Genome analysis of Legionella pneumophila ST901 an Italian endemic strain

Legionella pneumophila typing, based on SBT analysis, has been allowing to identify sequence types (ST) responsible for many Legionnaires’ disease cases. ST901 has so far been identified only in a town of the northern Italy, where it caused numerous travel-associated Legionnaires’ disease cases over a 32-year period. In this study, ST901 were analyzed by whole genome sequencing in looking for both differences and similarities inside this ST and with other unrelated Legionella strains. To this aim core genome multi locus sequence type, single nucleotide polymorphisms and pangenome analyses were performed. ST901 resulted highly similar each other, characterized by I-C CRISPR-cas system, located on the chromosome and by a putative plasmid, highly similar to that found in Lp strain Lens, which contains I-F CRISPR-cas system. Accessory genomic islands, either already described or specifically found in ST901, were also shown. In conclusion ST901 has been quite preserved over the time. The co-occurrence of two phage resistance systems and genomic islands of virulence could have made the ST901 enough virulent to cause such a high number of cases. Summary blurb ST901 appears as endemic of the Northern Italy, with virulence traits similar to those in Alcoy and Corby, and with two CRISPR-cas systems which probably preserved them in their environmental niche.