Infection micropaar

• Infection


  Invasion and growth of pathogens in the body
• Disease


  Abnormal state in which part or all of the body is incapable of performing normal functions
• Pathology


  The scientific study of disease, concerned with etiology (cause), pathogenesis (development), and effects of the disease
• Host


  An organism that shelters and supports the growth of pathogens
• Relationships with the host

  • Microbial antagonism: prevent pathogens from causing infection
  • Symbiosis: living together
  • Commensalism: one organism benefits, unaffected (Staphylococcus epidermidis)
  • Mutualism: both organism's benefit (E. coli)
  • Parasitism: one organism benefits and one is harmed (Influenza viruses)
• Koch's Postulates
• Syndrome


  A specific group of symptoms or signs that always accompanies a specific disease
• Communicable diseases


  Transmitted directly or indirectly from one host to another
• Contagious disease


  A very communicable disease that is capable of spreading easily and rapidly from one person to another
• Non-communicable diseases


  Caused by microorganisms that normally grow outside the human body and are not transmitted from one host to another
• Classifying infectious diseases by occurrence


  • Incidence: number of people contracting the disease
  • Prevalence: number of people with the disease in a defined population, in a specified time
• Classifying infectious diseases by severity or duration

  
• Extent of host involvement


  • Local infection affects a small area of the body
  • Systemic infection is spread throughout the body via the circulatory system
• Herd immunity


  Presence of immunity to a disease in most of the population
• Predisposing factors


  Factors that make the body more susceptible to disease or alter the course of a disease

  
• Reservoirs of infection


  • Human reservoirs: People who have a disease or are carriers of pathogenic
  • Animal reservoirs: Zoonoses are diseases that affect wild and domestic animals and can be transmitted to humans
  • Nonliving reservoirs: soil and water
• Healthcare-associated infections (HAIs)


  Infections patients acquire while receiving treatment for other conditions at a health care facility, or in-home health care environment
• Standard precautions

  • Hand hygiene
  • Use of protective equipment
  • Cough etiquette
  • Disinfection of patient-care equipment and instruments
• Transmission-based precautions

  • Contact
  • Droplet
  • Airborne
• Microbial mechanisms of pathogenicity

  • Gain access to the host
  • Adhere to host tissues
  • Penetrate or evade host defenses
  • Damage the host tissues
• Factors affecting occurrence of disease

  • The preferred portal of entry
  • Numbers of invading microbes
  • Adherence
• LD50


  Lethal dose for 50% of the inoculated hosts
• ID50


  Infectious dose for 50% of the inoculated hosts
• Adhesins


  Surface projections on a pathogen that adhere to complementary receptors on the host cells
• Biofilms


  Alternative lifestyle that provides attachment and resistance to antimicrobial agents, consisting of a matrix of polysaccharides, proteins, and nucleic acids that bind the cells together
• How bacterial pathogens penetrate host defenses

  • Capsules
  • Cell wall components
  • Enzymes
  • Antigenic variation
  • Penetration into the host
  • Biofilms
• How bacterial pathogens damage host cells

  • Using the host's nutrients
  • Causing direct damage in the immediate vicinity of the invasion
  • Producing toxins, transported by blood and lymph, that damage sites far removed from the original site of invasion
  • Inducing hypersensitivity reactions
• Siderophores


  Bacteria get iron from the host using siderophores
• Toxins


  Poisonous substances produced by microorganisms
• Toxemia


  The presence of toxins in the blood
• Toxigenicity


  The ability to produce toxins
• Exotoxins


  Produced by bacteria (inside) and released into the surrounding medium
• Toxoids


  Altered exotoxins (as vaccine, stimulates antitoxin production)
• Antitoxins


  Antibodies produced against exotoxins
• A-B toxins


  Consist of an active component that inhibits a cellular process and a binding component that attaches the two portions to the target cell
• Membrane-disrupting toxins


  Cause cell lysis by forming protein channels in the plasma membrane or disrupting the phospholipid portion of the membrane
• Hemolysins


  Destroy erythrocytes (red blood cells) by forming protein channels
• Superantigens


  Provoke the release of cytokines (produced by host T cells) that regulate immune response and mediate cell-to-cell communication, causing high levels of fever, nausea, and other symptoms
• Endotoxin


  The lipid A component of the cell wall of gram-negative bacteria that stimulates macrophages to release cytokines in very high concentrations causing fever and shock (decrease in blood pressure)
• Plasmids, lysogeny, and pathogenicity

  • Plasmids may carry genes for antibiotic resistance, toxins, capsules, and fimbriae
  • Lysogenic conversion can result in bacteria with virulence factors, such as toxins or capsules