Mycobacteria Lesson Notes

Mycobacteria Mycobacteria Tuberculosis ( TB) Leprosy Mycobacterium A photomicrograph of M. leprae from a leprosy skin lesion (CDC) Mycobacterium_avium-intracellulare Physiology and Structure  Rods, Nonmotile, Strictly aerobic, Non-spore-forming  Occasionally form branched filaments  Cell wall is rich in lipids (mycolic acid) (70 to 90 carbons)  Responsible for acid-fastness, slow growth, resistance to detergents and common antibacterial antibiotics, antigenicity, clumping Once stained, resist decolorization with acid-alcohol (acid-fast)  Most mycobacteria grow slowly (GT: 12-24 h)  High (61 to 71 mol%) (G+C) content Mycobacterial cell wall structure (A) plasma membrane, (B) peptidoglycans, (C) arabinogalactan, (D) mannosecapped lipoarabinomannan (Like O-antigen), (E) proteins, (F) mycolic acids, and (G) glycolipid surface molecules Physiology and Structure Basic structure of cell wall is typical of gram positive Lipid components comprise 60% of cell wall weight  Proteins 15 % cell wall layers (purified protein derivatives, or PPDs) Classification Traditional characteristics used to identify Mycobacterium  Rate of growth  Colony morphology  Pigment production  Nutritional requirements  Optimum incubation temperature  Biochemical test results Classification M. tuberculosis Strictly pathogenic M. Tuberculosis M. africanum Strictly pathogenic complex M. bovis Strictly pathogenic M. Microti Strictly pathogenic M. bovis (BCG strain) Sometimes pathogenic M. kansasii Usually pathogenic M. marinum Usually pathogenic M. simiae Usually pathogenic Non-Runyon Group Runyon Group I (Slow-Growing Photochromogens) Classification Runyon Group II M. szulgai Usually pathogenic (Slow-Growing M. scrofulaceum Sometimes pathogenic Scotochromogens) M. xenopi Sometimes pathogenic Runyon Group III M. avium complex Usually pathogenic (Slow-Growing M. haemophilum Usually pathogenic Nonchromogens) M. ulcerans Usually pathogenic M. abscessus Sometimes pathogenic Runyon Group IV M. chelonae Sometimes pathogenic (Rapid Growers) M. fortuitum Sometimes pathogenic M. mucogenicum Sometimes pathogenic Mycobacterium tuberculosis Virulence factors of Mycobacteria Cell wall components Lipoarabinomannan (LAM) – prevents phagocyte activation and digestion within phagocyte. Mycolic acids – resist phagocytic digestion. Trehalose di-mycolate (cord factor) – Inhibits phagocyte chemotaxis, activation, phagosome-lysosome fusions and digesion. Cell wall antigens in general induce DTH Pathogenesis and Immunity  M. tuberculosis is an intracellular pathogen  lifelong infection  Organism enters respiratory airways  Minute infectious particles penetrate to alveoli  Where they are phagocytized by alveolar macrophages Pathogenesis and Immunity Response to Infection  Four stages of infection 1. Contact with macrophage 2. Blood monocytes and other immune cells are attracted to site of infection 3. a few weeks later, when influx of antigen-specific T cells, that mycobacterial multiplication is controlled.  Secretion of IFN-γ 4. Final stage infection  Dormant or active disease Pathogenesis and Immunity  In response to infection with M. tuberculosis  Macrophages secrete (IL-12) and tumor necrosis factor alpha (TNF-α).  Increase localized inflammation with recruitment of T cells and natural killer (NK) cells into area of infected macrophages, inducing T-cell differentiation into THI cells (T-helper cells), with subsequent secretion of (IFN-γ).  In presence of IFN-γ, infected macrophages are activated, leading to increased phagosome-lysosome fusion and intracellular killing.  Patients with decreased production of IFN-γ or TNF-a, or who have defects in receptors for these cytokines, are at increased risk for severe mycobacterial infections. Pathogenesis and Immunity Effectiveness of bacterial elimination related to size of focus of infection  Localized collections of activated macrophages (granulomas) prevent further spread of bacteria  These macrophages can penetrate into small granulomas (< 3 mm)  Kill all organisms contained in granulomas Pathogenicity Pathogenicity Pathogenicity Pathogenesis and Immunity  Although  phagocytosis is initiated by alveolar macrophages Circulating macrophages and lymphocytes are attracted to infectious focus by bacteria Risk Groups  Anyone can get TB. However, some groups are at higher risk to get active TB disease.  People at high risk include those : 1. HIV infection 2. in close contact with TB 3. medical conditions 4. from countries with high TB rates 5. who work in or are residents of long-term care facilities (nursing homes, prisons, some hospitals) 6. who are alcoholics or IV drug users Clinical Diseases  Initial pulmonary focus is middle or lower lung fields  Where tubercle bacilli can multiply freely  Approximately 5% of patients exposed to M. tuberculosis progress to having active disease within 2 years  Another 5% to 10% experience disease sometime later in life  Patients typically have nonspecific complaints of malaise, weight loss, cough, and night sweats.  Sputum may be scant or bloody and purulent. Sputum production with hemoptysis is associated with tissue destruction Diagnosis of active tuberculosis ? Diagnosis of active tuberculosis  Patient history  Chest X‐ray  Acid‐fast bacilli staining  Culture  Nucleic acid amplification testing The Xpert MTB/RIF kit •Specificity: 99.2% Sensitivity: detection TB: 97.6% RIF: 98.1% •In comparison to IS6110 real‐time PCR Cellular immune response Tuberculin skin test Needle Too Shallow Needle Too Deep Inserted Properly Measure the Diameter Tuberculin skin test  An intradermal injection of mycobacterial antigens  0.1 μg [5 tuberculin units] of PPD)  Skin test reactivity is measured 48 hours later  A positive PPD reaction usually develops 3 to 4 weeks after exposure to M. tuberculosis Positive Reaction: 18mm Criteria Defining Positive Purified Protein Derivative Reactivity in Patients Exposed to M .tuberculosis Reactivity to PPD Populations HIV-positive patients ≥5 mm Patients receiving immunosuppressive therapy of induration Patients with abnormal chest radiographs consistent with prior tuberculosis Recent ≥ 10 mm of induration  Injection drug users  Residents and employees of highrisk settings Persons with conditions of high risk ( diabetes, chronic renal failure, hematologic disorders, significant weight loss, gastrectomy)  ≥ 15 mm of induration immigrants from high-prevalence countries children younger than 4 years or exposed to adults at high risk Persons at low risk for tuberculosis IGRA (interferon gamma release assay) 1st line anti-TB agents 2nd line anti-TB agents Isoniazid Amikacin, Capreomycin, Canamycin Rifampicin Ofloxacin, Ciprofloxacin Pyrazinamide Cycloserine, Clofazimine Ethambutol Ethionamide PAS (Para-aminosalicylic acid) MDR and XDR strains Treatment  Most treatment regimens begin  2 months of isoniazid (INH), ethambutol, pyrazinamide, and rifampin,  followed by 4 to 6 months of INH and rifampin or alternative combination drugs. Chemoprophylaxis  Prophylactic regimens for use in patients (HIV positive and HIV negative) exposed to M. tuberculosis.  Daily or twice weekly INH for 6 to 9 months or daily rifampin for 4 months.  Patients who have been exposed to drug-resistant M. tuberculosis should receive prophylaxis with pyrazinamide and either ethambutol or levofloxacin for 6 to 12 months.  BCG immunization Mycobacterium avium-intracellulare  M. avium: Infection in birds  A related organism  M. intracellulare cause of an outbreak of pulmonary infection  M. avium-intracelluare complex (MAIC) are widely distributed in nature (Worldwide distribution)  Soil, dust, animals and tap water, and any of these may be source of infection for immunocompromised patients  Exception: Congo and Kenya but where MAIC infection is uncommon in AIDS patients. Epidemiology  Before onset of HIV, epidemic infections with MAIC were not commonly recognised  Respiratory tract infections and associated with concomitant chronic lung disease or deficient cellular immunity  73% of patients had pre-existing pulmonary disease, 38% smoked and 33% reported alcohol abuse  A chronic lymphadenitis, usually in cervical and facial region, is most common presentation in children 1 and 10 years Epidemiology  Disseminated infection may occur in patients without AIDS, usually associated with malignancy and immunodeficiency.  In areas where M. tuberculosis is endemic, HIV-infected individuals are rarely infected with MAIC.  Ingestion of contaminated water or food  Inhalation of infectious aerosols : greatest risk for those who are immunocompromised (AIDS) Mycobacterium avium Complex  Diagnosis  Microscopy and culture are sensitive and specific  Treatment, Prevention, and Control  Infections treated for prolonged period with clarithromycin or azithromycin combined with ethambutol and rifabutin  Prophylaxis in patients with AIDS who have low CD4+ cell count consists of clarithromycin or azithromycin or rifabutin; Mycobacterium kansasii  Environmental sources  Is one of most common NTMs isolated  Infection is acquired from environment  swimming pools, hot and cold water supplies and storage tanks (hospital environment)  A history of cigarette smoking, Chronic lung conditions including, treated tuberculosis, chronic obstructive pulmonary disease Mycobacterium kansasii  Presentation frequently resembles tuberculosis  Cough, sputum production, hemoptysis  High Mortality rates  often due to severe underlying conditions that co-exist in these patients. Mycobacterium kansasii  Rifampicin is an essential component of successful regimens..  Isoniazid, rifampicin and ethambutol given daily for 18 months  Clarithromycin is alternative  All isolates are resistant to Pyrazinamide  Rifampicin resistance: clarithromycin and ciprofloxacin Mycobacterium simiae  First isolated from monkeys imported into Unites States.  Mycobacterium simiae shares many similarities with M. avium and M. scrofulaceum  Infections in HIV-infected individuals, which resemble M. avium-intracellulare disease  Treatment like M. avium. Mycobacterium iranicum  Rapidly growing scotochromogenic species isolated from clinical specimens on three different continents ‫ﺁﺳﺎﯾﺸﮕﺎﻩ ﺟﺬﺍﻣﻴــﺎﻥ ﺑﺎﺑﺎ ﺑﺎﻏﯽ‬ ‫‪Mycobacterium leprae‬‬ Mycobacterium leprae  Causes leprosy or Hansen’s Disease  Infection of skin, mucous membranes and peripheral nerves  Most cases are from warm climates  Bacteria infect cooler areas of body (ears, nose, eyebrows, fingers, toes)  Diagnosis made from finding acid-fast bacilli in scrapings from lesions  Not culturable, except in mouse foot pads Mycobacterium leprae  Leprosy was first described in 600 BC in ancient civilizations of China, Egypt, and India  More than 5 million cases in 1985 and fewer than 300,000 in 2005.  Currently, 90% of cases are in Brazil, Madagascar, Mozambique, Tanzania, and Nepal.  Leprosy is spread by person-to-person contact  May spread either through inhalation of infectious aerosols or through skin contact with respiratory secretions and wound exudates. Pathogenesis and Immunity  Because bacteria multiply very slowly,  incubation period is prolonged  with symptoms developing as long as 20 years after infection   Capable of intracellular growth Disease is mediated by host immune response to infection Types of leprosy 1- Tuberculoid leprosy (paucibacillary Hansen disease)  Strong cellular immune  Weak humoral antibody response  Few macular lesions, nerve enlargement, paresthesia  Many lymphocytes and granulomas in Infected tissue  Few bacteria  Damaged nerves causes loss of sensation and predispose to burns and trauma  Lepromin skin test: Positive (papular induration develops 3 to 4 weeks after intradermal injection of antigen) Types of leprosy 1- Lepromatous leprosy (multibacillary Hansen disease)  Strong antibody response  A specific defect in cellular response  Abundance of bacteria in dermal macrophages & Schwann cells of peripheral nerves  Most infectious form of leprosy  Lepromin test: Negative Clinical Findings Tuberculoid Borderline Tuberculoid Borderline lepromatous Lepromatous leprosy leprosy leprosy Treatment  Tuberculoid form is treated with rifampicin and dapsone for 6 months  Clofazimine is added to this regimen for treatment of lepromatous form  Therapy is extended to a minimum of 12 months Many investigators believe much longer therapy is required for optimum management of patients.