Mycobacteria Flashcards
Discuss the unique cell wall structure of Mycobacterium:
Cell wall is comprised of peptidoglycan complex and 60% lipids. The 60% lipids are compromised of mycelia acids, cord factor, and wax D.
Mycolic acid is a unique alpha branching lipid that is highly hydrophobic creating a lipid shell
Cord factor is a serpentine cord that is toxic and causes inhibition of PMNs
Wax D is the cell envelope
Describe the temperature pattern commonly seen with tuberculosis infections in humans:
Skin -
Lungs -
Skin - 30°C
Lungs - 37°C
42°C for rare Mycobacterium species (xenopi)
Name two acid-fast organisms and explain what is meant by the phrase “acid fast”:
M. tuberculosis and M. avium
Acid-Fast: resists decolorization with up to 3% hydrochloric acid and some also resist decolorization with 95% ethanol
Compare and contrast the Ziehl-Neelsen and the Kinyon methods of staining for acid fast bacilli:
Both methods utilize carbon fuchsin solution for the primary stain the difference between the two methods is how they get the primary stain into the cell wall of the organism. The Ziehl-Neelson method uses heat where as the Kinyon method uses the detergent phenol
3% acid - alcohol as a decolorizing agent The counter (2nd) stain used is Methylene blue counter stain
Define Multiple Drug Resistant TB:
This organism is resistant to at least one of the two of the anti TB drugs either ionized or rifampin or both and it may be necessary to use amikacin, streptomycin and ciprofloxacin
Discuss treatment options for TB:
First line: Isoniazid, Rifampin, Rifapentine
Second line: Clycloserine, Ethionamide, Levofloxacin, Gatifloxacin, Streptomycin
Initial treatment is a 8 week regiment of Isoniazid, rifampin and pyrazinamide
M. tuberculosis
Colony Morphology: Growth Rate: Heat Stable Catalase: Nitrate: Niacin: NaCl: Tween 80 Hydrolysis: Urease:
Colony Morphology: rough cords Growth Rate: slow Heat Stable Catalase: neg Nitrate: pos Niacin: pos NaCl: neg Tween 80 Hydrolysis: neg Urease: pos
M. avium complex
Colony Morphology: Growth Rate: Heat Stable Catalase: Nitrate: Niacin: NaCl: Tween 80 Hydrolysis: Urease:
Colony Morphology: smooth rough translucent Growth Rate: slow Heat Stable Catalase: w pos Nitrate: pos Niacin: neg NaCl: neg Tween 80 Hydrolysis: neg Urease: pos
M. kansasii
Colony Morphology: Growth Rate: Heat Stable Catalase: Nitrate: Niacin: NaCl: Tween 80 Hydrolysis: Urease:
Colony Morphology: smooth rough Growth Rate: slow Heat Stable Catalase: pos Nitrate: pos Niacin: neg NaCl: neg Tween 80 Hydrolysis: neg Urease: pos
M. foriticum
Colony Morphology: Growth Rate: Heat Stable Catalase: Nitrate: Niacin: NaCl: Tween 80 Hydrolysis: Urease:
Colony Morphology: smooth Growth Rate: rapid Heat Stable Catalase: pos Nitrate: pos Niacin: neg NaCl: pos Tween 80 Hydrolysis: pos Urease: pos
M. leprae Identification in the Lab
Cannot grow in the Lab, skin biopsy
What disease is caused by Hansen’s bacillus?
Leprosy - M. leprae Tuberculoid and Lepromatous
What is the purpose and type of stain for auramine-rhodamine florochrome stain?
Is more sensitive than the carbofuschin stains
Can be screened on a lower magnification
minimum of 300 fields
Orgs appear yellow-orange against a dark background
What is the BACTEC method for culturing Mycobacterium? PCR method?
BACTEC - radiometric culture system, isolation, susceptibility testing and an inhibitor to only allow M. tuberculosis to be detected. the org may be isolated for ID within 3 weeks instead of the traditional 6 weeks
PCR technique - now becoming available for use
What are the criteria for specimen collection for M. tuberculosis?
Resp. secretions most common, sputum, first morning specimens most concentrated. Collect first in morning
Gastric, urine, stool, blood, CSF and tissue samples are also possible.
Res secretions digestion and decontamination is necessary
What is the clinical significance and method of differentiation for the following Non-tuberculosis mycobacterium?
M. kansasii-
M. fortuitum-chelonae-
M. kansasii- pulmonary disease of upper lobes, usually with cavitation and scarring. photochromogen, cat pos, nitrate pos
M. fortuitum-chelonae- variety of infections of skin, lungs, bone, CNS, both are rapid growers, nitrate neg
What is the clinical significance and method of differentiation for the following Non-tuberculosis mycobacterium?
M. bovis-
M. avium -
M. bovis- disease manifestation looks like M. tuberculosis in pt., grows more slowly, niacin neg, nitrate neg, don’t grow in TCH, in cattle
M. avium - usually appears as a lung disease, disseminated in immunosuppressed pts. swine poultry
Discuss media used for the isolation of Mycobacterium:
Media: Egg based media, Lowenstein-Jensen, American thoracic society (ATS), Petragnan. They contain malachite green to inhibit normal flora, pH between 6.5 to 6.8, and need an increased humidity
Serum or agar based: 7H10 and 7H11 agars
Liquid: BACTEC systems
Principle of the acridine orange test
emits green fluorescence when bound to dsDNA(at 520) and red fluorescence when bound to ssDNA or RNA(at 650 nm)
Describe and identify the general characteristics of the Runyon groups of Mycobacterium.
Photochromogen
Scotochromogens
Nonchromogenic
Rapid growers
Photochromogen - little or no pigment when grown in the dark but becomes highly pigmented when grown in light.
Scotochromogens - slow-growing and produce a yellow-orange pigment regardless of whether they are grown in the dark or the light.
Nonchromogenic - Nonphotoreactive; pertains to lack of pigment production when colonies are exposed to light.
Rapid growers - grow rapidly
Which of the following Mycobacterium spp. can be differentiated by the rapid hydrolysis of Tween 80?
Mycobacterium kansasii
