Ciprofloxacin as a representative of disk diffusion in vitro susceptibility of enrofloxacin for bacterial organisms from the middle-ear tissue of dogs with end-stage otitis externa.

The purposes of this study were to determine whether ciprofloxacin disk diffusion susceptibility test (DDT) results could be used to assess the in vitro susceptibility of otic bacterial organisms to enrofloxacin and to determine the effect of concurrent enrofloxacin administration on the DDT results for enrofloxacin and ciprofloxacin. Thirty dogs with end-stage otitis externa undergoing unilateral total ear canal ablation were enrolled. The dogs were randomized to one of four enrofloxacin-treatment groups or to the control group. Each dog in the treatment groups received two intravenous doses of enrofloxacin prior to surgical removal of the middle-ear tissue while the control group did not receive any enrofloxacin. One dog was excluded from the study as no middle-ear tissue was removed during surgery. Twenty-four dogs were in the enrofloxacin-treatment groups and five dogs were in the control group. In 12 of 29 dogs (41.4%), 14 of 82 (17.1%) of bacteria had discrepancies in DDT results for enrofloxacin and ciprofloxacin. Discrepancies between the control group and treatment groups were not significantly different even though the percentage of discrepancies for the combined treatment group was 19.4% compared to 6.7% for the control group. In this study, ciprofloxacin DDT results were not an accurate indicator of the in vitro susceptibility of enrofloxacin for bacteria isolated from the middle-ear tissue of dogs with end-stage otitis.

Infection with Corynebacterium pseudotuberculosis in five alpacas.

Among the population of an alpaca breeding farm, 5 alpacas (22 days to 14 months old) developed focal swellings in the subcutaneous tissues of the head or neck. Infection with Corynebacterium pseudotuberculosis was confirmed on the basis of results of microbial culture of abscess material and a serum hemolysis inhibition assay to detect C. pseudotuberculosis toxin. The dams of the affected alpacas were seronegative for C. pseudotuberculosis toxin. The affected alpacas underwent surgical excision of the abscesses and were isolated from herdmates for 90 days; treatment was successful, and no other alpacas in the herd became infected. Common risk factors for sources of infection in the affected alpacas included housing in a maternity barn and a pasture. Also, the infection potentially originated from new alpacas introduced into the herd during the preceding 3 months. Infection with C. pseudotuberculosis should be considered as a differential diagnosis for camelids with peripheral lymphadenopathy or abscesses in subcutaneous tissues.