dr d

• Factors that make someone more susceptible to infection

  • Age (very young or very old)
  • Genetic defects
  • Pregnancy
  • Surgery
  • Organ transplants
  • Other underlying diseases
  • Chemotherapy
  • Immunosuppressive drugs
  • Stress
  • Fatigue
• Endogenous infection


  An infection caused by the normal microbiota getting introduced into a previously sterile site
• How we get our normal microbiota


  1. Fetus is relatively germ-free

  2. Exposed to mother's vaginal biota during birth

  3. Can also gain microbes from breast milk
• Pathogen


  A germ or microbe whose relationship with the host is parasitic, resulting in an infection
• True pathogen


  A pathogen capable of causing disease in healthy persons with normal immune systems
• Opportunistic pathogen


  A pathogen that can cause disease if the host's defenses are compromised
• Virulence


  The degree of pathogenicity, or the capability of a microorganism to cause disease
• Virulence factors


  Any characteristic or structure of a microbe that helps it cause disease
• Infectious dose (ID)


  The minimum number of microbes required for an infection to proceed
• More pathogenic microbes tend to have a lower infectious dose
• How microbes cause disease in a host


  1. Find a portal of entry into the host

  2. Attach to host tissues

  3. Survive host defenses

  4. Damage host tissues

  5. Exit the host to spread
• For an infection to lead to disease


  The pathogen must damage the host
• How pathogens can damage the host


  1. Release enzymes

  2. Release toxins

  3. Cause a massive allergic reaction

  4. Cause epigenetic changes in the host's chromosome
• Portals of exit for pathogens


  • Respiratory means (coughing, sneezing, spitting)
  • Fecal matter
  • Blood
  • Urogenital tracts
  • Skin cells
• All mechanisms that help a pathogen cause disease are called virulence factors
• Host barriers against microbes


  • Respiratory tract (cilia to beat debris out)
  • Stomach acid
  • Skin
  • Eyes (flushing)
  • Ear wax
• TORCH


  Toxoplasmosis, Other diseases, Rubella, Cytomegalovirus, Herpes simplex virus - common infections of the fetus and neonate
• Adhesion is very important for the disease process
• Microbial adhesion mechanisms


  • E. coli - fimbriae
  • Pseudomonas - slime layer
  • Influenza virus - viral spike proteins
• Virulence factors


  Anything that can help a pathogen cause disease
• Antiphagocytic factors


  Factors that prevent the microorganism from getting phagocytosed or allow it to survive inside the phagocyte
• Asymptomatic carrier


  Infected but not showing disease
• How pathogens can cause disease


  1. Secrete enzymes or toxins to damage host tissues

  2. Trigger an overreaction of the host's immune system
• Diseases with multiple stages

  • Syphilis - primary, secondary, tertiary
• Tissue-degrading enzymes


  • Mucinase
  • Caseinase
  • Hyaluronidase
• Enzymes that degrade the connections between cells allow pathogens to penetrate tissues
• Exoenzymes


  Enzymes secreted into the environment by pathogens
• Hemolysins


  Enzymes that cause red blood cells to be destroyed
• Toxins


  Chemicals produced by microbes that are hazardous and cause cell damage
• Endotoxin


  Lipid A component of the outer membrane of gram-negative bacteria
• Exotoxin


  Protein toxin secreted by microbes
• Exotoxins are heat-labile and can be destroyed by heat, but endotoxins are heat-stable
• Exotoxins are antigenic and easily recognized by the immune system
• Exotoxins are proteins that can be destroyed by cooking food thoroughly
• Endotoxins are lipids that cannot be destroyed by cooking and remain toxic even after cooking
• Antigenic


  Elicits an immune response
• Many vaccines are just a protein, like the tetanus vaccine which is the denatured tetanus toxin protein
• The COVID vaccine is just the spike protein, not the entire virus
• Endotoxin


  A lipid that does not elicit a strong immune response
• Exotoxins are more antigenic than endotoxins and lead to production of antibodies