A 65-kilobase pathogenicity island is unique to Philadelphia-1 strains of Legionella pneumophila.

@article{Brassinga2003A6P,
  title={A 65-kilobase pathogenicity island is unique to Philadelphia-1 strains of Legionella pneumophila.},
  author={Ann Karen C. Brassinga and Margot F Hiltz and Gary R Sisson and Michael G. Morash and N. Hill and Elizabeth R Garduno and Paul H. Edelstein and Rafael A. Gardu{\~n}o and Paul S. Hoffman},
  journal={Journal of bacteriology},
  year={2003},
  volume={185 15},
  pages={4630-7}
}
Nucleotide sequence analysis of an approximately 80-kb genomic region revealed an approximately 65-kb locus that bears hallmarks of a pathogenicity island. This locus includes homologues of a type IV secretion system, mobile genetic elements, and known virulence factors. Comparative studies with other Legionella pneumophila strains and serogroups indicated that this approximately 65-kb locus is unique to L. pneumophila serogroup 1 Philadelphia-1 strains.