Dissection of a New qnrD2 M. morganii Plasmid Isolated from Systematically Diseased Cold-Blooded Amphibians

Fluoro(quinolones) are important antimicrobials for treatment of animal and human infections. Several plasmid-mediated resistance factors were reported to be involved in the occurrence of quinolone resistant bacteria. This study was initiated to compare stability, antimicrobial susceptibility and the genetic background of qnrD plasmids from M. morganii comprising different pentapeptide repeat protein D subclones. Bacteriological investigation of systemic diseased African bullfrogs (P. edulis), resulted in the isolation of four M. morganii isolates exhibiting reduced susceptibility to fluoroquinolones and nalidixic acid. Molecular analysis indicated the presence of different small qnrD plasmids. The genetic background of the plasmids was determined and analyzed by bioinformatics. Furthermore, the plasmid stability and the resistance behavior of the plasmids were compared in E. coli, S. Typhimurium and Y. enterocolitica. Plasmid profiling revealed the presence of a previously described 2.7 kb plasmid in three and a novel 1.9 kb plasmid in one of the investigated isolates. Sequence analysis showed, that the smaller plasmid encodes a qnrD2 gene variant. In contrast to the predominant qnrD plasmid prototype, the replication stability seems to be limited over long-time periods under nonselective conditions among various genera of the Enterobacteriaceae. This study disclosed the existence of