Mycobacterium Flashcards
List at least 5 general characteristics of mycobacterium.
- Thin, rod shape
- Obligate aerobe
- Cell wall with N-glucolylmuramic acid (high LIPID content)
- Resistant to antibiotics (b/c of cell wall)
- Slow-growing (4-8 weeks for colonies to be seen)
List the components that can cause TB.
Mtb complex can cause tuberculosis (TB). These are non-pigmented colonies when seen ion Lowernstein-Jensen agar.
What is the mode by which M. Tuberculosis (Mtb) is reanimated and causes human disease?
Transmitted from person to person via droplets in the air (sneeze, cough)
Name at least 5 factors that affect the probability of Mtb transmission.
- Susceptibility of exposed person
- Infectiousness of TB patient
- Environment in which the exposure occurred
- Exposure length, proximity and duration
- Virulence (strength) of tubercle bacilli
What is the histopathological feature of Late TB Infection (LTBI)?
Granulomas as low power and Langerhan’s giant cell in faster
_________ is less transmissible than M. Tuberculosis.
M. Bovine BCG
Describe the characteristic of mycobacteria that can be obtained from a lung biopsy.
Slender acid-fast positive, slightly curved and beaded bacilli
Describe the Tuberculin Skin test.
aka the Mantoux test involves a tuberculin (Mtb extract) that can recruit specific T-cells that make IFN-gamma to activate macrophages > inflammation.
Contrast latent Mtb infection from active Mtb infection.
Latent Mtb infection can remain latent due to delayed type hypersensitivity seen by (+) IFN-gamma release of TST.
Active Mtb infection presents as reactivation, reinfection or progressive primary infection.
How is the TST read and measured?
The Ring of induration is measured at 48-72 hours (DTH).
> 5 mm: (+) for HIGH-risk populations (organ transplants, HIV)
> 10 mm: (+) for moderate-risk populations (recent immigrants of high prevalent countries)
>15 mm: (+) for any persons
List the advantages of Interferon-gamma release assays (IGRAs) over TST.
Whole blood plus Mtb peptides measure response to RECOMBINANT SPECIFIC Mtb antigens
Under what conditions would both TST and IGRAs be performed?
- Likely to be infected, HIGH-risk progression in children < 5 y.o.a. (TST > 5mM)
- Likely to be infected at low to moderate risk progression (TST > 10 mM)
- Unlikely to be infected (TST > 15 mM)
Why would a physician perform a 2nd TST with an initial negative result? What of after an initial positive result?
- Doc would perform a 2nd test when the initial is negative to increase sensitivity (and pick up a possible missed positive result)
- She may perform another test after an initial positive as a confirmatory test for people unlikely to be infected with MTB
List some high risk factors for HIGH risk of TB progression.
HIV infection, immunosuppressive therapy, silicosis and present in children <5 y.o.a.
Compare LTBI (latent) from Active TB Disease.
LTBI = no symptoms, cannot spread to others, needs treatment for LTBI to prevent active form for up to a year
Active TB = symptoms of persistent, productive cough (>3 weeks), chest pain, fever, sweating at night; may spread to others, abnormal chest X-ray, needs multi drug therapy as treatment
List some advantages of using molecular tools to detect mycobacteria over direct microscopic culture.
- Fluorocarbons stain is more sensitive than Acid-fast stain. Positives must be confirmed by acid-fast stain
2.
What is an important virulent factor for Mtb that is dangerous for phagocytes?
Cord factor (trehalose dimycolate); *Anti-cord antibodies are protective.*
Describe the purpose of using nuclei acid amplification test on respiratory specimen of patients susceptible to TB.
A positive NAAT can be used as a presumptive piece of evidence of pulmonary TB disease in susceptible patients.
What are non-tuberculosis mycobacteria?
These are ubiquitous env organisms that can be caused by trauma, inhalation or ingestion of them. They are Runyon classified into 4 groups
What Group I NTM causes chronic pulmonary infection of the upper lung lobes and can be ID by DNA probe?
M. Kansasii is a photochromogen that has a major reservoir in tap water and grows slowly
What Group I NTM causes “swimming pool granuloma” and can be identified by biochemical or molecular methods?
M. Marinum causes a cutaneous infection associated with exposure to salt/ freshwater after trauma
Describe at least 5 features of M. Leprae.
- LEPROSY aka Hansen’s disease
- Spread from person-person via nasal secretions
- Causes single, multiple or widespread anaesthetic skin lesions
- Bacteria grow very slowly (years to decades incubation period)
- Tuberculosis
What feature of M. tuberculosis leads to effective transmission between hosts?
Impermeable lipid-rich envelope
