Greater Invasion and Persistence of Bearing Plasmids in Escherichia coli than in Klebsiella pneumoniae.

The emergence of the plasmid-borne polymyxin resistance gene threatens the clinical utility of last-line polymyxins. Although has disseminated to various species, the prevalence of is the highest among Escherichia coli isolates while remaining low in Klebsiella pneumoniae. The reason for such a difference in prevalence has not been investigated. In this study, we examined and compared the biological characteristics of various plasmids in these two bacterial species. Although -bearing plasmids were stably maintained in both E. coli and K. pneumoniae, the former presented itself to be superior by demonstrating a fitness advantage while carrying the plasmid. The inter- and intraspecies transferability efficiencies were evaluated for common -harboring plasmids (IncX4, IncI2, IncHI2, IncP, and IncF types) with native E. coli and K. pneumoniae strains as donors. Here, we found that the conjugation frequencies of plasmids were significantly higher in E. coli than in K. pneumoniae, regardless of the donor species and Inc types of the plasmids. Plasmid invasion experiments revealed that plasmids displayed greater invasiveness and stability in E. coli than in K. pneumoniae. Moreover, K. pneumoniae carrying plasmids showed a competitive disadvantage when cocultured with E. coli. These findings indicate that plasmids could spread more easily among E. coli than among K. pneumoniae isolates and that plasmid-carrying E. coli has a competitive advantage over K. pneumoniae, leading to E. coli being the main reservoir. As infections caused by multidrug-resistant "superbugs" are increasing globally, polymyxins are often the only viable therapeutic option. Alarmingly, the wide spread of the plasmid-mediated polymyxin resistance gene is restricting the clinical utility of this last-line treatment option. With this, there is an urgent need to investigate the factors contributing to the spread and persistence of -bearing plasmids in the bacterial community. Our research highlights that the higher prevalence of in E. coli than in K. pneumoniae is attributed to the greater transferability and persistence of -bearing plasmid in the former species. By gaining these important insights into the persistence of in different bacterial species, we will be able to formulate effective strategies to curb the spread of and prolong the clinical life span of polymyxins.