Mobile insertion cassette elements found in small non-transmissible plasmids in Proteeae may explain qnrD...

Area of Science:

• Microbiology
• Genetics
• Molecular Biology

Background:

• The plasmid-mediated quinolone resistance gene qnrD is found in Enterobacteriaceae.
• qnrD encodes a pentapeptide repeat protein distinct from other Qnr proteins.
• Most qnrD-positive strains belong to the Proteus or Providencia genera.

Purpose of the Study:

• To investigate the origin and genetic support of the qnrD gene.
• To test the hypothesis that qnrD originated in Proteeae bacteria.
• To understand the dissemination mechanisms of qnrD.

Main Methods:

• Screening of 317 Proteeae strains for qnrD using PCR.
• Nucleotide sequencing of qnrD-bearing plasmids.
• Comparative analysis of plasmid sequences and identification of mobile genetic elements.

Main Results:

• Seven qnrD-positive strains were identified (4 Proteus mirabilis, 1 Proteus vulgaris, 2 Providencia rettgeri).
• qnrD was located on small, non-transmissible plasmids, distinct from other qnr genes.
• A mobile insertion cassette (mic) element similar to one found in Providencia vermicola plasmid (pVERM) was identified, potentially explaining qnrD insertion and mobilization.

Conclusions:

• The small non-transmissible qnrD-plasmids likely arose from recombination between a qnrD progenitor and pVERM.
• Proteeae harbors these plasmids, serving as a reservoir for qnrD.
• The mic element facilitates qnrD mobilization to other Enterobacteriaceae plasmids, potentially leading to recombination with larger multi-resistant plasmids.