Pseudomonas aeruginosa and microbial keratitis.

Pseudomonas aeruginosa, a versatile Gram-negative pathogen that can cause a wide range of infections, is the most common causative agent in cases of bacterial keratitis associated with contact-lens use. Corneal infections with P. aeruginosa often have poor clinical outcomes and can result in long and costly treatments. During the infection process, the pathogen exploits its large genome, encoding complex regulatory networks and a wide range of virulence factors, including motility and the secretion of various proteases and toxins. Although antibiotic resistance levels in the UK are low, higher levels have been seen in some other countries. In the face of increasing antibiotic resistance, alternative therapeutic approaches such as antivirulence strategies and phage therapy are being developed. There is increasing evidence to suggest that keratitis infections are associated with a phylogenetic subgroup of P. aeruginosa isolates carrying the gene encoding the potent cytotoxin exotoxin U, one of two mutually exclusive exotoxins secreted via the type III secretion system. The mechanisms behind this association are unclear, but understanding the genetic differences that predispose P. aeruginosa to cause corneal infections may allow for the development of targeted and more effective future treatments to reduce the morbidity of P. aeruginosa keratitis. In order to minimize the risk of severe P. aeruginosa eye infections, a wide range of contact-lens disinfection solutions are available. Constant exposure to biocides at a range of concentrations, from sub-inhibitory to inhibitory, could contribute to the development of resistance to both antibiotics and disinfectants.