Chapter 15 Flashcards
Pathogenicity
the ability to cause disease
virulence
the extent of pathogenicity
portals of entry
mucous membrane -gastrointestinal tract -respiratory tract - genitourinary tract skin parenteral route
preferred portal of entry
organisms can enter more than one way but many do not cause disease unless they enter the preferred portal of entry
numbers of invading microbes
- ID50- infectious dose of 50% of test population
- LD50- lethal dose (of a toxin) for 50% of the test population
- wide variation from one kind of pathogen to another
Bacillus Anthracis
portal of enter
- skin- (ID50)- 10-50 endospores
- inhalation (ID50)- 10,000-20,000 endospores
- ingestion (ID50)- 250,000-1,000,000 endospores
Adherence/ ligands
- bind to receptors on host cells
- attachment is necessary step in pathogenicity; non-pathogens can have attachment molecules
- adhesions located on cells glycocalyx, pili, fimbriae or flagella
- adhesions made of glycoproteins and lipoproteins
- receptors on host cells are usually sugars
adherence examples
- glycocalyx: Streptocouccs mutans
- Fimbriae: Escherichia coli
- M protein: Streptococcus pyogenes
- Opa protein : Neisseria gonorrhoeae
- Tapered end: Treponema
Biofilms (adherence)
- communities of microbes that live together in masses on a surface
- produce extracellular products such as polysaccharides to hold the microbes together
- biofilms are much more organized than appear
- channels for nutrients and oxygen to penetrate
- cell to cell communication-quorum sensing
- 1000x more resistant to biocides than individual cells because of the extracellular materials
- very important in pathogenicity
- 65% of infections may involve biofilms; catheters commonly involved
Extracellular enzymes (factors that make pathogens invasive: enzymes)
help bacteria invade tissues (exoenzymes)
Coagulase (factors that make pathogens invasive: Enzymes)
Coagulate (clot) fibrinogen of blood
-Staphylococcus aureus may produce; helps wall of boils
Kinases (factors that make pathogens invasive: enzymes)
digest fibrin clots
-some Staphylococcus and Streptococcus produce
Hyaluronidase (factors that make pathogens invasive: enzymes)
- hydrolyses hyaluronic acid which holds certain cells of the body together
- gas gangrene caused by Clostridium
Collagenase (Factors that make pathogens invasive: enzymes)
hydrolyzes collagen (forms the connective tissue of muscles) -several species of Clostridium which are involved in gas gangrene
IgA proteases (factors that make pathogens invasive)
enzymes produced by the bacteria which destroy IgA antibodies that would attack the bacteria