Prevalence of colistin resistance in clinical isolates of Enterobacteriaceae: A four-year cross-sectional study.

OBJECTIVES

The objectives were to determine the prevalence of colistin resistance in clinical isolates of Enterobacteriaceae, and to gain knowledge on the epidemiological and clinical features of the patients.

METHODS

All colistin-resistant Enterobacteriaceae consecutively isolated from clinical samples in our institution from 2012 to 2015, were included in this cross-sectional study. Intrinsic-resistant species were excluded. Minimum inhibitory concentration was performed by gradient diffusion. Detection of plasmid-encoded colistin resistance genes mcr-1 and mcr-2 was performed by amplification. Epidemiological and clinical features were reviewed.

RESULTS

Of 13579 Enterobacteriaceae isolates, 91 were colistin-resistant. The overall prevalence of colistin resistance was 0.67%. The rates were higher in Enterobacter cloacae (4.2%) than Escherichia coli (0.5%) and Klebsiella pneumoniae (0.4%). One third of the isolates were multi-drug resistant (MDR). While mcr-2 was not detected, mcr-1 was detected only in E. coli. Regarding these infections, 23% were community-acquired. 89% of the patients had not received colistin previously. There were no significant differences between infections caused by mcr-1 and non-mcr-1-carrying isolates.

CONCLUSIONS

Colistin resistance was not restricted to MDR isolates and to clinical settings. Most patients had no record of previous administration of colistin.