Drug resistance detection and whole genome sequencing of a multi-drug resistant Escherichia coli strain from sewage

Abstract:

[Background] The water environment with wide distribution and high mobility is the main medium for the spread of drug resistant bacteria and genes. [Objective] To understand the drug resistance genes and mobile genetic elements carried by Escherichia coli from a sewage plant in northern China. [Methods] A multi-drug resistant strain of E. coli was isolated from the sewage plant. The antimicrobial susceptibility test was carried out. The 96-well plate method was employed to determine the minimum inhibitory concentrations of antibiotics against this strain. The effects of antibiotics at sub-inhibitory concentrations on the growth of the strain were explored by a microplate reader. The whole genome sequencing was carried out to predict the resistance genes and mobile genetic elements carried by the strain. [Results] E. coli WEC was resistant to tetracycline, ciprofloxacin, norfloxacin, and erythromycin. Sub-inhibitory concentrations of tetracycline, ciprofloxacin, and norfloxacin stagnated or inhibited the growth of strains. The genome of WEC was composed of a circular chromosome of 4 782 114 bp and two circular plasmids of 60 306 bp (pWEC-1) and 92 065 bp (pWEC-2), respectively. The strain carried 129 drug resistance genes, of which 128 were located on the chromosome. Prophages, gene islands, and insertion sequences was predicted to be present on the chromosome, and some mobile genetic elements carried drug resistance genes. There was no drug resistance gene in plasmid pWEC-1, and pWEC-2 carried one drug resistance gene. Prophages and insertion sequences were predicted to be present in the plasmid genome. [Conclusion] E. coli WEC from sewage is a multi-drug resistant strain. Carrying drug resistance genes and a variety of mobile genetic elements, the strain has the potential of drug resistance transfer.