Microbial Pathogenicity & Asepsis

• Disease


  Any condition in which the normal structure or functions of the body are damaged or impaired
• Infection


  The successful colonization of a host by a microorganism
• Pathogen


  Microorganisms that can cause disease
• Signs of disease


  Objective and measurable, can be directly observed by a clinician
• Vital signs


  • Body Temperature (normally 37 °C [98.6 °F])
  • Heart Rate (normally 60–100 beats per minute)
  • Breathing Rate (normally 12–18 breaths per minute)
  • Blood Pressure (normally between 90/60 and 120/80 mm Hg)
• Syndrome


  A specific group of signs and symptoms characteristic of a particular disease
• Asymptomatic/Subclinical


  Diseases that do not present any noticeable signs or symptoms
• Infectious disease


  Any disease caused by the direct effect of a pathogen
• Communicable disease


  Diseases capable of being spread from person to person through either direct or indirect mechanisms
• Contagious disease


  Diseases that are easily spread from person to person
• Iatrogenic disease


  Diseases that are contracted as the result of a medical procedure
• Zoonotic disease


  Transmission of diseases from animals to humans
• Non-communicable infectious disease


  Diseases that are not spread from one person to another
• Types of noninfectious diseases

  • Inherited
  • Congenital
  • Degenerative
  • Nutritional deficiency
  • Endocrine
  • Neoplastic
  • Idiopathic
• Incubation period


  The time after the initial entry of the pathogen into the host when the pathogen begins multiplying, but there are insufficient numbers to cause signs and symptoms
• Factors involved in determining the length of the incubation period are diverse: strength of the pathogen, strength of the host immune defenses, site of infection, type of infection, size infectious dose received
• Acute disease


  Pathologic changes occur over a relatively short time (e.g., hours, days, or a few weeks) and involve a rapid onset of disease conditions
• Chronic disease


  Pathologic changes can occur over longer time spans (e.g., months, years, or a lifetime)
• Acute disease


  Disease condition with an incubation period of approximately 1–2 days, where infected individuals can spread the disease to others for approximately 5 days after becoming ill, after which individuals enter the period of decline
• Chronic disease


  Disease condition where pathologic changes can occur over longer time spans (e.g., months, years, or a lifetime)
• Acute disease


  • Influenza (caused by Influenzavirus)
• Chronic disease


  • Chronic gastritis (inflammation of the lining of the stomach) caused by the gram-negative bacterium Helicobacter pylori
• Latent disease


  Disease condition where the causal pathogen goes dormant for extended periods of time with no active replication
• Latent diseases


  • Herpes (herpes simplex viruses [HSV-1 and HSV-2]), chickenpox (varicella-zoster virus [VZV]), and mononucleosis (Epstein-Barr virus [EBV])
• Pathogenicity


  The ability of a microbial agent to cause disease
• Virulence


  The degree to which an organism is pathogenic
• Highly virulent pathogens


  Will almost always lead to a disease state when introduced to the body, and some may even cause multi-organ and body system failure in healthy individuals
• Less virulent pathogens


  May cause an initial infection, but may not always cause severe illness, and would more likely result in mild signs and symptoms of disease, such as low-grade fever, headache, or muscle aches
• Median infectious dose (ID50)

  The number of pathogen cells or virions required to cause active infection in 50% of inoculated animals
• Median lethal dose (LD50)

  The number of pathogenic cells, virions, or amount of toxin required to kill 50% of infected animals
• Primary pathogens


  Can cause disease in a host regardless of the host's resident microbiota or immune system
• Opportunistic pathogens


  Can only cause disease in situations that compromise the host's defenses, such as the body's protective barriers, immune system, or normal microbiota
• Primary pathogens


  • Enterohemmoragic E.Coli - which produces a virulence factor known as Shiga toxin
• Opportunistic pathogens


  • Candida species, Staphylococcus epidermis
• Stages of pathogenesis


  1. Exposure (contact)

  2. Adhesion (colonization)

  3. Invasion

  4. Infection
• Exposure (contact)


  An encounter with a potential pathogen
• Portal of entry


  An anatomic site through which pathogens can pass into host tissue
• Parenteral route


  Pathogens entering the body through a breach in the protective barriers of the skin and mucous membranes
• Adhesion


  The capability of pathogenic microbes to attach to the cells of the body using adhesion factors
• Adhesins


  Molecules (either proteins or carbohydrates) found on the surface of certain pathogens that bind to specific receptors (glycoproteins) on host cells