Microbiology chapter 15 Flashcards
pathogenicty vs virulence
Pathogenicity: the ability to cause disease
Virulence: the extent of pathogenicity
pathogenicity steps
Entry Attachment Penetration This may involve avoiding host defense mechanisms. Host cell damage Exit
Portals of Entry
Portals of Entry Mucous membranes Skin Parenteral route A particular microorganism has a preferred portal of entry
Numbers of Invading Microbes:
ID 50, LD 50
ID50: infectious dose for 50% of the test population
LD50: lethal dose (of a toxin) for 50% of the test population
adherence is when Adhesins/ligands of microorganism bind to receptors on host cells, which cause?
Adherence allows for the formation of biofilms
How Bacterial Pathogens Penetrate Host Defenses
capsules, cell wall components, enzymes
Capsules penetrate by
Prevent phagocytosis Streptococcus pneumoniae Haemophilus influenzae Bacillus anthracis What else can the capsule do for “its” bacterium?
cell wall components are used to?
Examples M protein resists phagocytosis Streptococcus pyogenes Opa protein inhibits T helper cells Neisseria gonorrhoeae Mycolic acid (waxy lipid) resists digestion by phagocytes Mycobacterium tuberculosis
Enzymes are used to enter by
Coagulase: coagulates fibrinogen Kinases: digest fibrin clots Hyaluronidase: hydrolyzes hyaluronic acid Collagenase: hydrolyzes collagen IgA proteases: destroy IgA antibodies
Penetration into the Host Cell Cytoskeleton
Invasins
Salmonella alters host actin to enter a host cell
Use actin to move from one cell to the next
Listeria
Salmonella entering intestinal epithelial cells as a result of ruffling
Many vaccines provide years of protection against a disease. Why doesn’t the influenza vaccine offer more than a few months of protection?
antigenic variation
How Bacterial Pathogens Damage Host Cells
Siderophores,Direct Damage,Toxins,Exotoxins
Siderophores damage
Stealing nutrients from the host
Direct Damage
Disrupt host cell function
Produce waste products
Toxins
Toxins terminology: toxin, toxigenicty,toxemia,toxoid,antitoxin
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
Many of these terms apply to exotoxins more than to endotoxins
exotoxins
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.
endotoxins
Endotoxins are the lipid portions of lipopolysaccharides (LPS) that are part of the outer membrane of the cell wall of gram-negative bacteria (lipid A; see Figure 4.13c). The endotoxins are liberated when the bacteria die and the cell wall breaks apart
Exotoxins work by
Specific for a structure or function in host cell Mechanisms A-B Toxins Membrane-Disrupting Toxins Superantigens
Toxins-Membrane-Disrupting Exotoxins
Lyse host’s cells by Making protein channels in the plasma membrane Leukocidins Hemolysins Streptolysins Disrupting phospholipid bilayer
Toxins-Superantigen Exotoxins
Cause an intense immune response due to release of cytokines from host cells
Symptoms: fever, nausea, vomiting, diarrhea, shock, and death
Endotoxins and the pyrogenic response
1.A macrophage ingests
a gram-negative bacterium.
2.The bacterium is
degraded in a vacuole, releasing endotoxins
that induce the macrophage to
produce cytokines IL-1 and TNF-.
3.The cytokines are
released into the bloodstream by the macrophages,
through which they travel to the hypothalamus of the brain.
4.The cytokines induce the hypothalamus to produce prostaglandins,
which reset the body’s
“thermostat” to a
higher temperature,
producing fever.
Endotoxins-Limulus Amebocyte Lysate (LAL) Assay
Assay for presence of endotoxins
Mechanism
Amebocyte lysis produces a clot
Endotoxin causes lysis
Food poisoning can be divided into two categories:
food infection and food intoxication. On the basis of toxin production by bacteria, explain the difference between these two categories.
Viral Cytopathic Effects
No host cell macromolecule synthesis Release of cellular enzymes from lysosomes Inclusion bodies Syncytium Change in host cell function Production of interferons Antigenic change of host cell Chromosomal changes Contact inhibition
Pathogenic Properties of Algae
Paralytic shellfish poisoning
Dinoflagellates
Saxitoxin
A neurotoxin
Portals of Exit
Respiratory tract Coughing and sneezing Gastrointestinal tract Feces and saliva Genitourinary tract Urine and vaginal secretions Skin Blood Arthropods that bite; needles or syringes
Microbial Mechanisms of Pathogenicity: factors
portals of entry, penetration of cells, host cell damage, portals of exit
