A pursuit of Staphylococcus aureus continues: a role of persister cells

Osteomyelitis-relevant antibiotics at clinical concentrations show limited effectivity against acute and chronic intracellular S. aureus infections in osteocytes

Osteomyelitis caused by Staphylococcus aureus can involve the persistent infection of osteocytes. We sought to determine if current clinically utilized antibiotics were capable of clearing an intracellular osteocyte S. aureus infection. Rifampicin, vancomycin, levofloxacin, ofloxacin, amoxicillin, oxacillin, doxycycline, linezolid, gentamicin, and tigecycline were assessed for their minimum inhibitory concentration (MIC) and minimum bactericidal concentrations against 12 S. aureus strains, at pH 5.0 and 7.2 to mimic lysosomal and cytoplasmic environments, respectively. Those antibiotics whose bone estimated achievable concentration was commonly above their respective MIC for the strains tested were further assayed in a human osteocyte infection model under acute and chronic conditions. Osteocyte-like cells were treated at 1×, 4×, and 10× the MIC for 1 and 7 days following infection (acute model), or at 15 and 21 days of infection (chronic model). The intracellular effectivity of each antibiotic was measured in terms of CFU reduction, small colony variant formation, and bacterial mRNA expression change. Only rifampicin, levofloxacin, and linezolid reduced intracellular CFU numbers significantly in the acute model. Consistent with the transition to a non-culturable state, few if any CFU could be recovered from the chronic model. However, no treatment in either model reduced the quantity of bacterial mRNA or prevented non-culturable bacteria from returning to a culturable state. These findings indicate that S. aureus adapts phenotypically during intracellular infection of osteocytes, adopting a reversible quiescent state that is protected against antibiotics, even at 10× their MIC. Thus, new therapeutic approaches are necessary to cure S. aureus intracellular infections in osteomyelitis.

Pheromone cCF10 inhibits the antibiotic persistence of Enterococcus faecalis by modulating energy metabolism

Introduction

Bacterial resistance presents a major challenge to both the ecological environment and human well-being, with persistence playing a key role. Multiple studies were recently undertaken to examine the factors influencing the formation of persisters and the underlying process, with a primary focus on Gram-negative bacteria and Staphylococcus aureus (Gram-positive bacteria). Enterococcus faecalis (E. faecalis) is capable of causing a variety of infectious diseases, but there have been few studies of E. faecalis persisters. Previous studies have shown that the sex pheromone cCF10 secreted by E. faecalis induces conjugative plasmid transfer. However, whether the pheromone cCF10 regulates the persistence of E. faecalis has not been investigated.

Methods

As a result, we investigated the effect and potential molecular mechanism of pheromone cCF10 in regulating the formation of persisters in E. faecalis OG1RF using a persistent bacteria model.

Results and discussion

The metabolically active E. faecalis OG1RF reached a persistence state and temporarily tolerated lethal antibiotic concentrations after 8  h of levofloxacin hydrochloride (20 mg/mL) exposure, exhibiting a persistence rate of 0.109 %. During the growth of E. faecalis OG1RF, biofilm formation was a critical factor contributing to antibiotic persistence, whereas 10 ng/mL cCF10 blocked persister cell formation. Notably, cCF10 mediated the antibiotic persistence of E. faecalis OG1RF via regulating metabolic activity rather than suppressing biofilm formation. The addition of cCF10 stimulated the Opp system and entered bacterial cells, inhibiting (p)ppGpp accumulation, thus maintaining the metabolically active state of bacteria and reducing persister cell generation. These findings offer valuable insights into the formation, as well as the control mechanism of E. faecalis persisters.

Beyond the double helix: the multifaceted landscape of extracellular DNA in Staphylococcus aureus biofilms

Staphylococcus aureus forms biofilms consisting of cells embedded in a matrix made of proteins, polysaccharides, lipids, and extracellular DNA (eDNA). Biofilm-associated infections are difficult to treat and can promote antibiotic resistance, resulting in negative healthcare outcomes. eDNA within the matrix contributes to the stability, growth, and immune-evasive properties of S. aureus biofilms. eDNA is released by autolysis, which is mediated by murein hydrolases that access the cell wall via membrane pores formed by holin-like proteins. The eDNA content of S. aureus biofilms varies among individual strains and is influenced by environmental conditions, including the presence of antibiotics. eDNA plays an important role in biofilm development and structure by acting as an electrostatic net that facilitates protein-cell and cell-cell interactions. Because of eDNA's structural importance in biofilms and its ubiquitous presence among S. aureus isolates, it is a potential target for therapeutics. Treatment of biofilms with DNase can eradicate or drastically reduce them in size. Additionally, antibodies that target DNABII proteins, which bind to and stabilize eDNA, can also disperse biofilms. This review discusses the recent literature on the release, structure, and function of eDNA in S. aureus biofilms, in addition to a discussion of potential avenues for targeting eDNA for biofilm eradication.

Comparative analysis of genes expression involved in type II toxin-antitoxin system in Staphylococcus aureus following persister cell formation

BACKGROUND

The formation of persister cells is the main reason for persistent infections. They are associated with antibiotic treatment failure and subsequently chronic infection. The study aimed to assess the expression of type II toxin/antitoxin (TA) system genes in persister cells of Staphylococcus aureus in the presence of the following antibiotics vancomycin, ciprofloxacin, and gentamicin in exponential and stationary phases.

METHODS AND RESULTS

The colony count was used to evaluate the effect of different types of antibiotics on S. aureus persister cell formation during exponential and stationary phases. Moreover, the expression level of TA systems and clpP genes in the persister population in exponential and stationary phases were measured by quantitative reverse transcriptase real-time PCR (qRT-PCR). The results of the study showed the presence of persister phenotype of S. aureus strains in the attendance of bactericidal antibiotics in comparison to the control group during the exponential and stationary phases. Moreover, qRT-PCR resulted in the fact that the role of TA systems involved in the persister cell formation depends on the bacterial growth phase and the type of strain and antibiotic.

CONCLUSIONS

In total, the present study provides some data on the persister cell formation and the possible role of TA system genes in this process.

Bacterial Efflux Pump Inhibitors Reduce Antibiotic Resistance

Bacterial resistance is a growing problem worldwide, and the number of deaths due to drug resistance is increasing every year. We must pay great attention to bacterial resistance. Otherwise, we may go back to the pre-antibiotic era and have no drugs on which to rely. Bacterial resistance is the result of several causes, with efflux mechanisms widely recognised as a significant factor in the development of resistance to a variety of chemotherapeutic and antimicrobial medications. Efflux pump inhibitors, small molecules capable of restoring the effectiveness of existing antibiotics, are considered potential solutions to antibiotic resistance and have been an active area of research in recent years. This article provides a review of the efflux mechanisms of common clinical pathogenic bacteria and their efflux pump inhibitors and describes the effects of efflux pump inhibitors on biofilm formation, bacterial virulence, the formation of bacterial persister cells, the transfer of drug resistance among bacteria, and mismatch repair. Numerous efforts have been made in the past 20 years to find novel efflux pump inhibitors which are known to increase the effectiveness of medicines against multidrug-resistant strains. Therefore, the application of efflux pump inhibitors has excellent potential to address and reduce bacterial resistance.

Drug repurposing: insights into the antimicrobial effects of AKBA against MRSA

Staphylococcus aureus is a major threat in infectious diseases due to its varied infection types and increased resistance. S. aureus could form persister cells under certain condition and could also attach on medical apparatus to form biofilms, which exhibited extremely high resistance to antibiotics. 3-Acetyl-11-keto-beta-boswellic acid (AKBA) is a well-studied anti-tumor and antioxidant drug. This study is aimed to determine the antimicrobial effects of AKBA against S. aureus and its persister cells and biofilms. The in vitro antimicrobial susceptibility of AKBA was assessed by micro-dilution assay, disc diffusion assay and time-killing assay. Drug combination between AKBA and conventional antibiotics was detected by checkerboard assay. And the antibiofilm effects of AKBA against S. aureus were explored by crystal violet staining combined with SYTO/PI probes staining. Next, RBC lysis activity and CCK-8 kit were used to determine the cytotoxicity of AKBA. In addition, murine subcutaneous abscess model was used to assess the antimicrobial effects of AKBA in vivo. Our results revealed that AKBA was found to show effective antimicrobial activity against methicillin-resistant S. aureus (MRSA) with the minimal inhibitory concentration of 4-8 µg/mL with undetectable cytotoxicity. And no resistant mutation was induced by AKBA after 20 days of consecutive passage. Further, we found that AKBA could be synergy with gentamycin or amikacin against S. aureus and its clinical isolates. By crystal violet and SYTO9/PI staining, AKBA exhibited strong biofilm inhibitory and eradication effects at the concentration of 1 ~ 4 µg/mL. In addition, the effective antimicrobial effect was verified in vivo in a mouse model. And no detectable in vivo toxicity was found. These results indicated that AKBA has great potential to development as an alternative treatment for the refractory S. aureus infections.

Repurposing of the antimalarial agent tafenoquine to combat MRSA

IMPORTANCE

This study represents the first investigation into the antimicrobial effect of TAF against S. aureus and its potential mechanisms. Our data highlighted the effects of TAF against MRSA planktonic cells, biofilms, and persister cells, which is conducive to broadening the application of TAF. Through mechanistic studies, we revealed that TAF targets bacterial cell membranes. In addition, the in vivo experiments in mice demonstrated the safety and antimicrobial efficacy of TAF, suggesting that TAF could be a potential antibacterial drug candidate for the treatment of infections caused by multiple drug-resistant S. aureus.

Galangin: A food-derived flavonoid with therapeutic potential against a wide spectrum of diseases

Galangin is an important flavonoid with natural activity, that is abundant in galangal and propolis. Currently, various biological activities of galangin have been disclosed, including anti-inflammation, antibacterial effect, anti-oxidative stress and aging, anti-fibrosis, and antihypertensive effect. Based on the above bioactivities, more and more attention has been paid to the role of galangin in neurodegenerative diseases, rheumatoid arthritis, osteoarthritis, osteoporosis, skin diseases, and cancer. In this paper, the natural sources, pharmacokinetics, bioactivities, and therapeutic potential of galangin against various diseases were systematically reviewed by collecting and summarizing relevant literature. In addition, the molecular mechanism and new preparation of galangin in the treatment of related diseases are also discussed, to broaden the application prospect and provide reference for its clinical application. Furthermore, it should be noted that current toxicity and clinical studies of galangin are insufficient, and more evidence is needed to support its possibility as a functional food.

Ampelopsin attenuates Staphylococcus aureus Alpha-Toxin-Induced Lung Injury

Staphylococcus aureus is a prevalent cause of lung infections in hospitals and communities, and can cause a wide spectrum of human infections. Due to the bottleneck caused by antibiotic resistance and substantial increases in morbidity and mortality, targeting the virulence factors released by S. aureus as an alternative prevention and treatment method has become a promising approach. Ampelopsin, a component of vine tea, has promising potential for treating S. aureus-induced acute lung injury. In this study, the effects of ampelopsin were investigated on a mouse model of acute lung injury established using S. aureus 8325-4 and the α-hemolysin (hla) silent strain DU1090. The hla silent strain did not cause mortality in mice, whereas lethal and sublethal concentrations of S. aureus 8325-4 caused high mortality. Notably, ampelopsin treatment protected against mortality stemming from S. aureus infection. Ampelopsin yielded enhancements in lung barrier function, decreased total protein leakage in the alveolar lavage fluid, and modulated inflammatory signaling pathway-related proteins, thereby reducing the release of pro-inflammatory factors and improving respiratory dysfunction. Moreover, ampelopsin prevented the upregulation of ADAM10 activity, leading to E-cadherin mucin cleavage. In conclusion, our findings establish the key role of alpha -toxin in infectious lung injury in S. aureus and provide support for ampelopsin as an effective therapeutic approach to improve lung injury.

Repurposing anti-inflammatory drugs for fighting planktonic and biofilm growth. New carbazole derivatives based on the NSAID carprofen: synthesis, in silico and in vitro bioevaluation

Introduction

One of the promising leads for the rapid discovery of alternative antimicrobial agents is to repurpose other drugs, such as nonsteroidal anti-inflammatory agents (NSAIDs) for fighting bacterial infections and antimicrobial resistance.

Methods

A series of new carbazole derivatives based on the readily available anti-inflammatory drug carprofen has been obtained by nitration, halogenation and N-alkylation of carprofen and its esters. The structures of these carbazole compounds were assigned by NMR and IR spectroscopy. Regioselective electrophilic substitution by nitration and halogenation at the carbazole ring was assigned from H NMR spectra. The single crystal X-ray structures of two representative derivatives obtained by dibromination of carprofen, were also determined. The total antioxidant capacity (TAC) was measured using the DPPH method. The antimicrobial activity assay was performed using quantitative methods, allowing establishment of the minimal inhibitory/bactericidal/biofilm eradication concentrations (MIC/MBC/MBEC) on Gram-positive (Staphylococcus aureus, Enterococcus faecalis) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) strains. Computational assays have been performed to assess the drug- and lead-likeness, pharmacokinetics (ADME-Tox) and pharmacogenomics profiles.

Results and discussion

The crystal X-ray structures of 3,8-dibromocarprofen and its methyl ester have revealed significant differences in their supramolecular assemblies. The most active antioxidant compound was 1i, bearing one chlorine and two bromine atoms, as well as the CO2Me group. Among the tested derivatives, 1h bearing one chlorine and two bromine atoms has exhibited the widest antibacterial spectrum and the most intensive inhibitory activity, especially against the Gram-positive strains, in planktonic and biofilm growth state. The compounds 1a (bearing one chlorine, one NO2 and one CO2Me group) and 1i (bearing one chlorine, two bromine atoms and a CO2Me group) exhibited the best antibiofilm activity in the case of the P. aeruginosa strain. Moreover, these compounds comply with the drug-likeness rules, have good oral bioavailability and are not carcinogenic or mutagenic. The results demonstrate that these new carbazole derivatives have a molecular profile which deserves to be explored further for the development of novel antibacterial and antibiofilm agents.

Repurposing CD5789 as an Antimicrobial Agent Against MRSA and Its High Resistant Phonotypes

Methicillin-resistant Staphylococcus aureus (MRSA) poses a great threat to human health, and the formation of biofilm and persister cells make the situation even worse. Drug repurposing is an effective way to solve this problem by shortening the drug development times and reducing the research costs. In this study, CD5789 (trifarotene), a fourth-generation retinoid to be approved by the FDA in 2019 for the topical acne vulgaris regimens, was exhibited antimicrobial activity against MRSA type strains and its clinical isolates with the minimal concentration (MIC) of 2-4 μg/mL and 4-16 μg/mL, respectively, in a dose-dependent manner. By crystal violet staining, we found that CD5789 could inhibit the biofilm formation by MRSA and could further eradicate the pre-formed biofilm at the concentration of 8 μg/mL. By checkerboard dilution assay, sub-MIC of CD5789 showed synergistic antimicrobial effects with sub-MIC of gentamycin against MRSA type strains as well as clinical isolates. In addition, CD5789 also exhibited effective bactericidal activity against MRSA persister cells at the concentration of 8 ~ 16 μg/mL. Extremely low cytotoxicity of CD5789 was observed by CCK-8 assay indicated the well tolerability to human body. In all, CD5789 has the potential to be an alternative for the treatment of refractory MRSA-related infections.

Hydrogen Peroxide, Povidone-Iodine and Chlorhexidine Fail to Eradicate Staphylococcus aureus Biofilm from Infected Implant Materials

Hydrogen peroxide, povidone-iodine, and chlorhexidine are antiseptics that are commonly added to irrigants to either prevent or treat infection. There are little clinical data available that demonstrate efficacy of adding antiseptics to irrigants in the treatment of periprosthetic joint infection after biofilm establishment. The objective of the study was to assess the bactericidal activity of the antiseptics on S. aureus planktonic and biofilm. For planktonic irrigation, S. aureus was exposed to different concentrations of antiseptics. S. aureus biofilm was developed by submerging a Kirschner wire into normalized bacteria and allowing it to grow for forty-eight hours. The Kirschner wire was then treated with irrigation solutions and plated for CFU analysis. Hydrogen peroxide, povidone-iodine, and chlorhexidine were bactericidal against planktonic bacteria with over a 3 log reduction (p < 0.0001). Unlike cefazolin, the antiseptics were not bactericidal (less than 3 log reduction) against biofilm bacteria but did have a statistical reduction in biofilm as compared to the initial time point (p < 0.0001). As compared to cefazolin treatment alone, the addition of hydrogen peroxide or povidone-iodine to cefazolin treatment only additionally reduced the biofilm burden by less than 1 log. The antiseptics demonstrated bactericidal properties with planktonic S. aureus; however, when used to irrigate S. aureus biofilms, these antiseptics were unable to decrease biofilm mass below a 3 log reduction, suggesting that S. aureus biofilm has a tolerance to antiseptics. This information should be considered when considering antibiotic tolerance in established S. aureus biofilm treatment.

Evaluation of Antibacterial Activity of Thiourea Derivative TD4 against Methicillin-Resistant Staphylococcus aureus via Destroying the NAD+/NADH Homeostasis

To develop effective agents to combat bacterial infections, a series of thiourea derivatives (TDs) were prepared and their antibacterial activities were evaluated. Our results showed that TD4 exerted the most potent antibacterial activity against a number of Staphylococcus aureus (S. aureus), including the methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis and Enterococcus faecalis strains, with the minimum inhibitory concentration (MIC) at 2-16 µg/mL. It inhibited the MRSA growth curve in a dose-dependent manner and reduced the colony formation unit in 4× MIC within 4 h. Under the transmission electron microscope, TD4 disrupted the integrity of MRSA cell wall. Additionally, it reduced the infective lesion size and the bacterial number in the MRSA-induced infection tissue of mice and possessed a good drug likeness according to the Lipinski rules. Our results indicate that TD4 is a potential lead compound for the development of novel antibacterial agent against the MRSA infection.

A Rapid Antimicrobial Resistance Diagnostic Platform for Staphylococcus aureus Using Recombinase Polymerase Amplification

Antimicrobial resistance (AMR) has posed a global threat to public health. The Staphylococcus aureus strains have especially developed AMR to practically all antimicrobial medications. There is an unmet need for rapid and accurate detection of the S. aureus AMR. In this study, we developed two versions of recombinase polymerase amplification (RPA), the fluorescent signal monitoring and lateral flow dipstick, for detecting the clinically relevant AMR genes retained by S. aureus isolates and simultaneously identifying such isolates at the species level. The sensitivity and specificity were validated with clinical samples. Our results showed that this RPA tool was able to detect antibiotic resistance for all the 54 collected S. aureus isolates with high sensitivity, specificity, and accuracy (all higher than 92%). Moreover, results of the RPA tool are 100% consistent with that of PCR. In sum, we successfully developed a rapid and accurate AMR diagnostic platform for S. aureus. The RPA might be used as an effective diagnostic test in clinical microbiology laboratories to improve the design and application of antibiotic therapy. IMPORTANCE Staphylococcus aureus is a species of Staphylococcus and belongs to Gram-positive. Meanwhile, S. aureus remains one of the most common nosocomial and community-acquired infections, causing blood flow, skin, soft tissue, and lower respiratory tract infections. The identification of the particular nuc gene and the other eight genes of drug-resistant S. aureus can reliably and quickly diagnose the illness, allowing doctors to prescribe treatment regimens sooner. The detection target in this work is a particular gene of S. aureus, and a POCT is built to simultaneously recognize S. aureus and analyze genes representing four common antibiotic families. We developed and assessed a rapid and on-site diagnostic platform for the specific and sensitive detection of S. aureus. This method allows the determination of S. aureus infection and 10 different AMR genes representing four different families of antibiotics within 40 min. It was easily adaptable in low-resource circumstances and professional-lacking circumstances. It should be supported in overcoming the continuous difficulty of drug-resistant S. aureus infections, which is a shortage of diagnostic tools that can swiftly detect infectious bacteria and numerous antibiotic resistance indicators.

Allosteric inhibition of Staphylococcus aureus MenD by 1,4-dihydroxy naphthoic acid: a feedback inhibition mechanism of the menaquinone biosynthesis pathway

Menaquinones (MKs) are electron carriers in bacterial respiratory chains. In Staphylococcus aureus (Sau), MKs are essential for aerobic and anaerobic respiration. As MKs are redox-active, their biosynthesis likely requires tight regulation to prevent disruption of cellular redox balance. We recently found that the Mycobacterium tuberculosis MenD, the first committed enzyme of the MK biosynthesis pathway, is allosterically inhibited by the downstream metabolite 1,4-dihydroxy-2-naphthoic acid (DHNA). To understand if this is a conserved mechanism in phylogenetically distant genera that also use MK, we investigated whether the Sau-MenD is allosterically inhibited by DHNA. Our results show that DHNA binds to and inhibits the SEPHCHC synthase activity of Sau-MenD enzymes. We identified residues in the DHNA binding pocket that are important for catalysis (Arg98, Lys283, Lys309) and inhibition (Arg98, Lys283). Furthermore, we showed that exogenous DHNA inhibits the growth of Sau, an effect that can be rescued by supplementing the growth medium with MK-4. Our results demonstrate that, despite a lack of strict conservation of the DHNA binding pocket between Mtb-MenD and Sau-MenD, feedback inhibition by DHNA is a conserved mechanism in Sau-MenD and hence the Sau MK biosynthesis pathway. These findings may have implications for the development of anti-staphylococcal agents targeting MK biosynthesis. This article is part of the theme issue 'Reactivity and mechanism in chemical and synthetic biology'.

Antibacterial Components and Modes of the Methanol-Phase Extract from Commelina communis Linn

Infectious diseases caused by pathogenic bacteria severely threaten human health. Traditional Chinese herbs are potential sources of new or alternative medicine. In this study, we analyzed for the first time antibacterial substances in the methanol-phase extract from a traditional Chinese herb-Commelina communis Linn-which showed an inhibition rate of 58.33% against 24 species of common pathogenic bacteria. The extract was further purified using preparative high-performance liquid chromatography (Prep-HPLC), which generated four single fragments (Fragments 1 to 4). The results revealed that Fragment 1 significantly increased bacterial cell surface hydrophobicity and membrane permeability and decreased membrane fluidity, showing disruptive effects on cell integrity of Gram-positive and Gram-negative bacteria, such as Bacillus cereus, Enterococcus faecalis, Staphylococcus aureus, and Salmonella enterica subsp., compared to the control groups (p < 0.05). In sum, 65 compounds with known functions in Fragment 1 were identified using liquid chromatography and mass spectrometry (LC-MS), of which quercetin-3-o-glucuronide was predominant (19.35%). Comparative transcriptomic analysis revealed multiple altered metabolic pathways mediated by Fragment 1, such as inhibited ABC transporters, ribosome, citrate cycle and oxidative phosphorylation, and upregulated nitrogen metabolism and purine metabolism, thereby resulting in the repressed bacterial growth and even death (p < 0.05). Overall, the results of this study demonstrate that Fragment 1 from C. communis Linn is a promising candidate against common pathogenic bacteria.

Variability in Adaptive Resistance of Salmonella Typhimurium to Sublethal Levels of Antibiotics

This study was designed to evaluate the adaptive resistance of Salmonella Typhimurium under continuous sublethal selective pressure. Salmonella Typhimurium ATCC 19585 (STATCC) and S. Typhimurium CCARM 8009 (STCCARM) were sequentially cultured for 3 days at 37 °C in trypticase soy broth containing 1/2 × MICs of cefotaxime (CEF1/2), chloramphenicol (CHL1/2), gentamicin (GEN1/2), and polymyxin B (POL1/2). The STATCC and STCCARM exposed to CEF1/2, CHL1/2, GEN1/2, and POL1/2 were evaluated using antibiotic susceptibility, cross-resistance, and relative fitness. The susceptibilities of STATCC exposed to GEN1/2 and POL1/2 were increased by a 2-fold (gentamicin) and 8-fold (polymyxin B) increase in minimum inhibitory concentration (MIC) values, respectively. The MIC values of STCCARM exposed to CEF1/2, CHL1/2, GEN1/2, and POL1/2 were increased by 4-fold (cefotaxime), 2-fold (chloramphenicol), 2-fold (gentamicin), and 8-fold (polymyxin B). The highest heterogeneous fractions were observed for the STATCC exposed to CEF1/2 (38%) and POL1/2 (82%). The STCCARM exposed to GEN1/2 was cross-resistant to cefotaxime (p < 0.05), chloramphenicol (p < 0.01), and polymyxin B (p < 0.05). The highest relative fitness levels were 0.92 and 0.96, respectively, in STATCC exposed to CEF1/2 and STCCARM exposed to POL1/2. This study provides new insight into the fate of persistent cells and also guidance for antibiotic use.

Outer Surface-Labeled Bacteria as Live Sensors Accurately Quantitating Interfacial pH: A Smart Technique for Antimicrobial Resistance

The techniques to quantitatively monitor environmental factors surrounding the bacterial outer surface rather than the host's subcellular regions (e.g., lysosomes) should be the key to evaluate bacterial immune escape behavior. We report wild Staphylococcus aureus (SA) and methicillin-resistant Staphylococcus aureus (MRSA) labeled with a fluorescent resonance energy transfer probe, 4SR-L-BDP, on their outer surfaces as smart live sensors to quantify interfacial pH. The dual emission of 4SR-L-BDP affords high sensitivity to pH change in a ratiometric way in the pH range of 4-8 with high precision. Notably, 4SR-L-BDP possesses an anchoring group to fix on the bacterial surface for sensing the microenvironment encountered. Super-resolution imaging clearly demonstrates the specific labeling of bacterial membranes. These live sensors are applied in two-channel ratiometric imaging to dynamically visualize and quantify their interfacial pH changes during infection of macrophages. It is found that the interfacial pH of MRSA is lower by 0.2 units compared to that of SA. Such small but critical difference in pH reflects MRSA's ability to adapt to microenvironmental pH inside macrophages. These labeled bacteria as live sensors are also proven to be practically applicable in mice models with immune deficiency and immune activation.

Immune Responses to Gene Editing by Viral and Non-Viral Delivery Vectors Used in Retinal Gene Therapy

Inherited retinal diseases (IRDs) are a leading cause of blindness in industrialized countries, and gene therapy is quickly becoming a viable option to treat this group of diseases. Gene replacement using a viral vector has been successfully applied and advanced to commercial use for a rare group of diseases. This, and the advances in gene editing, are paving the way for the emergence of a new generation of therapies that use CRISPR-Cas9 to edit mutated genes in situ. These CRISPR-based agents can be delivered to the retina as transgenes in a viral vector, unpackaged transgenes or as proteins or messenger RNA using non-viral vectors. Although the eye is considered to be an immune-privileged organ, studies in animals, as well as evidence from clinics, have concluded that ocular gene therapies elicit an immune response that can under certain circumstances result in inflammation. In this review, we evaluate studies that have reported on pre-existing immunity, and discuss both innate and adaptive immune responses with a specific focus on immune responses to gene editing, both with non-viral and viral delivery in the ocular space. Lastly, we discuss approaches to prevent and manage the immune responses to ensure safe and efficient gene editing in the retina.

In Vitro and In Vivo Bactericidal and Antibiofilm Efficacy of Alpha Mangostin Against Staphylococcus aureus Persister Cells

The formation of persister cells is associated with recalcitrance and infections. In this study, we examined the antimicrobial property of alpha mangostin, a natural xanthone molecule, against methicillin-resistant Staphylococcus aureus (MRSA) persisters and biofilm. The MIC of alpha mangostin against MRSA persisters was 2 µg/ml, and activity was mediated by causing membrane permeabilization within 30 min of exposure. The membrane activity of alpha mangostin was further studied by fast-killing kinetics of MRSA persiste r cells and found that the compound exhibited 99.99% bactericidal activity within 30 min. Furthermore, alpha mangostin disrupted established MRSA biofilms and inhibited bacterial attachment as biofilm formation. Alpha mangostin down-regulated genes associated with the formation of persister cells and biofilms, such as norA, norB, dnaK, groE, and mepR, ranging from 2 to 4-folds. Alpha mangostin at 16 μg/ml was non-toxic (> 95% cell survival) to liver-derived HepG2 and lung-derived A549 cells, similarly. Still, alpha mangostin exhibited 50% cell lysis of human RBC at 16 μg/ml. Interestingly, alpha mangostin was effective in vivo at increasing the survival up to 75% (p<0.0001) of Galleria mellonella larvae infected with MRSA persister for 120 h. In conclusion, we report that alpha mangostin is active against MRSA persisters and biofilms, and these data further our understanding of the antistaphylococcal activity and toxicity of this natural compound.

Sensitivity and Specificity of a Novel Colony Characteristic for Determination of Methicillin-Resistant Staphylococcus aureus

Purpose: To assess colony morphology of Staphylococcus aureus isolates for target shape (T1) and its utility in the identification of methicillin-resistant S. aureus (MRSA).

Methods: Staphylococcus species isolated from blood cultures were studied for colony morphology characteristics. A polymerase chain reaction (PCR) test was performed on positive blood culture bottles for the detection of S. aureus and methicillin resistance. Colony morphology was read at 24 and 48 hours and defined as follows: target shaped (T1) - an elevated colony center encircled by a pale zone, which is surrounded by a single ring of peripheral enhancement giving a ‘target’ appearance; dome-shaped (T2) with an elevated center lacking the ‘target’ appearance.

Results: At 48 hours, 73.7% of MRSA and 59.5% of coagulase-negative staphylococci (CoNS) showed T1 morphology. T1 morphology has a sensitivity of 73.68% and specificity of 93.55% amongst S. aureus for identification of methicillin resistance and a high positive predictive value (95.45%) at 48 hours.

Conclusion: T1 morphology has a modest sensitivity with specificity and positive predictive value amongst S. aureus for identification of methicillin resistance at 48 hours. It can be potentially used for the identification of MRSA, especially in resource-limited settings and wherein a molecular test is not repeated if PCR testing has already identified methicillin-sensitive S. aureus (MSSA) on a recent specimen on the same patient.

Luteolin Inhibits the Biofilm Formation and Cytotoxicity of Methicillin-Resistant Staphylococcus aureus via Decreasing Bacterial Toxin Synthesis

Owing to the fact that luteolin has antibacterial activity against Staphylococcus aureus (S. aureus) and methicillin-resistant S. aureus (MRSA), its specific mechanism in MRSA is worthy of investigation, which is the focus of this study. Initially, the collected S. aureus strains were treated with luteolin. Then, the minimum inhibitory concentration (MIC) of luteolin against the S. aureus strains was measured by the broth microdilution. The growth curves, biofilm formation, and cytotoxicity of treated S. aureus were detected using a microplate reader. The live and dead bacteria were evaluated using confocal laser scanning microscopy, the bacterial morphology was observed using scanning electron microscopy, and the S. aureus colony-forming unit (CFU) numbers were assessed. The levels of alpha hemolysin (α-hemolysin), delta hemolysin (δ-hemolysin), and hlaA were detected via western blot and RT-PCR. The mortality of mouse model with S. aureus systemic infection was analyzed, and the levels of IL-6, IL-8, IL-10, and TNF-α were quantitated using ELISA. Concretely, the MIC of luteolin against MRSA N315 was 64 μg/mL. Luteolin at 16 μg/mL did not affect the growth of MRSA N315, but inhibited the biofilm formation and CFU, and promoted the morphological changes and death of MRSA N315. Luteolin decreased the cytotoxicity and the levels of α-hemolysin, δ-hemolysin, and hlaA in MRSA N315, elevated MRSA-reduced mice survival rate, and differentially modulated the inflammatory cytokine levels in MRSA-infected mice. Collectively, luteolin inhibits biofilm formation and cytotoxicity of MRSA via blocking the bacterial toxin synthesis.

Investigation of hub gene associated with the infection of Staphylococcus aureus via weighted gene co-expression network analysis

Introduction

Staphylococcus aureus is a gram-positive bacterium that causes serious infection. With the increasing resistance of bacteria to current antibiotics, it is necessary to learn more about the molecular mechanism and cellular pathways involved in the Staphylococcus aureus infection.

Methods

We downloaded the GSE33341 dataset from the GEO database and applied the weighted gene co-expression network analysis (WGCNA), from which we obtained some critical modules. Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) were applied to illustrate the biological functions of genes in these modules. We constructed the protein-protein interaction (PPI) network by Cytoscape and selected five candidate hub genes. Five potential hub genes were validated in GSE30119 by GraphPad Prism 8.0. The diagnostic values of these genes were calculated and present in the ROC curve based on the GSE13670 dataset. Their gene functions were analyzed by Gene Set Enrichment Analysis (GSEA).

Results

A co-expression network was built with 5000 genes divided into 11 modules. The genes in green and turquoise modules demonstrated a high correlation. According to the KEGG and GO analyses, genes in the green module were closely related to ubiquitination and autophagy. Subsequently, we picked out the top five hub genes in the green module. And UBB was determined as the hub gene in the GSE30119 dataset. The expression level of UBB, ASB, and MKRN1 could significantly differentiate between Staphylococcus aureus infection and healthy controls based on the ROC curve. The GSEA analysis indicated that lower expression levels of UBB were associated with the P53 signal pathway.

Conclusions

We identified some hub genes and significant signal enrichment pathways in Staphylococcus aureus infection via bioinformatics analysis, which may facilitate the development of potential clinical therapeutic strategies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02392-y.

Evolutionary trade-offs between growth and survival: The delicate balance between reproductive success and longevity in bacteria

All living cells strive to allocate cellular resources in a way that promotes maximal evolutionary fitness. While there are many competing demands for resources the main decision making process centres on whether to proceed with growth and reproduction or to "hunker down" and invest in protection and survival (or to strike an optimal balance between these two processes). The transcriptional programme active at any given time largely determines which of these competing processes is dominant. At the top of the regulatory hierarchy are the sigma factors that commandeer the transcriptional machinery and determine which set of promoters are active at any given time. The regulatory inputs controlling their activity are therefore often highly complex, with multiple layers of regulation, allowing relevant environmental information to produce the most beneficial response. The tension between growth and survival is also evident in the developmental programme necessary to promote biofilm formation, which is typically associated with low growth rates and enhanced long-term survival. Nucleotide second messengers and energy pools (ATP/ADP levels) play critical roles in determining the fate of individual cells. Regulatory small RNAs frequently play important roles in the decision making processes too. In this review we discuss the trade-off that exists between reproduction and persistence in bacteria and discuss some of the recent advances in this fascinating field.

Identification of Potential Inhibitors of MurD Enzyme of Staphylococcus aureus from a Marine Natural Product Library

Staphylococcus aureus is an opportunistic pathogen that can cause fatal bacterial infections. MurD catalyzes the formation of peptide bond between UDP-N-acetylehyl-l-alanine and d-glutamic acid, which plays an important role in the synthesis of peptidoglycan and the formation of cell wall by S. aureus. Because S. aureus is resistant to most existing antibiotics, it is necessary to develop new inhibitors. In this study, Schrodinger 11.5 Prime homology modeling was selected to prepare the protein model of MurD enzyme, and its structure was optimized. We used a virtual screening program and similarity screening to screen 47163 compounds from three marine natural product libraries to explore new inhibitors of S. aureus. ADME provides analysis of the physicochemical properties of the best performing compounds during the screening process. To determine the stability of the docking effect, a 100 ns molecular dynamics was performed to verify how tightly the compound was bound to the protein. By docking analysis and molecular dynamics analysis, both 46604 and 46608 have strong interaction with the docking pocket, have good pharmacological properties, and maintain stable conformation with the target protein, so they have a chance to become drugs for S. aureus. Through virtual screening, similarity screening, ADME study and molecular dynamics simulation, 46604 and 46608 were selected as potential drug candidates for S. aureus.

No Change, No Life? What We Know about Phase Variation in Staphylococcus aureus

Phase variation (PV) is a well-known phenomenon of high-frequency reversible gene-expression switching. PV arises from genetic and epigenetic mechanisms and confers a range of benefits to bacteria, constituting both an innate immune strategy to infection from bacteriophages as well as an adaptation strategy within an infected host. PV has been well-characterized in numerous bacterial species; however, there is limited direct evidence of PV in the human opportunistic pathogen Staphylococcus aureus. This review provides an overview of the mechanisms that generate PV and focuses on earlier and recent findings of PV in S. aureus, with a brief look at the future of the field.

Bacterial Persister-Cells and Spores in the Food Chain: Their Potential Inactivation by Antimicrobial Peptides (AMPs)

The occurrence of bacterial pathogens in the food chain has caused a severe impact on public health and welfare in both developing and developed countries. Moreover, the existence of antimicrobial-tolerant persisting morphotypes of these pathogens including both persister-cells as well as bacterial spores contributes to difficulty in elimination and in recurrent infection. Therefore, comprehensive understanding of the behavior of these persisting bacterial forms in their environmental niche and upon infection of humans is necessary. Since traditional antimicrobials fail to kill persisters and spores due to their (extremely) low metabolic activities, antimicrobial peptides (AMPs) have been intensively investigated as one of the most promising strategies against these persisting bacterial forms, showing high efficacy of inactivation. In addition, AMP-based foodborne pathogen detection and prevention of infection has made significant progress. This review focuses on recent research on common bacterial pathogens in the food chain, their persisting morphotypes, and on AMP-based solutions. Challenges in research and application of AMPs are described.