6 - Toxins and Anaerobes Flashcards
What are properties of a successful pathogen? What are the two mechanisms of pathogenesis?
- Gain access into the host
- Colonize the host
- Resist host defense mechanisms
- Damage host
Two mechanisms of pathogenesis: invasiveness and toxigenicity.
What are characteristics of anaerobic bacteria/anaerobic infections?
Located on mucosal surfaces, infections are mixed, opportunistic infections, and include either/both aerobic or anaerobic bacteria.
How do anaerobes deal with oxygen/oxygen radicals? What are they sensitive to?
They are sensitive of O2 intermediates and have superoxide dismutase to remove O2 radicals
Have low amounts of catalase to remove H2O2
Often lack cytochromes and use fermentation.
What are the sites of infections of anaerobic gram negative pathogens? How would you describe these infections?
Colon (intra-abdominal abscess) mouth, skin. Foul-smelling.
Gas producing (diagnostic).
Poly-microbial nature of anaerobic infections.
Void of aerobic bacteria (anoxic).
What is a common gram - anaerobic pathogen that causes most intra-abdominal infections? What are characteristics of type of bacterial infection?
Bacteriodes fragilis: some are more virulent than others, some produce capsules.
Aerotolerant and encode two major oxidative stress response genes: catalase and superoxide dismutase.
Often isolated in mixed bacterial infection with other anaerobes (like peptostreptococcus)
What is the appearance of bacteroides fragilis? How can it be grown selectively out of the gut?
Pleomorphic: extended bacteria in the culture
Gram negative bacilli.
How can bacteroides fragillis be grown selectively out of the gut?
On bile-esculin agar with gentamicin, because most other bacteria (aerobic and anaerobic) are inhibited by bile and gentamicin.
Appears black on this plate due to its degradation of esculin.
Sites of infection are _____ and ______ infections are common.
Pathogen-specific
Mixed infections are common
What types of pathogens are associated with surgical site infections in cardiac surgery patients?
Gram + organisms (48%)
Gram negative organisms (40%)
Fungi (12%)
What are the characteristics of clostridia? Where are they commonly found? What are the two different types of pathogenesis found?
Anaerobic gram + spore forming bacilli; obligate anaerobes or aerotolerant.
Pathogenic due to invasiveness or producing an exotoxin.
Inhabitants of soil and the intestinal tract.
Which type of clostridia is invasive? What is it’s mechanism of action?
C. perfringens
Alpha toxin with phospholipase that damages tissue
Which types of clostridia produce toxins? What does each produce and what type of disease is each associated with?
C. difficile: GI disease - produces toxin A and B
C. tetani: tetanus - tetanuc toxin
C. botulinum: botulism/food poisening - botulinum toxin
Which type of clostridia is histotoxic and causes extensive destruction of muscle and connective tissue and is characterized by the formation of gas? What predisposes someone to this?
C. perfringens: produces alpha toxin and causes most clostridial-mediated myonecrosis.
A deep wound to muscle predisposes someone.
Can cause gas gangrene and requires antibiotic treatment and sometimes amputation.
How does C. perfringens cause tissue damage?
It reduces tissue redox potential causes host cell death.
Uses nutrients from host proteases for growth.
Produces alpha toxin (phospholipase) that causes tissue damage.
What are the four types of bacterial toxins?
- Surface-acting toxins
- Pore-forming toxins
- A/B toxins
- Type III and IV secretion
What are general characteristics of bacterial toxins?
Have a catalytic component (enzyme) that modifies specific host macromolecules (post-translational modification)
and host cell binding component that’s tissue specific (such as clostridial neurotoxin) or non-tissue specific (diptheria toxin).
