Epidemic characterization and molecular genotyping of Shigella flexneri isolated from calves with diarrhea in Northwest China

Abstract

BackgroundThe widespread presence of antibiotics resistance genes in pathogenic bacteria can cause enormous problems. Food animals are one of the main reservoirs of intestinal pathogens that pose a potential risk to human. Analyzing the epidemiological characteristics and resistance patterns of Shigella flexneri in calves is necessary for animal and human health.Methods and resultsA total of 54 Shigella flexneri isolates, including six serotypes (1a, 2a, 2b, 4a, 6 and Xv), were collected from 837 fecal samples obtained from 2014 to 2016. We performed pulsed-field gel electrophoresis (PFGE) and applied the restriction enzyme NotI to analyze the genetic relatedness among the 54 isolates and to categorize them into 31 reproducible and unique PFGE patterns. According to the results of antimicrobial susceptibility tests, all 26 Shigella flexneri 2a serotypes were resistant to cephalosporin and/or fluoroquinolones. The genes bla TEM-1, bla OXA-1, and bla CTX-M-14 were detected in 19 cephalosporin-resistant S. flexneri 2a isolates. Among 14 fluoroquinolone-resistant isolates, the aac(6′)-Ib-cr gene was largely present in each strain, followed by qnrS (5). Only one ciprofloxacin-resistant isolate harbored the qepA gene. Sequencing the quinolone resistance determining regions (QRDRs) of the fluoroquinolone-resistant isolates revealed two point mutations in gyrA (S83 L, D87N/Y) and a single point mutation in parC (S80I). Interestingly, two gyrA (D87N/Y) strains were resistant to ciprofloxacin.ConclusionsThe current study enhances our knowledge of Shigella in cattle, although continual surveillance is necessary for the control of shigellosis. The high level of cephalosporin and/or fluoroquinolone resistance in Shigella warns us of a potential risk to human and animal health.

<p><em>Shigella</em>: Antibiotic-Resistance Mechanisms And New Horizons For Treatment</p>

“…qnr genes, which are often incorporated into integrons, may allow for dissemination among Shigella and possibly other members of the Enterobacteriaceae family, and then quinolone-resistance isolates may spread across geographic regions and even across countries with population mobility 65,67. The aac(6′)-Ib-cr gene encodes an acetyltransferase associated with reduced quinolone activity, and is identified in many members of the Enterobacteriaceae family 68. PMQRs have been identified widely among human and animal isolates, and have become a pressing issue worldwide.…”

Epidemic and molecular characterization of fluoroquinolone-resistant Shigella dysenteriae 1 isolates from calves with diarrhea

“…It has been reported that aac(6')-Ib-cr signi cantly increases the frequency of selection of chromosomal mutants to reduce cipro oxacin activity by N-acetylation at the amino nitrogen on its piperazinyl substituent [36]. The aac(6')-Ib-cr-positive Shigella was rst isolated in 1998 [37]; however, the most striking nding of our previous and present study was the aac(6′)-Ib-cr allele wide penetration in all quinolone-resistant isolates [38,39]. The qnr family could protect DNA gyrase against quinolones and confer low-level resistance to nalidixic acid and reduced susceptibility to uoroquinolone, especially to cipro oxacin [40].…”

Epidemic and molecular characterization of fluoroquinolone-resistant Shigella dysenteriae 1 isolates from calves with diarrhea

“…40 The aac(6')-Ib-cr-positive Shigella was rst isolated in 1998; 41 however, the most striking nding of our previous and present study was the aac(6′)-Ib-cr allele wide penetration in all quinolone-resistant isolates. 42,43 The qnr family could protect DNA gyrase against quinolones and confer low-level resistance to nalidixic acid and reduced susceptibility to uoroquinolone, especially to cipro oxacin. 44 The qnr gene has occurred worldwide and contains a variety of subtypes, but it was not a common epidemic genotype according to our study.…”