HIGH DIVERSITY OF PLASMIDS CARRYING QNR RESISTANCE GENES IN FLUOROQUINOLONE RESISTANT ESCHERICHIA COLI ISOLATED IN GERMANY IN 2017

Aim: The prevalence and diversity of qnr-carrying isolates among (fluoro-)quinolone (FQ)-resistant, commensal E. coli from the German annual antimicrobial resistance monitoring in livestock and food in 2017 was determined. The data will be used to understand mechanisms involved in FQ-resistance development and the diversity of mobile genetic elements associated with their spread.

Methods: A total of 3,409 E. coli isolates from the German National Reference Laboratory for Antimicrobial Resistance was investigated. Antimicrobial resistance testing was conducted by broth microdilution according to CLSI guidelines. MIC values for ciprofloxacin and nalidixic acid were evaluated using EUCAST epidemiological cut-off values. Isolates exhibiting resistances to FQ were subjected to qnr-PCR, XbaI-/S1-PFGE, whole genome sequencing (WGS) and bioinformatics analysis.

Results: Overall, 504 isolates were classified as quinolone-resistant, while only 107 of them harbored a qnr gene. XbaI-macrorestriction demonstrated a high heterogeneity, letting us assume that no predominant E. coli lineages are associated with FQ resistance development in Germany. S1-PFGE analysis showed a variety of extrachromosomal elements of various sizes. Short-read WGS revealed qnr to be associated with bla as well as with the disinfectant qacEΔ1. The most abundant plasmid replicon type among our identified qnr reference plasmids were IncN, IncY and IncX1-IncX3. Further, we frequently detected chromosomal point mutations leading to an altered susceptibility against FQs.

Conclusions: qnr genes were shown to be carried by multiple plasmid types and in frequent association with other resistance genes. This diversity of qnr plasmids in combination with their multi-resistance demonstrates the risk associated with qnr positive E. coli.