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