Inhibitory and bactericidal concentrations of current and new antibiotics for Methicillin-resistant Staphylococcal ocular infections Yousuf Qureshi, M.D. Darlene Miller, DHSc Neither author has any financial disclosures. Bascom Palmer Eye Institute, Department of Microbiology, Miami, Florida. Abrams Ocular Microbiology Laboratory Phone: X6034 McKnight Building, 1st floor

Background and Purpose Staphylococcus aureus remains the most common ocular pathogen recovered from ocular infections.Staphylococcus aureus remains the most common ocular pathogen recovered from ocular infections. Increasing recovery of multidrug resistant isolates compromises the selection of appropriate antibiotics for prophylaxis and treatment of these infections.Increasing recovery of multidrug resistant isolates compromises the selection of appropriate antibiotics for prophylaxis and treatment of these infections. This study evaluates the percentage susceptible and in vitro minimum inhibitory and bactericidal (MIC and MBC) concentrations of standard and new antibiotics for methicillin-resistant staphylococcus aureus (MRSA) derived from cases of clinical ophthalmic infection.This study evaluates the percentage susceptible and in vitro minimum inhibitory and bactericidal (MIC and MBC) concentrations of standard and new antibiotics for methicillin-resistant staphylococcus aureus (MRSA) derived from cases of clinical ophthalmic infection.

Increasing MRSA prevalence Data collected from the Bascom Palmer Eye Institute (BPEI) microbiology laboratory in Miami, Florida

Methods One hundred and one random MRSA isolates (collected at the BPEI microbiology laboratory from January 2005 and February 2009) were selectedOne hundred and one random MRSA isolates (collected at the BPEI microbiology laboratory from January 2005 and February 2009) were selected 40 Conjunctival 40 Conjunctival 30 Corneal or Contact lens 30 Corneal or Contact lens 31 Periocular soft tissue sources 31 Periocular soft tissue sources Mean inhibitory concentrations (MIC 50 & 90 ) were determined using the Sensititre® microtiter assayMean inhibitory concentrations (MIC 50 & 90 ) were determined using the Sensititre® microtiter assay Trek Diagnostic Systems; Cleveland, OH; Trek Diagnostic Systems; Cleveland, OH; Mean bactericidal concentrations (MBC 50 & 90 ) were also determined for commonly used ophthalmic antibiotics by plating the “no-grow” wells on blood agarMean bactericidal concentrations (MBC 50 & 90 ) were also determined for commonly used ophthalmic antibiotics by plating the “no-grow” wells on blood agar Sensitivity data of the MRSA isolates were determinedSensitivity data of the MRSA isolates were determined Standard MIC90 data derived from Clinical and Laboratory Standards Institute (formerly NCCLS), Wayne, PA and data supplied by the British Society for Antimicrobial Chemotherapy, February 2008 Standard MIC90 data derived from Clinical and Laboratory Standards Institute (formerly NCCLS), Wayne, PA and data supplied by the British Society for Antimicrobial Chemotherapy, February 2008

Antibiotics Evaluated in Study Methods Macrolides Azithromycin Azithromycin Erythromycin Erythromycin Clarithromycin Clarithromycin Miscellaneous Peptide antibiotics Vancomycin Vancomycin Tricyclic Glycopeptides Tricyclic Glycopeptides Daptomycin* Daptomycin* Lipopeptide LipopeptideLincosamide Clindamycin ClindamycinKetolide Telithromycin* Telithromycin*Rifamycin Rifampin Rifampin Fluoroquinolones Ciprofloxacin Moxifloxacin Gemifloxacin* Aminoglycosides Gentamicin Streptomycin Dihydrofolate reductase inhibitor Trimethoprim Non-macrolide 50s ribosome inhibitor Chloramphenicol (UK) Glycylcycline Tigecycline* Oxazolidinone Linezolid* Streptogramins Quinpristin* Quinpristin* Dalfopristin* Dalfopristin*Nitrofuran Nitrofurantoin NitrofurantoinSulfonamide Sulfamethoxazole SulfamethoxazoleTetracycline Tetracycline TetracyclinePenicillins Penicillin Penicillin Ampicillin Ampicillin Oxacillin Oxacillin * emerging antibiotic

Data Sheet Utilized Methods

Results for Common Antibiotics against MRSA (All sources) Drug % Susceptible MIC 50 (ug/mL) MIC 90 (ug/mL) MBC 50 (ug/mL) MBC 90 (ug/mL) Vancomycin (MIC 90 ≤ 2) Moxifloxacin (MIC 90 ≤ 0.5) 24.8>4>4>4>4 Gentamicin (MIC 90 ≤ 4) 77.22>168>16 Chloramphenicol (MIC 90 ≤ 8) >16>16 Ciprofloxacin (MIC 90 ≤ 1) 18.8>2>2>2>2 (Percent susceptible data determined using MIC90 values from the Interpretation by Clinical and Laboratory Standards Institute, Wayne, PA)

Results for New Antibiotics against MRSA (All sources) Drug % Susceptible MIC 50 (ug/mL) MIC 90 (ug/mL) Quinpristin / dalfopristin (MIC 90 ≤ 1) Telithromycin >2 Daptomycin Linezolid (MIC 90 ≤ 4) Tigecycline (MIC 90 ≤ 0.5) Gemifloxacin (MIC 90 ≤ 0.25) 24.8>0.25>0.25 (Percent susceptible data determined using MIC 90 values from the Interpretation by Clinical and Laboratory Standards Institute, Wayne, PA and data supplied by the British Society for Antimicrobial Chemotherapy, February 2008)

Does source affect antibiotic efficacy in ophthalmic MRSA infections? MoxifloxacinCornea Soft Skin Conjunctiva # Sensitive 2185 # Resistant Total # Chi square comparison of MRSA sources and moxifloxacin using the Pearson coefficient of significance (95% CI)Source Cornea and Conjunctiva Cornea and Soft Skin Conjunctiva and Soft Skin p value p = p =

Conclusion There is an increasing prevalence of MRSA ophthalmic infectionsThere is an increasing prevalence of MRSA ophthalmic infections Ocular MRSA isolates are rarely resistant to vancomycinOcular MRSA isolates are rarely resistant to vancomycin In our series, 97% were susceptible In our series, 97% were susceptible Four of the newer antibiotics proved potent against MRSA ocular isolatesFour of the newer antibiotics proved potent against MRSA ocular isolates Isolate susceptibility was at least 92% when testing Daptomycin, Tigecycline, Linezolid, and Quinpristin / dalfopristin Isolate susceptibility was at least 92% when testing Daptomycin, Tigecycline, Linezolid, and Quinpristin / dalfopristin Adaptation of these for ocular use may prove vitally important Adaptation of these for ocular use may prove vitally important Sensitivity of ocular MRSA isolates to varying antibiotics depends on the sourceSensitivity of ocular MRSA isolates to varying antibiotics depends on the source Moxifloxacin has statistically greater efficacy against soft skin infections (presumed community acquired variants) versus conjunctival and corneal infections Moxifloxacin has statistically greater efficacy against soft skin infections (presumed community acquired variants) versus conjunctival and corneal infections