EVALUATION OF A MODIFIED BACTEC METHOD TO STUDY THE ACTIVITY OF DISINFECTANTS AGAINST MYCOBACTERIUM-TUBERCULOSIS

Setting: BACTEC radiometry could provide a useful tool for evaluating the effect of disinfectants on mycobacteria. Objective: The aim of this study was to improve the recovery of mycobacteria in the BACTEC system and thereby develop a new method for disinfectant testing with Mycobacterium tuberculosis. Design: Protein was added to BACTEC 7H12B media. Growth and the recovery of M. tuberculosis after exposure to disinfectants was measured using viable counts and BACTEC radiometry. Results: Protein additives enhanced growth in 7H12B media. After serial dilution of inoculum, 7H12B plus 10% egg yolk recovered mycobacteria from a 10(-2) higher dilution than viable counts. After 5 min disinfection with 3% peroxygen compound (Virkon), 3% Virkon plus saline or 2% gluteraldehyde (Cidex) no mycobacteria were recovered using standard 7H12B. However, using 7H12B plus protein, growth was detected in all of these within 30 days. In contrast, viable counts detected growth with Cider and Virkon after 5 min disinfection but not from Virkon in saline. Viable counts took 3-8 weeks to determine. Conclusion: Using this modified BACTEC system for the evaluation of disinfectant action on mycobacteria pro,ides advantages in speed, sensitivity and ease of use when compared with viable counts.