micro quiz 6

infection

microbes that grow on or within a multicellular host

disease

tissue is damaged with impaired function

pathogen

microbe that is the causative agent of an infectious disease

symptom

phenotypic effect of the infection on the host

first stage of infection

involves adherence of the bacteria to a surface within the host

second stage of infection

after adhering the cells can invade the host cells and multiply and cause disease, or they can colonize the surface of the host cell forming a biofilm which can cause disease, in multiplication toxins can be secreted

infection process

exposure, adherence, invasion, multiplication

disease process

toxicity/invasiveness, tissue or systemic damage

adherence

ability of a bacteria to bind to a cell or inorganic surface, cell interacts with host through cell-surface receptors

adhesins

receptors of the pathogen surface which are composed of glycoprotein or lipoprotein bound to the outer layer of the cell

• capsules, fimbriae, pili, flagella also aid in adhesion to target cell

colonization

growth of a bacteria after it gains access to a host tissue, typically begins a site in the mucous membranes of host

oral pathogens

use adhesions and quorum-sensing methods to initiate biofilm formation on mucous membranes

oral pathogens in the mouth

form a biofilm called plaque which is a hospitable environment for many bacterial species resulting in mixed biofilm

invasion

ability of a pathogen to enter host cells or tissues, spread, and cause disease

• some remain localized in the site of infection but some spread around and enter the bloodstream

bacteremia

an asymptomatic disease in which the bacteria enter the bloodstream and are killed by the host

septicemia

where a bacteria enters the bloodstream, multiplies, and spreads systemically around the body

pathogenicity of bacteria

overall ability to cause disease in a host

virulence

measure of pathogenicity, both can vary between species and strains

attenuation

when a strain of bacteria has significantly reduced virulence

virulence factors

genetically encoded factors (usually proteins) that contribute to pathogenicity

salmonella virulence

causative agent of GI-related infections, contains various pathogenicity islands which encode virulence factors, deletion of factors results in the bacteria being unable to establish an infection

enzymes

proteins which catalyze chemical reactions resulting in tissue damage, only affect local regions and can’t spread throughout a multicellular organisms

streptococcus pyogenes

“fish-eating bacteria”, the enzyme hyaluronidase promotes tissue invasion by digesting epithelial cells

toxins

specialized proteins/components that cause damage locally and systemically throughout the host, almost all pathogens use enzyme only some use toxins

toxicity

ability of an organism to cause disease using a toxin

exotoxins

proteins secreted by pathogens

• AB toxins

• cytolytic toxins

  • superantigen toxins

endotoxins

certain cellular components of the pathogen

• toxic upon cell lysis

AB type exotoxins

found in diphtheria and tetanus infections, bipartite (2 parts)

• B component binds to the host cell surface facilitating the transfer of the A component

  • A component enters the cell performing a reaction which damages the cell

cytotoxin

soluble proteins secreted by a pathogen, cause damage the cell membrane of target cells, secreted and degrade the phospholipid membrane resulting in host-cell lysis

blood plates

use these to see the ability to degrade cells, contain erythrocytes that have zones of clearance when lysis occurs

clostridium perfringens

uses the a-toxin to kill blood cells to release proteins which can be fermented

lipopolysaccharides (LPS)

found on the cell wall of gram - bacteria

• core polysaccharide - make the toxic product soluble

• lipid A - toxic part of the LPS

• endotoxin can stimulate a strong immune response leading to fever and inflammation which can result in kidney failure

pathogen

microbe that is the causative agent of an infectious disease

disease

tissue is damaged with impaired functioni

immunology

understand how organisms resist pathogens and handle infectious disease

vertebrate immunity

innate - inborn defenses (broad)

adaptive - acquired defenses (specific)

physical barriers of body

skin and mucus layers, which prevent attachment of pathogens

chemical barriers of body

low pH of the stomach which kills infectious organisms, enzymes like lysozome degraded the cell walls of pathogens

microbiological barriers of body

normal healthy microbiota competes with pathogenic bacteria for inhabitable spaces and nutrients preventing infection

immune system

sole function is to detect and destroy pathogenic bacteria within the body

innate immunity

generalized response to a pathogenic organism, requires phagocytes as primary effector cells which can respond to a broad range of pathogens, responses are rapid and enable an immediate fight against the pathogen by the host

• neutrophils

• dendritic cells

• macrophage

blood and lympathic systems

circulatory systems

two major blood cells

erythrocytes - red

leukocytes - white

circulatory system

provide tissues with oxygen, carries erythrocytes

lymphatic system

provide nutrients and proteins to cells and tissues while helping the body fight infection, carries leukocytes

erythrocytes

most common form of blood cell found in the body, uniform in shape and structure and lack a nucleus

leukocytes

1000-fold less abundant, diverse structures and function, contain nucleus

• grainy - can be referred to as granulocytes

hematopoietic stem cells

can differentiate various leukocytes used in the innate immune response

differentiation into two subclasses occurs

monocytes - dendritic cells and macrophages

granulocytes - neutrophils, eosinophils, basophils, mast cells

monocytes

ingest pathogens and present pieces of the pathogen on their cell surface, this piece of pathogen is referred to as an antigen

granulocytes

contain toxins and enzymes that are used to destroy target cells

phagocytes

leukocytes which recognize, engulf, and kill pathogens usually by digestion, they drive the rapid response of innate immunity

phagocyte recruitment example

needle breaks skin introducing pathogenic bacteria, circulating macrophages encounter the pathogen and become activated, activated macrophages produce cytokines

cytokines

signaling compounds related to immunity

chemokines

type of cytokine which recruits circulating phagocytes, such as neutrophils to the target area, here they will begin targeting pathogenic cells

pathogen-associated molecular patterns (PAMPs)

broadly conserved microbial components which are not present in human cells

• lipipolysaccharides (proteobacteria)

• peptidoglycan (cell wall)

  • flagellin (flagella)

pattern recognition receptors (PPRs)

cell surface receptors on leukocytes which recognize PAMPs

• result in engulfment of the pathogen

  • activate other phagocytes, ensuring clearance of infection

reacting to pathogens

phagocytes bind pathogens via PPRs, often toll-like receptor proteins, each TLR on a human phagocyte recognize a specific PAMP, TLR2 recognizes peptidoglycan on the bacterial cell wall

recognition of the PAMP

results in a signaling cascade, regulates gene expression within the phagocyte, changes results in pathogen killing, inflammation, and tissue healing

phagocytosis

process of pathogen engulfment by phagocyte, via endocytosis

phagosome

membrane bound vesicle containing the pathogen

lysosome

membrane bound vesicles containing reactive oxygen species (ROSs)

• exposure of pathogen to these ROSs results in respiratory burst killing the pathogen

phagolysosome

phagosome and lysosome fuse to form this

inflammation

localized redness, swelling pain, and heat, caused by the release of proinflammatory cytokines which increase vascular permeability

increased permeability

diverts fluid from blood to lymphatic system, strengthening the immune response and preventing bacteremia, changes result in the symptoms of inflammation

fever

systemic temperature increase from 37C to 38-40C, this lowers the growth rate of some pathogens and increases clearance

adaptive immunity

specific response to a pathogenic organism, relies on specificity, memory, and tolerance

specificity

recognizes pathogenic molecular structures (antigens)

memory

activation of lymphocytes which replicate and persist in case re-infection occurs

tolerance

avoiding recognition of hosts own molecules (self-antigens)

primary response in adaptive immunity

takes longer to clear an infection than innate immunity, it can remember the infection and combat it effectively when reinfection occurs, secondary response is much stronger

t cells

immunity cells which mature in the thymus of a human, contain t cell receptors on their surface which recognize and defend against pathogens, result in cellular killing of pathogens (form of cell-mediated immunity)

b cells

immunity cells which mature in the bone marrow of a human, produce antibodies which recognize specific antigens on a pathogen, targets the pathogen for destruction by the immune system (antibody-mediated immunity)

antigen

portion of the invading pathogen, can be a protein, toxin, virus, etc

antigen-presenting cells

immune cells that present antigens derived from engulfed pathogens

• b lymphocytes

  • macrophages and dendritic cells (innate)

antigen-presenting cells

engulf pathogens by phagocytosis after which they digest the pathogen, wearing portions of the pathogen on their membrane, shows immune system what to look for

major histocompatibility complex

proteins which present antigens to other immune cells, recognized t cells and trigger their activation (cell-mediated immunity)

MHC class 1

created by cells which are infected with a pathogen

MHC class 2

present antigens after phagocytosis of a target cell

cells presenting antigens

bound by the t cells that secrete protein cytokines which activate the adaptive immune response, can be done in multiple ways

th1 cells (t-helper cells)

release cytokines which activate other cells in the area to perform phagocytosis and trigger inflammation in the target area

tc cells (t-cytotoxic cells)

produce enzymes which degrade nearby target cells, such as pathogenic bacteria

th17 cells

interact with a pathogenic stimulated dendritic cell (innate immune response), interaction triggers the recruitment of nuetrophils to the infected area which results in inflammation and pathogen control, protecting the host from microbial infection

false positive response to a non-pathogenic source

body creates treg cells that interact with inactivated dendritic cells, they produce proteins and cytokines which suppress inflammation and recruitment of immune cells, results in suppression of immune responses and prevents an autoimmune response to self-antigens

B cell – T cell interaction and immunity

b-cells encounter, engulf, and degrade a pathogen and present the antigen on their surface in conjugation with a cell-surface protein

B cell – T cell interaction and immunity cont

antigen-cell-surface complex recognized by a t-cell surface protein it will bind and t-cell will release cytokines which trigger the b-cell to produce plasma and memory b cells

two b cells

plasma - produce antibodies which clear infection

memory - circulate in environment, waiting to respond to reinfection

antibodies

proteins which bind to a specific molecular feature (epitope), epitopes found on the antigen, single protein can contain various epitopes, antibodies bind a specific protein or entire pathogen

antibodies don’t directly kill pathogen, they perform two roles

opsonization - making antigen for destruction by receptor-mediated phagocytosis

neutralization - binding the infectious protein/pathogen preventing binding to their target

antibody production during infection

1. primary response - involve the production of IgM which help fight initial infection

2. once memory is established reinfection will trigger secondary response

   1. secondary response produces high titers of IgG preventing reinfection

natural/artificial methods

natural - involve processes which occur without human intervention

artificial - involve processes that utilize human intervention

active/passive immunity

active - body can make the antibodies required for immunity itself

passive - transient antibodies are introduced into the body