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C. V. Sundar-Raj, E. C. Wu, F. S. Mah, E. G. Romanowski, R. P. Kowalski, Y. J. Gordon, R. M. Q. Shanks; DuraSite and Azithromycin Inhibit Staphylococcal Biofilm Formation in vitro. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5715.
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© ARVO (1962-2015); The Authors (2016-present)
Bacteria attached to surfaces (biofilms) are associated with chronic and antibiotic resistant infections, and may be a major component of infectious blepharitis. We tested the hypothesis that AzaSite® and its components (DuraSite®, azithromycin (AZM), benzalkonium chloride (BAK)) inhibits biofilm formation by clinical conjunctivitis and blepharitis isolates of Staphylococcus aureus and coagulase negative Staphylococcus (CNS).
Four AZM resistant, and 4 susceptible de-identified clinical isolates were used in all experiments. Bacteria were normalized to A600 nm = 0.01 and incubated with a concentration range of AzaSite, DuraSite, AZM, and BAK in polystyrene microtiter plates. Biofilms were allowed to form for 20 hours, bacterial growth was assessed (A600 nm), non-adherent bacteria were removed, and biofilms were stained with crystal violet (CV) (0.1% w/v). To measure biofilms, CV was solubilized with glacial acetic acid (30% v/v) and measured by absorbance at 590 nm. Experiments were repeated at least two times on different days in triplicate.
AZM resistant strains treated with Azasite® at concentrations of 0.5%, 0.25%, and 0.125% demonstrated a statistically significant reduction in biofilm formation compared to controls (p<0.05), whereas bacterial growth showed no statistically significant difference. AZM did not affect bacterial growth in AZM resistant strains but did have a small but statistically significant effect on biofilm formation at concentrations of 1%, 0.5%, 0.25%, and 0.125% in most tested strains. Surprisingly, DuraSite® conferred a statistically significant reduction in biofilm formation at concentrations of 1%, 0.5%, and 0.25% in all studied bacterial strains (p<0.05) without changing growth. BAK inhibited both bacterial growth and biofilm formation between concentrations of 0.0375% and 0.0042% (p<0.005).
Azasite® inhibited biofilm formation by staphylococcal ocular clinical isolates regardless of their AZM resistance status. Data supports that this inhibition was caused by DuraSite® for AZM resistant strains. The current mechanism for this inhibition is unknown. Though less dramatically than DuraSite®, AZM inhibited biofilm formation at subinhibitory doses, suggesting that AZM inhibits the ability of staphylococci to attach to surfaces.
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