Antimicrobial Activity of Ophthalmic Antibiotics Against Bacterial Isolates From Aqueous and Vitreous Humor

Saturday, April 18, 2015: 1:39 PM
Room 1A (San Diego Convention Center)
Francis S. Mah, MD
Christine M. Sanfilippo, PhD

Decolonization of the ocular surface prior to invasive procedures may decrease the likelihood of intraocular infections. Antibiotic resistance is widespread and can negate antibiotic treatment. We evaluated the resistance profile of 115 bacterial isolates from the vitreous and aqueous humor for antibiotics commonly used in ophthalmic practice.

Vitreous and aqueous humor isolates (n=155) collected across the USA from 2009 to 2012 for the ARMOR antimicrobial surveillance study were studied.  These included 5 Haemophilus influenzae, 5 Pseudomonas aeruginosa, 16 Streptococcus pneumoniae, 22 Staphylococcus aureus, and 67 Coagulase-negative staphylococci (CoNS) isolates.  The minimum inhibitory concentrations (MIC), in µg/ml, were determined by the broth microdilution method according to Clinical and Laboratory Standards Institute’s guidelines. Where applicable, isolates were categorized as susceptible, intermediate, or resistant based on systemic breakpoints.

All H. influenzae and P. aeruginosa isolates were susceptible to all antibiotics tested, except for 1 ciprofloxacin-intermediate P. aeruginosa isolate. Among S. pneumoniae isolates, resistance was observed only for azithromycin (31%) and chloramphenicol (13%). S. aureus isolates included strains resistant to methicillin (27%), ciprofloxacin (27%), azithromycin (45%) and others.  CoNS had the highest resistance: ciprofloxacin (60%), methicillin (54%), and azithromycin (57%).  Maximum fluoroquinolone MICs for all staphylococci were 4 (besifloxacin), 128 (moxifloxacin/gatifloxacin), and 256 (ciprofloxacin/levofloxacin); ciprofloxacin and levofloxacin were most potent against P. aeruginosa.

Antibiotic resistance impacts the choice of topical antibiotic to decolonize the ocular surface. CoNS, organisms frequently associated with intraocular infections, showed the highest antibiotic resistance rates. Topical besifloxacin could be an appropriate choice for reducing ocular surface bacterial loads prior to invasive ocular procedures.