In vitro assessment of antibiotic-resistance reversal of a methanol extract from Rosa canina L

• The MIC of a methanol extract from Rosa canina (RC) was determined against MDR and effluxing MRSA bacterial strains.
• The bacterial resistance modulation activity of RC extracts against effluxing bacterial strains was investigated.
• The inhibition of the conjugal transfer of plasmids PKM101 and TP114 by the RC extract was evaluated.
• The HPLC-DAD fingerprints and SRB cytotoxicity of the RC extract were determined.

The crude methanol extract of Rosa canina (RC) fruit was tested against multidrug-resistant (MDR) bacterial strains, including methicillin-resistant Staphylococcus aureus SA1199B, EMRSA16 and XU212 harbouring NorA, PBP2a and TetK resistance mechanisms, respectively, as well as S. aureus ATCC25923, a standard antimicrobial susceptible laboratory strain. The inhibition of the conjugal transfer of plasmid PKM101 and TP114 by the RC extract was also evaluated. The RC extract demonstrated a mild to poor antibacterial activity against the panel of bacteria having MIC values ranging from 256 to > 512 μg/mL but strongly potentiated tetracycline activity (64-fold) against XU212, a tetracycline-effluxing and resistant strain. Furthermore, the extract showed moderate capacity to inhibit the conjugal transfer of TP114 and PKM101; transfer frequencies were between 40% and 45%. Cytotoxicity analysis of the RC extract against HepG2 cells line showed the IC50 > 500 mg/L and, thus, was considered non-toxic towards human cells. Phytochemical characterisation of the extracts was performed by the assessment of total phenolic content (RC: 60.86 mg TAE/g) and HPLC fingerprints with five main peaks at 360 nm. The results from this study provide new mechanistic evidence justifying, at least in part, the traditional use of this extract. However, the inhibition of bacterial plasmid conjugation opens the possibility of combination therapies to overcome antibiotic resistance.