Antibacterial susceptibility patterns for microbial isolates associated with infectious keratitis in horses: 63 cases (1986-1994)
Moore, C.P.; Collins, B.K.; Fales, W.H.
Journal of the American Veterinary Medical Association 207(7): 928-933
1995
ISSN/ISBN: 0003-1488 PMID: 7559027 Document Number: 441775
Of 73 aerobic bacteria isolated from 64 eyes of 63 horses with infectious keratitis, 42 (58%) were gram-positive (g+, 10 genera) and 31 (42%) were gram-negative (g-, 5 genera). After local antimicrobial treatment, repeat cultures from samples obtained from 15 eyes of hospitalized horses yielded 21 secondary bacterial isolates. Staphylococcus spp and Streptococcus spp were the commonest g+ isolates and accounted for 79% of g+ organisms isolated initially. Antibiograms revealed ticarcillin to be the most efficacious antibiotic tested on g+ organisms, with 28 of 30 (93%) being susceptible. Of commercially available topical ophthalmic antibiotics tested on g+ organisms, erythromycin was the most efficacious, with 32 of 35 (91%) isolates susceptible. Pseudomonas spp, Escherichia coli, and Acinetobacter spp accounted for 68% of g- organisms isolated initially. Gentamicin, tobramycin, polymyxin B, and neomycin were highly effective in vitro against initial g- isolates. Chloramphenicol was ineffective against g+ and g- organisms isolated initially. A higher frequency of g- organisms was noticed on repeat cultures after intensive topical antimicrobial treatments than isolated at the initial examination. Pseudomonas organisms isolated from second cultures were resistant to gentamicin, but susceptible to ciprofloxacin. Overall, secondary g- isolates were more susceptible to ciprofloxacin, neomycin, tobramycin, or amikacin than to gentamicin. Fungi were isolated in 24 of 63 (38%) horses. 25 filamentous fungi and 2 yeasts were identified from 24 eyes. Aspergillus spp was the dominant fungi; it was detected in 17 of 22 (77%) eyes in which filamentous fungi were identified.