Gate-tunable transport in van der Waals topological insulator Bi4Br4nanobelts.

Bi4Br4is a quasi-one-dimensional van der Waals topological insulator with novel electronic properties. Several efforts have been devoted to the understanding of its bulk form, yet it remains a challenge to explore the transport properties in low-dimensional structures due to the difficulty of device fabrication. Here we report for the first time a gate-tunable transport in exfoliated Bi4Br4nanobelts. Notable two-frequency Shubnikov-de Haas oscillations oscillations are discovered at low temperatures, with the low- and high-frequency parts coming from the three-dimensional bulk state and the two-dimensional surface state, respectively. In addition, ambipolar field effect is realized with a longitudinal resistance peak and a sign reverse in the Hall coefficient. Our successful measurements of quantum oscillations and realization of gate-tunable transport lay a foundation for further investigation of novel topological properties and room-temperature quantum spin Hall states in Bi4Br4.

Two novel blaNDM-1-harbouring transposons on pPrY2001-like plasmids coexisting with a novel cfr-encoding plasmid in food animal source Enterobacteriaceae.

OBJECTIVES: This study reports identification of the carbapenemase-encoding gene from carbapenem-resistant Enterobacterales from food animals. METHODS: A total of 40 bacterial isolates recovered from 475 faecal swabs obtained on one farm were tested for the presence of the blaNDM-1 gene by PCR. Species identification of three blaNDM-1-positive strains was conducted by MALDI-TOF/MS. Antimicrobial susceptibility testing was performed by broth microdilution. Transferability of the blaNDM-1 and cfr genes was determined by filter mating. The genetic environment of blaNDM-1 and cfr was analysed by whole-genome sequencing. RESULTS: Two Proteus mirabilis (JPM24 and YPM35) and one Providencia rettgeri (YPR25) carried blaNDM-1. The blaNDM-1 genes were located on conjugable pPrY2001-like plasmids often reported to carry important antimicrobial resistance genes (ARGs). YPR25 and YPM35 shared two almost identical conjugable plasmids, one carrying blaNDM-1 and the other cfr. The blaNDM-1 gene in YPR25 (same as YPM35) and JPM24 was located in two novel transposons, designated Tn6922 and Tn6923, respectively. Tn6922 and Tn6923 carried 14 and 7 ARGs, respectively, and both contained multiple copies of IS26 in the same direction, with a high degree of similarity. Additionally, cfr was located on a plasmid with an unreported high frequency of conjugative transfer in YPR25 (same as YPM35). CONCLUSION: We identified two novel blaNDM-1-containing transposons (Tn6922 and Tn6923) present on pPrY2001-like plasmids. The pPrY2001-like blaNDM-1 plasmids coexisted with a novel cfr plasmid, and both could transfer at high frequency, highlighting the importance of continuous surveillance of multiresistant Enterobacterales of animal origin that can serve as a reservoir for ARGs.

Research Note: Epidemiological cutoff values and acquired resistance mechanisms of three veterinary antibiotics against Escherichia coli from chicken respiratory tract infections.

Florfenicol, apramycin, and danofloxacin are antibiotics approved only for veterinary use and that have good therapeutic effects on chicken respiratory infections caused by Escherichia coli. We established epidemiological cutoff values (ECV) for these antibiotics using 363 E. coli isolates from tracheal samples of chickens in 5 veterinary clinics in Guangdong Province, China. The minimum inhibitory concentrations (MIC) were determined using the agar dilution method as per Clinical and Laboratory Standards Institution guidelines. The ECV were then calculated using the statistical method and verified by normalized resistance interpretation and ECOFFinder software programs. The ECV of florfenicol, apramycin, and danofloxacin against E. coli were 16, 16, and 0.125 µg/mL, respectively. Susceptibility tests indicated that these isolates were resistant to florfenicol (66.7%), apramycin (22.3%), and danofloxacin (92.3%). Strains carrying floR were distributed in the range of MIC ≥32 µg/mL for florfenicol. Apramycin resistance was found in 77 strains (77/363, 21.1%), and isolates that carried aac(3)-IV were all in the range of MIC ≥512 µg/mL. Danofloxacin resistance was found in the range of MIC ≤0.125 µg/mL, but there were no mutations in the quinolone resistance-determining regions and plasmid-mediated quinolone resistance genes qnrA, qnrB, qnrC, qnrD, aac-(6')-Ib-cr, qep, and oqxB. The presence of the qnrS gene was verified in a few of the strains with an MIC of 0.06 µg/mL. The establishment of ECV was significant for monitoring of resistance development and therapy guidance.