Colistin is one of the last-resort therapeutic agents to combat multidrug-resistant Gram-negative bacteria (GNB) including Klebsiella pneumoniae. Although it happens rarely, resistance to colistin has been reported for several GNB. A total of 20 colistin resistant (col-R) and three colistin susceptible (col-S) clinical isolates of K. pneumoniae were studied to explore the underlying mechanisms of colistin resistance. The presence of plasmid encoded resistance genes, mcr-1, mcr-2, mcr-3, and mcr-4 genes were examined by PCR. The nucleotide sequences of pmrA, pmrB, phoP, phoQ, and mgrB genes were determined. To evaluate the association between colistin resistance and upregulation of pmrHFIJKLM and pmrCAB operons, transcriptional level of the pmrK and pmrC genes encoding for lipopolysaccharide target modifying enzymes was quantified by RT-qPCR analysis. None of the plasmid encoded resistance genes were detected in the studied isolates. Inactivation of MgrB due to nonsense mutations and insertion of IS elements was observed in 15 col-R isolates (75%). IS elements (IS5-like and IS1-like families) most commonly targeted the coding region and in one case the promoter region of the mgrB. Complementation with wild-type MgrB restored colistin susceptibility in isolates with altered mgrB. All col-R isolates lacked any genetic alterations in the pmrA, phoP, and phoQ genes and substitutions identified in the pmrB were not found to be involved in resistance conferring determined by complementation assay. Colistin resistance linked with upregulation of pmrHFIJKLM and pmrCAB operons with the pmrK and pmrC being overexpressed in 20 and 11 col-R isolates, respectively. Our results demonstrated that MgrB alterations are the major mechanisms contributing to colistin resistance in the tested K. pneumoniae isolates from Iran.

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We propose a new type of bilayer dispersion-flattened waveguides that have four zero-dispersion wavelengths. Low and flat dispersion can be achieved by using two different material combinations, with a much smaller index contrast as compared to the previously proposed slot-assisted dispersion-flattened waveguides. Without using a nano-slot, dispersion becomes less sensitive to waveguide dimensions, which is highly desirable for high-yield device fabrication. Ultra-low dispersion, high nonlinearity, and fabrication-friendly design would make it promising for practical implementation of nonlinear photonic functions. The proposed waveguide configuration deepens our understanding of the dispersion flattening principle.

We propose a new type of dispersion flattening technology, which can generate an ultra-flat group velocity dispersion profile with five and six zero-dispersion wavelengths (ZDWs). The dispersion value varies from −0.15 to 0.35 ps/(nm•km) from 4 to 8 μm, which to the best of our knowledge is the flattest one reported so far, and the dispersion flatness is improved by more than an order of magnitude. We explain the principle of producing six ZDWs. Mode distribution in this waveguide is made stable over a wide bandwidth. General guidelines to systematically control the dispersion value, sign, and slope are provided, and one can achieve the desired dispersion by properly adjusting the structural parameters. Fabrication tolerance of this waveguide is also examined.

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This ex vivo study compared saliva coronal microleakage in root canals filled with Resilon/Epiphany Self-Etch (SE) system after final irrigation with different solutions. A total of 60 extracted single-rooted human teeth were instrumented using Mtwo Ni-Ti rotary instruments and divided into two experimental groups (n = 20 each) and positive and negative control groups (n = 10 each). The canals were irrigated with 1.3% NaOCl during instrumentation. After removing the smear layer with 17% EDTA, the root canals in groups A and B were flushed with distilled water and 2% chlorhexidine (CHX), respectively, after which they were obturated with Resilon/Epiphany SE using lateral compaction technique. After sterilizing the whole system with gamma-rays, saliva leakage was tested using a split-chamber model. Specimens were monitored every 24 h for 60 days. The data collected were then analyzed using the chi-square test and Kaplan-Meier survival analysis. As compared with group A, the specimens in group B tended to be more resistant to saliva leakage; however, the difference was not significant (P > 0.05). In conclusion, our findings suggest that 2% CHX is a good conditioner for root canal dentin before use of Resilon/Epiphany SE.

A strip/slot hybrid arsenic tri-sulfide waveguide with a horizontal silicon dioxide slot is proposed. The waveguide exhibits an ultra-flat and low dispersion profile with four zero-dispersion wavelengths. Tuning structural parameters of the waveguide causes tailoring the dispersion. There is only a low dispersion of approximately ± 3 ps/(nm · km) over a 1035 nm bandwidth. It is shown that the waveguide has less sensitivity to the variations of the structural parameters and fabrication errors compared to silicon waveguides. Moreover, nonlinear coefficient, figure of merit, third-order dispersion and phase-matching condition in four-wave mixing are studied. This waveguide has a great potential for nonlinear applications in a wide range of wavelengths.