Host Microbe Relationship Patricia Sidelsky 2007

Microbe host relationships  Symbiosis – Coexistence of two or more organisms to the success of the other in the environment. Can evolve specific mechanisms to maintain this relationship 1. Mutualism 1. Mutualism 2. Commensalism 2. Commensalism 3. Parasitism 3. Parasitism

Mutualism  Both partners in a relationship are dependent upon each other  Each contributes to the success of the other organism in a particular environmemt

Rhizobium and legumes

Coral and Zooxanthellae

Coral Bleaching can lead to death of the reef

Leaf cutter ants

Ruminants - Gut reactions: Sequencing ruminal bacteria

Commensalism  Microbes that share space on the skin as well as the metabolic products  Coexist – the partners in the relationship do not contribute to the success of their fellow microbes, but neither are they harmed

E. Coli in the gut  E. coli lives in an enriched environment high in nutrients  In return E. coli produces Vitamin K for blood clotting

Parasitism and Pathogens  Pathogens are disease producing organisms  The parasite benefits from the relationship  The host is harmed  +/- relationship

Flat worms - Platyhelminthes  Cestodes  Trematodes

Schistosomiasis

Schistosomes

Clinorchis senensis - Liver

Tapeworm

Tapeworm

Protozoan parasites – Plasmodium vivax and Plasmodium falciparum

Giardia lamblia

Entamoeba histolytica

Key terms  Infection refers to the presence or a parasitic organism or pathogen( implies that they are established and reproducing)  Infestation – A word usually limited to larger parasites like helminths or worms  Contamination – refers to the presence of microbes( can be on the surface of an inanimate object )

Disease  Disturbance in the state of health that may result in the infection of human tissue by microbes  Changes in the host that interfere with normal function  Fever, diarrhea, inflammation, irreparable damage

Pathogenicity  Ability to produce disease  Invasion of pathogen  Release of molecules by pathogen  Host response to invader

Relationships  Normal flora – normal microbiota – Many organisms have well established associations with humans  Resident microbiota – microbes that are always present – skin, orifices, interior of nose and throat – Tend to colonize mucous membranes

Transient microbes  Present under certain conditions  May require special nutrients  Not as adaptive OPPORTUNISTIC ORGANISMS MAY BE TRANSIENT

Opportunistic organisms  Able to penetrate the immune defenses if there is another infectious agent present  Immunocompromised due to malnutrion or other extenuating factor  Introduced at an inappropriate body site  Imbalance of the normal flora due to antibiotic therapy  Imbalance of the normal flora due to chemotherapy

Candida

C. difficile

Burkholderia cepacia

How Microbes Cause Disease  Adherence  Colonization  Invasiveness  Virulence factors and Toxins  Growth and Multiplication in the host  Exiting the host  Cell injury and destruction

Adherence  Adhesins - molecules that are adhesive in nature and are found on the tips of the fimbriae  These adhere to the host cell membrane( specificity involved between pathogen and host)

Receptors that are specific for infective agents  CCR5 receptor on macrophages that binds to both bacteria and viruses  Yersinia pestis - causative agent of the plague  HIV- causative viral agent of AIDS

CCR5 receptor

Anthrax and receptors

Invasiveness  Ability to grow in the host  To spread through tissues  To avoid the immune defenses

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

Coagulase( staphlococcus aureus)  Causes blood to clot – fibrin clot protects the bacteria  Walls off microorganisms so that they can avoid macrophages and neutrophils

Streptokinase  Dissolves blood clots  Pathogens trapped in blood clots are freed

Exotoxin or endotoxin  Exotoxins secreted or released by bacteria into the host tissues  Endotoxins – Molecules present in the cell wall or exterior covering of a bacterium

Hemolysins( Exotoxins)  Burst red blood cells and release hemoglobin to be used for the cell’s metabolism  Alpha  Beta ( clear area around bacteria on blood agar) page 397  Gamma

Exotoxins against WBC  Leukocidins – release by strep and staphylococci – destroys white blood cells that are able to phagocytosed bacteria

Neutrophil and infection

Endotoxins  LPS ( A antigen)  Produced by Gram negative organisms  Endotoxins released when bacteria are killed by antibiotic  Can cause severe reaction