Gentamicin-resistant pseudomonal infection. Rationale for a redefinition of ophthalmic antimicrobial sensitivities.

Eight pseudomonal species were involved in 106 invasive infections of the eye; all were community acquired. Eighteen percent of the total and 9% of the Pseudomonas aeruginosa strains were gentamicin resistant, as defined using conventional criteria. All 10 cases of "resistant" pseudomonal (nine P. aeruginosa) keratitis responded satisfactorily to treatment with gentamicin. The resistance breakpoint (defined by safe serum levels in parenteral therapy) for most P. aeruginosa is much lower than ocular gentamicin levels achievable by optimal local application. We argue for a specific ophthalmologic definition of antibiotic resistance in infections of the cornea and external eye. MIC quantitative determinations of ocular isolates would provide more useful information to ophthalmologists than conventional qualitative disc sensitivity testing.