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DRUG RESISTANCE IN TUBERCULOSIS
Lina Deodhar, Priya Miskeen, Sweta Chomal
Department of Microbiology, Bombay Hospital and Medical Research Centre,
Mumbai - 400 020
Over a period of two and half years, 707 cultures of M. tuberculosis were tested for drug susceptibility against commonly used anti-tuberculosis drugs. A combined resistance to isoniazid and rifampicin (multi drug resistant tuberculosis) was observed in 25.2 per cent of the strains. 3.25 per cent strains were sensitive to all the drugs.
Tuberculosis (T.B.) is a major cause of morbidity and mortality in India. According to World Health Organization (WHO) reports, each year an estimated eight million new cases of tuberculosis occur, leading to three million deaths; and almost a third of the world’s population is infected by the causative organism, Mycobacterium tuberculosis. [1]
In India, the number of tuberculosis patients is 1.5 million per year, and a quarter of these are sputum positive. Thus, about 40 per cent of all Indians are infected with tuberculosis. [2]
Recently, several outbreaks of multidrug resistant tuberculosis (MDR-TB) have been reported from different parts of the world. [1] Patients infected with human immuno deficiency virus (HIV) are particularly at risk of developing MDR-TB.
This study is undertaken to assess the prevalence of MDR-TB and observed pattern to commonly used antituberculous drugs in our region.MATERIAL AND METHODS
Samples for the study included sputum, bronchial lavage, lymph node aspirates, pus, pleural fluid, cerebro-spinal fluid, urine etc. Specimens like body fluids were centrifuged and the deposit was used for microbiological studies while specimens like sputum, pus, lymph node aspirates were decontaminated first, by using standard procedures. [3] Smears were stained by acid-fast (Ziehl-Neelsen) stain and fluorochrome stain. [3] Culturing of all samples was done on Lowenstein-Jensen (L-J) medium; the cultures were incubated at 37oC and examined weekly upto a period of six to eight weeks. [3] Any growth seen on L.J. medium was confirmed by acid-fast stained smear. Biochemical tests (to differentiate the species of mycobacteria) were done wherever necessary.
In vitro drug sensitivity tests were carried out by absolute concentration method and the concentrations of the drugs were as described by Gangadharam. [4] Amikacin and Ciprofloxacin (20 micrograms per ml each) were also added to standard anti-tuberculous drug list. Results were read after a period of six weeks and compared with those obtained with a standard strain of M. tuberculosis H37 RV.
The period of study extended from January, 1996 to June, 1998.RESULTS AND DISCUSSION
A total of 3181 samples were processed for isolation of tubercle bacilli; and 707 samples were culture positive. The pattern of drug resistance is shown in Table 1.
A comparison of results of the present study with those of our earlier study [5] showed that there was an increase in the pattern of drug resistance to isoniazid. Almost 30.5 per cent of the strains were resistant to this drug as compared to the earlier figure which was low (15 per cent).
M. tuberculosisDrug Per cent Resistance Isoniazid 30.41 Rifampicin 58.55 Streptomycin 46.95 Ethambutol 3.67 Cycloserine 24.32 Kanamycin 14.42 Ethionamide 60.67 Amikacin 15.84 Ciprofloxacin 7.49
The increase in multidrug resistant tuberculosis (MDR-TB) that is, a combined resistance to isoniazid and rifampicin, has increased from 10.7 per cent [5] (earlier study, 1995) to 25.25 per cent (present study, 1998). A similar study from Haryana [6] shows incidence of MDR-TB of the same order (24.00 per cent). A smaller number of strains in the year 1996 (five per cent) showed resistance to a single drug whereas 21.4 per cent strains were resistant to two drugs. The trend of resistance in the year 1998 showed these figures much higher i.e. 16.82 and 25.23 per cent respectively.
The earlier study in 1995 [5] showed that 4.6 per cent of all strains of M. tuberculosis were sensitive to all the drugs, whereas in the present study, this figure was relatively low (3.25 per cent).
In India, it has been observed that private practitioners use different drug regimens to treat tuberculosis and very few regimens match with the standard (recommended by WHO)
The problem of acquired drug resistance (ADR) is truly man made. [6] Poorly administered tuberculosis control programme, inadequate dosages, monotherapy, insufficient durations of treatment, irregularity in drug intake, frequent defaults are some of the common reasons for emergence of ADR. [6] In addition, HIV is quickening the pace at which tuberculosis is spreading. Therefore, tuberculosis is becoming the leading killer disease of HIV-positive people.REFERENCES
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