Mycobacteria Flashcards
(27 cards)
Describe the cell wall of Mycobacterium
it has mycolic acids and high lipid content
lipids are 60-90 hydrocarbons long so it is very hydrophobic and repels typical stains
how do mycobacteria look on gram stains?
like ghosts
Why do mycobacteria grow slowly?
due to their hydrophobic cell surface
Name the 9 members of the Mycobacterium tuberculosis complex
Remember your ABCs from the University of MTb:
africanum, bovis, BCG, canettii, caprae, ulcerans, microti, tuberculosis
1) M. tuberculosis
2) M. bovis (unpasteurized milk)
3) M. orygis
4) M. africanum (Africa)
5) M. canettii - most likely the founder strain
6) M. pinnipedii (seals and humans)
7) M. microti (rare human pathogen)
8) M. Caprae (goat and human)
9) M. mungi (meerkats)
Features of the Non Tuberculosis Mycobacterium
NTM complex
All other mycobacterium spp
1) reduced virulence
2) isolation from respiratory tract (sputum) does not indicated infection
3) most people have them because they are found in water and soil (mode of transmission)
4) only reportable species is M. leprae which is very contagious (leprosy-armadillos)
Name the communicable Mycobacterium
an illness that can spread from one person or animal to another, or from a surface or food
M. TB Complex
M. leprae
Chance of disease when isolated
M. interjectum
M. chelonae
M. gordonae
M. fortuitoum
M. intracellulare
the NTM species that might be isolated but not causing disease
<20
Chance of disease
M. abscessus
M. avium
40% of causing disease
M. xenopi (photochromogenic)
M. malmoense
M. kansassii
Causative agents of disease?
60-80% disease if isolated
M. szulgai
M. celatum
M. genavense
Chance of disease?
100% chance of disease
How do we establish evidence of disease caused by NTM (4)
1) multiple positive cultures from mucosal sites, lungs, urine
2) isolated from sterile sites: bones, joints, brain, internal organs
3) histological evidence (granulomas, positive stains)
4) clinical evidence of disease
Rapid growers (FACS)
<7 days. These also cause skin infections when disseminated
M. chelonae - opp pathogen
M. abscessus- opp pathogen
M. fortuitoum- opp pathogen
M. smegamatis - saprophyte
Conventional (weeks)
Slow growers too
(weeks)
*M. avium - opp pathogen
- M. tuberculosis - true pathogen
MAC and MTB
Slow growers
M. xenopi – opp pathogen (scotochromagenic)
M. ulcerans - true pathogen
M. kansasii - opp pathogen (photochromogenic)
M. marinum - true Pathogen (Photochromogenic)
M. leprae- true pathogen
Examples of Mycobacteria that do not grow in culture
M. genavense
M. microti
How are Mycobacterium classified?
1) GROWTH RATE
*Rapid (<7 days)
*Slow (months)
*Conventional (weeks)
*Non-growers (don’t grow in artificial media)
2) PIGMENT PRODUCTION
*Scotochromogen (M. xenopi) colors develop in the dark
*Photochromogen (M. marinum) color develops after light exposure
*Non-chromogen (M. tb)
Multibacillary disease
Skin smears are POSITIVE and/or biopsies indicate advanced disease
Paucibacillary TB
form of TB where the amount of bacteria (bacilli) in a patient’s body is low, making it difficult to detect through traditional smear microscopy
Skin smears are NEGATIVE and biopsies show NO advanced diseas
Growth media
solid
1) Lowenstein Jensen-doesnt require CO2 (slower growth)
2) 7H11
3) 7H11 selective - antimicrobials polymyxin B, carbenicillin, amphotericin B andtrimethoprim added for greater selectivity
Growth media
Broth
1) 7H9 - non selective
2) MGIT - 7H11 broth made selective with polymyxin, amphotericin,nalidixic acid, trimethoprim and azlocillin (PANTA)
Name the 3 Mycobacteria species/complexes associated with majority of disseminated skin infections
1) M. fortuitum (rapid grower) soft tissue infections after trauma
2) M. chelonae (rapid grower) disseminated skin infection in immunosuppressed, rarely causes lung infections
3) M. abscessus (rapid grower) common case of lung disease and may cause severe/disseminated disease in immunocompromised
Name the pathogenic species in M. fortuitum group
M. fortuitum
M. porcium
Name the pathogenic species in M. chelonae group
M. chelonae
Less pathogenic:
M. franklinii
M. immunogenum
Name the pathogenic species in M. abscessus group
M. abscessus abscessus
M. abscessus bolletii - infrequent
