Comparative activity of antimicrobials against <i>Pseudomonas aeruginosa</i>, <i>Achromobacter xylosoxidans</i> and <i>Stenotrophomonas maltophilia</i> keratitis isolates.

Abstract

<i>Achromobacter xylosoxidans</i> and <i>Stenotrophomonas maltophilia</i> are emerging corneal pathogens, which are closely related to <i>Pseudomonas aeruginosa</i>, and have intrinsic resistance to many commonly available antimicrobials. The purpose of this study is to compare the in vitro efficacy of 12 antimicrobial agents against <i>A. xylosoxidans</i>, <i>S. maltophilia</i> and <i>P. aeruginosa</i> isolates recovered from clinical cases of keratitis. Recovered corneal isolates (n=58) were identified and extracted from the Microbiology Data Bank of the Bascom Palmer Eye Institute. Comparative in vitro minimum inhibitory concentration (MIC) susceptibility profiles for fluoroquinolones, aminoglycosides, beta-lactams and miscellaneous antibiotics were recorded using the E-test methodology. Pharmacodynamic indices (Cmax/MIC) were calculated. <i>A. xylosoxidans</i> and <i>S. maltophilia</i> isolates were resistant to fluoroquinolones, aminoglycosides and ceftazidime (susceptibility rate ranging from 0% to 30%) while <i>P. aeruginosa</i> 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 <i>S. maltophilia</i> isolates and Cmax/MIC=10.19. Ninety to 100% susceptibility rates were found for minocycline and trimethoprim/sulfamethoxazole for both <i>A. xylosoxidans</i> and <i>S. maltophilia</i>. One hundred per cent of the <i>A. xylosoxidans</i> isolates were susceptible to piperacillin/tazobactam and ticarcillin/clavulanic acid. There is a significant difference in susceptibility patterns between <i>A. xylosoxidans</i>, <i>S. maltophilia</i> and <i>P. aeruginosa</i>. Fluoroquinolones and aminoglycosides may not be effective against <i>A. xylosoxidans</i> and <i>S. maltophilia</i>. Antibiotics that are not commercially available as eye drops, such as beta-lactams for <i>A. xylosoxidans</i>, and trimethoprim/sulfamethoxazole and minocycline for both <i>A. xylosoxidans</i> and <i>S. maltophilia</i> should be considered.