Curcumin is a major phenolic constituent of turmeric (Curcuma longa L.) rhizomes. This substance has been described as an anti-inflammatory, antibacterial, and antifungal agent. Unfortunately, the literature data concerning its antimicrobial activity provide very diverse results. Moreover, some of them are doubtful, especially when curcumin has been dissolved in chemical compounds inhibiting bacterial growth: ethanol or methanol. Therefore, the purpose of the present work was to carry out comparative analyses of the antimicrobial activity of curcumin using recommendations prepared by the Clinical and Laboratory Standards Institute (CLSI).
In the study, there were tested six Gram-positive (Enterococcus faecalis, Staphylococcus aureus, methicillin-resistant S. aureus /MRSA/, S. epidermidis, Streptococcus agalactiae, S. pyogenes) and five Gram-negative bacteria (Acinetobacter lwoffii, Escherichia coli, Klebsiella oxytoca, Proteus mirabilis, Pseudomonas aeruginosa) as well as pathogenic fungus Candida albicans. For each species, four clinical strains were used. The minimal inhibitory concentrations (MICs) of curcumin were determined by the micro-dilution method described in details in our previous publications [1,2]. Curcumin was dissolved in 40% water solution of dimethyl sulfoxide (DMSO), which in this concentration has not antimicrobial effect.
In vitro analyses have shown a large diverse of curcumin activity. This plant metabolite did not inhibit the growth of C. albicans, MRSA, S. agalactiae, and P. mirabilis (MICs >1000 μg/mL), while it demonstrated very strong effect on strains of S. epidermidis (MICs: 15.6-31.25 μg/mL) and S. pyogenes (62.5-125 μg/mL). Curcumin sensitivity was also observed for A. lwoffii (125-250 μg/mL), P. aeruginosa (250-500 μg/mL) as well as E. coli and K. oxytoca (500-1000 μg/mL). Among S. aureus and E. faecalis strains, we found both resistant (MICs >1000 μg/mL) and sensitive (500 μg/mL) bacteria.
Summarizing our study, curcumin belongs to the potent natural antibacterial agents of plant origin, but its activity varies greatly depending on the species and even the bacterial strain. The above-mentioned compound was very strong against S. epidermidis and S. pyogenes, and at the same time it had weak or no activity on other Gram-positive bacteria. In the case of Gram-negative ones, curcumin exhibited moderate, weak or none antibacterial effect.
 Karpiński T.M. Efficacy of octenidine against Pseudomonas aeruginosa strains. Eur J Biol Res. 2019, 9, 135-140.
 Karpiński T.M., Adamczak A. Fucoxanthin - an antibacterial carotenoid. Antioxidants 2019; 8(8): 239.