Anaerobes Flashcards
What are 3 possible reasons why an anaerobe cannot grow in the presence of oxygen?
1) No cytochrome systems for the metabolism of O2.
2) Little / no superoxide dismutase.
3) Little / no catalase.
Most clinical isolates are what form of anaerobe? what do they have small amounts of?
moderately obligate anaerobes
have small amount of both catalase and superoxide dismutase.
What are the three methods for excluding oxygen in bacterial culture?
- Liquid media containing fresh animal tissue or 0.1% agar containing a reducing agent, thioglycollate
- Anaerobic jar using gas packs or gas replacement system
- Anaerobic chamber
Which of the methods is most commonly used by labs?
Anaerobic jar
What is used as an indicator in anaerobic jars for the presence of oxygen?
Methylene blue - will remain blue if oxygen is present
What two species of anaerobes are endogenous to the skin?
Propionibacterium, Peptostreptococcus
How are anaerobes able to live on the skin? (2 reasons)
- Aerobes consume O2 and lower the Redox potential2. Anaerobes live in microfissures / biofilm
What species of bacteria tend to inhabit the upper respiratory tract
Propionibacterium
What species of anaerobic bacteria inhabit the mouth? what % of mouth bacteria are anaerobes?
Fusobacterium, Actinomyces
90%
What species of anaerobic bacteria inhabit the GI tract?
Bacteroides and Fusobacterium
What species of anaerobic bacteria inhabit the vagina?
Lactobacillus
Wiping out endogenous flora with antibiotics heavily favours the growth and development of..?
Anaerobes
What are 2 ways in which Anaerobes contribute to host physiology?
- Prevent colonization of invading pathogens
- Prevent attachment, decrease pH, nutrient robbing, toxic metabolites - Production of metabolites like B. fragilis synthesizing vitamin K and conjugating bile acids
If someone has an anaerobic infection, the source of the infection tends to be..?
usually the endogenous flora of host
What are 3 common features of an anaerobic infection?
- Abscess forming
- Formation of exotoxins
- Tend to be polymicrobial
What are 6 factors that predispose patients to developing an anaerobic infection?
- Trauma to mucous membranes/skin
- Interruption of blood flow
- Tissue necrosis
- Decrease in redox potential in tissue
- Prior antibiotic treatment
- Immunosuppression
What are 6 virulence factors that anaerobes might have?
- Polysaccharide capsule
- Adherence factors
- Toxins (some can be necrotizing)
- Hyaluronidase
- Lipases
- Enzymes- i.e. proteases / phospholipases
What are some indicators of an anaerobic infection?
- Foul smell
- Black discolouration
- Production of gas (crackling sound)
- Pus producing
- Close to mucosal surface
- Persistence of infection despite antibiotic treatment
What are 4 types of specimins for anaerobic culture?
- Swab
- Aspirate
- Tissue
- Blood
How long are the primary cultures allowed to incubate before examination?
48 hours
What is done if no growth is observed after 48 hours?
The sample is re-incubated for up to 5 days
What are 4 indications (in culture) that you are dealing with an anaerobe?
- Foul smell when you open the dish
- Double hemolysis observed
- Failure to grow in aerobic conditions
- Pigmented or fluorescent colonies
What do you do if you observe growth under anaerobic conditions?
- Subculture anaerobically and aerobically to check if it’s a facultative anaerobe
- Gram stain suspicious colonies
- ex: if you notice spore production you can be sure it’s either Clostridium (anaerobe) or Bacillus (aerobe)
Is antimicrobial susceptibility typically done for anaerobes? Under what conditions?
no
Done for monomicrobial infections
What is the anaerobic drug(s) of choice?
Metronidazole, as well as Amox-clav / Pip-tazo
What are 3 treatment protocols for anaerobic infections?
- Surgical intervention (draining of source or removal of necrotic tissue)
- Antibiotics
- Antitoxins
