Download Mycobacterium tuberculosis

Mycobacterium tuberculosis
Introduction:Mycobacteria are Gram-resistant (waxy cell walls), non-motile, pleomorphic
rods, related to the Actinomyces. Most Mycobacteria are found in habitats such as
water or soil. Tuberculosis , MTB or TB (short for tubercles bacillus However, a few
are intracellular pathogens of animals and humans. Mycobacterium tuberculosis,
along with M. bovis, M. africanum, and M. microti all cause the disease known as
tuberculosis (TB) and are members of the tuberculosis species complex. Each member
of the TB complex is pathogenic, but M. tuberculosis is pathogenic for humans while
M. bovis is usually pathogenic for animals.
Classification:-Kingdom
Bacteria.
-Phylum
Actinobacteria.
-Order
Actinomycetales.
-Suborder
Corynebacteriaceae.
-Family
Mycobacteriaceae.
-Genus
Mycobacterium.
-Species
M. tuberculosis
approximately (100) species
Tuberculosis complex organisms are:
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
Obligate aerobes growing most successfully in tissues with a high oxygen
content, such as the lungs.
Facultative intracellular pathogens usually infecting mononuclear phagocytes
(e.g. macrophages).
Slow-growing with a generation time of 12 to 18 hours (c.f. 20-30 minutes for
Escherichia coli). So grow sloly in branching chains resembling fungal
hyphae.
Hydrophobic with a high lipid content in the cell wall. Because the cells are
hydrophobic and tend to clump together, they are impermeable to the usual
stains, e.g. Gram's stain.
Known as "acid-fast bacilli" because of their lipid-rich cell walls, which are
relatively impermeable to various basic dyes unless the dyes are combined
with phenol. Once stained, the cells resist decolonization with acidified
organic solvents and are therefore called "acid-fast". (Other bacteria which
also contain mycolic acids, such as Nocardia, can also exhibit this feature.)
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Symptoms of tuberculosis include:
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Fever
Night-time sweating
Loss of weight
Persistent cough
Constant tiredness
Loss of appetite
Culture media:1- LOWENSTEIN-jensen (LJ)
- Gold standard of tb media
- Egg based media
- Whole egg (white & yolk),
-Potato flour, glycerol
- Malachite green.
2- Middlebrook media.
3- ATS media (American Thoracic Society)
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Identification group for T.B
niacin
nitrate
urease
68c
catalase
M. tuberculosis
+
+
+
0
M. avium-intra-
0
0
0
+
M. bovis
v
0
+
0
M. ulcerans
0
0
v
+
cellular
Modern testing:1- Bactec 460
2- GLC & HPLC
3- PCR
4- Nucleic acid probes
5- Restriction fragment length polymorphism
Diagnosis:1- positive tuberculin skin test (Mantoux skin test 0.1 ml in 5 tuberculin units of
PPD )
2- An immune reaction to a small quantity of tuberculosis antigens.
3- It can be confirmed by X rays of the chest and microscopic examination of
sputum.
4- Detection of significant numbers of acid-fast bacilli (using the Ziehl-Neelsen
stain) in sputum or tissue samples is considered a positive diagnosis,
5- Although disease may confirmed by laboratory culture of the bacterium
(difficult, dangerous and slow - takes at least 4 weeks).
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Ziehl-Neelsen acid-fast staining procedure:
1. Heat fix cells on glass microscope slide.
2. Flood the slide with carbol fuchsin stain.
3. Heat the slide gently until it steams (5 min).
4. Pour off the carbol fuchsin.
5. Wash slide thoroughly with water.
6. Decolourize with acid-alcohol (5 min).
7. Wash slide thoroughly with water.
8. Flood slide with methylene blue counterstain for 1 min.
9. Wash with water.
10. Blot excess water and dry in hand over bunsen flame.
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Transmission:
1-Transmission of TB occurs primarily by the aerosol route.
2- through the gastrointestinal tract.
3- Coughing by people with active TB produces droplet nuclei containing infectious
organisms which can remain suspended in the air for several hours. Infection occurs if
inhalation of these droplets results in the organism reaching the alveoli of the lungs.
Only 10% of immunocompetent people infected with M. tuberculosis develop active
disease in their lifetime - the other 90% do not become ill and cannot transmit the
organism. However, in some groups such as infants or the immunodeficient (e.g.
those with AIDS or malnutrition), the proportion who develop clinical TB is much
higher.
In the lung, the organism is taken up by alveolar macrophages and carried to lymph
nodes, from where it may spread to multiple organs. Two to eight weeks after
infection, cell mediated immunity (CMI) and hypersensitivity (DTH) develop leading
to the characteristic reaction to the tuberculin test and, in immunocompetent
individuals, containment of infection. Inflammatory immune responses eventually
result in lung damage.
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TB treated:TB is currently treated by means of combination therapy, using cocktails of 3-4 drugs
with different properties:
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Antibacterial activity: e.g. isoniazid, rifampin, streptomycin
Inhibiting the development of resistance: e.g. isoniazid, rifampin, ethambutol
Many countries use Bacillus Calmette-Guérin (BCG) vaccine as part of their
TB control programmes,
References :^ a b c Ryan KJ, Ray CG (editors) (2004). Sherris Medical Microbiology (4th
ed.). McGraw Hill. ISBN 0-8385-8529-9.
2.
^ Cole ST, Brosch R, Parkhill J, et al. (June 1998). "Deciphering the biology
of Mycobacterium tuberculosis from the complete genome sequence". Nature 393
(6685): 537–44. doi:10.1038/31159. PMID 9634230.
3.
^ Camus JC, Pryor MJ, Médigue C, Cole ST (October 2002). "Re-annotation
of the genome sequence of Mycobacterium tuberculosis H37Rv". Microbiology
(Reading,
Engl.)
148
(Pt
10):
2967–73.
PMID 12368430.
http://mic.sgmjournals.org/cgi/pmidlookup?view=long&pmid=12368430.
4. ^ Arnvig KB, Young DB (August 2009). "Identification of small RNAs in
Mycobacterium tuberculosis". Mol. Microbiol. 73 (3): 397–408. doi:10.1111/j.13652958.2009.06777.x.
PMC 2764107.
PMID 19555452.
http://www3.interscience.wiley.com/resolve/openurl?genre=article&sid=nlm:pubmed&is
sn=0950-382X&date=2009&volume=73&issue=3&spage=397. Retrieved 2010-08-31.
1.
Assist-Lecturer
Abdul-Karim S. Alyassaree
Microbiology department
College of veterinary medicine /Babylon university
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