Decontamination of sputum for longer time in sodium hydroxide for isolation of Mycobacterium tuberculosis

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 30min. 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 72h. 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.