Abstract: Background – Evidence-based guidelines to optimize blood culture sensitivity are needed in veterinary medicine. Objectives – Evaluate the effects of inoculum size, transit temperature, and transit time on sensitivity and time to detection of Escherichia coli, Staphylococcus pseudintermedius, and Clostridium perfringens in canine blood using the Oxoid SIGNAL manual blood culture system. Animals – Canine packed red blood cell units (PRBC) were purchased. Methods - Canine PRBC samples were inoculated with 5 or 50 colony forming units (CFU) of bacteria and stored at room temperature (21 °C) or refrigerated (5 °C) for 1, 24, 48, 72, or 96 hours prior to incubation. Matrix-associated laser desorption/ionization and Gram staining confirmed bacterial growth. Negative controls were PRBC samples without bacteria. Cox hazard regression modeled time to detection of bacterial growth. Results – Sensitivity was high, regardless of transit time or temperature, for E. coli (98%) and S. pseudintermedius (94%), with median detection times of one day from initiation of incubation. Overall sensitivity for C. perfringens was markedly low (21%). Multivariate Cox regression revealed that higher inoculum size and room temperature storage significantly increased sensitivity and shortened time to C. perfringens detection. Transit time was not significantly associated with sensitivity or time to detection. Conclusions and Clinical Importance – Long transit times should not dissuade veterinarians from submitting blood cultures. For C. perfringens, higher CFU/mL (larger patient blood volume) and room temperature storage may optimize blood culture sensitivity. C. perfringens and other anaerobes may not be well detected in this blood culture system.
