Curcumin, a Natural Antimicrobial Agent with Strain-Specific Activity.

Curcumin, a principal bioactive substance of turmeric ( L.), is reported as a strong antioxidant, anti-inflammatory, antibacterial, antifungal, and antiviral agent. However, its antimicrobial properties require further detailed investigations into clinical and multidrug-resistant (MDR) isolates. In this work, we tested curcumin's efficacy against over 100 strains of pathogens belonging to 19 species. This activity was determined by the broth microdilution method and by calculating the minimum inhibitory concentration (MIC). Our findings confirmed a much greater sensitivity of Gram-positive than Gram-negative bacteria. This study exhibited a significantly larger variation in the curcumin activity than previous works and suggested that numerous clinical strains of widespread pathogens have a poor sensitivity to curcumin. Similarly, the MICs of the MDR types of , , , and were high (≥2000 µg/mL). However, curcumin was effective against some species and strains: (median MIC = 31.25 µg/mL), methicillin-sensitive (250 µg/mL), (250 µg/mL), and individual strains of and (62.5 µg/mL). The sensitivity of species was not associated with its affiliation to the genus, and it could differ a lot (e.g., , and , ). Hence, curcumin can be considered as a promising antibacterial agent, but with a very selective activity.