Acid-fast Bacteria Flashcards

1
Q

Rod-shaped, aerobic bacteria that do not form spores.
They are difficult to be stained by ordinary stain due to the high content of lipoid substances in the cell wall

A

Mycobacterium

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2
Q

causes tuberculosis and is a very important pathogen of humans.

A

M tuberculosis

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3
Q

Causes leprosy

A

Mycobacterium leprae

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4
Q

Frequently infect patients with AIDS, are opportunistic pathogens in other immunocompromised persons, and occasionally cause disease in patients with normal immune systems.

A
  • Mycobacterium avium-intracellulare (M avium complex, or MAC)
  • other nontuberculous mycobacteria (NTM)
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5
Q

The media for primary culture of mycobacteria

A

nonselective medium and a selective medium.

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6
Q

Are useful for observing colony morphology, for detection of mixed cultures, for antimicrobial susceptibility testing, and can also provide some indication of the quantity of organisms in a particular specimen.

A

Agar-based (solid) media

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7
Q

Obligate aerobes and derive energy from the oxidation of many simple carbon compounds

A

Mycobacterium

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8
Q

Enhances grow rate since they have slower growth rate than most bacteria

A

Increased CO2 tension

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9
Q

The doubling time of tubercle bacilli

A

18 hours

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10
Q

Tend to be more resistant to chemical agents than other bacteria because of the hydrophobic nature of the cell surface and their clumped growth.

A

Mycobacteria

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11
Q

Are resistant to drying and survive for long periods in dried sputum

A

Tubercle bacilli

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12
Q

Are emitted in droplets smaller than 25 um in diameter when infected persons cough, sneeze, or speak.

A

Mycobacteria

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13
Q

What happens inside the alveoli after Mycobacteria enters the host

A

The host’s immune system responds by release of cytokines and lymphokines that stimulate monocytes and macrophages.

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14
Q

Appear in the lung 1–2 months after exposure.

A

Pathogenic lesions associated with infection

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15
Q

The production and development of lesions and their healing or progression are determined chiefly by

A

(1) the number of mycobacteria in the inoculum and their subsequent multiplication
(2) the type of host and immune response

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16
Q

Two Principal Lesions
of Mycobacterium

A

Exudative type

Productive (proliferative) type

17
Q

When fully developed, this productive type of lesion, a chronic granuloma, consists of three zones:

A
  • a central area of large, multinucleated giant cells containing tubercle bacilli;
  • a mid zone of pale epithelioid cells, often arranged radially
  • a peripheral zone of fibroblasts, lymphocytes, and monocytes.
18
Q

Later, peripheral fibrous tissue develops, and the central area undergoes caseation necrosis

19
Q

Clinical manifestation of Tubercle bacillus

20
Q

Can occur in the absence of other signs of tuberculosis

A

Meningitis or urinary tract involvement

21
Q

Bloodstream dissemination leads to ______ with lesions in many organs and a high mortality rate.

A

miliary tuberculosis

22
Q

Specimens of M tuberculosis

A
fresh sputum, 
gastric washings, 
urine, 
pleural fluid, 
cerebrospinal fluid, 
joint fluid, 
biopsy material, 
blood, or other suspected material
23
Q

Specimens from sputum and other nonsterile sites should be liquefied with __________, neutralized with _____, and concentrated by _______.

A
  • N-acetyl-L-cysteine decontaminated with NaOH (kills many other bacteria and fungi)
  • buffer
  • centrifugation
24
Q

Specimens from sterile sites, such as cerebrospinal fluid can be directly

A

Centrifuged, examined, and cultured.

25
Stains of gastric washings and urine generally are not recommended because
saprophytic mycobacteria may be present and yield a positive stain.
26
Is more sensitive than traditional acid-fast stains, such as Ziehl-Neelsen, and is the preferred method for clinical material of tubercle bacilli
Fluorescence microscopy with auramine-rhodamine stain
27
Is the most sensitive method and provides results most rapidly.
Selective broth culture
28
Incubation for myvobacterial infection
35–37°C in 5–10% CO2 for up to 8 weeks
29
If culture results are negative in the setting of a positive acid-fast stain or if slowly growing NTM are suspected, then a set of inoculated media should be incubated
at a lower temperature (eg, 24–33°C) and both sets incubated for 12 weeks.
30
Produce pigment in light but not in darkness
Photochromogens
31
Develop pigment when growing in the dark
Scotochromogens
32
Are nonpigmented or have light tan or buff-colored colonies.
Nonchromogens (nonphotochromogens)
33
The two major drugs used to treat tuberculosis
INH and RMP
34
The other first-line drugs in treating tuberculosis
pyrazinamide (PZA) and ethambutol (EMB)
35
If the isolate is susceptible to INH and RMP, PZA and EMB can be discontinued, and the remaining treatment
with INH and RMP is continued to complete a 6-month course.
36
Most frequent source of infection of tuberculosis is
humans
37
Infection occurs at an earlier age in
urban than in rural populations.
38
T/F Patients who have had tuberculosis can be infected exogenously a second time.
True
39
Endogenous reactivation tuberculosis occurs most commonly among persons with
AIDS immunosuppression and elderly malnourished or alcoholic destitute men