Augmenting the potency of third-line antibiotics with Berberis aristata: In vitro synergistic activity against carbapenem-resistant Escherichia coli.

The aim of this study was to analyse the in vitro synergistic antibacterial potential of an aquoethanolic extract of the stem bark of Berberis aristata (PTRC-2111-A) with third-line antibiotics against carbapenem-resistant Escherichia coli. PTRC-2111-A was prepared and was characterised using phytochemical- and bioactivity-based fingerprinting. Fourier transform infrared spectroscopy (FTIR) and liquid chromatography-mass spectrometry (LC-MS) analyses were performed, and superoxide and hydroxyl scavenging activities were assessed in conjunction with in vitro antimicrobial efficacy testing against the test micro-organism. Analysis of drug combinations of PTRC-2111-A and third-line antibiotics was performed using CompuSyn software. PTRC-2111-A from B. aristata was found to have seven common functional groups in comparison with the pre-identified marker compound quercetin, and phytochemical quantitation analysis revealed the presence of 25.44% alkaloids. Moreover, PTRC-2111-A was found to contain isoquinoline alkaloids, namely berbamine, berberine, reticuline, jatrorrhizine, palmatine and piperazine, as elucidated in the LC-MS analysis. Analysis of combinations of PTRC -2111-A and antibiotics revealed synergistic behaviour [fractional inhibitory concentration index (FICI)<1] with colistin, tigecycline and amoxicillin/clavulanate potassium (Augmentin(®)), whereas antagonism (FICI>1) was seen with ertapenem and meropenem.