Transcript Cellular Biology

Infection
Chapter 9
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Microorganism/Human
Relationship
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Mutual relationship
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Normal flora
Relationship can be breached by injury
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Leave their normal sites and cause infection elsewhere
Opportunistic microorganisms
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Stages of Infection
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Colonization
Invasion
Multiplication
Spread
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Factors for Infection
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Mechanism of action
Infectivity
Pathogenicity
Virulence
Immunogenicity
Toxigenicity
Portal of entry
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Classes of Infectious Microorganisms
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Virus
Chlamydia
Rickettsia
Mycoplasma
Bacteria
Fungi
Protozoa
Helminths
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Pathogen Defense Mechanisms
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Surface coats
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Inhibit phagocytosis, surface receptors to bind
host cells, and toxins
Antigenic variation
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Mutation
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Recombination
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Antigenic drift
Antigenic shifts
Gene switching
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Bacterial Virulence and Infectivity
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Bacteria must have iron to multiply
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Siderophores (iron receptors)
Presence of polysaccharide capsules
Suppression of complement activation
Bacterial proliferation rates can surpass
protective response
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Bacterial Virulence and Infectivity
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Toxin production
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Exotoxins
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Enzymes released during growth causing specific
responses
Immunogenic
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Antitoxin production
Endotoxins
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Lipopolysaccharides contained in the cell walls of
gram-negative organisms
Pyrogenic effects
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Toxin Production
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Bacterial Virulence and Infectivity
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Bacteremia or septicemia
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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
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Viral Infection and Injury
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Obligate intracellular parasites
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Dependent on host cells
No metabolism or incapable of independent
reproduction
Permissive host cell
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Virion binds to receptors on the plasma membrane
Usually a self-limiting infection
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Spreads cell to cell
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Viral Replication
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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
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Viral Replication
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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
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Viral Replication
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Cellular Effects of Viruses
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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
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Fungal Infection and Injury
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Large microorganisms with thick cell walls
Eukaryotes
Exist as single-celled yeasts, multicelled
molds, or both
Pathogenicity
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Adapt to host environment
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Wide temperature variations, digest keratin, low
oxygen
Suppress the immune defenses
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Fungal Infection and Injury
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Diseases caused by fungi are called mycoses
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Superficial, deep, or opportunistic
Fungi that invade the skin, hair, or nails are
known as dermatophytes
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The diseases they produce are called tineas
(ringworm)
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Tinea capitis, tinea pedis, and tinea cruris
Deep fungal infections are life threatening and
are commonly opportunistic
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Fungal Infection and Injury
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Clinical Manifestations of
Infectious Disease
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Variable depending on the pathogen
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Directly caused by the pathogen or indirectly
caused by its products
Fever
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Resetting the hypothalamus
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Exogenous pyrogens
Endogenous pyrogens
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Countermeasures
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Vaccines
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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
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Countermeasures
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Antimicrobials
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Inhibit synthesis of cell wall
Damage cytoplasmic membrane
Alter metabolism of nucleic acid
Inhibit protein synthesis
Modify energy metabolism
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Pathogenic Adaptations
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Suppression of immune response
Antigenic changes
Development of resistance
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