Acid-fast Bacteria

Question 1

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

Answer 1

Mycobacterium

Question 2

causes tuberculosis and is a very important pathogen of humans.

Answer 2

M tuberculosis

Question 3

Causes leprosy

Answer 3

Mycobacterium leprae

Question 4

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

Answer 4

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

Question 5

The media for primary culture of mycobacteria

Answer 5

nonselective medium and a selective medium.

Question 6

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.

Answer 6

Agar-based (solid) media

Question 7

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

Answer 7

Mycobacterium

Question 8

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

Answer 8

Increased CO2 tension

Question 9

The doubling time of tubercle bacilli

Answer 9

18 hours

Question 10

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

Answer 10

Mycobacteria

Question 11

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

Answer 11

Tubercle bacilli

Question 12

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

Answer 12

Mycobacteria

Question 13

What happens inside the alveoli after Mycobacteria enters the host

Answer 13

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

Question 14

Appear in the lung 1–2 months after exposure.

Answer 14

Pathogenic lesions associated with infection

Question 15

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

Answer 15

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

Question 16

Two Principal Lesions
of Mycobacterium

Answer 16

Exudative type

Productive (proliferative) type

Question 17

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

Answer 17

• 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.

Question 18

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

Answer 18

tubercle

Question 19

Clinical manifestation of Tubercle bacillus

Answer 19

protean

Question 20

Can occur in the absence of other signs of tuberculosis

Answer 20

Meningitis or urinary tract involvement

Question 21

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

Answer 21

miliary tuberculosis

Question 22

Specimens of M tuberculosis

Answer 22

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

Question 23

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

Answer 23

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

Question 24

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

Answer 24

Centrifuged, examined, and cultured.

Question 25

Stains of gastric washings and urine generally are not recommended because

Answer 25

saprophytic mycobacteria may be present and yield a positive stain.

Question 26

Is more sensitive than traditional acid-fast stains, such as Ziehl-Neelsen, and is the preferred method for clinical material of tubercle bacilli

Answer 26

Fluorescence microscopy with auramine-rhodamine stain

Question 27

Is the most sensitive method and provides results most rapidly.

Answer 27

Selective broth culture

Question 28

Incubation for myvobacterial infection

Answer 28

35–37°C in 5–10% CO2 for up to 8 weeks

Question 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

Answer 29

at a lower temperature (eg, 24–33°C) and both sets incubated for 12 weeks.

Question 30

Produce pigment in light but not in darkness

Answer 30

Photochromogens

Question 31

Develop pigment when growing in the dark

Answer 31

Scotochromogens

Question 32

Are nonpigmented or have light tan or buff-colored colonies.

Answer 32

Nonchromogens (nonphotochromogens)

Question 33

The two major drugs used to treat tuberculosis

Answer 33

INH and RMP

Question 34

The other first-line drugs in treating tuberculosis

Answer 34

pyrazinamide (PZA) and ethambutol (EMB)

Question 35

If the isolate is susceptible to INH and RMP, PZA and EMB can be discontinued, and the remaining treatment

Answer 35

with INH and RMP is continued to complete a 6-month course.

Question 36

Most frequent source of infection of tuberculosis is

Answer 36

humans

Question 37

Infection occurs at an earlier age in

Answer 37

urban than in rural populations.

Question 38

T/F

Patients who have had tuberculosis can be infected exogenously a second time.

Answer 38

True

Question 39

Endogenous reactivation tuberculosis occurs most commonly among persons with

Answer 39

AIDS immunosuppression and elderly malnourished or alcoholic destitute men