Detection and genetic characterization of bla-carrying plasmids of cloacal Escherichia coli isolates from white stork nestlings (Ciconia ciconia) in Spain.

OBJECTIVES

This study aimed to characterize Escherichia coli isolates from cloacal samples of white stork nestlings, with a special focus on extended-spectrum β-lactamases (ESBLs)-producing E. coli isolates and their plasmid content.

METHODS

Cloacal samples of 88 animals were seeded on MacConkey-agar and chromogenic-ESBL plates to recover E. coli and ESBL-producing E. coli. Antimicrobial susceptibility was screened using the disc diffusion method, and the genotypic characterization was performed by polymerase chain reaction (PCR) and subsequent sequencing. S1 nuclease Pulsed-Field-Gel-Electrophoresis (PFGE), Southern blotting, and conjugation essays were performed on ESBL-producing E. coli, as well as whole-genome sequencing by short- and long-reads. The four bla-carrying plasmids were completely sequenced.

RESULTS

A total of 113 non-ESBL-producing E. coli isolates were collected on antibiotic-free MacConkey-agar, of which 27 (23.9%) showed a multidrug-resistance (MDR) phenotype, mainly associated with β-lactam-phenicol-sulfonamide resistance (bla/cmlA/floR/sul1/sul2/sul3). Moreover, four white stork nestlings carried ESBL-producing E. coli (4.5%) with the following characteristics: bla/ST38-D, bla/ST58-B1, bla/ST162-B1, and bla/ST155-B1. Whole-genome sequencing followed by Southern blot hybridizations on S1-PFGE gels in ESBL-positive isolates proved that the bla gene and one of the bla genes were carried by IncI1/pST3 plasmids, while the second bla gene and the bla gene were located on IncF plasmids. The two bla genes and the two bla genes had similar but non-identical close genetic environments, as all four genes were flanked by a variety of insertion sequences.

CONCLUSION

The role played by several genetic platforms in the mobility of ESBL genes allows for interchangeability on a remarkably small scale (gene-plasmid-clones), which may support the spread of ESBL genes.