Abstract
The plasmid-borne colistin-resistant gene mcr-1 has rapidly become a worldwide public health concern. This study aims to determine the host bacterial strains, plasmids, and genetic contexts of mcr-1 in hospital sewage. A 1-ml hospital sewage sample was cultured. Colistin-resistant bacterial colonies were selected on agar plates and were subjected to whole genome sequencing and subsequent analysis. The transfer of mcr-1 between bacterial strains was tested using conjugation. New variants of mcr-1 were cloned to test the impact of variations on the function of mcr-1. Plasmids carrying mcr-1 were retrieved from GenBank for comparison based on concatenated backbone genes. In the sewage sample, we observed that mcr-1 was located in various genetic contexts on the chromosome, or plasmids of four different replicon types (IncHI2, IncI2, IncP, and IncX4), in Klebsiella pneumoniae, Kluyvera spp. and seven Escherichia coli strains of six different sequence types (ST10, ST34, ST48, ST1196, ST7086, and ST7087). We also identified two new variants of mcr-1, mcr-1.4 and mcr-1.7, both of which encode an amino acid variation from mcr-1. mcr-1-carrying IncX4 plasmids, which have a global distribution across the Enterobacteriaceae, are the result of global dissemination of a single common plasmid, while IncI2 mcr-1 plasmids appear to acquire mcr-1 in multiple events. In conclusion, the unprecedented remarkable diversity of species, strains, plasmids, and genetic contexts carrying mcr-1 present in a single sewage sample from a single healthcare site highlights the continued evolution and dynamic transmission of mcr-1 in healthcare-associated environments.
Highlights
Colistin is an antibiotic and has long been one of the last resort treatments for infections caused by multi-drug resistant Gram-negative bacteria
During a screening study for colistinresistant bacterial isolates in hospital sewage, we found that mcr-1 genes including two new variants were carried by plasmids of various replicon types in multiple E. coli strains
All of the isolates were mcr-1 in Sewage identified as E. coli, were resistant to colistin (MICs, 4 or 8 μg/ml) and polymyxin B (MIC, 4 μg/ml), and were found to carry mcr-1 by PCR
Summary
Colistin ( known as polymycin E) is an antibiotic and has long been one of the last resort treatments for infections caused by multi-drug resistant Gram-negative bacteria. Bacterial strains that acquired resistance to colistin resistance have emerged worldwide (Olaitan et al, 2014). The mechanisms mediating resistance to colistin are mainly due to mutations or insertions in the chromosomal genes such as the phoP-Q and Frontiers in Microbiology | www.frontiersin.org Isolate ST ST complex. IncX4, 33,309 aac(3)-IId, strA, strB, aadA22 aph(4)-Ia, aph(3 )-Ia, aac(3)-IVa, aadA2, aadA1
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