MICR 454L Emerging and Re-Emerging Infectious Diseases Lecture 7: M. tuberculosis Dr. Nancy McQueen & Dr. Edith Porter.

MICR 454L

Emerging and Re-EmergingInfectious Diseases

Lecture 7:M. tuberculosis

Dr. Nancy McQueen & Dr. Edith Porter

Overview M. tuberculosis Morphology

Growth and metabolic characteristics

Virulence factors Diseases Diagnosis

Culture PCR Immune response

Therapy Threats

Mycobacterium tuberculosis

M. tuberculosis

Acid fast rods Lipid-rich cell wall

Mycolic acids Lowenstein Jensen

agar Eggs Potatoes Malachite green

Slow growth Up to 6 weeks

http://www.ann-clinmicrob.com/content/figures/1476-0711-4-18-5.jpg

M. tuberculosis: Virulence Factors Lipid-rich cell wall

Mycolic acids Resistant to host defense Intracellular survival in macrophages

Iron capturing ability Sulfolipids prevent phagsome-lysosome fusion

Requires a T-cell mediated immune response for infection control/eradication

Granuloma formation

The Course of TB Infection and Disease

Airborne Infection

No symptomsNot sick

Cannot spread disease

Chest X Ray and sputum are normal

AIDS increases susceptibility

Reactivation(secondary) TB

Untreated:Severe illness,

Death

SymptomsCan sp[read

infectionPositive skin test

Possible abnormal chest X ray

Positive sputum smear or cultureDissemination

Latent TB TB Disease

10 %90 %

M. tuberculosis: Diseases

General Symptoms Feelings of sickness or weakness Weight loss Fever Night sweats

Lung tuberculosis Coughing Chest pain Hemoptysis

Extrapulmonary Depends on localization

Lung Tuberculosis

Extrapulmonary Tuberculosis

M. tuberculosis: Diagnosis

History Physical exam Mantoux Skin test (tuberculin test with

purified protein derivative) QuantiFERON®-TB Gold Test Chest radiograph Sputum smear Culture

Principle of the Tuberculin Test

QuantiFERON®-TB Gold Test

Measure IFN production by patient peripheral blood leukocytes in response to M. tuberculosis antigens (protein antigens ESAT-6 and CFP-10)

Rapid T cell response only in primed individuals

Interpretation of Tuberculin and QuantiFERON

Positive = previous contact with M. tuberculosis

Positive DOES NOT mean TB disease

M. tuberculosis: Therapy

Isoniazid (INH) Rifampin (RIF) Ethambutol Pyrazinamide

DOTS Direct observational therapy short course

At least 2 in combination (INH + RIF)Prolonged time (at least 6 months)

Anti-Tuberculosis Drug Targets

Mycolic acid INH inhibits mycolic acid synthesis Ethambutol inhibits mycolic acid

incorporation into the cell wall

Fatty acid synthetase I (FASI) Pyrazinamide inhibits fatty acid

synthesis

RNA synthesis Inhibited by rifampin

Resistance of M. tuberculosis

Mutations in codon 306 of the embB gene (ethambutol) are discussed as marker and predictor of resistance development to multiple antibiotics Not all mutated strains are resistant but resistant

strains are mutated. Alterations in RNA polymerase (Rifampicin)

Worldwide Threats byM. tuberculosis

1/3 of world population is infected Each year ~ 9 million new cases 5 – 10 % will develop active tuberculosis (TB) Worldwide ~ 1.5 million deaths from TB

However: In 2006, a total of 13,767 tuberculosis (TB) cases (4.6 per

100,000 population) in the US 3.2% decline from 2005

Co-infection with HIV Multidrug resistant TB Extremely drug-resistant TB

3 cases reported in the US in 2006

Extremely Drug-Resistant M. tuberculosis XDR TB Resistant to almost all drugs used to treat TB,

including the two best first-line drugs: isoniazid and rifampin

Resistant to the best second-line medications: fluoroquinolones (DNA gyrase mutations)

And at least one of three injectable drugs (i.e., amikacin, kanamycin, or capreomycin; mutations in 16sRNA and ribosomal protein genes).

Possibly involvement of drug efflux pumps. 49 cases of XDR TB have been reported between

1993 and 2006 in the US

Reported Cases of XDR in the US

MMWR Weekly, March 23rd, 2007

New Drugs are Needed

Immune modulators IL-2, IFN-gamma, GM-CSF, IL-12

New chemicals targeting essential genes of M. tuberculosis

Take Home Message

One third of the world population is infected with M. tuberculosis but only 10% develop active disease.

The lipid rich cell wall and slow growth contribute to resistance to host defense and difficulties in antibiotic treatment.

The emergence of extremely drug resistant tuberculosis strains poses a great threat to the public.

Additional Resources The Microbial Challenge, by Krasner, ASM Press, Washington DC, 2002. Brock Biology of Microorganisms, by Madigan and Martinko, Pearson Prentice Hall, Upper

Saddle River, NJ, 11th ed, 2006. Immunobiology, by Janeway,, Travers, Walport, and Shlomchik, Garland Science, 6 th ed, 2005. Malak Kotb Genetics of Susceptibility to Infectious Diseases Volume 70, Number 10, 2004 / ASM

News Y 457-463 htttp://www.cdc.gov/ulcer/keytocure.htm#whatis http://dermatlas.med.jhmi.edu/derm/resultNoCache.cfm Zager and McNerney (2008) Multidrug-resistant tuberculosis. BMC Infectious Disease. 8: 10. Safi H, Sayers B, Hazbón MH, Alland D. (2008) Antimicrob Agents Chemother. Mar 31

[Epub ahead of print] Transfer of embB306 mutations into clinical Mycobacterium tuberculosis alters susceptibility to ethambutol, isoniazid and rifampin.

Zimhony O et al. (2000) Pyrazinamide inhibits the eukaryotic-like fatty acid synthetase I (FASI) of Mycobacterium tuberculosis. Nat Med. Sep;6(9):1043-7.

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