Background: The emergence of a novel plasmid-mediated colistin resistance mechanism, encoded by the mcr-1 gene, represents a major public health concern. The mechanism of resistance to colistin, mediated by plasmids, is a serious problem, both for its ability to be transferred to other species, and for infections caused by carbapenem-resistant Gram-negative, in which colistin is used as an antimicrobial drug of last line for the treatment of these infections. The present study highlights the first isolation and genetic evaluation of detecting plasmid-mediated resistance to colistin in a multidrug-resistant (MDR) Escherichia coli (E. coli) isolated from a clinical sample in the metropolitan city of Naples, Italy.
Results: Colistin-resistant E. coli isolate was identified in August 2020 from the blood culture of a male patient with multiple comorbidities. The minimum inhibitory concentration (MIC) of colistin was 8 mg/L. In addition to colistin, the isolate was resistant to third-generation cephalosporins (cefotaxime and ceftazidime), penicillin (amoxicillin and piperacillin), aminoglycosides (gentamicin and tobramycin), and fluoroquinolones (ciprofloxacin and levofloxacin). However, it showed susceptibility to carbapenems (ertapenem, imipenem, and meropenem), tetracyclines (tigecycline), and piperacillin-tazobactam. The results of the PCR confirmed the presence of the mcr-1 resistance gene.
Conclusion: This study confirms the presence of resistance to colistin mediated by the mcr-1 gene in a clinical isolate of E. coli. Although resistance to colistin caused by the mcr-1 gene is not common in our region, it should not be ignored. Therefore, further surveillance studies are recommended to monitor the spread of plasmid-mediated colistin resistance genes in Gram-negative MDR bacteria.