4b). At a concentration of 500 μg mL−1, CP251 decreased

the number of bacteria from 7.84 × 104 to 3.60 × 102 CFU mL−1 (the bactericidal rate was 99.5%). While the DTPA decreased the growth of V. parahaemolyticus from 7.84 × 104 to 8.90 × 103 CFU mL−1 (the bactericidal rate was 87.4%), and CP252 caused a decrease in growth of V. parahaemolyticus from7.84 × 104 to 2.21 × 103 CFU mL−1 (the bactericidal rate was 95.9%) at the same concentration. CP251 also effectively inhibited the growth of E. coli, decreasing the number of bacteria from 3.76 × 104 to 1.62 × 102 CFU mL−1 (the bactericidal rate was 99.6%) at a concentration of 250 μg mL−1. However, DTPA decreased the growth of E. coli from 3.76 × 104 to 5.60 × 102 CFU mL−1 click here (the bactericidal LGK-974 price rate was 98.5%), and CP252 decreased the

growth of E. coli from 3.76 × 104 to 7.90 × 103 CFU mL−1 (the bactericidal rate was 79.0%) (Fig. 4c). In each case, CP251 was found to be the most effective inhibitor with the Gram-negative bacteria. It is generally accepted that the iron chelators inhibit microbial growth by reducing iron absorption by microorganisms. Based on this concept, the higher the iron-binding constant for the iron chelator, the stronger the predicted antimicrobial activity. However, N,N′-bis(2-hydroxybenzyl)ethylenediamine-N,N′-diacetic acid, possessing very high affinity for iron (logK=40), was found to be a relatively weak inhibitor of bacteria (Chew et al., 1985), clearly indicating that the composition of the microorganism’s cell wall and the physical nature of the iron chelator also affect the inhibition of bacterial growth. A broad range of structurally different siderophores are produced by Gram-positive and Gram-negative bacteria (Hider & Kong, 2010). Siderophores can extract iron from various other soluble and insoluble iron Selleck C225 compounds, such as

ferric citrate, ferric phosphate, Fe-transferrin, ferritin, iron bound to sugars and glycosides or even from synthetic chelators such as EDTA and nitrilotriacetate. Catecholate siderophores predominate in certain Gram-negative genera, such as Enterobacteria and the genus Vibrio, the reasons for this being manifold, including complex stability, high environmental pH and a weak capability for nitrogen metabolism (Winkelmann, 2002). The Gram-positive Streptomycetes produces hydroxamate-type ferrioxamines and the ascomycetous and basidiomycetous fungi synthesize ester- and peptide-containing hydroxamate siderophores that are acid-stable and well-suited for environmental iron solubilization. Both the Streptomycetes and fungi show a versatile nitrogen metabolism with active N-oxygenases (Winkelmann, 2002). Because of structurally different siderophores and different cell wall types, it can be expected that iron(III)-selective chelators will have a differential influence on a range of bacteria. Of the three iron(III)-selective chelators investigated, CP251 was found to possess the strongest antimicrobial activity, followed by DTPA and CP252.