Evaluation of Legionella pneumophila SGUT serotypes isolated from bath water using multiplex-PCR serotyping assay

Abstract

Legionella pneumophila, the primary causative agent of Legionnaires’ disease, is classified into at least 15 serogroups (SGs). Before genotyping, serotyping is first performed to limit the sources of L. pneumophila infections that cause outbreaks. Serotyping using multiplex polymerase chain reaction (M-PCR) was recently developed for L. pneumophila, in addition to conventional assays using monoclonal or polyclonal antisera. In this study, we applied the M-PCR system to 41 strains that remained to be SGUT (untypable) by the slide agglutination tests among 220 L. pneumophila strains isolated from bath water in Kobe City during 2016–2020 to determine SG-genotypes (SGg) by the PCR amplification of the specific target gene of SGs. Among the 41 SGUT strains, SGg4/10/14 was the most predominant strain (24/41, 58.5%), followed by SGg1 (7/41, 17.1%). Seven strains, except for the strains determined as SGg1, were identified as belonging to a single SGg using M-PCR serotyping [SGg5 (3/41, 7.3%), SGg8 (3/41, 7.3%), and SGg7 (1/41, 2.4%)]. Furthermore, we found that the seven strains identified as SGg1 harbored particular genotypes. In conclusion, the M-PCR serotyping assay will be helpful in investigating the distribution of L. pneumophila in environmental and clinical settings.