Interspecies plasmid transfer appears rare in sequential infections with extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae.

From a cohort of 1836 Swedish patients infected with ESBL-producing Enterobacteriaceae (EPE) during 2004-2014, 513 patients with recurrent EPE infection were identified. Only in 14 of the 513 patients was a change of species (ESBL-E. coli to ESBL-K. pneumoniae or vice versa) found between the index and subsequent infection. Eleven sequential urine isolates from 5 of the 14 patients were available for further analysis of possible transfer of ESBL-carrying plasmids. The plasmid content was studied using optical DNA mapping (ODM), PCR-based replicon typing, and ESBL gene sequencing. ODM allowed us to directly compare whole plasmids between isolates and found similar ESBL-carrying plasmids in 3 out of the 5 patients. The ODM results and the rarity in shift of species between ESBL-E. coli and ESBL-K. pneumoniae imply that in recurrent EPE infections interspecies plasmid transfer is uncommon.