PURPOSE: Eye infections are caused by a range of Gram-negative and Gram-positive bacteria which can result in permanent damage, if not treated. Tears contain a number of antimicrobial factors such as lipids which provide natural defence against ocular pathogenic bacteria. Phosphatidylcholine (PC) and cholesteryl esters (CE) are found in the lipid layer of the tear film. PC has been reported to enhance the antibacterial activity of antibiotics while displaying antibacterial properties against Staphylococcus aureus. While CE have been shown to provide antibacterial activity in the human nasal fluid against Pseudomonas aeruginosa. This study aimed at exploring the effect of PC and CE against ocular pathogenic bacteria as an antibacterial compound.
METHOD: Using broth dilution method, the susceptibility of ocular pathogenic bacteria (Staphylococcus aureus 31 and Pseudomonas aeruginosa 19) was tested with a range of concentration of PC or CE in an artificial tear and Mueller-Hinton media at a 9:1 ratio. Time-kill assay was performed to observe total viable counts of bacteria surviving the different lipid treatments.
RESULTS: Data showed that both PC and CE inhibit growth of ocular pathogenic bacteria. Treatment with PC showed a low percentage growth inhibition of Staphylococcus aureus 31 (0-4% for 1-32µg/ml of PC), while a moderate growth inhibition of Pseudomonas aeruginosa (0-40% for 1-32µg/ml of PC). Treatment with CE showed more growth inhibition of Staphylococcus aureus 31 ((0-100% for 0.05-16mg/ml of CE) than Pseudomonas aeruginosa 19 (0-37% for 0.05-16mg/ml of CE). Time kill assay suggested that bacterial cell death of both bacteria was not affected with treatment of either PC or CE.
CONCLUSION: These results indicated that PC and CE may play a role in the antimicrobial defence of tears at the ocular surface against Gram-negative and Gram-positive bacteria. Exploring the antibacterial effects of these lipids in combination may also lead to further understanding of the natural defence of tears.