Microbiology: Anaerobic Bacteria Flashcards
1
Q
Types of anaerobes
A
- Obligate anaerobe: unable to grow in and are killed by oxygen (clostridia)
- Facultative anaerobe: can grow in both conditions (normally found in aerobic)
- Microaerophile: use low levels of O2 to respire but are inhibited at high levels
- Aerotolerant: can survive O2 but will always use fermentation as metabolism
2
Q
Characteristics of anaerobes
A
- Found in all groups of bacteria
- Some have catalase/SOD (usually the pathogenic ones)
- Normally found in many areas of body (commensal GI), can cause disease when displaced into other regions
- Tend to be polymicrobic infections: multiple strains causing a single infection
- Tend to occur as localized abscess
- Tend to be penicillin resistant
- Virulence factors: adhesins, capsule, catalase/SOD, exo/binary toxins
3
Q
Clostridium Perfringens
A
- Found in soil, GI tract, all Clostridium are GP bacilli (spore formers)
- Expresses many exonzs, which are degradative to tissue
- Can present as gastroenteritis or soft tissue infections
- Gastroenteritis: due to consumption of contaminated food like meats (vegetative cells are etiologic agent). They produce numerous exotoxins and enterotoxins that cause abdominal pain and diarrhea
- Soft tissue infections: due to trauma, presents as cellulitis, suppurative myositis, or myonecrosis (all associated w/ gas gangrene). Complications include septicemia and death (poor prognosis)
4
Q
C. Botulinum and C Tetani neurotoxins
A
- Botulinum (BoNT) and Tetanus (TeNT) toxins have similar mechanisms of action, but because they act on different cells they have opposite effects
- Both are binary toxins, and the A domains are protein-specific endopeptidases. Both of them affect the SNARE complexes involved in neurotransmitter vesicle exocytosis
- BoNT targets the NMJ, preventing the release of ACh from the neurons and thus causing paralysis
- TeNT targets inhibitory neurons (GABAergic and Glycinergic) afferent to motor neurons, preventing the inhibition of the motor neuron. This results in constant tetany of the muscle
5
Q
Clostridium Difficile
A
- Commensal found in lower GI tract, can express exotoxin based on the environment (turns it on during stress)
- Different species release different antibiotics to compete with each other to maintain a balance of flora in the GI
6
Q
Exotoxins of C. Difficile
A
- Has enterotoxin (toxA) and cytotoxin (toxB), either alone is sufficient for virulence
- Both are glycosyltransferases that modify Rho-GTPases, leading actin dysregulation
- Manifests are chronic diarrhea and colitis (pseudomembranous colitis), often seen in patients undergoing antibiotic therapy
- Antibios will disrupt the flora balance and allow C difficile to flourish
- The exotoxin can be detected in feces
- The antibio therapy should be stopped, and it is possible to do a fecal transplant
- The bacterium produces spores, which can be a source of relapse if antibios are started again
