Modulation of Pseudomonas aeruginosa adherence to the corneal surface by mucus.

To gain access to the corneal epithelium and cause infections keratitis, bacterial pathogens must first interact with ocular surface factors that could affect bacterial adherence. In this study, we demonstrated that the mucus layer, and, in particular, the mucin fraction of mucus, modulated adherence to intact corneal epithelium of Pseudomonas aeruginosa but not that of Staphylococcus aureus or Streptococcus pyogenes. Removal of endogenous mucus from rat or rabbit eyes increased the adherence of P. aeruginosa by 3- to 10-fold. Ocular mucus obtained from rat eyes, porcine stomach mucin, or bovine submaxillary gland mucin inhibited adherence of P. aeruginosa to uninjured corneal epithelium. The mucin fraction of ocular mucus, purified by ultracentrifugation, was found to contain the inhibitory activity, and inhibition was demonstrated at concentrations of mucin as low as 35 micrograms/ml. Ocular mucin was the only material tested that inhibited adherence of P. aeruginosa to an injured cornea. However, the binding of P. aeruginosa to immobilized substrates in vitro did not predict which fraction would possess antiadherence activity: bacteria bound well to whole ocular mucus, mucin, the nonmucin fraction of ocular mucus, and dilute human tears as well as to porcine stomach mucin and bovine submaxillary gland mucin. The effectiveness of the mucin fraction of ocular mucus at inhibiting the binding of P. aeruginosa to the cornea implies that this material is a barrier that protects the surface of the eye from P. aeruginosa adherence.