In oral biofilms, two of the major environmental challenges encountered by the dental pathogen Streptococcus mutans are acid and oxidative stresses. Previously, we showed that the S. mutans ...transcriptional regulators SpxA1 and SpxA2 (formerly SpxA and SpxB, respectively) are involved in stress survival by activating the expression of classic oxidative stress genes such as dpr, nox, sodA and tpx. We reasoned that some of the uncharacterized genes under SpxA1/A2 control are potentially involved in oxidative stress management. Therefore, the goal of this study was to use Spx-regulated genes as a tool to identify novel oxidative stress genes in S. mutans. Quantitative real-time PCR was used to evaluate the responses of ten Spx-regulated genes during H2O2 stress in the parent and Δspx strains. Transcription activation of the H2O2-induced genes (8 out of 10) was strongly dependent on SpxA1 and, to a lesser extent, SpxA2. In vitro transcription assays revealed that one or both Spx proteins directly regulate three of these genes. The gene encoding the FeoB ferrous permease was slightly repressed by H2O2 but constitutively induced in strains lacking SpxA1. Nine genes were selected for downstream mutational analysis but inactivation of smu127, encoding a subunit of the acetoin dehydrogenase was apparently lethal. In vitro and in vivo characterization of the viable mutants indicated that, in addition to the transcriptional activation of reducing and antioxidant pathways, Spx performs an important role in iron homeostasis by regulating the intracellular availability of free iron. In particular, inactivation of the genes encoding the Fe-S biogenesis SUF system and the previously characterized iron-binding protein Dpr resulted in impaired growth under different oxidative stress conditions, increased sensitivity to iron and lower infectivity in rats. These results serve as an entryway into the characterization of novel genes and pathways that allow S. mutans to cope with oxidative stress.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Candida tropicalis
is one the most relevant biofilm-forming fungal species increasingly associated with invasive mucosal candidiasis worldwide. The amplified antifungal resistance supports the ...necessity for more effective and less toxic treatment, including the use of plant-derived natural products. Scopoletin, a natural coumarin, has shown antifungal properties against plant yeast pathogens. However, the antifungal activity of this coumarin against clinically relevant fungal species such as
C. tropicalis
remains to be established. Here, we investigated the potential antifungal properties and mechanisms of action of scopoletin against a multidrug-resistant
C. tropicalis
strain (ATCC 28707). First, scopoletin was isolated by high-performance liquid chromatography from
Mitracarpus frigidus
, a plant species (family
Rubiaceae
) distributed throughout South America. Next, scopoletin was tested on
C. tropicalis
cultivated for 48h in both planktonic and biofilm forms. Fungal planktonic growth inhibition was analyzed by evaluating minimal inhibitory concentration (MIC), time-kill kinetics and cell density whereas the mechanisms of action were investigated with nucleotide leakage, efflux pumps and sorbitol and ergosterol bioassays. Finally, the scopoletin ability to affect
C. tropicalis
biofilms was evaluated through spectrophotometric and whole slide imaging approaches. In all procedures, fluconazole was used as a positive control. MIC values for scopoletin and fluconazole were 50 and 250 μg/L respectively, thus demonstrating a fungistatic activity for scopoletin. Scopoletin induced a significant decrease of
C. tropicalis
growth curves and cell density (91.7% reduction) compared to the growth control. Its action was related to the fungal cell wall, affecting plasma membrane sterols. When associated with fluconazole, scopoletin led to inhibition of efflux pumps at the plasma membrane. Moreover, scopoletin not only inhibited the growth rate of preformed biofilms (68.2% inhibition at MIC value) but also significantly decreased the extent of biofilms growing on the surface of coverslips, preventing the formation of elongated fungal forms. Our data demonstrate, for the first time, that scopoletin act as an effective antifungal phytocompound against a multidrug-resistant strain of
C. tropicalis
with properties that affect both planktonic and biofilm forms of this pathogen. Thus, the present findings support additional studies for antifungal drug development based on plant isolated-scopoletin to treat candidiasis caused by
C. tropicalis.
Early childhood caries (ECC) recurrence occurs in approximately 40% of treated cases within one year. The association of Streptococcus mutans and Candida albicans with the onset of ECC is well known. ...Also, S. mutans strains harboring collagen-binding proteins (Cbps) avidly bind to collagen-rich dentin and are linked to increased caries risk. Here, we investigated the presence of Cbp
S. mutans and C. albicans in saliva and dental plaque of children with varying caries statuses, and their salivary microbiome. In this cross-sectional study, 143 children who were caries-free (n = 73), treated for ECC with no signs of recurrence after 6 months (n = 45), or treated for ECC and experiencing recurrence within 6 months following treatment (n = 25) were enrolled. Co-infection with C. albicans and S. mutans, especially Cbp
S. mutans, was strongly associated with caries recurrence. Subjects of the recurrence group infected with Cbp
S. mutans showed a greater burden of Candida spp. and of Mutans streptococci in dentin than those infected with Cbp
strains. Salivary microbiome analysis revealed that Streptococcus parasanguinis was overrepresented in the caries recurrence group. Our findings indicate that Cbp
S. mutans and C. albicans are intimately associated with caries recurrence, contributing to the establishment of recalcitrant biofilms.
Annona muricata L. (soursop) is traditionally used in the treatment of inflammatory diseases, cancer, and infections caused by fungi. The therapeutic activity explored by its medicinal use is ...generally associated with its phytoconstituents, such as acetogenins and alkaloids. However, its potential antifungal bioactivity as well as its mechanism of action remains to be established.
Aim of the study: To evaluate the antifungal activity of the ethanolic extract of A. muricata leaves against multidrug-resistant Candida albicans (ATCC® 10231).
Phytoconstituents were detected by UFLC-QTOF-MS. The minimum inhibitory concentration was determined, followed by the determination of the minimum fungicidal concentration. For planktonic cells, the growth curve and cell density were evaluated. Studies to understand the mechanism of action on the cell envelope involved crystal violet permeability, membrane extravasation, sorbitol protection, exogenous ergosterol binding assay, metabolic activity, and cell viability. Furthermore, mitochondrial membrane potential was assessed.
Our analyses demonstrated a significant inhibitory effect of A. muricata, with the ability to reduce fungal growth by 58% and cell density by 65%. The extract affected both the fungal plasma membrane and cell wall integrity, with significant reduction of the cell viability. Depolarization of the fungal mitochondrial membrane was observed after treatment with A. muricata. Rutin, xi-anomuricine, kaempferol-3O-rutinoside, nornuciferine, xylopine, atherosperminine, caffeic acid, asimilobine, s-norcorydine, loliolide, annohexocin, annomuricin, annopentocin, and sucrose were identified as extract bioactive components.
Our findings show that the A. muricata extract is a source of chemical diversity, which acts as a potential antifungal agent with promising application to the therapy of infections caused by C. albicans.
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•Antifungal Annona muricata extract targets the cell envelope of resistant Candida albicans.•Annona muricata extract alters mitochondrial membrane polarization.•Annona muricata extract is a promising antifungal agent.
Psychorubrin, a natural pyranonaphthoquinone found in different plants, has become an interesting compound in the search for new antimicrobial therapeutic agents. Here, we investigated the potential ...antagonistic activity of psychorubrin against planktonic and biofilm bacteria. First, psychorubrin was tested against several Gram-positive and Gram-negative bacteria strains by a broth microdilution susceptibility method. Second, bacterial killing assay, bacterial abundance, and membrane viability were evaluated. The nucleotide leakage assay was used to verify membrane destabilization while antibiofilm activities were analyzed by the effect on established biofilm, static biofilm formation, isolation of biofilm matrix assay and scanning electron microscopy. In parallel, the combinatorial effect of psychorubrin and chloramphenicol was evaluated by the checkerboard method. Psychorubrin was active against Gram-positive bacteria, showing rapid time-dependent kinetics of bacterial killing, amplified nucleotide leakage, and greater activity against the methicillin-resistant species (MRSA)
33591 and 33592 and
10096. Psychorubrin also interfered with the composition of the biofilm matrix by reducing the total content of carbohydrates and proteins. A synergic effect between psychorubrin and chloramphenicol was observed for
33592 and
10096 while an additive effect was detected for
33591. Our findings demonstrate, for the first time, an antagonistic activity of psychorubrin against bacteria not only in their planktonic forms but also in biofilms, and identify bacterial membranes as primary targets for this compound. Based on these observations, psychorubrin has a good potential for the design of novel antimicrobial agents.
Summary
In oral biofilms, the major environmental challenges encountered by Streptococcus mutans are acid and oxidative stresses. Previously, we showed that the transcriptional regulators SpxA1 and ...SpxA2 are involved in general stress survival of S. mutans with SpxA1 playing a primary role in activation of antioxidant and detoxification strategies whereas SpxA2 serves as a back up activator of oxidative stress genes. We have also found that spxA1 mutant strains (∆spxA1 and ∆spxA1∆spxA2) are outcompeted by peroxigenic oral streptococci in vitro and have impaired abilities to colonize the teeth of rats fed a highly cariogenic diet. Here, we show that the Spx proteins can also exert regulatory roles in the expression of additional virulence attributes of S. mutans. Competence activation is significantly impaired in Δspx strains and the production of mutacin IV and V is virtually abolished in ΔspxA1 strains. Unexpectedly, the ∆spxA2 strain showed increased production of glucans from sucrose, without affecting the total amount of bacteria within biofilms when compared with the parent strain. By using the rat caries model, we showed that the capacity of the ΔspxA1 and ΔspxA2 strains to cause caries on smooth tooth surfaces is significantly impaired. The ∆spxA2 strain also formed fewer lesions on sulcal surfaces. This report reveals that global regulation via Spx contributes to the cariogenic potential of S. mutans and highlights that animal models are essential in the characterization of bacterial traits implicated in virulence.
In this article, we considered all aspects of acidity (nature of acid sites, strength, density, etc.) in solid catalysts and in zeolites in particular. After reminding the definition of acidity in ...liquid and solid acids, we emphasized acidity characterization by the most used physical techniques, such as Hammett's indicator titration, microcalorimetry of adsorbed probe molecules (ammonia, pyridine or other amines for acidity characterization and CO
2
or SO
2
for basicity characterization), ammonia or any amine thermodesorption, IR spectroscopy of hydroxyl groups and of several probe molecules adsorbed (ammonia, pyridine, piperidine, amines, CO, H
2
, etc.), MAS-NMR of
27
Al,
29
Si,
1
H elements and of
1
H,
13
C,
31
P, etc. of adsorbed probe molecules, and model catalytic reactions.
Modeling the way the acid features of zeolites influence the catalytic activity of these catalysts toward acid-catalyzed reactions (relation between ammonia desorption activation energy values and catalytic activities, reaction mechanism, and kinetics) completes the general analysis of acidity and zeolite chemistry.
An inertial fusion implosion on the National Ignition Facility, conducted on August 8, 2021 (N210808), recently produced more than a megajoule of fusion yield and passed Lawson's criterion for ...ignition Phys. Rev. Lett. 129, 075001 (2022). Here we describe the experimental improvements that enabled N210808 and present the first experimental measurements from an igniting plasma in the laboratory. Ignition metrics like the product of hot-spot energy and pressure squared, in the absence of self-heating, increased by ~ 35%, leading to record values and an enhancement from previous experiments in the hot-spot energy (~ 3×), pressure (~ 2×), and mass (~ 2×). These results are consistent with self-heating dominating other power balance terms. The burn rate increases by an order of magnitude after peak compression, and the hot-spot conditions show clear evidence for burn propagation into the dense fuel surrounding the hot spot. These novel dynamics and thermodynamic properties have never been observed on prior inertial fusion experiments.
Single-shot absorption measurements have been performed using the multi-keV x rays generated by a laser-wakefield accelerator. A 200 TW laser was used to drive a laser-wakefield accelerator in a mode ...which produced broadband electron beams with a maximum energy above 1 GeV and a broad divergence of ≈15 mrad FWHM. Betatron oscillations of these electrons generated 1.2±0.2×10^{6} photons/eV in the 5 keV region, with a signal-to-noise ratio of approximately 300∶1. This was sufficient to allow high-resolution x-ray absorption near-edge structure measurements at the K edge of a titanium sample in a single shot. We demonstrate that this source is capable of single-shot, simultaneous measurements of both the electron and ion distributions in matter heated to eV temperatures by comparison with density functional theory simulations. The unique combination of a high-flux, large bandwidth, few femtosecond duration x-ray pulse synchronized to a high-power laser will enable key advances in the study of ultrafast energetic processes such as electron-ion equilibration.
Since the end of 2020, there has been a great deal of international concern about the variants of SARS-COV-2 B.1.1.7, identified in the United Kingdom; B.1.351 discovered in South Africa and P.1, ...originating from the Brazilian state of Amazonas. The three variants were associated with an increase in transmissibility and worsening of the epidemiological situation in the places where they expanded. The lineage B.1.1.7 was associated with the increase in case fatality rate in the United Kingdom. There are still no studies on the case fatality rate of the other two variants. The aim of this study was to analyze the mortality profile before and after the emergence of the P.1 strain in the Amazonas state.
We analyzed data from the Influenza Epidemiological Surveillance Information System, SIVEP-Gripe (Sistema de Informação de Vigilância Epidemiológica da Gripe), comparing two distinct epidemiological periods: during the peak of the first wave, between April and May 2020, and in January 2021 (the second wave), the month in which the new variant came to predominate. We calculated mortality rates, overall case fatality rate and case fatality rate among hospitalized patients; all rates were calculated by age and gender and 95% confidence intervals (95% CI) were determined.
We observed that in the second wave there were a higher incidence and an increase in the proportion of cases of COVID-19 in the younger age groups. There was also an increase in the proportion of women among Severe Acute Respiratory Infection (SARI) cases from 40% (2,709) in the first wave to 47% (2,898) in the second wave and in the proportion of deaths due to COVID-19 between the two periods varying from 34% (1,051) to 47% (1,724), respectively. In addition, the proportion of deaths among people between 20 and 59 years old has increased in both sexes. The case fatality rate among those hospitalized in the population between 20 and 39 years old during the second wave was 2.7 times the rate observed in the first wave (female rate ratio = 2.71; 95% CI: 1.9-3.9, p <0.0001; male rate ratio = 2.70, 95%CI:2.0-3.7), and in the general population the rate ratios were 1.15 (95% CI: 1.1-1.2) in females and 0.78 (95% CI: 0.7-0.8) in males.
Based on this prompt analysis of the epidemiological scenario in the Amazonas state, the observed changes in the pattern of mortality due to COVID-19 between age groups and gender simultaneously with the emergence of the P.1 strain suggest changes in the pathogenicity and virulence profile of this new variant. Further studies are needed to better understanding of SARS-CoV-2 variants profile and their impact for the health population.
There was no funding for this study.
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