Discovery of similar multidrug resistance regions in nosocomial Enterobacteriaceae outbreaks in three hospitals in the Netherlands

Introduction: Transmission of antimicrobial resistance genes between bacteria increases the threat posed by antimicrobial resistance worldwide. In 2019, three hospitals in Limburg (the Netherlands) detected multidrugresistant Enterobacteriaceae with similar phenotypes. We investigated whether these similar resistance patterns resulted from clonal spread, plasmids or other mobile genetic elements conferring resistance. Methods: Forty-nine Enterobacteriaceae isolates with similar multidrug-resistant phenotypes were sequenced to assess clonality and to characterize resistance genes, their co-localisation, and plasmid association. The national and international relevance of our findings were assessed using published data. Results: Whole genome sequencing ruled out clonal transmission among the hospitals, as clonal relationships were only identified between isolates from the same hospital. However, 37 isolates of two different species from two hospitals harboured blaCTX-M-15, which co-occurred with a set of 10 other resistance genes (tet(A), dfrA14, qnrB1, aac(6)-Ib-cr, blaOXA-1, aac(3)-IIe, sul2, aph(3 '')-Ib, aph(6)-Id, and blaTEM-1). Further characterisation revealed that in 22 of these isolates, these genes were located adjacent to aadA1, catA1, and Delta catB3 in a comparable genomic region that was either plasmid-borne or chromosomally integrated. Co-occurrence of this gene set is common in older strains from the Netherlands and globally. Conclusions: The multidrug-resistance phenotypes of different Enterobacteriaceae species obtained from clinical and environmental samples were conferred by a conserved, plasmid-borne or chromosomally integrated multi-drug resistance region. This finding highlights the need to broaden antibiotic resistance dissemination studies beyond clonality assessment and plasmid comparison.