Evaluation of hypertonic saline–sodium hydroxide method for isolation of Mycobacterium tuberculosis on Lowenstein–Jensen medium

Abstract

Background: Decontamination of sputum specimen is a crucial procedure for successful isolation of Mycobacterium tuberculosis (MTB) using Lowenstein–Jensen (LJ) media. The aim of this study was to evaluate hypertonic saline–sodium hydroxide (HSSH) method for decontamination of sputum specimens for the isolation of MTB on LJ medium. Methods: The sputum specimens were divided into three aliquots and were decontaminated by HSSH method, N-acetyl L-cysteine-sodium hydroxide (NALC-NaOH) method, and modified Petroff's method. We have compared the smear positivity, isolation rate, and contamination rate of HSSH method with that of NALC-NaOH method and modified Petroff's method for decontamination of sputum specimens for LJ culture. Results: Sputum samples from 270 patients were processed by the three decontamination methods, of which 24 (8.9%) were smear and culture positive by one or more decontamination methods. Of the 24 smear-positive cases, 23 (95.8%) were positive by NALC-NaOH method, 21 (87.5%) were positive by HSSH method, and 17 (70.8%) were positive by modified Petroff's method. The contamination rate of HSSH method, NALC-NaOH method, and modified Petroff's method was 2.2% (6/270), 8.9% (24/270), and 6.7% (18/270), respectively. The MTB isolation rate of HSSH method, NALC-NaOH method, and modified Petroff's method was 7.0% (19/270), 4.1% (11/270), and 3.3% (9/270), respectively. Conclusion: Among the three decontamination methods, a significantly higher isolation rate and a lower contamination rate were observed with HSSH method. Therefore, we recommend HSSH method for decontamination of sputum samples for the isolation of MTB using LJ medium.