The effect of copper(ii), iron(ii) sulphate, and vitamin C combinations on the weak antimicrobial activity of (+)-catechin against Staphylococcus aureus and other microbes

Abstract

Few attempts have been made to improve the activity of plant compounds with low antimicrobial efficacy. (+)-Catechin, a weak antimicrobial tea flavanol, was combined with putative adjuncts and tested against different species of bacteria. Copper(II) sulphate enhanced (+)-catechin activity against Pseudomonas aeruginosa but not Staphylococcus aureus, Proteus mirabilis or Escherichia coli. Attempts to raise the activity of (+)-catechin against two unresponsive species, S. aureus and E. coli, with iron(II) sulphate, iron(III) chloride, and vitamin C, showed that iron(II) enhanced (+)-catechin against S. aureus, but not E. coli; neither iron(III) nor combined iron(II) and copper(II), enhanced (+)-catechin activity against either species. Vitamin C enhanced copper(II) containing combinations against both species in the absence of iron(II). Catalase or EDTA added to active samples removed viability effects suggesting that active mixtures had produced H(2)O(2)via the action of added metal(II) ions. H(2)O(2) generation by (+)-catechin plus copper(II) mixtures and copper(II) alone could account for the principal effect of bacterial growth inhibition following 30 minute exposures as well as the antimicrobial effect of (+)-catechin-iron(II) against S. aureus. These novel findings about a weak antimicrobial flavanol contrast with previous knowledge of more active flavanols with transition metal combinations. Weak antimicrobial compounds like (+)-catechin within enhancement mixtures may therefore be used as efficacious agents. (+)-Catechin may provide a means of lowering copper(II) or iron(II) contents in certain crop protection and other products.

Heat treatment enhances the antimicrobial activity of (+)-Catechin when combined with copper sulphate

“…These results extend previous findings that (+)‐Cat‐Cu 2+ combinations can damage bacteria (Holloway et al . ).…”

“…; Holloway et al . ). Therefore, freshly made 1 mmol l −1 flavanol isomers of (+)‐Cat as well as 10 min HT and 14 day stored (+)‐Cat were tested for H 2 O 2 generation in the presence of equimolar copper sulphate (214 μ mol l −1 , f.c.).…”

“…; Holloway et al . ). Heating of some phenolics can also enhance antimicrobial activity (Kim et al .…”

“…Previous studies have investigated the extent to which flavanols and their synthetic analogues generate antimicrobial activity as well as their mechanisms of action. Others have shown that flavanol activity can be enhanced by adjuncts, such as conventional antibiotics, vitamin C, and transition metal ions (Stapleton et al 2004a(Stapleton et al ,b, 2006(Stapleton et al , 2007Hatano et al 2008;Holloway et al 2012). Heating of some phenolics can also enhance antimicrobial activity (Kim et al 2010).…”

“…(+)-Cat, which is a common but weak antimicrobial flavanol, is a suitable candidate for investigating the possibility of antimicrobial enhancement by heating and the addition of copper sulphate (Holloway et al 2012). (+)-Cat lacks the features typically found in compounds with higher antimicrobial activities, i.e.…”