CLS04 - Mycobacteria

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  1. Micobacteria general characteristics - ___robic, micro appearance, important biochem
    • Intracellular pathogens
    • Aerobic (mostly obligate)
    • micro: very thin, slightly curved, may branch
    • gram +, but probably won't take stain
    • biochem: acid fast cell wall (N-glycolymuramic acid, high lipid content)
    • Non-spore forming (except M. marinum)
    • SLOW GROWING
  2. What is the Mycobacterium tuberculosis Complex?
    • A group of mycobacterium capable of causing tuberculosis (pulmonary or other)
    • M. tuberculosis (most common)
    • M. bovis
    • M. africanum
    • M. caprae
    • M. microti
    • M. canetti
    • M. pinnipedii
  3. What are the basic categories of mycobacterium? What are their habitats?
    • Mycobacterium Tuberculosis complex
    • Nontuberculous mycobacteria - slow growing
    • Nontuberculous mycobacteria - rapid growing
  4. MTC - colony appearance, infection
    • Colony: slow growing (~6 wks), nonpigmented
    • Infection: inhalation of a SINGLE organism can lead to infection
    • M. tuberculosis - person-to-person via droplets
    • M. bovis - associated w/ ingestion of milk from infected cows, penetrates mucosa
    • *NOTE - BCG vaccine is attenuated M. bovis
    • Individuals with HIV are more susceptible to TB
  5. Describe tuberculosis (disease - symptoms, global perspective)
    • Chronic pulmonary disease (most cases)
    • Can disseminate to every organ system
    • Cavity formation and bronchial spread
    • Rapid progression of pneumonia in AIDS patients (no cell-mediated immunity)
    • Global: 2nd leading cause of death from single infections microorganism
    • 1/3 world population has TB
    • Common among poor, homeless, IV drug users
    • 46% of notified TB patients had HIV test results
    • *NOTE - US and CA rates are declining
  6. Describe tuberculosis transmission
    • Respiratory spread: almost all cases
    • droplet nuclei hang in the air
    • infectious dose 10 bacilli
    • AFB smear positive = active infection (contagious)
    • *NOTE - highly contagious in AIDS patients w/o cavity formation (normal X-Ray)
    • Ingestion: rare
    • milk from infected cow
    • Skin innoculation: very rare
    • predominantly accident in lab
  7. Describe tuberculosis infection/repl
    • Airborne droplet nuclei reach terminal air spaces and multiply (usually mid-lung)
    • MTB ingested by alveolar M0
    • small numbers eliminated
    • large numbers allow growth within M0, then destroy M0
    • more M0 invade site, carry MTB to lymph nodes
    • nonimmune host: spreads directly into blood/body sites
    • hypersensitivity develops 3-8wks after infection preventing further dissemination
    • granulomas: "problem spots" in X rays, contain viable MTB for later reactivation
  8. What is NTB? Where is it normally found?  How is it classified?
    • All mycobacteria not found in the MTB complex
    • Widely distributed in nature (water, soil)
    • Runyon classification (old) (new is PCR)
    • Group I - photochromogens
    • Group II - Scotochromogens
    • Group III - Nonphotochromogens
    • *NOTE Group I-III = slow growers
    • Group IV - Rapid growers (<7 days)
    • *NOTE - M. leprae is noncultivatable
  9. What is the Photo Activation Test? Procedure? Results?
    • USED TO DETERMINE Runyon Group for NTB
    • Procedure: Innoculated 7H10 plates or tubes are immediately protected from light
    • (caps must be loose for growth)
    • Uncover tube then do light activation on it
    • Results
    • colonies become pigmented in light - Group I Photochromogens
    • colonies pigmented in dark OR light - Group II - Scotochromogens
    • colonies never pigment - Group III - Nonphotochromogens
  10. Photochromogens - group, details, examples
    • Group I
    • Slow growing
    • become pigmented when exposed to light
    • M. kansasii (most common)
    • M. asiaticum
    • M. marinum
    • M. intermedium
    • M. novocastrense
  11. Scotochromogens - group, details, examples
    • Group II
    • Slow growing
    • Colonies pigment in dark OR light
    • RARELY RECOVERED (contaminants)
    • M. szulgai
    • M. scrofulaceum
    • M. interjectum
    • M. heckeshornense
    • M. tusciae
    • M. kubicae
    • M. gordonae
    • M. cookii
    • M. hiberniae
  12. Nonphotochromogens - group, details, examples
    • Group III
    • Slow growing
    • Colonies produce no pigment in dark or light
    • MOST are pathogenic
    • M. avium complex (important)
    • M. xenopi
    • M. ulcerans
    • M. malmoense
    • M. genavense
    • M. haemophilum (rare, needs heme disc and cool temp to grow)
    • M. heidelbergense
    • M. shimoidei
    • M. simiae
    • M. celatum
    • M. conspicuum
  13. What is M. avium complex?  Diseases/groups? Members?
    • Most commonly isolated NTB species
    • Incidence higher in immunosuppressed
    • Respiratory disease in adults
    • Lympadenitis in children
    • Disseminated infection in HIV patients
    • Consists mainly of M avium and M. intracellulare
  14. rapid growers - group, details, examples,
    • Group IV
    • Rapid growring (<7 days)
    • can grow on routine media
    • Weakly gram positive
    • most common in posttraumatic wound infections
    • M. abscessus
    • M. fortuitum
    • M. chelonae
  15. Mycobacterium leprae - disease, forms?
    • Causes leprosy (Hansen disease)
    • chronic disease of skin, membranes, nerve tissue
    • bacilli multiplying in peripheral nerves cause sensory impairement
    • Tuberculoid: normal
    • no immune defect, localized to skin/nerves, few organisms present in lesions
    • WBC stops spread
    • Lepromatous: very bad
    • extensive skin lesions, NUMEROUS acid-fast bacilli, dissemination
    • organism unchecked, problematic
  16. M. leprae - isolation and ID
    • Detection via stains and molecular amplification (can't culture)
    • NOT CUTIVATABLE IN VITRO (cultivated in armadillo or mice footpads)
    • *NOTE - these tests are not yet refined
    • Clinical manifestations are best method of ID
  17. Describe blood cultures from mycobacterium w/ major use
    • major use: M. avium-intracellulare
    • automated detection system: specific media for direct culture from blood sample
    • loaded into bactec instrument for each reading
    • Isolator tube: functions as t.port/processing tube
    • sample must be innoculated to media
  18. Describe Lower Respiratory Samples from mycobacterium w/ major use
    • Expectorated sputum: early morning samples allow pooling
    • 1 per day for 3 days, MINIMUM
    • Induced sputum: use of expectorant if pt can't produce
    • Brochoscopy: last resort if sampling problems occur (surgical)
    • *NOTE - if positive for AFB 3 samples are enough, if negative 4-5 samples required
    • Monthly collections during therapy allow monitoring of results
  19. Describe Gastric Aspirates from mycobacterium w/ major use
    • Mainly used in children (can't produce sputum)
    • early morning samples allow pooling of swallowed sputum
    • 1 per day for 3 days
    • AFB smears are not reliable (false pos from NTB)
    • *NOTE - collection must be neutralized w/ NaCO3 within 4 hours
  20. Describe Body Fluids/CSF from mycobacterium w/ major use
    • CSF: 10mL minimum
    • Low # of organisms
    • AFB smear RARELY positive
    • Other fluids: collect as much as possible, then pellet
    • RARE
  21. Describe Wounds, Tissues, Aspirates from mycobacterium w/ major use
    • Biopsy: best sample
    • 1cm cube
    • often a punch biopsy
    • Aspirates: good sample
    • collect as much as possible
    • Swabs: worst sample
    • should not be used, may be rejected
    • always contains excess microbes
    • *NOTE - tissue samples must be ground prior to processing
  22. Describe stool samples from mycobacterium w/ major use
    • Collect >1 gram
    • MAC (avian) colonization: common in HIV pts
    • MTB - VERY rarely
    • *can be difficult to use due to contamination
  23. Describe urine asmples from mycobaterium w/ major use
    • Collect first morning urine (organisms accumulate in bladder)
    • 1 sampler per day for 3 days
    • Pooled samples unacceptable
    • Catheter required if clean catch impossible
  24. What are the direct detection methods for Acid-Fast bacilli?
    • Acid-fast stains
    • Fluorochrome - easy to read (glow)
    • Ziehl-Neelsen - not usually used due to heat requirement
    • Kinyoun - uses phenol instead of heat
    • Nucleic acid probes
    • Antigen protein detection
    • Immunodiagnostic testing
    • PCR/sequencing
    • Chromatographic analysis
    • Gas chromatography (mostly reference)
  25. How do acid fast stains work?
    • Drive the stain (carbol fuchsin) into the cell
    • Stain complexes with mycolic acids in cell wall
    • Resists decolorization (3% HCl in alcohol)
    • Counter stain with methylene blue
    • *NOTE - the bright pink is unmistakable
    • For fluorochrome stains
    • auramine-rhodamine replaces carbol fuchsin
    • acid decolorizer is 0.5% in alcohol
    • counter stain is potassium permanganate
    • orgaisms fluorese orange/yellow under UV microscope
    • *NOTE - fluorochrome method more sensitive (used more), can review 30 fields instead of 300 fields
  26. How are fluorochrome stains reported?
    • 20x ocular (standardized)
    • none: no AFB seen
    • suspicious: 1-2/30 fields
    • 1+: 1-9/10 fields
    • 2+: 1-9/1 field
    • 3+: 10-90/1 field
    • 4+: >90/1 field
    • *NOTE - positive culture is diagnostic for TB, positive smear indicates any mycobacterium
  27. What methods are available for identification of mycobacteria?
    • Acid-fast stain to confirm mycobacteria
    • Phenotypic tests: growth rate, pigment production, colony morphology, biochemical testing (Niacin, Nitrate, Catalse, PZA)
    • Molecular methods: accuprobe/genprobe
    • high sensitivity and specificity
    • chemiluminescent label on DNA probes to rRna
    • available - MTBC, MAC, M. gordonae, M. kansasii
  28. Susceptibility testing for MTB?
    • Proportional susceptibility method: plates incubated for 2-3 weeks with antimocrobial in 3/4 quadrants
    • >1% growth = resistant
    • Bactec 460 method: most common
    • results available in 5-7 days
    • broth (bactect) uses critical concentration for each drug
    • >1% growth = resistant
    • other systems available/developing
    • 2nd line testing: IF isolate is resistant to rifampin, isonazid, pyrazinamide
    • comprehensive panel of agents
    • not common in hospital
  29. What is MDRTB and XDRTB?
    • MDRTB: multiple drug-resistant TB
    • resistant to isoniazid and rifampin (two most potent TB drugs)
    • XDRTB: extensively drug-resistant TB (rare)
    • resistant to isoniazid, rifampin, fluoroquinolone, and at least 1/3 injectable second-line drugs
    • available treatments are much less effective
    • special concern for HIV patients, more likely to develop TB disease, higher risk of death

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Author:
victimsofadown
ID:
317643
Filename:
CLS04 - Mycobacteria
Updated:
2016-03-21 00:10:29
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CLS04 Mycobacteria
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CLS04
Description:
CLS04 - Mycobacteria
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