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Mercy CLS 2: Microbiology > Mycobacteria > Flashcards

Mycobacteria Flashcards

1
Q

TB transmission

A

droplet nuclei 1-5 microns

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2
Q

2 types of TB

A

latent TB infection
TB disease

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3
Q

highest risk of progression from LTBI to TBD

A

first 2 years of infection

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4
Q

significant comorbidity with TB

A

HIV

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5
Q

2 types of TB disease

A

pulmonary
extrapulmonary

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6
Q

3 LTBI tx methods

A
  1. 9 months isoniazid
  2. 4 months rifampin
  3. weekly dose of isoniazid + rifapentine for 12 weeks
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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
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8
Q

MDR-TB is resistant to…

A

isoniazid or rifampin

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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)

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10
Q

safe level of TB exposure

A

none; 1-10 orgs can cause infection

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11
Q

when is an aerosol created?

A

when you add energy to a liquid

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12
Q

order to put on PPE

A
  • gown
  • mask
  • eyewear
  • gloves
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13
Q

order to remove PPE

A
  • gloves
  • eyewear
  • gown
  • mask
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14
Q

tuberculocidal chemicals

A

phenolic
iodophors
chlorine compounds
alcohols

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15
Q

protocol for collecting specimens for initial dx

A
  • 3 sputums
  • 8-24 hours apart
  • at least 1 is early morning
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16
Q

during transport, TB samples should be kept…

A

cold

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17
Q

minimum BAL or endotracheal aspirate volume

A

3 mL

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18
Q

doubling time for TB

A

12-24 hours

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19
Q

samples submitted for disseminated M. avium complex (MAC)

A

stool
blood (HIV pts)

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20
Q

do not refrigerate —– samples for TB

A

CSF

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21
Q

Hydrophobicity of TB cell inhibits…

A

transfer to media from a swab

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22
Q

gastric lavage must be neutralized within…

A

1 hour of collection

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23
Q

TB samples require a ——— packaging system

A

triple

category B biological substance

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24
Q

3 steps of specimen processing for TB sputums

A
  1. digestion – mucolytic agent
  2. decontamination – kill NURF
  3. concentration – refrigerated centrifuge
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25
Q

most common digestion/decontamination method

method used to kill Pseudo from CF pts

A

NALC-NaOH (Petroff’s method)

5% oxalic acid

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26
Q

NALC-NaOH final concentrations

A

2% NALC
1% NaOH

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27
Q

NALC-NaOH method steps

A
  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
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28
Q

only a ——- processing control is recommended

A

negative

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29
Q

CF sputum often heavily contaminated with…

A

P. aeruginosa

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30
Q

how are gastric and urine samples processed differently?

A

concentrated, and then the pellet goes through the digestion and decontamination process

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31
Q

decontamination not required in processing

A

samples from sterile body sites

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32
Q

RCF =

A

1.12r(RPM/1000)^2

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33
Q

acceptable rates of contamination

A

solid media: 2-5%
liquid media: 7-8%

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34
Q

contamination rate less than acceptable indicates…

A

decontamination is too harsh
conc. of NaOH too high, or contact time too long

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35
Q

smear-positive patients are ———————- more infectious than smear-negative patients

A

5-10x

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36
Q

bacterial load required for smear positive result

A

5000 - 10,000 AFB/mL

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37
Q

2 types of AFB smears (timing)

A
  • direct (before processing)
  • concentrated
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38
Q

2 methods of staining AFB

A
  • auramine staining (fluorescence)
  • carbol-fuschin staining (bright field)
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39
Q

carbol-fuschin stain appearance

A

red/pink AFB on blue/green background

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40
Q

fluorescent stains

A

auramine O
auramine-rhodamine

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41
Q

2 carbol-fuschsin staining methods

A
  • Ziehl-Neelson (ZN) – heat required
  • Kinyoun
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42
Q

primary stain and counterstain functions

A

primary stain stains AFB
counterstain provides contrasting background

43
Q

fluorescent counterstain

A

potassium permanganate

44
Q

how often are + and = control slides stained?

A

every day of use and ideally with each run

45
Q

water used in fluorescent staining must not contain…

46
Q

heavily stained areas in the AFB

47
Q

species that may appear acid-fast on smear

A

Corynebacterium
Nocardia
some fungal species

48
Q

does not require oil immersion

A

fluorescent stain

49
Q

you should read at least ——– AFB smears to maintain proficiency

A

15 per week

50
Q

3 culture options for AFB

A
  • liquid/blood culture bottles
  • egg-based LJ media
  • agar-based 7H10/7H11 media
51
Q

a negative AFB report is issued ——- weeks after media inoculation

52
Q

minimum AFB ID

A

M. tuberculosis complex or non-tuberculous mycobacteria

53
Q

ideal TAT for ID of MTBC

A

<= 21 days

54
Q

all initial MTBC isolates are tested for susceptibility to…

A
  • rifampin
  • isoniazid
  • ethambutol
  • pyrazinamide
55
Q

MTBC isolates tested against second-line drugs

A

those resistant to rifampin or any other 2 first-line drugs

56
Q

AFB/mL of sputum required for positive culture vs smear

57
Q

Lowenstein-Jensen agar

A
  • egg-based
  • malachite green selects against contaminants
  • MTBC grows better than NTM
58
Q

time to detection of growth is less for (agar/LJ) media

59
Q

incubation for tubed solid media

A
  • first 7 days: screwed loose, at a slant
  • after 7 days: screwed shut, upright
60
Q

incubation for plated media

A
  • media side down
  • in CO2 permeable polyethylene bag
  • no more than 6 high
61
Q

incubate media at 37° and at 25-33° for ———- samples

A

skin, bone and joint biopsies

62
Q

optimal atmosphere for TB

63
Q

solid media is held for…

A

6-8 weeks
weekly reads

64
Q

avg growth time for AFB in liquid media

65
Q

best time for negative interim report – no growth to date

66
Q

most common contaminant

67
Q

LJ tubes to be discarded due to contamination

A
  • mold
  • discoloration
  • liquification
68
Q

sign of contamination of liquid media

A

homogeneous turbidity

69
Q

overall contamination

A

contamination of both liquid and solid media in one culture

70
Q

growth rate

A

number of days before visible colonies grow on solid media

71
Q

2 mycobacteria growth rates

A

rapid growers: <7 days
slow growers: >7 days

72
Q

photochromogens

A

require light to form pigment

73
Q

scotochromogens

A

form pigment in light or dark

74
Q

nonphotochromogen

A

do not form pigment

75
Q

classic MTBC colony morph

A

rough and buff
dry and wrinkled
nonpigmented

76
Q

in-solution hybridization assay for ID of growth on solid or liquid media

A

Hologic Accuprobe

77
Q

ssDNA probes bind to target RNA in sample and the complex is detected by chemiluminescence

A

Hologic Accuprobe

78
Q

nitrocellulose strip used to ID mycobacteria by reverse hybridization

A

line probe assay

79
Q

no nucleic acid amplification occurs, so the organism in the sample must be sufficient

A

Hologic Accuprobe

80
Q

genes commonly sequenced for ID

A

rpoB
hsp65
16S rRNA

81
Q

cannot ID species within MTBC

82
Q

for patients who have ——- and ——-, must extend tx with isoniazid and rifampin for an additional 3 months

A

cavitation on initial chest x-ray
positive cultures after 2 months of therapy

83
Q

treatment failure if cultures positive after…

84
Q

other species within MTBC

A

M. bovis
M. bovis BCG
M. caprae
M. microti
M. africanum
M. canettii
M. pinnipedii
M. mungi

85
Q

should always be ID’d within MTBC due to intrinsic PZA drug resistance

A

M. bovis
M. bovis BCG

86
Q

MTBC and broths known to be + for MTBC are transported as…

A

category A: infectious material

87
Q

regulate transportation of samples

A

department of transportation
international air transportation association

88
Q

NALC

A

N-acetyl-l-cysteine

89
Q

ideal sputum volume

90
Q

prefer 25-33° and require 2 sets of media at 2 temps

A

M. marinum
M. ulcerans

91
Q

require hemin/X for growth

A

M. haemophilum

92
Q

source of M. gordonae contaminant

93
Q

serpentine cording

A

virulent strains of MTBC; formed in liquid media

94
Q

5 categories of Runyoun groups + organism for each

A
  • MTBC – M. tuberculosis
    1. Photochromogens – M. marinum
    2. Scotochromogens – M. gordonae
    3. Nonchromogens – M. avium
    4. Rapid growers – M. fortuitum
95
Q

induration >— mm after PPD skin test indicates M. tuberculosis exposure

A

10

<10 for NTM

96
Q

principle of PPD test

A

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
Q

principle of QuantiFERON test

A

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
Q

IGRAs

A

interferon gamma release assays

99
Q

most common NTM causing extrapulmonary infections. It usually causes nosocomial infection of the skin and soft tissues

A

M. fortuitum

100
Q

tends to cause six clinical patterns of infection: pulmonary disease, skin and soft tissue disease, musculoskeletal infections, disseminated disease, catheter-associated disease, and lymphadenitis

A

M. kanasii

101
Q

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.

A

M. marinum

102
Q

has never been successfully grown in artificial media, but can be propagated in the mouse footpad and the nine-banded armadillo

103
Q

key biochemicals for MTBC

A
  • nitrate reducation
  • niacin accumulation
  • 68° catalase test

Mercy CLS 2: Microbiology (16 decks)

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