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Abstract Background There is a serious public health concern regarding the emergence of carbapenem-resistant Escherichia coli (CREC). The purpose of this study is to identify the molecular characterization and risk factors of CREC in Fujian province, China. Methods A total of 48 CREC isolates were collected from various clinical samples. The strains were identified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/MS). Susceptibility to antibiotics was determined by the standard broth microdilution method. Polymerase chain reaction (PCR) was used to screen common drug resistance genes. Multilocus sequence typing (MLST) was used to type isolates. RT-qPCR was used to detect gene expression of acrA, acrB, and tolC. Conjugation assays were used to analyze the transferability of plasmids carrying mcr-1 or bla NDM. Risk factors for CREC infection were identified by logistic regression analysis. Results 48 CREC strains were collected, with 81.25% producing carbapenemase (CP-CREC), and 18.75% were not producing carbapenemase (no-CP-CREC). They belonged to 21 sequence type (STs) and five unknown STs. Perianal swabs were the main sample type, with 25 patients found to have hematological malignancies. All isolates of CP-CREC were found to contain bla NDM (bla NDM−5 (n = 32), bla NDM−1 (n = 5), bla NDM−4 (n = 1), and bla NDM−13 (n = 1)), among which one isolate co-existence bla NDM−5 and bla OXA−48. Two bla NDM-positive strains, specifically bla NDM−5 and bla NDM−4, were found to co-habor mcr-1 with ST617. Conjugation assays confirmed that bla NDM−1, bla NDM−13, and most bla NDM−5(68.75%, 22/32) could be transferred between E. coli strains. Four of the 9 non-CP-CREC isolates had deletions in ompC and ompF with bla CTX−M production, while the other five showed high expression of acrA, acrB, and tolC. Antibiotics usage, antifungal treatment, detection of other pathogens (prior to CREC infection), and respiratory disease were identified as independent risk factors for CREC infection. The area under the receiver operating characteristic curve for the scoring system was 0.937. Youden’s index, with sensitivity and specificity of 0.96 and 0.78, was maximal when 2 points were scored. Conclusions In CP-CREC, carbapenem resistance is caused primarily by multiple types of bla NDM, while non-CP-CREC is caused by loss of porin protein or high expression of efflux pumps coupled with carrying bla CTX−M. CREC isolates were highly diverse in terms of ST, with a total of 21 STs identified. Here, we first describe a clinical strain of CREC from China both mcr-1 and bla NDM −4 with ST617. An easy-to-use scoring system was developed to diagnose CREC infections.

In order to improve the mechanical properties and corrosion resistance of 2A97 aluminum-lithium alloy, this research develops a novel strain heat-treatment technology. Surprisingly, 2A97 alloy treated by 4% pre-strain and 48 h deep cryogenic aging exhibits excellent mechanical properties, whose yield strength, tensile strength, and elongation are 573.7 MPa, 593.6 MPa, and 14.25%, respectively. Furthermore, the corrosion resistance of samples treated by the above pre-strain deep cryogenic aging process is two times as much as traditional T6 aged. This study deeply investigates the influence of various precipitates in 2A97 alloy on its performance through microstructure analysis. The results show that the introduction of pre-strain inhibits the precipitates of the T1 and δ′ phases at the grain boundaries, and prevents the formation and widening of precipitate-free zones. At the same time, it reduces the potential difference between grain boundaries and matrix, and enhances the corrosion resistance of 2A97 alloy. Deep cryogenic can inhibit recovery and maintain deformation dislocation, so that a large number of defects produced by pre-strain promote the nucleation and diffusion of precipitates in the matrix, resulting in tiny and uniformly distributed precipitates. Therefore, the novel pre-strain deep cryogenic aging not only endues 2A97 alloy excellent performance, but also offers a new strategy for controlling precipitation.

We developed a simple method of in-situ synthesize carbon nanotubes (CNTs) on Ti–6Al–4V (TC4) alloy powder to fabricate CNTs/TC4 compound powders through plasma-enhanced chemical vapor deposition (PECVD). By this approach, CNTs on TC4 alloy powder exhibit better uniform dispersion and morphology compared with the traditional CVD methods. In order to reveal the growth behavior of CNTs during the PECVD process, XRD, SEM, TEM, and Raman spectroscopy were used to analyze the morphology and graphitization of CNTs at different synthesis conditions. The plasma is benefit to the pyrolysis of CH4, but overmuch plasma bombardment also reduces the yield and quality of CNTs. The number of CNTs can be significantly improved with appropriately increasing the temperature and time, but excessive temperature, time and carbon concentration can increase the number of impurities such as amorphous carbon. Significantly, the growth mechanism of CNTs synthesized in TC4 powders is following tip-growth mode in PECVD process. Additionally, the quantity and quality were satisfactory at 600 °C for 30 min with 50 W plasma power. This study about PECVD process lays a foundation for improving the comprehensive properties of CNTs/TC4 composites in the future.