Staphylococcus epidermidis is the most frequent cause of nosocomial sepsis and catheter-related infections, in which biofilm formation is considered to be the main virulence mechanism. Quorum-sensing ...systems have been recognized as important regulators of virulence and biofilm formation in many bacteria. There is a single quorum-sensing system in S. epidermidis encoded by the agr operon. To investigate quorum-sensing control of biofilm formation, we constructed an agr deletion mutant, assayed for the different stages of biofilm formation, and determined agr-dependent regulation of biofilm factors. The agr mutant showed increased biofilm formation, primary attachment, and expression of the autolysin AtlE, but lacked δ-toxin production. However, the level of polysaccharide intercellular adhesin expression was equivalent to the isogenic wild-type strain. In contrast to AtlE, which is known to influence primary attachment, δ-toxin appeared to exert its effect on attachment to polystyrene during later stages of biofilm formation. Importantly, addition of cross-inhibiting pheromones mimicked an agr mutation and significantly enhanced biofilm formation, which suggests that care should be used when treating S. epidermidis infections with cross-inhibiting peptides. Our data demonstrate the importance of quorum sensing in the establishment of a biofilm in this critical human pathogen
Prior to 2007, highly pathogenic avian influenza (HPAI) H5N1 viruses isolated from poultry and humans in Vietnam were consistently reported to be clade 1 viruses, susceptible to oseltamivir but ...resistant to amantadine. Here we describe the re-emergence of human HPAI H5N1 virus infections in Vietnam in 2007 and the characteristics of the isolated viruses.
Respiratory specimens from patients suspected to be infected with avian influenza in 2007 were screened by influenza and H5 subtype specific polymerase chain reaction. Isolated H5N1 strains were further characterized by genome sequencing and drug susceptibility testing. Eleven poultry outbreak isolates from 2007 were included in the sequence analysis. Eight patients, all of them from northern Vietnam, were diagnosed with H5N1 in 2007 and five of them died. Phylogenetic analysis of H5N1 viruses isolated from humans and poultry in 2007 showed that clade 2.3.4 H5N1 viruses replaced clade 1 viruses in northern Vietnam. Four human H5N1 strains had eight-fold reduced in-vitro susceptibility to oseltamivir as compared to clade 1 viruses. In two poultry isolates the I117V mutation was found in the neuraminidase gene, which is associated with reduced susceptibility to oseltamivir. No mutations in the M2 gene conferring amantadine resistance were found.
In 2007, H5N1 clade 2.3.4 viruses replaced clade 1 viruses in northern Vietnam and were susceptible to amantadine but showed reduced susceptibility to oseltamivir. Combination antiviral therapy with oseltamivir and amantadine for human cases in Vietnam is recommended.
Novel antimicrobial strategies are urgently required because of the rising threat of multi drug resistant bacterial strains and the infections caused by them. Among the available target structures, ...the so-called penicillin binding proteins are of particular interest, owing to their good accessibility in the periplasmic space, and the lack of homologous proteins in humans, reducing the risk of side effects of potential drugs. In this report, we focus on the interaction of the innovative β-lactam antibiotic AIC499 with penicillin binding protein 3 (PBP3) from
and
. This recently developed monobactam displays broad antimicrobial activity, against Gram-negative strains, and improved resistance to most classes of β-lactamases. By analyzing crystal structures of the respective complexes, we were able to explore the binding mode of AIC499 to its target proteins. In addition, the apo structures determined for PBP3, from
and the catalytic transpeptidase domain of the
orthologue, provide new insights into the dynamics of these proteins and the impact of drug binding.
High-temperature stability of the Nb/Ni and Ni/Nb Ohmic contacts to n-type 4H-SiC was investigated and compared after being aged at 400 °C for 100 h in N2 ambient. The electrical properties and ...surface morphologies of the contacts were characterized by using the combination of the current-voltage measurements and microscopic imaging. While the Nb/Ni/4H-SiC ohmic contact failed after 10-h aging, the Ni/Nb/4H-SiC contact still exhibited good ohmic characteristics with a slight increase of specific contact resistance after being aged for 100 h. According to the microscopic imaging results, though the Ni/Nb/4H-SiC contact has a rougher surface morphology compared to that of the Nb/Ni/4H-SiC contact, the Ni/Nb/4H-SiC has a better ability to collect excess carbon atoms at the interface, ensuring stable operation in a high temperature environment. The ability to collect excess carbon atoms of the Ni/Nb/4H-SiC is revealed by the formation of Nb6C5 which is confirmed by two-dimensional X-ray diffraction, hard X-ray photoelectron spectroscopy, and transmission electron microscopy analysis. The experimental results indicated that the Ni/Nb/4H-SiC ohmic contact is a potential candidate for high temperature and harsh environment applications.
•Ni/Nb/4H-SiC contact showed excellent high-temperature reliability.•Ni2Si plays an important role in low specific contact resistance even in presence of Nb.•Carbon agglomeration causes the degradation of the Nb/Ni/4H-SiC contact.•Nb improves the thermal stability of the Ni/Nb/4H-SiC contact.
The alarming threat of the spread of multidrug resistant bacteria currently leaves clinicians with very limited options to combat infections, especially those from Gram-negative bacteria. Hence, ...innovative strategies to deliver the next generation of antibacterials are urgently needed. Penicillin binding proteins (PBPs) are proven targets inhibited by β-lactam antibiotics. To discover novel, non-β-lactam inhibitors against PBP3 of Pseudomonas aeruginosa, we optimised a fluorescence assay based on a well-known thioester artificial substrate and performed a target screening using a focused protease-targeted library of 2455 compounds, which led to the identification of pyrrolidine-2,3-dione as a potential scaffold to inhibit the PBP3 target. Further chemical optimisation using a one-pot three-component reaction protocol delivered compounds with excellent target inhibition, initial antibacterial activities against P. aeruginosa and no apparent cytotoxicity. Our investigation revealed the key structural features; for instance, 3-hydroxyl group (R2) and a heteroaryl group (R1) appended to the N-pyrroldine-2,3-dione via methylene linker required for target inhibition. Overall, the discovery of the pyrrolidine-2,3-dione class of inhibitors of PBP3 brings opportunities to target multidrug-resistant bacterial strains and calls for further optimisation to improve antibacterial activity against P. aeruginosa.
Patients with complicated urinary tract infections (cUTIs) frequently receive broad-spectrum antibiotics. We aimed to determine the prevalence and predictive factors of multidrug-resistant ...gram-negative bacteria in patients with cUTI.
This is a multicenter, retrospective cohort study in south and eastern Europe, Turkey and Israel including consecutive patients with cUTIs hospitalised between January 2013 and December 2014. Multidrug-resistance was defined as non-susceptibility to at least one agent in three or more antimicrobial categories. A mixed-effects logistic regression model was used to determine predictive factors of multidrug-resistant gram-negative bacteria cUTI.
From 948 patients and 1074 microbiological isolates,
was the most frequent microorganism (559/1074), showing a 14.5% multidrug-resistance rate.
was second (168/1074) and exhibited the highest multidrug-resistance rate (54.2%), followed by
(97/1074) with a 38.1% multidrug-resistance rate. Predictors of multidrug-resistant gram-negative bacteria were male gender (odds ratio OR, 1.66; 95% confidence interval CI, 1.20-2.29), acquisition of cUTI in a medical care facility (OR, 2.59; 95%CI, 1.80-3.71), presence of indwelling urinary catheter (OR, 1.44; 95%CI, 0.99-2.10), having had urinary tract infection within the previous year (OR, 1.89; 95%CI, 1.28-2.79) and antibiotic treatment within the previous 30 days (OR, 1.68; 95%CI, 1.13-2.50).
The current high rate of multidrug-resistant gram-negative bacteria infections among hospitalised patients with cUTIs in the studied area is alarming. Our predictive model could be useful to avoid inappropriate antibiotic treatment and implement antibiotic stewardship policies that enhance the use of carbapenem-sparing regimens in patients at low risk of multidrug-resistance.
There are two methods of reverse transcription polymerase chain reaction (RT-PCR) that have been the common methods to detect influenza infections: conventional and real-time RT-PCR. From December ...2017 to March 2018, several missed diagnoses of influenza A(H1)pdm09 using real-time RT-PCR were reported in northern Viet Nam. This study investigated how these missed detections occurred to determine their effect on the surveillance of influenza.
The haemagglutinin (HA) segments of A(H1N1)pdm09 from both real-time RT-PCR positive and negative samples were isolated and sequenced. The primer and probe sets in the HA gene were checked for mismatches, and phylogenetic analyses were performed to determine the molecular epidemiology of these viruses.
There were 86 positive influenza A samples; 32 were A(H1)pdm09 positive by conventional RT-PCR but were negative by real-time RT-PCR. Sequencing was conducted on 23 influenza (H1N1)pdm09 isolates that were recovered from positive samples. Eight of these were negative for A(H1)pdm09 by real-time RT-PCR. There were two different mismatches in the probe target sites of the HA gene sequences of all isolates (
= 23) with additional mismatches only at position 7 (template binding site) identified for all eight negative real-time RT-PCR isolates. The prime target sites had no mismatches. Phylogenetic analysis of the HA gene showed that both the positive and negative real-time RT-PCR isolates were grouped in clade 6B.1; however, the real-time RT-PCR negative viruses were located in a subgroup that referred to substitution I295V.
Constant monitoring of genetic changes in the circulating influenza A(H1N1)pdm09 viruses is important for maintaining the sensitivity of molecular detection assays.
The pressure dependent high-order harmonic generation in a semi-infinite gas cell with two different absorbing gaseous media (argon and helium) is analyzed to reveal the influence of absorption on ...the radiation process in the extreme ultraviolet region. The absorption cross section of a particular wavelength in this region is measured. Moreover, in consideration of macroscopic response, the geometrical phase mismatch and the dipole phase mismatch which are independent to the pressure are clearly studied. A Young's double slit experiment is also performed to indicate a high spatial coherence of the harmonic radiation. This measurement shows that a narrow bandwidth, bright, and highly coherent high harmonic source can be generated in gas cell filled with absorbing gases which could be useful for coherent diffractive imaging.
Recently, Staphylococcus aureus strains with intermediate resistance to vancomycin, the antibiotic of last resort, have been described. Multiple changes in peptidoglycan turnover and structure ...contribute to the resistance phenotype. Here, we describe that structural changes of teichoic acids in the cell envelope have a considerable influence on the susceptibility to vancomycin and other glycopeptides. S. aureus cells lacking D-alanine esters in teichoic acids exhibited an at least threefold-increased sensitivity to glycopeptide antibiotics. Furthermore, the autolytic activity of the D-alanine mutant was reduced compared to the wild-type, and the mutant was more susceptible to the staphylolytic enzyme lysostaphin. Vancomycin inhibited autolysis at very high concentrations but neither in the wild-type nor in the mutant was the autolytic activity influenced in the range of the MIC. Mutant cells had a considerably higher capacity to bind vancomycin.
Objectives
Influenza A/H1N1pdm09 virus was first detected in Vietnam on May 31, 2009, and continues to circulate in Vietnam as a seasonal influenza virus. This study has monitored genotypic and ...phenotypic changes in this group of viruses during 2010–2013 period.
Design and setting
We sequenced hemagglutinin (HA) and neuraminidase (NA) genes from representative influenza A/H1N1pdm09 and compared with vaccine strain A/California/07/09 and other contemporary isolates from neighboring countries. Hemagglutination inhibition (HI) and neuraminidase inhibition (NAI) assays also were performed on these isolates.
Sample
Representative influenza A/H1N1pdm09 isolates (n = 61) from ILI and SARI surveillances in northern Vietnam between 2010 and 2013.
Main outcome measures and results
The HA and NA phylogenies revealed six and seven groups, respectively. Five isolates (8·2%) had substitutions G155E and N156K in the HA, which were associated with reduced HI titers by antiserum raised against the vaccine virus A/California/07/2009. One isolate from 2011 and one isolate from 2013 had a predicted H275Y substitution in the neuraminidase molecule, which was associated with reduced susceptibility to oseltamivir in a NAI assay. We also identified a D222N change in the HA of a virus isolated from a fatal case in 2013.
Conclusions
Significant genotypic and phenotypic changes in A/ H1N1pdm09 influenza viruses were detected by the National Influenza Surveillance System (NISS) in Vietnam between 2010 and 2013 highlighting the value of this system to Vietnam and to the region. Sustained NISS and continued virological monitoring of seasonal influenza viruses are required for vaccine policy development in Vietnam. 3
PDF
