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We investigated the in vitro susceptibilities of 23 Propionibacterium acnes ophthalmic isolates to ertapenem, meropenem, and cefepime by utilizing the Etest. The MICs ranged from 0.094 microg/ml to 0.75 microg/ml, 0.094 microg/ml to 1.5 microg/ml, and 1 microg/ml to 12 microg/ml for ertapenem, meropenem, and cefepime, respectively. Based on our excellent in vitro carbapenem susceptibility results, in vivo studies using ertapenem and meropenem in a rabbit model of P. acnes endophthalmitis are warranted.

Purpose: To determine the antibacterial activity of fluoroquinolones, vancomycin, and gentamicin against methicillin-resistant Staphylococcus aureus (MRSA) ocular surface isolates., Design: Retrospective review., Methods: MRSA isolates were obtained from 21 patients. The MIC(50) (mean inhibitory concentration)(microg/ml) values of 31 MRSA ocular surface isolates were determined for gatifloxacin, moxifloxacin, ciprofloxacin, ofloxacin, vancomycin, and gentamicin using the Etest (AB Biodisk, Solna, Sweden) or the VITEK system (bioMérieux, Inc, Durham, North Carolina, USA). Susceptibility data were interpreted based on criteria specified by the Clinical and Laboratory Standards Institute (CLSI)., Main Outcome Measures: MIC(50) values in microg/ml and interpretation of susceptibility or resistance., Results: In vitro resistance rates and median MIC(50) in microg/ml for the MRSA isolates were: gatifloxacin (71%, 8.0), moxifloxacin (68%, 8.0), ciprofloxacin (94%, 8.0), ofloxacin (94%, 8.0), vancomycin (0%, 1.0), and gentamicin (3%, 0.5)., Conclusions: MRSA ocular isolates exhibited a relatively high rate of in vitro resistance to all fluoroquinolones tested, including the fourth generation. In contrast, MRSA isolates were found to be highly sensitive to vancomycin and gentamicin.