Actinobacillus lignieresii infection in two horses

A 10-year-old pregnant Norwegian Fjord horse was examined for gross swelling of the muzzle of 2 years' duration. Examination of biopsy specimens revealed diffuse dermal fibrosis, micropustule formation, and vascular thrombosis; large numbers of Actinobacillus lignieresii were isolated in pure culture. Prolonged treatment with i.v. administration of sodium iodide and oral administration of trimethoprim-sulfamethoxazole caused regression of the swelling and did not induce abortion. A 5-month-old American Paint filly was examined for swelling in the udder region. Bacteriologic culture of purulent material obtained from the left teat revealed A lignieresii. Treatment with oral administration of rifampin and trimethoprim-sulfamethoxazole resulted in complete resolution of clinical signs. To the authors' knowledge, these findings represent the first report of mastitis and chronic nasal cellulitis caused by A lignieresii infection in horses.

In vitro antimicrobial susceptibility of Actinobacillus actinomycetemcomitans

The agar dilution technique was used for determination of the antibiotic susceptibilities of 57 oral isolates and 2 nonoral isolates of Actinobacillus actinomycetemcomitans. Tetracycline, minocycline, and chloramphenicol inhibited more than 96% of the strains tested at a concentration of less than or equal to 2 micrograms/ml; 89% of the strains were inhibited by 2 micrograms of carbenicillin per ml. The other antimicrobial agents tested were less active. Approximately 10% of the A. actinomycetemcomitans strains were resistant to ampicillin, erythromycin, and penicillin G at concentrations of 32 to 64 micrograms/ml. These data suggest that tetracycline and minocycline may be valuable drugs in the treatment of A. actinomycetemcomitans infections.