EXAM 1 Mycobacteriology Flashcards
describe mycobacteria
- bacilli, obligate aerobes
- cell wall
- high lipid content
- acid fast bacilli (AFB)
describe the cell wall of mycobacteria
- high lipid content
- mycolic acids
- lipoarabinomannan
- waxy coat
- acid fast bacilli (AFB)
- binds carbol fuchsin dye so that it is not removed by acid alcohol
- acid fastness = resistance to decolorization by acid
name the mycobacterium tuberculosis complex pathogens
these are all AFB
- m. tuberculosis (MTB)
- m. africanum
- m. bovis (bovine bacillus)
- m. bovis bacille calmette-guerin (BCG)
- m. caprae (goat bacillus)
- m. microti (vole bacillus)
- m. pinnipedii (seal bacillus)
cause disease in humans
describe mycobacterium tuberculosis (MTB)
- transmission via the respiratory route
- particles can remain suspended in air for several hours
- large droplets are carried more than 6m away by exhaled air at a velocity of 50m/s (sneezing)
- more than 2m away at a velocity of 10m/s (coughing)
- less than 1m away at a velocity of 1m/s (breathing)
- particles can remain suspended in air for several hours
what is a ghon complex?
calcified focus of infection and associate lymphnode
persons at high risk for developing TB active disease fall into which 2 categories?
- those who have an increased likelihood of exposure to persons with TB disease
- those with clinical conditions that increase their risk of progressing LTBI to TB disease
in a montoux tuberculin skin test, what is indicated by an induration of 5 or more millimeters?
1) HIV-infected persons
2) A recent contact of a person with TB disease
3) Persons with fibrotic changes on chest radiograph consistent with prior TB
4) Patients with organ transplants
5) Persons who are immunosuppressed for other reasons (e.g., taking the equivalent of >15 mg/day of prednisone for 1 month or longer, taking TNF-a antagonists)
in a montoux tuberculin skin test, what is indicated by an induration of 10 or more millimeters?
1) Recent immigrants (< 5 years) from high-prevalence countries
2) Injection drug users
3) Residents and employees of high-risk congregate settings
4) Mycobacteriology laboratory personnel
5) Persons with clinical conditions that place them at high risk
6) Children < 4 years of age
7) Infants, children, and adolescents exposed to adults in high-risk categories
in a montoux tuberculin skin test, what is indicated by an induration of 15 or more millimeters?
1) is considered positive in any person, including persons with no known risk factors for TB.
2) However, targeted skin testing programs should only be conducted among high-risk groups.
describe testing for TB infection and the delayed hypersensitivity
- antigen is introduced into subcutaneous tissue and processed by local antigen-presenting cells
- a Th1 effector cell recognizes antigen and releases cytokines which act on vascular endothelium
- recruitment of T cells, phagocytes, fluid, and protein to site of antigen injection causes visible lesion
- takes 24 to 72 hours
what are the advantages and disadvantages of TST (two step booster test)
- advantages
- no special equipment
- lots of experience
- predictive value
- effectiveness of treatment for LTBI
- disadvantages
- requires follow up
- false positives
- false negatives
- rare adverse skin reactions
what are the advantages and disadvantages of IGRA (interferon-gamma release assays)?
- advantages
- no follow up visit
- no interference from BCG vaccine and most other NTM
- disadvantages
- requires a blood draw and equipment
- cost
- false positives
- false negatives
T or F
neither TST or IGRA can tell you if a patient has active TB
true
what are some clinical features of active tuberculosis?
- cough is one of the earliest signs with production of sputum as tissue necrosis progresses
- dyspnea a later symptom indicating extensive involvement of pulmonary parenchyma
- fever and weight loss reflecting systemic actions of IL-1 and TNF-alpha secreted by activated macrophages
differentiating active from latent TB is very important. why?
treatment and infection control measures are different
