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Comparative activity of antimicrobials against Pseudomonas aeruginosa, Achromobacter xylosoxidans and Stenotrophomonas maltophilia keratitis isolates

Poster Details

First Author: O.Spierer ISRAEL

Co Author(s):    D. Miller   T. O’Brien                 

Abstract Details


Achromobacter xylosoxidans and Stenotrophomonas maltophilia are emerging corneal pathogens, which are closely related to Pseudomonas aeruginosa, and have intrinsic resistance to many commonly available antimicrobials. The purpose of this study is to investigate the in vitro efficacy of 12 antimicrobial agents in the treatment of infectious keratitis caused by A. xylosoxidans and S. maltophilia and to compare it to P. aeruginosa.


Fifty eight recovered corneal isolates were identified and extracted from the Microbiology Data Bank of the Bascom Palmer Eye Institute.


The antimicrobial activity of 12 antibiotics was tested, including fluoroquinolones (ciprofloxacin, moxifloxacin), aminoglycosides (amikacin, tobramycin), beta-lactams (ceftazidime, imipenem, piperacillin/tazobactam, ticarcillin/clavulanic acid) and miscellaneous antibiotics (polymyxin B, trimethoprim/sulfamethoxazole, chloramphenicol, minocycline). Efficacy for each antibiotic was defined by the MIC90. The E-test methodology was used. Pharmacodynamic indices (Cmax/MIC) were calculated.


A. xylosoxidans and S. maltophilia isolates were resistant to fluoroquinolones, aminoglycosides and ceftazidime (susceptibility rate ranging from 0% to 30%). However P. aeruginosa isolates showed a susceptibility rate of 95-100% to these antimicrobials (p< 0.00001 for the various antimicrobials). Exception was moxifloxacin with 80% of susceptibility rate to S. maltophilia isolates and Cmax/MIC=10.19. More than 90% susceptibility rates were found for minocycline and trimethoprim/sulfamethoxazole for both A. xylosoxidans and S. maltophilia. One hundred percent of the A. xylosoxidans isolates were susceptible to piperacillin/tazobactam and ticarcillin/clavulanic acid.


There is a significant difference in susceptibility patterns between A. xylosoxidans, S. maltophilia and P. aeruginosa. Fluoroquinolones and aminoglycosides may not be effective against A. xylosoxidans and S. maltophilia. Antibiotics that are not commercially available as eye drops, such as the beta-lactams imipenem, piperacillin/tazobactam and ticarcillin/clavulanic acid for A. xylosoxidans, and trimethoprim/sulfamethoxazole and minocycline for both A. xylosoxidans and S. maltophilia should be considered.

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