A retrospective study at the University of Pennsylvania showed a possible pattern of resistance to antibiotics by the isolates. During the five-year study period, 1,604 horses underwent “clean” elective surgical procedures. Of those, 23 (1.43%) had postoperative wound infections, and Actinobacillus species were isolated from 10 of the 23 (43%). Seven horses survived and three were euthanized. All 10 Actinobacillus isolates were resistant to penicillin, according to the study, and six were resistant to trimethroprim-sulfamethoxazole. All isolates were susceptible to ceftiofur and gentamicin.

During the study period, Actinobacillus organisms were isolated from 35 of 513 (6.8%) samples from the general hospital population submitted for bacterial culture and antimicrobial susceptibility testing, according to the study.

“Susceptibility profiles fro these isolates were different from typical susceptibility profiles for Actinobacillus isolates, suggesting that a pattern of resistance may be emerging,” noted the study published in the Nov. 1 issue of the Journal of the American Veterinary Medical Association.

Actinobacillus species were found in higher than expected numbers in the aborted fetuses of mares during the mare reproductive loss syndrome (MRLS) crisis of 2001 and 2002