Download MICR420 S2010 Lec 6 MT - Cal State LA

MICR 454L
Emerging and Re-Emerging
Infectious Diseases
Lecture 7:
M. tuberculosis
Dr. Nancy McQueen & Dr. Edith Porter
Overview
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M. tuberculosis
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Morphology
Growth and metabolic
characteristics
Virulence factors
Diseases
Diagnosis
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Culture
PCR
Immune response
Therapy
Threats
M. tuberculosis
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Acid fast rods
Lipid-rich cell wall
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Lowenstein Jensen
agar
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Mycolic acids
Eggs
Potatoes
Malachite green
Slow growth
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Up to 6 weeks
http://www.annclinmicrob.com/content/figures/14760711-4-18-5.jpg
M. tuberculosis: Virulence
Factors
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Lipid-rich cell wall
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Resistant to host defense
Intracellular survival in macrophages
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Mycolic acids
Iron capturing ability
Sulfolipids prevent phagsome-lysosome fusion
Eventually escape into the cytoplasm
Requires a T-cell mediated immune response for infection
control/eradication
Granuloma formation
Removal of M. tuberculosis
Depends on the Cell-Mediated
Arm of Host Defense
The Course of TB Infection
and Disease
Airborne Infection
90 %
10 %
Latent TB
TB Disease
No symptoms
Not sick
Cannot spread
disease
Chest X Ray and
sputum are normal
Symptoms
Can sp[read
infection
Positive skin test
Possible abnormal
chest X ray
Positive sputum
smear or culture
Dissemination
AIDS increases
susceptibility
Reactivation
(secondary) TB
Untreated:
Severe illness,
Death
M. tuberculosis: Diseases
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General Symptoms
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Lung tuberculosis
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Feelings of sickness or weakness
Weight loss
Fever
Night sweats
Coughing
Chest pain
Hemoptysis
Extrapulmonary
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Depends on localization
Lung Tuberculosis
Extrapulmonary Tuberculosis
M. tuberculosis: Diagnosis
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History
Physical exam
Mantoux Skin test (tuberculin test with
purified protein derivative)
QuantiFERON®-TB Gold Test
Chest radiograph
Sputum smear
Culture
Transmission of Tuberculosis
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Inhalation of aerosols containing
mycobacteria
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Bacteria can float in the air for several hours
Ingestions (M. bovis)
According to CDC, TB is not spread by
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Handshaking
Sharing food or a drink\touching bed lines or toilet
seats
Sharing tooth brushes
Kissing
Principle of the Tuberculin Test
QuantiFERON®-TB Gold Test
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Measure IFNg 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
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Positive = previous contact with M.
tuberculosis
Positive DOES NOT mean TB disease
M. tuberculosis: Therapy
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Isoniazid (INH)
Rifampin (RIF)
Ethambutol
Pyrazinamide
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DOTS
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At least 2 in combination (INH + RIF)
Prolonged time (at least 6 months)
Direct observational therapy short course
Anti-Tuberculosis Drug Targets
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Mycolic acid
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Fatty acid synthetase I (FASI)
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INH inhibits mycolic acid synthesis
Ethambutol inhibits mycolic acid
incorporation into the cell wall
Pyrazinamide inhibits fatty acid
synthesis
RNA synthesis
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Inhibited by rifampin
Resistance of M. tuberculosis
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Mutations in codon 306 of the embB gene
(ethambutol) are discussed as marker and
predictor of resistance development to
multiple antibiotics
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Not all mutated strains are resistant but resistant
strains are mutated.
Alterations in RNA polymerase (Rifampicin)
Worldwide Threats by
M. tuberculosis
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Large fraction of the world population is
infected
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1/3 of world population is infected ~ (1.7
billion people)
Each year ~ 9 million new cases world wide
5 – 10 % will develop active tuberculosis (TB)
Worldwide almost 2 million deaths from TB
TB is the leading killer of people who are HIV
infected
Even though TB has is declining in the
US, the decline of the average annual
percentage rate is slowing down
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From 1993 – 2000 ~ 6.6% decline /year
From 2003 – 2008 only ~ 3.4% decline/year
In the US decline of cases
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In 2008 12,904 TB cases reported
Worldwide Threats by
M. tuberculosis
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Multidrug resistant TB
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Case rates have also declined (407 cases
in 1993 and 86 cases in 2008)
Result from sequential mutations
Extremely drug-resistant TB
 First reported in 2005
 3 cases reported in the US in 2006
 Increase in Europe observed
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7.3% of all MDR strains
Extremely Drug-Resistant M.
tuberculosis
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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.
Reported Cases of XDR in the US
MMWR Weekly, March 23rd, 2007
New Drugs are Needed
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Immune modulators
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IL-2, IFN-gamma, GM-CSF, IL-12
New chemicals targeting essential genes of
M. tuberculosis
Take Home Message
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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
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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, 6th 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.
http://images.google.com/imgres?imgurl=http://www.biozentrum.uniwuerzburg.de/fileadmin/REPORT/BIOTE/pic/biote016_img_0.jpg&imgrefurl=http://www.biozentrum.uniwuerzburg.de/fileadmin/REPORT/BIOTE/biote016.htm&h=734&w=488&sz=82&hl=en&start=4&tbnid=_R4zGz7SCgf70M:&tbnh=141&tbn
w=94&prev=/images%3Fq%3Dmycobacterium%2Btuberculosis%2Bcell%2Bwall%26gbv%3D2%26hl%3Den (accessed 4 15 08)