Module 5: Microbial and Host Interactions Flashcards
What are Koch’s postulates? (4)
- Microorganism must be found in every case of disease to be the CAUSATIVE AGENT
- Microorganism must be isolated from host and grown in a PURE CULTURE
- Disease must be REPRODUCED when pure culture is injected in healthy individuals
- Microorganism must be RECOVERABLE from injected host
Define normal flora
Bacteria normally found on outer surfaces and mucous membranes
Fairly consistent with site, but differs from others
Define transient normal flora
When might it occur?
Bacteria different from normal flora and present for short time
May be from antibiotic use, hospitalization
Define contamination
When might it occur?
Bacteria not part of normal flora present on body site but not actually growing, NO INFECTION
ex: fecal contamination
Define colonization
When might it occur?
Bacteria not part of normal flora present on body site and growing, NO HOST REACTION, NO INFECTION
ex: gram negative rods growing in the throat
Define infection
Bacteria growing in or on body and causing host reaction/infection
Define pathogenicity
Ability for organism to cause disease
Define virulence
Degree of pathogenicity
Define pathogen
Bacteria capable of causing disease
Define nonpathogen
Not capable of causing disease
Very few, as most can cause disease somewhere to a degree under certain conditions
List the 6 virulence factors
- Capsules
- Hyaluronidase
- Collagenase
- Hemolysins
- Leukocidins
- Kinases
How are capsules a virulence factor?
Prevent phagocyte attachment and phagocytosis
What is hyaluronidase? How is it a virulence factor?
Extracellular enzyme produced by gram positives
Dissolves hyaluronic acid (in connective tissue) allowing bacteria to spread
How is collagenase a virulence factor?
Breaks down collagen, allows spread of bacteria in connective tissue
How is hemolysins a virulence factor?
Lyses red blood cells, decreases host’s immunity
How are leukocidins a virulence factor?
Kill phagocytic cells
Creates pus
How are kinases a virulence factor?
Break down fibrin clots formed to isolate infection
Allows bacterial spread
Define exotoxins
Toxins produced mostly from GPOs that have a specific site of action in the host
What are exotoxins made of? How do they enter the body?
Mainly protein, are excreted from the bacteria
How can exotoxins be used in terms of immunization?
They are antigenic and cause immune responses so can be converted to toxoids for immunization
Give examples of exotoxins (3)
Clostridium botulinum - Botulism toxin acts on neuron and muscle cell junction
Clostridium tetani - Tetanus toxin excites the CNS causing muscle spasms
Staphylococcal enterotoxin - affects intestine causing diarrhea