LECTURE OVERVIEW.
Mycobacteria
Epidemiology of Tuberculosis
Pathogenesis of pulmonary TB and clinical presentation
Laboratory diagnosis
Treatment of pulmonary TB: British Thoracic Society guidelines and NICE guidelines
LECTURE OVERVIEW.
Mycobacteria
Epidemiology of Tuberculosis
Pathogenesis of pulmonary TB and clinical presentation
Laboratory diagnosis
Treatment of pulmonary TB: British Thoracic Society guidelines and NICE guidelines
TUBERCULOSIS AND MYCOBACTERIA: INTRODUCTION.
1/3 world population is infected and 1.4 million deaths annually; common in
developing nations
Respiratory TB / Non-Respiratory TB
Who catches TB, a DDW:
(a) close contacts of infected cases; (b) travellers to endemic regions; (c) individuals with
weakened immune systems eg. HIV / elderly; (d) homeless, drug abusers, alcoholics
TB is caused by Mycobacterium tuberculosis, M. bovis, M. africanum, M .microti, M.
abscessus and M. canetii. M. tuberculosis accounts for 98% of infections in UK.
Mycobacteria other than tuberculosis (atypical / MOTT) or non-tuberculous
mycobacteria (NTM) can also cause infections (respiratory / non-respiratory)
TB is a Disease of the developing world
People who have TB are latently asymptomatic.
Risk factors:
Close contact with infected individuals.
Travelers to endemic regions- Mumbai has a high region of tuberculosis.
Individuals with weakened immune system, if you have HIV/ are elderly/homeless/drug
abusers/alcoholics.
Mycobacterium bovis vector is cows. – bovine tuberculosis- we can contract this.
Mycobacterium absessus is a non-tuberculosis bacteria that rapidly grows.
MYCOBACTERIA ASSOCIATED WITH HUMAN DISEASE
SPECIES RESERVOIR VIRULENCE FOR CLINICAL DISEASE
HUMANS
Mycobacterium HUMANS +++ TB
tuberculosis
M. africanum
M. microti
M. canetii
M. bovis ANIMALS +++ BOVINE TB
M. leprae Humans +++ LEPROSY
, (Hansen’s bacillus) 800,000 worldwide
M. abscessus Environment: water + ONLY INFECTS PEOPLE
systems WITH UNDERLYING LUNG
CONDITION- CYCSTIC
FIBROSIS/BRONCHIECTASIS
M. avium-intracellulare Environment; birds + TB-LIKE LUNG INFECTION
OR DISSEMINATED
INFECTION IN AIDS
PATIENTS.
Mycobacterium tuberculosis is highly virulent, it is a true pathogen, have to extremely
careful when working with TB.
Transmitted from humans to humans.
M.Bovis circulates around animals, such as cattle, causes bovine TB but it can cause TB in
humans as well. Can cause chronic respiratory infection in humans aswell.
Leprosy- extremely virulent. Hard to research because we cannot grow it in lab or in cells. it
is fastidious.
Only one known animal vector, banded armadillo. Symptoms of leprosy: highly nodulated
and disorted extremities, feet and hands have infected lesions. Causes a lot of contortion,
blindness and impacts the nervous system and impacts your physiology severely. Fatal if left
untreated.
M.abscessus- environmental found in water systems- however it only infects you if you are
immunocomprimised with cystic fibrosis, underlying respiratory conditions predispose
people to infection with this.
M.Avium intracellulare – tends to come from birds, impacts patients who have aids and are
highly immunocompromised.
Not so virulent but if you are immunocompromised, it is dangerous.
CHARACTERISTICS OF MYCOBACTERIUM SPECIES.
Phylum: Actinobacteria; filamentous
Acid Fast: Cell envelope contains 60% long-chain branched hydrocarbons (waxes)
Mycolic acid most abundant – virulence factor
Trehalose dimycolate (TDM) –CORD FACTOR
(a) Reduces permeability to many molecules: Confers resistance to chemicals, stains,
antibiotics
(b) Confers resistance to drying: Increased survival in environment
(c) Intracellular survival
Slow growing: generation time 15-22 hours
(cf 1 hour staphylococci)
Characteristics of mycobacteria.
They are filamentous- when we see them down a microscope, we can see filaments which
are referred to as serpentine cords.
If you are doing microscopy on a suspected microbacterium sample, such as a sputum
sample, you would be looking for serpentine cords.
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