Co-production of MCR-1 and extended-spectrum β-lactamase in Escherichia coli recovered from urinary tract infections in Switzerland.

The first patient was an 83-year-old man who presented a urinary tract infection caused by E. coli following the urological surgery in December 2015. The E. coli isolate (CDF6) showed resistance to broad-spectrum cephalosporins, and the patient was therefore treated by ertapenem for ten days. The second patient was a 75-year-old man who was admitted for the treatment of an adenocarcinoma in January 2016, and had a nephrostomy due to a renal failure. He presented a first urinary tract infection caused by a Proteus mirabilis isolate. After treatment by cefuroxime for 14 days, an E. coli isolate showing resistance to broad-spectrum cephalosporins (CDF8) was recovered from urine. None of those patients received prior treatment with polymyxin, nor traveled abroad. Both isolates were tested for colistin resistance with the Rapid Polymyxin NP test (ELITech, Signes, France) and were found positive after 2 h of incubation. Disk diffusion susceptibility testing performed on Muller–Hinton (MH) agar (Bio-Rad, Cressier, Switzerland) showed that both isolates exhibited an ESBL profile. Minimal inhibitory concentrations (MICs) were determined using the broth microdilution method using cation-adjusted MH broth (Bio-Rad) and both isolates showed an MIC of colistin at 8 μg/ml. PCR amplifications followed by sequencing detected the mcr-1 gene in both isolates. In addition, the isolates were positive for the blaCTX-M-1 and blaCTX-M-15 ESBL encoding genes, respectively. Multilocus sequence types were determined by amplification and sequencing of seven housekeeping genes, and sequence types were assigned using the Warwick E. coli MLST database (http://mlst.warwick.ac.uk/mlst/dbs/ Ecoli). Phylogenetic groups were determined by the PCRbased Clermont method consisting in the detection of specific virulence genes. Isolates CDF-6 and CDF-8 belonged to ST446 and ST164, respectively, and to the commensal B1 and C phylogenetic groups, respectively. Conjugation followed by PCR-based replicon typing analyzes and plasmid Sir,