Anaerobes Flashcards
3 ways to determine MIC
E test
Agar dilution
Broth microdilution
How does MacConkey stop the growth of gram positive organisms
Bile salts and crystal violet
Can get them without the crystal violet to allow for the growth of Strep
Ecchymosis
Bruising not due to trauma
Blood pools under the skin
Crepitus
Gas
Can press on the tissue and it sounds like you’re bursting bubbles
2 clues to tell it is Clostridium perfringins on a microscope slide
- Big gram positive bacilli
2. No neutrophils in sample (it produces a toxin that destroys leukocytes)
What is the difference in paralysis between botulism and tetanus?
Botulism: flaccid paralysis
Tetanus: rigid paralysis
3 possible mechanisms of why anaerobic bacteria cannot grow in the presence of oxygen
- No cytochrome systems for the metabolism of O2
- Little/no superoxide dismutase
- Little/no catalase
3 enzymes required for oxygen metabolism
Catalase
Superoxide dismutase
Peroxidase
3 methods for excluding oxygen to grow anaerobes
- Liquid media containing fresh animal tissue or 0.1% agar containing a reducing agent, thioglyocollate
- Anaerobic jar: gas packs (has sodium bicarb and sodium borohydride that eat up all the oxygen) or gas replacement (computerized pump that sucks out all the air and replaces it with an inert gas)
- Anaerobic chamber
What colour is methylene blue with or without oxygen
Aerobic: blue
Anaerobic: colourless
Do aerobes raise or lower the redox potential?
They consume O2 and LOWER the redox potential
What does B. fragilis do? (2)
Synthesizes vitamin K
Conjugates bile acids
6 Clinical features of anaerobic infections
- Source is usually endogenous flora
- Alterations of hosts tissue provides suitable conditions for opportunistic infections
- Typically polymicrobial
- Abscess formation
- Exotoxin involvement
- Smells really bad
6 factors that predispose patients for anaerobic infections
Trauma to mucosal membranes or skin Interruption of blood flow Tissue necrosis Decrease in redox potential in tissues Prior antibiotic therapy Immuno-suppression
7 Anaerobic virulence factors
- Polysaccharide capsule
- Adherence factors
- Toxins
- Hyaluronidase
- Lipases
- Enzymes (ex: proteases, phospholipases)
- Necrotizing toxins