Relationship between microbes and host.

There are three types of relationship between microbes and host.

  • 'Normal' microflora
  • Virus Host Relationship

'Normal Microflora'

Human babies are free from microbes in utero while lactobacilli in the mother’s vagina. There are many sources of flora in newborns babies and some of the examples are their families, personal or family doctors and those people who had physical contact with the babies. In a healthy individual, the internal tissues are free from microbes but the surface tissues are usually colonized by microbial species and the most common is bacteria, or sometimes fungi.


However, there are 2 views of viral flora in humans.
  • Yes, able to isolate viruses from seemingly 'healthy' people
  • No, these 'healthy' people are already immuno-compromised

Virus-Human Relationship

There are three types of virus-human relationship.

  • Commensalism – a class of relationship between two organisms where one organism benefits but the other is unaffected.


  • Mutualism - is a biological interaction between two organisms, where each individual derives a fitness benefit (i.e. increased survivorship). Similar interactions within a species are known as cooperation.


  • Parasitism – Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the host.

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