Clostridia Flashcards
Clostridium general characteristics
Strict anaerobe
Gram-positive rods
Produces Endospores
Produces proteinaceous toxins that are responsible for disease symptoms
Clostridium species
C difficile
C perfringens
C botulinum
C tetani
Spores
Few bacteria have the ability to form endospores
Metabolically inactive state in which organisms can remain viable for hundreds of years
Resistant in adverse conditions
What causes spore induction
Unfavorable environmental conditions (heat, dry, radiation - things that would cause nutrient depletion)
When do spores germinate?
When conditions become favorable for vegetative growth
What bacteria can form endospores?
Bacillus and Clostridium
C. difficile characteristics
Not easy to culture Spores are resistant to antibiotics Currently the leading cause of nosocomial diarrhea Pseudomembranous colitis Secretes C difficile toxins A and B
Pseudomembranous colitis
Yellow plaques containing fibrin and cellular debris in ulcers of colonic mucosa
C difficile Toxin A
Enterotoxin - fluid production and damage to the mucosa
C difficile Toxin B
Cytotoxin - rounding of tissue-culture cells
C perfringens characteristics
Found in soil and intestinal tracts of animals
Environmental pathogen found in every soil except Sahara desert sand
Major pathogen of wound infections (especially war wounds)
Both local damage and systemic effects
C perfringens tissue infections
Severe trauma introduces spores from environment, which germinate under anaerobic conditions, compromsed blood supply, calcium ions, and availability of peptides and amino acids. All of these occur with tissue damage. Produces toxins that cause cellulitis leading to gangrene
Gangrene
A necrotizing, gas forming process of muscle atrophy associated with systemic signs of shock. Caused by C perfringens
Treatment of C perfringens
Surgical removal of infected muscles.
Antibiotics to control infection (amputation still necessary)
Can also introduce antitoxin from horses (little effect), or high oxygen concentration (rarely works)
Other than gangrene, C perfringens can also cause…
Food poisoning.
Produces an enterotoxin in intestines of people who have consumed contaminated meat.
Diarrhea in 12-24 hours
Self-limiting and dissapears in 1-3 days
C. botulinum characteristics
Found in soils and marine sediments Produces heat-resistant spores that often survive food processing (canned food) Causative agent of botulism Produces toxins Bioweapon threat
C botulinum toxins
Produces 8 neurotoxins: A-G
Amongst the most poisonous substances known
Most common C botulinum toxins in humans
A, B, E
Lethal dose of C botulinum toxins
< 1ug
C botulinum toxin mechanisms
- Prevents release of ACh
- Zinc metalioprotease cleaves proteins involved in docking neurotransmitter vesicles
C botulinum toxin effects
Flaccid paralysis within 12-36 hours
Cranial nerves are effected first, and then it descends causing respiratory failure
3 Types of Botulism
Food-bourne
Wound
Infant
Food-bourne botulism
Ingestion of preformed toxin in foods that have not been canned properly
Wound botulism
Rare
Systemic spread of toxin produced by organisms inhabiting wounds
Caused by trauma, surgery, subcutaneous heroin injections, and sinusitis from intranasal cocaine abuse
Infant botulism
Intestinal colonizaiton of organisms in infants younger than 1 year old
Slow onset
Favorable outcome
Hypotonic (“floppy”) state
Botulism Treatment
Current mortality rate with care is about 25%
A trivalent antitoxin (isolated form horses) should be administered asap
Some muscles are permanently damaged
Why aren’t antibiotics necessary in treating botulism?
We’re treating the toxin, not the organism
Clostridium tetani characteristics
Ubiquitous in the GI tract of humans and animal
Also in soil
Spores resistant to environment
Infection usually associated with traumatic wounds
Leads to tetanus
Tetanus cause
Germination of spores and production of toxin (tetanospasmin).
Can be caused by wounds or neonatal contamination of umbilical cord at delivery
Tetanospasmin
Major toxin of tetanus
Responsible for all symptoms
150 kDa protein
Made of heavy and light chain connected by a disulfide bond (nontoxic individually)
Tetanospasmin mechanism
Attaches to peripheral nerves near the wound and travels to cranial nerve nuclei
Inhibits neurotransmitter release for normal inhibitory input (GABA)
Results are reflex spasms and spastic paralysis
Tetanus characteristics
Trismus (lockjaw) in 80% of cases
Descends to neck and back muscles and produces rigidity of abdomen and stiffness of extremities
Leads to respiratory failure form paralysis of chest muscles
Treatment and Prevention of Tetanus
Completely preventable with DPT vaccine
Human globulin is sometimes given as a passive immunization in “tetanus-prone wounds”
Antitoxin should be administered immediately
Antibodies are not produced due to low amounts of toxin pressent
Surgical debridement
