[Bacteriostatic - bactericidal].

Action of chemotherapeutics on bacteria can be described as "bacteriostatic" or "bactericidal". In vitro, "bactericidal" agents are able to kill >or= 99.9% bacteria of the inoculum within 18-24 h. However, "bactericidal" or "bacteriostatic" effects are dependent on several variables, e.g., inoculum, species, or medium. The number of bacteria found in an infectious process amounts to 10(8)-10(10) CFU/ml (colony-forming units per milliliter) and is far beyond the in vitro test inoculum of 5 x 10(5) CU/ml. Contrary to the term "bactericidal", in vivo a significant number of bacteria will survive. These bacteria are able to regrow, to mutate and to support infection. It is thought that a special advantage of "bactericidal" agents is the rapid killing of bacteria, thus avoiding or at least slowing down development of resistance. Contrary to this assumption, there is now an alarming increase in resistance including third-generation cephalosporins, quinolones and even carbapenems.Recent randomized clinical studies comparing "bacteriostatic" and "bactericidal" regimens revealed an equivalent clinical success. It became obvious that therapy with certain "bacteriostatic" agents even in severe infections is not harmful to patients. In addition, e.g. tetracyclines are able not only to fight bacteria but also to modulate immune response of the host. This property may offer possibilities to develop new strategies in treating infections.