LECTURE Flashcards
is the only genus in the Mycobacteriaceae family.
Mycobacterium
All mycobacteria are called [?]
acid-fast organisms
is a term that is used to describe bacteria that resist decolorization with acidified alcohol once they have been stained
Acid-fast
Acid-fast retain the pink to red color with
carbol fuchsin
The acid-fastness property of mycobacteria, that distinguishes them from other bacteria, depends on the integrity of their [?] that contain large amounts of lipids (long-chain fatty acids C78–C90) called mycolic acids or [?]
unique cell walls
hydroxymethoxy acids
Mycobacterium generally are considered gram-positive. However, because of their [?], the bacterial cells of mycobacteria do not stain well with crystal violet, the primary stain used in the Gram’s stain.
thick waxy cell wall
Mycobacterium are observed as [?] surrounded by a clear halo.
poorly or nonstaining bacilli
They may appear as either [?], which represents nonuniform staining of the bacilli, or almost as a [?] against the counterstained background, thus they are described as
beaded
negative image
“gram neutral,” or “gram ghost”
- Acid-fast bacilli (AFB), very thin, slightly curved or straight rods (0.2-0.6 x 1-10 µm)
- Nonmotile
- Non–spore forming
- Aerobic
- Grow more slowly than most other human pathogenic bacteria
Mycobacterium
spore forming Mycobacterium
Mycobacterium marinum
The mycobacteria are divided into 3 major groups of based on fundamental differences in [?] and [?]
epidemiology and association with disease
refers to the mycobacterial species that occur in humans and are capable of causing tuberculosis: M. tuberculosis (MTB), M. bovis, and M. africanum.
Mycobacterium tuberculosis complex (MTBC)
consists of mycobacterial species that do not belong to the MTBC, thus it is also known as Mycobacteria Other Than Tubercle Bacilli (MOTT).
Nontuberculous Mycobacteria (NTM)
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
- Koch’s bacillus
* Human Tubercle Bacillus
Mycobacterium tuberculosis
- Thin, slightly curved bacilli that measure 0.3 to 0.6 × 1 to 4 µm
- Strongly acid-fast (pink to red staining), with a distinct beaded appearance due to volutin granules known as Much’s granules
- Either grow as discrete rods in Chinese letter (X, Y, V & L) configuration, or as aggregates of numerous bacilli that are arranged in long, parallel strands called serpentine cords; cording is associated with virulent strains of MTB (due to cord factor, the unique mycolic acid (trehalose-6’6-dimycolate), and is observed in smear preparations from broth cultures.
- Nonmotile
- Non-spore-forming
- Strict aerobe
- Slow grower, with a generation time of 15-20 hours
- Produces niacin
- Produces heat-sensitive catalase
Mycobacterium tuberculosis
Humans are the only reservoir which generally infects the lungs, as facultative intracellular parasites in alveolar macrophages. But, they can also affect other parts of the body.
Mycobacterium tuberculosis
Transmission is by inhalation of droplet nuclei from a person with active disease in the lungs. It is estimated that less than 10 bacilli may initiate a pulmonary infection in a susceptible individual.
Mycobacterium tuberculosis
are propelled into the air when infectious person coughs, sneezes, sings, talks, or spits, or during respiratory manipulations such as bronchoscopy. They are more than 5 µm in diameter, so they immediately settle out of air. When inhaled, they become lodged in the [?] (the nose and throat), where infection is unlikely to develop. However, the smaller droplet nuclei, which are the dried-out residuals of droplets, may reach the alveoli, where infection begins.
Droplets containing tubercle bacilli
upper respiratory tract
When tubercle bacilli are inhaled, they reach the alveoli where they are phagocytized by alveolar macrophages and multiply.
Tuberculosis (TB)
Whether or not a person develops TB is determined by:
- immune status of the host
- amount of exposure
- strain of MTB
- number of tubercle bacilli inhaled
- virulence
- anti-mycobacterial cellular immune response
- amount of exposure
- strain of MTB
- immune status of the host
This is also referred to as “active tuberculosis”. It is a chronic (long-term) inflammatory disease, which presents as pulmonary TB (PTB) that may progress into extrapulmonary TB (EPTB), leading into death of patients who do not receive treatment.
TB disease