Characterisation of extended-spectrum β-lactamase/plasmid AmpC-β-lactamase-producing Escherichia coli isolates from long-term recurrent bloodstream infections.

The aim of this study was to investigate recurrent infections in individual patients caused by extended-spectrum β-lactamase and plasmid AmpC β-lactamase-producing Escherichia coli (ESBL/pAmpC-Ec) isolates with >12-month interval. The Danish national collection of ESBL/pAmpC-Ec isolates collected from January 2014 through June 2017 was screened for patients with multiple isolates with >12 months between the episodes. Isolates underwent whole-genome sequencing and were analysed for antimicrobial resistance genes, virulence genes and multilocus sequence typing (MLST). Isolates were subtyped by core genome MLST (cgMLST) and CH typing. From a total of 970 patients, 15 unrelated patients experienced recurrent infections with ESBL/pAmpC-Ec. Of the 15 patients, 10 (67%) were found to be infected a second or third time with a genetically identical or similar strain. The resistance and virulence properties of the strains were similar in individual patients, however they were quite diverse when comparing between patients. Recurrent ESBL/pAmpC-Ec bloodstream infections of genetically related strains occurring with >12-month interval might be related to the previous episode and to a lesser extent be caused by re-infection. With >1000 days between the first and second episode of genetically similar strains (four allele differences), the recurrent infection is likely due to long-term host colonisation by ESBL/pAmpC-Ec. From this analysis, strains able to cause such recurrent infection were relatively diverse between patients. Knowledge about host and strain factors influencing such recurrent infections is needed to implement preventive measures.