Mycobacteria (acid-fast bacteria) Flashcards
TALK ABOUT MYCOBACTERIUM
Mycobacteria are aerobic, acid-fast (rods). Mycobacterium tuberculosis is an obligate aerobe ( intrinsic )
they are inable to gram stain because they have mycolic acids ( UNUSUAL CELL WALL)
The major pathogens are Mycobacterium tuberculosis, the cause of tuberculosis,
and Mycobacterium leprae, the cause of leprosy.
TALK ABOUT Mycobacterium tuberculosis
causes tuberculosis , Mycobacterium tuberculosis can be cultured on bacteriologic media, whereas M. leprae cannot
Cord factor is major virulence of the organism
it has several proteins that are the antigens in the purified protein derivative (PPD) skin test (also known as the tuberculin skin test).
A lipid located in the bacterial cell wall called phthiocerol dimycocerosate is required for pathogenesis in the lung
Mycobacterium tuberculosis is relatively resistant to acids and alkalis
Transmission & Epidemiology of Mycobacterium tuberculosis
• The portal of entry is the respiratory tract, and the initial site of infection is the
lung, • Macrophages kill most, but not all, of the infecting organisms. The
ones that survive can continue to infect other adjacent cells or can disseminate to
other organs
• Humans are the natural reservoir of M. tuberculosis
what are the two types of tuberculosis
Primary tuberculosis
(Primary TB) is defined as infection occurring in previously uninfected host
If the primary infection heals without causing disease, it is called a latent
infection
Secondary tuberculosis or chronic TB
is a reactivation of previous latent infection, The granulomatous inflammation is much more florid and
widespread
pathogenesis OF Mycobacterium tuberculosis
M. tuberculosis produces two proteins
- One is tuberculosis necrotizing toxin (TNT),
- The other is early secreted antigen-6 (ESAT-6)
• Mycobacterium tuberculosis infects alveolar macrophages.
Mycobacterium tuberculosis survives and multiplies within a cellular
vacuole called a phagosome.
The organism produces a protein called exported repetitive protein that prevents the phagosome from fusing with the lysosome,
Immunity & Hypersensitivity OF M.T
After recovery from the primary infection, resistance to the organism is
mediated by cellular immunity (by CD4-positive T cells and macrophages).
A positive skin test result indicates previous infection by the
organism but not necessarily active disease.
Laboratory Diagnosis OF M.T
• Acid-fast staining of sputum or other specimens is the usual initial test
, M. tuberculosis produces niacin, whereas almost no other mycobacteria do. It also produces catalase
Nucleic acid amplification tests (NAATs) can be used to detect the presence
of M. tuberculosis directly in clinical specimens such as sputum
treatment and prevention of M.T
Isoniazid (INH),
M. tuberculosis produces β-lactamase, SO ITS resistant to
many penicillins and cephalosporins.
BCG vaccine can be used to induce partial resistance to tuberculosis. The
vaccine contains a strain of live, attenuated M. bovis called bacillus
Calmette-Guérin
TALK ABOUT MYCOBACTERIUM LEPRAE
causes leprosy, also known as “Hansen’s disease , it damages the peripheral
nerves and targets the skin, eyes, nose, and muscles
Mycobacterium leprae has not been grown in the laboratory, The optimal temperature for growth (30°C)
Loss of sensation due to nerve damage is often seen in leprosy
Prolonged therapy (9 months or longer) is required to prevent recurrence.
In lepromatous leprosy, large numbers of organisms are usually seen in acid-fast–
stained smears.
The disfiguring appearance of the disease of leprosy
• (1) the skin anesthesia results in burns and other traumas, which often
become infected;
• (2) resorption of bone leads to loss of features such as the nose and
fingertips;
• (3) infiltration of the skin and nerves leads to thickening and folding of the
skin.
TREATMENT ANF PREVENTION OF LEPREA
dapsone and rifampin are given for 6 to 12 months
Prevention
• Isolation of all lepromatous patients,
• There is no vaccine
MORE ABOUT LEPREA
It can be grown in experimental animals,
such as mice.
• Humans are the natural hosts, although the armadillo appears to be a
reservoir for human infection. In view of this, leprosy can be thought of as
a zoonotic disease
