Evaluation of the performance of a novel sputum processing ReaSLR methodology for culture of sputum samples in solid and liquid media in comparison with modified Petroff's method.

Background: Early case detection by sputum smear microscopy is a crucial step in the control of pulmonary tuberculosis in high burden countries. Due to low sensitivity of this rapid and cost effective method, culture of Mycobacterium tuberculosis (MTB) is considered as the gold standard. Modified Petroff's method using 2%-4% sodium hydroxide (NaOH) and N-acetyl- l-cysteine (NALC) to digest and at the same time to decontaminate the specimen is widely used in developing countries prior to culture. This method is considered tedious and cumbersome. A novel ReaSLR (ReaMetrix's Sputum Liquefying Reagent) methodology has been proposed as a simple and low-cost method for sputum processing. This study was undertaken to evaluate the performance of the ReaSLR method of sputum processing prior to culture in comparison to the modified Petroff's method.

Methods: Early morning sputum samples, collected from suspected TB patients, were divided into two equal halves and processed by two different methods i.e modified Petroff's method and ReaSLR method. After processing with different methods, each sample was inoculated in Lowenstein Jensen (LJ) medium and Mycobacteria growth indicator tube (MGIT). Smears were also prepared from the samples processed with modified Petroff's method and graded according to Centers for Disease Control and Prevention (CDC) grading after microscopic examination. Culture results of both the methods were recorded and analysed using SPSS 20.0 version.

Results: On comparing different methods of sputum processing for culture in solid and liquid media, the rate of contamination in both the media was significantly high with ReaSLR method as compared with modified Petroff's method. Also, the mean time-to-detection of MTB growth in LJ medium was significantly less with modified Petroff's method i.e 30.21 days as compared to ReaSLR method (34.23 days; p < 0.001). However, the mean time-to-detection of MTB growth in MGIT was similar with both the methods.

Conclusion: Due to the high contamination rate in solid and liquid culture media, ReaSLR method cannot be considered as an alternative to modified Petroff's method for sputum processing prior to culture. The detection of growth of MTB in LJ media was also earlier with modified Petroff's method than ReaSLR method.