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Rotation: Microbiology > Mycobacteria > Flashcards

Mycobacteria Flashcards

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1
Q

characteristics of mycobacteria

A

aerobic, non-spore forming, nonmotile straight or curved rods, cell walls are rich in lipids

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2
Q

gram stain of mycobacteria

A

ghost cells: faint, unstained images in the background material

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3
Q

why does mycobacteria stain poorly?

A

because the cell wall lipids interfere with the penetration of crystal violet and safranin into cell

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4
Q

acid-fast stain

A

using phenol to force mycobacterial cells to complex with a special dye

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5
Q

what makes an organism ‘acid fast’?

A

when the special dyes are retained in the cells even when treated with strong decolorizers like acid-alcohol

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6
Q

causative agent of tuberculosis

A

mycobacterium tuberculosis

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7
Q

how is mycobacterium tuberculosis (mtb) transmitted?

A

inhalation of droplet nuclei (small particles formed by coughing)

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8
Q

granulomas

A

tumorlike, inflammatory lesions that may occur in a variety of microbial diseases

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9
Q

tubercles

A
  • tuberculous granulomas
  • often have necrotic centers with a soft, cheesy appearance
  • caseous
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10
Q

primary tuberculosis

A

an infection in a previously uninfected individual

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11
Q

miliary tuberculosis

A
  • disseminated tuberculosis
  • small tubercles scattered throughout the body resemble millet seeds
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12
Q

body sites where mycobacterium tuberculosis (mtb) can cause disease

A
  • lungs
  • meninges
  • kidneys
  • bones
  • genital tractt
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13
Q

tuberculin skin test

A
  • injecting purified protein derivative, a mycobacterium tuberculosis (mtb) antigen, into the skin to observe for reaction within 48 to 72 hours
  • infected individuals become hypersensitive to mycobacterium tuberculosis (mtb) protein antigens
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14
Q

mycobacterium tuberculosis complex

A
  • mycobacterium tuberculosis
  • mycobacterium bovis
  • mycobacterium africanum
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15
Q

mycobacterium avium complex

A
  • mycobacterium avium
  • mycobacterium intracellulare
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16
Q

characteristics of mycobacterium avium complex

A
  • found in the environment
  • can cause pulmonary disease and mycobacterial lymphadenitis in immunocompetent individuals
  • can cause gastrointestinal or disseminated disease in patients with AIDS
  • most common cause of nontuberculous mycobacteria infections
  • resistant to many antimycobacterial drugs
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17
Q

mycobacterium fortuitum complex

A
  • mycobacterium fortuitum
  • mycobacterium chelonae
  • mycobacterium abscessus
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18
Q

characteristics of mycobacterium fortuitum complex

A
  • environmental mycobacteria that cause a variety of diseases including wound infections, abscesses, osteomyelitis, pulmonary infection
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19
Q

mycobacterium haemophilum

A
  • causes skin ulcers, lymphadenitis, disseminated disease in immunocompromised individuals
  • requires hemin, hemoglobin, or ferric ammonium citrate for growth
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20
Q

mycobacterium kansasii

A
  • common cause of nontuberculous mycobacterium pulmonary disease
  • infects variety of body sites including joints, bone marrow, skin, lymph nodes
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21
Q

mycobacterium leprae

A
  • causative agent of leprosy aka Hansen’s disease
  • does not grow in-vitro but can be grown in mouse footpads and armadillos
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22
Q

what is the diagnosis for leprosy based on?

A
  • patient’s clinical manifestations
  • presence of nonculturable acid-fast bacilli in skin biopsies
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23
Q

mycobacterium marinum

A
  • causes swimming-pool granuloma
  • acquired when traumatized skin comes in contact with fresh or salt water
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24
Q

mycobacterium scrofulaceum

A

causative agent of scrofula aka mycobacterial cervical lymphadenitis

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25
Q

mycobacterium ulcerans

A

causes skin ulcers aka buruli ulcers or bairnsdale ulcers in africa and australia

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26
Q

other pathogenic mycobacterium

A
  • mycobacterium genavense
  • mycobacterium simiae
  • mycobacterium xenopi
  • mycobacterium szulgai
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27
Q

mycobacterium gordone

A

common laboratory contaminant and is known as the ‘tap-water bacillus’ or ‘tap-water scotochromogen’

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28
Q

other nonpathogenic mycobacterium

A
  • mycobacterium flavescens
  • mycobacterium phlei
  • mycobacterium smegmatis
  • myobacterium terrae complex
  • mycobacterium baccae
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29
Q

what specimens can be submitted for mycobacterial cultures?

A
  • respiratory tract specimens
  • gastric aspirates or lavages
  • urine
  • stool
  • blood
  • bone marrow
  • normally sterile body fluids
  • tissue
  • wound aspirate
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30
Q

what are inappropriate specimens for mycobacterial cultures?

A
  • swabs
  • pooled sputum specimens
  • pooled urine specimens
31
Q

how are mycobacterial specimens processed?

A
  • concentration: more to inoculate
  • decontamination: to remove normal flora organisms and avoid overgrowing over mycobacteria
  • digestion: to free mycobacteria from clumps of protein and allows organisms to sediment during centrifugation
32
Q

NALC + 2% NaOH Method

A
  • NALC: mucolytic agent used to digest mucus
  • NaOH: decontaminates specimen
  • phosphate buffer: dilutes bactericidal activity of NaOH and lowers specific gravity of specimen to enhance sedimentation of mycobacteria during centrifugation
  • albumin: protein used to buffer and detoxify specimen sediments
33
Q

ziehl-neelson stain

A

hot method; carbolfuchsin reagent must be heated for stain to work
- smear is flooded with carbolfuchsin and heated until it has steamed for several minutes
- after cooled, rinse with water
- decolorized with acid alcohol
- rinse slide and counterstain with methylene blue or brilliant green
- rinse with water

  • acid-fast organisms: red with maybe beaded appearance
  • non-acid-fast organisms: blue or green depending on stain
34
Q

kinyoun stain

A

cold method; carbolfuchsin reagent has high concentration of phenol and basic fuchsin and does not need to be heated

35
Q

fluorochrome stain

A

uses auramine o which can be combined with rhodamine to stain acid-fast organisms

36
Q

egg-based media

A

contain fresh eggs that have been inspissated and malachite green

37
Q

nonselective egg-based medias

A
  • petragnani: has high concentration of malachite green and used for specimens that are likely to be contaminated
  • american thoracic society medium: low concentration of malachite green and recommended for culturing body fluids
  • lowenstein-jensen medium: most commonly used
38
Q

agar-based media

A

contain a variety of nutrients, albumin, and a very low concentration of malachite green

39
Q

nonselective agar-based media

A
  • middlebrook 7H10
  • middlebrook 7H11
40
Q

selective agar-based media

A
  • mitchison’s selective 7H11 (7H11S)
  • mycobactosel-middlebrook 7H11
41
Q

liquid media

A

enriched with variety of nutrients and contains tween 80
- dubos tween albumin broth
- middlebrook 7H9 broth
- middlebrook 7H12 broth
- middlebrook 7H13 broth

42
Q

mycobacterium haemophilum culture media

A

requires hemin, hemoglobin, or ferric ammonium citrate for growth

43
Q

what temperature are most mycobacterium incubated at?

A

35-37 C

44
Q

what mycobacterium organisms have a lower optimal incubation temperature and at what temperature?

A

25-33 C
- mycobacterium marinum
- mycobacterium haemophilum
- mycobacterium fortuitum complex
- mycobacterium ulcerans

45
Q

photoreactivity test

A

checks isolates for their ability to produce pigment and if pigmentation is induced by light

46
Q

photochromogens

A

mycobacteria that produce pigment when exposed to light but not in darkness

47
Q

scotochromogens

A

produce pigment in the light and in the dark

48
Q

nonphotochromogens/nonchromogens

A

do not produce pigment in the light or in the dark

49
Q

arylsulfatase

A
  • test substrate: tripotassium phenolphthalein disulfate
  • pH indicator: phenolphthalein is produced when the sulfate group is removed form the substrate
  • sodium carbonate detects the free phenolphthalein to produce alkaline conditions and turn the phenolphthalein red
    **most mycobacteria are arylsulfatase positive and the test system is adjusted to be used as an identification tool
50
Q

catalase

A

nearly all mycobacteria are catalase positive but the catalases produced by mycobacteria have different properties

51
Q

heat-stable (68 C) catalase

A
  • two tubes suspended with organism
  • one tube heated in a 68 C water bath for 20 minutes and one tube kept at room temperature
  • tween 80-hydrogen peroxide reagent is added to observe for mycobacterial clumps
  • bubbles are positive
52
Q

semiquantitative catalase

A

measuring the amount of catalase produced by adding tween 80-hydrogen peroxide to an lowenstein-jensen deep and measuring the height of the bubble column
- > 45 mm = high catalase producer
- < 45 mm = low catalase producer

53
Q

drop method (catalase)

A

used to test for isoniazid resistant mycobacterium tuberculosis strains by adding tween 80-hydrogen peroxide reagent to test colonies and observing for presence of bubbles
- bubbles = susceptibility cannot be determined
- no bubbles = presumptive resistance

54
Q

iron uptake

A

testing for mycobacteria that can convert ferric ammonium citrate to iron oxide; positive results shows tan discoloration and rusty colored colonies

55
Q

niacin accumulation

A
  • all mycobacteria produce niacin but not all can convert it into nicotinic acid mononucleotide
  • for mycobacteria that cannot convert niacin, the niacin will accumulate which can be tested by adding water, cyanogen bromide, and aniline and left to sit for fifteen minutes
  • yellow color indicates the presence of niacin
56
Q

nitrate reduction

A

inoculating the mycobacterial isolate into a tube with nitrate substrate for 2 hours and adding dilute HCl, sulfanilamide, N-naphthylethylenediamine dihydrochloride, and maybe zine if the red color does not appear after adding the other reagents

57
Q

pyrazinamidase

A

testing for the presence of pyrazinamidase, an enzyme that deaminates pyrazinamide to form pyrazinoic acid and ammonia; pyrazinoic acid complexes with ferrous ammonium sulfate to form a pink color

58
Q

tween 80 hydrolysis

A

detected by a color change that occurs when neutral red is released from tween 80-neutral red complexes; when neutral red is released from the complex, it turns red indicating a positive result

59
Q

serpentine cords

A

mycobacterium tuberculosis are frequently arranged this way because of a special glycolipid known as cord factor which is responsible for ropelike or snakelike formations

60
Q

identification characteristics of mycobacterium tuberculosis

A
  • niacin and nitrate production
  • nap susceptible
  • negative 68 C catalase test
61
Q

identification characteristics of mycobacterium bovis

A
  • nap susceptible
  • 68 C catalase, niacin, nitrate negative
    ** only mycobacterium susceptible to tch
62
Q

identification characteristics of mycobacterium kansasii

A
  • photochromogen
  • loose strands colonies
  • on smears, appears long, broad, banded
  • hydrolyzes tween 80
  • nitrate positive
  • high catalase producer
63
Q

identification characteristics of mycobacterium marinum

A
  • appears as long rods with cross bands in smears
  • photochromogen
  • grows best at 30 C
  • low catalase producer
  • hydrolyzes tween 80 and urease
  • pza positive
  • nitrate negative
64
Q

identification characteristics of mycobacterium gordonae

A
  • scotochromogen
  • nitrate negative
  • tween 80 positive
65
Q

identification characteristics of mycobacterium scrofulaceum

A
  • scotochromogen
  • nitrate negative
  • tween 80 hydrolysis negative
  • many strains are urease positive
66
Q

identification characteristics of mycobacterium avium complex

A
  • inactive biochemically
  • low catalase producers
  • tween 80, nitrate, urease negative
67
Q

identification characteristics of mycobacterium xenopi

A
  • most are nonchromogenic, some are scotochromogenic
  • distinctive bird’s nest appearance
  • optimal incubation temperature is 42 C
  • nitrate, tween 80, urease negative
68
Q

identification characteristics of mycobacterium fortuitum complex

A
  • optimal incubation temperature is 28 C but grow rapidly at 37 C
  • arylsulfatase positive
    ** chelone and abscessus should be differentiate from fortuitum becuase they are more resistant to antibacterial agents used to treat infections
  • fortuitum reduces nitrate and takes up iron but chelone and abscessus do not
69
Q

proportion test

A

using quadrant plates, control quadrant contains only culture medium while other quadrants contain culture medium and test drug at appropariate concentration to examine for growth compared to drug-free quadrant
- resistant = growth in drug-containing quandrant is +1% of growth in control quadrant

70
Q

mycobacterial photochromogens

A
  • mycobacterium kansasii
  • mycobacterium marinum
71
Q

mycobacterial scotochromogens

A
  • mycobacterium gordonae
  • mycobacterium scrofulaceum
  • mycobacterium xenopi (some)
71
Q

mycobacteria positive for tween 80

A
  • mycobacterium kansasii
  • mycobacterium marinum
  • mycobacterium gordonae
72
Q

mycobacterial nonphotochromogens/nonchromogens

A
  • mycobacterium avium complex
  • mycobacterium haemophilum
  • mycobacterium ulcerans
  • mycobacterium xenopi (most)
72
Q

mycobacteria positive for nitrate

A
  • tuberculosis
  • kansasii
  • fortuitum

Rotation: Microbiology (5 decks)

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