A 5‐year‐old, male, entire labrador was treated for grade III tetanus, developing aspiration pneumonia and undergoing mechanical ventilation. However, 5 days after weaning from mechanical ventilation, the dog developed a new pyrexia. Investigations documented circulating intracellular bacteria, a bacterial peritonitis and a large right jugular thrombus. Blood, peritoneal and urinary cultures yielded a multidrug‐resistant Escherichia coli. The jugular catheter had been in place for 10 days, and the dog had received parenteral nutrition. The pyrexia resolved immediately after catheter removal and there was no echocardiographic evidence of endocarditis. No abdominal source of infection was identified by computed tomography and the septic peritonitis was managed conservatively, including percutaneous placement of an indwelling peritoneal drain for drainage and lavage. The dog was escalated to intravenous gentamicin antibiosis with ongoing supportive care, and discharged with cefovecin, making a full recovery after 20 days in the intensive care unit.