Rat-Bite Fever: Updated Recommendations For Culture And Isolation Of Streptobacillus Moniliformis Using An Automated Continuous Blood Culture Instrument In A Clinical Setting

Abstract

Abstract Introduction/Objective Rat-bite fever and Haverhill fever are difficult to diagnose in a clinical setting due mostly to clinicians and laboratory professionals being unable to culture the causative agent-Streptobacillus moniliformis. SPS in blood culture bottles has historically been implicated as the complicating factor. Methods Utilizing the BDFX40 automated continuous blood culture bottle system and novel quantitative PCR data, we present how blood volume is critical in order to consistently detect, isolate and grow the organism in the presence of SPS using modern laboratory instrumentation in a clinical setting. Results We demonstrate here that 10ml of blood was determined to provide optimal results for detection and growth of S. moniliformis in 0.05% SPS. For all isolates tested, 100% (n=56) were detected or alerted as positive by the instrument, with the longest time required for detection being 102 hours (n=1) and the fastest time to detection being recorded at 13.4 hours. (n=1) with an average time of 26.5 hours (n=56). Conclusion During the course of this study, we determined that blood inoculum volume played a significant role in organism growth and detection. We found that in 100% of the isolates tested (and all the variations of testing within), SPS (up to a concentration of 0.05% w/v) in blood culture media appeared to be counteracted, allowing for the growth detection and culturing of S. moniliformis using an automated continuous blood culture system when 10ml of blood was used as an inoculum. This is the first study to report and suggest that a specific blood volume is critical when utilizing a closed commercial blood culture system to detect S. moniliformis, this research is the largest study of Streptobacillus moniliformis isolates to date.