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Understanding Microorganisms: Infection Dynamics and Defense Mechanisms

Explore the symbiotic relationship between microorganisms and the human body, the stages of infection, factors influencing infection, classes of infectious microorganisms, pathogen defense mechanisms, viral and bacterial virulence, toxin production, viral replication, cellular effects, fungal infections, clinical manifestations of diseases, and countermeasures to combat infections.

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Understanding Microorganisms: Infection Dynamics and Defense Mechanisms

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  1. Infection Chapter 9

  2. Microorganism/Human Relationship • Mutual relationship • Normal flora • Relationship can be breached by injury • Leave their normal sites and cause infection elsewhere • Opportunistic microorganisms

  3. Stages of Infection • Colonization • Invasion • Multiplication • Spread

  4. Factors for Infection • Mechanism of action • Infectivity • Pathogenicity • Virulence • Immunogenicity • Toxigenicity • Portal of entry

  5. Classes of Infectious Microorganisms • Virus • Chlamydia • Rickettsia • Mycoplasma • Bacteria • Fungi • Protozoa • Helminths

  6. Pathogen Defense Mechanisms • Surface coats • Inhibit phagocytosis, surface receptors to bind host cells, and toxins • Antigenic variation • Mutation • Antigenic drift • Recombination • Antigenic shifts • Gene switching

  7. Bacterial Virulence and Infectivity • Bacteria must have iron to multiply • Siderophores (iron receptors) • Presence of polysaccharide capsules • Suppression of complement activation • Bacterial proliferation rates can surpass protective response

  8. Bacterial Virulence and Infectivity • Toxin production • Exotoxins • Enzymes released during growth causing specific responses • Immunogenic • Antitoxin production • Endotoxins • Lipopolysaccharides contained in the cell walls of gram-negative organisms • Pyrogenic effects

  9. Toxin Production

  10. Bacterial Virulence and Infectivity • Bacteremia or septicemia • Presence of bacteria in the blood due to a failure of the body’s defense mechanisms • Usually caused by gram-negative bacteria • Toxins released in the blood cause the release of vasoactive peptides and cytokines that produce widespread vasodilation

  11. Viral Infection and Injury • Obligate intracellular parasites • Dependent on host cells • No metabolism or incapable of independent reproduction • Permissive host cell • Virion binds to receptors on the plasma membrane • Usually a self-limiting infection • Spreads cell to cell

  12. Viral Replication • DNA or RNA • Single or double stranded • Protein receptor–binding site • Virus uncoats • Most RNA viruses directly produce mRNA • DNA “provirus” enters nucleus is are transcribed into mRNA

  13. Viral Replication • Translation of mRNA results in the production of viral proteins • New virions are released through budding • Viral DNA that is integrated in host cell DNA is transmitted to daughter cells by mitosis

  14. Viral Replication

  15. Cellular Effects of Viruses • Inhibition of host cell DNA, RNA, or protein synthesis • Disruption of lysosomal membranes • Promotion of apoptosis • Fusion of infected, adjacent host cells • Alteration of antigenic properties • Transformation of host cells into cancerous cells • Promotion of secondary bacterial infections

  16. Fungal Infection and Injury • Large microorganisms with thick cell walls • Eukaryotes • Exist as single-celled yeasts, multicelled molds, or both • Pathogenicity • Adapt to host environment • Wide temperature variations, digest keratin, low oxygen • Suppress the immune defenses

  17. Fungal Infection and Injury • Diseases caused by fungi are called mycoses • Superficial, deep, or opportunistic • Fungi that invade the skin, hair, or nails are known as dermatophytes • The diseases they produce are called tineas (ringworm) • Tinea capitis, tinea pedis, and tinea cruris • Deep fungal infections are life threatening and are commonly opportunistic

  18. Fungal Infection and Injury

  19. Clinical Manifestations of Infectious Disease • Variable depending on the pathogen • Directly caused by the pathogen or indirectly caused by its products • Fever • Resetting the hypothalamus • Exogenous pyrogens • Endogenous pyrogens

  20. Countermeasures • Vaccines • Induction of long-lasting protective immune responses that will not result in disease in a healthy recipient • Attenuated organism • Killed organisms • Recombinant viral protein • Bacterial antigens • Toxins

  21. Countermeasures • Antimicrobials • Inhibit synthesis of cell wall • Damage cytoplasmic membrane • Alter metabolism of nucleic acid • Inhibit protein synthesis • Modify energy metabolism

  22. Pathogenic Adaptations • Suppression of immune response • Antigenic changes • Development of resistance

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