Objectives: The main aim of this study was to investigate the prevalence and molecular characteristics of the mcr-1  gene in Escherichia coli  isolates obtained from all patients with bloodstream infections over a year in a Chinese teaching hospital. We also assessed the susceptibility profiles of the mcr-1 -positive strains and prognostic impact of this gene on the patients.
Methods: A total of 144 consecutive, non-repetitive E. coli  isolates causing bloodstream infections were collected at a teaching hospital in Changsha, China from January to December 2016. The presence of the mcr-1  gene was assessed by PCR. All mcr-1 -positive E coli  isolates were characterized by antimicrobial susceptibility testing, multilocus sequence typing (MLST), a conjugation experiment, and plasmid replicon typing. Clinical data were obtained from medical records.
Results: The mcr-1  gene was detected in three (2.1%) of the 144 E. coli  isolates. The three mcr-1 -positive E. coli  isolates were resistant to colistin. All three isolates showed a lower resistance to other classes of antibacterials, with all three being susceptible to carbapenems. The MLST results indicated that the three E. coli  isolates were assigned to three different sequence types: ST457, ST101, and ST1413, respectively. The conjugation experiment showed that the mcr-1  gene was successfully transferred to the recipient (E. coli  EC600) from two isolates, one of which possessed IncI1 replicons and the other of which carried IncHI2 and IncN replicons. The patients with bloodstream infections caused by mcr-1 -positive isolates had severe underlying diseases and were cured after antibacterial treatment.
Conclusion: The prevalence of the mcr-1  gene in patients with E. coli  bloodstream infection was 2.1% in Changsha, China. The mcr-1 -positive E. coli  isolates had varied susceptibility profiles, although all three were susceptible to carbapenems. This therapeutic window is crucial given the risk of rapid deterioration in high-incidence areas worldwide.
Keywords: E. coli , mcr-1 , colistin resistance, bloodstream infection, clinical characteristics