Objective: To describe the bacterial bio-burden of open-treated wounds and make comparisons with bite wounds. Design: Retrospective multicentre study. Sample: Microbial culture between 2011 and 2013 from open-treated wounds in dogs and cats (initiation of therapy n=88, follow-up n=52) were compared to those from bite wounds (n=184). Procedures: Bacteria were identified and tested for antibiotic susceptibility by two accredited laboratories. Results: In total, 77/88 (88%) of open-treated wounds yielded positive bacterial cultures at the beginning of treatment, decreasing to 27/52 (52%) during treatment. Upon initial evaluation, 42/88 (48 %) of open-treated wounds were considered infected with multi-drug-resistant bacteria, with a drop to 22/52 (41%) during therapy. Bite wounds yielded fewer positive cultures 88/184 (48%) with only 11/182 (6%) being affected by multi-drug-resistant bacteria. Bacteria found most commonly in open-treated wounds were Enterococcus subspecies, Escherichia coli, Staphylococcus pseudintermedius and Pseudomonas aeruginosa. Conclusion: The bacterial populations of open-treated wounds differed markedly from the bite wounds. The high incidence of multi-drug-resistant strains in open wounds highlights the need for alternatives to antibiotics.