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

The anaerobic intestinal spirochaete Brachyspira (Serpulina) pilosicoli has been isolated from the bloodstream of French patients by manual blood cult ure systems. The purpose of this study was to determine whether the automat ed and manual blood culture systems used in Australia are suitable for grow th and detection of this organism. Strains of B. pilosicoli were added to h uman blood to give concentrations ranging from 1x10(4) to 1x10(1) spirochae tes/ml and 10-ml volumes were inoculated into the media. Three strains of B , pilosicoli grew slowly in all manual Hemoline and BBL Septi-Chek formulat ions tested. Subcultures taken between 2 and 10 days after inoculation yiel ded growth only after incubation for a further 5-8 days. Growth and automat ed detection were achieved in the BACTEC system with Anaerobic/F medium wit h or without Fastidious Organism Supplement. Minimum time to signal for nin e strains varied between 5.6 and 14.9 days, with a minimum concentration of 10(1) spirochaetes/ml of blood being detected. None of nine strains gave a positive signal in the BacT/Alert system when FAN Anaerobic culture bottle s were used; however, four strains were detected by subculture taken at 7 o r 14 days after inoculation. When Anaerobic medium was used in the BacT/Ale rt system, two of three strains gave a signal and the other strain grew and was detected by subculture. Spirochaetaemias caused by B, pilosicoli may b e unrecognised because detection time by the signal or subculture exceeds 5 days.