A Novel Trimethoprim Resistance Gene, <italic toggle="yes">dfrA36</italic>, Characterized from <named-content content-type="genus-species">Escherichia coli</named-content> from Calves

Abstract

ABSTRACT Whole-genome sequencing of trimethoprim-resistant Escherichia coli strains MF2165 and PF9285 from healthy Swiss fattening calves revealed a so far uncharacterized dihydrofolate reductase gene, dfrA36. Functionality and association with trimethoprim resistance were demonstrated by cloning and expressing dfrA36 in E. coli. The DfrA36 protein showed the closest amino acid identity (49.4%) to DfrA20 from Pasteurella multocida and to the Dfr determinants DfrG (41.2%), DfrD (40.8%), and DfrK (40.0%) found in Gram-positive bacteria. The dfrA36 gene was integrated within a florfenicol/chloramphenicol-sulfonamide resistance ISCR2 element (floR-ISCR2-dfrA36-sul2) next to a Tn21-like transposon that contained genes with resistance to sulfonamides (sul1), streptomycin (aadA1), gentamicin/tobramycin/kanamycin (aadB), and quaternary ammonium compounds (qacEΔ1). A search of GenBank databases revealed that dfrA36 was present in 26 other E. coli strains from different origins as well as in Acinetobacter. IMPORTANCE The presence of dfrA36 associated with ISCR2 in Escherichia coli from animals, as well as its presence in other E. coli strains from different sources and countries and in Acinetobacter, highlights the global spread of this gene and its potential for further dissemination. The genetic link of ISCR2-dfrA36 with other antibiotic and disinfectant resistance genes showed that multidrug-resistant E. coli may be selected and maintained by the use of either one of several antimicrobials.

Keywords

• Escherichia coli
• animals
• antibiotic resistance
• gene cassettes
• trimethoprim