Rare Plasmid-Mediated AmpC Beta-Lactamase DHA-1 Located on Easy Mobilized IS26-Related Genetic Element Detected in <i>Escherichia coli</i> from Livestock and Food in Germany
2024
Chiara Manfreda | Annemarie Kaesbohrer | Silvia Schmoger | Tanja Skladnikiewicz-Ziemer | Mirjam Grobbel | Alexandra Irrgang
AmpC beta-lactamases cause resistance to third-generation cephalosporins, including beta-lactamase inhibitors. In <i>Escherichia coli</i> 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 <i>E. coli</i> (<i>n</i> = 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 <i>bla</i><sub>DHA-1</sub> together with <i>qnrB4</i>, <i>sul1</i> and <i>mph(A)</i> 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.
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