Bacteriophage-derived lysins are cell-wall-hydrolytic enzymes that represent a potential new class of antibacterial therapeutics in development to address burgeoning antimicrobial resistance. CF-301, ...the lead compound in this class, is in clinical development as an adjunctive treatment to potentially improve clinical cure rates of
bacteremia and infective endocarditis (IE) when used in addition to antibiotics. In order to profile the activity of CF-301 in a clinically relevant milieu, we assessed its
activity in human blood versus in a conventional testing medium (cation-adjusted Mueller-Hinton broth caMHB). CF-301 exhibited substantially greater potency (32 to ≥100-fold) in human blood versus caMHB in three standard microbiologic testing formats (e.g., broth dilution MICs, checkerboard synergy, and time-kill assays). We demonstrated that CF-301 acted synergistically with two key human blood factors, human serum lysozyme (HuLYZ) and human serum albumin (HSA), which normally have no nascent antistaphylococcal activity, against a prototypic methicillin-resistant
(MRSA) strain (MW2). Similar
enhancement of CF-301 activity was also observed in rabbit, horse, and dog (but not rat or mouse) blood. Two well-established MRSA IE models in rabbit and rat were used to validate these findings
by demonstrating comparable synergistic efficacy with standard-of-care anti-MRSA antibiotics at >100-fold lower lysin doses in the rabbit than in the rat model. The unique properties of CF-301 that enable bactericidal potentiation of antimicrobial activity via activation of "latent" host factors in human blood may have important therapeutic implications for durable improvements in clinical outcomes of serious antibiotic-resistant staphylococcal infections.
MgrA is an important global virulence gene regulator in Staphylococcus aureus. In the present study, the role of mgrA in host-pathogen interactions related to virulence was explored in both ...methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) strains.
In vitro susceptibilities to human defense peptides (HDPs), adherence to fibronectin (Fn) and endothelial cells (ECs), EC damage, α-toxin production, expression of global regulator (eg, agr RNAIII) and its downstream effectors (eg, α-toxin hla and Fn binding protein A fnbA), MgrA binding to fnbA promoter, and the effect on HDP-induced mprF and dltA expression were analyzed. The impact of mgrA on virulence was evaluated using a mouse bacteremia model.
mgrA mutants displayed significantly higher susceptibility to HDPs, which might be related to the decreased HDP-induced mprF and dltA expression but decreased Fn and EC adherence, EC damage, α-toxin production, agr RNAIII, hla and fnbA expression, and attenuated virulence in the bacteremia model as compared to their respective parental and mgrA-complemented strains. Importantly, direct binding of MgrA to the fnbA promoter was observed.
These results suggest that mgrA mediates host-pathogen interactions and virulence and may provide a novel therapeutic target for invasive S. aureus infections.
Discovery of magnetic Weyl fermions: Dirac fermions split into pairs of Weyl fermions by slow magnetic fluctuations.
Weyl fermions as emergent quasiparticles can arise in Weyl semimetals (WSMs) in ...which the energy bands are nondegenerate, resulting from inversion or time-reversal symmetry breaking. Nevertheless, experimental evidence for magnetically induced WSMs is scarce. Here, using photoemission spectroscopy, we observe that the degeneracy of Bloch bands is already lifted in the paramagnetic phase of EuCd
2
As
2
. We attribute this effect to the itinerant electrons experiencing quasi-static and quasi–long-range ferromagnetic fluctuations. Moreover, the spin-nondegenerate band structure harbors a pair of ideal Weyl nodes near the Fermi level. Hence, we show that long-range magnetic order and the spontaneous breaking of time-reversal symmetry are not essential requirements for WSM states in centrosymmetric systems and that WSM states can emerge in a wider range of condensed matter systems than previously thought.
bacteremia represents a serious and increasing clinical problem due to the high mortality and treatment failures because of high rates of antibiotic resistance. Any additional new therapies for
...bacteremia would address a growing unmet medical need. ARV-1502 (designated as Chex1-Arg20 or A3-APO monomer in prior publications) is a designer proline-rich antimicrobial peptide chaperone protein inhibitor derived from insects and has demonstrated potent activity against multi-drug resistant (MDR) Gram-negative bacteria. In the current studies, we investigated the therapeutic efficacy of ARV-1502 administered intravenously (iv) alone and in combination with imipenem/cilastatin (IPM/CIL) in a mouse bacteremia model due to a MDR clinical
strain, HUMC1. All ARV-1502 regimens (1.25, 2.5 and 5.0 mg/kg) significantly reduced bacterial density in the target tissues in a dose-dependent manner, as compared to the untreated control and IPM/CIL monotherapy (40 mg/kg) groups in the model. In addition, ARV-1502 treatment, even at the lowest dose, significantly improved survival vs. the control and IPM alone groups. As expected, IMP/CIL monotherapy had no therapeutic efficacy in the model, since the HUMC1 strain was resistant to IMP in vitro. However, the combination of ARV-1502 and IPM/CIL significantly enhanced the efficacy of ARV-1502, except the lowest dose of ARV-1502. The superior efficacy of ARV-1502 in the bacteremia model caused by MDR
provides further support for studying this compound in severe infections caused by other MDR Gram-positive and -negative pathogens.
Endovascular infections caused by methicillin-resistant
(MRSA) are a major health care concern, especially infective endocarditis (IE). Standard antimicrobial susceptibility testing (AST) defines ...most MRSA strains as "resistant" to β-lactams, often leading to the use of costly and/or toxic treatment regimens. In this investigation, five prototype MRSA strains, representing the range of genotypes in current clinical circulation, were studied. We identified two distinct MRSA phenotypes upon AST using standard media, with or without sodium bicarbonate (NaHCO
) supplementation: one highly susceptible to the antistaphylococcal β-lactams oxacillin and cefazolin (NaHCO
responsive) and one resistant to such agents (NaHCO
nonresponsive). These phenotypes accurately predicted clearance profiles of MRSA from target tissues in experimental MRSA IE treated with each β-lactam. Mechanistically, NaHCO
reduced the expression of two key genes involved in the MRSA phenotype,
and
, leading to decreased production of penicillin-binding protein 2a (that mediates methicillin resistance), in NaHCO
-responsive (but not in NaHCO
-nonresponsive) strains. Moreover, both cefazolin and oxacillin synergistically killed NaHCO
-responsive strains in the presence of the host defense antimicrobial peptide (LL-37) in NaHCO
-supplemented media. These findings suggest that AST of MRSA strains in NaHCO
-containing media may potentially identify infections caused by NaHCO
-responsive strains that are appropriate for β-lactam therapy.
Persistent methicillin-resistant Staphylococcus aureus (MRSA) endovascular infections represent a significant clinically challenging subset of invasive, life-threatening S. aureus infections. We have ...recently demonstrated that purine biosynthesis plays an important role in such persistent infections. Cyclic di-AMP (c-di-AMP) is an essential and ubiquitous second messenger that regulates many cellular pathways in bacteria. However, whether there is a regulatory connection between the purine biosynthesis pathway and c-di-AMP impacting persistent outcomes was not known. Here, we demonstrated that the purine biosynthesis mutant MRSA strain, the Δ
strain (compared to its isogenic parental strain), exhibited the following significant differences
: (i) lower ADP, ATP, and c-di-AMP levels; (ii) less biofilm formation with decreased extracellular DNA (eDNA) levels and Triton X-100-induced autolysis paralleling enhanced expressions of the biofilm formation-related two-component regulatory system
and its downstream gene
; (iii) increased vancomycin (VAN)-binding and VAN-induced lysis; and (iv) decreased wall teichoic acid (WTA) levels and expression of the WTA biosynthesis-related gene,
. Substantiating these data, the
(encoding diadenylate cyclase enzyme required for c-di-AMP synthesis) mutant strain (
strain versus its isogenic wild-type MRSA and
-complemented strains) showed significantly decreased c-di-AMP levels, similar
effects as seen above for the
mutant and hypersusceptible to VAN treatment in an experimental biofilm-related MRSA endovascular infection model. These results reveal an important intersection between purine biosynthesis and c-di-AMP that contributes to biofilm-associated persistence in MRSA endovascular infections. This signaling pathway represents a logical therapeutic target against persistent MRSA infections.
Persistent endovascular infections caused by MRSA, including vascular graft infection syndromes and infective endocarditis, are significant and growing public health threats. A particularly worrisome trend is that most MRSA isolates from these patients are "susceptible"
to conventional anti-MRSA antibiotics, such as VAN and daptomycin (DAP), based on Clinical and Laboratory Standards Institute breakpoints. Yet, these antibiotics frequently fail to eliminate these infections
. Therefore, the persistent outcomes in MRSA infections represent a unique and important variant of classic "antibiotic resistance" that is only disclosed during
antibiotic treatment. Given the high morbidity and mortality associated with the persistent infection, there is an urgent need to understand the specific mechanism(s) of this syndrome. In the current study, we demonstrate that a functional intersection between purine biosynthesis and the second messenger c-di-AMP plays an important role in VAN persistence in experimental MRSA endocarditis. Targeting this pathway may represent a potentially novel and effective strategy for treating these life-threatening infections.
Antibiotic-resistant
was increasingly found in infected individuals, which resulted in treatment failure and required alternative therapeutic strategies. Daphnetin, a coumarin-derivative compound, ...has multiple pharmacological activities.
The mechanism of daphnetin on
was investigated focusing on its effect on cell morphologies, transcription of genes related to virulence, adhesion, and cytotoxicity to human gastric epithelial (GES-1) cell line.
Daphnetin showed good activities against multidrug resistant (MDR)
clinical isolates, with minimal inhibitory concentration (MIC) values ranging from 25 to 100 μg/mL. In addition, daphnetin exposure resulted in
morphological changes. Moreover, daphnetin caused increased translocation of phosphatidylserine (PS), DNA damage, and
expression, and RecA protein production vs. control group. Of great importance, daphnetin significantly decreased
adhesion to GES-1 cell line vs. control group, which may be related to the reduced expression of colonization related genes (e.g.,
and
).
These results suggested that daphnetin has good activity against MDR
The mechanism(s) of daphnetin against
were related to change of membrane structure, increase of DNA damage and PS translocation, and decrease of
attachment to GES-1 cells.
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