1.15.4 TCH
TCH agar (thiophen-2-carboxylic acid hydrazide) can be used to
differentiate M. bovis from M. tuberculosis, as well as other nonchromogenic SGM. M. bovis is typically sensitive to TCH
(at 1–5 μg/mL), while most other SGM species (such as M. tuberculosis) are resistant.
1.15.5 Iron
M. fortuitum and a few other rapid and slow growers can convert
ferric ammonium citrate to iron oxide. To do this, L-J media can be
supplemented with 2.5% ferric ammonium citrate to differentiate
mycobacteria on the basis of iron-uptake ability. To further differentiate these rapid growers from slow growers, L-J media can also
be supplemented with 5% NaCl to differentiate based on salt tolerance. Mycolicibacillus triviale and Mycolicibacterium flavescens can
grow on salt-containing medium, however M. chelonae subsp. chelonae will not, distinguishing it from other members of the
M. fortuitum complex.
1.15.6 MacConkey
and Arylsulfatase
To further differentiate rapid growers, MacConkey agar without
crystal violet can be used. Two formulations of this agar allow for
better recovery of rapid growers such as M. fortuitum–chelonae
complex. Saprophytic strains of rapidly growing mycobacteria are
inhibited by the medium. In addition, the arylsulfatase 3- and
14-day test can be performed to differentiate M. fortuitum from
saprophytic mycobacteria by their ability to produce the arylsulfatase enzyme at a detectable level after 3 days incubation. Other
species of mycobacteria may produce this enzyme but do so more
slowly; in this case, the 14-day test is implemented to identify SGM
species.
1.15.7 Catalase
Lastly, a series of catalase tests can be used to identify and distinguish mycobacteria. AFB produce catalase; furthermore, a semiquantitative catalase test will divide mycobacteria into two groups:
the first group being M. kansasii, M. simiae, most scotochromogens, the nonphotochromogenic saprophytes, and the rapid
growers, and the second group being M. tuberculosis,
M. marinum, M. avium complex, M. xenopi, and Mycobacterium
gastri. Additionally, catalase at 68
C, pH 7.0, will distinguish the
thermostable
Mycobacterium
scrofulaceum
from
the
scotochromogens.
1.16 Growth
of M. tuberculosis
Under Hypoxic
Conditions
Several pathogenic Mycobacterium species, including members of
the tuberculosis complex, are capable of surviving during sustained
hypoxic environments. During that time, changes in metabolic
processes, including respiration and carbon utilization, structural,
including cell wall remodeling, and replicative process, occur as an
adaptation to hypoxia. Matched cultures of cells grown under
consistent, regulated, and monitored normoxic and hypoxic environments enable the study of these adaptations to advance research
22
Elizabeth Wallace et al.
TCH agar (thiophen-2-carboxylic acid hydrazide) can be used to
differentiate M. bovis from M. tuberculosis, as well as other nonchromogenic SGM. M. bovis is typically sensitive to TCH
(at 1–5 μg/mL), while most other SGM species (such as M. tuberculosis) are resistant.
1.15.5 Iron
M. fortuitum and a few other rapid and slow growers can convert
ferric ammonium citrate to iron oxide. To do this, L-J media can be
supplemented with 2.5% ferric ammonium citrate to differentiate
mycobacteria on the basis of iron-uptake ability. To further differentiate these rapid growers from slow growers, L-J media can also
be supplemented with 5% NaCl to differentiate based on salt tolerance. Mycolicibacillus triviale and Mycolicibacterium flavescens can
grow on salt-containing medium, however M. chelonae subsp. chelonae will not, distinguishing it from other members of the
M. fortuitum complex.
1.15.6 MacConkey
and Arylsulfatase
To further differentiate rapid growers, MacConkey agar without
crystal violet can be used. Two formulations of this agar allow for
better recovery of rapid growers such as M. fortuitum–chelonae
complex. Saprophytic strains of rapidly growing mycobacteria are
inhibited by the medium. In addition, the arylsulfatase 3- and
14-day test can be performed to differentiate M. fortuitum from
saprophytic mycobacteria by their ability to produce the arylsulfatase enzyme at a detectable level after 3 days incubation. Other
species of mycobacteria may produce this enzyme but do so more
slowly; in this case, the 14-day test is implemented to identify SGM
species.
1.15.7 Catalase
Lastly, a series of catalase tests can be used to identify and distinguish mycobacteria. AFB produce catalase; furthermore, a semiquantitative catalase test will divide mycobacteria into two groups:
the first group being M. kansasii, M. simiae, most scotochromogens, the nonphotochromogenic saprophytes, and the rapid
growers, and the second group being M. tuberculosis,
M. marinum, M. avium complex, M. xenopi, and Mycobacterium
gastri. Additionally, catalase at 68
C, pH 7.0, will distinguish the
thermostable
Mycobacterium
scrofulaceum
from
the
scotochromogens.
1.16 Growth
of M. tuberculosis
Under Hypoxic
Conditions
Several pathogenic Mycobacterium species, including members of
the tuberculosis complex, are capable of surviving during sustained
hypoxic environments. During that time, changes in metabolic
processes, including respiration and carbon utilization, structural,
including cell wall remodeling, and replicative process, occur as an
adaptation to hypoxia. Matched cultures of cells grown under
consistent, regulated, and monitored normoxic and hypoxic environments enable the study of these adaptations to advance research
22
Elizabeth Wallace et al.