Anaerobic Bacteria Flashcards
Anaerobes have certain molecules that they can ferment and certain waste products that they can produce. What is a tool that can be used to identify these anaerobes via these specific products? What are some other techniques to identify anaerobes?
Gas chromatography can be used to evaluate the waste products to identify the anaerobes. Gram staining and chemical tests can also help with the identification process.
How do anaerobic bacteria get energy? What are some of the waste products?
Fermentation pathway using intermediate waste product, pyruvate to re-oxidize NAD. Waste products include organic acids, alcohols, solvents.
Why do anaerobes grow slowly in culture?
Their metabolism is inefficient.
The 2 common sources of anaerobic infections are:
1) normal flora -anaerobes escape normal compartment and cause abscesses
2) soil
A. Spores enter thru wounds, germinate and produce exotoxins (c tetani and c perfringes)
B. spores germinate in vacuum-packed foods (food has exotoxins) (c botulism and c perfringes)
Explain procedure of culturing anaerobic bacteria
Take simple liquid culture
- Inoculate test tube of media
- Add reducing agent (thioglycolate) to eliminate oxygen
- Fill completely, stopper tightly and incubate without shaking
What is thioglycolate?
A reducing agent added in anaerobic culture to remove oxygen
Explain the results of anaerobic culturing as in where would you see growth?
Obligate anaerobe will grow at bottom of tube while obligate aerobe will grow at top of tube and facultative anaerobes will grow thru out
If the anaerobe is reasonably aero tolerant or can form spores (only the clostridium), then you can quickly streak them on plates. Explain procedure of streaking plates
- Quickly streak onto agar media
- Place plates in anaerobic culture jar
- Add gas-pak, a chemical system, to eliminate oxygen and an indicator to see if oxygen was successfully removed
- Place whole jar into incubation for 48 hrs
- Open in glovebox
What are the 4 kinds of anaerobic bacteria?
- Clostridium
- Bacteroides
- Prevotella
- Actinomyces
Bacteroides and ore corella are gram negative anaerobes and can be grouped together called “GNAB”
Clostridium and Actinomyces are gram positive. All are rod shaped.
Do all anaerobic bacteria form spores?
No, only the clostridium form spores.
What is the significance of spores?
Allow clostridium species to survive the move from soil reservoir to humans.
The main virulence factors for anaerobes are
Exotoxins
List the 4 different species of clostridium
Clostridium perfringes
Clostridium botulism
Clostridium tetani
Clostridium difficile
Of the 4 species of clostridium, which is part of the normal flora?
Clostridium difficile
What is tetanospasmin?
The exotoxin that is secreted by c tetani. It has a b subunit for docking and an a subunit that has protease activity to cleave synaptobrevin. Hence tetanospasmin interferes with signal transduction.
C. difficile attacks people with gut issues already. It secretes exotoxin A and B
Exotoxin A disrupts tight junctions.
Exotoxin B disrupts cytoskeleton by depolymerization
Dying cells caused by C. difficile will form yellow plaques called
Pseudomembrane
Transmission of C. difficile
- normal gut flora leaving normal compartment
- hospitals
- fecal-oral especially from spores on hospital instruments or on hands of healthcare workers
Transmission of c tetani
Soil contamination of wounds, splinters, thorns, punctures
Pathogenesis of c tetani
Spores get beneath skin (in anaerobic environment), germinate. Then vegetative cells release exotoxin, tetanospasmin which will cleave synaptobrevin. Full body symptoms and high mortality unless given tetanus toxoid and/or antitoxin depending on previous immunizations
Treatment of C. difficile
- Withdraw initial abx can cure 20% of infected people
- Use metronidazole
- Might need surgical interventions for sicker patients (colonic perforation and toxic mega colon)
Explain the different treatments of anaerobic infections
If there’s an abscess, then drain it. If it’s toxigenic like tetanus and botulism, give antitoxins. In foodbourne infections (botulism and perfringens) might not require abx. The abx of choice is metronidazole.
Which anaerobic bacteria are part of normal flora?
GNAB (bacteroides and prevotella), clostridium difficile, Actinomyces
C tetani and c botulism secrete neurotoxin whereas c perfringens secrete
Tissue degrading enzymes causing gangrenes and pus
