Acinetobacter baumannii in Norwegian chicken farms: A One Health perspective

Abstract

The Gram-negative bacterium, Acinetobacter baumannii, is one of the leading causes of drug resistant hospital-acquired infections in humans. Owing to its ability to easily acquire resistance genes and to survive in the hospital environment for long periods of time, A. baumannii has become a major problem worldwide. Despite much effort trying to find out where it naturally resides, less is known about its native habitat or the reservoirs for the isolates found in the clinic. Thus, in this thesis, multilocus sequence typing (MLST) was performed on a collection of environmental A. baumannii isolates sampled from Norwegian chicken farms in 2016, to uncover the phylogenetic diversity and the relationship between the isolates. The isolates were screened for resistance toward selected clinically relevant antimicrobials using both a disc diffusion and broth microdilution method, in order to investigate whether Norwegian chicken farms could constitute potential reservoirs of carbapenem resistant isolates. Additionally, the isolates were examined for their ability to switch from the opaque to translucent colony morphology, a newly discovered phenomenon in A. baumannii believed to constitute a phase variation mechanism. The MLST analysis revealed both close and distant relationships between the chicken farm isolates, and 36 novel and 18 previously known sequence types were identified. A possible connection between some of the chicken farm isolates and a clinical A. baumannii isolate retrieved from a Norwegian hospital was found. Only one allelic mismatch separated some of the chicken farm isolates from the clinical isolate, harboring the same sequence type as the international clonal lineage 8. Furthermore, it was determined that none of the isolates from chicken farms were resistant to any of the antibiotics tested, putatively indicating that Norwegian chicken farms do not constitute reservoirs of carbapenem resistant A. baumannii. This study presents the first data showing that non-clinical isolates of A. baumannii can switch from the opaque to translucent colony phase, and that frequencies of switching can be highly variable from one isolate to another. Altogether, this study indicates that chicken farms may be an important source of A. baumannii and that phase variation may be a natural inherent mechanism of this species.