Transcript Host Microbe Relationship

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
2. Commensalism
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