20-08-2012, 04:17 PM
Comparative study of MGIT 960, ZIEHL NEELSEN STANING and PCR for the detection of Pulmonary & Extra pulmonary tuberculosis
Comparative study.pdf (Size: 2.83 MB / Downloads: 135)
ABSTRACT:
Tuberculosis (TB) is an infectious disease that causes considerable morbidity and mortality. It is a major socio-economic burden in India, afflicting 14 million people, mostly in the reproductive age group (15-45 years). It is involved in about 5-16% of cases of infertility among Indian women, though the actual incidence may be under-reported due to asymptomatic presentation of genital tuberculosis (GTB) and paucity of investigation. Tuberculosis is bacterial born disease, causative agent is Mycobacterium tuberculosis. It is estimated that one third of the world’s population is infected with the tubercle bacilli, but only a small fraction go on to develop the full disease.
Involvement of Extra pulmonary TB in all TB cases is 20%. 60% of patients with extra pulmonary manifestations of TB have no evidence of pulmonary infection on chest radiographs or sputum culture. So, the detection of the disease by radiometric culture and polymerase chain reaction (PCR) test for diagnosis of extra pulmonary tuberculosis (TB) was evaluated by diagnosis subjecting clinical samples obtained from 200 cases of suspected tuberculosis radiometric BACTEC culture and PCR test by amplifying MBP64 antigen coding region of mycobacterium tuberculosis (MTB) genome at Auroprobe Laboratories.. PCR test was found to be much more sensitive than BACTEC culture in the diagnostic of tuberculosis (TB). On the other hand, PCR test gave a positive result with in 24 hrs. The present study reaffirms the fact that PCR is much more sensitive then BACTEC culture test for diagnosing extra pulmonary tuberculosis.
INTRODUCTION
Tuberculosis is an airborne infectious disease that is preventable and curable and is caused by gram positive, aerobic and slow growing Mycobacterium. (Madison B 2001)1.
In humans Mycobacterium tuberculosis mainly attacks the lungs but can also affect the gastrointestinal tract, central nervous system, lymphatic system, circulatory system, genitourinary system, bones, joints and even the skin. (Davies , 2002)2.
Other mycobacterium such as Mycobacterium bovis, Mycobacterium africanum, Mycobacterium canetti, Mycobacterium microti also causes tuberculosis but these species are less common in humans (Reed , 1957; Kraus et al, 2001)
Mycobacterium tuberculosis (MTB) is a pathogenic, gram-positive bacterium which causes tuberculosis, the leading cause of infectious disease mortality. Tuberculosis (TB) is a potentially fatal and contagious disease that can affect almost any part of the body, but is mainly an infection of the lungs, caused by bacteria i.e Tubercle Bacillus Mycobacterium tuberculosis. It is an aerobic bacterium; Gram-positive that divides every 16 to 20 hours, an extremely slow compared with other bacteria (Madison B 2001).
Tuberculosis is an epidemic that is increasing in prevalence with time. The lung infections caused by epidemics of tuberculosis kill two million people each year around the world (K. Lee Lerner, 2003).
Symptoms of tuberculosis depend on where in the body Mycobacterium tuberculosis is growing. Tuberculosis in the lungs may cause symptoms such as a chronic cough, pain in chest, coughing up blood or sputum. Other symptoms of active tuberculosis are weakness, fatigue, weight-loss, loss of appetite, chills, fever and sweating at night. Mycobacterium tuberculosis was discovered by Robert Koch in 1882 and his studies on tuberculosis won him a noble prize for Physiology and Medicine in 1905 . (Sakula , 1882,VanGuilder et al., 2008).
BASIC MORPHOLOGY
Characteristics:
Mycobacterium tuberculosis is a fairly large nonmotile rod-shaped bacterium distantly related to the Actinomycetes. Many non-pathogenic mycobacteria are components of the normal flora of humans, found most often in dry and oily locales. The rods are 2-4 micrometers in length and 0.2-0.5 um in width.(Kenneth Todar 2004)20. In addition to being non-motile, M. tuberculosis is an obligate aerobe, meaning that the bacterium can only survive in an environment that contains oxygen.
Although Mycobacterium tuberculosis possesses a Gram-positive type cell wall, a cell wall with extensive peptidoglycan and no outer membrane, the bacterium does not stain with Gram stain reagents. Gram stain reagents are unable to penetrate the cell wall of the bacillus because layers of lipids surround the peptidoglycan in mycobacteria. Unlike most Gram-negative bacteria, which have a 5-20% lipid content by weight, M. tuberculosis and other mycobacteria are composed of up to 60% lipids. Many of these lipids are in the form of mycolic acids.
Mycobacterial Capsule
The outermost component of the cell envelope consists of a mixture of polysaccharides, proteins and lipids, and is called capsule. The earliest mention of mycobacterial capsule was by Chapman in1959, who called the space between the phagosomal membrane of the infected cell and the wall of the enclosed mycobacterium a capsular space or halo. Chemically, a clear distinction between the wall associated compounds and capsular constituents, experimentally has not been possible so far and many substances are found in more than one envelop compartments. However, electron microscopic studies have proved existence of capsule in mycobacteria. It is also established now that most part of the capsule is lost from the mycobacteria during the conventional processing of the sample for microscopy. Most of the species of mycobacteria are known to possess the capsule, but it is not known that the thickness varied from species to species. The capsule consist of mainly the polysaccharides, the proteins and lipids.
PATHOGENESIS:
Infection with Mycobacterium tuberculosis begins when droplet nuclei are inhaled into the upper respiratory tract through the mouth or the nose (FIG 7,box 1). From the upper respiratory tract, the bacilli travel through the bronchi until they reach the alveoli of the lungs (FIG 7,box2). Once inside the lungs, alveolar macrophages (immune cells that engulf foreign particles) ingest the pathogenic organisms, but the mycobacteria do not die. Instead, the bacilli multiply within the macrophage hosts, causing the macrophages to rupture. The continued division of M. tuberculosis every 18 to 24 hours attracts more and more immune cells to the area. In an attempt to control the infection, some of these cells produce toxic substances that are supposed to kill the bacilli. The bacilli do not immediately die, however, so the release of toxic substances also damages the surrounding lung tissue. When macrophages and other cells of the immune system encircle this area of dead tissue, the lesion is called a tubercle or granuloma .