Synthesis, characterization and the antimicrobial effect of diiodothiocyanate (I₂SCN-) on escherichia coli and enterococcus faecalis.

Abstract

The threat posed by antimicrobial resistance is rising to dangerously high levels worldwide. However, chemical species such as iodide-based interpseudohalogen are attracting attention as potential new class of antimicrobials. Previously, these compounds were ignored based on low availability of I- in most physiological fluids. Recently, it was shown that the peroxidase system LPO-H2O2-SCN-/I- produces a highly cytotoxic cyanogen iodide (ICN) which plays a key role in killing bacteria. Research efforts to find new chemical species with antimicrobial properties from non-enzymic reactions of iodine (I2/I-) with thiocyanate (SCN-) are currently underway. Herein, we describe the formation of the interpseudohalogen, diiodothiocyanate (I2SCN-) in two different media, i.e. water and acetonitrile. The formation of I2SCN- was confirmed by 13C NMR spectroscopy, UV-visible spectrophotometer, stopped-flow technique and Job’s plot. The biological activities of I2SCN- against strains of Escherichia coli and Enterococcus faecalis bacteria were determined by zone of inhibition plate tests and traditional optical density (OD) measurements. Reaction mixtures of I2 and SCN- at various ratios showed inhibition against both Gram-positive (E faecalis) and Gram-negative (E coli) strains of bacteria. The results indicate that I2SCN- was more effective against E coli compared to E faecalis due to differences in the structural features of the two bacteria. The E faecalis has a thicker cell wall compared to E coli which makes it difficult for any antibacterial compound to penetrate and kill the bacteria. Reaction mixtures of I2 and SCN- at various ratios showed antibacterial activity against both Gram-positive (E. faecalis) and Gram-negative (E. coli) strains of bacteria, with the equimolar solution being the most efficient. The I2SCN- compound was more effective against E. coli compared to E. faecalis. This is due to differences in the structural features of the two bacteria, E. faecalis has a thicker cell wall compared to E. coli which makes it difficult for antibacterial compounds to penetrate the bacteria.