Related Experiment Video
Updated: Mar 27, 2026
Isolation and Identification of Waterborne Antibiotic-Resistant Bacteria and Molecular Characterization of their Antibiotic Resistance Genes
Published on: March 3, 2023
qnrA6 genetic environment and quinolone resistance conferred on Proteus mirabilis
Aurélie Jayol1, Frédéric Janvier2, Thomas Guillard3
1Univ. Paris Diderot, Sorbonne Paris Cité, Inserm IAME, UMR 1137, F-75018 Paris, France AP-HP, Lariboisière-Fernand Widal, Bacteriology, F-75010 Paris, France.
Objectives:
To determine the genetic location and environment of the qnrA6 gene in Proteus mirabilis PS16 where it was first described and to characterize the quinolone resistance qnrA6 confers.
Methods:
Transformation experiments and Southern blotting were performed for plasmid and genomic DNA of P. mirabilis PS16 to determine the qnrA6 location. Combinatorial PCRs with primers in qnrA6 and genes usually surrounding qnrA genes were used to determine the genetic environment. The qnrA6 coding region, including or not the promoter region, was cloned into vectors pTOPO and pBR322 and the MICs of six quinolones were measured for transformants of Escherichia coli TOP10 and P. mirabilis ATCC 29906 Rif(R).
Results:
qnrA6 was shown to be chromosomally encoded in P. mirabilis PS16 and its genetic environment was 81%-87% similar to that of qnrA2 in the Shewanella algae chromosome. The 5138 bp region up- and downstream of qnrA6 contained an IS10 sequence surrounded by two ISCR1. This resulted in qnrA6 being displaced 1.9 kb from its native promoter but supplied a promoter present in ISCR1. qnrA6 cloned into pTOPO and pBR322 conferred a 4-32-fold increase in fluoroquinolone MICs when expressed in E. coli but only 2-3-fold in P. mirabilis. When including the promoter region, a further increase in resistance was observed in both species, reaching MIC values above clinical breakpoints for only P. mirabilis.
Conclusions:
qnrA6 is the first chromosomally located qnrA gene described in Enterobacteriaceae. The quinolone resistance conferred by qnrA6 depends on the proximity of an efficient promoter and the host strain where it is expressed.
Insights
The qnrA6 gene in Proteus mirabilis is chromosomally located and confers quinolone resistance. Its expression and resistance levels depend on promoter proximity and host strain.
Area of Science:
- Microbiology
- Genetics
- Molecular Biology
Background:
- The qnrA gene family confers resistance to quinolone antibiotics.
- Understanding the genetic basis of antibiotic resistance is crucial for public health.
- Proteus mirabilis is an opportunistic pathogen where novel resistance mechanisms may emerge.
Purpose of the Study:
- To determine the genetic location and environment of the qnrA6 gene in Proteus mirabilis.
- To characterize the quinolone resistance conferred by the qnrA6 gene.
- To investigate the role of promoter elements and host factors in qnrA6-mediated resistance.
Main Methods:
- Southern blotting and transformation experiments to locate the qnrA6 gene.
- Combinatorial PCR to determine the genetic environment surrounding qnrA6.
- Cloning of qnrA6 with and without its promoter into expression vectors.
- Determination of minimum inhibitory concentrations (MICs) of six quinolones in transformant strains.
Main Results:
- The qnrA6 gene was found to be chromosomally encoded in Proteus mirabilis PS16.
- The genetic environment of qnrA6 showed similarity to qnrA2, with ISCR1 elements potentially providing a promoter.
- Cloned qnrA6 conferred increased fluoroquinolone MICs in Escherichia coli and Proteus mirabilis, with higher levels when the promoter was included.
- Resistance levels exceeded clinical breakpoints in Proteus mirabilis when the promoter was present.
Conclusions:
- qnrA6 is the first chromosomally located qnrA gene identified in Enterobacteriaceae.
- The level of quinolone resistance conferred by qnrA6 is influenced by the proximity of an effective promoter.
- Host strain background significantly impacts the expression and effectiveness of qnrA6-mediated quinolone resistance.
Related Concept Videos
01:25Mechanism of Antibiotic Resistance in MRSA
01:28Inhibitors of Bacterial DNA Synthesis
01:28Gene Regulation in Microbial Communities: Quorum Sensing
01:30Development of Antibiotic Resistance
01:25Clinical Significance of Antibiotic Resistance
00:57Antibiotic Selection