A rapid and reliable method for early identification and characterization in support of the epidemiology study.

INTRODUCTION

Legionnaires' disease is a severe pneumonia predominantly caused by (Lp), whose major reservoirs are artificial water systems. As most human infections are caused by serogroup 1 (Lp1), a reliable method for Lp distinction can be crucial for bacterial spread prevention. As the ability to withstand in environments and to cause the waterborne disease is strongly related to specific genes, the identification of virulent strains can be of great relevance to implement water environmental monitoring and to contain harmful outbreaks to public health. We aimed to test an assay for Lp identification among different species, and to determine the serogroups. Additionally, we investigated the carriage of virulence and antimicrobial resistance genes.

METHODS

A total of 90 spp. isolates identified by phenotypic tests were subjected to the designed quantitative PCR assay targeting specific for Lp, for Lp1, and for biofilm production. Eleven serogroups were investigated in all our isolates tested positive for gene, subsequently analyzed for 12 virulence and 8 antimicrobial resistance genes.

RESULTS

Only the 70 Lp isolates were positive for . Out of 27 Lp isolates belonging to serogroup 1 based on agglutination test, 23 (85.2%) carried . The presence of and was found in 94.3 and 98.6% of Lp isolates, respectively. By multiplex PCR, all 23 -positive strains were confirmed as serogroup 1 that was the most predominant (33%). At least one virulence gene was detected in all Lp isolates. The most frequent gene was (100%), followed by (96%), and (93%), (91%), (74%), (61%), and (54%). The other genes were less diffused in Lp strains ( 44%; , 47%; , 27%; , 24%). Of the macrolide resistance genes, the was found in 84% of Lp strains, while only 14 (20%) harbored the among the efflux pump genes.

CONCLUSION

The assays validated in this study enable the simultaneous Lp and Lp1 detection. The differentiation of Lp strains according to their virulence properties could be useful to predict the bacterial ability to survive and to cause the disease.