Pathogenicity

• Infection


  The invasion or colonization of the body by pathogenic microorganisms
• Infection


  The presence of a particular type of microorganism in a part of the body where it is not normally found and may lead to disease
• Urinary Tract Infection (UTI)

  • Infection of the urinary tract with E. coli usually results in what disease
• Disease


  Occurs when an infection results in any change from a state of health
• Disease


  An abnormal state in which part or all of the body is incapable of performing its normal functions
• Pathogenicity


  The ability to cause disease by overcoming host defenses
• Virulence


  The degree of pathogenicity
• 
  

  1. Gain access to the host

  2. Adhere to host tissues

  3. Penetrate or evade host defenses

  4. Damage the host tissues

  To cause disease, most pathogens must
• Portals of Entry for Pathogens

  • Mucous membranes
  • Skin
  • Direct deposition beneath the skin or membranes (the parenteral route)
• Mucous Membranes


  • Many bacteria and viruses gain access to the body by penetrating the ------------------- lining the respiratory tract, gastrointestinal tract, genitourinary tract, and conjunctiva
• Conjunctiva


  • It is a portal of entry which causes the Conjunctivitis, Trachoma, and Ophthalmia neonatorumthat
• Skin

  • It is a portal of entry where some microbes gain access to the body through openings in the ----, such as hair follicles and sweat gland ducts
  • Some fungi grow on the keratin in the ---- or infect the ---- itself
• Parenteral Route


  Portal of entry for pathogens by deposition directly into tissues beneath the skin and mucous membranes when these barriers are penetrated or injured
• Parenteral Route


  • Punctures
  • Injections
  • Bites
  • Cuts
  • Wounds
  • Surgery
  • Splitting of the skin or mucous membrane due to swelling or drying
• Adherence


  Attachment of a microbe or phagocyte to another's plasma membrane or other surface. It is important part of pathogenecity
• Adhesin


  • Also called a ligand
  • A carbohydrate-specific binding protein that projects from prokaryotic cells
  • Binds specifically to complementary surface receptors on the cells of certain host tissues
  • Used for adherence
  • May be located on a microbe's glycocalyx or on other microbial surface structures, such as pili, fimbriae, and flagella
• biofilms

  • Microbes have the ability to come together in masses, cling to surfaces, and take in and share available nutrients in communities called --------
• Treponema pallidum

  • the causative agent of syphilis, uses its tapered end as a hook to attach to host cells
• Listeria monocytogenes

  • causes meningitis, spontaneous abortions, and stillbirths, produces an adhesin for a specific receptor on host cells
• Neisseria gonorrhoeae

  • the causative agent of gonorrhea, has fimbriae containing adhesins that permit attachment to cells with appropriate receptors in the genitourinary tract, eyes, and pharynx
• Staphylococcus aureus

  • which can cause skin infections, produces adhesins that bind to laminin and fibronectin on skin cells
• phagocytosis

  • Capsules resist the host's defenses by impairing ------------, the process by which certain cells of the body engulf and destroy microbes
• M protein

  • Cell wall components can contribute to virulence, such as the ------ produced by Streptococcus pyogenes that mediates attachment to epithelial cells and helps resist phagocytosis
• Opa

  • Neisseria gonorrhoeae grows inside human epithelial cells and leukocytes using fimbriae and an outer membrane protein called --- to attach to host cells
• How Bacterial Pathogens Penetrate Host Defenses

  • The waxy lipid (mycolic acid) in the cell wall of Mycobacterium tuberculosis increases virulence by resisting digestion by phagocytes, allowing the bacteria to multiply inside phagocytes

  
• How Bacterial Pathogens Penetrate Host Defenses

  • Extracellular enzymes (exoenzymes) and related substances produced by some bacteria can digest materials between cells and form or digest blood clots, aiding virulence

  
• How Bacterial Pathogens Penetrate Host Defenses

  • Coagulases are bacterial enzymes that coagulate (clot) the fibrinogen in blood, forming a fibrin clot that may protect the bacterium from phagocytosis and isolate it from other defenses

  
• How Bacterial Pathogens Penetrate Host Defenses

  • Fibrinolysin (streptokinase) is a bacterial kinase that breaks down fibrin and digests clots formed by the body to isolate the infection

  
• How Bacterial Pathogens Penetrate Host Defenses

  • Hyaluronidase is an enzyme secreted by certain bacteria that hydrolyzes hyaluronic acid, a type of polysaccharide that holds together certain cells of the body

  
• How Bacterial Pathogens Penetrate Host Defenses

  • Collagenase, produced by several species of Clostridium, breaks down the protein collagen, which forms the connective tissue of muscles and other body organs and tissue, facilitating the spread of gas gangrene

  
• How Bacterial Pathogens Penetrate Host Defenses

  • Some pathogens produce enzymes called IgA proteases that can destroy the IgA antibodies the body produces as a defense against adherence to mucosal surfaces

  
• Antigenic Variation


  Changes in surface antigens that occur in a microbial population
• Antigenic Variation


  By the time the body mounts an immune response against a pathogen, the pathogen has already altered its antigens and is unaffected by the antibodies
• Microbes Capable of Antigenic Variation

  • Influenza virus
  • Neisseria gonorrhoeae
  • Trypanosoma brucei gambiense

  
• Penetration into the Host

  When microbes attach to host cells by adhesins, the interaction triggers signals in the host cell that activate factors that can result in the entrance of some bacteria

  
• Antigens


  Substances that can trigger an immune response, leading to the production of antibodies
• Antibodies


  Proteins produced by the body in response to antigens, which bind to and inactivate or target the antigens for destruction
• By the time the body mounts an immune response against a pathogen, the pathogen has already altered its antigens and is unaffected by the antibodies
• Microbes capable of antigenic variation

  • Influenza virus
  • Neisseria gonorrhoeae
  • Trypanosoma brucei gambiense

  
• How bacterial pathogens penetrate host defenses

  1. Attachment to host cells via adhesins

  2. Activation of host cell signals

  3. Entrance into host cells facilitated by host cell cytoskeleton