What is Normal Flora and why is it Important?
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.
Many circumstances can change normal flora, e.g. normal flora of the human body begins to change after admission to a hospital or long-term care facility. The process usually begins around day 4 of admission; this is why after 4 days of admission the antibiotics for hospital acquired infections change. It is not because the severity of the illness is different.
Knowledge of the normal flora of the human body allows:
Nothing is 100% accurate but it’s a good place to start. Knowing where bacteria normally live can help you work out when they are in the wrong place. This knowledge allows the prediction of the likely causes of disease and hence the choice of a suitable antibiotic for empirical therapy.
Knowing what factors affect normal flora allows predictions to be made as to what the flora will become under the influence of those factors, e.g. exposure to antibiotics removes sensitive bacteria, so if a patient with a cut hand, and a sensitive Staphylococcus aureus (MSSA) in their normal flora, is given Flucloxacillin for the cut, a void will be left behind, which could be filled by a Flucloxacillin resistant bacteria such as Meticillin resistant Staphylococcus aureus (MRSA).
Many circumstances can change normal flora, e.g. normal flora of the human body begins to change after admission to a hospital or long-term care facility. The process usually begins around day 4 of admission; this is why after 4 days of admission the antibiotics for hospital acquired infections change. It is not because the severity of the illness is different.
Knowledge of the normal flora of the human body allows:
- Prediction of the pathogens causing infection as bacteria tend to grow in specific body sites e.g. Streptococcus pneumoniae from the upper respiratory tract causing pneumonia or Staphylococcus aureus from the skin causing intravenous cannula infections.
- Investigation for underlying abnormalities in specific areas of the body when bacteria are isolated from normally sterile sites e.g. Escherichia coli isolation from blood cultures indicates probable intra-abdominal pathology because Escherichia coli is part of the normal gastrointestinal flora, or isolation of a Viridans Streptococcus in blood cultures may indicate infective endocarditis as a result of poor dentition as Viridans Streptococcus are part of the normal mouth flora
Nothing is 100% accurate but it’s a good place to start. Knowing where bacteria normally live can help you work out when they are in the wrong place. This knowledge allows the prediction of the likely causes of disease and hence the choice of a suitable antibiotic for empirical therapy.
Knowing what factors affect normal flora allows predictions to be made as to what the flora will become under the influence of those factors, e.g. exposure to antibiotics removes sensitive bacteria, so if a patient with a cut hand, and a sensitive Staphylococcus aureus (MSSA) in their normal flora, is given Flucloxacillin for the cut, a void will be left behind, which could be filled by a Flucloxacillin resistant bacteria such as Meticillin resistant Staphylococcus aureus (MRSA).
Click for a larger image
NB More resistant microorganisms are shown in red
NB More resistant microorganisms are shown in red
Topics in Basic Concepts:
All these topics are covered in the book...Ready to buy your copy? Click here to buy your copy of "Microbiology Nuts & Bolts" Its updated and amazingly only slightly larger as its got 1/3 more in it! (11cmx18cmx2.5cm).
- What is Infection? Infection vs. Colonisation vs. Contamination
- Source of Infection: Endogenous vs. Exogenous
- Bacteraemia vs. Septicaemia
- Types of Infectious Microorganisms
- The Anatomy of a Bacterium
- What is Normal Flora and why is it Important?
- Circumstances Affecting Normal Flora
- How Antibiotic Prescribing Influences Normal Flora and the Ward Environment
- Bacterial Flora in a Normal Person in the Community
- Bacterial Flora in a Normal Person in a Hospital or Long-term Care Facility
- Significance of Bacteria in the Bloodstream (Bacteraemia)
- Diagnosing Infection: History
- Diagnosing Infection: Examination and Non-Microbiological Investigations
- Immunodeficiency States
All these topics are covered in the book...Ready to buy your copy? Click here to buy your copy of "Microbiology Nuts & Bolts" Its updated and amazingly only slightly larger as its got 1/3 more in it! (11cmx18cmx2.5cm).
