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DISEASE TRIAD
PATHOGEN ENVIRONMENT Microbial Interactions
OTHER MICROBES
REVIEW
ACQUIRING INFECTIOUS AGENTS
PORTAL OF ENTRY/EXIT INGESTION INHALATION
DIRECT PENETRATION
Trauma or Surgical Procedure Needlestick
Arthropod Bite Sexual Transmission Transplacental
REVIEW
PATHOGENICITY vs. VIRULENCE
PATHOGENICITY: the quality of producing disease or the ability to produce pathologic changes or disease
VIRULENCE: a measure of pathogenicity; a measurement of the degree of disease-producing ability of a microorganism as indicated by the severity of the disease produced; commonly ascertained by measuring the dosage required to caused a specific degree of pathogenicity; one general standard is the LD50 (lethal dose 50%)
REVIEW
INFECTION vs. DISEASE
INFECTION: the colonization and/or invasion and multiplication of pathogenic microrganisms in the host with or without the manifestation of disease
DISEASE: an abnormal condition of body function(s) or structure that is considered to be harmful to the affected individual (host); any deviation from or interruption of the normal structure or function of any part, organ, or system of the body
REVIEW
KOCH'S POSTULATES
Four criteria that were established by Robert Koch to identify the causative agent of a particular disease, these include:
1.the microorganism (pathogen) must be present in all cases of the disease
2.the pathogen can be isolated from the diseased host and grown in pure culture
3.the pathogen from the pure culture must cause the same disease when inoculated into a healthy,
susceptible laboratory animal
4. the pathogen must be reisolated from the new host and shown to be the same as the originally inoculated pathogen REVIEW
Bacterial Virulence Mechanisms
Adherence (Colonization) Invasion
Degradative enzymes Exotoxins
Endotoxin
Induction of excess inflammation
Evasion of phagocytic & immune clearance Byproducts of growth (gas, acid) Superantigen
Resistance to antibiotics
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BASIC EFFECTS of ENDOTOXIN
FEVER: any elevation of body temperature above normal
LEUKOPENIA/LEUKOCYTOSIS: abnormal reduction in number of leukocytes in blood, (<5000/mm3) / abnormally large number of leukocytes in blood, as during hemorrhage, infection, inflammation, or fever (>12,000mm3)
METABOLIC EFFECTS : pathogenic organisms can affect any of the body systems with disruptions in metabolic processes, e.g.,hypotension, hypoglycemia, etc.
RELEASE OF LYMPHOCYTE FACTORS: agranular leukocyte concentrated in lymphoid tissue; active in immunological responses, including production of antibodies
CELLULAR DEATH:
SEPTIC SHOCK: associated with overwhelming infection resulting in vascular system failure with sequestration of large volumes of blood in capillaries and veins; activation of the complement and kinin systems and the release of histamines,
prostaglandins, and other mediators may be involved
DISSEMINATED INTRAVASCULAR COAGULATION (DIC): disorder
characterized by a reduction in the elements involved in blood coagulation due to their utilization in widespread blood clotting within the vessels; late stages marked by profuse hemorrhaging
ORGAN NECROSIS: the sum of morphological changes indicative of cell death
and caused by the progressive degradative action of enzymes
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EXOTOXINS
TWO-COMPONENT (BIPARTITE) A-B TOXINS with INTRACELLULAR TARGETS: conform to
general structural model; usually one component is a binding domain (B subunit) associated with absorption to target cell surface and transfer of active component across cell membrane, the second component is an enzymatic or active domain (A subunit) that enzymatically disrupts cell function
BACTERIAL CYTOLYSINS (a.k.a. Cytotoxins) with CELL MEMBRANE TARGETS: hemolysis, tissue
necrosis, may be lethal when administered intravenously
REVIEW
BACTERIAL CYTOLYSINS
with
CELL MEMBRANE TARGETS
Three Major Types:
1.Hydrolyze membrane phospholipids (phospholipases); e.g., Clostridium, Staphylococcus
2.Thiol-activated cytolysins (oxygen-labile) alter membrane
permeability by binding to cholesterol; e.g., Streptococcus, Clostridium
3. Detergent-like activity on cell membranes; e.g.,
Staphylococcus, rapid rate of lysis
REVIEW