Comparison of bacterial culture results collected via direct corneal ulcer vs conjunctival fornix sampling in canine eyes with presumed bacterial ulcerative keratitis.

OBJECTIVE

To compare aerobic bacterial culture results between samples obtained from the corneal ulcer versus lower conjunctival fornix in eyes with presumed bacterial ulcerative keratitis.

ANIMALS STUDIED

Fifty five client-owned dogs diagnosed with ulcerative keratitis.

PROCEDURES

Ophthalmic examinations were performed on each dog including slit-lamp biomicroscopy and indirect ophthalmoscopy. Microbial swabs were collected by direct sampling of the infected corneal ulcer as well as the lower conjunctival fornix, of the same eye, using a sterile rayon-tipped swab. Samples were submitted to an outside reference laboratory for aerobic bacterial culture and sensitivity.

RESULTS

One hundred twelve samples were obtained from 56 eyes (55 dogs). Sixty-eight samples yielded bacterial growth. Positive growth from both sites was obtained in 31 eyes (55%). Six eyes yielded bacterial growth from the conjunctival fornix but not from the cornea. No bacterial growth was obtained from either sampling site in 19 eyes. Overall, 31/56 (55%) corneal samples were positive and 37/56 (66%) conjunctival fornix samples were positive. Comparison of organisms isolated from the two collection sites of the same eye revealed an exact correlation in 42/56 (75%) eyes and differed in 14/56 (25%) eyes. Twenty different bacterial isolates were obtained from 68 positive samples. Gram-positive (71%) organisms were more common than Gram-negative (29%). The most commonly isolated organisms were Staphylococcus pseudintermedius (25%), beta-hemolytic Streptococcus spp. (23%), and Pseudomonas aeruginosa (12%). Methicillin-resistant organisms were isolated in 9% of samples.

CONCLUSION

Sampling from the conjunctival fornix may be a suitable alternative to direct ulcer sampling in eyes with compromised corneal structural integrity.