Inter-bottle transfer of mycobacteria by the BACTEC 460.

As a result of several episodes of inter-bottle transfer of molds and mycobacteria in our BACTEC 460 TB System (Johnston Laboratories, Towson, MD), we designed some experiments to attempt to reproduce the transfer process. We demonstrated that organism transfer could occur with our instrument during routine use without any indication of instrument malfunction. Utilizing a redesigned A1B4 circuit board that extends the time of the needle heating cycle to 85 sec and increases the needle heater maximum temperature, we were not able to effect organism transfer even from bottles with very high growth indices. We also demonstrated that even with the redesigned A1B4 circuit board, the needles were not heated sufficiently to sterilize them after direct insertion into a mycobacterial suspension. Organism transfer also occurred while using a second redesigned A1B4 circuit board which extends the needle heating cycle to 75 sec. Users should be aware that organism transfer can occur with the BACTEC 460 under certain circumstances. Maintenance and testing recommendations from Johnston Laboratories should be scrupulously followed, and we suggest some additional procedures that might further reduce the possibility of organism transfer.