Effects of Curcumin and Silymarin on the Shigella dysenteriae and Campylobacter jejuni In vitro

Antimicrobial properties of silymarin and curcumin have been assessed against several infectious agents. The aim of this study was to investigate the anti-apoptotic and antibacterial effects of both compounds on the expression of genes among Shigella dysenteriae ATCC 12022 and Campylobacter jejuni subsp. jejuni strain ATCC 33560 standard strains.

S. dysenteriae and C. jejuni standard strains were prepared from reference laboratory. Additionally, two clinical multidrug-resistant (MDR) isolates were adopted. Silymarin and curcumin stocks were purchased from Sigma Corporation (USA), and after preparation of dilutions (0.5–512 μg/ml), the minimum inhibitory concentration (MIC) and minimum bactericidal concentrations (MBC) were determined. Furthermore, the effect of 100 μg/ml of each compound was also evaluated on the expression of two gyrB and 16S rRNA housekeeping genes by quantitative real-time PCR (qRT-PCR).

Silymarin MIC and MBC were 512 μg/ml and > 512 μg/ml against S. dysenteriae and > 512μg/ml against C. jejuni standard strains, respectively. Moreover, curcumin MIC and MBC concentrations were 256 μg/ml and 512 μg/ml, respectively for ATCC strains. Silymarin down-expressed the expression of gyrB gene in S. dysenteriae and gyrB and 16srRNA gene in C. jejuni significantly (p < 0.05) compared with unexposed strains. In addition, curcumin could down-express the both gyrB and 16S rRNA genes in both strains significantly (p < 0.05). For two MDR clinical isolates, both MIC and MBC of compounds were > 512 μg/ml. Addition of 100 μg/ml curcumin and silymarin to ampicillin (10 μg/ml) lowered the MIC of MDR S. dysenteriae to 256 μg/ml and 512 μg/ml, respectively. However, no MIC change was observed with regard to C. jejuni.

In this study, curcumin and silymarin could inhibit the growth of S. dysenteriae and C. jejuni and 100 μg/ml sub-MIC levels exhibited the suppression of housekeeping genes. Combating pathogenic bacteria by compounds alternative to antibiotics in the era of antibiotic resistance is a proper strategy, though more studies using combinations of them are needed.