Tuberculosis Mycobacteria Are Acid Fast Bacilli Biology Essay

Mycobacterias are acerb fast B which is due to the high lipid content of their cell wall.They are neither gram positive or gram negative. Mycobacteria is a genus within the order Actinomycetales that comprise a big figure of good characterised species. The major pathogens are Mycobacterium Tuberculosis the cause of TB and mycobacteria leprae, the cause of leprosy.Atypical mycobacteriums such as Mycobacterium avium-intracellular composite and Mycobacterium kansaii, can do TB like disease but are less frequent pathogens ( Brooks,2007 )

M.tuberculosis is slow turning, it has a doubling clip of 18 hours in contrast to most bacteriums in which it is normally an hr or less. Because growing is slow, specimens are normally held for up to 8 hebdomads until deemed to be negative. It is an obligate aerobe which explains the predomination of disease in the upper lobe of the lung and in the kidneys as they are extremely oxygenated countries. M.tuberculosis is carried in airborne atoms called droplet karyon of 1-5 micrometers in diameter depending on the environment the atoms can stay suspended in the environment for several hours ( Brooks,2007 ) . The likeliness of transmittal depends on the infectivity of the beginning of the instance, the grade of exposure to the instance ( e.g propinquity, airing and length of exposure ) and susceptibleness of the individual in contact with an septic instance ( BMJ,2013 ) .

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The development of TB requires infection by M TB and unequal containment by the immune system. Patients infected with thousand TB who have no clinical, bacteriological or radiographic grounds of Active TB are said to hold a latent TB infection. Active Terbium may happen from re activation of antecedently latent infection or from patterned advance of primary infection. Transmission of TB occurs from persons infected with pneumonic disease ( BMJ,2013 ) .

Pathogenesis of disease

Infection occurs by aerosol transmittal, droplet karyon incorporating tubercle B which reach air sac of the lungs. The being deposits in the air sac M. TB preferentially engulfs alveolar macrophages and other reticuloendothelial cells.It multiplies and survives within a phagosome. m.tuberculosis produces a protein called “ exported insistent protein ” that prevents the phagosome from blending with the lysosome, so the being escapes the degradative enzymes in the lysosome ( Lange ) this allows proliferation of TB within the macrophages. Cell Mediated Immune response Development of an activated lymph cell response to m.tuberculosis antigen produces a type IV hypersensitivity response to the being which consequences in the outgrowth of activated macrophages that can consume and destruct the B. ( rubins ) Exposure may take to clearance of M.tuberculosis, relentless latent infection or patterned advance to primary disease.T cells and macrophages form a granuloma with a Centre that contains necrotic stuff, m.yuberculosis, and peripheral granulation tissue dwelling chiefly of macrophages and lymph cells, the granuloma serves to forestall furthrer growing and spread of m. tuberculosis.Theses patients are non infective and have latent TB.Active Terbium occurs through a procedure of reactivation.Approximately 10 % of patients with latent infection will travel on to develop active disease.

Mycobacteria does non bring forth exotoxins nor does it hold any endotoxins in its cell wall. The being has developed mechanisms that allow for its endurance in macrophages. Properties that contribute to its virulency include Mechanism of cell entry, the tubercle B can adhere straight to mannose receptors on macrophages via cell wall associated mannosylated glycolipid. M.Tuberculosis can turn intracellularly.When TB has been phagocytosed it can suppress the merger of the lysosome and phagosome by releasing a protein that modifies the membrane of the phagosome. The slow coevals clip of TB may take to the immune system non recognizing the bacterium therefore the immune system is non triggered adequately plenty. The high lipid content in the cell wall explains the ground for the impermeableness and opposition to antimicrobic agents ( text book bacteriology ) .Cord factor ( trehalose dimycolate ) is associated with virulency.Virulent strains grow in a cordlike form unlike avirulent strains which do non. M.tuberculosis contains several proteins that when combined with waxes provoke delayed hypersensitivity.These proteins are antigens in the tuberculi tegument test.It is immune to hydration and survives in dry phlegm this may be of import I aerosol transmittal ( Lange )

Symptoms include cough, fever anorexia weight loss and unease which are common.

Pulmonary TB locates in the lungs most instances are pneumonic. Extrapulmonartry TB occurs in topographic points other than the lungs such as the voice box, lymph nodes, pleura, encephalon, kidneys, castanetss and joints.This is found more ofet in HIV infected or other immunosuppressed people and immature kids. Miliary TB is carried out to all parts of the organic structure through the blood stream nevertheless this is the more rare signifier.

Epidemiologic facets

Worldwide m.tuberculosis causes more deceases worldwide than any other individual microbic agent ( lange reappraisal )

Close contact for illustration with household or exposure from a infirmary brand transmittal easier by droplet karyon. Susceptibility to TB is the hazard of geting the infection and so the hazard of disease after infection. A tuberculin negative individual depends on the beginning of the positive B in order for them to be affected particularly when there are sputum positive patients. Risk is shown to be proptrional to the rate of active infection in the population, herding, socio economic disadvantage and insufficiency of medical attention. In More likely to get the infection at an earlier age in urban countries instead than rural populations. However disease merely occurs in a little population of those affected with infection. Epidemiologic forms have been shown from population in the United States in which some persons are more at hazard than others. Minorities, preponderantly African American and Hispanics, HIV infected patients, stateless individuals and the really immature and really old.

Killings about 3 million people and affects about 9 million per twelvemonth. Affects evident healthy persons every bit good as immunocompromised, peculiarly obvious with patients with AIDs ( mims )

MDR TB caused by beings immune to both INH and Rifampin which are the two most effectual anti-TB drugs. These drugs are considered first line drugs. Foreign born individuals increased from 325 % in 1993 to 88 % in 2009 ( CDC web )

XDR TB is a comparatively rare type of drug immune Terbium that is immune to isoniazid and rifampin plus any fluoroquinolone and at least one of three injectable 2nd line drugs. ( CDC website ) No evident tendency in the figure of instances over clip in the USA. Greatest figure of instances was 10 in 1993 no instances reported in 2003 or 2009.

The revival of TB disease began in the mid 1980s with increasing instances until it peaked in 1992.The figure of instances began worsening in 1993.In 2009 marked the 17th twelvemonth of diminution in entire figure of reported instances from the United States. From 1993 until 2002 the entire figure of instances declined around 5 % -7 % yearly. Further to this rates continued to worsen from 2003 to 2008 but at a much slower gait. In 2009 50 provinces reported 11,545 instances. This represents a diminution of 10.5 % from 2008 ( cdc alteration diction )

Diagnostic scheme

Because of drug opposition particularly to INH susceptibleness trial should be performed. Because the being grows really easy the trials normally takes several hebdomads which is excessively long to steer the pick of drugs. The luciferase check can observe drug resistant organsims within a few yearss

First line trial for active probe include CXR, 3 phlegm samples nucleic acerb elaboration trial, FBC and electrolytes.


phlegm smear the ezaminer looks for AFB at least three samples should be collected minimal 8 hours apart including early forenoon specimen best to observe thousand TB. If phlegm is positive graded from 1+ to 4+ depending on figure of beings seen.This may assist to gauge the grade of infectiousness.

A sputum civilization should ever be performed as it is the most sensitive and specific trial.It is required for precise designation and drug susceptibleness testing.Growth may take 4to 8 hebdomads and is reoted on the same graduated table as the phlegm smear.The patient will hold phlegm civilizations performed at least monthly until two back-to-back civilizations are negative.

A full blood count conducted shows leucocytosis and anaemia, this has been shown in 10 % of pateints. Other abnormalcies include elevated monocyte and eosinophil counts.

Nucleic acerb elaboration trial ( NAAT ) Deoxyribonucleic acid or RNA elaboration trials can be carried out for rapid diagnosing on phlegm or any unfertile organic structure fluid. Consequences are available in less than 8 hours. This is utile in smear positive disease to corroborate that ascertained mycobacteriums are M TB and in smear negative disease for rapid diagnsosis.

Other trials to see include stomachic aspirate used normally in patients unable to bring forth phlegm, would demo positive consequence positive for AFB. Bronchoscopy is utile when other diagnosings considered in patients in whom pneumonic Terbium is still suspected after other methods proved not diagnostic.

Tuberculin skin trial, interferon gamma release assays step response of T cells to TB antigen in order to name anterior exposure. genotyping, susceptibleness testing. ( best prac )

Progression nad monitoring of disease

Liver map shoud be checked anterior to gazing therapy.Monthly LFTs should be obtained in pateints with unnatural basleine liver map, underlying liver disease HIV carbon monoxide infection gestation and other hazard factors for hepatitis. In general patients should hold a CXR at the completion of intervention for pneumonic TB.In patients with multi drug opposition near follow up two old ages after completion of intervention is recommended.

Hazard of developing TB is the highest after 2 old ages of infection ( Center for Disease Control and Prevention )


Multi drug therapy is used in intervention to forestall drug resitant mutations emerging during the 6 to 9 month period of intervention. So if the being becomes resitant to one drug will be inhibited bty the other. There are 10 drugs presently approved by the FDA for intervention of Tuberculosis there are five chief first line anti TB agents which include ; Isoniazid ( INH ) , Rifampin ( RIF ) , Ethambutol ( EMB ) , Pyrazinamide ( PZA ) .Treatment for most patients with pneumonic tuberculsosis is with INH, Rifampin and Pyrazinamide. INH and Rifadin are given for 6 months but pyrazinamide intervention is stopped after two months. In immunocompromised patients, and are likely to hold INH resitance. ethambutol is besides given. The four drugs are given for 9-12 months Although the sputum sample becomes not infective withi 2-3 hebdomads the long therapy clip is required because of the location of the being is intracellular, the blocking of the entry of the drug, the being grows easy, some metabolically inactive beings in the lesions remain therefore the drugs do non take consequence on these so infection may reoccur at some phase. ( cdc web site non pdf )

Increasingly resiatance to INH and other drugs used for intervention of TB is being recognized in the United provinces this is particularly true amongst immigrants from Latin America and South East Asia. Strains have emerged which are multidrug resistant ( MDR ) seen specifically amongst AIDs patients Largely shown to be resitant to INH and Rifampin nevertheless some isolates have shown to be immune to three or four drugs. ( lange reappraisal )

Soon the bar of spread depends on rapid designation and intervention of patients. The use of masks and respiratory isolation is required to halt the spread to medical staff. Contact tracing of persons exposed to a patient who has been coughing. PPD ski trial is of import tool in bar this is used to place recent coverters ( ? ) and to give intervention for latent infections Gropus that should be screened with PPD trial include people with HIV infection, close contacts of patients with acive TB, low income populations and endovenous drug users.As there were some jobs associated with the skin trial such as the measuring and reading of consequences.A laboratory trial to to observe latent infection was developed. This trial called quantiFERON-TB, this step the sum of I’ interferon released from pateints lymph cells afetr exposure to PPD in cell civilization.

BCG vaccinum can be used to bring on partial opposition to TB. The vaccinum conatins a strain of unrecorded, attenuated m.bovis called bacillus Calmette-GuerinThe vaccinum is effectual in forestalling the visual aspect of TB as a clinical disease, particularly in kids although it does non forestall infection by M.tuberculosis. However a mjor job with the vaccinum is its variable effectivity which can run from 0 % to 70 % .It is used chiefly inareas of the universe where incidence of the diease is high. ( Lange )


New methods fpr diagnosing may good extinguish the demand for smear and civilization are under decelopment. The new methods are nbased on the sensing of specific constituents of the being or on sensing of specific antibodies produced by the patient. Although some methods will necessitate expensive equipment doing it leess avalible to those in developing states. The usage of cistron investigations for diagnosing of TB is in usage although on a limited graduated table. This rticle suggests tha in the close hereafter that nucleic acid techniques will be developed for worldwide usage. The techniques will hold the highest degree of sensitiveness and specificity of all time achieved ( Crawford et al 1989 ) A survey demonstrated the importance of mycobacterial polyose as a possible mark for protective antibodies. Several past surveies have indicated the importance of antibodies to mycobacterial polyoses were associated with protection.

Case survey

A 65 twelvemonth old adult male was admitted to hospital with a 5 month history of progressive failing and a weight loss of 13 kilogram. He besides had fever icinesss and a chronic cough productive eof xanthous phlegm on occasion streaked with blood.

The patient drank a batch of intoxicant anlived in a embarkation house following door to the tavern.He had smoked one battalion of curie garettes a twenty-four hours for the past 45 old ages. The patient had no history of TB, no record of anterior tegument trials for TB or unnatural thorax radiogram, and no known exposure to TB ( Lange )

Clinical Features

Temperature of 39A°C, pulse 110/min, blood force per unit area 120/80 millimeter Hg.Head and cervix scrutiny was normal.During chest scrutiny cracklings were heard over the upper lung Fieldss.

Lab Findingss

Haematocrit was low ( 30 % ) and white blood cell count was 9600/Aµl.Other blood trials were normal.However chest radiogram showed extended pit infiltrates in both upper lobes.Tuberculin skin trial was negative.A phlegm sample obtained instantly and anacid fast stain.Numerous acid-fast bacteriums were seen on the smear.Culture of decontaminated and concentrated phlegm was positive for acerb fast bacteriums after 14 yearss incubation.Mycobacterium TB was identified by molecular investigations after 2 days.Susceptibilty trials of theorganism showed susceptibiltity to isoniazid, Rifadin, pyranazamide and streptomycin.


The patient was treated with INH, Rifadin, pyranazamide and streptomycin for two hebdomads followed by straight observed twice hebdomadal disposal of INH and and rifampin for 16 hebdomads.Follow up sputum civilization were negative for thousand TB.



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