical isolates than the environmental isolates, regardless of the country of origin. These findings are in accordance with a report of a study in the USA, in which 75% of the L. pneumophila sg1 clinical isolates but only 8% of environmental isolates harbored the lag-1 gene (P = 0.0001 based on χ 2 test on proportions) (Kozak et al, 2009)
Summary
Legionella, the causative agent of Legionnaires’ disease, is a facultative intracellular Gram-negative bacteria that is ubiquitous in natural and man-made water systems (Rowbotham, 1980). The monoclonal types of sg were subdivided according to the presence or absence of the virulence-related epitope recognized by mAb 3/1 This epitope is not expressed by strains belonging to any of the other serogroups (Helbig et al, 2002). A previous study has established simple and rapid genotyping methods for culture-independent discrimination between serogroups of L. pneumophila and monoclonal subgroups of serogroup 1 (Thurmer et al, 2009) They identified a serogroup 1-specific genomic region, and developed two independent and suitable PCR assays for detecting serogroup 1 strains of L. pneumophila (Thurmer et al, 2009). We used conventional PCR methods to identify L. pneumophila sg subgroups in clinical and environmental isolates from Japan and China. We further characterized these isolates using the sequence-based typing (SBT) method, which is the most widely used molecular tool for epidemiological typing of L. pneumophila (Gaia et al, 2005; Ratzow et al, 2007)
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