The integrity of human skin is central to the prevention of infection. Acute and chronic wounds can develop when the integrity of skin as a barrier to infection is disrupted. As a multi-functional organ, skin possesses important biochemical and physical properties that influence its microbiology. These properties include a slightly acidic pH, a low moisture content, a high lipid content (which results in increased hydrophobicity) and the presence of antimicrobial peptides. Such factors have a role to play in preventing exogenous microbial colonisation and subsequent infection. In addition, the properties of skin both select for and enhance colonisation and biofilm formation by certain 'beneficial' micro-organisms. These beneficial micro-organisms can provide further protection against colonisation by potential pathogens, a process known as colonisation resistance. The aim of this paper is to summarise the microflora of skin and wounds, highlighting the role of certain micro-organisms and biofilms in associated infections.

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Wound exudate is all too often perceived as a clinical management problem. While this can be the case, it should be recognized that exudate does fulfil an important function in the healing process. Gradual acceptance of the benefits of moist wound healing, combined with the current goals of the ‘ideal’ moist environment, focuses attention on the role of exudate. This review is intended to define the components and functions of ‘normal’ exudate and differentiate it from abnormal exudate.

Clinical criteria for the identification of wound infection are regularly based on a list created by Cutting and Harding (1994). This list was established from empirical data generated in a large, multidisciplinary clinical practice, and is now widely accepted as a seminal article in wound care. Both Cutting (1998) and Gardner et al (2001) have conducted validation exercises on these wound infection criteria, based on the assumption that the criteria broadly apply to most wound types. Although many of the original criteria do apply across the spectrum of wound types, the major categories of wounds should be considered separately to avoid the possibility of overlooking the presence of infection. The focus of this article is a review of the published literature on wound infection criteria for acute and surgical wounds, diabetic foot ulcers, venous and arterial leg ulcers, pressure ulcers and burns. All known criteria for each wound type are presented, as well as an outline of the ongoing research project to refine the criteria by wound type using a Delphi panel technique. No attempt has been made to correlate visual signs and symptoms with microbiological sampling techniques. It is clear that there are subtle variations between infection criteria for wound types and that these should be recognized if treatment is to be given appropriately and promptly, and morbidity avoided.

Criteria used to identify infection may often be restricted to the presence of pus, or pus with inflammation. Traditional criteria have been used in many surveys and their advantage is that they are simple, reproducible and easily recognised by different observers. However, identification of infection may be difficult in some circumstances, and identifying patients who are likely to develop infection is rare.