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Brief information on mycobacterium tuberculosis which is causative agent of Tuberculosis. prepared by Mahmoud Khalil Pirani, Soran University
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Mycobacterium tuberculosisMycobacterium tuberculosisby
Mahmoud Kh. Mahmoud
Soran UniversityDepartment of Microbiology
Medical Bacteriology13 May 2014 Tuesday
What is Mycobacterium TuberculosisM. tuberculosis and seven very closely related
mycobacterial species (M. bovis, M. africanum, M. microti, M. caprae, M. pinnipedii, M. canetti and M. mungi) together comprise what is known as the M. tuberculosis complex. Most, but not all, of these species have been found to cause disease in humans. The majority of TB cases are caused by M. tuberculosis.
M. tuberculosis organisms are also called tubercle bacilli.
TB is an airborne disease caused by the bacterium Mycobacterium tuberculosis (M. tuberculosis)
CharacteristicsConsidered as weak Gram positive Obligate aerobeNon-spore-formingNon-motile rod0.2 to 0.6 x 2-4umSlow generation time: 15-20 hours
• May contribute to virulenceLipid rich cell wall contains mycolic acid—
50% of cell wall dry weight
Cell Wall StructureCell wall composed of mycolic acid, a waxy lipid
made of 60-90 carbon atomsThe high concentration of lipids gives these
properties: Impermeability to stains and dyes Resistance to many antibiotics Resistance to killing by acidic and alkaline
compounds Resistance to osmotic lysis via complement
deposition Resistance to lethal oxidations and survival
inside of macrophages
Mycobacteia sometimes show branching, filamentous forms resembling fungal mycelium
ClassificationThe genus Mycobacterium contains two
groupsObligate parasites Opportunistic pathogens
Taxonomy classificationKingdom: Bacteria Phylum: Actinobacteria Order: Actinomycetales Suborder: Corynebacterineae Family: Mycobacteriaceae Genus: Mycobacterium Species: Mycobacterium
tuberculosis
Brief HistoryHistorically known by a variety of names,
including:ConsumptionWasting diseaseWhite plague
TB was a death sentenceUntil mid-1800s, many believed TB was
hereditary1882 Robert Koch discovered M.
tuberculosis, the bacterium that causes TB
DiagnosisBiochemical Test Reaction
niacin accumulation Positive
nitrate reduction Positive
pyrazinamidase activityPositive
urease activity Positive
catalase test Negative (heat-labile)
iron uptake Negative
NaCl tolerance Negative
tellurite reduction Negative
Pathogenesis of TBInfection occurs when a person inhales droplet
nuclei containing tubercle bacilli that reach the alveoli of the lungs. These tubercle bacilli are ingested by alveolar macrophages; the majority of these bacilli are destroyed or inhibited. A small number may multiply intracellularly and are released when the macrophages die. If alive, these bacilli may spread by way of lymphatic channels or through the bloodstream to more distant tissues and organs (including areas of the body in which TB disease is most likely to develop: regional lymph nodes, apex of the lung, kidneys, brain, and bone).
TuberculosisTuberculosisM. tuberculosis causes disease
(Tuberculosis) in healthy individuals transmitted man-man airborne droplets
Five stages of tuberculosisStage 1-5
TB InfectionTB disease in lungs
MTB presentMTB present
Tuberculin skin test positiveTuberculin skin test positive
Chest X-ray normalChest X-ray usually reveals lesion
Sputum smears and cultures negative
Sputum smears and cultures positive
No symptomsSymptoms such as cough, fever, weight loss
Not infectious Often infectious before treatment
Not defined as a case of TBDefined as a case of TB
Symptoms of TB
Fever Fatigue WeaknessWeight loss Night sweats
How is TB treated?Optimal treatment of TB utilizes a combination
of 2 to 3 antibiotics taken over a period of 6 to 9 months. Drug resistant strains of TB are not uncommon, which is why multiple antibiotics are used together during treatment. Drugs used most commonly to treat TB include isoniazid, rifampin, ethambutol, and pyrazinamide.
Is there a vaccine for this TB?
BCG (Bacille Calmette-Guerin) vaccine is an attenuated vaccine that is used in many countries around the world where TB prevalence is high. In the U.S. however, the vaccine is not generally recommended because of the low risk of infection, its variable effectiveness, and its interference with TB skin test reactivity.
Thank You For Listening !
Prepared by: Mahmoud Kh. MahmoudPrepared by: Mahmoud Kh. Mahmoud
Soran UniversityMicrobiology Dept.
Medical Bacteriology