Lecture 12 - Gram positive rods Flashcards
Describe each of the 4 Koch’s postulates
- Microorganism must be found in abundance in all organisms suffering from the disease but not in healthy animals
- Must be isolated from diseased organism and grown in pure culture
- Should cause disease when reintroduced into healthy organism
- Must be reisolated from the inoculated, diseased experimental host and identified as identical to original
3 characteristics of Corynebacterium diphtheriae
Gram positive
No Spores
Rods (bacilli)
Where is Corynebacterium diphtheriae found?
Skin, upper respiratory tract, GI tract
What is the major mode of action by Corynebacterium diphtheriae?
A-B exotoxin blocks protein production in cells by EF-2
How does Diptheria work?
It does not enter the blood stream. It is a local infection that releases its exotoxin into blood causing systemic disease. Toxin production only occurs when the bacillus is itself stably infected by a bacteriophage carrying the genetic info for the toxin.
What must occur before Corynebacterium diphtheriae can release its toxin?
It must be infected by a bacteriophage carrying the genetic info for the toxin.
Where does the B subunit bind on the A-B exotoxin for diptheria?
It binds to heart and nerve cells
How is diptheria transmitted?
Respiratory droplets. Maintained in population by asymptomatic carriage in Throat
The infection of diptheria produces what?
thick, gray-white, adherent exudate called pseudomembrane. It is difficult to dislodge without making underlying tissue bleed.
What are the main tissues affected in diptheria
Affects upper respiratory tract, cardiac tissues and can cause heart damage.
What is treatment for diptheria
Early administration of diptheria anti-toxin to neutralize exotoxin
Toxoid can be used to immunize people before the infection
What is a toxoid:
has been modified so that it can no longer cause pathology but is still immunogenic
T or F, spores are always G negative
False. Some are G+, never G-
What are the two bacteria that we talked about as spore formers?
Clostridium and Bacillus
Physiologic makeup of a spore
Inner membrane
Large peptidoglycan cortex
Thick keratin-like protein coat
3 characteristics of Clostridium (oxygen dependence, gram stain, spores or no spores)
Obligate Anaerobic
G+ Bacilli
Spore-forming
What type of exotoxin do C. tetani and C. botulinum have and what cells do they attack?
A-B exotoxins
Attack nerves
C. tetani is also called:
Tetanus or spastic paralysis
Difference in mode of infection for C. tetani and C. botulinum
Tetani:Spores typically infect and germinate in a deep wound where anaerobic conditions can be found
Botulinum: Spores or toxins are consumed in food
C. tetani local or systemic?
They multiply locally and secrete A-B toxin into blood
How does C. tetani target nerve cells?
A-subunit blocks neurotransmitter release at inhibitory synapses. causes prolonged muscle-spasms
How does C. botulinum target nerve cells?
Blocks releases of Acetylcholine, prevents muscle contraction causing flaccid paralysis
Another name for C. botulinum
Flaccid Paralysis or Botulism
What type of nerves does C. botulinum attack?
Cholinergic nerves
C. botulinum is most common in what age groups?
Infants
C. perfringens can cause:
Gas gangrene and Food poisoning
How does C. perfringens cause gas gangrene
Infect a dirty wound, huge number of exotoxins (mostly cytolytic) and spreading factors are released, infection spreads through surrounding tissue and kills cells
Food poisoning in C. perfringens results from what?
eating food contaminated by C. perfringens spores that have germinated before eating. Not true food poisoning
C. dificile causes what?
Pseudomembranous colitis which is also called “antibiotic colitis”. Occurs in individuals undergoing antibiotic therapy. Antibiotics clear up space in the existing flora for C. dificile to take their spot.
2 characteristics of Bacillus anthracis
Gram positive
Spore forming
where is Bacillus anthracis commonly found?
In soil, affects grazing animals that ingest spores
3 types of anthrax in humans
- Cutaneous anthrax - spore enters skin through cut
- Pulmonary anthrax - airborne spores
- GI tract anthrax - contaminated food
What are the two A-B exotoxins released by B. anthracis
Edema toxin and Lethal toxin
How is B. anthracis taken deeper into the body
Macrophages act as ‘taxi’s’ and take bacteria deeper into the body. Macrophages have difficulty killing bacteria.
Do B. anthracis have a capsule
Yes
