Cations antibacterial

The degree of ionization of acidic and basic antimicrobial agents depends on pH. Some compounds are active only in the unionized state (e.g., phenolics) whereas others are preferentially active as either the anion or cation. It therefore follows that the activity of a particular concentration of an agent will be enhanced at a pH that favors the formation of the active species. Thus, cationic antibacterials such as acridines and quaternary ammonium compounds are more active under alkaline conditions. Conversely, phenols and benzoic acid are more active in an acid medium. Chlorbutol is less active above pH 5 and unstable above pH 6. Phenylmercuric nitrate is only active at above pH 6 whereas thiomersal is more active under acid conditions. The sporicidal activity of glutaraldehyde is considerably enhanced under alkaline conditions whereas hypochlorites are virtually ineffective at above pH 8. 

Cationic antibacterials that have the aminoacridine type of action... 

Incompatibility between Anionic and Cationic Antibacterial Agents and Other Anionic and Cationic Drugs... 

FIXATION OF CATIONIC ANTIBACTERIAL PRODUCTS BEFORE DYEING A MORE ECOLOGICAL PROCESS... 

Cotton fabrics (15g) were modified using isothermic exhaustion process (75 C). The bath was prepared with 15% (owf) of cationic antibacterial product (monocationic salt) and epichlorohydrin (molar ratio 1 1) and 20 gL of sodium hydroxide. The liquor ratio was 1 20. 

Since the objective of this work was the evaluation of the exhaustion process, for the exhaustion process different concentrations of antibacterial product were applied and their impact in dye uptake evaluated. Figure 2 compares the exhaustion of dye for cotton treated with 15% (w.o.f) and 7.5% (o.w.f.). As expected the exhaustion of dye reflects the quantity of cationic antibacterial compound in fibre, being about 20% lower when using half the amount. If the lower concentration of antibacterial is sufficient for the objective, then for hi er exhaustion some salt should be used. 

The process of insertion causes changes in phase and/or motion of the tipids of the target membrane (112). However, the lipid composition can dramatically influence the possibility of insertion, and positively charged phospholipids and cholesterol decreased the formation of membrane channels by cecropin by 5- to 60 fold (36). Indeed, this may explain, in addition to the difference in the selectivity of cationic antibacterial pep tides for bacteria over eukaryotes, since the former lack cholesterol, which is abundant in eukaryotic membranes, whereas anionic phosphatidyl glycerol and cardiodipin. major components of bacterial membranes, represent excellent target lipids. 

The magaiitins are a class of hnear, cationic, faciaUy amphipathic and hehcal antibacterial peptides derived from frog skin [51]. The magaiitins exhibit highly selective and potent antimicrobial activity against a broad spectrum of organisms [52, 53]. As these peptides are faciaUy amphipathic, the magainins have a cationic heli-... 

As such, the magainins provide a useful initial target for peptoid-based peptido-mimetic efforts. Since the helical structure and sequence patterning of these peptides seem primarily responsible for their antibacterial activity and specificity, it is conceivable that an appropriately designed, non-peptide helix should be capable of these same activities. As previously described (Section 1.6.2), peptoids have been shown to form remarkably stable hehces, with physical characterishcs similar to those of peptide polyprohne type-I hehces (e.g. cis-amide bonds, three residues per helical turn, and 6A pitch). A faciaUy amphipathic peptoid helix design, based on the magainin structural motif, would therefore incorporate cationic residues, hydrophobic aromatic residues, and hydrophobic aliphathic residues with threefold sequence periodicity. 

Chlorhexidine base is not readily soluble in water therefore the freely soluble salts, acetate, gluconate and hydrochloride, are used in formulation. Chlorhexidine exhibits the greatest antibacterial activity at pH 7-8 where it exists exclusively as a di-cation. The cationic nature of the compound results in activity being reduced by anionic compounds including soap and many anions due to the formation of insoluble salts. Anions to be wary of include bicarbonate, borate, carbonate, chloride, citrate and phosphate with due attention being paid to the presence of hard water. Deionized or distilled water should preferably be used for dilution purposes. Reduction in activity will also occur in the presence of blood, pus and other organic matter. 

In other cases the activity ofthe drug is due to the ionized molecule. For example, with the antibacterial acridine dyestuffs it is the cation which is the active agent and factors favouring ionization, all other things being equal, enhance their antibacterial activity (see Chapter 12). 

Usually the antibacterial activity of cationic detergents sueh as cetrimide and the aeridines inereases with increase of pH (section 2.3.3). 

Application of some kind of sample treatment may have the potential to improve substantially the detection of certain antibacterials in milk by microbial routine methods (59). Treatment, for example, of milk samples with ammonium oxalate solution prior to analysis can lead to lower limits of detection of tetracyclines by both microbial inhibition and microbial receptor assays. This is due to the fact that tetracycline residues tend to form chelates with divalent cations and bind to proteins, which reduce their antibacterial efficacy. However, the oxalate treatment causes splitting of complex and/or protein bonds without increasing the detection limits of other antibacterials commonly used in dairy cows. 

---