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Pathogen
- Can cause disease in a susceptible host
- yersinia pestis, bacilus anthracis
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Opportunistic pathogens
- Can cause disease only if a significant change occurs in host resistance
- Can be part of normal flora
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Latrogenic infection
- Result of mediical treatment
- Catheter,antibiotics,immunosuppressive drugs
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Virulence
Relative ability of a microorganism to cause disease or degree of pathogenicity
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Virulance is measured by?
The number of microorganisms neccessary to cause infection in the host
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FDoes virulance correlate with disease?
Not neccessarily
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Virulance factors
Capsules, toxins, enzymes, cell wall receptors, pili
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The bodies defense mechanisms and barriers are
- Skin
- Mucus
- Ciliated epithelial cells
- Secretions containing antibacterial substances
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Specialized cells of mucous membrane are
- Mucosal cells
- Goblet cells
- Mucosa-associated lymphoid tissue
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Function of mucus is
- Trap bacteria before it reaches the outer surface of the cells
- Lubricates the cells preventing damage
- Contains numerous specific and nonspecific antibacterial substances
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Location of ucosa-associated lymphoid tissue
Below the outer cell layer
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Function of mucosa-associated lymphoid tissue
Mediates specific responces against bacteria that penetrate the outer layer
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Different types of host resistant factors
- Physical barriers
- Cleansing mechanisms
- Antimicrobil substances
- Indigenous microbial flora
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Forms of cleansing mechanisms
- Cell shedding
- fluid in eye, respiratory,digestive,urinary,genital tracts
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OForms of antimicrobial substances
- HCI in stomach
- Secretory IgA/antibodies
- Lysozyme
- B-lysins
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Adhesins def.
Bind specific receptors on the tissue surface, which keeps them from being washed away
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Adherins are present
At the tis of fimbrae and bind tightly to specific carbohydrates on the target tissues
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Biofilm
- Special bac. adaptation that facilitates colonization
- Often occur in sergical appliances (artificial valves,indwelling catheters)
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Toxins def
Bacterial prducts that directly harm tissue or trigger destructive biologival activity
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Endotoxin
- Part cell wall
- Gram-postitive
- Damaging response mediated by host immune system
- Lipid A portion of LPS is released and acts as a direct endotoxin
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Exotoxins
- Gram-positive & gram-negative
- Include cytolyic enzymes and receptor binding proteins that alterfunction or kill cell
- A-B toxis
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Superantigens
- Endotoxins
- Activate T cells by binding to T-cell receptor and MHC mlc. at the same time
- Does not require antigen
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Superantigens can trigger
Life-threating autoimmune-like responses
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Different infectious agent factors are
- Adherence
- Proliferation
- Tissue damage
- Invasion
- Dissemination
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Adherence
- Infectious agent factor
- In most diseases bacteria must adhere to host cell to initate infection
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Proliferation
- Infectous agent factor
- Bacteria have to overcome host factors- IgA protease, capsules
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Tissue damage
- Infectious agent factor
- Exotoxins or endotoxins
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Invasion
- Infectious agent factors
- Penetrating and growing in tissues
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Dissemination
- Infectious agent factors
- Spread of organisms to distant sites via blood or lymph
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Capsules are made of
- Polysaccharides (poor immunogens)
- or
- Substances that mimic human tissues, no immune response is induced
- slimmy texture makes hard grasp by phagocytes
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Bacteria can evade antibody rsponses by
- Intracellular growth
- Antigentic variation
- Inactivation of antibody or complement
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host resitance factors are
- phagocytosis
- Inflamation
- immune responces
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phagocytosis consists of what kind of material
polymorphonuclear nut
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