Consolidation

CONSOLIDATION

To be successful, a pathogen must be able to survive at its initial portal of entry, frequently in competition with the commensal flora and generally while subject to the attention of macrophages and wandering white blood cells. Such survival invariably requires the organism to attach itself firmly to the epithelial surface, eventually forming a biofilm. The initial attachment must be highly specific in order to displace the commensal microflora, and subsequently governs the course of an infection. Attachment can be mediated through provision, on the bacterial surface, of adhesive substances such as mucopeptide and mucopolysaccharide slime layers, fimbriae, pili and agglutinins. These are often highly specific in their binding characteristics, differentiating, for example, between the tips and bases of villi in the large bowel and the epithelial cells of the upper, mid and lower gut. Secretory antibodies, which are directed against such adhesions, block the initial attachment of the organism and thereby confer resistance to infection.

The outcome of the encounter between the tissues and potential pathogens is governed by the ability of the microorganism to multiply at a faster rate than it is removed from those tissues. Factors that influence this are the organism’s rate of growth, the initial number arriving at the site and their ability to resist the efforts of the host tissues at removing/starving/killing them. The outcome of an encounter between a microorganism and a host can therefore be described as a balance between the accumulation of the pathogen and its elimination by the host.

The definition of virulence (i.e. the degree of pathogenicity caused by a microorganism) for pathogenic microorganisms must include the MIN. This will vary between individuals, but will invariably be lower in compromised hosts such as those who are catheterized, diabetics, smokers and cystic fibrosis patients, and those suffering trauma such as malnutrition, chronic infection or physical damage.