Actinobacillus Species Resistance

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.

At the Hagyard-Davidson-McGee veterinary associates’ medicine unit in Lexington, Ky., where many of the MRLS mares and foals were seen in intensive care unit, Nathan Slovis, DVM, Dipl. ACVIM, reviewed the 2002 sensitivity reports on uterine cultures, transtracheal washes, blood cultures, and joint aspirates at the clinic. He noted that, “the sensitivity patterns do not reveal a resistance pattern.”


About the Author

Kimberly S. Brown

Kimberly S. Brown was the Publisher/Editor of The Horse: Your Guide To Equine Health Care from June 2008 to March 2010, and she served in various positions at Blood-Horse Publications since 1980.

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