Zhangqi Shen

Objectives The objective of this study was to investigate the prevalence and antimicrobial resistance of Campylobacter isolated from broiler chickens and swine during 2008–14. Methods Campylobacter isolates were collected from samples of intestinal content and excreta from broiler chickens and swine from slaughter houses as well as conventional farms in five Chinese provinces during 2008–14. The agar dilution method was used to determine the susceptibility of Campylobacter isolates to seven antimicrobial agents. The χ² test and Fisher's exact test were used to perform the statistical analysis. Results In total, 989 Campylobacter jejuni and 1991 Campylobacter coli were isolated from 10 535 samples. MIC results revealed a high prevalence of multidrug resistance among these Campylobacter isolates. In addition, we observed an apparent shift of the dominant species from C. jejuni to C. coli in chickens and this species shift coincided with an increased prevalence of macrolide-resistant C. coli. It is worth noting that almost 100% of the C. jejuni and C. coli isolates were resistant to fluoroquinolones. Conclusions The high prevalence of fluoroquinolone and macrolide resistance in Campylobacter suggests that these two clinically important antibiotic classes may no longer be suitable for the treatment of human campylobacteriosis in China. Thus, enhanced surveillance and control efforts are needed to reduce antimicrobial resistance in this group of major foodborne pathogens.

To determine the stability of erm(B) and its associated type VII MDRGI in transformants, two transformants (C179b_11168 and C179b_81-176) were subcultured daily

Macrolide is the drug of choice to treat human campylobacteriosis, but Campylobacter resistance to this antibiotic is rising. The mechanisms employed by Campylobacter jejuni to adapt to erythromycin treatment remain unknown and are examined in this study. The transcriptomic response of C. jejuni NCTC 11168 to erythromycin (Ery) treatment was determined by competitive microarray hybridizations. Representative genes identified to be differentially expressed were further characterized by constructing mutants and assessing their involvement in antimicrobial susceptibility, oxidative stress tolerance, and chicken colonization. Following the treatment with an inhibitory dose of Ery, 139 genes were up-regulated and 119 were down-regulated. Many genes associated with flagellar biosynthesis and motility was up-regulated, while many genes involved in tricarboxylic acid cycle, electron transport, and ribonucleotide biosynthesis were down-regulated. Exposure to a sub-inhibitory dose of Ery resulted in differential expression of much fewer genes. Interestingly, two putative drug efflux operons (cj0309c-cj0310c and cj1173-cj1174) were up-regulated. Although mutation of the two operons did not alter the susceptibility of C. jejuni to antimicrobials, it reduced Campylobacter growth under high-level oxygen. Another notable finding is the consistent up-regulation of cj1169c-cj1170c, of which cj1170c encodes a known phosphokinase, an important regulatory protein in C. jejuni. Mutation of the cj1169c-cj1170c rendered C. jejuni less tolerant to atmospheric oxygen and reduced Campylobacter colonization and transmission in chickens. These findings indicate that Ery treatment elicits a range of changes in C. jejuni transcriptome and affects the expression of genes important for in vitro and in vivo adaptation. Up-regulation of motility and down-regulation of energy metabolism likely facilitate Campylobacter to survive during Ery treatment. These findings provide new insight into Campylobacter adaptive response to antibiotic treatment and may help to understand the mechanisms underlying antibiotic resistance development.

The prevalence of fluoroquinolone (FQ)-resistant Campylobacter has become a concern for public health. To facilitate the control of FQ-resistant (FQ^R) Campylobacter, it is necessary to understand the impact of FQ^R on the fitness of Campylobacter in its natural hosts as understanding fitness will help to determine and predict the persistence of FQ^RCampylobacter. Previously it was shown that acquisition of resistance to FQ antimicrobials enhanced the in vivo fitness of FQ^RCampylobacter. In this study, we confirmed the role of the Thr-86-Ile mutation in GyrA in modulating Campylobacter fitness by reverting the mutation to the wild-type (WT) allele, which resulted in the loss of the fitness advantage. Additionally, we determined if the resistance-conferring GyrA mutations alter the enzymatic function of the DNA gyrase. Recombinant WT gyrase and mutant gyrases with three different types of mutations (Thr-86-Ile, Thr-86-Lys, and Asp-90-Asn), which are associated with FQ^R in Campylobacter, were generated in E. coli and compared for their supercoiling activities using an in vitro assay. The mutant gyrase with the Thr-86-Ile change showed a greatly reduced supercoiling activity compared with the WT gyrase, while other mutant gyrases did not show an altered supercoiling. Furthermore, we measured DNA supercoiling within Campylobacter cells using a reporter plasmid. Consistent with the results from the in vitro supercoiling assay, the FQ^R mutant carrying the Thr-86-Ile change in GyrA showed much less DNA supercoiling than the WT strain and the mutant strains carrying other mutations. Together, these results indicate that the Thr-86-Ile mutation, which is predominant in clinical FQ^RCampylobacter, modulates DNA supercoiling homeostasis in FQ^RCampylobacter.