pMEX01, a 70kb plasmid isolated from Escherichia coli that confers resistance to multiple β-lactam antibiotics

Abstract

Multidrug-resistant microorganisms are of great concern to public health. Genetic mobile elements, such as plasmids, are among the most relevant mechanisms by which bacteria achieve this resistance. We obtained an Escherichia coli strain CM6, isolated from cattle presenting severe diarrheic symptoms in the State of Querétaro, Mexico. It was found to contain a 70kb plasmid (pMEX01) with a high similarity to the pHK01-like plasmids that were previously identified and described in Hong Kong. Analysis of the pMEX01 sequence revealed the presence of a bla_CTX-M-14 gene, which is responsible for conferring resistance to multiple β-lactam antibiotics. Several genes putatively involved in the conjugative transfer were also identified on the plasmid. The strain CM6 is of high epidemiological concern because it not only displays resistance to multiple β-lactam antibiotics but also to other kinds of antibiotics.

Keywords: Antibiotic resistance; Escherichia coli; Plasmid; bla(CTX-M-14) gene.

Fig. 1

Circular map of pMEX01 (inner map) compared to pHK17a (outer map). The length of pMEX01 is 70,093 bp. Dark green, ORF related to plasmid replication; light green, ORF related to plasmid stabilization; red, CTX-M-14 β-lactamase; gray, ORF related to transposases, insertion sequences; yellow, ORF related ABC transport system; light blue, ORF related to plasmid conjugation, transfer; dark blue, miscellaneous ORF. Inner circle indicates a GC plot, with purple and brown indicating below and above average GC contents, respectively. Asterisks indicate ORF with significant differences.

Fig. 2

Phylogenetic dendrogram for pMEX01. The assembled sequence was compared with the NCBI Plasmid database (accessed April 2016) with Blastn (megablast) to identify highly similar full plasmid sequences with E-value < 10⁻¹⁰. Plasmid sequences were aligned and a dendrogram was generated using the NJ algorithm in ClustalW v2.1 with the default parameters.