Biofilms & Polymicrobial Infections I

• What is a classical infection?

  One caused by a single organism which is of exogenous source i.e. not part of normal flora such asBacillus anthracis

  
• What are polymicrobial infections?

  An infection associated with more than 1 microbe and because no single organism is specifically associated with the disease state, it makes it impossible to apply Koch's postulates

  
• What can cause poymicrobial infections?

  Either:

  A mixture of 1 type of microorganism e.g. different species of bacteria

  
  

  Combinations of different types of microorganism e.g. bacteria & viruses, bacteria & protozoa, fungi etc.
• What can initial infection sometimes be predisposed to?

  A more serious secondary infection

  
  

  e.g. getting a bad case of influenza or RSV can lead to you getting pneumonia
• How do you get a more serious secondary infection of pneumonia?

  Initial viral infection causes damage to lung tissue

  
  

  Tissue damage exposes basement membrane elements such as fibrinogen to which bacteria can adhere & infiltrate into the host

  
  

  Viral infection itself facilitates secondary bacterial infection by releasing neuraminidase which cleaves sialic acid residues on host cells, creating more bacterial binding sites

  
  

  This results in either bronchitis or pneumonia, conditions which are often associated with an impaired host immune response
• What is the nature of the impairment of the host immune response?

  Over-activity of immune system; an overproduction of pro-inflammatory cytokines, leading to infiltration of bacteria, lymphocytes, neutrophils & macrophages: damages alveolar architecture
• What can a secondary bacterial infection lead to?

  More prolonged & severe clinical symptoms when compared to viral infections alone

  Bacterial invasion can also lead tosepticaemia, which is a frequent cause of death, especially in the elderly
• What 3 things do you need to get septicaemia?

  Initial viral infection

  Secondary bacterial infection

  Dysregulated host immune response

  
• How can you prevent primary viral infection?

  Vaccination
• Are antibiotics recommended to treat viral diseases?

  No because of antibiotic resistance, however in vulnerable populations such as elderly patients, aggressive antiviral & antibacterial therapy at the first sign of viral infection is warranted to prevent secondary bacterial infection
• What is a biofilm?

  
• Is the structure of a biofilm static?

  No it's dynamic; the composition of a biofilm changes over time from person to person, between individual substrates & tissue sites & in response to changes in the environment

  Biofilm development in the oral cavity is continuous & sequential
• What are the 4 main stages of biofilm development?

  1. Primary colonisers adhere to the conditioning film through electrostatic forces of attraction

  
  

  2.Primary colonisers undergo cell division and form structures called micro colonies that produce EPS

  
  

  3.Adhesion of secondary colonisers occur and succession (selective pressure which is opposed upon a developing population of microbes and so the composition of biofilm changes overtime until equilibrium is reached.

  
  

  4.Climax community