nature of P. aeruginosa. Enzymes LigDs form a subfamily of the DNA ligases. These all have a LigDom/ligase domain, but many bacterial LigDs also have separate polymerase domains/PolDoms and nuclease domains/NucDoms. In P. aeruginosas case the nuclease domains are N-terminus, and the polymerase domains are C-terminus, extensions of the single central ligase domain. Pathogenesis An opportunistic, nosocomial pathogen of immunocompromised individuals, P. aeruginosa typically infects the airway, urinary tract, burns, and wounds, and also causes other blood infections. It is the most common cause of infections of burn injuries and of the outer ear (otitis externa), and is the most frequent colonizer of medical devices (e.g., catheters). Pseudomonas can be spread by equipment that gets contaminated and is not properly cleaned or on the hands of healthcare workers. Pseudomonas can, in rare circumstances, cause community-acquired pneumonias, as well as ventilator-associated pneumonias, being one of the most common agents isolated in several studies. Pyocyanin is a virulence factor of the bacteria and has been known to cause death in C. elegans by oxidative stress. However, salicylic acid can inhibit pyocyanin production. One in ten hospital-acquired infections is from Pseudomonas. Cystic fibrosis patients are also predisposed to P. aeruginosa infection of the lungs due to a functional loss in chloride ion movement across cell membranes as a result of a mutation. P. aeruginosa may also be a common cause of "hot-tub rash" (dermatitis), caused by lack of proper, periodic attention to water quality. Since these bacteria thrive in moist environments, such as hot tubs and swimming pools, they can cause skin rash or swimmer's ear. Pseudomonas is also a common cause of postoperative infection in radial keratotomy surgery patients. The organism is also associated with the skin lesion ecthyma gangrenosum. P. aeruginosa is frequently associated with osteomyelitis involving puncture wounds of the foot, believed to result from direct inoculation with P. aeruginosa via the foam padding found in tennis shoes, with diabetic patients at a higher risk. A comparative genomic analysis of 494 compete Pseudomonas genomes, including 189 complete P. aeruginosa genomes, identified several proteins that are shared by the vast majority of P. aeruginosa strains, but are not observed in other analyzed Pseudomonas genomes. These aeruginosa-specific core proteins, such as CntL, CntM, PlcB, Acp1, MucE, SrfA, Tse1, Tsi2, Tse3, and EsrC are known to play an important role in this species' pathogenicity. Toxins P. aeruginosa uses the virulence factor exotoxin A