[Physiologic factor in intractable bacterial infections]

A patient with a bacterial infection is usually cured by his own defense mechanisms against the infectious agents. However, defense mechanisms are frequently damaged by physiologic factors. In this chapter, we described the important physiologic factors which weakened defenses of urinary, respiratory or alimentary tracts and others against bacterial infection. For example, defects of the skin or mucosa is one of the most important factors, because these tissue have natural defense which are low pH, keratin, normal bacterial flora, lysozyme, lactoferrin, secretory IgA and so on. Foreign bodies, urinary or vascular catheters or stones damage normal defenses of mucosa or vascular wall. Many species of bacteria make biofilm, which is consisted of grown bacteria, glycocalyx matrix, fibrin and platelets, around the foreign bodies or catheters. This matrix substance have characteristic of an ion exchange filter which traps aminoglycoside antibiotics, and beta-lactam antibiotics are not effective in the biofilm because of lower growth rate. Furthermore, obstruction of urinary, respiratory or alimentary tracts is also important factor because of decrease of clearance of bacteria from these tissue by urine stream, pilial or bowel movement, and decrease of perfusion of antimicrobial agents from blood stream to the tissue.