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