Functional Identification and Evolutionary Analysis of Two Novel Plasmids Mediating Quinolone Resistance in Proteus...

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Plasmid-mediated quinolone resistance (PMQR) is a key mechanism for bacterial quinolone resistance.
• PMQR plays a significant role in the horizontal transmission of antibiotic resistance genes (ARGs).

Purpose of the Study:

• To identify and characterize novel plasmids mediating quinolone resistance in Proteus vulgaris.
• To elucidate the regulatory mechanism of qnrD expression and its role in quinolone resistance.
• To investigate the evolutionary origins and transfer mechanisms of qnrD-carrying plasmids.

Main Methods:

• Plasmid identification and characterization.
• Conjugation experiments for plasmid transfer into Escherichia coli.
• Minimum Inhibitory Concentration (MIC) assays.
• Plasmid curing/complementation and qRT-PCR for gene expression analysis.
• Sequence alignment and phylogenetic analysis of plasmids.

Main Results:

• Two novel plasmids, p3M-2A and p3M-2B, were identified in Proteus vulgaris, with p3M-2B carrying the qnrD gene.
• Both plasmids were transferable to Escherichia coli; p3M-2B increased ciprofloxacin resistance.
• Plasmid p3M-2A was found to directly regulate qnrD expression on p3M-2B, with ORF1 playing a crucial role.
• Phylogenetic analysis revealed conserved backbones (ORF1-4) essential for qnrD-carrying plasmid function and suggested p3M-2B's origin from a known qnrD plasmid.

Conclusions:

• This study reports the first identification of a novel qnrD-carrying plasmid from a shrimp-origin P. vulgaris strain.
• A novel regulatory mechanism for qnrD expression involving p3M-2A was discovered.
• The findings provide insights into plasmid evolution, horizontal gene transfer of ARGs, and the potential for plasmid recombination.