In vitro antibacterial and time-kill evaluation of phosphanegold(I) dithiocarbamates, R3PAu[S2CN(iPr)CH2CH2OH] for R = Ph, Cy and Et, against a broad range of Gram-positive and Gram-negative bacteria

The in vitro antibacterial activity of a series of phosphanegold(I) dithiocarbamates, R3PAu[S2CN(iPr)CH2CH2OH] where R = Ph (2), Cy (3) and Et (4), against 25 strains of Gram-positive and Gram-negative bacteria were determined through the disk diffusion method, the determination of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) and by time-kill assay. Compounds 2 and 3 have been shown to be specifically active against the tested Gram-positive bacteria, with MIC values ranging from 7.81 to 125 μg/ml. Compound 4 has a broad-spectrum activity against 24 strains of Gram-positive and Gram-negative bacteria, with MIC values ranging from 0.98 to 1,000 μg/ml. Noteworthy was that 4, with a very low MIC value of 0.98 μg/ml, is particularly effective against methicillin-resistant Staphylococcus aureus (MRSA) and Bacillus sp., as effective as the standard antibiotic ciprofloxacin. In time-kill studies, the bacteriostatic and bactericidal activities of the tested compounds towards susceptible strains were similar to their characteristics determined by MBC/MIC ratios. In the time-kill assay, 2 and 3 showed only bactericidal activity towards the susceptible strains tested, whereas 4 revealed varying degrees of bactericidal and bacteriostatic activities, results indicating different antibacterial mechanisms are involved.