Lec8 pathogens

Lec8 pathogens - Biol 115: Infectious Diseases Spring 2009,...

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Biol 115: Infectious Diseases Spring 2009, T. Bekyarova
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Readings: Mader Chapter 7 section 7.1
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What are microbes? Microbes are microscopic organisms and particles that include: Bacteria Viruses Prions Others (fungi, multicellular parasites, single- celled protistans)
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Most Infectious Diseases are Caused by Microbes Microbes are very abundant in the environment and as well as in and on our bodies Most microbes are harmless or even beneficial Bacterial "flora" in gut and on skin Bacteria and yeasts used in biotechnology Microbes in the soil recycle nutrients or "fix" nitrogen
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Pathogens Microbes which cause disease are called pathogens Normally benign microbes may cause disease by "opportunistic" growth Pathogenic bacteria release enzymes and toxins which attack tissues
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Bacteria are Prokaryotic Cells i.e. lack a nucleus and other organelles Have DNA in a single chromosome Have ribosomes Some have accessory rings of DNA called plasmids Can occur as individual cells (mono-) or long chains (strepto-) Usually have a rigid cell wall Some have a slimy external capsule Common forms are bacilli, cocci, and spirilla
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Fig. 7.1a
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Bacterial Morphology Cocci Bacilli Spirilla
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Bacteria Frequently have flagella and rigid projections called pilli Pilli help in attachment to cells to be infected May form "endospores" which allow them to remain dormant until conditions improve
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Bacteria Reproduce by “Binary Fission”
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Prokaryotic vs. Eukaryotic Cell
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Gram-Negative vs, Gram-Positive Bacteria “Gram-positive and Gram-negative” bacteria have different cell walls Bind and don’t bind “Gram’s stain” respectively Gram positive bacteria have thick peptidoglycan layer Gram negative have much thinner peptidoglycan layer
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Gram-Negative vs Gram-Positive Bacteria
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Gram Negatives Have an Outer Membrane Lipo-polysaccharides in the outer membrane of gram negative bacteria Release of Lipo-polysaccharides during attack by immune system frequently cause fevers and inflammation
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Pathogenicity Pathogenicity can be acquired by previously benign organisms Microbes can become pathogenic by acquiring one or more “virulence factors” Produce a toxin Ability to adhere to surfaces Ability to invade organs or cells Bacteria promiscuously release and take up DNA into the environment and so can take up virulence factors at any time
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Toxins Are poisons that damage cells or tissues Small organic molecules, peptides and sometimes parts of bacterial cell walls. Toxins can travel in bloodstream to places far away from original infection
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Examples of Toxins: Clostridium tetani is an anaerobe that can be established in the body from a puncture wound Produces tetanus – toxin prevents muscle relaxation “Tetanus shots” produce antibodies to toxins
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Not All E coli Species are Dangerous E. coli is a normal component of gut flora.
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This note was uploaded on 04/07/2009 for the course BIOL 115 taught by Professor Irving during the Spring '08 term at Illinois Tech.

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Lec8 pathogens - Biol 115: Infectious Diseases Spring 2009,...

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