Retrospective Identification of Bacterial Isolates From Emergency Laparotomy Surgical Site Infections in Horses

Surgical site infection (SSI) with multiresistant bacteria is an important cause of postoperative morbidity after laparotomy in horses. The objective of this study was to identify bacteria isolates and their antibiotic resistance patterns associated with the development of wound infection in horses after laparotomy. This is a retrospective case series. Medical records of horses that underwent ventral midline exploratory laparotomy in a four-year period at one equine hospital were reviewed. Results of microbiologic culture and susceptibility testing are described. The study group consisted of 183 (100%) horses that recovered from anesthesia after laparotomy. The prevalence of infection was 19% (24/124) after first surgery and 83% (19/23) after relaparotomy. The most common microbial isolates were bacteria of the family Enterobacteriaceae followed by Staphylococcus ssp., Enterococcus ssp., Streptococcus ssp., and Bacteroides ssp. Bacteria from the family Enterobacteriaceae showed the lowest resistance to amphenicols, cephalosporins, and quinolones groups of antibiotics. Coagulase-positive Staphylococci were sensitive to amphenicols and only 33% were resistant to trimethoprim/sulfamethoxazole. The most commonly used perioperative and postoperative antibiotics were gentamicin and amoxicillin. Limitations include poor control over exposure factors, covariates, and potential confounders during the surgery, recovery time, or period of hospitalization; relying on others for accurate outcome assessment and recordkeeping; lack of follow-up information once animals were discharged from the hospital. Despite 5 days of antibiotic prophylaxis, the rate of incisional infection is still high. The most common isolates from SSI belong to the family Enterobacteriaceae and the genus Staphylococcus, which showed high resistance to the antibiotics used before the gastrointestinal surgery.