Mycobacteriology Flashcards
Mycobacterium tuberculosis complex
MTB Africanum Bovus (including BCG) Canetii Microti
Mycobacterial drug resistance patterns
MDR: resists isoniazid and rifampin
XDR: MDR, also resists second-line drugs (aminoglycoside, quinolone)
TDR: Totally resistant…
TB treatment
RIPE: Isoniazid, rifampin, ethambutol, pyrazinamide.
1st-line. Treat for 4-6 months
2nd-line: Add a fluoroquinolone or aminoglycoside
Slow-growing photochromogens
Pigmented with light, not pigmented without.
Kansasii
Marinum
Szulgai (if grown cold)
Slow-growing scotochromogens
Pigmented regardless of light exposure
Gordonae
Scrofulaceum
Szulgai (if grown warm)
*Xenopi?
Slow-growing non-chromogens
MAC
Haemophilum
Simiae
Mycobacterial stains
Ziehl-Neelsen: Heating step.
Kinyoun: No heating. Standard.
Modified acid-fast: Weaker decolorizer. eg, Fite stain. For Nocardia, Leprae
Auramine fluorochrome: For direct/rapid visualization
Nocardia
Filamentous/branchine beaded bacteria.
Gram-positive. Modified fite stain positive
Lab workup of mycobacteria.
Start with AFB smear and direct visualization (flurochrome). If positive, do NAT to ID and culture for sens.
Always also culture (liquid brother with solid agar backup). Follow positive results with DNA probes to identify MTB complex members. Can also use MALDI, NGS, or biochem methods for final identification
Molecular identification of mycobacterial species
rpoB gene (qPCR? sequencing?)
IS6110 RFLP analysis
Mycobacterium bovis
MTB complex. Slow growing non-chromogen. Smooth colonies.
Causes abdominal infections (often mass-forming). Dairy.
Negative for niacin, nitrate. TCR sensitive. Resists pyrazinimide.
Mycobacterium avium complex
1 cause of nontuberculoidal pulm disease. Can cause scrofula. Whipple-like gastrointestinal disease in the immunocompromised.
Slow-growing non-chromogen.
Mycobacterium haemophilum
Slow-growing non-chromogen.
Needs iron supplementation to grow
Mycobacterial culture media
Lowenstein-Jensen (egg-based, old), Middlebrook (7H10, 7H11)
Broths (standard, based on middlebrook formulas)
Mycobacterium leprae
Cannot be routinely cultured. Has tropism for cooler tissues. Armadillos.
Diagnose with lepromin skin test (if immunocompetent) or direct skin biopsy.
Response patterns may be lepromatous (ineffectual, disfiguring) or tuberculoid (effective; paucicellular)
TB testing
PPD: 10mm normal response, 5mm in immunocompromised
IGRA: Peripheral lymphocyte release in contact with various mycobacterial antigens.
Fast-growers
Chelonae
Fortuitum
Abscessus
Mycobacterium kansasii
Slow-growing photochromogen
Causes systemic disease.
Nitrate positive.
Mycobacterium marinum
Slow-growing photochromogen. Prefers colder temperatures.
Causes skin infections in association with marine life (fish-tank granuloma).
Lymphangitic spread.
Mycobacterium scrofulaceum
Slow-growing scotochromogen
Causes scrofula (cervical LAD), usually in children.
Mycobacterium tuberculosis
Rough colonies.
Niacin+, nitrate+, resistant to TCH but susceptible to NAP/PNB. Trehalose accumulates in cords in agar.
Mycobacterium xenopi
Slow-growing scotochromogen? Prefers hot temperatures (42-45C).
Causes pulmonary disease.
Arylsulfatase+. “Birds-egg nest” colonies
Mycobacteria in cystic fibrosis patients
When culturing pulmonary samples, must add oxalic acid to inhibit growth of pseudomonas
Mycobacterium chelonae
Fast-grower.
Citrate+. Salt-susceptible.
Mycobacterium fortuitum
Fast-grower.
Nitrate+. Salt-resistant.
Mycobacterium abscessus
Fast-grower.
Salt resistant.
Mycobacterium ulcerans
Produces “mycolactone” toxin which causes ulceration
Nonpathogenic mycobacterial species
Gordonae
Lentiflavum
Mucigenicum
Terrae
