Mycobacteriology Flashcards
General characteristics
Pathogenic, opportunistic, normal flora
Capable of producing severe illness in humans by invading body tissues and systems
Causes for tuberculosis, leprosy, and non-tuberculosis pulmonary diseases
Mycobacterium structure
Aerobic bacilli (non spore forming and non motile)
Cell wall is rich in lipids which allows them to be acid-fast organisms (resist alcohol decolorization)
Very slow growing (typically take 2-6 WEEKS)
Require special media to grow
Environment
Typically found in soil, water, food, and several animal species throughout the world
Only a few species are actually pathogenic to humans to animals
Every year a few more species pop up and become opportunistic organisms in immunocompromised patients
Runyon classifications
Classified based on pigment production, effect of light on pigment, a growth time
Pigment vary from buff to orange because of carotene pigments (think carrots)
Pigment and light on pigment
Photochromogenic - pigment requires light exposure
Scotochromogenic - has pigment in the dark but the pigment becomes darker when exposed to light
Mycobacterium tuberculosis
Organism that causes tuberculosis (obvi)
Referred to as “consumption” in the 19th century
Discovered by Robert Koch and he was able to create an extraction from killed tuberculosis bacteria which has become the basis for the skin testing today
Means of transmission is inhalation of droplet nuclei from coughing/sneezing and it will settle in the lungs
Surprisingly the disease is usually asymptomatic
Most people find out they are infected through chest x-rays or positive skin tests
Very slow grower (taking about 21 days on average)
Grows rough, dry, buff-colored colonies
Exhibits “serpentine cording” on smears from culture
M. tuberculosis ID
Specimens need to be digested and decontaminated prior to culturing to remove normal flora and thick respiratory mucus
NALC (N-acetyl-L-cystine) is a mucolytic agent that digests the sample
NaOH acts as a decontaminant
Requires egg, potato, and serum cofactors in order to grow
Double sets of media are inoculated, one to grow in light and one to grow in dark
Tuberculosis direct examination
Stains - Carbol fuschin primary stain used
Ziehl Neelsen (uses heat), Kinyoun (cold), and fluorochrome (acridine orange and methylene blue fluorescence) are also used
Tuberculosis additional testing
Niacin - nicotinic acid test
Nitrate test
Catalase - semi quantitative or heat stable
TCH - sensitivity test to distinguish between M. bovis and M. tuberculosis (TB wont grow)
Tween 80 hydrolysis - a detergent some mycobacteria can hydrolyze into oleic acid and polyoxyethylated sorbitol (used to speciate within Runyon groups)
Mycobacterium leprae
Causative agent of Leprosy (Hansen’s Disease)
Characteristic arrangement of a “bundle of cigars”
Leprosy is a chronic disease of the skin, mucous membranes, and nervous system
Highly contagious but ~95% of the population is resistant to it
Endemic in Southern hemisphere with some cases in TX, CA, LA, HI, and PR (<100 yearly)
Nine banded armadillos can be a reservoir because they are naturally infected with M. leprae
There needs to be a defect in cell-mediated immunity for a person to become infected
Untreated disease can lead to disfigurement
Typically treated with Rifampin for several years
M. leprae ID
Is an obligate intracellular bacillus that has never been cultured in vivo
Diagnosis is typically made by histology smear of skin or earlobe tissue
Serological testing is available using “lepronin” which is a skin antigen type of testing
Mycobacterium kansasii
Second most common NTM to cause lung disease
Causes skin and soft tissue infections, lymphadenitis, and can cause disseminated disease in immunocompromised patients
Slow growing (2-3 weeks) organism that causes pulmonary disease in men over the age of 45 with emphysema
Photochromogen - buff colonies that turn “bright lemon yellow” when exposed to light
Can ID by 16sRNA probe
Mycobacterium gordonae
AKA “Tap water bacillus”
Found in water from faucets or natural settings in the soil
Rarely associated with human disease, seen as a laboratory contaminant
Scotochromogen - deep yellow/orange in dark that turns dark red in the light
Mycobacterium marinum
Rapid grower
Found in water (marinum = marina)
Associated with lesions of the skin (abraded skin that comes into contact with contaminated water)
Grows best at 30 degrees Celsius
Photochromogen
AKA “swimming pool granuloma”
Mycobacterium scrofulaceum
Causes adenitis (inflammation of a gland), bone, and other infections, especially in children (commonly in Africa)
Slow grower
Yellow colonies in both light and dark
Long term light exposure will turn colonies orange to a dark brick red
Scotochromogen
