Identification of Novel tet(X3) Variants Resistant To Tigecycline in Acinetobacter Species.

The emergence of the tet(X) gene is a severe challenge to global public health security, as clinical tigecycline resistance shows a rapidly rising trend. In this research, we identified two tigecycline-resistant Acinetobacter sp. strains containing seven novel tet(X3) variants recovered from fecal samples from Chinese farms. The seven Tet(X3) variants showed 15.4% to 99.7% amino acid identity with Tet(X3). By expressing tet(X3.7) and tet(X3.9), the tigecycline MIC values for Escherichia coli JM109 increased 64-fold (from 0.13 to 8 mg/L). However, the other tet(X3) variants did not have a significant change in the MIC of tigecycline. We found that the 26th amino acid site of Tet(X3.7) changed from proline to serine, and the 25th amino acid site of Tet(X3.9) changed from glycine to alanine, which reduced the MIC of tigecycline by 2-fold [the MIC of tet(X3) to tigecycline was 16 mg/L] but did not affect its expression to tigecycline. The tet(X3) variants surrounded by mobile genetic elements appeared in the structure of gene clusters with tandem repeat sequences and were adjacent to the site-specific recombinase-encoding gene xerD. Therefore, there is a risk of horizontal transfer of resistant genes. Our study reports seven novel tet(X3) variants; the continuing emergence of tigecycline variants makes continuous monitoring of resistance to tigecycline even more critical. IMPORTANCE Although it is illegal to use tigecycline and carbapenems to treat bacterial infections in animals, we can still isolate bacteria containing both mobile resistance genes from animals, and tet(X) is currently an essential factor in degrading tigecycline. Here, we characterized two multidrug-resistant Acinetobacter sp. strains that contained vital resistance genes, such as sul2, a blaOXA-164-like gene, floR, tetM, and multiple novel tet(X3) variants with different tandem structures. It is of paramount significance that their mechanism may transfer to other Gram-negative pathogens, even if their tandem structures have no cumulative effect on tigecycline resistance.

Spread and Molecular Characteristics of Enterobacteriaceae Carrying fosA-Like Genes from Farms in China.

In this study, we aimed to investigate the occurrence and molecular characteristics of fosfomycin-resistant Enterobacteriaceae isolates from pig, chicken and pigeon farms in Guangxi Province of China. A total of 200 fosfomycin-resistant strains were obtained from food animals and their surrounding environments, with the fosA, fosA3, and fosA7.5 genes being detected in 26% (52/200), 10% (20/200), and 5% (10/200), respectively. Surprisingly, three fosA7.5-producing E. coli isolates were found to be concomitant with fosA3. Most of the fosA-like-gene-positive isolates were multidrug-resistant strains and consistently possessed blaCTX-M-1/CTX-M-9, floR, and blaTEM genes. Only fosA3 was successfully transferred to the recipient strains, and the 29 fosA3-carrying transconjugants exhibited high-level resistance to fosfomycin (MIC ≥ 512 µg/mL). Multilocus sequence typing (MLST) combined with enterobacterial repetitive intergenic consensus-PCR (ERIC-PCR) analyses indicated that fosA3 or fosA7.5 genes were spread by horizontal transfer as well as via clonal transmission between E. coli. We used the PCR mapping method to explore the genetic contexts of fosA-like genes, and two representative strains (fEc.1 and fEcg99-1) were fully sequenced. Six different genetic structures surrounding fosA3 were detected and one infrequent context was discovered among the conjugable fosA3-positive E. coli isolates. The five genetic environments of fosA were identified and found to be highly similar to the partial sequence of transposon Tn2921. Furthermore, whole-genome sequencing (WGS) results showed that fosA7.5 was colocalized with mcr-3, blaCMY-63, sul3, tet(A), dfrA, and a number of virulence-related factors on the same chromosomes of strains, and various insertion sequences (IS3/ISL3) were detected upstream or downstream of fosA7.5. The phylogenetic analysis revealed that both fosA7.5- and fosA3-carrying E. coli ST602 and fosA7.5-carrying E. coli ST2599 were closely related to E. coli isolates from humans, which may indicate that they pose a threat to human health. IMPORTANCE Here, we report the widespread and complex genetic environments of fosA-like genes in animal-derived strains in China. The fosA7.5 gene was identified in this study and was found to confer resistance to fosfomycin. The high prevalence of fosA-like genes in farms indicates that food animals serve as a potential reservoir for the resistance genes. This study also discovered that fosfomycin resistance genes were always associated with mobile elements, which would accelerate the transmission of fosA-like genes in strains. Importantly, E. coli ST602 and ST2599 carrying fosA3 or fosA7.5 from food animals had high similarity to E. coli isolates from humans, suggesting that fosA-like genes can be transmitted to humans through the food chain, thus posing a serious threat to public health. Therefore, the prevalence of fosA-like genes isolated from animals should be further monitored.

Significance of the 'line sign' in the diagnosis of congenital imperforate anus on prenatal ultrasound.

BACKGROUND: The prenatal diagnosis of foetal imperforate anus is difficult. Most previous studies have been case reports. To provide useful information for diagnosing foetal imperforate anus, a retrospective review of diagnostic approaches was conducted. Ultrasonography was performed in 19 cases of foetal imperforate anus from 2016 to 2019 at our prenatal diagnostic centre. The prenatal sonographic features and outcomes of each case were collected and evaluated. RESULT: The anal sphincter of a normal foetus shows the 'target sign' on cross-sectional observation. Of the 19 cases of imperforate anus, 16 cases were diagnosed by the ultrasound image feature called the 'line sign'. 1 case with tail degeneration was low type imperforate anus with the irregular 'target sign' not a real 'target sign'. There was two false-negative case, in which the 'target sign' was found, but irregular. CONCLUSION: In this study, we find that the anus of a foetus with imperforate anus presents a 'line sign' on sonographic observation. The absence of the 'target sign' and then the presence of the 'line sign' can assist in the diagnosis of imperforate anus. The 'line sign' can be used as a secondary assessment to determine the type of the malformation following non visualization of the 'target sign'. The higher the position of the imperforate anus is, the more obvious the 'line sign'. It is worth noting that the finding of the short 'line sign' and irregularr 'target sign' can not ignore the low type imperforate anus.

Fermi Velocity Reduction of Dirac Fermions around the Brillouin Zone Center in In2 Se3 -Bilayer Graphene Heterostructures.

Emergent phenomena such as unconventional superconductivity, Mott-like insulators, and the peculiar quantum Hall effect in graphene-based heterostructures are proposed to stem from the superlattice-induced renormalization of (moiré) Dirac fermions at the graphene Brillouin zone corners. Understanding the corresponding band structure commonly demands photoemission spectroscopy with both sub-meV resolution and large-momentum coverage, beyond the capability of the current state-of-the-art. Here the realization of moiré Dirac cones around the Brillouin zone center in monolayer In2 Se3 /bilayer graphene heterostructure is reported. The renormalization is evidenced by reduced Fermi velocity (≈23%) of the moiré Dirac cones and the reshaped Dirac point at the Γ point where they intersect. While there have been many theoretical predictions and much indirect experimental evidence, the findings here are the first direct observation of Fermi velocity reduction of the moiré Dirac cones. These features suggest strong In2 Se3 /graphene interlayer coupling, which is comparable with that in twisted bilayer graphene. The strategy expands the choice of materials in the heterostructure design and stimulates subsequent broad investigations of emergent physics at the sub-meV energy scale.

The application of prenatal ultrasound in the diagnosis of congenital duodenal obstruction.

BACKGROUND: The purpose of this research is to summarize the prenatal ultrasound characteristics of congenital duodenal obstruction (CDO), especially in the diagnosis of duodenal diaphragm and annular pancreas. At present, few researchers have summarized the specific ultrasound features of duodenal diaphragm and annular pancreas. METHODS: In this study, a retrospective analysis of 40 patients diagnosed with CDO between January 2016 and December 2019 was carried out. Data on the diagnosis, ultrasound images and outcomes of the patients were gathered, and the features of the patients were analyzed. RESULTS: The results showed that there were 17 patients (42.5%) of congenital duodenal diaphragm, all with a 'rat tail' sign on the ultrasound images. Moreover, there were 4 patients (10.0%) of CDO caused by annular pancreas, all with a 'pliers' sign on the ultrasound images. We summarized the imaging features of the 'rat tail' sign and the 'pliers' sign. CONCLUSION: The main conclusion of this study was that the 'rat tail' sign could be used as an indirect ultrasound feature to diagnose duodenal diaphragm. The 'pliers' sign could be used as a direct ultrasound feature in the diagnosis of annular pancreas in CDO.

Detecting mode hopping in single-longitudinal-mode fiber ring lasers based on an unbalanced fiber Michelson interferometer.

A method of detecting mode hopping for single-longitudinal-mode (SLM) fiber ring lasers has been proposed and experimentally demonstrated. The method that is based on an unbalanced Michelson interferometer (MI) utilizing phase generated carrier modulation instantly transforms mode-hopping dynamics into steep phase changes of the interferometer. Multiform mode hops in an SLM erbium-doped fiber ring laser with an 18.6 MHz mode spacing have been detected exactly in real-time domain and discussed in detail. Numerical results show that the MI-based method has a high testing sensitivity for identifying mode hopping, which will play a significant role in evaluating the output stability of SLM fiber lasers.