Mycobacteria Flashcards
1
Q
TB transmission
A
droplet nuclei 1-5 microns
2
Q
2 types of TB
A
latent TB infection
TB disease
3
Q
highest risk of progression from LTBI to TBD
A
first 2 years of infection
4
Q
significant comorbidity with TB
A
HIV
5
Q
2 types of TB disease
A
pulmonary
extrapulmonary
6
Q
3 LTBI tx methods
A
- 9 months isoniazid
- 4 months rifampin
- weekly dose of isoniazid + rifapentine for 12 weeks
7
Q
6 month standard tx regimen for TBI (susceptible)
A
- Intensive phase: 2 months isoniazid, rifampin, ethambutol and pyrazinamide
- Continuation phase: 4 months isoniazid and rifampin
8
Q
MDR-TB is resistant to…
A
isoniazid or rifampin
9
Q
XDR-TB is resistant to…
A
isoniazid or rifampin, plus at least one fluoroquinalone and at least one second-line injectable drug (amikacin, kanamycin, capreomycin)
10
Q
safe level of TB exposure
A
none; 1-10 orgs can cause infection
11
Q
when is an aerosol created?
A
when you add energy to a liquid
12
Q
order to put on PPE
A
- gown
- mask
- eyewear
- gloves
13
Q
order to remove PPE
A
- gloves
- eyewear
- gown
- mask
14
Q
tuberculocidal chemicals
A
phenolic
iodophors
chlorine compounds
alcohols
15
Q
protocol for collecting specimens for initial dx
A
- 3 sputums
- 8-24 hours apart
- at least 1 is early morning
16
Q
during transport, TB samples should be kept…
A
cold
17
Q
minimum BAL or endotracheal aspirate volume
A
3 mL
18
Q
doubling time for TB
A
12-24 hours
19
Q
samples submitted for disseminated M. avium complex (MAC)
A
stool
blood (HIV pts)
20
Q
do not refrigerate —– samples for TB
A
CSF
21
Q
Hydrophobicity of TB cell inhibits…
A
transfer to media from a swab
22
Q
gastric lavage must be neutralized within…
A
1 hour of collection
23
Q
TB samples require a ——— packaging system
A
triple
category B biological substance
24
Q
3 steps of specimen processing for TB sputums
A
- digestion – mucolytic agent
- decontamination – kill NURF
- concentration – refrigerated centrifuge
25
most common digestion/decontamination method
method used to kill Pseudo from CF pts
NALC-NaOH (Petroff's method)
5% oxalic acid
26
NALC-NaOH final concentrations
2% NALC
1% NaOH
27
NALC-NaOH method steps
1. Add equal volume of NALC-NaOH to sputum
2. Invert; vortex 5-20 sec
3. Let stand for 15 min at RT, occasionally shaking
4. Add sterile DI or pH 6.8 phosphate buffer to 50 mL line and mix
5. Centrifuge for 15 min at 3000 x g
28
only a ------- processing control is recommended
negative
29
CF sputum often heavily contaminated with...
P. aeruginosa
30
how are gastric and urine samples processed differently?
concentrated, and then the pellet goes through the digestion and decontamination process
31
decontamination not required in processing
samples from sterile body sites
32
RCF =
1.12r(RPM/1000)^2
33
acceptable rates of contamination
solid media: 2-5%
liquid media: 7-8%
34
contamination rate less than acceptable indicates...
decontamination is too harsh
conc. of NaOH too high, or contact time too long
35
smear-positive patients are ---------------------- more infectious than smear-negative patients
5-10x
36
bacterial load required for smear positive result
5000 - 10,000 AFB/mL
37
2 types of AFB smears (timing)
- direct (before processing)
- concentrated
38
2 methods of staining AFB
- auramine staining (fluorescence)
- carbol-fuschin staining (bright field)
39
carbol-fuschin stain appearance
red/pink AFB on blue/green background
40
fluorescent stains
auramine O
auramine-rhodamine
41
2 carbol-fuschsin staining methods
- Ziehl-Neelson (ZN) -- heat required
- Kinyoun
42
primary stain and counterstain functions
primary stain stains AFB
counterstain provides contrasting background
43
fluorescent counterstain
potassium permanganate
44
how often are + and = control slides stained?
every day of use and ideally with each run
45
water used in fluorescent staining must not contain...
chlorine
46
heavily stained areas in the AFB
beads
47
species that may appear acid-fast on smear
Corynebacterium
Nocardia
some fungal species
48
does not require oil immersion
fluorescent stain
49
you should read at least -------- AFB smears to maintain proficiency
15 per week
50
3 culture options for AFB
- liquid/blood culture bottles
- egg-based LJ media
- agar-based 7H10/7H11 media
51
a negative AFB report is issued ------- weeks after media inoculation
6-8 weeks
52
minimum AFB ID
M. tuberculosis complex or non-tuberculous mycobacteria
53
ideal TAT for ID of MTBC
<= 21 days
54
all initial MTBC isolates are tested for susceptibility to...
- rifampin
- isoniazid
- ethambutol
- pyrazinamide
55
MTBC isolates tested against second-line drugs
those resistant to rifampin or any other 2 first-line drugs
56
AFB/mL of sputum required for positive culture vs smear
10
5000
57
Lowenstein-Jensen agar
* egg-based
* malachite green selects against contaminants
* MTBC grows better than NTM
58
time to detection of growth is less for (agar/LJ) media
agar
59
incubation for tubed solid media
- first 7 days: screwed loose, at a slant
- after 7 days: screwed shut, upright
60
incubation for plated media
- media side down
- in CO2 permeable polyethylene bag
- no more than 6 high
61
incubate media at 37° and at 25-33° for ---------- samples
skin, bone and joint biopsies
62
optimal atmosphere for TB
5-10% CO2
63
solid media is held for...
6-8 weeks
weekly reads
64
avg growth time for AFB in liquid media
14 days
65
best time for negative interim report -- no growth to date
4 weeks
66
most common contaminant
mold
67
LJ tubes to be discarded due to contamination
- mold
- discoloration
- liquification
68
sign of contamination of liquid media
homogeneous turbidity
69
overall contamination
contamination of both liquid and solid media in one culture
70
growth rate
number of days before visible colonies grow on solid media
71
2 mycobacteria growth rates
rapid growers: <7 days
slow growers: >7 days
72
photochromogens
require light to form pigment
73
scotochromogens
form pigment in light or dark
74
nonphotochromogen
do not form pigment
75
classic MTBC colony morph
rough and buff
dry and wrinkled
nonpigmented
76
in-solution hybridization assay for ID of growth on solid or liquid media
Hologic Accuprobe
77
ssDNA probes bind to target RNA in sample and the complex is detected by chemiluminescence
Hologic Accuprobe
78
nitrocellulose strip used to ID mycobacteria by reverse hybridization
line probe assay
79
no nucleic acid amplification occurs, so the organism in the sample must be sufficient
Hologic Accuprobe
80
genes commonly sequenced for ID
rpoB
hsp65
16S rRNA
81
cannot ID species within MTBC
MALDI
82
for patients who have ------- and -------, must extend tx with isoniazid and rifampin for an additional 3 months
cavitation on initial chest x-ray
positive cultures after 2 months of therapy
83
treatment failure if cultures positive after...
4 months
84
other species within MTBC
M. bovis
M. bovis BCG
M. caprae
M. microti
M. africanum
M. canettii
M. pinnipedii
M. mungi
85
should always be ID'd within MTBC due to intrinsic PZA drug resistance
M. bovis
M. bovis BCG
86
MTBC and broths known to be + for MTBC are transported as...
category A: infectious material
87
regulate transportation of samples
department of transportation
international air transportation association
88
NALC
N-acetyl-l-cysteine
89
ideal sputum volume
5-10 mL
90
prefer 25-33° and require 2 sets of media at 2 temps
M. marinum
M. ulcerans
91
require hemin/X for growth
M. haemophilum
92
source of M. gordonae contaminant
tap water
93
serpentine cording
virulent strains of MTBC; formed in liquid media
94
5 categories of Runyoun groups + organism for each
- MTBC -- M. tuberculosis
1. Photochromogens -- M. marinum
2. Scotochromogens -- M. gordonae
3. Nonchromogens -- M. avium
4. Rapid growers -- M. fortuitum
95
induration >--- mm after PPD skin test indicates M. tuberculosis exposure
10
<10 for NTM
96
principle of PPD test
intradermal injection of **tuberculin** material, which stimulates a **delayed-type hypersensitivity** response mediated by T lymphocytes and, in patients with **prior** mycobacterial exposure, causes **induration** at the injection site within 48 to 72 hours
97
principle of QuantiFERON test
measure **IFN-γ** secreted by the patient's T lymphocytes on stimulation with **M. tuberculosis-specific antigens** that are not found in BCG vaccines or most NTM species
98
IGRAs
interferon gamma release assays
99
most common NTM causing extrapulmonary infections. It usually causes nosocomial infection of the skin and soft tissues
M. fortuitum
100
tends to cause six clinical patterns of infection: pulmonary disease, skin and soft tissue disease, musculoskeletal infections, disseminated disease, catheter-associated disease, and lymphadenitis
M. kanasii
101
a known fish pathogen but can also cause human disease. It usually causes cutaneous lesions but in rare cases may originate more invasive diseases with the involvement of deep structures.
M. marinum
102
has never been successfully grown in artificial media, but can be propagated in the **mouse footpad and the nine-banded armadillo**
M. leprae
103
key biochemicals for MTBC
- nitrate reducation
- niacin accumulation
- 68° catalase test
