Basic concepts of microbial pathogenicity

• Describe how microbial infections remain a leading cause of death

  • Increasing antibiotic and drug resistance
  • Emerging and re-emerging infectious diseases
  • Large outbreaks of food and water borne infections due to globalisation
  • Hospital acquired (nosocomial) infections
  • Microbiota shift disease- opportunistic microbes
  • Bioterrorism- use of infectious agents as weapons of terrorism
• What are the 3 classes of emerging/re-emerging infectious disease?

  Class I: diseases caused by previously unidentified microbes that have only recently entered the human population, such as Covid-19

  Class II: known diseases with only recently identified microbial cause, such as gastroenteritis and campylobacter jejenum

  Class III: old diseases that have re-emerged due to favourable conditions, such as re-emergence of tuberculosis as a result of HIV, which increased the number of immunocompromised people.
• Describe the 4 commandments of Koch’s postulates

  1. The microbe must be associated with symptoms of the disease and be present at the site of infection
  2. The microbe must be isolated from disease lesions and grown as a pure culture
  3. Cultured microbe should reproduce the disease when inoculated into a susceptible healthy host
  4. The microbe must be re-isolated from the inoculated host
  5. Proposed 5th: knowledge of the microbe should enable effective therapeutic or preventative measures
• Describe the issues with the 4 commandments of Koch’s postulates

  • 1: opportunistic microbes can cause infection in some individuals and not others so will not always associated with disease symptoms
  • 2: many microbes cannot be cultured, such as the organism that causes syphilis (treponema pallidum)
  • 3: ethics of inoculating a human with a disease causing pathogen
• Define pathogenicity islands

  These are DNA segments containing clusters of genes involved in pathogenesis
• What are the two major modes of transmission?

  • Direct contact
  • Indirect contact: inhalation of airborne droplets, ingestion of contaminated food or water, via animals or insects.
• Define true and opportunistic pathogens

  True pathogens tend to produce disease readily in healthy hosts whereas opportunistic pathogens generally only cause a disease in immunocompromised host or when a particular microbe enters an unusual site in a host.