Drug Susceptibility Testing of M. tuberculosis to Isoniazid and Rifampicin- A Comparison between MTT Tube Method and LJ Proportion Method.

Aim: To evaluate the methodology of MTT tube assay and compare it with standard proportion method for detection of drug susceptibility of M. tuberculosis to rifampicin (RIF) and isoniazid (INH). Study Design: Prospective. Place and Duration of Study: Sher-i-Kashmir Institute of Medical Sciences, Kashmir, India. One year study. Methodology: MTT [3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide] assay was performed on 60 clinical isolates of M. tuberculosis. An inoculum of 107CFU/ml prepared in Middlebrook 7H9 with OADC (Oleic acid, albumin, dextrose and catalase) was chosen as standard. For each drug three tubes were used, one drug containing (INH 0.2 μg/ml or RIF 1 μg/ml), second inoculum control and third blank control. The method was performed after incubating the tubes at 37°C for 4 days for RIF and 7 days for INH. Results were read visually and by spectrophotometer at 570 nm. Relative optical density units of 0.2, was taken as cutoff. Results of drug susceptibility were compared with those obtained by Lowenstein Jensen proportion method. Results: For RIF, sensitivity was 88.9% and 94.4%; specificity was 100% and 97.6% for visual MTT and MTT by RODU respectively. For INH similar sensitivity of 95.1% was seen while specificity was 97.0% and 95.0% by visual MTT and MTT by RODU respectively. There was almost perfect agreement between proportion and MTT method for both drugs. Turn-around time for MTT assay was 7 days. Conclusion: The MTT tube assay can be used for rapid drug susceptibility testing of M. tuberculosis to RIF and INH.

Bacterial and fungal profile of corneal ulcers--a prospective study.

Corneal ulceration continues to be one of the most important causes of ocular morbidity and blindness worldwide. Between April 1999 and May 2001, 80 patients with corneal ulceration were examined to find the causative microorganisms, the sensitivity pattern of bacterial isolates to antibiotics, the predisposing factorsfor ulcerative keratitis and the comparison between culture and gram staining results. Corneal ulceration was seen more in males than females, predominantly in farmers (61.25%) and trauma was the commonest predisposing factor, the agents being mainly organic agricultural materials. Of the 80 corneal ulcers, 32(40%) yielded pure bacterial growth while fungal growth was seen in 10(12.5%). Streptococcus pneumoniae was the commonest bacterium while Aspergillus fumigatus and Fusarium species were the commonest fungi isolated. Most of the bacterial isolates were sensitive to chloramphenicol and tetracycline followed by the quinolones. The overall sensitivity and specificity of Gram staining as compared to culture was 57.14% and 94.7% respectively.