Transcript Hypersensitivities/ Infections

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 pH
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
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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
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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