Targeting the host–pathogen interface for treatment of Staphylococcus aureus infection

Barriers to and Facilitators of Hepatitis B Vaccination among the Adult Population in Indonesia: A Mixed Methods Study

To reach the goals of the Global Hepatitis Elimination 2030 program, Indonesia is now preparing a new regulation for hepatitis B vaccinations for adult population. This study aimed to determine the factors influencing vaccine uptake for hepatitis B in the adult population, and identify barriers to, and facilitators of, hepatitis B vaccination programmes. An explanatory sequential mixed methods design was implemented in this study. We conducted a survey involving 893 participants in the general population followed by 14 in-depth interviews with health providers. The survey found that only 15% (95% confidence interval 13-18%) of participants received at least one dose of the hepatitis B vaccine. Factors associated with vaccine uptake were, living in Yogyakarta compared to living in Aceh, having secondary and higher education compared to primary education, working as a health worker compared to working in other sectors, and having health insurance that covered hepatitis B vaccination compared to not having such health insurance. Our qualitative study also identified several barriers to the adult hepatitis B vaccination programme in Indonesia such as the high cost of vaccination, lack of vaccine availability in certain areas, limited human resources to implement the hepatitis B vaccination programme, and the ineffective dissemination of hepatitis B vaccination. This study highlights that accessibility and affordability of vaccinations are important determinants of vaccination uptake that should be taken into account when planning vaccination campaigns.

Cyanidin chloride protects mice from methicillin-resistant Staphylococcus aureus-induced pneumonia by targeting Sortase A

Methicillin-resistant Staphylococcus aureus (MRSA) has been developing rapidly in recent years. It poses a severe peril to global health care, and the new strategies to against the MRSA is urgently needed. Sortase A (SrtA) regulates the anchoring of many surface proteins. Compounds repress Staphylococcus aureus (S. aureus) cysteine transpeptidase SrtA are considered adequate potent virulence inhibitors. Then, we describe the identification of an effective SrtA inhibitor, cyanidin chloride, a bioflavonoid compound isolated from various plants. It has a reversible inhibitory effect on SrtA activity at an IC₅₀ of 21.91 μg/mL. As a SrtA inhibitor, cyanidin chloride antagonizes SrtA-related virulence phenotypes due to its breadth and specificity, including fibrinogen adhesion, A549 cell invasion, biofilm formation, and surface protein (SpA) anchoring. Subsequently, molecular docking and fluorescence quenching revealed that SrtA and cyanidin chloride had robust mutual affinity. Further mechanistic studies revealed that Arg-197, Gly-167, and Sep-116 were the key-binding sites mediating the interaction between SrtA and cyanidin chloride. Notably, a significant therapeutic effect of cyanidin chloride in vivo was also observed on the mouse pneumonia model induced by MRSA. In conclusion, our study indicates that cyanidin chloride potentially represents a new candidate SrtA inhibitor for S. aureus and potentially be developed as a new antivirulence agent.

In Vitro Antibacterial Experiments of Qixingjian Decoction and Its Synergistic Interaction with Oxacillin against Clinical Isolates of Methicillin-Resistant Staphylococcus aureus

Background

With the widespread use and abuse of antimicrobial drugs, the problem of bacterial resistance is becoming increasingly prominent. The clinical detection rate of drug-resistant bacteria is increasing year by year, so there is an urgent need to develop new antimicrobial drugs. Qixingjian Decoction (QXJT) is a formula commonly used in Chinese medicine for the treatment of sepsis caused by acute purulent infections of the face, hands, and feet. There are many compounds with antimicrobial effects that are available, but little is known about their mode of action. In this study, we mainly evaluated the antimicrobial activity of QXJT and explored its synergistic interaction with oxacillin (OX) and the mechanism of its antimicrobial activity.

Methods

The antimicrobial activity of QXJT against methicillin-resistant Staphylococcus aureus (MRSA) was determined by the microdilution method, the broth macrodilution method, and the time-kill curve method. The main compounds in QXJT were analyzed by ultra-performance liquid chromatography. The synergistic interaction of QXJT and oxacillin (OX) was determined by checkerboard assay, and the antimicrobial mechanism of QXJT, OX, and QXJT + OX was evaluated by transmission electron microscopy (TEM) technique. The expression of MRSA superantigen virulence factors (sea, seb, and tst), and drug resistance gene (mecA) was detected to provide a new strategy for new antibiotic drugs.

Results

QXJT exhibited antimicrobial activity against both clinical isolates of MRSA, MICs ranging from 18.75 to 37.5 mg/mL. Active substances such as Scutellarein, Scutellarin, Apigenin, and Wogonin 7-O-glucuronide were detected in the phytochemical analysis that may be associated with the antimicrobial activity of QXJT. The synergistic effect of QXJT and OX was determined by checkerboard assay (FICI = 0.5), and TEM images showed that QXJT could cause the disruption of MRSA cell wall, and QXJT + OX could produce greater disruption of MRSA cell wall, elucidating the synergistic effect of the two together on cell wall disruption by microscopic mechanisms. Our study shows that the combination of QXJT and OX can inhibit the expression of MRSA virulence factor, reduce the virulence of MRSA, and have no significant effect on the expression of MRSA resistance gene mecA.

Conclusion

The results of this study provide scientific experimental data for the traditional application of QXJT and initially explore the mechanism of action of QXJT combined with OX.

Structurally distinct unfolding intermediates formed from a staphylococcal capsule-producing enzyme retained NADPH binding activity

CapF, a capsule-producing enzyme expressed by Staphylococcus aureus, binds NADPH and exists as a dimer in the aqueous solution. Many other capsule-producing virulent bacteria also express CapF orthologs. To understand the folding-unfolding mechanism of S. aureus CapF, herein a recombinant CapF (rCapF) was individually investigated using urea and guanidine hydrochloride (GdnCl). Unfolding of rCapF by both the denaturants was reversible but proceeded via the synthesis of a different number of intermediates. While two dimeric intermediates (rCapF4 and rCapF5) were formed at 0.5 M and 1.5 M GdnCl, three dimeric intermediates (rCapF1, rCapF2, and rCapF3) were produced at 1 M, 2 M, and 3 M urea, respectively. rCapF5 showed 3.6 fold less NADPH binding activity, whereas other intermediates retained full NADPH binding activity. Compared to rCapF, all of the intermediates (except rCapF3) had a compressed shape. Conversely, rCapF3 possessed a native protein-like shape. The maximum shape loss was in rCapF4 though its secondary structure remained unperturbed. Additionally, the tertiary structure and hydrophobic surface area of the intermediates neither matched with each other nor with those of the native rCapF. Of the four Trp residues in rCapF, one or more Trp residues in the intermediates may have higher solvent accessibility. Using sequence alignment and a tertiary structural model of CapF, we have demonstrated that the region around Trp 137 of CapF may be most sensitive to unfolding, whereas the NADPH binding motif carrying region at the N-terminal end of this protein may be resistant to unfolding, particularly at the low denaturant concentrations.Communicated by Ramaswamy H. Sarma.

Alternative Sigma Factor of Staphylococcus aureus Interacts with the Cognate Antisigma Factor Primarily Using Its Domain 3

σ^B, an alternative sigma factor, is usually employed to tackle the general stress response in Staphylococcus aureus and other Gram-positive bacteria. This protein, involved in S. aureus-mediated pathogenesis, is typically blocked by RsbW, an antisigma factor having serine kinase activity. σ^B, a σ⁷⁰-like sigma factor, harbors three conserved domains designated σ^B2, σ^B3, and σ^B4. To better understand the interaction between RsbW and σ^B or its domains, we have studied their recombinant forms, rRsbW, rσ^B, rσ^B2, rσ^B3, and rσ^B4, using different probes. The results show that none of the rσ^B domains, unlike rσ^B, showed binding to a cognate DNA in the presence of a core RNA polymerase. However, both rσ^B2 and rσ^B3, like rσ^B, interacted with rRsbW, and the order of their rRsbW binding affinity looks like rσ^B > rσ^B3 > rσ^B2. Furthermore, the reaction between rRsbW and rσ^B or rσ^B3 was exothermic and occurred spontaneously. rRsbW and rσ^B3 also associate with each other at a stoichiometry of 2:1, and different types of noncovalent bonds might be responsible for their interaction. A structural model of the RsbW-σ^B3 complex that has supported our experimental results indicated the binding of rσ^B3 at the putative dimeric interface of RsbW. A genetic study shows that the tentative dimer-forming region of RsbW is crucial for preserving its rσ^B binding ability, serine kinase activity, and dimerization ability. Additionally, a urea-induced equilibrium unfolding study indicated a notable thermodynamic stabilization of σ^B3 in the presence of RsbW. Possible implications of the stabilization data in drug discovery were discussed at length.

Cajanin Stilbene Acid Inhibited Vancomycin-Resistant Enterococcus by Inhibiting Phosphotransferase System

Antimicrobial resistance has become a serious threat to human and animal health, and vancomycin-resistant Enterococcus has become an important nosocomial infection pathogen, causing thousands of deaths each year. In this study, after screening a variety of natural products, we found that cajanin stilbene acid (CSA) had significant inhibitory effect on sensitive and vancomycin-resistant Enterococcus (VRE) in vitro. And we also confirmed that CSA had significant anti-VRE infection ability in vivo. Subsequently, we studied the antibacterial mechanism of CSA through proteomics experiments, and the results showed that CSA killed Enterococcus by inhibiting the phosphotransferase system of Enterococcus, thus hinders the normal growth and metabolic functions of bacteria. The results of this study provided evidence for the in-depth study on the mechanism of the antibacterial action of CSA and also provided a candidate for the development of anti-VRE drugs.

Baicalin suppress growth and virulence-related factors of methicillin-resistant Staphylococcus aureus in vitro and vivo

A Staphylococcus aureus (S.aureus) was isolated from pigs suffered in pneumonia that can't be cured by antibiotic such as methicillin and vancomycin. It was demonstrated that baicalin, an active natural compound extracted from the traditional Chinese medicinal, possess antimicrobial activity. In the present study, we evaluate it efficacy in vitro and vivo against this isolated methicillin-resistant S.aureus (MRSA). Our findings demonstrated that baicalin can inhibit S. aureus growth in a dose-dependent manner and attenuate the biofilm formation. Scanning electron microscopies showed that cell membrane was damaged and accompany with contents leaks after treated with high concentration of baicalin. In addition, baicalin exerted inhibitory effects on the expression of S.aureus virulence-related factors. Moreover, baicalin treated mice had enhanced survival after a lethal dose of S.aureus infection compared with untreated mice. Simultaneously, the pathological tissue damage and bacterium burden were decrease in baicalin treated mice. These data demonstrated that baicalin displayed a high effectiveness in vitro and vivo against MRSA infection, suggesting that baicalin may potentially be used to treat MRSA infection.

Daphnetin prevents methicillin-resistant Staphylococcus aureus infection by inducing autophagic response

The bacterial pneumonia caused by methicillin-resistant Staphylococcus aureus (MRSA) is a potentially fatal disease, featured with extensive infection, inflammation, and airway dysfunction. With the increasing emerging of drug-resistant strains, new therapeutic strategies beyond canonical antibiotic treatment are pressingly needed. Daphnetin (DAPH) is a natural coumarin derivative with anti-inflammation, anti-microorganism and anti-oxidative properties. However, the protective effect of DAPH on S. aureus-caused pneumonia and the mechanism involved are never explored. Here we show that DAPH treatment conferred substantial protection against S. aureus-induced pneumonia, characterized by the reduced inflammatory responses, the augmented bacterial clearance and the alleviated tissue damage. Our study indicates that DAPH significantly enhanced mTOR-dependent autophagic pathway, leading to the boosted microphage bactericidal activity and the suppressed inflammatory responses. Inhibition of autophagic pathway therefore largely abolished DAPH-elicited repression of inflammatory response and macrophage anti-bacterial capability. Together, we herein not only identify a novel, natural agent to combat bacterial pneumonia, but also underscore the significance of autophagic pathway in orchestrating antimicrobial and anti-inflammatory responses, which may have important implication for the treatment of the infectious diseases, particularly that caused by obstinate, antibiotic-resistant pathogens such as MRSA.

Statins: antimicrobial resistance breakers or makers?

Introduction

The repurposing of non-antibiotic drugs as adjuvant antibiotics may help break antimicrobial resistance (AMR). Statins are commonly prescribed worldwide to lower cholesterol. They also possess qualities of AMR “breakers”, namely direct antibacterial activity, synergism with antibiotics, and ability to stimulate the host immune system. However, statins’ role as AMR breakers may be limited. Their current extensive use for cardiovascular protection might result in selective pressures for resistance, ironically causing statins to be AMR “makers” instead. This review examines statins’ potential as AMR breakers, probable AMR makers, and identifies knowledge gaps in a statin-bacteria-human-environment continuum. The most suitable statin for repurposing is identified, and a mechanism of antibacterial action is postulated based on structure-activity relationship analysis.

Methods

A literature search using keywords “statin” or “statins” combined with “minimum inhibitory concentration” (MIC) was performed in six databases on 7th April 2017. After screening 793 abstracts, 16 relevant studies were identified. Unrelated studies on drug interactions; antifungal or antiviral properties of statins; and antibacterial properties of mevastatin, cerivastatin, antibiotics, or natural products were excluded. Studies involving only statins currently registered for human use were included.

Results

Against Gram-positive bacteria, simvastatin generally exerted the greatest antibacterial activity (lowest MIC) compared to atorvastatin, rosuvastatin, and fluvastatin. Against Gram-negative bacteria, atorvastatin generally exhibited similar or slightly better activity compared to simvastatin, but both were more potent than rosuvastatin and fluvastatin.

Discussion

Statins may serve as AMR breakers by working synergistically with existing topical antibiotics, attenuating virulence factors, boosting human immunity, or aiding in wound healing. It is probable that statins’ mechanism of antibacterial activity involves interference of bacterial cell regulatory functions via binding and disrupting cell surface structures such as wall teichoic acids, lipoteichoic acids, lipopolysaccharides, and/or surface proteins. The widespread use of statins for cardiovascular protection may favor selective pressures or co-selection for resistance, including dysbiosis of the human gut microbiota, sublethal plasma concentrations in bacteremic patients, and statin persistence in the environment, all possibly culminating in AMR.

Conclusion

Simvastatin appears to be the most suitable statin for repurposing as a novel adjuvant antibiotic. Current evidence better supports statins as potential AMR breakers, but their role as plausible AMR makers cannot be excluded. Elucidating the mechanism of statins’ antibacterial activity is perhaps the most important knowledge gap to address as this will likely clarify statins’ role as AMR breakers or makers.

Genomic Heterogeneity of Methicillin Resistant Staphylococcus aureus Associated with Variation in Severity of Illness among Children with Acute Hematogenous Osteomyelitis

Introduction

The association between severity of illness of children with osteomyelitis caused by Methicillin-resistant Staphylococcus aureus (MRSA) and genomic variation of the causative organism has not been previously investigated. The purpose of this study is to assess genomic heterogeneity among MRSA isolates from children with osteomyelitis who have diverse severity of illness.

Materials and Methods

Children with osteomyelitis were prospectively studied between 2010 and 2011. Severity of illness of the affected children was determined from clinical and laboratory parameters. MRSA isolates were analyzed with next generation sequencing (NGS) and optical mapping. Sequence data was used for multi-locus sequence typing (MLST), phylogenetic analysis by maximum likelihood (PAML), and identification of virulence genes and single nucleotide polymorphisms (SNP) relative to reference strains.

Results

The twelve children studied demonstrated severity of illness scores ranging from 0 (mild) to 9 (severe). All isolates were USA300, ST 8, SCC mec IVa MRSA by MLST. The isolates differed from reference strains by 2 insertions (40 Kb each) and 2 deletions (10 and 25 Kb) but had no rearrangements or copy number variations. There was a higher occurrence of virulence genes among study isolates when compared to the reference strains (p = 0.0124). There were an average of 11 nonsynonymous SNPs per strain. PAML demonstrated heterogeneity of study isolates from each other and from the reference strains.

Discussion

Genomic heterogeneity exists among MRSA isolates causing osteomyelitis among children in a single community. These variations may play a role in the pathogenesis of variation in clinical severity among these children.

ω-Hydroxyemodin limits staphylococcus aureus quorum sensing-mediated pathogenesis and inflammation

Antibiotic-resistant pathogens are a global health threat. Small molecules that inhibit bacterial virulence have been suggested as alternatives or adjuncts to conventional antibiotics, as they may limit pathogenesis and increase bacterial susceptibility to host killing. Staphylococcus aureus is a major cause of invasive skin and soft tissue infections (SSTIs) in both the hospital and community settings, and it is also becoming increasingly antibiotic resistant. Quorum sensing (QS) mediated by the accessory gene regulator (agr) controls virulence factor production essential for causing SSTIs. We recently identified ω-hydroxyemodin (OHM), a polyhydroxyanthraquinone isolated from solid-phase cultures of Penicillium restrictum, as a suppressor of QS and a compound sought for the further characterization of the mechanism of action. At concentrations that are nontoxic to eukaryotic cells and subinhibitory to bacterial growth, OHM prevented agr signaling by all four S. aureus agr alleles. OHM inhibited QS by direct binding to AgrA, the response regulator encoded by the agr operon, preventing the interaction of AgrA with the agr P2 promoter. Importantly, OHM was efficacious in a mouse model of S. aureus SSTI. Decreased dermonecrosis with OHM treatment was associated with enhanced bacterial clearance and reductions in inflammatory cytokine transcription and expression at the site of infection. Furthermore, OHM treatment enhanced the immune cell killing of S. aureus in vitro in an agr-dependent manner. These data suggest that bacterial disarmament through the suppression of S. aureus QS may bolster the host innate immune response and limit inflammation.

Factores relacionados con la colonización por Staphylococcus aureus

Staphylococcus aureus tiene gran capacidad para colonizar la piel y las mucosas de los seres humanos y de diferentes animales. Varios estudios evidencian el papel de dicha colonización en la patogénesis y la epidemiología de las infecciones causadas por S. aureus. Se ha demostrado que los portadores nasales constituyen una fuente importante de propagación de la bacteria; una amplia proporción de las infecciones estafilocócicas invasivas asociadas al cuidado de la salud son de origen endógeno, y la colonización por cepas de S. aureus resistentes a meticilina (SARM), aún mal entendida, origina mayores complicaciones. La importancia de la colonización se ha definido con más profundidad en ambientes hospitalarios, pero recientemente se han hecho estudios en la comunidad con resultados contradictorios sobre la relación colonización-infección. En esta revisión se presentan algunas características relevantes del proceso de colonización por S. aureus, incluyendo las cepas de SARM, y se consideran los factores humanos y del microorganismo que influyen en él. Asimismo, se hace una revisión de los estudios colombianos al respecto.

Liposomal resiquimod for the treatment of Leishmania donovani infection

OBJECTIVES

The imidazoquinoline family of drugs are Toll-like receptor 7/8 agonists that have previously been used in the treatment of cutaneous leishmaniasis. Because of the hydrophobic nature of imidazoquinolines, they are traditionally not administered systemically for the treatment of visceral leishmaniasis. We formulated liposomal resiquimod, an imidazoquinoline, for the systemic treatment of visceral leishmaniasis.

METHODS

By using lipid film hydration with extrusion, we encapsulated resiquimod in liposomes. These liposomes were then injected intravenously to treat BALB/c mice infected with Leishmania donovani.

RESULTS

Treatment with liposomal resiquimod significantly decreased the parasite load in the liver, spleen and bone marrow. In addition, resiquimod treatment increased interferon-γ and interleukin-10 production in an antigen recall assay. Resiquimod was shown to be non-toxic in histology and in vitro culture experiments.

CONCLUSIONS

FDA-approved resiquimod, in a liposomal formulation, displays promising results in treating visceral leishmaniasis.