Bacterial and fungal isolates from Equidae with ulcerative keratitis.

Gram-negative bacteria were the most common microbial isolates from 38 eyes of 37 horses with ulcerative keratitis. Pseudomonas sp, Enterobacter group, and Acinetobacter sp were the most prevalent. Fungi were cultured from 15 eyes and included 7 genera, with Aspergillus sp being the most prevalent. Ten of the eyes with fungal keratitis had been treated with corticosteroids. Eleven of 38 eyes had mixed bacterial and fungal infections. Clinically, the most severe cases were those in which Aspergillus and gram-negative bacteria existed in a mixed infection. On the basis of susceptibility testing, gentamicin was highly efficacious (88.4%) against all bacterial isolates. Cephaloridine was slightly more efficacious than gentamicin against the gram-positive organisms. Only 32.3% of the gram-negative isolates were susceptible to chloramphenicol. Of the relatively small number of gram-positive organisms isolated, streptococci were more often susceptible to chloramphenicol, whereas staphylococci were more often susceptible to gentamicin.