Synergistic antibacterial activity of EGCGcombined with imipenem against planktonic Carbapenem-resistant Klebsiella pneumoniae and the evaluation of independent antibiofilm activity of EGCG

Abstract Purpose To explore the synergistic antibacterial activity of EGCG combined with IMP against planktonic CRKP and evaluate the independent antibiofilm activity of EGCG. Methods Broth microdilution method was determined the MIC of EGCG. synergistic antibacterial activity between EGCG and IMP against planktonic CRKP was assessed by the FIC index. MBIC and MBRC were determined to describe the antibiofilm activity of EGCG using a microtiter plate assay. PCR was carried out to detect the presences and the relative expressions of mrkA, wbbm and luxS gene in clinical CRKP strains. Result EGCG not only expressed a low tendency of bacterial resistance, but also dramatically increased the susceptibility of CRKP against IMP with a reduction in the MIC of IMP by up to 32-fold, even reversed the resistance to IMP. In addition, the sub-MIC of EGCG exhibited preferable antibiofilm activity, with MBIC90 of 8 µg/mL and MBRC of 64–128 µg/mL. PCR showed the highest correlation was showed between the mrkA and the biofilm biomass with a PCCS of 0.727 and the relative expression levels of the mrkA gene in the EGCG treated groups were down-regulated in a dose-dependent manner. Conclusion EGCG showed a high efficiency in synergistic antibacterial with a low tendency of EGCG-resistance development. And EGCG displayed the potential for prophylaxis and cure of biofilm-associated infections caused by CRKP via down-regulating the expression of mrkA gene.