Microbial Mecanisms Of Pathogenicity Flashcards
Pathogenicity
The ability to cause disease
Virulence
The extent of pathogenicity
What factors make a microbe a successful pathogen?
if it has the ability to enter and infect a host’s cells, cause damage to the host,
spread from one host to another,
adapt to changing environments and host immune systems,
persist in the environment or host tissues,
and have a broad host range or be specific to a particular host.
Portals of entry:
Mucous membranes
Skin
Parenteral route
Preferred portal of entry
Numbers of invading microbes:
ID50:
infectious dose for 50% of the test population
Number of invading microbes
LD50:
lethal dose (of a toxin) for 50% of the test population
Relative virulence of toxin
Adhesins/ligands bind to
Receptors on host cells
Glycocalyx: Streptococcus mutans
Fimbriae: Escherichia coli
M protein: Streptococcus pyogenes
Form biofilms
Capsules
Prevent phagocytosis
Streptococcus pneumoniae
Haemophilus influenzae
Bacillus anthracis
Cell Wall Components
M protein resists phagocytosis
Streptococcus pyogenes
Opa protein inhibits T helper cells Neisseria gonorrhoeae
Mycolic acid (waxy lipid) resists digestion Mycobacterium tuberculosis
Coagulase
Coagulates fibrinogen
Kinases
Digest fibrin clots
Hyaluronidase
Hydrolyzes hyaluronic acid
Collagenase
Hydrolyzes collagen
IgA proteases:
Destroy IgA antibodies (found in mucous membranes)
Using the Host’s Nutrients: Siderophores
Use host’s iron
Direct damage
● Disrupt host cell function
● Produce waste products
● Toxins
Toxin
substance that contributes 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
Exotoxins
Specific for a structure or function in host cell
Membrane-disrupting toxins
Lyse host’s cells by
Making protein channels in the plasma
membrane
Disrupting phospholipid bilayer
Leukocidins
Destroys leukocytes
Hemolysins
Destroys RBCs
Streptolysins
Destroys immune cells
Superantigens are usually an:
Exotoxin or other bacterial protein
Superantigens cause an:
Intense immune response due to release of excessive amounts of cytokines from host cells
Cytokines is a general term for:
cell communication and immune mediator chemicals (protein)
Superantigens symptoms of intense immune response:
fever, nausea, vomiting, diarrhea, shock, and death
Exotoxin sources
Exotoxins and lysogenic (virus stays dormant in cells) conversion
Endotoxins = only one type:
Lipid A released from dead Gram negative bacteria Lipopolysaccharide membrane
Exotoxins are proteins produced:
Inside pathogenic bacteria, most commonly gram-positive bacteria, as part of their growth and metabolism. The exotoxins are then secreted into the surrounding medium during log phase.
Exotoxin is a
Ex(s)?
toxic substance released outside the cell
Clostridium botulinum, an example of a gram positive bacterium that produces exotoxins
Endotoxins are the
Lipid portions of lipopolysaccharides (LPS) that are part of the outer membrane of the cell wall of gram-negative bacteria. The endotoxins are liberated when the bacteria die and the cell wall breaks apart.
Endotoxins are a
Ex(s)?
Toxin composed of lipids that are part of the
outer membrane
Ex: Salmonella typhimurium, an example of a gram-negative bacterium that produces endotoxins
Endotoxin and Fever (pyrogenic response)
A macrophage ingests:
a gram-negative bacterium.
Endotoxin and Fever (pyrogenic response)
The bacterium is digested in a
phagosome, releasing endotoxins that induce the macrophage to produce cytokines IL-1 and TNF-
Endotoxin and Fever (pyrogenic response)
The cytokines reach the
hypothalamus causing it to produce prostaglandins, which reset the body’s “thermostat” to a higher temperature, producing fever.
Endotoxin and Fever (pyrogenic response)
As long as cytokines remain in the blood:
temperature remains high. When cytokines are gone body temp will go back to normal
Endotoxins and the pyrogenic response (4 steps)
Cytopathic Effects of Viruses
● Cell lysis
● Inclusion bodies (what’s left behind)
● Stop macromolecular synthesis in host cell
● Cause cell fusion (syncytium)
● Interfere with cell functions
● Cause antigenic changes on host cell surface leading to cell being destroyed by the immune system
● Chromosomal changes (possibly activation of oncogenes)
● Transformation of host cells- loss of contact inhibition leading to unregulated cell growth
Pathogenic Properties of Fungi
-Fungal waste products may cause symptoms
-Chronic infections provoke an allergic response
-Trichothecene toxins inhibit protein synthesis :Fusarium
-Proteases:Candida, Trichophyton
-Capsule prevents phagocytosis: Cryptococcus
● Ergot toxin: Claviceps
● Aflatoxin: Aspergillus
● Mycotoxins: Neurotoxins: phalloidin,
amanitin
Pathogenic Properties of Protozoa
Presence of protozoa
Protozoan waste products may cause symptoms
Avoid host defenses by Growing in phagocytes Antigenic variation
Pathogenic Properties of Helminths
-Use host tissue
● Presence of parasite interferes with host function
● Parasite’s metabolic waste can cause symptoms
Pathogenic Properties of Algae
Paralytic shellfish poisoning
-Dinoflagellates
-Saxitoxin
Red tide: more algae than normal (irritating to skin)
Pathogenic Properties of Algae
Portals of Exit:
-Respiratory tract: Coughing and sneezing
Gastrointestinal tract: Feces and saliva
Genitourinary tract: Urine and secretions
-Skin
-Blood: Arthropods that suck blood; needles or syringes
Mechanisms of microbial pathogenicity is fundamental to understanding how pathogens are able to overcome the host’s defenses:
PORTALS OF ENTRY:
Mucous membranes
• Respiratory tract
• Gastrointestinal tract
• Genitourinary tract
• Conjunctiva
Skin
Parenteral route
Mechanisms of microbial pathogenicity is fundamental to understanding how pathogens are able to overcome the host’s defenses:
PENETRATION OR EVASION OF HOST DEFENSES:
Capsules
Cell wall components
Enzymes
Antigenic variation
Invasins
Intracellular growth
Mechanisms of microbial pathogenicity is fundamental to understanding how pathogens are able to overcome the host’s defenses:
DAMAGE TO HOST CELLS:
Siderophores
Direct damage
Toxins:
• Exotoxins
• Endotoxins
Lysogenic conversion
Cytopathic effects
Mechanisms of microbial pathogenicity is fundamental to understanding how pathogens are able to overcome the host’s defenses:
PORTALS OF EXIT:
Generally the same as the portals of entry for a given microbe:
• Mucous membranes
• Skin
• Parenteral route
