Mycobacterium species
Mycobacteria are widespread both in the environmental and in animal . They are aerobic ,acid and alcohol fast bacilli (not stained by the gram stain because of the high lipid component of the cell wall).The major medically important pathogens are:
-Mycobacterium tuberculosis : the agent of tuberculosis one of the top three infectious diseases affecting human globally. -M. bovis cause tuberculosis in human as well as in cattle. -M.africanum which also cause tuberculosis. -M.Leprae the agent of leprosy-a disease affecting millions in Asia &Africa. -Mycobacteria other than tuberculosis bacilli(MOTT) such as M.avium , M.intracellulare , M.marinum and M.kansasii which cause frequent disease in HIV infected patients.Mycobacterium tuberculosis
Habitat & transmission : Found in infected human ,mainly in the lungs Transmission by coughing ( droplet spread ).Virulent factors
Produce No endotoxin, exotoxin or invasive enzymes The pathogenicity is due to cell wall components, and substances inducing immunopathological reactions.
Virulent factors
1-Lipids in the cell wall Cord factor: lipoarabinomannan, damages mitochondria myramyl dipeptide (from peptidoglycan ) complexed with mycolic acid and cause granuloma formation . Phospholipids induce caseous necrosis.Virulent factors
2-Proteins e.g., Tuberculin protein mixed with wax D can induce hypersensitive reaction. 3-Polysaccharide Induce the immediate type of hypersensitivity can be as antigens in reaction with sera of infected persons. Bound to wax D to induce the infiltration of inflammatory cells.Characteristics
Acid and alcohol – fast 1-slender beaded bacilli , slightly curved rod with rounded ends 2- Aerobic bacteria3-stained difficulty by gram stain because of the long chain of fatty acids ( mycolic acid ) and stained by special stain which called ziehl-neelsen stain 4-Non motile 5-non spore formingCulture
Do not grow on ordinary medium. Lowenstein-Jensen medium (whole egg , aspargin , glycerol and malachite green ) the widely used medium for cultivating Mycobacterium tuberculosis. In this medium, Malachite green →inhibited all bacteria except Mycobacterium . Species.Glycerol → inhibited M .bovis and allow to grow of M .tuberculosis.The growth rate is slower than most other bacteria. The doubling time is about 18 hours , slow growing (2-3 weeks sometimes up to 6 weeks) at 37C.Colony on Lowenstein-Jensen medium appears as brown, granular colonies sometimes called (rough, tough, and buff). Rough :due to dry irregular growth Tough :due to difficulty in lifting the colony from the surface. Buff : due to the pale yellow colour
Colony on Lowenstein-Jensen medium appear rough ,tough, buff
PathogenicityTuberculosis is a chronic granulomatous ,slowly progressive infection usually of lungs, eventually many other organs and tissues may be affected. Mycobacterium transmitted by droplets by cough ,sneeze or speak .the droplets evaporate leaving bacteria which are small enough when inhaled, to be deposited in alveoli .inside the alveoli ,the host immune system responds by release of cytokines and lymphokines that stimulate monocytes and macrophages,tb begin to multiply in macrophages , some of macrophage enhanced to kill the bacteria tb while other may be killed by the bacilli
After 1-2 months following exposure pathogenic lesions associated with infection appear in the lung two types of lesions: 1-exudative type :consist of an acute inflammation reaction ,with edema fluid ,polymorphonuclear leukocytes and later monocytes around the tubercle bacilliit may lead to massive necrosis in tissue. 2-productive type: this lesion a chronic granuloma consists of three zones a-central area (tubercle bacilli ) b-mid zone epithelioid cell c-peripheral zone of fibroblast ,lymphocytes and monocytes . Later peripheral fibrous tissue develops and the central area undergoes caseation necrosis called tubercle . A caseous tubercle may break into bronchus ,empty it contents there and form cavity .it may subsequently heal by fibrosis or calcification.
lesions calcify
cavity
Chest x ray
Tuberculin skin test+ve
_ve
Niacin test used to differentiate between human tb &bovine tb
Treatmentlong term therapy (6-9)months with (rifampin & streptomycin) multiple drugs resistance (MDR-TB) tubercle bacillus grows slowly hidden by macrophages or other locations difficult to reach with antibiotics
VACCIN
Prevention is by BCG (bacilli calmette –Guerin) which contain live attenuated bacteria of M.bovis .
Mycobacterium bovis
Cause disease in cattle. Human become infected by ingestion M.bovis in milk . Cause the childhood disease scrofuloderma by enlarged ,caseous cervical lymphnodes. Poor growth on Lowenstein-jensen medium Prevention by pasteurization of milk.Mycobacterium leprae
CharacteristicsAerobic acid fast bacilli No known toxin Can not be cultured in in vitro but grows on foot pads of mice causing chronic granulomas at inoculation site.
It is an obligate intracellular microbe that multiplies slowly. It can cause disease of human body (skin, peripheral nerves, nose, anterior chamber of the eyes). It has 3 main targets: peripheral neural tissues (Schwann cells), small vessels, and monocytes.The skin and nerves are the most commonly affected organs.
Incubation
children younger than two years do not have leprosy symptoms. In addition, people residing in nonendemic countries who have visited a site with endemic leprosy may develop the disease many years after the initial exposureLeprosy is a chronic disease with a long incubation periodthe incubation period is estimated to range from 2–12 years ( can be longer). Like those infected with TB, only about 10% of those infected with leprosy go on to develop the diseaseMainly respiratory route . Others (broken skin lesion ,Pregnancy, insect or contact with animals that harbor the organism)
Armadillos
Some types of monkeysRabbits and Mices (foot pads)
Pathogenicity
The leprosy bacilli cause progressive chronic disease of skin and nerves. Two forms of leprosy are recognized :1-Lepromatous leprosy
T cell mediated immune response is depressed or absent. M.Leprae bacilli are usually seen in large number in the lesion and in blood, commonly involves mucosa especially the nose and lead to much deformed.
2-Tuberculoid leprosy
Associated with an intense cell immuneresponse to the organism ,involves the nerves ,and damage the legs and hands and caused loss of finger and toes.Hypopigmented patches
Nodules on the earsNerve enlargment
Neurological deficits
MOOT (mycobacterium other than tuberculosis bacilli)
Include the species:M.avium M.intracellulare M.marinum M.Kansasii And others Habitat Isolated from : Soil Water Birds And animals