Evaluation of blood culture systems for detection of the intestinal spirochaete Brachyspira (Serpulina) pilosicoli in human blood

The anaerobic intestinal spirochaete Brachyspira (Serpulina) pilosicoli hasbeen isolated from the bloodstream of French patients by manual blood culturesystems. The purpose of this study was to determine whether the automated andmanual blood culture systems used in Australia are suitable for growth anddetection of this organism. Strains of B. pilosicoli wereadded to human blood to give concentrations ranging from 1×104 to 1×101spirochaetes/ml and 10-ml volumes were inoculated into the media. Three strainsof B. pilosicoli grew slowly inall manual Hémoline and BBL Septi-Chek formulations tested. Subcultures takenbetween 2 and 10 days after inoculation yielded growth only after incubationfor a further 5–8 days. Growth and automated detection were achieved in theBACTEC system with Anaerobic/F medium with or without Fastidious OrganismSupplement. Minimum time to signal for nine strains varied between 5.6 and 14.9days, with a minimum concentration of 101 spirochaetes/ml of blood beingdetected. None of nine strains gave a positive signal in the BacT/Alert systemwhen FAN Anaerobic culture bottles were used; however, four strains weredetected by subculture taken at 7 or 14 days after inoculation. When Anaerobicmedium was used in the BacT/Alert system, two of three strains gave a signaland the other strain grew and was detected by subculture. Spirochaetaemiascaused by B. pilosicoli may beunrecognised because detection time by the signal or subculture exceeds 5 days.