Mycobacterium tuberculosis-Characteristics

1
Mycobacterium tuberculosis-Characteristics

• Gram positive
• Obligate aerobe
• Non-spore-forming
• Non-motile rod
• Mesophile
• 0.2 to 0.6 x 2-4um1
• Slow generation time 15-20 hours
• May contribute to virulence1
• Lipid rich cell wall contains mycolic acid50 of
  cell wall dry weight1
• Responsible for many of this bacteriums
  characteristic properties
• Acid fastretains acidic stains
• Confers resistance to detergents, antibacterials

2

• Diagnostics of Mycobacterium
• Initial screening
• TB skin test (Purified Protein Derivative).
• Drawbacks BCG injected subjects are positive, 3
  days delay for result
• QFT-G test (measures INF-? response to TB
  specific antigen)
• TB tests Active, depending on the suspected
  location of bacterium
• 3-5 samples of sputum
• multiple gastric aspirate
• urine (UTI)
• CSF (meningeal)2
• Cultures
• Samples are processed for fast acid stain (FAS
  smear positive indicates Mycobacterium) and
  cultured after alkali decontamination (30s in
  1-2 NaOH)
• Molecular methods use species-specific genes,
  including light and heave ribosomal RNA3

Clinical specimen/ decontamination
culture

• Direct detection
• Microscopy
• PCR
• MTB rifampin resistance

• Species identification
• 16S rRNA hybridization (MTB and MAC)
• 16S rRNA gene PCR sequencing (NTM)
• restriction fragment length polymorphism

Susceptibility testing Rifampin resistance (PCR
oligohybridization sequencing)
3
M. Tuberculosis mechanisms

• Facultative intracellular pathogen
• Does not produce toxin
• Manipulates phagocytosis
• -uses phagocytic vacuole for survival and
  replication
• -uses multiple ligand-receptor interactions to
  promote phagocytosis
• - prevents fusion of phagosome with lysosome5

4
Benefits of Phagocytosis

• Protection from expulsion
• Less hostile environment with supplied nuturients
• Allows for mobility5

5
Pathogen Targets

• Inactive disease- latent stage

• Active Disease
• --pulmonary tuberculosis
• -extrapulmonary tuberculosis
• -disseminated tuberculosis
• -lymph node tuberculosis
• -pleural tuberculosis
• -genitourinary tuberculosis
• -skeletal tuberculosis
• -central nervous system tuberculosis
• -abdominal tuberculosis
• -pericardial tuberculosis6

6
Symptoms

• What are the symptoms of TB?
• Fever
• Fatigue
• Weakness
• Weight loss
• Night sweats
• Symptoms of pulmonary TB include
• Coughing
• Pleurisy (pain when taking deep breaths)
• Coughing up blood4.

7
How is TB treated?
Optimal treatment of TB utilizes a combination of
2 to 3 antibiotics taken over a period of 6 to 9
months. Drug resistant strains of TB are not
uncommon, which is why multiple antibiotics are
used together during treatment. Drugs used most
commonly to treat TB include isoniazid, rifampin,
ethambutol, and pyrazinamide7.
8
What are some complications that can occur from
TB infection?

• Untreated TB infections can cause severe damage
  in the infected organ,
• miliary TB develop which is TB that has spread
  throughout the entire body,
• and death. It is important that patients adhere
  to their medication during the
• full duration of their treatment, otherwise drug
  resistance can develop8.

9
Is there a vaccine for this TB?
BCG (Bacille Calmette-Guerin) vaccine is an
attenuated vaccine that is used in many countries
around the world where TB prevalence is high. In
the U.S. however, the vaccine is not generally
recommended because of the low risk of infection,
its variable effectiveness, and its interference
with TB skin test reactivity9.
10
Drug sensitivity The raise of drug-resistance
strains makes strain identification necessary for
the selection of the proper pharmacological
treatment. Several genes have been found to
confer specific drug-resistances. Such genes are
now readily identified using molecular techniques
(most of them PCR-amplification based), at least
for the already sequenced drug-resistance
associated genes. Identification and
characterization of unknown types of resistance
requires de-novo studies3.
Antimycobacterial agent Genetic marker
Primary agents
Rifampin rpoB (RNA polymerase subunit)
Isoniazid katG (catalase-peroxidase)
inhA (enoyl-acyl carrier protein reductase)
ahpC (alkyl-hydroperoxide reductase)
kasA (keto-acyl synthase)
Ndh (NADH dehydrogenase)
Pyrazinamide pncA (pyrazinamidase)
Streptomycin rpsL (S12), rrs (16S rDNA)
Ethambutol embB (arabinosyl transferase)
Secondary agents
Capreomycin
Kanamycin
Cycloserine
Ethionamide inhA (enoyl-acyl carrier protein reductase)
Alternative agents
Rifapentine rpoB
Rifabutin rpoB
Amikacin
Quinolones, ciproflaxin gyrA, gyrB (DNA gyrase)
Genetic targets relevant for direct detection of
antimycobacterial drug resistance development
11
References
1. Todar, K. (2009). Mycobacterium
tuberculosis and Tuberculosis. Retrieved
November 2, 2009 from Online Textbook of
Bacteriology website http//www.textbookofbacteri
ology.net/ tuberculosis.html. 2. Centers for
Disease Control and Prevention, American
Association for Clinical Chemistry, ed. board
R.B. Carey, PhD, Chief, Epidemiology and
Laboratory Branch, published Sept. 29, 2008, last
modified on November 6, 2009 http//www.labtestso
nline.org/understanding/conditions/tuberculosis-3.
html 3. S.V. Balasingham, T. Davidsen, I.
Szpinda, S.A. Frye, T. Tønjum. Molecular
diagnostics in tuberculosis basis and
implications for therapy. Mol Diagn Ther. (2009)
vol. 13 p. 137-51. doi 10.2165/01250444-20091303
0-00001. Review 4. County of Orange, CA Health
Care Agency. Tuberculosis Treatment and
Services. Retrieved November 6, 2009 from
http//www.ochealthinfo.com/docs/public/tb/tb-broc
hure.pdf. 5. Ernst, JD, Stendahl, O (2006).
Mycobacterium tuberculosis mechanisms of
phagocytosis and intracellular survival. In
Henderson, B, Wilson, M, Coates A, Curtis, M
(Eds.), Phagocygtosis of Bacteria and Bacterial
Pathogenicity (chp. 8, pp. 246-265). Cambridge
Cambridge University Press. 6. Cole, ST (2005).
Overview of clinical tuberculosis. In Cole, ST,
Eisenach, KD, McMurray, DN, Jacobs, WR (Eds.),
Tuberculosis and the tubercle Bacillus (chp. 2,
pp. 17-29). Washington ASM Press. 7.
"Tuberculosis." American Lung Association. ALA, 1
Jan. 2004. Web. 20 Oct. 2009. ltwww.lungusa.org/lun
g-disease/tuberculosis.htmgt. 8. "Tuberculosis."
Global Tuberculosis Institute. New Jersey Medical
School, 1 May 2009. Web. 20 Oct. 2009.
ltwww.umdnj.edu/ntbcseb/diagnosis.htmgt. 9. "BCG
Vaccine." CDC.com. Centers for Disease Control, 1
June 2009. Web. 20 Oct. 2009. ltwww.cdc.gov/tb/publ
ications/factsheets/prevention/BCG.htmgt.