Combined treatment with the antibiotics kanamycin and streptomycin promotes the conjugation of Escherichia coli

It is widely accepted that antibiotics provide a critical selective pressure for the horizontal transfer of antibiotic resistance between bacterial species. This study demonstrated that a combination of low doses of kanamycin and streptomycin, which inhibited the growth of recipient and donor cells, respectively, had positive effects on the transmission of the conjugation plasmids pRK2013, pSU2007, and RP4 from Escherichia coli DH5 to HB101 at their minimum inhibitory concentrations (MICs). Administration of either antibiotic alone as well as other antibiotics in combination or alone did not have this effect. Two-dimensional electrophoresis revealed that 60 proteins were downregulated and 14 proteins were upregulated in the conjugation of E.coli DH5 (pRK2013) and HB101 in the presence of kanamycin and streptomycin. Of these proteins, 64 were subsequently identified by mass spectrometry. Two antibiotic-induced genes encoding oligopeptide-binding protein (OppA) and ribose-binding protein (RbsB) were further confirmed by quantitative real-time PCR. When these genes were deleted, the number of transconjugants decreased in the same fashion as when the cells were treated with kanamycin and streptomycin. These results indicate that the process of E.coli conjugation may be promoted by combination treatment with kanamycin and streptomycin and that two proteins potentially participated in this process.