Mycobacterium Flashcards
Define Mycobacterium?
Mycobacteria are aerobic and nonmotile bacteria (except for the species Mycobacterium marinum, which has been shown to be motile within macrophages) that are characteristically acid fast. Mycobacteria have an outer membrane.
Name an ‘fast growing’ mycobacterium.
M. fortuitous
What are Photochromogens, Scotochromogens, Non-chromogens? Give examples.
Photochromogens (eg M. kansasii) produce nonpigmented colonies when grown in the dark and pigmented colonies only after exposure to light and reincubation.
Scotochromogens (eg M. gordonae) produce deep yellow to orange colonies when grown in the presence of either the light or the dark.
Non-chromogens (M. tuberculosis) nonpigmented in the light and dark or have only a pale yellow, buff or tan pigment that does not intensify after light exposure.
Why are mycobacteria acid fast?
The high mycolic acid content of Mycobacteria is responsible for the staining pattern of poor absorption followed by high retention.
They are able to retain the Ziehl–Neelsen stain,
The distinguishing characteristic of all Mycobacterium species is that the cell wall is thicker than in many other bacteria, being hydrophobic, waxy, and rich in mycolic acids. The cell wall consists of the hydrophobic mycolate layer and a peptidoglycan layer held together by a polysaccharide, arabinogalactan.
What is the virulence advantage for mycobacteria being acid fast?
The cell wall has a high lipid content and is thus extremely hydrophobic.
This gives it the ability to survive in the environment, resist, intra-cellular phagocytosis, complement lysis and antibiotics (impermeable).
Describe the genome of M. tuberculosis.
Around 4000 genes are in the M. tb genome (within a 4,411,532 bp genome), with function known in roughly 60% of genes.
A large number of functional genes are involved in lipid metabolism
Why do their genomes vary within the mycobaterium genus?
Their genome size relates to the environment they live in. Those live in the soil have a large genome than those that are human/animal adapted, which tend to reduce their genome. Those in the soil have larger genome as they have deal with lots of environmental carbon sources and stresses.
Describe the prevalence, transmission, treatment, diagnosis of Hansen’s?
The oldest known human-specific infection 232,000 new cases in 2012-Diagnoses upon identification of skin lesion consistent with leprosy and with definite sensory loss and positive skin smears.-Treatment is a multi drug therapy of rifampicin, clofazimine, dapsone for 6 months.
What are the 2 types of leprosy?
Paucibacillary: few bacteria due to good immune response. Skin lesions (<5)
Multibacillary: immune response doesn’t response normally so can’t control the bacteria growth very well where they go into the nerves causing lost of sensation and losing digits.
What does M. ulcerans cause? Treatment?
Mycobacterium ulcerans is a slow-growing mycobacterium that classically infects the skin and subcutaneous tissues, giving rise to indolent nonulcerated (nodules, plaques) and ulcerated lesions.
Treatment: drugs (rifampicin and streptomycin) and surgery
What does M. marinum cause and what does cause M. avium complex?
Swimming pool granuloma: is a free-living bacterium, which causes opportunistic infections in humans, often affects individuals who work with fish or keep home aquariums
Lymphadenitis in immune-competent children and lung disease in adults with co-existing lung disease. MAC causes disseminated disease in up to 40% of people with human immunodeficiency virus (HIV)
Describe the current TB prevalence?
Roughly one-third of the world’s population has been infected with M. tuberculosis with new infections occurring in about 1% of the population each year. However, most infections with M. tuberculosis do not cause TB disease, and 90–95% of infections remain asymptomatic.
Outline the prospects for TB control and elimination
BCG vaccine
