RESUMO
Decontamination by modified Petroff s method is being practiced in many laboratories carrying out Mycobacterium tuberculosis culture and drug susceptibility testing. The method exposes mycobacteria to 4% sodium hydroxide for 30 min. However, laboratories in developing countries with limited resources might be using a type of centrifuge that does not open during power failures and exposes the mycobacteria to alkali for longer periods. Out of 28 smear-positive specimens processed, 85.7%, 85.7% and 60.7% of specimens showed a positive culture after exposure to alkali for 0.5, 1.0 and 72 h. Laboratories compelled to expose the mycobacteria for a longer duration of time can still attempt isolation for culture as only a small amount of bacteria are needed for culture positivity