Do post‐surgical multiresistant urinary infections occur in horses? Case of unilateral pyelonephritis caused by extended‐spectrum beta‐lactamase‐producing bacteria as a complication of cystotomy

Pyelonephritis is a serious condition that is rarely described in horses. In contrast, urinary tract infections are common in humans and small animals, and multi‐drug‐resistant urinary infections are an emerging threat. In this report, we describe a horse with unilateral pyelonephritis caused by extended‐spectrum beta‐lactamase‐producing bacteria belonging to the Enterobacter cloacae complex. [Correction added on 9 August 2023, after first online publication: The preceding sentence was corrected.] An 11‐year‐old Swedish warmblood gelding was diagnosed with a cystolith and a cystotomy through an open left para‐inguinal approach was performed. Seven days after surgery the horse presented with pyrexia, dullness and colic. Diagnostic testing and renal transabdominal ultrasonography confirmed the presence of a right‐sided pyelonephritis. Culture and antimicrobial susceptibility testing revealed a pure growth of extended‐spectrum beta‐lactamases‐producing E. cloacae complex bacteria with resistance against beta‐lactams, aminoglycoside and trimethoprim–sulphonamide classes. Treatment included prolonged oral antimicrobials according to susceptibility testing results (enrofloxacin), judicious use of non‐steroidal anti‐inflammatory drugs, fluid therapy and gastric ulcer prophylaxis. The horse recovered successfully and is currently in good health (follow‐up of 5 years). Once the infection resolved, unilateral renal scarring occurred. Multidrug‐resistant upper‐urinary infections occur in horses and should be considered in a post‐surgical patient that develops fever. Early diagnosis, urine bacterial culturing and antimicrobial susceptibility testing were crucial in this case to successful management.