Inhibitory and bactericidal concentrations of current and new antibiotics for Methicillinresistant S

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• 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 Email
dmiller_at_med.miami.eduPhone 305-326-6000 X6034
McKnight Building, 1st floor
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Background and Purpose

• 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.
• 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.

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

• One hundred and one random MRSA isolates
  (collected at the BPEI microbiology laboratory
  from January 2005 and February 2009) were
  selected
• 40 Conjunctival
• 30 Corneal or Contact lens
• 31 Periocular soft tissue sources
• Mean inhibitory concentrations (MIC50 90) were
  determined using the Sensititre microtiter assay
  
• Trek Diagnostic Systems Cleveland, OH
  http//www.trekds.com.
• Mean bactericidal concentrations (MBC50 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
  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

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Antibiotics Evaluated in StudyMethods

• Streptogramins
• Quinpristin
• Dalfopristin
• Nitrofuran
• Nitrofurantoin
• Sulfonamide
• Sulfamethoxazole
• Tetracycline
• Tetracycline
• Penicillins
• Penicillin
• Ampicillin
• Oxacillin

• Macrolides
• Azithromycin
• Erythromycin
• Clarithromycin
• Miscellaneous Peptide antibiotics
• Vancomycin
• Tricyclic Glycopeptides
• Daptomycin
• Lipopeptide
• Lincosamide
• Clindamycin
• Ketolide
• Telithromycin
• Rifamycin

• Fluoroquinolones
• Ciprofloxacin
• Moxifloxacin
• Gemifloxacin
• Aminoglycosides
• Gentamicin
• Streptomycin
• Dihydrofolate reductase inhibitor
• Trimethoprim
• Non-macrolide 50s ribosome inhibitor
• Chloramphenicol (UK)
• Glycylcycline
• Tigecycline
• Oxazolidinone

emerging antibiotic
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Data Sheet UtilizedMethods
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Results for Common Antibiotics against MRSA(All
sources)
(Percent susceptible data determined using MIC90
values from the Interpretation by Clinical and
Laboratory Standards Institute, Wayne, PA)
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Results for New Antibiotics against MRSA(All
sources)
(Percent susceptible data determined using MIC90
values from the Interpretation by Clinical and
Laboratory Standards Institute, Wayne, PA and
data supplied by the British Society for
Antimicrobial Chemotherapy, February 2008)
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Does source affect antibiotic efficacy in
ophthalmic MRSA infections?
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Conclusion

• There is an increasing prevalence of MRSA
  ophthalmic infections
• Ocular MRSA isolates are rarely resistant to
  vancomycin
• In our series, 97 were susceptible
• Four of the newer antibiotics proved potent
  against MRSA ocular isolates
• Isolate susceptibility was at least 92 when
  testing Daptomycin, Tigecycline, Linezolid, and
  Quinpristin / dalfopristin
• Adaptation of these for ocular use may prove
  vitally important
• Sensitivity 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