Abstract
Purpose: :
Due to the development of resistance, new and safe antimicrobial agents are always needed. Lacritin, a natural tear glycoprotein, increases tear flow in animal models and has bactericidal effects at low micromolar concentrations in vitro (both gram positive & negative). In this study, the antimicrobial effect of topical lacritin N-65 and pLac was evaluated in a rabbit keratitis model of Pseudomonas aeruginosa infection.
Methods: :
Anesthetized White New Zealand rabbits were injected midstromally in the cornea of one eye (10 µL, containing 1000 CFU of Pseudomonas aeruginosa). 16 hours after injection, 50 µL aliquots of N-65 lacritin or pLac (both at 250 µg/mL), 0.3% gatifloxacin (positive control) or saline (negative control) were administered as follows: 5 doses / every 15 min, followed by 14 doses / every 30 min. 1 hr after the last dose, animals were graded via semi-quantitative slit lamp examination for inflammation, chemosis, iritis, hypopyon, corneal infiltrate, anterior chamber fibrin and corneal edema and then were euthanized. Aqueous humor and corneas were then extracted to remove bacteria, extracts cultured and colonies counted, permitting the four treatments to be compared.
Results: :
The infection was localized to the cornea, with virtually no measurable bacterial activity in the aqueous humor. N-65 treatment significantly reduced slit lamp scores compared to saline control (p<0.007) and was not significantly different from the reduction by gatifloxacin treatment (p<0.4). pLac treatment did not significantly reduce the slit lamp scores compared to saline control.N-65 treatment was not significantly effective in reducing bacterial loads. pLac did significantly reduce corneal bacterial loads compared to saline controls (p<0.05). The commercial gatifloxacin preparation reduced bacterial loads significantly more than pLac. The gatifloxacin effect may have been enhanced by 100 fold greater molar concentration compared to pLac and also by the bactericidal effects of 0.005% BAK, used as a preservative in this commercial preparation.
Conclusions: :
We speculate that the lower molecular weight N-65 may be a more effective anti-inflammatory agent due to its readily diffusing into the anterior chamber, but the larger pLac may be more stable to degradation and therefore have a more pronounced antimicrobial effect.
Keywords: antibiotics/antifungals/antiparasitics • anterior chamber • keratitis