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Regis P Kowalski, Lisa M Karenchak, Eric G Romanowski, Robert M Q Shanks, Deepinder Dhaliwal, Alex Mammen; The Resurgence of Penicillin-Susceptible Staphylococcus aureus Isolated from Infectious Keratitis. Invest. Ophthalmol. Vis. Sci. 2016;57(12):344.
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© ARVO (1962-2015); The Authors (2016-present)
Penicillin is not considered a first-line antibiotic for the treatment of Staphylococcus aureus (SA) keratitis. This consideration is supported by low concentrations achieved in the blood-serum after systemic administration, rather than concentrations achieved in the cornea by using topical therapy. We re-evaluated the in vitro susceptibility of pencillin for SA isolated from infectious keratitis patients to determine trends of antibiotic susceptibility, and the potential of topical penicillin to re-emerge as a treatment for SA keratitis.
MICs were determined on 333 SA isolated from keratitis patients between 1993 to 2014 to penicillin and oxacillin.The 22 years were divided into 5 time periods: 1993-1997 (N=105), 1998-2001 (N=51), 2002-2005 (N=53), 2006-2009 (N=53), and 2010-2014 (N=68). The SA were grouped as MSSA and MRSA. The MSSA MICs for penicillin were analyzed non-parametrically. Percent susceptibilities were determined based on the serum standard (MIC < 0.12 µg/ml), and arbitrary concentrations that may be reached in topically treated corneas (4, 8,16, 32, and 64 µg/ml).
SA were comprised of 251 (75%) MSSA and 82 (25%) MRSA. The descriptive statististics of the MSSA for MIC50, MIC90, median, and range were 4, 64, 4, and 0.03 - 128 µg/ml, respectively. The median MIC for ‘2010-2014’ (2 µg /ml) was statistically lower (p=0.005) than ‘1993-1997’ (16 µg/ml) indicating increased penicillin susceptibility. Susceptibility based on the serum standard was 10% (25/251). Corneal concentrations based on 4, 8, 16, 32, and 64 µg/ml would increase susceptibilities to 50% (126/251), 57% (144/251), 69% (174/251), 82% (207/251), and 94% (237/251), respectively.
The MICs of SA isolated from cornea samples to penicillin have decreased over the last 22 years indicating that topical penicillin may have a renewed potential as an effective antibiotic for the treatment of MSSA keratitis. In vivo rabbit topical treatment studies for correlation are warranted.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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