Analysis of population structure among Korean and Japanese Legionella pneumophila isolates using hsp60 sequences

Abstract

The population structure of Korean (150 strains) and Japanese (92 strains) Legionella pneumophila isolates along with 18 reference strains were investigated using hsp60 sequence (1647 bp) analysis. Twelve clonal subgroups (hsP-I to hsP-X and hsF-I and hsF-II) were designated on the hsp60 tree, inferred from representative sequences using the neighbor-joining method. Some of the isolates showed unique subgroups depending on the source of isolates, including hsP-I, hsF-I, and hsF-II from cooling tower water, and subgroups hsP-VIII and hsP-X from circulating hot water bath. These subgroups may be useful for epidemiological studies to chase or specify sources of infection in Korea and Japan. Key words genotype analysis, hsp60, Legionella pnuemophila.More than 70 serogroups in 54 Legionella species have been characterized and at least 21 species are known to be pathogenic to humans (1). Among them Legionella pneumophila is the most important human pathogen as it is the causative agent of many epidemics (2-8). It is frequently isolated from various aquatic habitats including ponds, water from cooling towers, and evaporative condensers, which become the sources of infection. Because L. pneumophila occupies the largest portion of isolates from community-acquired infections and nosocomial infection, it continues to attract more public attention than any other Legionella species. Thus, it is important to take preventive measures against the spread of an epidemic through diagnosis and treatment based on quick and precise isolation/identification of the bacteria as well as deter- mining the source of the infection through translational research.A variety of gene analysis methods have been used in translational research (9) for L. pneumophila, such as target gene sequencing (10) as in other microbiological infections. Recently, rpoB and dotA were used (11) to determine the population structures of the Korean and Japanese isolates. Although unique subgroup populations were identified and predominant clonality was observed, other house-keeping gene analysis may be required depending on the source of the isolates. In this study, we sequenced the hsp60 gene in Korean and Japanese isolates and type strains of L. pneumophila, and analyzed the genetic population structures based on the results. From these results we were able to construct a useful database 572

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“…Despite these shortcomings, culture remains the method of choice. Other methods, such as qRT-PCR, can yield faster results and are highly sensitive and specific (16,17). However, qRT-PCR has the disadvantage that it cannot differentiate between live and dead bacteria, therefore it may yield false high counts (15).…”

“…The detection of Legionella in water samples is conventionally performed using a selective culture method (15), however, interference of background microorganisms may lead to false low counts (16), not to mention the necessary expertise in interpreting growth (14). Additionally, culture methods do not detect viable but nonculturable bacteria, which may also represent a health hazard (14).…”

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