Rare Plasmid-Mediated AmpC Beta-Lactamase DHA-1 Located on Easy Mobilized IS26-Related Genetic Element Detected in Escherichia coli from Livestock and Food in Germany

Abstract

AmpC beta-lactamases cause resistance to third-generation cephalosporins, including beta-lactamase inhibitors. In Escherichia coli from the German food production chain, the majority of AmpC beta-lactamase activity can be attributed to plasmid-mediated CMY-2 or overproduction of chromosomal AmpC beta-lactamase, but occasionally other enzymes like DHA-1 are involved. This study investigated the prevalence of the AmpC beta-lactamase DHA-1 in ESBL/AmpC-producing E. coli (n = 4706) collected between 2016 and 2021 as part of a German antimicrobial resistance monitoring program along the food chain. Eight isolates (prevalence < 0.2%) were detected and further characterized by PFGE, transformation and conjugation experiments as well as short-read and long-read sequencing. All eight strains harbored bla_DHA-1 together with qnrB4, sul1 and mph(A) resistance genes on an IS26 composite transposon on self-transferable IncFII or IncFIA/FIB/II plasmids. During laboratory experiments, activation of the translocatable unit of IS26-bound structures was observed. This was shown by the variability of plasmid sizes in original isolates, transconjugants or transferred plasmids, and correspondingly, duplications of resistance fragments were found in long-read sequencing. This activation could be artificial due to laboratory handling or naturally occurring. Nevertheless, DHA-1 is a rare AmpC beta-lactamase in livestock and food in Germany, and its dissemination will be monitored in the future.

Keywords: AmpC beta-lactamase; DHA-1; E. coli; Enterobacterales; food; livestock.

Figure 1

Phylogenetic relationship of DHA-1-producing E. coli. Single linkage tree based on cgMLST analysis. The numbers on the branches indicate the number of allele differences.

Figure 2

Genetic organization of the bla_DHA-1 region. The bla_DHA-1 gene is located on an IS26 composite transposon with the same structure in all isolates, except for 19-AB01500, in which additional resistances were incorporated. Flanking sequences of the IS26 composite transposon showed variabilities. The same colors in the boxes indicate the same genetic structures. Orientation of the gene fragments according to the position under (−) or above (+) the line is indicated by an arrow. The illustration is schematic and not to scale.

Figure 3

Mapping of bla_DHA-1-harboring plasmids in livestock and food in Germany against IncFII plasmid p133355_SW_C4_Cam-1 in Citrobacter amalonaticus (NZ_CP041363); genes with an asterisk are truncated or incomplete in the reference.