BIOL 506 quiz 1 (ch. 1-2)

• pathogen: a bacterium, virus, or other microorganism (fungi, protozoa, worms) that can cause disease
• pathogenicity: ability of a pathogen to cause disease; represents a genetic component of pathogen and overt damage done to the host is property of host-pathogen interactions; qualitative trait
• virulence: degree of pathology caused by the organism; quantitative measure of pathogenicity (i.e. LD50, TD50, ID50)
• opportunistic pathogen: normally commensal infectious microorganism or one that does not typically harm host; can cause disease when host's resistance is low
• colonization: presence of microorganism on mucosal and body surfaces
• infection: inflammatory response to microbes or the invasion of normally sterile tissue by those organisms; not synonymous with disease
• disease: signs and symptoms of illness; consequence of presence of offending microorganism
• tools in the arsenal against bacterial infectious disease

  • hand washing
  • disinfectants
  • nutrition
  • pasteurization
  • clean drinking water
  • improved sanitation infrastructure
  • vaccines
  • antibiotics
• why are infectious diseases still commonplace?

  • aging population
  • cancer chemotherapy/organ transplant= immunosuppression
  • diabetes= immunosuppression
  • HIV AIDS
  • medical procedures
  • emergence of new strains of bacteria due to horizontal gene transfer (HGT)
  • global travel
  • human encroachment into wildlife habitats
  • food processing and distribution
  • modern conveniences (ex. airconditioning)
  • global climate change
• immunity: ability to resist disease caused by pathogen
• epithelia refers to the cell layers that covers the parts of the body exposed to external environment
• tight junctions between epithelia cells are important because they prevent microbes from crossing epithelia layer
• the lung has simple squamous epithelium
• the kidneys and gland ducts have simple cuboidal epithelium
• the skin, vagina, and cervix have stratified squamous epithelium
• the stomach and colon have simple columnar epithelium
• the small intestine, upper airway, fallopian tubes, and ear canal have ciliated columnar epithelium
• epidermis defenses

  1. keratinocytes
  2. arid environments
  3. desquamation
  4. acidic (pH 5), fatty acids
  5. sebum components
  6. temp. 34-35°C
  7. normal flora
• defense of a dry, acidic environment 


  prevents growth of many bacteria
• defense of cooler temperature than internal body temp 


  slows growth of bacteria that prefer optimal internal body temp of ~37°C
• defense of dead, keratinized cells 


  hard to degrade and penetrate, discourages colonization
• defense of sloughing of surface cells (desquamation) 


  removes bacteria that adhere to surface cells
• defense of sebum containing toxic lipids, lysozymes, and defensins


  protects hair follicles, sweat glands, and sebaceous glands by preventing bacteria growth or killing bacteria
• defense of normal microbiota 


  competes with pathogens for nutrients, colonization sites
• defense of SALT underlying immune cells comprised of phagocytic cells (Langerhan cells), T cells and B cells


  combats bacteria that manage to reach the dermis and tissue below it by initiating protective immune response
• defense of tight junctions between epithelia cells 


  prevents bacteria from crossing and gaining access to internal body tissue
• mucus is composed primarily of mucin which has glycoprotein components and is resistant to microbial proteases
• mucus is gel-like and sticky; can trap microbes
• mucus-associated antimicrobial proteins of the mucosa

  • lactoferrin
  • lactoperoxidase
  • defensins
  • lysozymes
  • phospholipase A2
  • sIgA
• lactoferrin removes iron and prevents growth of bacteria
• lactoperoxidase uses hydrogen peroxide to oxidize thiocyanite (SCN-) into hypothiolcyanite (OSCN-), which attacks thiol groups on bacterial proteins; most abundant in oral cavity and lung secretion
• lysozymes digest peptidoglycan and lyses growing bacteria; found in mucus, tears, saliva, and milk
• sIgA (secreted IgA) are glycosylated protein complexes that bind and coat bacterial surfaces and mucin, traps bacteria in mucus that is sloughed off
• protectants in mucin include lysozymes, sIgA, lactoferrin, and phospholipase A2
• phospholipase A2 digests bacterial cytoplasmic membrane
• defensins are amphipathic, antimicrobial, cationic proteins that disrupts bacterial cell integrity by inserting and forming pores
• lysozymes hydrolyze the B-1,4 glycosidic bond between NAM and NAG (components of peptidoglycan)
• due to their cationic nature, lysozymes are also able to insert into bacterial membranes and form pores
• mucosa-associated lymphoid tissue (MALT) are the immune cells underlying mucosal surfaces or extrude between epithelial cells; includes T cells, B cells, M cells, and phagocytic cells like macrophages and dendritic cells
• T cells recognize antigen bound APCs and regulate immune system