The study found that two common preservative‑free eye drops (Refresh Plus and TheraTears) that contain carboxymethylcellulose (CMC) dramatically blunt the natural antibacterial action of the body's own peptides LL‑37 and hBD‑2 against eye‑infecting bacteria, while drops without CMC (Visine Tears, Tears Naturale Free) do not.

Human beta-defensin-2 (hBD-2) and cathelicidin LL-37 are salt-sensitive cationic antimicrobial peptides expressed by ocular surface epithelia. The goal of this study was to investigate the effect of preservative-free artificial tears on hBD-2 and LL-37 antimicrobial activity against Pseudomonas aeruginosa. P. aeruginosa was incubated with hBD-2 or LL-37 in the absence or presence (70% vol/vol) of different preservative-free artificial tears--Visine Tears (300 mOsm/kg), Tears Naturale Free (261 mOsm/kg), TheraTears (185 mOsm/kg), and Refresh Plus (325 mOsm/kg)--for 2 hours at 37 degrees C. In some experiments, P. aeruginosa was incubated with hBD-2 or LL-37 and Visine Tears or Tears Naturale Free with or without carboxymethylcellulose (0.5% vol/vol final concentration). Plates were inoculated with samples of each reaction mixture and then incubated for 24 hours at 37 degrees C. Visine Tears and Tears Naturale Free had little or no effect on the antimicrobial activity of 100 microg/mL hBD-2 or LL-37. In the presence of Refresh Plus and TheraTears, the activity of 100 microg/mL hBD-2 or LL-37 was reduced by 90% to 100%. Carboxymethylcellulose, at a concentration comparable to that present in Refresh Plus, reduced the effectiveness of hBD-2 or LL-37 by 40% to 90% in the presence of Tears Naturale Free and Visine Tears. Human beta-defensin-2 and cathelicidin LL-37 inhibit the growth of P. aeruginosa in vitro, but this activity is markedly reduced in the presence of Refresh Plus and TheraTears. These results suggest that carboxymethylcellulose-containing artificial tears may reduce the activity of the endogenously produced antimicrobial peptides.