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Testing the Role of Multicopy Plasmids in the Evolution of Antibiotic Resistance
Published on: May 2, 2018
New plasmid-mediated quinolone resistance gene, qnrC, found in a clinical isolate of Proteus mirabilis
Minghua Wang1, Qinglan Guo, Xiaogang Xu
1Institute of Antibiotics, Huashan Hospital, Fudan University, 12 M. Wulumuqi Rd., Shanghai 200040, People's Republic of China.
Abstract:
Since the discovery of qnrA in 1998, two additional qnr genes, qnrB and qnrS, have been described. These three plasmid-mediated genes contribute to quinolone resistance in gram-negative pathogens worldwide. A clinical strain of Proteus mirabilis was isolated from an outpatient with a urinary tract infection and was susceptible to most antimicrobials but resistant to ampicillin, sulfamethoxazole, and trimethoprim. Plasmid pHS10, harbored by this strain, was transferred to azide-resistant Escherichia coli J53 by conjugation. A transconjugant with pHS10 had low-level quinolone resistance but was negative by PCR for the known qnr genes, aac(6')-Ib-cr and qepA. The ciprofloxacin MIC for the clinical strain and a J53/pHS10 transconjugant was 0.25 microg/ml, representing an increase of 32-fold relative to that for the recipient, J53. The plasmid was digested with HindIII, and a 4.4-kb DNA fragment containing the new gene was cloned into pUC18 and transformed into E. coli TOP10. Sequencing showed that the responsible 666-bp gene, designated qnrC, encoded a 221-amino-acid protein, QnrC, which shared 64%, 42%, 59%, and 43% amino acid identity with QnrA1, QnrB1, QnrS1, and QnrD, respectively. Upstream of qnrC there existed a new IS3 family insertion sequence, ISPmi1, which encoded a frameshifted transposase. qnrC could not be detected by PCR, however, in 2,020 strains of Enterobacteriaceae. A new quinolone resistance gene, qnrC, was thus characterized from plasmid pHS10 carried by a clinical isolate of P. mirabilis.
Insights
A novel quinolone resistance gene, qnrC, was identified in a Proteus mirabilis strain. This gene, located on plasmid pHS10, confers low-level quinolone resistance in gram-negative pathogens.
Area of Science:
- Microbiology
- Genetics
- Molecular Biology
Background:
- Quinolone resistance in gram-negative pathogens is a growing global health concern.
- Plasmid-mediated quinolone resistance genes (e.g., qnrA, qnrB, qnrS) contribute significantly to this issue.
- The emergence of new resistance mechanisms necessitates continuous surveillance and characterization.
Purpose of the Study:
- To identify and characterize novel quinolone resistance genes in clinical isolates.
- To investigate the genetic basis of quinolone resistance in a Proteus mirabilis strain.
- To determine the prevalence and genetic environment of newly discovered resistance genes.
Main Methods:
- Conjugation experiments to transfer resistance plasmids.
- Polymerase Chain Reaction (PCR) to screen for known resistance genes.
- Plasmid DNA digestion, cloning, and sequencing to identify novel genes.
- Bioinformatic analysis to compare the novel gene with known resistance genes.
Main Results:
- A Proteus mirabilis clinical isolate exhibited resistance to ampicillin, sulfamethoxazole, and trimethoprim, with low-level quinolone resistance.
- Conjugation of plasmid pHS10 to Escherichia coli J53 resulted in increased ciprofloxacin Minimum Inhibitory Concentration (MIC).
- Sequencing identified a novel 666-bp gene, designated qnrC, encoding a 221-amino-acid protein with varying homology to other Qnr proteins.
- A novel insertion sequence, ISPmi1, was found upstream of qnrC.
- qnrC was not detected by PCR in 2,020 Enterobacteriaceae strains.
Conclusions:
- A new plasmid-mediated quinolone resistance gene, qnrC, has been identified and characterized.
- The qnrC gene confers low-level quinolone resistance and is associated with a novel insertion sequence.
- Further surveillance is needed to understand the prevalence and spread of qnrC in clinical settings.
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