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Review
. 2015 Jun;34(6):698-703.
doi: 10.1097/ICO.0000000000000431.

Antibiotic Resistance in the Treatment of Staphylococcus aureus Keratitis: a 20-Year Review

Victoria S Chang  1 , Deepinder K Dhaliwal, Leela Raju, Regis P Kowalski
Affiliations
Review

Antibiotic Resistance in the Treatment of Staphylococcus aureus Keratitis: a 20-Year Review

Victoria S Chang et al. Cornea. 2015 Jun.

Abstract

Purpose: We compared the resistance patterns of methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible Staphylococcus aureus (MSSA) keratitis isolates with the common topically applied ophthalmic antimicrobials.

Methods: We reviewed the antibiotic susceptibility results of 122 MRSA and 276 MSSA keratitis isolates from January 1993 to November 2012. In vitro susceptibility testing of each Staphylococcus aureus (SA) isolate was performed using Kirby-Bauer disk diffusion based on modified serum interpretations for cefoxitin, bacitracin, cefazolin, ciprofloxacin, gatifloxacin, gentamicin, moxifloxacin, ofloxacin, polymyxin B, sulfamethoxazole, tobramycin, and trimethoprim.

Results: MRSA represented 30.7% (122 of 398) of the total SA isolates. All the SA isolates were susceptible to vancomycin, whereas they were less susceptible to the fluoroquinolones than to the non-fluoroquinolones. In comparison with MSSA, MRSA was significantly more resistant to all the antibiotics tested other than polymyxin B (both equally resistant) and vancomycin (both equally susceptible) (P < 0.001). Besides vancomycin, MRSA demonstrated the best susceptibilities to sulfamethoxazole (94.3%), bacitracin (89.3%), trimethoprim (88.5%), and gentamicin (86.1%). Additionally, MRSA was found to be significantly more resistant to the second-generation fluoroquinolones (ciprofloxacin and ofloxacin) than to the fourth-generation fluoroquinolones (moxifloxacin and gatifloxacin). An increase in resistance to the fourth-generation fluoroquinolones was detected for both MRSA and MSSA over the study period.

Conclusions: The in vitro susceptibilities of commonly used topical antibiotics differ for MRSA and MSSA isolates; thus, successful treatment of bacterial keratitis should be supported with laboratory studies. Vancomycin remains the treatment of choice for MRSA keratitis. The empiric use of second-generation fluoroquinolones seems to be contraindicated in the treatment of MRSA keratitis.

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Conflict of interest statement

Disclosure: The authors have no proprietary interest in the products discussed in this article. No conflicting relationship exists for any author.

Figures

FIGURE 1
FIGURE 1
The distribution of 1576 bacterial keratitis isolates from January 1993 to November 2012.
FIGURE 2
FIGURE 2
MSSA and MRSA: Increasing resistance against the fluoroquinolones over 20 years.
See this image and copyright information in PMC

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