The new generation of radio interferometers is characterized by high sensitivity, wide fields of view and large fractional bandwidth. To synthesize the deepest images enabled by the high dynamic ...range of these instruments requires us to take into account the direction-dependent Jones matrices, while estimating the spectral properties of the sky in the imaging and deconvolution algorithms. In this paper we discuss and implement a wideband wide-field spectral deconvolution framework (ddfacet) based on image plane faceting, that takes into account generic direction-dependent effects. Specifically, we present a wide-field co-planar faceting scheme, and discuss the various effects that need to be taken into account to solve for the deconvolution problem (image plane normalization, position-dependent Point Spread Function, etc). We discuss two wideband spectral deconvolution algorithms based on hybrid matching pursuit and sub-space optimisation respectively. A few interesting technical features incorporated in our imager are discussed, including baseline dependent averaging, which has the effect of improving computing efficiency. The version of ddfacet presented here can account for any externally defined Jones matrices and/or beam patterns.
Summary
A literature review was undertaken to ascertain the molecular basis for tigecycline and colistin resistance mechanisms and the experimental basis for the detection and delineation of this ...resistance particularly in carbapenemase‐producing Gram‐negative bacteria. Pubmed, Google Scholar and Science Direct were searched with the keywords colistin, tigecycline, resistance mechanisms and detection methods. Trans‐complementation and comparative MIC studies, mass spectrometry, chromatography, spectrofluorometry, PCR, qRT‐PCR and whole genome sequencing (WGS) were commonly used to determine tigecycline and colistin resistance mechanisms, specifically modifications in the structural and regulatory efflux (acrAB, OqxAB, kpgABC adeABC‐FGH‐IJK, mexAB‐XY‐oprJM and soxS, rarA robA, ramRAB marRABC, adeLRS, mexRZ and nfxb) and lipid A (pmrHFIJFKLM, lpxA, lpxC lpxD and mgrB, pmrAB, phoPQ,) genes respectively. Mutations in the ribosomal 16S rRNA operon rrnBC, also yielded resistance to tigecycline through target site modifications. The mcr‐1 gene conferring resistance to colistin was identified via WGS, trans‐complementation and a murine thigh infection model studies. Common detection methods are mainly antibiotic sensitivity testing with broth microdilution while molecular identification tools are mostly PCR and WGS. Spectrofluorometry, MALDI‐TOF MS, micro‐array and real‐time multiplex PCR hold much promise for the future as new detection tools.
ABSTRACT
We present MeerKAT 1.28 GHz total-intensity, polarization, and spectral-index images covering the giant (projected length l ≈ 1.57 Mpc) X-shaped radio source PKS 2014−55 with an ...unprecedented combination of brightness sensitivity and angular resolution. They show the clear ‘double boomerang’ morphology of hydrodynamical backflows from the straight main jets deflected by the large and oblique hot-gas halo of the host galaxy PGC 064440. The magnetic field orientation in PKS 2014−55 follows the flow lines from the jets through the secondary wings. The radio source is embedded in faint ($T_\mathrm{b} \approx 0.5 \mathrm{\, K}$) cocoons having the uniform brightness temperature and sharp outer edges characteristic of subsonic expansion into the ambient intragroup medium. The position angle of the much smaller (l ∼ 25 kpc) restarted central source is within 5° of the main jets, ruling out models that invoke jet re-orientation or two independent jets. Compression and turbulence in the backflows probably produce the irregular and low polarization bright region behind the apex of each boomerang as well as several features in the flow with bright heads and dark tails.
Aims
This study aimed at investigating the use of metal chelators as potential metallo‐β‐lactamase inhibitors (MBL).
Methods and Results
The minimum inhibitory concentration (MIC) of meropenem was ...ascertained alone and in combination with various concentrations of macrocyclic (1,4,7‐ triazacyclononane‐1‐glutaric acid‐4,7‐diacetic acid = NODAGA) peptide derivatives and acyclic (N,N,N′,N′‐Tetrakis(2‐pyridylmethyl)ethylenediamine = TPEN and di‐(2‐picolyl)amine = DPA) metal chelators using the broth microdilution method. MICs of meropenem against carbapenem‐resistant enterobacteriaceae (CRE) producing MBLs were decreased to concentrations as low as 0·06 mg l−1 in the presence of some metal chelators. TPEN at 4 and 8 mg l−1 showed the best activity by decreasing meropenem MICs to 0·5 and 0·06 mg l−1, respectively, for some New Delhi Metallo‐beta‐lactamase (NDM) and Verona integron‐encoded metallo‐β‐lactamase (VIM) ‐producing enterobacteriaceae. DPA at 8 and 16 mg l−1 was also able to decrease meropenem MICs to 1 and 0·125 mg l−1, respectively, for these CREs. NODAGA peptide derivatives showed the least inhibition as 32 mg l−1 was required for meropenem MICs to be decreased to 0·06 mg l−1 against an NDM‐1 producing isolate.
Conclusion
The various metal chelators, TPEN, DPA and NODAGA peptide derivatives were able to inhibit the MBLs in decreasing order of activity, rendering CREs susceptible to meropenem.
Significance and Impact of the Study
In the absence of new antibiotics, this study evaluated metal chelators as potential MBL inhibitors.
Aims
We hypothesized and confirmed that tannic acid (TA) reverses carbapenem resistance by inhibiting carbapenemases in class A and B carbapenemase‐producing Enterobacteriaceae.
Methods and Results
...Minimum inhibitory concentrations of carbapenems in the presence and absence of TA and other efflux pump inhibitors, TA‐carbapenemases inhibition assays and computational studies showed that TA had the greatest effect on metallo‐β‐lactamases (MBLs) followed by class A serine‐β‐lactamases (SBLs). TA completely reversed the MICs of MBL producers from between 32 and ≥512 mg l−1 to susceptible values (<4 mg l−1) while substantially reducing the MICs of SBLs from between 16 and >512 mg l−1 to <4 to 16 mg l−1. Tolerable cytotoxic effect was observed for the concentrations tested (8–1024 mg l−1). TA inhibited enzymes with a marked difference of ≈50% inhibition (IC50) for NDM‐1 (270 μmol l−1) and KPC‐2 (15 μmol l−1).
Conclusion
TA inhibited both MBLs and SBLs by targeting their hydrophobic sites. Moreover, TA had a stronger binding affinity for MBLs than SBLs as the MBLs, specifically VIM‐1 (−43·7220 ± 0·4513 kcal mol−1) and NDM‐1(−44·2329 ± 0·3806 kcal mol−1), interact with a larger number of their catalytic active‐site residues than that of OXA‐48 (−22·5275 ± 0·1300 kcal mol−1) and KPC‐2 (−22·1164 ± 0·0111 kcal mol−1).
Significance and Impact of the Study
Tannic acid or its analogues could be developed into carbapenemase‐inhibiting adjuvants to restore carbapenem activity in CRE infections, save many lives and reduce healthcare associated costs.
To investigate the dissemination of Salmonella spp. within four levels of government hospitals in KwaZulu-Natal, South Africa.
The identification of Salmonella spp. was performed by amplification of ...the invA gene. Isolates were subjected to antimicrobial susceptibility testing and molecular characterization of eight resistance genes (qnrA, qnrB, qnrS, tetA, tetB, tetC, tetG, ermB) and three virulence genes (sitC, spvA, spv). Genetic relatedness between isolates was determined using enterobacterial repetitive intergenic consensus (ERIC) polymerase chain reaction.
Ninety-four isolates were obtained. The largest source of isolates was the regional hospital. Paediatric wards had the highest prevalence of isolates. Nurses' tables contained the most isolates out of all sites sampled. Twenty-two clusters indicating diverse isolates were obtained via molecular typing. Four main ERIC types were identified, each unique to a specific hospital. A possibility of dissemination across the wards was noted as highly related isolates were present at various sites within the wards. Many of these sites were highly trafficked areas by healthcare staff. Ten multi-drug-resistant isolates were found.
This study suggests that infection prevention and control strategies that involve environmental cleaning and decontamination may not be enough, or adhered to sufficiently, to prevent the dissemination of Salmonella spp.
Objectives Campylobacter jejuni isolated from broiler and layer chickens from registered abattoirs in KwaZulu-Natal, South Africa, were tested for their susceptibility to eight antibiotics. Methods ...Using agar dilution, susceptibility to eight antibiotics was determined for C. jejuni recovered from the caeca. Results A total of 155 isolates were collected of which 77 were identified as C. jejuni (broilers n = 56 and layers n = 21). Resistance was highest to tetracycline (broilers 98.2% and layers 100%) and ceftriaxone (broilers 96.4% and layers 100%). High susceptibility was found to ciprofloxacin (broilers 91% and layers 76%) and gentamicin (broilers 98% and layers 81%). Susceptibilities to each of the antibiotics for the broilers and layers, respectively, were: 50% and 57% for erythromycin, 45% and 24% for clarithromycin, 68% and 43% for ampicillin and 64% and 48% for nalidixic acid. Statistically significant differences were detected for the MIC50 of gentamicin, ciprofloxacin and tetracycline between broilers and layers (P < 0.001) with the MIC90 of gentamicin also of significant difference (P = 0.01). Multiresistance was detected in 23% and 43% of the isolates from broiler and layer chickens, respectively. Conclusions Mass therapy procedures used in animal husbandry have a potential impact on antibiotic resistance development in C. jejuni.
ABSTRACT
We present the results from studying 140 radio sources in the GLEAM (GaLactic and Extragalactic All-sky MWA Murchison Widefield Array) 4-Jy (G4Jy) Sample. These sources were followed-up with ...MeerKAT to assess their radio morphology and enable host-galaxy identification, as existing radio images of 25 to 45-arcsec resolution do not provide sufficient information. We refer to these sources as the MeerKAT-2019 subset. The aim is to identify the host galaxy of these sources by visually inspecting the overlays comprising radio data from four surveys (at 150, 200, 843/1400, and 1300 MHz). Our morphological classification and host-galaxy identification relies upon the ∼7-arcsec resolution images from MeerKAT (1300 MHz). Through the visual inspection of the overlays, 14 radio sources in the MeerKAT-2019 subset have wide-angle tail morphology, 10 are head-tail, and 5 have X-, S-/Z-shaped morphology. Most of the remaining sources have the radio morphology of typical symmetric lobes. Of 140 sources, we find host galaxies for 98 sources, leaving 42 with no identified host galaxy. These 42 sources still have ambiguous identification even with higher resolution images from MeerKAT.
ABSTRACT
MIGHTEE is a galaxy evolution survey using simultaneous radio continuum, spectropolarimetry, and spectral line observations from the South African MeerKAT telescope. When complete, the ...survey will image ∼20 deg2 over the COSMOS, E-CDFS, ELAIS-S1, and XMM-Newton Large Scale Structure field (XMM-LSS) extragalactic deep fields with a central frequency of 1284 MHz. These were selected based on the extensive multiwavelength data sets from numerous existing and forthcoming observational campaigns. Here, we describe and validate the data processing strategy for the total intensity continuum aspect of MIGHTEE, using a single deep pointing in COSMOS (1.6 deg2) and a three-pointing mosaic in XMM-LSS (3.5 deg2). The processing includes the correction of direction-dependent effects, and results in thermal noise levels below 2 $\mathrm{\mu }$Jy beam−1 in both fields, limited in the central regions by classical confusion at ∼8 arcsec angular resolution, and meeting the survey specifications. We also produce images at ∼5 arcsec resolution that are ∼3 times shallower. The resulting image products form the basis of the Early Science continuum data release for MIGHTEE. From these images we extract catalogues containing 9896 and 20 274 radio components in COSMOS and XMM-LSS, respectively. We also process a close-packed mosaic of 14 additional pointings in COSMOS and use these in conjunction with the Early Science pointing to investigate methods for primary beam correction of broad-band radio images, an analysis that is of relevance to all full-band MeerKAT continuum observations, and wide-field interferometric imaging in general. A public release of the MIGHTEE Early Science continuum data products accompanies this article.
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