Role of SigB and Staphyloxanthin in Radiation Survival of Staphylococcus aureus

Comparative genomic analysis and multilocus sequence typing of Staphylococcus aureus reveals candidate genes for low-temperature tolerance

Staphylococcus aureus is one of the most frequently detected foodborne pathogens in cold chain foods. Worryingly, small colony variants (SCVs) can survive in cold environments for a long time and can revert to rapidly growing cells in suitable environments, causing serious food safety issues. This study investigated the underlying mechanism of SCV formation at low temperature (4 °C) via comparative genomics. Multilocus sequence typing (MLST) of 105 strains of S. aureus was divided into 9 sequence types. The ST352 strains exhibited the greatest tolerance to low temperature, with a mean reduction in survival rate of 10.34 % (p < 0.05). Comparative genomics revealed a total of 1941 core genes in the three S. aureus strains, and BB-1 had 468 specific genes, which were enriched mainly in translation, DNA recombination, DNA repair, metabolic pathways, two-component systems, and quorum sensing. Molecular docking analysis revealed that the binding of the RsbW protein to the SigB protein of BB-1 decreased due to base mutations in rsbW, while the binding to the RsbV protein was enhanced. In addition, the results of real-time quantitative PCR showed that the RsbV-RsbW/SigB system of BB-1 may play a role in the low-temperature survival of S. aureus and the formation of SCVs. These results suggest that genes specific to BB-1 may contribute to the mechanism of adaptation to low temperature and the formation of SCVs. This study helps elucidate the causes of SCV formation by S. aureus at low temperature at the molecular level and provides a basis for exploring the safety control of cold chain food environments.

Identification of staphyloxanthin and derivates in yellow-pigmented Staphylococcus capitis subsp. capitis

Introduction

Staphylococcus capitis naturally colonizes the human skin but as an opportunistic pathogen, it can also cause biofilm-associated infections and bloodstream infections in newborns. Previously, we found that two strains from the subspecies S. capitis subsp. capitis produce yellow carotenoids despite the initial species description, reporting this subspecies as non-pigmented. In Staphylococcus aureus, the golden pigment staphyloxanthin is an important virulence factor, protecting cells against reactive oxygen species and modulating membrane fluidity.

Methods

In this study, we used two pigmented (DSM 111179 and DSM 113836) and two non-pigmented S. capitis subsp. capitis strains (DSM 20326T and DSM 31028) to identify the pigment, determine conditions under which pigment-production occurs and investigate whether pigmented strains show increased resistance to ROS and temperature stress.

Results

We found that the non-pigmented strains remained colorless regardless of the type of medium, whereas intensity of pigmentation in the two pigmented strains increased under low nutrient conditions and with longer incubation times. We were able to detect and identify staphyloxanthin and its derivates in the two pigmented strains but found that methanol cell extracts from all four strains showed ROS scavenging activity regardless of staphyloxanthin production. Increased survival to cold temperatures (-20°C) was detected in the two pigmented strains only after long-term storage compared to the non-pigmented strains.

Conclusion

The identification of staphyloxanthin in S. capitis is of clinical relevance and could be used, in the same way as in S. aureus, as a possible target for anti-virulence drug design.

Phenotypic Variation in Clinical S. aureus Isolates Did Not Affect Disinfection Efficacy Using Short-Term UV-C Radiation

Pigmentation, catalase activity and biofilm formation are virulence factors that cause resistance of Staphylococcus aureus to environmental stress factors including disinfectants. In recent years, automatic UV-C room disinfection gained greater importance in enhanced disinfection procedures to improve disinfection success in hospitals. In this study, we evaluated the effect of naturally occurring variations in the expression of virulence factors in clinical S. aureus isolates on tolerance against UV-C radiation. Quantification of staphyloxanthin expression, catalase activity and biofilm formation for nine genetically different clinical S. aureus isolates as well as reference strain S. aureus ATCC 6538 were performed using methanol extraction, a visual approach assay and a biofilm assay, respectively. Log₁₀ reduction values (LRV) were determined after irradiation of artificially contaminated ceramic tiles with 50 and 22 mJ/cm² UV-C using a commercial UV-C disinfection robot. A wide variety of virulence factor expression was observed, indicating differential regulation of global regulatory networks. However, no direct correlation with the strength of expression with UV-C tolerance was observed for either staphyloxanthin expression, catalase activity or biofilm formation. All isolates were effectively reduced with LRVs of 4.75 to 5.94. UV-C disinfection seems therefore effective against a wide spectrum of S. aureus strains independent of occurring variations in the expression of the investigated virulence factors. Due to only minor differences, the results of frequently used reference strains seem to be representative also for clinical isolates in S. aureus.

Transcriptome analysis reveals the molecular mechanism of cinnamaldehyde against Bacillus cereus spores in ready-to-eat beef

The purpose of this study was to investigate the antibacterial effect and mechanism of cinnamaldehyde on Bacillus cereus spores in ready-to-eat beef. The colour difference and texture of the ready-to-eat beef supplemented with cinnamaldehyde did not differ greatly from the colour and texture of the blank beef. However, cinnamaldehyde has an effective antibacterial effect on the total number of bacterial colonies and B. cereus spores in ready-to-eat beef. Transmission electron microscopy (TEM) analysis revealed that the cell membrane of B. cereus was disrupted by cinnamaldehyde, leading to leakage of intracellular components. Transcriptome sequencing (RNA-seq) indicated that the B. cereus spore resistance regulation system (sigB, sigW, rsbW, rsbV, yfkM and yflT) and phosphoenolpyruvate phosphotransferase system (PTS) (ptsH, ptsI and ptsG) respond positively to cinnamaldehyde in an adverse environment. Intracellular disorders due to damage to the cell membrane involve some transporters (copA, opuBA and opuD) and some oxidative stress systems (ywrO, scdA and katE) in the regulation of the body. However, downregulation of K⁺ transport channels (kdpD and kdpB), osmotic pressure regulation (opuE) and some oxidative stress (norR and srrA)-related genes may accelerate spore apoptosis. In addition, cinnamaldehyde also effectively inhibits the spore germination-related genes (smc, mreB and gerE). This study provides new insights into the molecular mechanism of the antibacterial effect of cinnamaldehyde on B. cereus spores in ready-to-eat beef.

Phenotypic and genomic assessment of the potential threat of human spaceflight-relevant Staphylococcus capitis isolates under stress conditions

Previous studies have reported that spaceflight specific conditions such as microgravity lead to changes in bacterial physiology and resistance behavior including increased expression of virulence factors, enhanced biofilm formation and decreased susceptibility to antibiotics. To assess if spaceflight induced physiological changes can manifest in human-associated bacteria, we compared three spaceflight relevant Staphylococcus capitis isolates (DSM 111179, ISS; DSM 31028, clean room; DSM 113836; artificial gravity bedrest study) with the type strain (DSM 20326T). We tested the three strains regarding growth, colony morphology, metabolism, fatty acid and polar lipid pattern, biofilm formation, susceptibility to antibiotics and survival in different stress conditions such as treatment with hydrogen peroxide, exposure to desiccation, and irradiation with X-rays and UV-C. Moreover, we sequenced, assembled, and analyzed the genomes of all four strains. Potential genetic determinants for phenotypic differences were investigated by comparative genomics. We found that all four strains show similar metabolic patterns and the same susceptibility to antibiotics. All four strains were considered resistant to fosfomycin. Physiological differences were mainly observed compared to the type strain and minor differences among the other three strains. The ISS isolate and the bedrest study isolate exhibit a strong delayed yellow pigmentation, which is absent in the other two strains. Pigments were extracted and analyzed by UV/Vis spectroscopy showing characteristic carotenoid spectra. The ISS isolate showed the highest growth rate as well as weighted average melting temperature (WAMT) of fatty acids (41.8°C) of all strains. The clean room isolate showed strongest biofilm formation and a high tolerance to desiccation. In general, all strains survived desiccation better in absence of oxygen. There were no differences among the strains regarding radiation tolerance. Phenotypic and genomic differences among the strains observed in this study are not inevitably indicating an increased virulence of the spaceflight isolate. However, the increased growth rate, higher WAMT and colony pigmentation of the spaceflight isolate are relevant phenotypes that require further research within the human spaceflight context. We conclude that combining genetic analysis with classical microbiological methods allows the detailed assessment of the potential threat of bacteria in highly regulated and extreme environments such as spaceflight environments.

Small-molecule compound SYG-180-2-2 attenuates Staphylococcus aureus virulence by inhibiting hemolysin and staphyloxanthin production

Multi-drug resistant Staphylococcus aureus infection is still a serious threat to global health. Therefore, there is an urgent need to develop new antibacterial agents based on virulence factor therapy to overcome drug resistance. Previously, we synthesized SYG-180-2-2 (C₂₁H₁₆N₂OSe), an effective small molecule compound against biofilm. The aim of this study was to investigate the anti-virulence efficacy of SYG-180-2-2 against Staphylococcus aureus. MIC results demonstrated no apparent antibacterial activity of the SYG-180-2-2. The growth curve assay showed that SYG-180-2-2 had nonlethal effect on S. aureus. Besides, SYG-180-2-2 strongly inhibited the hemolytic activity and staphyloxanthin synthesis in S. aureus. Inhibition of staphyloxanthin by SYG-180-2-2 enhanced the sensitivity of S. aureus to oxidants and human whole blood. In addition, SYG-180-2-2 significantly decreased the expression of saeR-mediated hemolytic gene hlb and staphyloxanthin-related crtM, crtN and sigB genes by quantitative polymerase chain reaction (qPCR). Meanwhile, the expression of oxidative stress-related genes sodA, sodM and katA also decreased. Galleria Mellonella assay revealed that SYG-180-2-2 was not toxic to larvae. Further, the larvae infection model showed that the virulence of bacteria was significantly reduced after 4 μg/mL SYG-180-2-2 treatment. SYG-180-2-2 also reduced skin abscess formation in mice by reducing bacterial burden and subcutaneous inflammation. In conclusion, SYG-180-2-2 might be a promising agent to attenuate the virulence of S. aureus by targeting genes associated with hemolytic activity and staphyloxanthin synthesis.

Comparative Transcriptomic Analysis of Staphylococcus aureus Reveals the Genes Involved in Survival at Low Temperature

In food processing, the temperature is usually reduced to limit bacterial reproduction and maintain food safety. However, Staphylococcus aureus can adapt to low temperatures by controlling gene expression and protein activity, although its survival strategies normally vary between different strains. The present study investigated the molecular mechanisms of S. aureus with different survival strategies in response to low temperatures (4 °C). The survival curve showed that strain BA-26 was inactivated by 6.0 logCFU/mL after 4 weeks of low-temperature treatment, while strain BB-11 only decreased by 1.8 logCFU/mL. Intracellular nucleic acid leakage, transmission electron microscopy, and confocal laser scanning microscopy analyses revealed better cell membrane integrity of strain BB-11 than that of strain BA-26 after low-temperature treatment. Regarding oxidative stress, the superoxide dismutase activity and the reduced glutathione content in BB-11 were higher than those in BA-26; thus, BB-11 contained less malondialdehyde than BA-26. RNA-seq showed a significantly upregulated expression of the fatty acid biosynthesis in membrane gene (fabG) in BB-11 compared with BA-26 because of the damaged cell membrane. Then, catalase (katA), reduced glutathione (grxC), and peroxidase (ahpC) were found to be significantly upregulated in BB-11, leading to an increase in the oxidative stress response, but BA-26-related genes were downregulated. NADH dehydrogenase (nadE) and α-glucosidase (malA) were upregulated in the cold-tolerant strain BB-11 but were downregulated in the cold-sensitive strain BA-26, suggesting that energy metabolism might play a role in S. aureus under low-temperature stress. Furthermore, defense mechanisms, such as those involving asp23, greA, and yafY, played a pivotal role in the response of BB-11 to stress. The study provided a new perspective for understanding the survival mechanism of S. aureus at low temperatures.

Staphyloxanthin as a Potential Novel Target for Deciphering Promising Anti-Staphylococcus aureus Agents

Staphylococcus aureus is a fatal Gram-positive pathogen threatening numerous cases of hospital-admitted patients worldwide. The emerging resistance of the pathogen to several antimicrobial agents has pressurized research to propose new strategies for combating antimicrobial resistance. Novel strategies include targeting the virulence factors of S. aureus. One of the most prominent virulence factors of S. aureus is its eponymous antioxidant pigment staphyloxanthin (STX), which is an auspicious target for anti-virulence therapy. This review provides an updated outline on STX and multiple strategies to attenuate this virulence factor. The approaches discussed in this article focus on bioprospective and chemically synthesized inhibitors of STX, inter-species communication and genetic manipulation. Various inhibitor molecules were found to exhibit appreciable inhibitory effect against STX and hence would be able to serve as potential anti-virulence agents for clinical use.

Insights Into the Cultivable Bacterial Fraction of Sediments From the Red Sea Mangroves and Physiological, Chemotaxonomic, and Genomic Characterization of Mangrovibacillus cuniculi gen. nov., sp. nov., a Novel Member of the Bacillaceae Family

Mangrove forests are dynamic and productive ecosystems rich in microbial diversity; it has been estimated that microbial cells in the mangrove sediments constitute up to 91% of the total living biomass of these ecosystems. Despite in this ecosystem many of the ecological functions and services are supported and/or carried out by microorganisms (e.g., nutrient cycling and eukaryotic-host adaptation), their diversity and function are overlooked and poorly explored, especially for the oligotrophic mangrove of the Red Sea coast. Here, we investigated the cultivable fraction of bacteria associated with the sediments of Saudi Arabian Red Sea mangrove forest by applying the diffusion-chamber-based approach in combination with oligotrophic medium and long incubation time to allow the growth of bacteria in their natural environment. Cultivation resulted in the isolation of numerous representatives of Isoptericola (n = 51) and Marinobacter (n = 38), along with several less abundant and poorly study taxa (n = 25) distributed across ten genera. Within the latest group, we isolated R1DC41^T, a novel member of the Bacillaceae family in the Firmicutes phylum. It showed 16S rRNA gene similarity of 94.59–97.36% with closest relatives of Rossellomorea (which was formerly in the Bacillus genus), Domibacillus, Bacillus, and Jeotgalibacillus genera. Based on the multilocus sequence analysis (MLSA), R1DC41^T strain formed a separated branch from the listed genera, representing a novel species of a new genus for which the name Mangrovibacillus cuniculi gen. nov., sp. nov. is proposed. Genomic, morphological, and physiological characterizations revealed that R1DC41^T is an aerobic, Gram-stain-variable, rod-shaped, non-motile, endospore-forming bacterium. A reduced genome and the presence of numerous transporters used to import the components necessary for its growth and resistance to the stresses imposed by the oligotrophic and salty mangrove sediments make R1DC41^T extremely adapted to its environment of origin and to the competitive conditions present within.

Measurement of Staphylococcus aureus Pigmentation by Methanol Extraction

Many S. aureus strains produce membrane-associated carotenoid pigments, advantageous secondary metabolites that can alter membrane fluidity, resistance to antimicrobial peptides (AMPs) and act as antioxidants, properties that can impact resistance against aspects of the host innate immune system. Several studies have reported connections between mutations in both regulatory (i.e., alternative sigma factor B) and metabolic (purine biosynthesis, oxidative phosphorylation) genes, and noticeable differences in carotenoid pigmentation. This chapter outlines a simple protocol to quantify cellular pigments using a methanol extraction method.

Staphyloxanthin inhibitory potential of thymol impairs antioxidant fitness, enhances neutrophil mediated killing and alters membrane fluidity of methicillin resistant Staphylococcus aureus

Staphylococcus aureus is a leading pathogen responsible for mild to severe invasive infections in humans. Especially, methicillin resistant Staphylococcus aureus (MRSA) is prevalent in hospital and community associated infections. Staphyloxanthin is a golden yellow color eponymous pigment produced by S. aureus and provides resistance to reactive oxygen species (ROS) and host neutrophil-based killing. In addition, this membrane pigment contributes to membrane rigidity and helps MRSA to survive under stress conditions. Targeting virulence of pathogen without exerting selection pressure is the recent approach to fight bacterial infections without developing drug resistance. The present study for the first time evaluated the staphyloxanthin inhibitory potential of thymol against MRSA. Qualitative and quantitative analyses demonstrated 90% of staphyloxanthin inhibition at 100 µg/mL concentration of thymol without alteration in growth. Molecular docking analysis and in vitro measurement of metabolic intermediates of staphyloxanthin revealed that thymol could possibly interact with CrtM to inhibit staphyloxanthin. Absorbance and infra red spectra further validated the inhibition of staphyloxanthin by thymol. In addition, thymol treatment significantly reduced the resistance of MRSA to ROS and neutrophil-based killing as exhibited by oxidant susceptibility assays and ex vivo innate immune clearance assay using human whole blood and neutrophils. Further, reduction in staphyloxanthin by thymol treatment increased the membrane fluidity and made MRSA cells more susceptible to membrane targeting antibiotic polymyxin B. Especially, thymol was found to be non-cytotoxic to human peripheral blood mononuclear cells. Our study validated the antivirulence potential of thymol against MRSA by inhibiting staphyloxanthin and suggests the prospective therapeutic role of thymol to combat MRSA infections.

Cumulative damage by nonthermal plasma (NTP) exceeds the defense barrier of multiple antibiotic-resistant Staphylococcus aureus: a key to achieve complete inactivation

Objectives

The aim of this study was to provide a comprehensive understanding of the nonthermal plasma (NTP)-induced inactivated behaviors on a multiple antibiotic–resistant (MAR) Staphylococcus aureus (S. aureus).

Materials and Methods

A dielectric barrier discharge (DBD) NTP system was employed for the inactivation of a MAR S. aureus under various applied powers of 35, 45, and 55 W, and gas distances of 4, 6, and 8 mm. The inactivation kinetics of S. aureus were estimated with linear and nonlinear predictive models. In addition, degradation of carotenoid pigment, peroxidation of fatty acids, oxidation of nucleic acids and proteins, and alteration in gene expression were analyzed after NTP treatment.

Results and Discussion

The computationally simulated results indicated that the densities of various reactive species increased with enhanced applied powers and decreased discharge distances. These species were further transformed into reactive oxidative and nitrogen species in the gas–liquid interphase and liquid phase. The oxidative and nitrosative stress of NTP resulted in severe damage to cellular components and the morphological structure of S. aureus. On the other hand, the plasma reactive species could also induce the sublethal injury of S. aureus through upregulating the general stress response, antioxidative and antinitrosative defensive systems. Once the cumulative damages overrode the stress tolerance of S. aureus, the completed cell death was finally achieved by NTP.

Conclusions

This work infers the possible risk of inducing the repair and resistant capacity of pathogens when the applied NTP parameters are inappropriate, which helps the optimization of NTP process to achieve sufficient inactivation.

The small molecule ZY-214-4 may reduce the virulence of Staphylococcus aureus by inhibiting pigment production

BACKGROUND

In recent years, clinical Staphylococcus aureus isolates have become highly resistant to antibiotics, which has raised concerns about the ability to control infections by these organisms. The aim of this study was to clarify the effect of a new small molecule, ZY-214-4 (C19H11BrNO4), on S. aureus pigment production.

RESULTS

At the concentration of 4 μg/mL, ZY-214-4 exerted a significant inhibitory effect on S. aureus pigment synthesis, without affecting its growth or inducing a toxic effect on the silkworm. An oxidant sensitivity test and a whole-blood killing test indicated that the S. aureus survival rate decreased significantly with ZY-214-4 treatment. Additionally, ZY-214-4 administration significantly reduced the expression of a pigment synthesis-related gene (crtM) and the superoxide dismutase genes (sodA) as determined by real-time quantitative polymerase chain reaction (RT-qPCR) analysis. ZY-214-4 treatment also improved the survival rate of S. aureus-infected silkworm larvae.

CONCLUSIONS

The small molecule ZY-214-4 has potential for the prevention of S. aureus infections by reducing the virulence associated with this bacterium.

Antimicrobial and Antivirulence Action of Eugenia brejoensis Essential Oil in vitro and in vivo Invertebrate Models

Eugenia brejoensis L. (Myrtaceae) is an endemic plant from caatinga ecosystem (brazilian semi-arid) which have an E. brejoensis essential oil (EbEO) with reported antimicrobial activity. In this work, in vitro and in vivo models were used to characterize the inhibitory effects of EbEO in relation to Staphylococcus aureus. EbEO inhibited the growth of all tested S. aureus strains (including multidrug resistance isolates) with values ranging from 8 to 516 μg/mL. EbEO also synergistically increased the action of ampicillim, chloramphenicol, and kanamycin. The treatment with subinhibitory concentrations (Sub-MIC) of EbEO decreased S. aureus hemolytic activity and its ability to survive in human blood. EbEO strongly reduced the levels of staphyloxanthin (STX), an effect related to increased susceptibility of S. aureus to hydrogen peroxide. The efficacy of EbEO against S. aureus was further demonstrated using Caenorhabditis elegans and Galleria mellonella. EbEO increased the lifespan of both organisms infected by S. aureus, reducing the bacterial load. In addition, EbEO reduced the severity of S. aureus infection in G. mellonella, as shown by lower levels of melanin production in those larvae. In summary, our data suggest that EbEO is a potential source of lead molecules for development of new therapeutic alternatives against S. aureus.

Protective Effect of the Golden Staphyloxanthin Biosynthesis Pathway on Staphylococcus aureus under Cold Atmospheric Plasma Treatment

Staphylococcus aureus infection poses a serious threat to public health, and antibiotic resistance has complicated the clinical treatment and limited the solutions available to solve this problem. Cold atmospheric plasma (CAP) is a promising strategy for microorganism inactivation. However, the mechanisms of microbial inactivation or resistance remain unclear. In this study, we treated S. aureus strains with a self-assembled CAP device and found that CAP can kill S. aureus in an exposure time-dependent manner. In addition, the liquid environment can influence the survival rate of S. aureus post-CAP treatment. The S. aureus cells can be completely inactivated in normal saline and phosphate-buffered saline but not in tryptic soy broth culture medium. Scanning and transmission electron microscopy revealed that the CAP-treated S. aureus cells maintained integrated morphological structures, similar to the wild-type strain. Importantly, the CAP-treated S. aureus cells exhibited a reduced pigment phenotype. Deletion of the staphyloxanthin biosynthetic genes crtM and crtN deprived the pigmentation ability of S. aureus Newman. Both the Newman-ΔcrtM and Newman-ΔcrtN mutants presented high sensitivity to CAP treatment, whereas Newman-ΔcrtO exhibited a survival rate comparable to wild-type Newman after CAP treatment. Our data demonstrated that the yellow pigment intermediates of the staphyloxanthin biosynthetic pathway are responsible for the protection of S. aureus from CAP inactivation. The key enzymes, such as CrtM and CrtN, of the golden staphyloxanthin biosynthetic pathway could be important targets for the design of novel sterilization strategies against S. aureus infections.IMPORTANCEStaphylococcus aureus is an important pathogen that can be widely distributed in the community and clinical settings. The emergence of S. aureus with multiple-antibiotic resistance has complicated staphylococcal infection control. The development of alternative strategies with powerful bactericidal effects is urgently needed. Cold atmospheric plasma (CAP) is a promising strategy for microorganism inactivation. Nevertheless, the underlying mechanisms of microbial inactivation or resistance are not completely illustrated. In this study, we validated the bactericidal effects of CAP on S. aureus, including antibiotic-resistant strains. We also found that the golden staphyloxanthin, as well as its yellow pigment intermediates, protected S. aureus against CAP, and blocking the staphyloxanthin synthesis pathway at the early steps could strengthen the sensitivity of S. aureus to CAP treatment. These data provide insights into the germicidal mechanism of CAP from the aspect of bacteria and suggest new targets against S. aureus infections.

The latex of Euphorbia tirucalli inhibits staphyloxanthin production and protects Tenebrio molitor larvae against Staphylococcus aureus infection

The latex of Euphorbia tirucalli L. (LET) has great etnopharmacological relevance for several traditional communities. In this study, the in vitro and in vivo (using Tenebrio molitor larvae) antimicrobial effects of LET were evaluated. LET did not inhibit the growth of S. aureus, however, a reduction on staphyloxanthin production (an important virulence factor of S. aureus) was observed. LET (at 10 μL/kg) was also able to enhance the survival of larvae infected with a lethal dose of S. aureus, an effect associated with reduction in the numbers of haemocytes. Furthermore, haemocytes from LET-treated larvae exhibited dysfunctional lysosome activity. These results indicate the effectiveness of LET as an anti-infective agent which could be useful as source of lead molecules for the development of new therapies against S. aureus-induced infections.