Infectious Disease Pathogens are microorganisms that cause disease
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Infectious Disease
• Pathogens are microorganisms that cause disease. • A host is any organism that is capable of supporting the nutritional and physical growth requirements of another organism. • Infection is the presence and multiplication of a parasitic organism in the host.
• Pathology depends on: – Organism – Site of infection • Treatment depends on the microorganism – Prokaryote vs. eukaryote vs. virus – Resistance to antibiotics
• Not all interactions between bacteria and humans are harmful – normal microbiota prevents the growth of pathogens. • Most microorganisms can be opportunistic pathogens which can cause disease if the host is immunocompromised or if they can enter the body in a place where they are not normally found. ( E. coli urinary tract infections)
Prions • Infectious proteins – Improperly folded proteins that cause other proteins to take on that shape – Extremely difficult to destroy – Discussed later with transmissible spongiform encephalopathies (TSE’s)
Bacteria • Prokaryotes – Lack a nucleus and membrane-bound organelles – Structurally simple but metabolically complex – Contain both DNA and RNA – Single circular chromosome – Plasmids : extrachromosomal DNA that provides information (antibiotic resistance) that can be shared with other bacteria.
Bacteria • Cytoplasmic membrane • Cell wall – peptidoglycan • May also produce a capsule of protein or carbohydrate – protects from the host immune system.
Virulence factors • Exotoxins – proteins released from a bacterial cell – enzymes that lead to cell death or dysfunction • Endotoxins- complex molecules made of lipid and polysaccharides found in the cell wall of gram-negative bacteria. Usually released when the cell is killed, can cause clotting, bleeding, inflammation, hypotension and fever.
Virulence factors • Adhesion factors – allow bacteria and viruses to attach to the host. – Receptor – Ligand or adhesin
Virulence factors • Evasive factors – – capsules, and slime layers evade phagocytes – Leukocidin C – Some survive and reproduce inside phagocytes – Coagulase – Enzymes that break up antibodies – Alter surface antigens during the disease course – Urea splitters raise environmental p. H
Virulence factors • Invasive Factors- products that facilitate the penetration of anatomic barriers and host tissue. These can destroy cell membranes, connective tissue, intercellular matrices, and structural protein complexes.
Viral Infection • Viruses extremely small – can infect bacteria • Usually just composed of DNA (or RNA) + protein “coat” or capsid • Can’t reproduce on their own – need to use a host cell
Infection • • Adsorbed to host cell receptor Penetration Coat removal Uses host enzymes to replicate nucleic acid and proteins • New viruses are assembled • Virus is released – Lytic cycle
Cellular effects • • • Decreased synthesis of host proteins Disruption of lysosomal membranes Changes in host cell membrane proteins Transform into cancer cell Tissue damage may promote bacterial infection
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