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L. M. Guogas, J. L. Boyer; Azithromycin Suppresses Bacterial Lipases Expressed by Staphylococcus. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5943.
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Bacteria produce virulence factors, including lipases, which lead to tear film instability and contribute to lid margin disease. We investigated the efficacy of azithromycin to inhibit the expression of bacterial lipases as compared to other antibiotics.
Saturated cultures of S. epidermidis (ATCC 14990) and S. aureus (ATCC 12600) were incubated at 37ºC in the presence of a range of concentrations of azithromycin, erythromycin, ofloxacin, doxycycline or left untreated for two hours. Following the drug incubation period, bacterial lipase levels were estimated from activity measurements in the culture media using a fluorogenic substrate. Viability of the cultures following incubation with drug compounds was assessed by colony count.
Azithromycin exhibited a ≥ 75% reduction of bacterial lipase activity in the culture media for S. aureus and S. epidermidis at concentrations above 2 and 4 µg/mL respectively, as compared to the untreated control. A >90% reduction in lipase activity was observed at the highest treatment dose, 16 µg/mL. The inhibition of lipase activity observed with erythromycin treatment was lower than with azithromycin at the same dose. Treatment with doxycycline showed a greater reduction in measured lipase activity than azithromycin; however, doxycycline treatment caused a significant reduction of bacterial viability in S. aureus. Ofloxacin was bactericidal in both Staphylococcus species and its effect on lipases could not be dissociated from its antibacterial effect. Azithromycin did not inhibit the enzymatic cleavage of the lipid substrate, suggesting that the effects of the drug are produced by inhibition of expression or secretion of lipases.
All antibiotics tested except ofloxacin reduced the level of lipase activity of S. epidermidis and S. aureus. However, azithromycin treatment resulted in the greatest reduction of lipase activity at concentrations below antibacterial activity in both Staphylococcus species. It is likely that azithromycin is acting to reduce the expression and/or secretion of lipases. Reduced production of bacterial lipases may be beneficial for alleviating the inflammation associated with lid margin disease.
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