6. MYCOBACTERIA.docx

MYCOBACTERIA Mycobacteria Species of mycobacteria Mycobacterium tuberculosis (Tuberculosis) Mycobacterium leprae (Leprosy) Non-tuberculoid mycobacteria (Examples) Mycobacterium avium complex (includes M. avium and M. intracellulare) Disseminated infection in AIDS patients and other immunocomprom...

MYCOBACTERIA Mycobacteria Species of mycobacteria Mycobacterium tuberculosis (Tuberculosis) Mycobacterium leprae (Leprosy) Non-tuberculoid mycobacteria (Examples) Mycobacterium avium complex (includes M. avium and M. intracellulare) Disseminated infection in AIDS patients and other immunocompromised patients Pulmonary disease Lymphadentitis Mycobacterium kansasii Pulmonary disease Disseminated infection in AIDS patients and other immunocompromised patients Acid fast bacillus - High lipid content in cell walls make Mycobacteria acid-fast on staining. Resist decolorization with acid alcohol Other organisms can be acid-fast, e.g. Nocardia spp. Clinical manifestations Primary tuberculosis – First exposure Spread by aerosol Usually subclinical (asymptomatic) lung infection Symptomatic primary tuberculosis is less frequently, more commonly found in children, elderly or immunocompromised. Cell-mediated immunity will wall off and suppress the bacteria Bacteria are basically dormant but can later be activated and cause disease. Secondary or reactivated tuberculosis Most cases of tuberculosis occur after the bacteria were dormant for some time. Assumed that temporary weakening of immune system triggers reactivation in any of the organs infected Pulmonary, pleural and pericardial, lymph node (cervical usually involved), Kidney, spinal, chronic arthritis, meningitis/brain, miliary (tiny granulomas spread over the body). Chronic disease with weight loss, low-grade fever, and symptoms related to organ system affected. Can be confused with cancer. Mycobacterium leprae Cause of leprosy, also called Hansen’s Disease WHO estimates about 2 million people infected with this organisms in the world Most in India, Brazil, Burma, Indonesia, Madagascar and Nepal In U.S., over 100 newly diagnosed cases per year. Usually in immigrants Impossible to grow this bacteria on artificial media Clinical manifestations are dependent upon 2 phenomenon: Severity dependent on host’s cell-mediated immune response Similar to that described for TB Bacteria appear to grow better in cooler body temperatures closer to skin surface Damages skin, superficial nerves, eyes, nose and testes Cell mediated immunity modulates form of disease/infection Lepromatous leprosy Severest form because patients can’t mount a cell-mediated immune response Skin, nerves, eyes and testes affected with bacteria found everywhere Skin lesions cover the body with lumps and thickening Face can look lion-like, with nose cartilage destroyed Eyes can be involved Loss of sensation in extremities because of nerve damage. Leads to repetitive trauma and loss of fingers and toes Eventually death Tuberculoid leprosy Cell-mediated immunity contains the infection Only a few skin lesions