Dielectric probing of low-temperature degradation resistance of commercial zirconia bio-ceramics.

OBJECTIVES: To investigate the effect of the stability of oxygen vacancies on the low-temperature degradation (LTD) resistance of two kinds of commercial zirconia-based materials (3Y-TZP ceramics and Ce-TZP/Al2O3 composites) via the dielectric probing methods. METHODS: The commercial 3Y-TZP ceramics and Ce-TZP/Al2O3 composites were prepared via conventional solid-state methods. Density, phase content, microstructure, strain, and biaxial flexural strength (BFS) of two materials were investigated using Archimedes method, XRD, SEM, strain-electric field (S-E) loops and ball-on-ring methods, respectively. The concentration of oxygen vacancies before and after LTD of two materials were evaluated using dielectric probing and XPS methods. RESULTS: The XRD analysis revealed that compared to the 3Y-TZP ceramics, the Ce-TZP/Al2O3 composites showed better LTD resistance, without clear LTD. The greater LTD resistance for Ce-TZP/Al2O3 composites was associated with their stability of oxygen vacancies, by higher activation energy based on the dielectric measurements and XPS results. For the 3Y-TZP ceramics that underwent the tetragonal to the monoclinic phase transition during the LTD treatment, the concentration of their oxygen vacancies decreased after LTD. In addition, the Ce-TZP/Al2O3 composites exhibited higher flexural strength and potential fracture toughness based on the BFS testing and strain vs electric field measurement results, indicating a great potential for use in fixed restorative dental applications. SIGNIFICANCE: This work suggested the stability of oxygen vacancies played a key role in the resistance to LTD. Optimizing the stability of the oxygen vacancies is key to the development of more reliable zirconia- based dental biomaterials with greater resistance to LTD.

Therapeutic efficacy of a K5-specific phage and depolymerase against Klebsiella pneumoniae in a mouse model of infection.

Klebsiella pneumoniae has become one of the most intractable gram-negative pathogens infecting humans and animals due to its severe antibiotic resistance. Bacteriophages and protein products derived from them are receiving increasing amounts of attention as potential alternatives to antibiotics. In this study, we isolated and investigated the characteristics of a new lytic phage, P1011, which lyses K5 K. pneumoniae specifically among 26 serotypes. The K5-specific capsular polysaccharide-degrading depolymerase dep1011 was identified and expressed. By establishing murine infection models using bovine strain B16 (capable of supporting phage proliferation) and human strain KP181 (incapable of sustaining phage expansion), we explored the safety and efficacy of phage and dep1011 treatments against K5 K. pneumoniae. Phage P1011 resulted in a 60% survival rate of the mice challenged with K. pneumoniae supporting phage multiplication, concurrently lowering the bacterial burden in their blood, liver, and lungs. Unexpectedly, even when confronted with bacteria impervious to phage multiplication, phage therapy markedly decreased the number of viable organisms. The protective efficacy of the depolymerase was significantly better than that of the phage. The depolymerase achieved 100% survival in both treatment groups regardless of phage propagation compatibility. These findings indicated that P1011 and dep1011 might be used as potential antibacterial agents to control K5 K. pneumoniae infection.

Antimicrobial resistance survey and whole-genome analysis of nosocomial P. Aeruginosa isolated from eastern Province of China in 2016-2021.

BACKGROUND: Pseudomonas aeruginosa is a major Gram-negative pathogen that can exacerbate lung infections in the patients with cystic fibrosis, which can ultimately lead to death. METHODS: From 2016 to 2021, 103 strains of P. aeruginosa were isolated from hospitals and 20 antibiotics were used for antimicrobial susceptibility determination. Using next-generation genome sequencing technology, these strains were sequenced and analyzed in terms of serotypes, ST types, and resistance genes for epidemiological investigation. RESULTS: The age distribution of patients ranged from 10 days to 94 years with a median age of 69 years old. The strains were mainly isolated from sputum (72 strains, 69.9%) and blood (14 strains, 13.6%). The size of these genomes ranged from 6.2 Mb to 7.4 Mb, with a mean value of 6.5 Mb. In addition to eight antibiotics that show inherent resistance to P. aeruginosa, the sensitivity rates for colistin, amikacin, gentamicin, ceftazidime, piperacillin, piperacillin-tazobactam, ciprofloxacin, meropenem, aztreonam, imipenem, cefepime and levofloxacin were 100%, 95.15%, 86.41%, 72.82%, 71.84%, 69.90%, 55.34%, 52.43%, 50.49%, 50.49%, 49.51% and 47.57% respectively, and the carriage rate of MDR strains was 30.69% (31/101). Whole-genome analysis showed that a total of 50 ST types were identified, with ST244 (5/103) and ST1076 (4/103) having a more pronounced distribution advantage. Serotype predictions showed that O6 accounted for 29.13% (30/103), O11 for 23.30% (24/103), O2 for 18.45% (19/103), and O1 for 11.65% (12/103) of the highest proportions. Notably, we found a significantly higher proportion of ExoU in P. aeruginosa strains of serotype O11 than in other cytotoxic exoenzyme positive strains. In addition to this, a total of 47 crpP genes that mediate resistance to fluoroquinolones antibiotics were found distributed on 43 P. aeruginosa strains, and 10 new variants of CrpP were identified, named 1.33, 1.34, 1.35, 1.36, 1.37, 1.38, 1.39, 1.40, 1.41 and 7.1. CONCLUSIONS: We investigated the antibiotic susceptibility of clinical isolates of P. aeruginosa and genomically enriched the diversity of P. aeruginosa for its prophylactic and therapeutic value.

Terahertz Faraday Rotation of SrFe12O19 Hexaferrites Enhanced by Nb Doping.

The magneto-optical and dielectric behavior of M-type hexaferrites as permanent magnets in the THz band is essential for potential applications like microwave absorbers and antennas, while are rarely reported in recent years. In this work, single-phase SrFe12-xNbxO19 hexaferrite ceramics were prepared by the conventional solid-state sintering method. Temperature dependence of dielectric parameters was investigated here to determine the relationship between dielectric response and magnetic phase transition. The saturated magnetization increases by nearly 12%, while the coercive field decreases by 30% in the x = 0.03 composition compared to that of the x = 0.00 sample. Besides, the Nb substitution improves the magneto-optical behavior in the THz band by comparing the Faraday rotation parameter from 0.75 (x = 0.00) to 1.30 (x = 0.03). The changes in the magnetic properties are explained by a composition-driven increase of the net magnetic moment and enhanced ferromagnetic exchange coupling. The substitution of the donor dopant Nb on the Fe site is a feasible way to obtain multifunctional M-type hexaferrites as preferred candidates for permanent magnets, sensors, and other electronic devices.

Characterization of Vibrio parahaemolyticus isolated from stool specimens of diarrhea patients in Nantong, Jiangsu, China during 2018-2020.

Vibrio parahaemolyticus is the leading cause of acute seafood-associated gastroenteritis worldwide. The aim of this study was to investigate the presence of virulence genes, biofilm formation, motor capacities and antimicrobial resistance profile of V. parahaemolyticus isolates isolated from clinical samples in Nantong during 2018-2020. Sixty-six V. parahaemolyticus strains isolated from stool specimens of diarrheal patients were examined. The PCR results showed that there were two tdh+trh+ isolates, four tdh-trh- isolates and sixty tdh+trh- isolates, accounting for 3.0%, 6.1% and 90.9%, respectively. All the tdh carrying isolates manifested the positive reactions for the Kanagawa phenomenon (KP) test. Most of the isolates harbored at least one of the specific DNA markers of 'pandemic group' strains, suggesting that the dominant isolates of V. parahaemolyticus in Nantong might belong to the new O3: K6 or its serovariants. All tdh+ isolates possessed the Vp-PAI genes, but no tdh-trh- isolates carried the T3SS2 genes. All isolates were biofilm producers and had relatively strong motor capacities. In addition, the V. parahaemolyticus isolates were resistant to ampicillin (98.5%), cefuroxime (75.6%), cefepime (66.7%), piperacillin (59.1%) and ampicillin/sulbactam (50.0%), but sensitive to ciprofloxacin (100.0%), levofloxacin (100.0%), trimethoprim-sulfamethoxazole (98.5%), gentamicin (98.5%), amikacin (97%), meropenem (71.2%), and ceftazidime (56.1%). Multidrug-resistant isolates in clinical might be related to the inappropriate use of antimicrobials in aquaculture.

Whole-genome analyses of APEC carrying mcr-1 in some coastal areas of China from 2019 to 2020.

OBJECTIVES: Polymyxin is considered as one of the 'last lines of defense' for the treatment of multidrug resistant bacteria. Increased use of polymyxin during recent years poses a risk to public health. The purpose of this study was to investigate the carrying situation of the mcr-1 drug-resistance gene in waterfowl in some coastal areas of China from 2019 to 2020. METHODS: Fifty-seven isolated avian pathogenic Escherichia coli strains were selected from 493 APEC isolates for whole-genome sequencing. The 24 mcr-1-positive APEC strains were tested for conjugation and genome-wide analysis, including sequence type (ST) analysis, serotype analysis, and drug-resistance gene analysis. Numerous mcr-1-positive E. coli were downloaded from the National Center for Biotechnology Information (NCBI) for comparative genomic analysis. RESULTS: Antimicrobial susceptibility test results showed that 57 APEC isolates were highly resistant to gentamicin, cefotaxime, and ofloxacin, and 24 mcr-1-positive APEC isolates were resistant to polymyxin. Fourteen isolates of mcr-1-positive APEC plasmids were successfully conjugated to EC600. Both ST156 and ST10 were found in high proportions in human and avian sources through genome-wide analysis; it is worth noting that these two isolates of APEC were detected to contain the blaNDM-1 and blaNDM-4 genes, respectively. CONCLUSION: In this study, the epidemiological investigation of the mcr-1 gene was carried out on APEC in some coastal areas of China from 2019 to 2020, and our results have enriched the data on the transmission of APEC isolates carrying the mcr-1 gene in waterfowl.

O145 may be emerging as a predominant serogroup of Avian pathogenic Escherichia coli (APEC) in China.

Among the numerous serotypes of Avian pathogenic Escherichia coli (APEC), O1, O2 and O78 have long been considered the predominant serogroups. O145, a pivotal serogroup in non-O157 Shiga toxin-producing Escherichia coli, has never been considered an important serogroup among APEC. The prevalence of APEC O145 was determined from the results of molecular serogrouping based on 42 sequenced isolates from Jiangsu and Guangxi Provinces in China. After realizing the potential importance of O145, 224 APEC isolates isolated from Jiangsu, Guangxi, Anhui, Shandong, Henan, Yunnan and Fujian provinces were screened using PCR amplification. The results showed that the proportion of O145 detected was 37.9 % (85/224), which was higher than those of the three traditional APEC serogroups. The virulence evaluation experiment showed that this serogroup may have stronger pathogenicity. Here, we report for the first time that O145 may be emerging as a predominant serogroup of APEC in China. The possible reasons for its prevalence and oversight were analyzed through genomic analysis. Furthermore, pangenome analysis with STEC O145 was performed to assess the potential threat to humans. The discovery of the ubiquity of O145 may not be coincidental, which may also account for the failure of vaccines that target the three major serogroups. Therefore, this newly predominant serogroup should be paid more attention and the focus should not be limited to the so-called three major APEC serogroups.

An Escherichia coli isolate from hospital sewage carries blaNDM-1 and blaoxa-10.

Carbapenems, as the "last line of defense" against Gram-negative bacteria, are increasingly being challenged by drug-resistant bacteria, especially Enterobacteriaceae. In this study, a carbapenem-resistant Gram-negative bacterium, named AH001, was isolated from hospital sewage, and a modified Hodge test confirmed that this bacterium can produce carbapenemase. Further analysis revealed that this bacterium exhibits multidrug resistance against an additional seven antibiotics. Whole-genome sequencing and analysis showed that AH001 could not be classified by existing MLST, and its serotype could not be distinguished among O9, O89 or O168 according to O antigen prediction. More attention should be given to the role of environmental sources of Escherichia coli in the development and transfer of drug resistance in the hospital environment.

Structural Evolution in BiNbO4.

The sequence of transitions between different phases of BiNbO4 has been thoroughly investigated and clarified using thermal analysis, high-resolution neutron diffraction, and Raman spectroscopy. The theoretical optical phonon modes of the α-phase have been calculated. Based on thermoanalytical data supported by density functional theory (DFT) calculations, the ß-phase is proposed to be metastable, while the α- and γ-phases are stable below and above 1040 °C, respectively. Accurate positional parameters for oxygen positions in the three main polymorphs (α, ß, and γ) are presented and the structural relationships between these polymorphs are discussed. Even though no significant changes, only relaxation phenomena, are observed in the dielectric behavior of α-BiNbO4 below 1000 °C, evidence of two further subtle transitions at ∼350 and 600 °C is presented through careful analysis of structural parameters from variable temperature neutron diffraction measurements. Such phase variations are also evident in the phonon modes in Raman spectra and supported by changes in the thermoanalytical data. These subtle transitions may correspond to the previously proposed antiferroelectric to ferroelectric and ferroelectric to paraelectric phase transitions, respectively.