Subinhibitory antibiotic concentrations promote the horizontal transfer of plasmid-borne resistance genes from Klebsiellae pneumoniae to Escherichia coli

Abstract

Horizontal gene transfer plays an important role in the spread of antibiotic resistance, in which plasmid-mediated conjugation transfer is the most important mechanism. While sub-minimal inhibitory concentrations (sub-MIC) of antibiotics could promote conjugation frequency, the mechanism by which sub-MIC levels of antibiotics affect conjugation frequency is not clear. Here, we used <i>Klebsiella pneumoniae</i> SW1780 carrying the multi-drug resistance plasmid pSW1780-KPC as the donor strain, to investigate the effects of sub-MICs of meropenem (MEM), ciprofloxacin (CIP), cefotaxime (CTX), and amikacin (AK) on conjugational transfer of pSW1780-KPC from SW1780 to <i>Escherichia coli</i> J53. Our results showed that the transfer frequencies increased significantly by treating SW1780 strain with sub-MIC levels of MEM, CIP, CTX and AK. Transfer frequencies at sub-MIC conditions in a <i>Galleria mellonella</i> were significantly higher than <i>in vitro</i>. To investigate gene expression and metabolic effects, RT-qPCR and LC-MS-based metabolome sequencing were performed. Transcript levels of T4SS genes <i>virB1</i>, <i>virB2</i>, <i>virB4</i>, <i>virB8</i>, and conjugation-related genes <i>traB</i>, <i>traK</i>, <i>traE</i>, and <i>traL</i> were significantly upregulated by exposure to sub-MICs of MEM, CIP, CTX, and AK. Metabolome sequencing revealed nine differentially regulated metabolites. Our findings are an early warning for a wide assessment of the roles of sub-MIC levels of antibiotics in the spread of antibiotic resistance.