Screening of Mycobacterium Tuberculosis by Selective Inhibition With Para-Nitrobenzoic Acid, its Cytochemical Staining and Drug Susceptibility to Primary Anti-Tubercular Drugs

Abstract

This diagnostic study was conducted at National Tuberculosis Centre (NTC), Thimi, Bhaktapur from September 2006 to June 2007; with the objectives of screening of Mycobacterium tuberculosis using para-nitrobenzoic acid (PNB) added to the culture medium, the virulence testing using neutral red and response of the isolates to primaryset of anti-tubercular drugs. Of 857 sputum samples taken, 68.3% were from male and 31.7% from female. Out oftotal, 28.7% were positive for acid fast bacilli (AFB) by fluorescence microscopy, of which 78.45% were male and 21.55% were female. Out of total smear positive cases,87% were also positive in culture on Ogawa medium. All the Ogawa culture positive samples failed to grow on LJ medium containing PNB.However all the isolates were neutral red test positive. The drop catalase test and 68°Clabile catalase test were also used for the confirmation of the isolated M. tuberculosis. The proportion method used for the drug susceptibility test showed that 43.46% of the culture positive isolates were sensitive to all four primary anti-tubercular drugs. The resistance rate to one drug was found in 11.21%, to two drugs in 14.95%, to three drugs in 13.55% and to four drugs in 16.82% of the isolates. Multi-drug resistance (MDR) was observed in 28.97% of the isolates. Hence, the use of PNB in culture media is useful in the screening of M. tuberculosis along with its differentiation from non-tuberculous mycobacteria. Similarly, neutral red,a biochemical test used for identification of other bacteria, can be used for the virulence testing of M. tuberculosis – the method which is easy and rapid. The susceptibility testing result can be used as the guidance for proper treatment and in the management of MDR cases.