Host Microbe Host Microbe RelationshipRelationshipPatricia SidelskyPatricia Sidelsky

20072007

Microbe host Microbe host relationshipsrelationships

Symbiosis – Coexistence of two or Symbiosis – Coexistence of two or more organisms to the success of more organisms to the success of the other in the environment. Can the other in the environment. Can evolve specific mechanisms to evolve specific mechanisms to maintain this relationshipmaintain this relationship

1. Mutualism1. Mutualism 2. Commensalism2. Commensalism 3. Parasitism3. Parasitism

MutualismMutualism

Both partners in a relationship are Both partners in a relationship are dependent upon each otherdependent upon each other

Each contributes to the success of Each contributes to the success of the other organism in a particular the other organism in a particular environmemtenvironmemt

RhizobiumRhizobium and legumes and legumes

Coral and ZooxanthellaeCoral and Zooxanthellae

Coral Bleaching can lead Coral Bleaching can lead to death of the reefto death of the reef

Leaf cutter antsLeaf cutter ants

Ruminants - Gut Ruminants - Gut reactions: Sequencing reactions: Sequencing ruminal bacteriaruminal bacteria

CommensalismCommensalism

Microbes that share space on the Microbes that share space on the skin as well as the metabolic skin as well as the metabolic productsproducts

Coexist – the partners in the Coexist – the partners in the relationship do not contribute to the relationship do not contribute to the success of their fellow microbes, but success of their fellow microbes, but neither are they harmedneither are they harmed

E. ColiE. Coli in the gut in the gut

E. coliE. coli lives in an enriched lives in an enriched environment high in nutrientsenvironment high in nutrients

In return E. coli produces Vitamin K In return E. coli produces Vitamin K for blood clottingfor blood clotting

Parasitism and Parasitism and PathogensPathogens

Pathogens are disease producing Pathogens are disease producing organismsorganisms

The parasite benefits from the The parasite benefits from the relationshiprelationship

The host is harmedThe host is harmed +/- relationship+/- relationship

Flat worms - Flat worms - PlatyhelminthesPlatyhelminthes

CestodesCestodes TrematodesTrematodes

SchistosomiasisSchistosomiasis

SchistosomesSchistosomes

Clinorchis senensis - Clinorchis senensis - LiverLiver

TapewormTapeworm

TapewormTapeworm

Protozoan parasites – Protozoan parasites – Plasmodium vivax and Plasmodium vivax and Plasmodium falciparumPlasmodium falciparum

Giardia lambliaGiardia lamblia

Entamoeba histolyticaEntamoeba histolytica

Key termsKey terms

Infection refers to the presence or a Infection refers to the presence or a parasitic organism or pathogen( implies parasitic organism or pathogen( implies that they are established and that they are established and reproducing)reproducing)

Infestation – A word usually limited to Infestation – A word usually limited to larger parasites like helminths or wormslarger parasites like helminths or worms

Contamination – refers to the presence of Contamination – refers to the presence of microbes( can be on the surface of an microbes( can be on the surface of an inanimate object )inanimate object )

DiseaseDisease

Disturbance in the state of health Disturbance in the state of health that may result in the infection of that may result in the infection of human tissue by microbeshuman tissue by microbes

Changes in the host that interfere Changes in the host that interfere with normal functionwith normal function

Fever, diarrhea, inflammation, Fever, diarrhea, inflammation, irreparable damageirreparable damage

PathogenicityPathogenicity

Ability to produce diseaseAbility to produce disease Invasion of pathogenInvasion of pathogen Release of molecules by pathogenRelease of molecules by pathogen Host response to invaderHost response to invader

RelationshipsRelationships

Normal flora – normal microbiota – Normal flora – normal microbiota – Many organisms have well Many organisms have well established associations with established associations with humanshumans

Resident microbiota – microbes that Resident microbiota – microbes that are always present – skin, orifices, are always present – skin, orifices, interior of nose and throat – Tend to interior of nose and throat – Tend to colonize mucous membranescolonize mucous membranes

Transient microbes Transient microbes

Present under certain conditionsPresent under certain conditions May require special nutrientsMay require special nutrients Not as adaptiveNot as adaptive

OPPORTUNISTIC ORGANISMS MAY BE OPPORTUNISTIC ORGANISMS MAY BE TRANSIENTTRANSIENT

Opportunistic organismsOpportunistic organisms

Able to penetrate the immune defenses if Able to penetrate the immune defenses if there is another infectious agent presentthere is another infectious agent present

Immunocompromised due to malnutrion Immunocompromised due to malnutrion or other extenuating factoror other extenuating factor

Introduced at an inappropriate body siteIntroduced at an inappropriate body site Imbalance of the normal flora due to Imbalance of the normal flora due to

antibiotic therapyantibiotic therapy Imbalance of the normal flora due to Imbalance of the normal flora due to

chemotherapychemotherapy

CandidaCandida

C. difficileC. difficile

Burkholderia cepaciaBurkholderia cepacia

How Microbes Cause How Microbes Cause DiseaseDisease

AdherenceAdherence ColonizationColonization InvasivenessInvasiveness Virulence factors and ToxinsVirulence factors and Toxins Growth and Multiplication in the hostGrowth and Multiplication in the host Exiting the hostExiting the host Cell injury and destructionCell injury and destruction

AdherenceAdherence

Adhesins - molecules that are Adhesins - molecules that are adhesive in nature and are found on adhesive in nature and are found on the tips of the fimbriaethe tips of the fimbriae

These adhere to the host cell These adhere to the host cell membrane( specificity involved membrane( specificity involved between pathogen and host)between pathogen and host)

Receptors that are Receptors that are specific for infective specific for infective agentsagents

CCR5 receptor on macrophages that CCR5 receptor on macrophages that binds to both bacteria and virusesbinds to both bacteria and viruses

Yersinia pestis - causative agent of Yersinia pestis - causative agent of the plaguethe plague

HIV- causative viral agent of AIDSHIV- causative viral agent of AIDS

CCR5 receptorCCR5 receptor

Anthrax and receptorsAnthrax and receptors

InvasivenessInvasiveness

Ability to grow in the hostAbility to grow in the host To spread through tissuesTo spread through tissues To avoid the immune defensesTo avoid the immune defenses

Virulence factorsVirulence factors

Hyaluronidase – enzyme that breaks Hyaluronidase – enzyme that breaks down connective tissue. Break down connective tissue. Break down of connnective tissue insures down of connnective tissue insures that the streptococci can spread that the streptococci can spread through epithelial tissues lining the through epithelial tissues lining the throatthroat

Coagulase( Coagulase( staphlococcus staphlococcus aureus)aureus)

Causes blood to clot – fibrin clot Causes blood to clot – fibrin clot protects the bacteriaprotects the bacteria

Walls off microorganisms so that Walls off microorganisms so that they can avoid macrophages and they can avoid macrophages and neutrophilsneutrophils

StreptokinaseStreptokinase

Dissolves blood clotsDissolves blood clots Pathogens trapped in blood clots Pathogens trapped in blood clots

are freedare freed

Exotoxin or endotoxinExotoxin or endotoxin

Exotoxins secreted or released by Exotoxins secreted or released by bacteria into the host tissuesbacteria into the host tissues

Endotoxins – Molecules present in Endotoxins – Molecules present in the cell wall or exterior covering of the cell wall or exterior covering of a bacteriuma bacterium

Hemolysins( Exotoxins)Hemolysins( Exotoxins)

Burst red blood cells and release Burst red blood cells and release hemoglobin to be used for the cell’s hemoglobin to be used for the cell’s metabolismmetabolism

AlphaAlpha Beta ( clear area around bacteria on Beta ( clear area around bacteria on

blood agar) page 397blood agar) page 397 GammaGamma

Exotoxins against WBCExotoxins against WBC

Leukocidins – release by strep and Leukocidins – release by strep and staphylococci – destroys white blood staphylococci – destroys white blood cells that are able to phagocytosed cells that are able to phagocytosed bacteriabacteria

Neutrophil and infectionNeutrophil and infection

EndotoxinsEndotoxins

LPS ( A antigen)LPS ( A antigen) Produced by Gram negative Produced by Gram negative

organismsorganisms Endotoxins released when bacteria Endotoxins released when bacteria

are killed by antibioticare killed by antibiotic Can cause severe reactionCan cause severe reaction