The ability to cause disease
The extent of pathogenicity
What must a microbe do to overpower the hosts' defense?
gain entry, adhere, penetrate, damage
How does the microbe gain access to the host?
through the portal of entry
What are the portals of entry?
Mucous membranes (respiratory, GI, urogenital, conjunctiva)
Parenteral route (puncture or injection)
Which portal is the easiest and most frequently used?
Respiratory tract because droplets or dust particles can be inhaled. Some common infections: common cold, tuberculosis, pneumonia, influenza, measles
Which portal is used to contract polio, hepatitis A, typhoid fever, amoebic dysentery and cholera?
Gastrointestinal tract by ingesting microorganisms in food and water, contaminated fingers
What is the tract called for sexually contracted diseases?
How can microorganisms penetrate skin?
Openings in the skin (hair follicles, sweat glands); Hookworm larvae bore into the skin; fungi grow on the keratin of skin or infect the skin itself
The deposition of microorganisms directly into the tissues beneath the skin or mucous membranes
Parenteral route (examples: punctures, injections, bites. cuts, wounds, surgery, splitting due to swelling or drying)
What is it called when not all microbes cause disease when they have entered the body?
Salmonella typhi produces disease when ingested, but not when placed on skin.
When Streptococcus is inhaled it causes pneumonia but when swallowed does not.
What determines the virulence of a disease?
1. route of bacteria
2. number of bacteria
When half of the hosts die after a certain amount of toxin is administered what is this called?
LD50 (lethal dose for 50% of hosts)
When half of the hosts become infected after a certain amount of toxins is administered what is this called?
ID50 (infectious dose in 50% of hosts)
After entry into a host, almost all pathogens have some method to attach themselves to the host - what is this called?
What are the pathogen's surface molecule called?
adhesins or ligands
The surface molecules on the host cell are called?
What are the mechanisms to adhere and avoid host defense?
What are the key traits to a pathogen? The ability to:
2. Avoid phagocytosis
4. Produce enzymes (local)
5. Produce toxins (distant)
What are the most common ways of penetrating host defenses?
Enzymes (leukocidins, hemolysins)
What is the function of capsules?
Prevent phagocytosis and help with attachment (adherence)
How do bacterial capsules resist phagocytosis?
Phagocytic cells cannot adhere to the bacterium.
How can encapsulated bacteria be destroyed?
Antibodies to the capsule can be made, in which case the bacteria are easily destroyed by phagocytosis
How do enzymes aid virulence?
Leukocidins destroy neutrophils and leukocytes that are active in phagocytosis.
Hemolysins causes lysis of erythrocytes (rbc)
What are streptolycins?
Hemolysins produced by Streptococci
Which hemolysin secretes hemolysis that causes the incomplete lysis of RBCs?
Alpha Hemolytic Streptococci
Which hemolysin secretes hemolysins that cause the complete lysis of RBCs?
Beta Hemolytic Streptococci
Which bacterial enzyme coagulates the fibrinogen in blood and what is the purpose of the clot?
Coagulases - clots may protect the bacteria from the phagocytosis and may be involved in walling off process of boils produced by staphylocci (to hide itself)
Which bacterial enzyme breaks down fibrin and dissolves clots formed by the body to isolate infections?
Kinases (to free itself)
Which enzyme is produced by Streptococcus pyogenes and used to dissolve some types of blood clots in heart attack patients?
Which enzyme is secreted by some bacteria, including streptococci (and some clostridia involved in gas gangrene)?
Hyaluronidase (dissolves connective tissue)
What does hyaluronidase do?
Hydrolyzes hyaluronic acid that holds together certain cells of the body, particularly in connective tissue; may be involved in blackening of tissue in wounds; helps microorganisms spread from initial site of infection
Which enzymes break down collagen (protein) which forms connective tissue of muscles and other tissues?
Collagenase (produced by species of Clostridium involved in gas gangrene)
Which substance scavenges iron from the host's body fluids?
What causes the rearrangement of actin filaments in the cell cytoskeleton to bring the bacterium into the cell?
invasins (produced by Salmonella typhimurium and enteropathogenic E. Coli)
Which toxin is produced inside the bacterium and then released into the surrounding medium?
What are the three groups of of exotoxins?
Cytotoxins - kills host cells or affect their function
Neurotoxins - interfere with nerve impulses
Enterotoxins - affect cells in gastrointestinal tract
What are inactivated exotoxins injected into the body to produce immunity?
What is life-threatening loss of blood pressure, when caused by Gram-negative organism?
Shock (septic shock)
Which toxin is part of the structure of the bacteria and the cell must be dead and also Gram negative?
Endotixin (lipid A)
What can be carried on the plasmid or lysogenic phages?
Defenses that protect against any pathogen, regardless of species?
What are the two lines of defense?
First - skin and mucous membranes
Second - phagocytes, inflammation, fever, and antimicrobial substances
What is a barrier against penetration by microorganisms?
Which defense dilutes the number of bacteria?
Which enzyme can breakdown the Gram positive cell wall (somewhat effective against Gram negative) and in all body fluids to kill bacteria?
What are the three categories of leukocytes (WBCs)?
What are lipase, proteinase, carbohydrase and nuclease?
Types of lysosome
Which phagocytic cells enlarge and become macrophages?
Which phagocytic cells migrate to the site of infection?
granulocytes and monocytes
Which phagocytic cells dominate the initial phase of bacterial infection?
What are the 4 main phases of phagocytosis?
Chemotaxis (chemical attraction to the microorganism)
Ingestion (engulfment by pseudopods, produces phagosome)
Digestion (phagosome fuses with lysosome to form a phagolyosome)
What is a defensive response triggered by damage to body tissues?
What are the 4 symptoms of inflammation or vasodilation?
What is the most important job of inflammation?
To repair or replace tissues damaged by the agent or its products
What is the increase in diameter of blood vessels?
Vasodilation - increases blood flow to damaged area; responsible for redness and heat associated with inflammation
Which substances lead to vasodilation/permeability?
Which substance is released by injured cells (send a help signal)?
Which substance is present in blood plasma?
Kinins - also play a role in chemotaxis of phagocytic granulocytes
Which substance is released by damaged cells; intensifies effects of histamines and kinins and helps phagocytes move through capillary walls?
Which substance is produced by mast cells?
Blood vessel constriction, increased rate of metabloism and shivering all contribute to
Period of sweating indicate two things...
crisis and temperature is falling
A defensive system containing serum proteins that participate in lysis of foreign cells, inflammation and phagocytosis
What are the components of the complement system?
protein C1 to C9
Which components are responsible for inflammation?
C3 (C3a and C3b) and C5 (C5a and C5b)
Which component(s) makes holes in cell wall and cause the cell to leak?
What is one of the consequences of complement activation that attaches and makes the foreign cell "edible?"
Opsonization (immune adherence - binding of C3b to the microbe can interact with receptors on phagocytes)
Which substance notifies the neighbor cell of infection to create antiviral proteins (AVPs)?
What do interferons do?
They interfere with viral multiplication and stimulate production of AVPs