Selective Inhibition of <i>Mycobacterium tuberculosis</i> by Para-Nitrobenzoic Acid (PNB) used in Lowenstein-Jensen Medium
Keywords:PNB, AFB, LJ medium, Mycobacterium tuberculosis
Background: Mycobacterial growth in media to which inhibitory substances are added has been used in species identification. Mycobacterium tuberculosis does not grow in Lowenstein-Jensen (LJ) medium containing para-nitrobenzoic acid (PNB); which can be a basis for its identification from other mycobacteria.
Setting: National Tuberculosis Centre (NTC), Thimi, Bhaktapur, Nepal.
Objectives: To evaluate usefulness of PNB containing LJ medium in identifying mycobacterial isolates.
Methodology: This diagnostic evaluation study based at NTC was conducted from Sep 2006-Jun 2007. During the study period, a total of 857 sputum samples collected from patients attending NTC were analyzed using fluorescence microscopy. The smear positive samples were confirmed by Ziehl-Neelsen (ZN) staining. Smear positive samples were cultured on LJ media with and without PNB; followed by biochemical tests.
Results: Out of total 857 sputum samples analyzed, 246 (28.7%) were positive for AFB on fluorescence staining and 214 (87%) of smear positive samples were also positive in culture. All the isolates which grow on LJ media without PNB did not grow on LJ media containing PNB.
Conclusion: Mycobacterium tuberculosis can be identified and differentiated from non-tuberculous mycobacteria using PNB containing media, easily in labs where culture is being done.
Keywords: PNB; AFB; LJ medium; Mycobacterium tuberculosis
SAARC J. Tuber. Lung Dis. HIV/AIDS 2008 Vol.5(1) 25-28
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