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 gangreneIgA proteases (factors that make pathogens invasive)
enzymes produced by the bacteria which destroy IgA antibodies that would attack the bacteria
Siderophores (factors that make pathogens invasive)
take iron from iron-binding proteins and make available for bacteria
Antigenic variation (factors that make pathogens invasive)
pathogen alters surface proteins so that the host antibodies aren’t effective
- influenzavirus; Neisseria gonorrhoeae
Capsules (factors that make pathogens invasive)
they help the bacterial cell avoid being engulfed by certain immune cells
- host immune cells engulf invading bacteria (phagocytosis) and destroy them inside the immune cell - capsule prevents the immune cell from attaching and engulfing bacteria
invasions (penetration into the host cell)
- produced by certain microbes when they come in contact with host cell membrane
- E. coli strains and Salmonella strains
- cause cell membrane to “ruffle” which is due to cytoskeleton being disrupted
- bacteria can enter cell
toxin
substances that contribute to pathogenicity
toxigenicity
ability to produce a toxin
toxemia
presence of toxin in the host’s blood
toxoid
inactivated toxin used in a vaccine
antitoxin
antibodies against a specific toxin
exotoxin
- source: gram +
- relation to microbe: By-products of growing cell
- chemistry: protein
- fever- no
- neutralized by antitoxin- yes
- LD50- small (bad that its a small amount)
- specific for a structure or function in host cell
- genes for toxin may be introduced into bacterial cell by a lysogenic phage; only those strains with lysogenic phage produce the toxin
3 types of Exotoxins
- A-B toxins - most common type
- two types: A-enzyme component, B- attachment component
ex: diphtheria toxin - Membrane-disrupting toxins
- lyse hosts cell by:- making protein channels in pm
- ex: leukocidins- kill phagocytic white BC & hemolysins- kill RBC
- disrupting phospholipid bilayer
- making protein channels in pm
- Superantigens
- cause an intense immune response due to release of cytokines from host cells
- fever, nausea, vomiting, diarrhea, shock and death
- ex: staphylococcal food poisoning exotoxin
endotoxins
- source: gram -
- relation to microbe- present in LPS of outer membrane
- chemistry- lipid
- fever- yes
- neutralized by antitoxin- no
- LD50- relatively large
-mechanism by which endotoxin in the gram neg cell causes a fever response in humans. macrophage is a type of WBC
endotoxin (figure slide 24)
- fever response (pyrogenic response)
- gram neg bacterium ingested by macrophage
- bacteria degraded in vacuole inside macrophage and the lipopolysaccharide (LPS) layer of cell wall is released; this causes the macrophage to release interleukin- 1 (IL-1)
- IL-1 is carried by blood to hypothalamus of brain (controls body temp)
- IL-1 causes hypothalamus to reset the body temp to higher temp –> fever
endotoxins cont.
- not destroyed by autoclaving temp
- can have dead bacterial cells and still have LPS from cell wall which will cause fever response
- drugs, injection materials and medical devices need to be LPS free
- LAL test- limulus amoebocyte lysate test- rapid test detect the presence of LAL in pharmaceutical products
cytopathic effects of viruses
- vary with the type of virus
- may stop cell division
- may produce inclusion bodies
- may cause cells to fuse together to produce large cell with multiple nuclei
- may affect cells so that they no longer stop dividing when they touch each other (contact inhibition) and keep on dividing to form a mass of cells
pathogenic properties of fungi
- fungal waste products may cause symptoms
- chronic infections provoke an allergic response
- tichothecene toxins produced by molds growing in a house or on grain inhibit protein synthesis
- ingesting the toxins causes chills, fever, nausea and vomiting
- Fusarium; Stachybotrys
aflatoxin
toxins produced by some Aspergillus growing under specific conditions; toxic if eaten
mycotoxins
neurotoxins; may be quite potent
portals of exit
- respiratory tract
- coughing and sneezing
- gastrointestinal tract
- feces and saliva
- genitourinary tract
- urine and vaginal secretions
- skin
- blood
- biting arthropods and needles or syringes
