The mycobacteria are divided into 3 major groups of based on fundamental
differences in
epidemiology and association with disease
refers to the mycobacterial species that occur in humans and are capable of causing tuberculosis
Mycobacterium tuberculosis complex (MTBC)
species under MTBC
M. tuberculosis (MTB)
M. bovis
M. africanum
consists of mycobacterial species that do not belong to the MTBC, thus it is also known as Mycobacteria Other Than Tubercle Bacilli (MOTT). It is a diverse group of organisms commonly
found in the environment, and the group includes both
saprophytes and opportunistic human pathogens.
Nontuberculous Mycobacteria (NTM)
causes leprosy (Hansen’s disease). It is distinct from other mycobacteria because it does not grow in artificial culture media.
Mycobacterium leprae
Slender with numerous tight coils; 0.1-0.18 um iwide x 6 20 um long; has 8-20 evenly spaced coils
Family Spirochaetaceae
Treponema
Axial filaments: 6-10
Insertion Disks: 1
Family Spirochaetaceae
Treponema
Thicker with fewer and looser coils; 0.3 µm wide x 3.0 µm long has 3-10 loose, irregular coils.
Family Spirochaetaceae
Borrelia
Axial filaments: 30-40
Insertion Disks: 2
Family Spirochaetaceae
Borrelia
Slender, tightly coiled; ends bent to form question mark-like hooks; 0.1–0.2 µm wide x 5-15 µm long
Family Leptospiraceae
Leptospira
Axial filaments: 2
Insertion Disks: 3-5
Family Leptospiraceae
Leptospira
A classification for Nontuberculous Mycobacteria (NTP) was introduced by Ernest Runyon in 1959. Four groups of NTM are classified based on 2 criteria
- Growth rate
2. Colonial pigmentation
a. Slow growers - produce colonies in >7 days
Runyon groups I, II, and III
b. Rapid growers - produce colonies in <7 days
Runyon groups IV
Colonial pigmentation - based on the abillity/inability of NTM to synthesize
[?] (a group of yellow to red pigments) with or without light
carotenoids
Photochromogens
Runyon group I
Scotochromogens
Runyon group II
Nonphotochromogens
Runyon groups III and IV
Assessment of Photoreactivity of Mycobacteria
- Inoculate the surfaces of three Löwenstein–Jensen slant media or three
[?] agar plates with fluid from a dilute broth culture of the
organism to be tested. Wrap two of the tubes or plates with aluminum
foil; leave the third exposed to the ambient light in the incubator.
Middlebrook 7H11
Assessment of Photoreactivity of Mycobacteria
- Incubate one of the wrapped tubes or plates at [?]; the other
wrapped tubes or plates at 37°C.
25°C–30°C
Assessment of Photoreactivity of Mycobacteria
- Several days after growth is noted in the light-exposed control tube or
plate, examine the [?] or plates for growth.
wrapped tubes
Assessment of Photoreactivity of Mycobacteria
- If early growth is detected in the wrapped tubes or plates, expose one of
each pair to a strong light for approximately 5 hours. A [?]
bulb or fluorescent equivalent is adequate. Loosen the cap of the culture
tube during this period of light exposure.
100-W tungsten
Assessment of Photoreactivity of Mycobacteria
- Following exposure to light, the tube or plate is returned to the incubator
and inspected after [?] for the appearance of yellow pigment.
24–48 hours
NTM colonies that develop yellow pigment on exposure to light after being grown in the dark (nonpigmented in dark) and take longer than 7 days to appear on solid media
Runyon Group I
PHOTOCHROMOGENS
