Suzanne M. Fleiszig

The role of pili in the attachment of Pseudomonas aeruginosa to unworn hydrogel contact lenses

Contamination of contact lenses is thought to increase the risk of infectious keratitis, yet factors promoting attachment of bacteria to contact lenses are not fully understood. It has been suggested that strains of Pseudomonas aeruginosa attach to mucosal surfaces via pili which are appendages found on some strains. This study investigated the role of pili and the effect of incubation time on the attachment of P. aeruginosa to 20 unworn hydrogel lenses representative of each of the four FDA categories. Ten lenses were incubated for 15 minutes and another ten for 180 minutes. Lenses were incubated with either PAK + P. aeruginosa which possessed pili or its isogenic mutant pair, PAK-, which was genetically similar except for the absence of pili. Bacteria were quantified, following homogenization of the contact lens, by viable counts. Non-piliated bacteria were significantly more likely to adhere to the lenses (p < 0.001). A significant interaction between lens type and incubation time was observed (p < 0.05); thus it is difficult to generalize about either of these effects in isolation. These results show that surface characteristics may confer an attachment advantage to bacteria.

Mucus and Pseudomonas Aeruginosa Adherence to the Cornea

Most of what we currently know about the initial interaction between Pseudomonas aeruginosa and the adult cornea has come from studies of bacterial adherence to overtly injured cornea. These investigations have focused on receptor-adhesin interactions between injured corneal cell associated molecules and the microbe.1 However, not all infections with P. aeruginosa are preceded by overt injury. For example, contact lens related keratitis is likely to follow more subtle disruptions to the ocular surface. In vivo, bacteria must pass through and interact with the tear film and the epithelial cell surface glycocalyx before they could adhere to corneal cells. This aspect of keratitis pathogenesis has received little attention.