On the proteolytic activity of contact lenses and bacteria

Contact lens wear (CLW) has been shown to cause an elevation in tear fluid (TF) plasmin levels. This study investigated whether the proteolytic activity assayed by a caseinolytic technique was also bound by CLs and whether certain bacterial species contribute to the production of plasmin. CLs worn by patients with corneal disease showed proteolytic activity in five out of nine cases when examined on casein agar. Histological and electron microscopic examination of the lenses revealed bacterial adherence and growth on both surfaces of the CLs. Strains of Staph. epidermidis, Staph. aureus, Pseudomonas aeruginosa and Branhamella catarrhalis, isolated from eyes with external infections, were cultured on a modified milk casein agar and examined for their proteolytic activity. Neither cultures of Branhamella catarrhalis nor Staph. aureus showed proteolytic activity when examined by direct caseinolytic assay. The proteolytic activity shown by Staph. epidermidis or Pseudomonas aeruginosa was not affected by a proteinase inhibitor aprotinin. However, when exogenous plasminogen was added into the casein agar, Staph. aureus was shown to produce caseinolytic activity. This activity was interpreted to be due to plasminogen activator (PA) activity. It was inhibited by aprotinin. Examination of culture fluids of the bacterial species mentioned above did not show caseinolytic activity. Culture fluid of Staph. aureus contained PA activity. The present study confirms the ability of certain bacterial species to adhere to CLs. Moreover, proteases such as plasmin and bacterial enzymes are present in TF during CL wear and may even adhere to the surface of CLs. Hence, bacterial growth probably contributes to the production of proteases on the ocular surface during CL wear.