Complicated bacterial infections should prompt clinicians to pursue a definitive diagnosis. Two methods of bacterial culture and antibiotic susceptibility testing are commonly used in veterinary medicine: (1) the disk diffusion technique and (2) the broth dilution technique. Both methods identify the infecting pathogen and the antibiotics that are likely to inhibit its growth. The broth dilution test also provides the minimal inhibitory concentration, which can help in making the best antibiotic choice.