Two phenotypes of
P. aeruginosa , based on the secretion of certain type III secretion system (T3SS) toxins, were previously discovered.
1 The T3SS is a specialized protein export system that forms a needle-like complex between bacterial and host cells for the transport and secretion of four exotoxins, ExoS, ExoU, ExoT, and ExoY.
27 The PscC protein is an essential structural component of the needle complex located on the outer membrane of
P. aeruginosa cells.
27,28 Mutation in the PscC protein results in loss of cytotoxicity and the T3SS exotoxin secretion.
28–30 As most strains carry the
exoT and e
xoY genes,
P. aeruginosa strains that have the
exoS gene encoding the protein ExoS but not the
exoU gene can invade corneal epithelial cells and are, thus, known as invasive strains.
1,31–34 Cytotoxic strains, on the other hand, carrying the
exoU-positive (
exoU +) and
exoS-negative (
exoS −) genotypes cause acute host cell lysis by the production of ExoU, a phospholipase.
32,35 Invasive and cytotoxic phenotypes with their respective
exoS and
exoU genotypes were found to be mutually exclusive in nearly all strains.
1 Previously, reports with a sufficient number of clinical
P. aeruginosa isolates found a significantly higher prevalence of cytotoxic strains among contact lens wearers.
36,37 Cytotoxic strains were also found to be highly correlated with antibiotic resistance.
38,39 Interestingly, environmental and clinical isolates from lung, urinary tract, or burn wound infections were mostly invasive.
37,40,41 Thus, the higher prevalence of the cytotoxic genotype specifically to contact lens wearers poses the possibility of T3SS involvement either directly or indirectly with adhesion to contact lens materials.