What is Infection? Infection vs. Colonisation
Infection is the presence of microorganisms causing damage to body tissues, usually in the presence of acute inflammation (pain, swelling, redness, heat and loss of function). For example Staphylococcus aureus on intact skin does not cause a problem; it is the normal flora for skin. However if you cut your skin, Staphylococcus aureus can cause infection in the cut with associated inflammation and tissue damage.
Microorganisms can also cause damage in the absence of inflammation but it is unusual, e.g. in neutropaenic patients with angio-invasive fungal infections causing tissue infarction.
Colonisation describes when bacteria grow on body sites exposed to the environment, without causing infection. This is a normal process. These bacteria may form part of the normal flora of the individual; however colonisation is not necessarily normal flora. Occasionally bacteria, which are not normally regarded as part of the normal flora can also colonise body areas e.g. Pseudomonas spp. in a wound is not normal flora of the skin or a wound but it is not actually causing tissue damage or infection it is just growing in the warm wet conditions of the wound. Pseudomonas spp. are the normal flora of warm wet places. Likewise some prosthetic devices can also become colonised with bacteria without causing infection e.g. urinary catheters.
Colonisation does not normally harm the patient and does not usually need treating with antibiotics e.g. Neisseria meningitidis can be found in up to 30% of the healthy population in their oropharynx. However, infection can result in harm and often needs treatment with antibiotics e.g. if Neisseria meningitidis enters the blood stream from the oropharynx to cause septicaemia, then it needs urgent treatment.
Microorganisms can also cause damage in the absence of inflammation but it is unusual, e.g. in neutropaenic patients with angio-invasive fungal infections causing tissue infarction.
Colonisation describes when bacteria grow on body sites exposed to the environment, without causing infection. This is a normal process. These bacteria may form part of the normal flora of the individual; however colonisation is not necessarily normal flora. Occasionally bacteria, which are not normally regarded as part of the normal flora can also colonise body areas e.g. Pseudomonas spp. in a wound is not normal flora of the skin or a wound but it is not actually causing tissue damage or infection it is just growing in the warm wet conditions of the wound. Pseudomonas spp. are the normal flora of warm wet places. Likewise some prosthetic devices can also become colonised with bacteria without causing infection e.g. urinary catheters.
Colonisation does not normally harm the patient and does not usually need treating with antibiotics e.g. Neisseria meningitidis can be found in up to 30% of the healthy population in their oropharynx. However, infection can result in harm and often needs treatment with antibiotics e.g. if Neisseria meningitidis enters the blood stream from the oropharynx to cause septicaemia, then it needs urgent treatment.
Topics in Basic Concepts:
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- 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).