Drug resistance in tubercle bacilli and its impact on the chemotherapy and epidemiology of tuberculosis

At the outset, I thank the Tuberculosis Association of India for selecting me for this Award. I am accepting this honour with the blessings of all the veterans and learned scholars in the field of tuberculosis in India for my future guidance. The subject I have chosen for the review is “Drug Resistance” which as you all know, is of most contemporary interest. The review covered all aspects of drug resistance in tubercle bacilli, particularly the genetic, biochemical and bacteriological aspects and also dealt briefly on the epidemiological control of tuberculosis. Time does not permit me to deal with all the aspects in detail. Hence, I am constrained to limit to a very brief presentation of all the salient aspects of my revie

Direct senstivity test for isoniazid.

IT is well known that the results of isoniazid sensitivity tests by the indirect method have prognostic significance in the treatment of tuberculosis with regimens containing isoniazid (Tuberculosis Chemotherapy Centre, Madras, 1960 ; Devadatta et al., 1961) ; the indirect method is, however, complex and time-consuming, and therefore not feasible in institutions with limited facilities. Direct sensitivity tests are attractive because they involve only one stage of handling (i.e. cultures need not be set up), are simpler and less expensive, and consume less time. Although the direct sensitivity test introduced by Middlebrook and co-workers (Middlebrook and Cohn, 1958 ; Russell and Middlebrook, 1961) using 7H10 agar medium yielded satisfactory results, it has certain disadvantages. Thus, the medium employed is expensive, the in are not readily available in this country and, in our experience at Madras, losses due to contamination can be considerable. This paper describes a direct sensitivity test for isoniaid using Lowenstein- Jensen medium, and compares the findings obtained by this method with those obtained by the indirect method

Effect of storage for three months at different temperatures on the sensitivity to streptomycin and isoniazid of cultures of tubercle bacilli

MAINTENANCE of bacterial strains by repeated subcultivation is both expensive, laborious and time-consuming ; moreover, there is always the possibility of contamination or of differential selection of sub-strains with specific properties. In consequence, several methods, such as freeze-drying or storage at low temperatures, have been introduced by which bacterial cultures can be kept alive for long periods with their reproductive and metabolic activity at an extremely low level. However, information is rather sparse on such methods for the storage of tubercle bacilli. For instance, Corper and Gauss (1923) found that tubercle bacilli remained viable in Petroff's egg medium or glycerol agar after storage in the incubator or refrigerator for 4 to 8 months. Later workers (Heckly, 1950 ; Stern and Tompsett, 1951 ; Jones, 1957 ; Tsukamura, 1965) suggested preservation of cultures by freezing them in various diluents. More recently, Tarshis (1961) compared storage of cultures in various diluents at –20°C. and concluded that, with minor exceptions, most types of mycobacteria (including tubercle bacilli) can be stored for at least 3 years without any major change in their viability or drug resistance. However, these procedures are time-consuming, expensive and require special equipment and are? therefore, not very practicable in developing countries with limited resources

A simple paper test for isoniazid in urine

Tests for the presence of chemotherapeutic drugs or their metabolites in urine play an important part in the management of the treatment of tuberculosis (Dixon et al., 1957; Fox, 1958). A previous report from this Centre (Gangadharam et al., 1958) presented a comparison of a number of methods for detecting isoniazid in urine including the direct naphthoquinone-mercuric chloride (N-M) test (Short and Case, 1957), and also a modification of this test which employed alkaline hydrolysis to liberate isoniazid from its conjugated forms. The direct-and hydrolysis N-M tests have been employed in this Centre for the past four years to control the self-administration of isoniazid used in the domiciliary treatment of pulmonary tuberculosis. The effect of irregularity in taking isoniazid as detected by these tests on the response to treatment has been reported elsewhere (Tuberculosis Chemotherapy Centre, 1960). Since this method has the disadvantage that it requires a certain amount of equipment and trained personnel, it is not suitable for routine use in all chest clinics or under field conditions. An attempt was therefore made in this Centre to simplify the direct N-M test by incorporating the reagents in absorbent papers; Though impregnation of the paper with the pHl0 buffer and naphthoquinone reagent was successful, impregnation with the aqueous solution of the mercuric chloride was unsatisfactory. In 1960, Cattaneo, Fantoli and Belasio published details of a paper test modification of the N-M test in which this difficulty was overcome by impregnating absorbent papers with a solution of mercuric chloride in ether. Since then this modification has been adopted for the preparation of the test-paper developed in this Centre. Since a lower concentration of the naphthoquinone reagent and a shorter period of exposure was used in the preparation of the testpaper developed in this Centre than described by Cattaneo et al. (1960), both the paper tests have been compared with the direct and combined N-M tests described previously (Gangadharam et al., 1958). This paper presents the results of the comparison and of an of the specificity of the paper test

Direct Test for Determining Sensitivity of M. Tuberculosis To Streptomycin

For a total of 400 sputum specimens, the sensitivity of M. tuberculosis to streptomycin was determined by direct inoculation of the sputum sediment on to drug-free and drugcontaining slopes of Lowenstein-Jensen medium, and also by a standard indirect test. Agreement between the two methods in the classification of strains as sensitive or resistant was of the order of 90%. The optimal time for reading the direct test is 6 weeks

Rate of Inactivation of Isoniazid in South Indian Patients with Pulmonary Tuberculosis 2. Clinical Implications in the Treatment of Pulmonary Tuberculosis with Isoniazid either Alone or in Combination with PAS

A series of studies on the rate of inactivation of isoniazid in Indian patients with pulmonary tuberculosis undergoing domiciliary chemotherapy with isoniazid, alone or in combination with p-aminosalicylic acid, has recently been undertaken by the Tuberculosis Chemotherapy Centre, Madras. In the first study, the serum isoniazid levels of the patients were determined four-and-a-half hours after intramuscular administration of a standard dose of 3 mg/kg body-weight of isoniazid and, according to whether the serum level was 0.58 μg/ml or above, or less than 0.58 μg/ml, the patient was classified as a slow or as a rapid inactivator. The present paper describes the second of these studies, in which the response to treatment of the slow and the rapid inactivators was compared. The results of this investigation suggested that there might be an association between response to treatment and rate of inactivation of isoniazid, since the slow inactivators were more often culturenegative during treatment and showed a higher proportion of individuals with bacteriologically quiescent disease at I2 months and a lower proportion with radiographic deterioration at six months than the rapid inactivators, while the slow inactivators who deteriorated radiographically or clinically to an extent warranting a change of treatment during the two years did so later than the corresponding rapid inactivators. There was slight evidence that the slow and the rapid inactivators differed in the speed of conversion to bacteriological negativity of those patients whose disease was bacteriologically quiescent at 12 months, but no evidence that they differed in the degree of positivity of sputum specimens that were positive on culture at six, nine or 12 months, or in the frequency with which the patients showed moderate or greater radiographic improvement at six months

The detection of airborne transmission of tuberculosis from HIV-infected patients, using an in vivo air sampling model

Background. Nosocomial transmission of tuberculosis remains an important public health problem. We created an in vivo air sampling model to study airborne transmission of tuberculosis from patients coinfected with human immunodeficiency virus (HIV) and to evaluate environmental control measures. Methods. An animal facility was built above a mechanically ventilated HIV‐tuberculosis ward in Lima, Peru. A mean of 92 guinea pigs were continuously exposed to all ward exhaust air for 16 months. Animals had tuberculin skin tests performed at monthly intervals, and those with positive reactions were removed for autopsy and culture for tuberculosis. Results. Over 505 consecutive days, there were 118 ward admissions by 97 patients with pulmonary tuberculosis, with a median duration of hospitalization of 11 days. All patients were infected with HIV and constituted a heterogeneous group with both new and existing diagnoses of tuberculosis. There was a wide variation in monthly rates of guinea pigs developing positive tuberculin test results (0%–53%). Of 292 animals exposed to ward air, 159 developed positive tuberculin skin test results, of which 129 had laboratory confirmation of tuberculosis. The HIV‐positive patients with pulmonary tuberculosis produced a mean of 8.2 infectious quanta per hour, compared with 1.25 for HIV‐negative patients with tuberculosis in similar studies from the 1950s. The mean monthly patient infectiousness varied greatly, from production of 0–44 infectious quanta per hour, as did the theoretical risk for a health care worker to acquire tuberculosis by breathing ward air. Conclusions. HIV‐positive patients with tuberculosis varied greatly in their infectiousness, and some were highly infectious. Use of environmental control strategies for nosocomial tuberculosis is therefore a priority, especially in areas with a high prevalence of both tuberculosis and HIV infection

The Regulation of Sulfur Metabolism in Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) has evolved into a highly successful human pathogen. It deftly subverts the bactericidal mechanisms of alveolar macrophages, ultimately inducing granuloma formation and establishing long-term residence in the host. These hallmarks of Mtb infection are facilitated by the metabolic adaptation of the pathogen to its surrounding environment and the biosynthesis of molecules that mediate its interactions with host immune cells. The sulfate assimilation pathway of Mtb produces a number of sulfur-containing metabolites with important contributions to pathogenesis and survival. This pathway is regulated by diverse environmental cues and regulatory proteins that mediate sulfur transactions in the cell. Here, we discuss the transcriptional and biochemical mechanisms of sulfur metabolism regulation in Mtb and potential small molecule regulators of the sulfate assimilation pathway that are collectively poised to aid this intracellular pathogen in its expert manipulation of the host. From this global analysis, we have identified a subset of sulfur-metabolizing enzymes that are sensitive to multiple regulatory cues and may be strong candidates for therapeutic intervention

Tuberculosis chemotherapy: current drug delivery approaches

Tuberculosis is a leading killer of young adults worldwide and the global scourge of multi-drug resistant tuberculosis is reaching epidemic proportions. It is endemic in most developing countries and resurgent in developed and developing countries with high rates of human immunodeficiency virus infection. This article reviews the current situation in terms of drug delivery approaches for tuberculosis chemotherapy. A number of novel implant-, microparticulate-, and various other carrier-based drug delivery systems incorporating the principal anti-tuberculosis agents have been fabricated that either target the site of tuberculosis infection or reduce the dosing frequency with the aim of improving patient outcomes. These developments in drug delivery represent attractive options with significant merit, however, there is a requisite to manufacture an oral system, which directly addresses issues of unacceptable rifampicin bioavailability in fixed-dose combinations. This is fostered by the need to deliver medications to patients more efficiently and with fewer side effects, especially in developing countries. The fabrication of a polymeric once-daily oral multiparticulate fixed-dose combination of the principal anti-tuberculosis drugs, which attains segregated delivery of rifampicin and isoniazid for improved rifampicin bioavailability, could be a step in the right direction in addressing issues of treatment failure due to patient non-compliance