Mycobacterium Flashcards
What subspecies make up the mycobacterium tuberculosis complex?
M. Tuberculosis
M. Bovis
M. Bovis -BCG
T/F: Mycobacterium are... Gm + Motile Spore forming encapsulated cocci
T F - non motile F - DO NOT FORM SPORES F - non-encapsulated F - rods
T/F: Mycobacterium are obligate aerobes
True…ish. All are except M. Bovis
Mycobacteria are/are not acid fast
ARE
What are mycolic acids and what is their significance
They are long-chain fatty acids found in mycobacterial cell walls. They provide mycobacteria with a high lipid content, and make 40 - 60 % of their dry weight. THEY ARE ABSENT IN MOST OTHER BACTERIA. THEY MAKE THINGS ACID FAST
Mycobacteria grow slow/fast in culture
SLOW (~18 hours for TB)
** M. Leprae CANNOT BE CULTURED ** EVER. EVER.
M. TB transmission
Human to Human, mostly acquired by inhalation of droplet nuclei, which can be suspended in air for very long periods of time.
Inhaled organisms ingested by macrophage - > transient bacteremia, granuloma formation in lung or other organs. Can become latent infection, or a symptomatic disease
T/F: LTBI can be symptomatic
FALSE, latent TB infection is always asymptomatic.
Disease state is always symptomatic
Ghon lesion, ghon complex, and Ranke complex are all:
Radiographic manifestation of a HEALED PRIMARY INNFECTION
Extrapulmonary TB can occur in:
Lymphatics (scrofula)
Skeletal (potts disease)
GU
CNS
TB often goes with HIV because
Critical role of CD4 cells in mycobacterial immunity, thus with HIV risk increases to progress from LTBI
What is an advantage of the AFB test in diagnosing ACTIVE TB?
Disadvantages?
Advantageous is that it gives a same day result.
Disadvantages include; limited sensitivity (10^5 organisms needed) and limited specificity (patients with Non-tuberculosis mycobacterium - NTMs - will also test positive)
TB treatment: what drugs are used for drug sensitive TB treatment and for how long?
4 “RIPE” drugs for 2 months - Rifampin, Isonazid, Pyrazinamide, Ethambutol
2 drugs for 4 months - Isonazid + Rifampin
MDR TB is resistant to:
at least Isonazid + Rifampin.
These resistant strains have chromosome-mediated mechanisms caused by PRIOR Rx or INADEQUATE TREATMENT
What type of reaction is the Tuberculin skin test used to diagnose Latent TB Infection (LTBI)? What is the reaction against?
It is a delayed type hypersensitivity reaction against ‘purified protein derivative’ - PPD
T/F: The result of the TST are based on measurement of the diameter of erythema at the injection site
FALSE. Cutoffs based on diameter of INDURATION, not redness
common mistake made on interpretation…
What are IRGAs used for
Interferon Gamma Release Assays are used as a blood assay to diagnose LTBI. It works because mononuclear cells from patients with TB infection produce IFN gamma in response to TB Ag.
Treatment regimen for Latent TB infection:
Isonazid- 9 months (best, used for HIV +’s)
Others:
Isonazid 6 mo
Rifampin 4 mo
Rifapentine +Isonazid 1x weekly for 12 weeks
T/F: M. Bovis causes TB in humans
True, but of a different form. M. Bovis produces TB in cows, but causes “gastrointestinal TB” in humans.
What is M. Bovis BCG?
M. Bovis Bacille Calamette Guerin - this is an attenuated strain of M. bovis used as a live vaccine against TB in humans
Efficacy of BCG vaccine
reduces childhood risk by 80% and all TB by 50%. Prevents other mycobacterial infection too. Provides protection from bacteremic related complications
T/F: the BCG vaccine is given orally
FALSE, given as ID injection in TB endemic part of world
Patient has PPD test and measures 13 mm induration. They have had the BCG vaccine. Should you be worried?
YES, patients with BCG vaccine WILL test positive BUT reactions would be under 10 mm.
T/F: Patients (without TB) that have had BCG vaccine will test negative on IGRA
TRUE, IGRAs for LTBI are not affected by previous BCG vaccination
Pathophysiology: Why does leprosy affect skin & mucous membranes?
Growth preference is at 27-33 degrees; thus it prefers cooler areas
T/F: M. Leprae is primarily transmitted skin to skin
False, it is primarily aerosol respiratory transmission, but skin to skin is possible
T/F: The typical incubation period for M. Leprae is 2 to 5 weeks
FALSE. 2 to 5 YEARS
- Can range from just a few months up to 30 years
The two forms of M. Leprae infection are:
Tuberculoid and Lepromatous
A pathology with macrophage stuffed with M. Leprae and FEW granulomas would be characteristic of Tuberculoid/Lepromatous infection?
Lepromatous.
Tuberculoid infection has a pathology of well-defined, non-caseating granulomas
Tuberculoid leprosy is ____-bacillary; Lepromatous leprosy is _____-bacillary.
Tuberculoid = paucibacillary (few bacteria) Lepromatous = multibacillary (many)
T/F: those who acquire leprosy often have a genetic predisposition
True
The prognosis for Tuberculoid leprosy is good/poor
For Lepromatous leprosy it is good/poor
Good for Tuberculoid
Poor for Lepromatous
T/F: an improved chemotherapy for leprosy includes Dapsone, Rifampin, and Clofazamine for 2-3 YEARS
TRUE.
steroids may also be used for complications.
The Runyon classification, based organism growth rate and color expression (in light vs. dark) is used to classify:
Nontuberculous Mycobacteria; there are many species…M. Avium most important
T/F: Nontuberculus mycobacteria (NTM) can be pathogenic
True. They are pathogenic in immunocompromised or normal hosts. They are often seen as lab contaminants and must be amplified to distinguish from TB
Mycobacterium avium complex is the most common NTM to cause human disease. Where is it found before transmission?
Widespread in water, soil, and birds
T/F: M. Avium infections are becoming less common
False, INCIDENCE IS INCREASING
Clinical syndrome of M. Avium in: Children - Lung disease patients - Normal people - AIDS patients -
Children - cervical adenitis or scrofula
Chronic lung disease patients -> pulmonary disease
Normal host - Pulmonary disease (especially old ladies)
AIDS patient - Disseminated infection
M. chelonae, M. fortuitum, and M. Abscessus are members of what mycobacterium group?
Rapidly Growing Mycobacterium (RGM)
INCIDENCE IS INCREASING!
Some syndromes associated with rapidly growing mycobacterium are: (4)
Skin disease/ wound infection
Prosthetic device infection
Pulmonary disease (in lung disease pts)
Disseminated infection (immunocomprimised)
