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J. L. Boyer, W. Bodnar, C. S. Crean, L. M. Guogas; Cell-Associated Azithromycin Confers Protection to Human Corneal Epithelial Cells From Staphylococcus aureus Infection. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2659.
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Topical administration of azithromycin (AZM) results in its high deposition and sustained levels in human ocular tissues. Using a cell-associated model of antibiotic efficacy developed by the Charles T. Campbell Laboratory (UPMC), this study evaluated the cytoprotective effects of AZM and other antibiotics against S. aureus infection.
Human corneal epithelial cells (HCE, ATCC CRL11516) were treated for 24 h with concentrations ranging from 4 to 512 µg/mL of AZM, erythromycin (ERY), moxifloxacin (MOX), ofloxacin (OFX), or doxycycline (DOX). Untreated cells were included as controls. Free antibiotic was subsequently removed and cells were washed twice prior to challenge with S. aureus (ATCC 12600, 5 x 105 cfu/mL). Challenged cells and uninfected controls were incubated for 24 h. An aliquot of media was plated for colony counting to assess bacterial number. Plates were washed and the destruction of the cell monolayer as evidence of bacterial infection (or drug toxicity) was assessed by staining with gentian violet. Cells receiving drug treatment but not bacterial challenge served as controls for antibiotic-induced toxicity. Parallel experiments were conducted to study the drug disposition in HCE cells.
Protection of HCE cells was observed for pre-treatment concentrations ≥16 µg/ml for AZM and ≥64 ug/mL for MOX and ERY. OFX was not protective in the assay. Protection by DOX could not be determined because DOX was not protective at <16 µg /mL and was cytotoxic at ≥16 µg/mL. Cell protective effects of AZM correlated with bacterial cell count since cytoprotective concentrations of AZM reduced bacterial load and infection while non-protective concentrations permitted bacterial growth and HCE cell death. Bioanalytical measurements of AZM suggest that a time-dependent release of cell-associated AZM may contribute to the cytoprotective effect against infection.
Azithromycin protected HCE cells from S. aureus challenge at a dose at least 4X lower than that of MOX, ERY and OFX. The cell-associated nature of AZM observed previously in ocular tissues likely contributes to its protective effect against bacterial infection of corneal epithelial cells.
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