Antimicrobial agent concentration effect

Figure 1.1. Opposite) Sulpha drugs and their mode of action. The first sulpha drug to be used medically was the red dye prontosil rubrum (a). In the early 1930s, experiments illustrated that the administration of this dye to mice infected with haemolytic streptococci prevented the death of the mice. This drug, while effective in vivo, was devoid of in vitro antibacterial activity. It was first used clinically in 1935 under the name Streptozon. It was subsequently shown that prontosil rubrum was enzymatically reduced by the liver, forming sulphanilamide, the actual active antimicrobial agent (b). Sulphanilamide induces its effect by acting as an anti-metabolite with respect to /iflra-aminobenzoic acid (PABA) (c). PABA is an essential component of tetrahydrofolic acid (THF) (d). THF serves as an essential co-factor for several cellular enzymes. Sulphanilamide (at sufficiently high concentrations) inhibits manufacture of THF by competing with PABA. This effectively inhibits essential THF-dependent enzyme reactions within the cell. Unlike humans, who can derive folates from their diets, most bacteria must synthesize it de novo, as they cannot absorb it intact from their surroundings...

There is some evidence that one potential effect of the release of fluoride is for it to act as an antimicrobial agent. It is known that millimolar concentrations of fluoride ion in water will affect a variety of activities in several types of cell [38]. It does this by denaturing the enzymes. In bacteria, the most important enzyme which can be affected is enolase, and this is responsible for the conversion of 2-P-glycerate to 2-enol pyruvate in the glycolic pathway. Enolase is a magnesium-containing... 

Despite the pronounced antimicrobial effect, silver ions have only limited usefulness as an antimiaobial agent in applications such as medicine, clothing, and household products. This is due to their rapid binding to or inactivating by components of the medium. This limitation can be overcome by using as an antimicrobial agent, silver nanoparticles, which continuously release Ag ions in sufficient concentration [16]. 

Silver nanoparticles synthesized by a cost-effective three-stage electrochemical technique have demonstrated great promise as antimicrobial agents. Nanosilver was less effective against E. coli, S. aureus, B. subtilis and P. phoeniceum compared to silver ions. However silver nanoparticles have prolonged bactericidal effect as a result of continuous release of Ag ions in sufficient concentration and thus nanoparticles can be more suitable in some bactericidal applications. The synthesized silver nanoparticles added to water paints or cotton fabrics have demonstrated a pronounced antibacterial/antifungal effect, despite the fact that they tend to agglomerate into clusters up to 200 nm. 

The relationship between concentration and antimicrobial effect differs among bactericidal agents but is constant for a particular antimicrobial agent. The relationship between concentration and antimicrobial effect is exponential in nature, with the general formula... 

Bacteriostat A chemical antimicrobial agent that can prevent the growth of microorganisms within an otherwise nutritious environment. This term is meaningless without specifying the concentration at which this effect is achieved. Bacteriostatic... 

The critical lethal parameters of the effectiveness of antimicrobial agents are the concentrations of the agents employed, the time of exposure, the types and numbers of organisms exposed, the pH of the environment or formulation, and the temperature of application. An understanding of the effects of these conditions upon the killing process and of the terms that describe such dependence is important to rationalize the use of preservatives in different situations and formulations. 

The maximum plasma concentration reflects the extent of drug bioavailability. It can be used in relation to minimum inhibitory concentration (MIC) to predict the efficacy of concentration-dependent antimicrobial agents (e.g. fluoroquinolones, aminoglycosides). Both the maximum (peak) and minimum (trough) plasma concentrations are used during therapeutic drug monitoring to maximize efficacy and minimize the occurrence of undesirable effects. 

---