Introduction

Humans are very susceptible to the tuberculosis

infection but are remarkably resistant to the tuberculosis

disease; which is dependent largely on the state of the

hosts immune system. Of all the mycobacterial species,

846 Concise Book of Medical Laboratory Technology: Methods and Interpretations

Mycobacterium tuberculosis remains the most common

cause of pulmonary tuberculosis and remains the most

virulent of all the mycobacterial species.

The disease, as now well known, is highly contagious.

Although the disease involves all susceptible individuals,

the incidence is higher among disadvantaged minorities.

Industrialization, increased crowded housing and

nutritional deprivation have influenced the spread.

With the emergence of HIV and resultant immunocompromise, TB has emerged as a major killer not only in the

third world countries but is also resurging in the Western

world. 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.

According to a study, in India, the number of tuberculosis

patients is increasing at the rate of 1.5 million per year, and

a quarter of these are sputum positive. Thus, about 4% of all

Indians are infected with Mycobacterium tuberculosis.

With the emergence of the multiple drug-resistant

strains due to poorly administered therapeutic measures

and patient non-compliance, Mycobacterium tuberculosis

is challenging its containment, on the basis of empirical

treatment alone.

Brief Microbiology

The genus Mycobacterium is composed of slow growing

organisms, which are “acid fast”. Currently about 55 species

of Mycobacteria are recognized. They are non-motile,

slightly curved or straight rods (0.2–0.6 × 1–10 µm) and

may occasionally demonstrate branching. The organisms

are aerobic and have a gram-positive cell wall, although

they do not Gram stain well.

The mycobacteria contain a lipid rich cell surface which

includes true waxes and glycolipids 60–90 carbon,