Effects of the Dibenzofuran, Usnic Acid, on Inhibition of Ocular Biofilm Formation Due to Coagulase-Negative Staphylococci

BACKGROUND: Coagulase-negative staphylococci (CoNS) are gram-positive, aerobic, commensal bacteria found on the skin and mucous membranes, including the conjunctiva. Usnic acid (UA) is a dibenzofuran derivative isolated from lichens. This study aimed to investigate the effects of usnic acid on inhibition of ocular biofilm formation due to CoNS. MATERIAL/METHODS: Nine Staphylococcus epidermidis isolates, 5 Staphylococcus hominis isolates, 2 Staphylococcus saprophyticus isolates, and 1 Staphylococcus capitis and Staphylococcus lentus isolates were taken as test bacteria. They were inoculated into brain heart infusion broth and incubated for 24 hours at 35°C and activated. Antibiotic susceptibility was investigated by Kirby-Bauer disc diffusion method. Biofilm production was determined using the microtiter plate method and optical densitometry was measured at 570 nm using an automated microplate reader. Anti-biofilm activity of UA was determined by microtitration method and biofilm removal percentage was calculated. RESULTS: All tested bacteria were found as high biofilm-producer strains; they were generally resistant to methicillin, but susceptible to vancomycin. UA inhibited the biofilm formation of S. epidermidis isolates, ranging from 5.7% to 81.5%. It inhibited the biofilm formation of S. saprophyticus and S. lentus by 73.3% and 74.3%, respectively. There was no effect of UA on mature biofilms of S. epidermidis 17.7H, S. epidermidis 15.41, S. hominis 9.3, S. hominis 17.2H, S. saprophyticus, and S. lentus. CONCLUSIONS: It was determined that UA exerted anti-biofilm activity on some CoNS isolated from the ocular surface. Anti-biofilm activity was found to be higher even in strains that did not show antibacterial activity.