Newest data on fluoroquinolone resistance mechanism of Shigella flexneri isolates in Jiangsu Province of China

Abstract

BackgroundTo determine the prevalence, antimicrobial susceptibility patterns and related presence of mutations in quinolone resistance-determining region (QRDR) genes and plasmid-mediated quinolone resistance (PMQR) among Shigella flexneri isolates obtained from Jiangsu Province, China.MethodsA total of 400 Shigella flexneri clinical isolates collected during 2012–2015 were identified by biochemical and serological methods, and the antimicrobial susceptibility pattern was evaluated using the disc-diffusion method. PCR and DNA sequencing were accomplished to identify mutations in gyrA, gyrB, parC and parE, and the presence of qnrA, qnrB, qnrC, qnrD, qnrS, qepA and aac(6′)-Ib-cr genes were also detected.ResultsOf all the Shigella flexneri, 75.8% were resistant to nalidixic acid, and 37.0% were categorized as norfloxacin resistant. Overall, 75.5% of isolates possessed gyrA mutations (Ser83Leu, Asp87Gly/Asn and His211Tyr), while 84.3% had parC mutations (Ser80Ile, Ala81Pho, Gln91His and Ser129Pro). The most prevalent point mutations in gyrA and parC were Ser83Leu (75.5%, 302/400) and Ser80Ile (74.5%, 298/400), relatively. Besides, the Gln517Arg alternation in gyrB was detected in 13 S. flexneri isolates and no mutations were identified in parE. PMQR determinations of qnrB, qnrS and aac(6′)-Ib-cr were detected among 16 strains (4.0%).ConclusionsThe results presented here show that fluoroquinolone resistance in these clinical isolates result from mutations in chromosome, besides, despite the low prevalence of PMQR determinants in Jiangsu, it is essential to continue surveillance PMQR determinants in this area.

Two novel mutations in parE among Shigella flexneri isolated from Jiangsu Province of China, 2016

“…Here, qnrS and aac(6')-Ib-cr were observed within six clinical isolates. It was different from our previous result (19) that qnrS became the most prevalent positive gene. In addition, all qnrS positive strains that conferred resistance to ciprofloxacin were involved in at least 3 mutations in gyrA and parC, especially at the position of Ser83 and Ser80.…”

“…Up to now, chromosomal mutation in target genes of QRDR remains the most significant mechanism for fluoroquinolone resistance, particularly the amino acid substitution in gyrA and parC (15,37), and a recent study based on structural level has reconfirmed this (38). In this research, unsurprisingly, Ser83Leu within gyrA was still described as the most dominant point mutation, consistent with previous study (19), with gyrA (His211) and parC (Ser80) being the predominant. Besides, among 57 nalidixic acid-resistant isolates, mutation Ser83Leu and His211Tyr in gyrA also played an important part.…”

“…Besides, among 57 nalidixic acid-resistant isolates, mutation Ser83Leu and His211Tyr in gyrA also played an important part. It could not be ignored that since the mutation His211Tyr (gyrA) was first detected in Bangladesh during 2009 (39), the quinolone-resistant S. flexneri isolates seemed to get more attention (19,40,41), and this made us keep thinking that whether this mutation could confer resistance to antibacterial agents. Then, our data also showed that multiple mutations will highly increase the risk of acquiring fluoroquinolone resistance (37), for 76.6% Shigella isolates expressed resistance to ciprofloxacin with 3 critical mutations at the same time, which were located at the position of Ser83 and Asp87 within gyrA in company with Ser80 in parC.…”

“…We have successively carried out detailed characterization and studies on S. flexneri isolates in Jiangsu Province of China from 2001 to 2015, especially in the aspect of antimicrobial resistance to quinolones and relevant molecular mechanism. The results of these studies have displayed the essentiality of continuous monitoring in this area (19,20). Based on this, we collected the S. flexneri isolates in Jiangsu Province of China in 2016, trying to observe the changes of resistance to fluoroquinolones , the prevalence of PMQR determinants, and ulteriorly explore whether new point mutation associated with resistance mechanism exists in the QRDR genes or not.…”

Out of Asia: the independent rise and global spread of fluoroquinolone-resistant Shigella

“…Later, a secondary mutation in gyrA delineated the Bangladeshi ( gyrA -D87N) and the Chinese ( gyrA -D87G) FQR isolates. However, the increasing isolation frequency of the gyrA -D87N variant in parts of China may be the result of a higher degree of trans-border dissemination from South Asia and/or the separate, indigenous emergence of a competent FQR subclone [ 31 ]. Due to the degree of genetic diversity and the complex population structures within S. flexneri , the true nature of such events cannot be easily measured using low-resolution molecular typing methods.…”