Wide-spreading of antibiotic resistance is one of the most important issues in not only public health but also a huge economic burden. Dissemination of multidrug resistance (MDR) gene(s) resulted in emergence of MDR bacteria, or casually called “superbugs”. These transmissions were often carried out by conjugative plasmids that also encode genes sufficient for a means of horizontal gene transfer, namely conjugation which is carried out by cell-to-cell contact. We are interested in dynamics of dissemination of MDR conjugative plasmid, using pESBL as our model plasmid. This plasmid was originally identified in Escherichia coli O104 outbreak strain in Germany in 2011, and participated the severity of outbreak as it provided MDR phenotype to the host cells.
Taking advantage of Transposon insertion site sequencing (Tnseq), a recently developed technique which allows the high-throughput quantitative fitness assessment of individual genomic loci, we identified genes involved in the conjugative transfer of pESBL. Surprisingly, Tnseq also unveiled a small regulatory region in pESBL: mutations in this region result in highly elevated transfer efficiency of the plasmid. This and other lines of evidence indicate that single mutations can create plasmids with substantially increased ability to spread, threatening emergence of ’superspreader’ mutants.
Transferred plasmid molecule has to be established in the recipient cell for the completion of the conjugative DNA transfer. I will also discuss our recent studies on various factors involved in this establishment, such as plasmid partitioning and a system counteracting host immunity.