I am often asked “why should I bother learning about normal flora, what I need to know is what bacteria cause infections”. This is an understandable approach however it doesn't allow for the fact that the presence of bacteria can be entirely normal and even healthy. The Microbiologist’s secret is that they know where these normal bacteria should be and recognise when they are in the wrong place. Treating normal flora is a very common mistake in medicine. Some doctors think that if bacteria are identified in a laboratory report these bacteria must be causing an infection and therefore prescribe an antibiotic. But this is not always the case. Microbiology laboratories report the presence or absence of bacteria. Depending on the clinical scenario the presence could be highly significant or alternatively just normal flora. As a student said last week “so what you’re saying is that a lot of antibiotics are given to try and treat normal flora not infection”. Yes, the presence of bacteria does not necessarily mean the presence of infection.
Normal flora are the microorganisms that live on another living organism (human or animal) or inanimate object without causing disease. The human body is not sterile; we become colonised by bacteria from the moment we are born. We are covered with, and contain within our intestines, approximately one hundred trillion bacteria that form the normal flora of our bodies. This normal flora helps to prevent us becoming colonised with more dangerous bacteria, which might lead to infection. Isolating microorganisms from their normal body site is normal and does not indicate infection.
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NB More resistant microorganisms are shown in red
NB More resistant microorganisms are shown in red
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