Mechanisms of Antibacterial Action

The mechanism of action of chlorhexidine and related biguanides was reviewed by researchers and reported in Block (2001). At relatively low concentrations, the action of chlorhexidine is bacteriostatic, and at higher concentrations, it is rapidly bactericidal, with the actual levels varying somewhat from species to species. 

The lethal process consists of a series of related cytologic and physiologic changes, some of which are reversible, that culminate in the death of the cell. The sequence is thought to be as follows (1) rapid attraction toward the bacterial cell (2) specific and strong adsorption to certain phosphate-containing compounds on 

Material Proteus mirabilis Pseudomonas aeruginosa Staphylococcus aureus 

Capric fatty acid (solid) 93.0 x 105 12.5 x10s 47.5 xlO4 

Note 1 All emulsions were prepared by the same formulation and methods 

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Mechanism of Antibacterial Action. In spite of the fact that the antibacterial activity of the amiaoglycosides has been known siace the 1940s, the mechanisms iavolved are stiU incompletely understood. Numerous reviews have appeared (eg, 108 —113) and the sequence of events seems to be as outlined below. 

Being chemically similar, the aminoglycosides have many features in common, in particular their mechanism of antibacterial action, a broad antibacterial spectrum,... 

Mechanism of antibacterial action is unclear, but it appears to necessitate reductive metabolism of the drug—bactericidal. 

Resistance to bacitracin does not emerge rapidly in originally susceptible strains. The thermal and storage stability of bacitracin is enhanced by the presence of an equimolar concentration of Zn " and the antibacterial action is potentiated by an excess of Zn " ". It has been suggested that Zn + is also associated with the mechanism of antibacterial action. No chemical assay methods are yet available for bacitracin. For the determination of potency the cylinder plate method with Micrococcus flavus (ATCC 10 240) as test organism is used. ... 

Describe the mechanism of antibacterial action of beta-lactam antibiotics. 

A) Oral bioavailability is affected by first-pass hepatic metabolism Only third-generation cephalosporins cross the blood-brain barrier Procaine penicillin G is the most commonly used intravenous form of the antibiotic Renal tubular reabsorption of beta-lactams is inhibited by probenecid Nafcillin and ceftriaxone are eliminated mainly via biliary secretion The mechanism of antibacterial action of cephalosporins involves (A) Inhibition of the synthesis of precursors of peptidoglycans Interference with the synthesis of ergosterol Inhibition of transpeptidation reactions Inhibition of beta-lactamases Binding to cytoplasmic receptor proteins... 

Describe the mechanisms of antibacterial action of sulfonamides and trimethoprim on bacterial folic acid synthesis and the mechanisms involved in bacterial resistance to the antifolate drugs. 

The mechanism of antibacterial action of the furan derivatives is unknown. However, the reduced forms of nitrofurans are highly reactive and are thought to inhibit many bacterial enzyme systems, including the oxidative decarboxylation of pyruvate to acetylcoenzyme A. Nitrofurans (see list in Table 1.7) are bacteriostatic but, at high concentrations, can be bactericidal to sensitive organisms. Both chromosomal and plasmid-mediated mechanisms of resistance to nitrofurantoin occur, and these most commonly involve the inhibition of nitrofuran reductase. 

It has been reported that silver ion-exchanged zeolites exhibit antibacterial activity [32]. The mechanism of antibacterial action of the zeolite is initiated when moisture or liquid film comes into contact with the ion exchange material and silver ions are exchanged with sodium (Na) or other cations from the environment [33]. The released silver ions attach to the bacteria by forming chelate complexes with deoxyribonucleic acid, which blocks the transport processes in the cell [34]. The use of zeolite as a filler in polymeric materials has been reported in the literature and it has been proved that they enhance the antibacterial activity of the polymer [35]. Furthermore, the effect of zeolite content on the physical and thermal properties of the polymer was also examined [35] increasing the silver/zeolite ratio in the polymer led to an increased antimicrobial activity (due to the higher silver ion concentration), but depending upon the application the zeolite content may influence physical, thermal and/or chemical properties of the polymeric material. 

Trombetta D, Casteiii F, Sarpietro MG, Venuti V, Cristani M, Daniele C, Saija A, Mazzanti G, Bisignano G (2005) Mechanisms of antibacterial action of three monoterpenes. Antimicrob Agents Chemother 49 2474-2478... 

The difference in activity for R- and -enantiomers of 7-(3-methylpiperazin-l-yl)quinolones, obtained from the corresponding (R)- and (5)-f-butyl-2-methylpiperazin-l-carboxylates, proved to be in the range from 2 to 64 folds in 52 % of cases [95]. In order to improve transport through biological membranes the piperazine moiety in norfloxacin was modified considerably and compound 26 was obtained [96]. To clarify the mechanism of antibacterial action of fluoroquinolones at the cellular level, two regioisomeric citrate-functionalized derivatives of ciprofloxacin 27a,b [97] (Scheme 14) have been obtained and studied. 

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