chap6-7

• Five Kingdom Classification (Robert Whittaker)

  • Animalia
  • Plantae
  • Protista: single celled eukaryotes (algae, amoeba, euglena, paramecium slime moulds, plasmodium. Protozoans)
  • Fungi: fungus-like and related eukaryotic organisms (yeast, molds, mushrooms)
  • Monera (Prokaryotes)
• Microorganisms are found in the soil, in the water, and on plants and animals. Billions are found in humans on the skin and in both the nasal and intestinal tracts
• Although most microorganisms live in harmony with the human body, some—called pathogens—can infect the body and cause disease. Infectious diseases range from mild illnesses, such as a cold, to fatal illnesses, such as AIDS
• We occasionally encounter people or animals that are infected and thus expose ourselves to the pathogens of their diseases. In fact, our environment is such that everyday we live with some risk of exposure to diseases
• Infection Disease Process


  The interaction between the pathogenic microorganism, the environment, and the host

  
• Six Links of Infection Process

  • Pathogen / Microorganism
  • Reservoir
  • Portal of Exit
  • Mode of Transmission
  • Portal of Entry
  • Susceptible Host

  
• Pathogen / Microorganism


  The first link in the chain of infection, can take the form of viruses, bacteria, fungi, parasitic protozoan diseases, or prions

  
• Pathogen


  • Pathogenicity - ability to produce disease
  • Degree of virulence - severity or harmfulness
  • Invasiveness - tendency to spread

  
• Reservoir


  The principal habitat in which a pathogen lives, flourishes and can multiply. Can be human, animal, insect or environmental
• Types of Human Reservoirs

  • Acute clinical cases
  • Carriers (incubatory, inapparent, convalescent, chronic)
• Any infectious disease that is transmitted under natural conditions from animal to human is referred to as zoonosis
• Portal of Exit


  Any route which enables a pathogen to leave the reservoir or host, such as alimentary, genitourinary, respiratory, skin, or trans-placental
• Mode of Transmission


  Direct transmission (direct contact) or indirect transmission (via animate or inanimate mechanisms, or airborne)
• Portal of Entry


  The means by which an infection is able to enter a susceptible host, such as inhalation, absorption, ingestion, inoculation, or introduction
• Susceptible Host


  The last link in the chain of infection, depends on factors like age, malnutrition, underlying disease, immobility, medication, and general resistance factors

  
• The healthcare environment can expose patients to infection risks that they may not encounter elsewhere
• There are opportunities to break or disrupt the chain of infection at any link
• Ways to break the chain of infection include cleaning hands frequently, staying up to date on vaccines, covering coughs and sneezes, staying home when sick, following isolation rules, using PPE properly, and cleaning/disinfecting the environment
• Pathogenicity


  The capability of a microorganism to cause a disease in a host; an innate property

  
• Virulence


  The quantity of pathogenicity of a microbe or a measure of the ability of the microbe to cause disease, determined by invasiveness and toxigenicity

  
• Adhesion Factor


  Specific virulence factors that enhance the ability of a microorganism to attach to the surface of mammalian cells
• Invasiveness


  The ability of microorganism to invade human tissues and to reproduce or multiply within the cells and tissues of the human body
• Growth and Survival Enhancing Factors

  The ability of bacteria to grow within the blood of the host by utilizing available iron
• Infective Dose


  The amount or quantity of microorganisms required to produce disease symptoms in a host

  
• Toxigenicity


  The ability of a microorganism to produce toxins
• Types of Toxins


  • Endotoxin (lipopolysaccharide component of gram-negative bacterial cell wall)
  • Exotoxins (protein toxins produced from various gram-negative and gram-positive pathogenic bacteria)
  • Neurotoxins (protein exotoxins that interfere with nervous system function)
  • Enterotoxins (stimulate gastrointestinal tract cells abnormally)
  • Cytotoxins (protein exotoxins that kill cells by enzymatic attack or blocking essential cellular metabolism)
• ENDOTOXIN


  Equated with the lipopolysaccharide component of gram-negative bacterial cell wall. When gram-negative bacteria die, their cell walls disintegrate and LPS endotoxin is released.
• EXOTOXINS


  Protein toxins produced from various gram-negative and gram-positive pathogenic bacteria; released by growing cells.
• NEUROTOXIN


  Protein exotoxins that interfere the functioning of the nervous system; usually work by blocking nerve cell transmissions.
• ENTEROTOXINS


  Stimulate the cells of the gastrointestinal tract in an abnormal way, which then causes inflammation of the tissues.
• CYTOTOXIN


  Protein exotoxins that kill cells by enzymatic attack or by blocking essential cellular metabolism; interfere with cellular functions (E.g. Hemolysin – lipids and proteins that causes lysis of red blood cells by disrupting the cell membrane, extremely common in E. coli infections.)
• Economic, medical and social factors, genetics or individual lifestyle choices can contribute to tipping the balance for or against microbial initiation of disease in a particular individual.
• Virtually any microorganism can cause disease under the right set of conditions.
• An infectious disease is as much the result of the failure of the human defense as it is the result of the special properties of pathogenic microorganisms.
• INFECTIOUS DOSE


  Number of pathogens needed to establish a disease. Factors that influence the infectious dose that is required to initiate a disease, including the route of entry of the pathogen and the state of the host defenses.

  
• Factors that weaken defenses of a Compromised Host

  • Malnutrition
  • Disease
  • Chemotherapy
  • Burns
  • Broken skin or mucous membrane
  • Suppressed immune system
  • Impaired cell activity
• Predisposing Factors


  • Gender
  • Genetic
  • Environment: Climate, weather, nutrition, lifestyle, age, fatigue, occupation, pre-existing illnesses or conditions and medications
• Disease Condition


  A state in which the body does not function normally
• Many microorganisms live on the surfaces of body tissues without causing disease. Such microorganisms constitute the so-called normal microbiota.
• The normal microbiota contribute to the body's defenses by competing with and wading off potentially invasive pathogens.