Emerging coexistence of three PMQR genes on a multiple resistance plasmid with a new surrounding genetic structure of qnrS2 in E. coli in China.
BACKGROUND
Quinolones are commonly used for treatment of infections by bacteria of the Enterobacteriaceae family. However, the rising resistance to quinolones worldwide poses a major clinical and public health risk. This study aimed to characterise a novel multiple resistance plasmid carrying three plasmid-mediated quinolone resistance genes in Escherichia coli clinical stain RJ749.


METHODS
MICs of ceftriaxone, cefepime, ceftazidime, ciprofloxacin, and levofloxacin for RJ749 and transconjugant c749 were determined by the Etest method. Conjugation was performed using sodium azide-resistant E. coli J53 strain as a recipient. The quinolone resistance-determining regions of gyrA, gyrB, parC, and parE were PCR-amplified.


RESULTS
RJ749 was highly resistant to quinolones, while c749 showed low-level resistance. S1-nuclease pulsed-field gel electrophoresis revealed that RJ749 and c749 both harboured a plasmid. PCR presented chromosomal mutation sites of the quinolone resistance-determining region, which mediated quinolone resistance. The c749 genome comprised a single plasmid, pRJ749, with a multiple resistance region, including three plasmid-mediated quinolone resistance (PMQR) genes (aac (6')-Ib-cr, qnrS2, and oqxAB) and ten acquired resistance genes. One of the genes, qnrS2, was shown for the first time to be flanked by two IS26s. Three IS26-mediated circular molecules carrying the PMQR genes were detected.


CONCLUSIONS
We revealed the coexistence of three PMQR genes on a multiple resistance plasmid and a new surrounding genetic structure of qnrS2 flanked by IS26 elements. IS26 plays an important role in horizontal spread of quinolone resistance.
['Tao|Ying|Y|', 'Zhou|Kaixin|K|', 'Xie|Lianyan|L|', 'Xu|Yanping|Y|', 'Han|Lizhong|L|', 'Ni|Yuxing|Y|', 'Qu|Jieming|J|', 'Sun|Jingyong|J|']
D000900:Anti-Bacterial Agents D000077723:Cefepime D002442:Ceftazidime D002443:Ceftriaxone D002681:China D002939:Ciprofloxacin D024901:Drug Resistance, Multiple, Bacterial D004926:Escherichia coli D029968:Escherichia coli Proteins D059646:Genome Size D064704:Levofloxacin D008826:Microbial Sensitivity Tests D009154:Mutation D010957:Plasmids D000073336:Whole Genome Sequencing
PMQR Plasmid qnrS2 Escherichia coli Antibiotic resistance Horizontal gene transfer