Clostridia And Other Anaerobes
These have complex nutritional requirements and will only grow when they are provided and therefore can be hard to culture. When an infection occurs, anaerobes tend to throw in with the aerobes.
Common infections
- Aspiration pneumonia
- Brain abscesses
- Female genital tract infections
- Human and animal bites
- Infections after surgeries involving mucosal surfaces
- Lung abscesses
- Peritonitis after perforated viscus
Bacteroides fragilis
Gram negative bacilli, non-motile, can grow on bile agar. Commonly infects abdominal tissue.
Produces Bacteroides fragilis toxin (BFT), which is associated with enteric diseases. Symptoms include abdominal abscesses, appendicitis, peritonitis.
Resistance mechanisms
- Antiphagocytic capsule
- Beta-lactamase: Inactivates penicillin and other beta lactams
Peptostreptococcus anaerobius
Gram positive cocci, motile, and sensitive to sodium polyanethol sulfonate. It's an opportunistic little bugger so infection sites are all over.
No specific toxins, but symptoms include pelvic inflammatory disease and bacterial vaginosis.
Resistance mechanisms
As it is opportunistic, if other bacteria produce beta-lactamase then it will be covered under that protection.
Cutibacterium acnes
Gram positive bacilli, aerotolerant, non-motile. Found on skin microbiota (in follicles). Commonly inhabits prosthetics and implants.
Syndromes include Post Operative Prosthetic/Implant Infections, CSF Shunt, pelvic inflammatory disease, bacterial vaginosis, acne, keratitis.
Resistance mechanisms
Forms a biofilms to create a protective layer, which is why surgical implant removal may be necessary.
Actinomyces
Gram positive bacilli, non motile. Lesions form yellow granule in pus and have outer zone of granulation. Found in the pelvis, abdomen, and face.
Syndromes include Oral Cervicofacial Disease (most common) which is a painless mass at angle of jaw, abdominal disease (appendicitis with perforation), pelvic disease (from copper IUDs), thoracic abscess, chronic cellulitis, draining sinuses
It is susceptible to various antibiotics.
Clostridium tetani
Gram positive bacilli, spore forming, motile. Found on the skin or any open wound.
Produces the Tetanospasmin (tetanus toxin), which is a strong inhibitor of the CNS, degrades synaptobrevin preventing neurotransmitter docking.
Generally lacks antibiotic resistance mechanisms.
Treatment
- Wound cleaning
- Antitoxin
- Tetanus vaccine
*Clostridium botulinum
Gram positive, spore forming, motile. Found in the intestine and CNS.
It produces toxins A, B, C, D, E, F, and G. These prevent acetylcholine release by binding to the presynaptic receptor. B/F cleave synaptobrevin while A/E act on synaptosomal-associated protein 25 (SNAP25).
Syndromes include food borne illness, wound botulism, infant botulism, and adult intestinal toxemia.
Resistance mechanisms
Varies by strain. Type A produces beta-lactamase and is therefore resistant to penicillin/other beta lactams.
Clostridium perfringens
Gram positive bacilli, spore forming, non-motile. Found in the GU tract or any traumatic wound with oxygen.
Syndromes include clostridial myonecrosis (gas gangrene) which is very painful and foul smelling. It also includes clostridial food poisoning, anaerobic cellulitis, and endometriosis.
Surgical debridement for gas gangrene is important. Penicillin + clindamycin will knock it out. If its polymicrobial, Piperacillin + Tazobactam (Zosyn) + clindamycin should do the trick.