Emergence of ADC-5 Cephalosporinase in environmental Acinetobacter baumannii from a German tank milk with a novel Sequence Type

Bacteria resistant to antibiotics arguably pose the greatest threat to human health in the twenty-first century. One such bacterium that typifies antibiotic resistance is Acinetobacter baumannii . Frequently, hospital strains of A. baumannii display multidrug resistant (MDR) or extensively drug resistant (XDR) phenotypes, often requiring the use of last resort antibiotics for treatment. In addition to hospital settings, A. baumannii has been isolated from many highly divergent sources including wastewater treatment plant effluent, soil, and agricultural run-off with global distribution. However, such isolates remain poorly characterized. In this study, we characterized a strain of A. baumannii, AB341-IK15, isolated from bulk tank milk in Germany that demonstrated resistance to ceftazidime and intermediate resistance to ceftriaxone and piperacillin/tazobactam. Further genetic characterization identified an ADC-5 cephalosporinase, first incidence in an environmental isolate; and an OXA-408 oxacillinase that may contribute to this phenotype. Interestingly, AB341-IK15 is of a novel sequence type. This research underscores the importance of studying isolates of A. baumannii of non-clinical origin to understand the antibiotic resistance and virulence potential of environmental isolates of A. baumannii as well to understand the diversity of this species.