Biology and Infection of Mycobacterium

Mycobacterium

Mycobacteria are slim rod microorganism that is stained with unique differential stains (Ziehl-Neelsen). Once the staining has taken, they cannot be detained with dilute acids, therefore the designation acid-fast. In terms of human sickness, the maximum crucial mycobacteria are the tuberculosis bacteria (TB) M. tuberculosis and M. bovis and the leprosy pathogen (LB) M. leprae. TB may be grown on lipid-rich lifestyle mediums. Their generation time is 12–18 hours. Initial droplet infection effects in primary tuberculosis, localized especially within the apices of the lungs. The primary disease develops with the Ghon focus (Ghon’s complicated), whereby the hilar lymph nodes are involved as nicely. 90 percent of number primary infection foci continue to be clinically silent. In 10% of folks infected, primary tuberculosis progresses to the secondary level (reactivation or organ tuberculosis) after a few months or maybe years, which is characterized by means of big tissue necrosis, as an example pulmonary caverns. The unique immunity and allergic reaction that broaden inside the route of an infection reflect T lymphocyte capabilities. The hypersensitivity is measured in terms of the tuberculin reaction to check for clinically inapparent infections with TB. Prognosis of tuberculosis calls for an identity of the pathogen via microscopy and culturing. modern molecular strategies at the moment are coming to the fore in TB detection. Manifest tuberculosis is dealt with two to 4 antitubercule chemotherapeutics in both a quick regimen lasting six months or a fashionable routine lasting 9 months.

In assessment to TB, the LB pathogens do not lend themselves to culturing on artificial nutrient mediums. Leprosy is manifested especially in skin, mucosa, and nerves. In medical terms, there is a (malignant) lepromatous kind leprosy and a (benign) tuberculoid type. Nondifferential bureaucracy is also common. Humans are the sole infection reservoir. Transmission of the disorder is through near contact with skin or mucosa. The genus Mycobacterium belongs to the Mycobacteriaceae family. This genus includes saprophytic species which are large in nature as well because the causative pathogens of the major human ailment complexes tuberculosis and leprosy. Mycobacteria are Gram-positive, although they do now not take gram staining properly. The cause of this is a cell wall structure rich in lipids that do not permit the alkaline stains to penetrate nicely. At any rate, as soon as mycobacteria have been stained (using radical strategies), they face up to destaining, in spite of HCl-alcohol. This belonging is called acid fastness.

Tuberculosis bacteria (TB)

History

The tuberculosis microorganism is complicated and includes the species Mycobacterium tuberculosis, M. bovis, and the rare species M. africanum. The scientific etiology of tuberculosis, a disease long recognized to man, turned into labored out in 1982 by means of R. Koch primarily based on normal isolation of pathogens from lesions. Tuberculosis is certainly among the maximum intensively studied of all human diseases. In view of the reality that tuberculosis can infect practically any organ in the body, it's far understandable why some of other clinical disciplines benefit from these studies further to microbiology and pathology.

Morphology and culturing

TB are slender, acid-fast rods, 0.4 mm wide, and three–four mm long, nonsporing and nonmotile. They can be stained with special retailers (Ziehl-Neelsen, Kinyoun, fluorescence. TB are obligate anaerobes. Their replica is better by means of the presence of 5–10% CO2 within the ecosystem. they may be grown on culture mediums with an excessive lipid content material, e.g., egg-enriched glycerol mediums in keeping with Lo¨wenstein- Jensen . The generation time of TB is about 12–18 hours, in order that cultures ought to be incubated for three to six or 8 weeks at 37 8C until proliferation becomes macroscopically seen.

Cell wall

The various unique traits of TB are ascribed to the chemistry of their cell wall, which capabilities a murein layer in addition to several lipids, the most crucial being the glycolipids (e.g., lipoarabinogalactan), the mycolic acids, mycosides, and wax D. Glycolipids and wax D.

1. responsible for resistance to chemical and bodily noxae.
2. Adjuvant effect (wax D), i.e., enhancement of antigen immunogenicity.
3. Intracellular staying power in nonactivated macrophages with the aid of inhibition of phagosome-lysosome fusion.
4. complement resistance.
5. cord component (trehalose 6,6-dimycolate). Tuberculoproteins.
6. The maximum vital of those is the 65 kDa protein.
7. partly purified tuberculin consists of a mixture of small proteins (10 kDa). Tuberculin is used to test for TB publicity.

Pathogenesis and clinical image:It's far necessary to distinguish between primary and secondary tuberculosis (reactivation or postprimary tuberculosis) . The clinical signs are based on reactions of the mobile immune device with TB antigens.

Primary tuberculosis

In most of the people of cases, the pathogens enter the lung in droplets, in which they are phagocytosed with the aid of alveolar macrophages. TB bacteria are capable of reproducing in those macrophages because of their ability to inhibit the formation of the phagolysosome. Within 10–14 days a reactive inflammatory awareness develops, the so-called primary awareness from which the TB bacteria move into the local hilar lymph nodes, in which they reproduce and stimulate a cell immune response, which in flip effects in clonal enlargement of precise T lymphocytes and attendant lymph node swelling. The Ghon’s complex (primary complicated, PC) develops between six and 14 weeks after infection. At the identical time, granulomas form on the number one contamination site and inside the affected lymph nodes, and macrophages are activated by using the cytokine MAF (macrophage activating element). A tuberculin allergic reaction also develops within the macroorganism. The in addition direction of the disorder relies upon at the final results of the interaction among the TB and the unique cellular immune defenses. Postprimary dissemination foci are occasionally observed as properly, i.e., development of local tissue disorder foci at other localizations, generally the apices of the lungs. Mycobacteria may also be transported to different organs through the lymph vessels or bloodstream and produce dissemination foci there. The host eventually prevails in over ninety% of instances:.The granulomas and foci fibrose, scar, and calcify, and the contamination stays clinically silent.

References:

D greenwood, Slack RCB and J Peutherer.Medical microbiology.2001.

JG College, AG Fraser and BP Marmion.Practical Medical microbiology.Fourteenth Edition. Churchill Livingstone, 1996.

JP Micheal, ECS Chan and NR Krieg.Microbiology.Fifth Edition. Delhi: Mcgraw-hill, 1993.

M Cheesbrugh.Medical laboratory manual for tropical countries.London, 2007.