Penicillin binding protein 2a: An overview and a medicinal chemistry perspective

Reliability of disc diffusion testing and molecular epidemiology of penicillin-susceptible Staphylococcus aureus bacteraemia

BACKGROUND

Recent studies have reported an increasing prevalence of penicillin-susceptible Staphylococcus aureus (PSSA) worldwide. The reliability of disc diffusion testing for detecting penicillin-resistance has been questioned, and the molecular epidemiology of PSSA has not been studied to the same extent as that of MRSA strains.

OBJECTIVES

To investigate the reliability of the disc diffusion method for detecting penicillin-resistance in S. aureus, and to examine the prevalence and molecular epidemiology of PSSA in bloodstream infections.

METHODS

A total of 258 bacteraemic isolates obtained from one geographic region in Sweden during 2018-2019 were analysed using the disc diffusion test to detect penicillin-resistance, and genome sequenced to examine the prevalence of the blaZ gene and the molecular epidemiology of PSSA.

RESULTS

Phenotypic susceptibility to penicillin correlated strongly with the absence of the blaZ gene, with nearly 98% concordance. The prevalence of PSSA among patients with bacteraemia was 35.1%, highlighting the need for penicillin-susceptibility testing. Additionally, population structure analyses revealed substantial genetic diversity, underscoring the complexity of the PSSA epidemiology. The PSSA belonged to diverse clonal lineages, with CC5 and CC45 dominating our cohort, similar to findings in Spain, Australia, and other parts of Sweden. However, our study revealed a higher prevalence of CC12 compared with other regions, underscoring the importance of local epidemiological surveillance.

CONCLUSIONS

These findings validate the reliability of EUCAST's disc diffusion method, showing a high prevalence of PSSA, and provide insight into the genetic underpinnings of penicillin-susceptibility in S. aureus.

Comprehensive wound healing using ETN@Fe7S8 complex by positively regulating multiple programmed phases

Wound healing requires coordinated progression through multiple programmed phases including hemostasis, infection control, inflammatory resolution, proliferation, and tissue remodeling. Many nanomaterials have shown great potential to promote wound healing, however, most of them only address partial aspects of these processes, making a recovery hard with adequate effects. In this study, we prepared a complex of nano-iron sulfide integrated with erythrocyte-templated nanozyme (ETN) (ETN@Fe7S8) for comprehensive treatment of wounds. Firstly, ETN served as a mediator to confine iron sulfide to form Fe7S8 nanocomposite in a solvothermal reaction. Secondly, the ETN@Fe7S8 demonstrated bactericidal effects against methicillin-resistant Staphylococcus aureus (MRSA) by releasing ferrous iron and polysulfide to induce ferroptosis-like cell death. Thirdly, ferrous iron along with polysulfide exerted anti-inflammatory effects by inhibiting the activation of the NF-κB signaling pathway, while the polysulfide also contributed to angiogenesis by promoting the activation of vascular endothelial growth factor A (VEGFA), initiated phosphorylation-mediated activation of the PI3K/AKT signaling pathway, a master regulatory cascade governing endothelial cell survival, migration, and angiogenesis. When employed for wound, ETN@Fe7S8 showed the ability to prevent infection, reduce inflammation, promote angiogenesis, enhance cell proliferation, and remodel keratinocytes. Along with the hemostatic effect, ETN@Fe7S8 thus performed comprehensive effects for wound healing in the whole recovery stages. Therefore, our findings provide a multifunctional candidate of ETN and nano-iron sulfide complex which is capable of regulating and promoting wound healing.

Guttiferone E from Brazilian red propolis inhibited wound-isolated methicillin-resistant Staphylococcus aureus and enhanced the bactericidal action of suppressed macrophages

BACKGROUND

Propolis has been traditionally used to treat inflammatory and infectious diseases, and it is still used and researched worldwide. Methicillin-resistant Staphylococcus aureus (MRSA) may cause invasive infections and propolis anti-MRSA activity has been analyzed.

PURPOSE

A standardized red propolis extract (SRPE), its benzophenones-rich fraction (BRF), and isolated benzophenones (guttiferone E - GUT E, and oblongifolin B - OBL B) were assayed for their antibacterial and immunomodulatory action.

METHODS

Formulations (BRP28, BRP29, BRP150, BRP153, and BRPLUS) were prepared and their minimum inhibitory concentrations (MIC) were assessed. The synergistic action of GUT E with antimicrobials was evaluated on a wound-isolated MRSA, as well as the inhibition of biofilm formation by the formulations (BRP28 and BRP29) and GUT E. Tohoku Hospital Pediatrics-1 (THP-1) cells were used to investigate cytokine production and the bactericidal activity of suppressed macrophages against MRSA. Computational predictions were performed with GUT E and antimicrobials to observe their interaction with the active and allosteric site of penicillin-binding protein 2a (PBP2a).

RESULTS

SRPE and BRF were not efficient against MRSA while GUT E and OBL B exerted a potent activity. GUT E exerted a synergistic effect with carbapenems and vancomycin. BRP28, BRP29, and GUT E inhibited biofilm formation and increased the antibacterial capacity of suppressed macrophages, with no differences in cytokine production. GUT E showed a high binding affinity to PBP2a.

CONCLUSION

GUT E exhibited a direct anti-MRSA activity and indirectly enhanced the macrophage bactericidal activity. Molecular docking suggested that GUT E has a versatile interaction with PBP2a.

Endophytic bacteria of Gracilaria edulis in combating human bacterial pathogens by PPDHMP - A crude to single molecule product development approach

Resistance in human bacterial pathogens and lack of novel antibiotic development has led to the need for new antibiotics. Therefore, the current study was focused on endophytic bacteria from Gracilaria edulis, an edible seaweed, capable of synthesizing novel bioactive compounds with potential applications in the inhibition of human pathogens. The endophyte, identified as Bacillus subtilis through 16S rRNA gene sequencing, exhibited significant antibacterial activity against bacterial human pathogens. Using GC-MS, FTIR and NMR the lead compound was identified as Pyrrolo[1,2-α] pyrazine-1,4-dione, hexahydro-3-(2-methylpropyl) (PPDHMP). Optimized media composition using glucose, proline and valine significantly enhanced the production of PPDHMP which was observed by the increase in zone of inhibition. Molecular docking of PPDHMP indicated a high binding affinity to beta-lactamase, suggesting its potential as a beta-lactamase inhibitor. PPDHMP exhibited cell wall inhibitory activity and ADMET analysis revealed promising pharmacokinetic and toxicity profiles indicating its potential for further evaluation as an oral antibiotic candidate. Phytotoxicity assessments and hemolytic assay confirmed the non-toxic nature of the metabolites produced. This research highlights the immense potential of marine endophytes in addressing the escalating issue of antibiotic resistance and paves the way for innovative solutions in antimicrobial therapy.

From Natural Products to Small Molecules: Recent Advancements in Anti-MRSA Therapeutics

The urgent need for unique small molecules to treat increasing resistance in gram-positive pathogens, particularly methicillin-resistant Staphylococcus aureus, has motivated several creative research endeavors over the past decade. Recent advances have been inspired by natural products such as pleuromutilin, discovered in high-throughput screens, or repurposed approved drugs like sorafenib. This microperspective spotlights bioactive compounds, ranging from natural products to small molecule scaffolds, that have been reported in recent literature, highlighting their mechanisms of action, structure-activity relationships, and future potential.

Uvarinol and Dichamanetin Derived from Uvaria chamae as Potential Dual-Site Inhibitors Against PBP2a in Methicillin Resistant Staphylococcus aureus: An In Silico Study

Background/Objectives: Methicillin-resistant Staphylococcus aureus (MRSA) is one of the resistant pathogenic microorganisms that poses a global health threat due to its resistance to β-lactam antibiotics where the protein penicillin-binding protein 2a (PBP2a) plays a crucial role in its resistance. This study explores the potential of phytochemicals from Uvaria chamae, a plant with known medicinal properties, to serve as dual-site inhibitors of PBP2a, targeting both the active and allosteric sites. Methods: Phytochemicals previously identified in U. chamae were subjected to molecular docking and molecular dynamics simulations to evaluate their binding affinities and stability at PBP2a's active and allosteric sites. The compounds' pharmacokinetic profiles were predicted in silico using SwissADME tools. Root-mean-square deviation (RMSD), radius of gyration, and binding free energy were analyzed for dynamic stability. Results: Among the evaluated compounds, Uvarinol and Dichamanetin demonstrated high binding affinities compared to the co-crystallized ligand and standard antibiotics like ceftaroline. Uvarinol exhibited the highest binding affinity at both sites, with a docking score of -14.94 kcal/mol and a predicted inhibition constant (Ki) of 0.01 nM. Molecular dynamics simulations further confirmed the robust stability of Uvarinol and Dichamanetin, as indicated by consistently lower RMSD values relative to the co-crystallized ligand. Pharmacokinetic predictions revealed favorable drug-likeness and low toxicity, although Uvarinol showed limited gastrointestinal absorption. Conclusions: Uvarinol and Dichamanetin show promise as dual-site PBP2a inhibitors, offering a novel strategy to combat MRSA resistance. Their structural and pharmacokinetic properties make them viable candidates for further development, though experimental validation and formulation optimization are necessary to overcome bioavailability challenges.

Non-Membrane Active Peptide Resensitizes MRSA to β-Lactam Antibiotics and Inhibits S. aureus Virulence

Methicillin-resistant Staphylococcus aureus (MRSA) is a serious global health threat due to its high morbidity and mortality rates, creating a dire need for novel therapeutic strategies. Antimicrobial peptides (AMPs), with broad-spectrum activity and low propensity for resistance development, show promise as effective antibiotic adjuvants to reverse multidrug-resistance in bacteria. Herein, it is uncovered that a potent and non-toxic AMP termed GN1 substantially resensitizes MRSA to multiple β-lactam antibiotics at low concentrations. Mechanistic studies indicate that GN1 functions by suppressing both the production and enzymatic activity of MRSA-associated resistance determinants, including penicillin-binding protein 2a (PBP2a) and β-lactamase. Additionally, GN1 exhibits a robust anti-virulence profile by inhibiting MRSA biofilm formation and staphyloxanthin production. Furthermore, GN1 induces bacterial metabolic perturbation, resulting in glutamate accumulation and oxidative damage. Importantly, the combination of GN1 with β-lactam antibiotics effectively mitigates MRSA-induced infections in the animal infection models. Collectively, these findings suggest that GN1 represents a potent β-lactam adjuvant and anti-virulence agent, offering a safe and versatile solution to combat MRSA infections.

Aromatic Herbs as a Source of Bioactive Compounds: An Overview of Their Antioxidant Capacity, Antimicrobial Activity, and Major Applications

Many aromatic herbs are conventionally used for flavoring various foods, but receive wide attention because of the variety of health-related properties. The aromatic herbs can be used either fresh or as dried powders and in the form of extracts, essential oils, or purified metabolites. In this review, the main functional properties, in terms of antioxidant and antimicrobial properties, and the applications of some of the commonly used aromatic herbs from the Lamiaceae family, are discussed. Herbs like oregano, rosemary, sage, thyme, summer savory, marjoram, and basil possess high levels of bioactive phytochemicals. They are particularly rich in phenolic acids, flavones, phenolic diterpenes, and flavanones, with various beneficial effects. The phytochemical profile of aromatic plants is highly influenced by genetic factors, environmental conditions, and their interaction. In cases of the extracts and essential oils, the extraction method has a strong effect on the final composition of the herb products. Most of the applications of these aromatic herbs are related to their antioxidant, antimicrobial, and flavoring properties. In particular, aromatic herb extracts and essential oils have multiple applications in fields like food, feed, pharmaceutical, cosmetics, biopesticides, and textile industries.

De novo Designing of the Antimicrobial Peptide as a Curative Agent for Methicillin-Resistant Staphylococcus aureus through a Computational Approach

BACKGROUND

The emergence of resistance to multiple drugs has posed a multitude of difficulties that demand immediate attention and solutions. Multiple drug resistance arises from the accumulation of numerous genes within a single cell, each conferring resistance to a specific drug, and from the heightened expression of genes responsible for multidrug efflux pumps. These pumps effectively expel a diverse array of drugs from the cell.

OBJECTIVE

The multi-drug-resistant organisms, including methicillin-resistant Staphylococcus aureus, are the hub of numerous diseases, from minute ailments to fatal diseases, like catheter infections. Nowadays, a combination of many antibiotics is given together as a multimodality therapy to cure MRSA infections. However, researchers are exploring novel approaches to find better solutions.

METHODS

De novo designing of the peptide sequences has been done through an in silico tool. The peptides were further screened using different computational methods. Following this, the selection was conducted utilizing physicochemical properties as criteria. Molecular docking of the selected peptide sequence was carried out. Based on the highest docking score, the model complex was chosen for validation purposes by conducting studies through molecular dynamics simulations.

RESULTS

A total of fifty-two novel antimicrobial peptides were designed and evaluated based on various parameters, targeting MRSA-specific proteins PBP2a and PVL toxin. Among these designed peptides, the peptide sequence VILRMFYHWAVKTNGP emerged as the optimal candidate, satisfying all the necessary parameters to be an effective antimicrobial peptide.

CONCLUSION

Molecular docking and MD simulation results showed that the designed peptide sequence could be the possible solution for MRSA treatment.

Antimicrobial and antibiofilm effect of cannabinoids from Cannabis sativa against methicillin-resistant Staphylococcus aureus (MRSA) causing bovine mastitis

Antimicrobial resistance (AMR) poses a serious threat to human, animal, and plant health on a global scale. Search and elimination techniques should be used to effectively counter the spread of methicillin-resistant Staphylococcus aureus (MRSA) infections. With only a few novel drugs in clinical development, the quest for plant-based alternatives to prevent the spread of antibiotic resistance among bacteria has accelerated. Treatment of MRSA infections is challenging owing to rapidly emerging resistance mechanisms coupled with their protective biofilms. In the present research, we examined the antibacterial properties of ten plant-derived ethanolic leaf extracts. The most effective ethanolic leaf extract against MRSA in decreasing order of zone of inhibition, Cannabis sativa L. > Syzygium cumini > Murraya koenigii > Eucalyptus sp. > while Aloe barbadensis, Azadirachta indica, had very little impact. Mangifera indica, Curcuma longa, Tinospora cordifolia, and Carica papaya did not exhibit inhibitory effects against MRSA; hence, Cannabis was selected for further experimental study. The minimal inhibitory concentration (MIC) of Cannabis sativa L. extract was 0.25 mg ml-1 with 86% mortality. At a sub-MIC dosage of 0.125 mg ml-1, the biofilm formation was reduced by 71%. The two major cannabinoids detected were cannabidiol and delta-9-tetrahydrocannabinol (Δ9-THC), which were majorly attributed to substantial inhibitory action against MRSA. The time-kill kinetics demonstrated a bactericidal action at 4 MIC over an 8-20-h time window with a 90% reduction in growth rate. The results from SEM, and light microscopy Giemsa staining revealed a reduction in cells in the treated group with increased AKP activity, indicating bacterial cell membrane breakdown. These findings suggested cannabinoids may be a promising alternative to antibiotic therapy for bovine biofilm-associated MRSA.

Conjugation of Polycationic Peptides Extends the Efficacy Spectrum of β-Lactam Antibiotics

Antibiotic-resistant enterococci represent a significant global health challenge. Unfortunately, most β-lactam antibiotics are not applicable for enterococcal infections due to intrinsic resistance. To extend their antimicrobial spectrum, polycationic peptides are conjugated to examples from each of the four classes of β-lactam antibiotics. Remarkably, the β-lactam-peptide conjugates gained an up to 1000-fold increase in antimicrobial activity against vancomycin-susceptible and vancomycin-resistant enterococci. Even against β-lactam-resistant Gram-negative strains, the conjugates are found to be effective despite their size exceeding the exclusion volume of porins. The extraordinary gain of activity can be explained by an altered mode of killing. Of note, the conjugates showed a concentration-dependent activity in contrast to the parent β-lactam antibiotics that exhibited a time-dependent mode of action. In comparison to the parent β-lactams, the conjugates showed altered affinities to the penicillin-binding proteins. Furthermore, it is found that peptide conjugation also resulted in a different elimination route of the compounds when administered to rodents. In mice systemically infected with vancomycin-resistant enterococci, treatment with a β-lactam-peptide conjugate reduced bacterial burden in the liver compared to its originator. Therefore, peptide modification of β-lactam antibiotics represents a promising platform strategy to broaden their efficacy spectrum, particularly against enterococci.

Essential oils of Eugenia spp. (myrtaceae) show in vitro antibacterial activity against Staphylococcus aureus isolates from bovine mastitis

Bovine mastitis, an inflammation of the mammary glands, is mainly caused by bacteria such as Staphylococcus aureus. While antibiotics are the primary treatment for this disease, their effectiveness is often diminished due to resistant strains and biofilm formation, creating the need for safer and more efficient therapies. Plant-based oil therapies, particularly those derived from the genus Eugenia, are gaining popularity due to their pharmacological potential and historical use. In this study, we evaluated the antibacterial, antibiofilm, and synergistic potential of essential oils (EOs) from four species of the genus Eugenia (E. brejoensis, E. gracillima, E. pohliana, and E. stictopetala) against S. aureus isolates from bovine mastitis. The EO of E. stictopetala was obtained by hydrodistillation, and its composition was analyzed using gas chromatography coupled with mass spectrometry. The experiment employed seven clinical isolates from mastitis and two control strains: ATCC 33591 (methicillin-resistant S. aureus - MRSA) and ATCC 25923 (methicillin-susceptible and biofilm producer). A broth microdilution assay was used to determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the EOs and oxacillin. The EO of E. stictopetala contained (E)-caryophyllene (18.01%), β-pinene (8.84%), (E)-nerolidol (8.24%), and α-humulene (6.14%) as major compounds. In the MIC assay, all essential oils showed bactericidal and bacteriostatic effects, especially the species E. brejoensis and E. pohliana, which had MICs ranging from 64 to 256 µg/mL. Regarding the antibiofilm effect, all essential oils were capable of interfering with biofilm formation at subinhibitory concentrations of ½ and ¼ of the MIC. However, they did not significantly affect pre-established biofilms. Additionally, a synergistic interaction was detected between the EOs and oxacillin, with a reduction of 75-93.75% in the antimicrobial MIC. Molecular docking studies indicated that the phytochemicals β-(E)-caryophyllene, (E)-nerolidol, Δ-elemene, and α-cadinol present in the EOs formed more stable complexes with penicillin-binding proteins, indicating a possible mechanism of antibacterial action. Therefore, these results show that the essential oils of Eugenia spp. are promising sources for the development of new therapeutic methods, opening new perspectives for a more effective treatment of bovine mastitis.

The effect of novel β-lactam derivatives synthesized from substituted phenethylamines on resistance genes of MRSA isolates

This study focuses on the activity of previously reported imine and β-lactam derivatives against methicillin-resistant Staphylococcus aureus (MRSA) isolates. The presence of mecA and blaZ genes in the isolates was determined, and the minimum inhibitory concentration (MIC) values were determined based on the antibacterial activity against these isolates. Active compounds were selected and their ability to act against resistant isolates in vitro was determined. Concurrently, biochemical (nitrocefin) and molecular (qRT-PCR) tests were used to investigate the ability of the compounds to induce resistance genes in MRSA isolates. The cytotoxicity of the compounds on human dermal fibroblasts (HDF) was investigated. The MIC values of compounds (10) and (12) against MSSA and MRSA isolates were 7.81 and 15.62 μg ml-1, respectively. The most active compounds were identified as (10) and (12), and it was observed that the isolates did not develop resistance to these compounds in vitro. These compounds were found to inhibit β-lactamase, reduce the expression of resistance genes, and exhibit reduced HDF cell toxicity in a dose-dependent manner. According to the findings of the study, it can be concluded that these compounds show promise as hits with an interesting mechanism of action for further chemical modifications to develop new MRSA inhibitors.

Unveiling the multitargeted potential of deprodone and control comparison with linezolid against hydrolase and transferase enzymes of methicillin-resistant Staphylococcus aureus

Staphylococcus aureus (S. aureus), commonly found on the skin and nose, causes minor skin conditions to life-threatening diseases, including boils or impetigo, pneumonia, and bloodstream infections. MRSA (Methicillin-Resistant S. aureus) is a strain resistant to many antibiotics and poses a significant challenge in clinical settings. Nowadays, the alternative drug Linezolid is used, and it is not clear when MRSA starts resistance to it, necessitating the need for more alternative drugs with the least chance of developing resistance. This study aims to identify a multitargeted drug candidate with better efficacy than Linezolid. We have taken three hydrolase and transferase proteins from S. aureus, performed the multitargeted docking studies with human-approved drugs, and compared them with the control drug Linezolid. The docking and MM\GBSA scores ranging from -6.79 to -5.78 Kcal/mol and - 37.47 to 30.16 Kcal/mol, respectively, that revealed Deprodone (used for inflammatory skin disorders, bowel disease, and fatty acid metabolism disorders) can be a far better and multitargeted drug candidate than Linezolid. We extended our studies to include extensive pharmacokinetics and molecular interaction fingerprints for interaction pattern studies. Also, the DFT computations optimised the drug, and we extended our studies for MD Simulation in water for 100 ns, which showed the complexes among the identified drug with proteins are entirely stable with acceptable deviation, fluctuations and many intermolecular interactions that make them stable. We also performed the MM\GBSA studies on MD simulation's all 1000 frames to understand the complex energy level. All the results reveal promising interactions between Deprodone and the targeted enzymes, suggesting its potential as a multitargeted therapeutic agent-however, experimental studies need to validate Deprodone against MRSA.

Synergistic potential of Leu10-teixobactin and cefepime against multidrug-resistant Staphylococcus aureus

Staphylococcus aureus (S. aureus) is a significant Gram-positive opportunistic pathogen behind many debilitating infections. β-lactam antibiotics are conventionally prescribed for treating S. aureus infections. However, the adaptability of S. aureus in evolving resistance to multiple β-lactams contributed to the persistence and spread of infections, exemplified in the emergence of methicillin-resistant S. aureus (MRSA). In the present study, we investigated the efficacies of the synthetic teixobactin analogue, Leu10-teixobactin, combined with the penicillinase-resistant cephalosporin cefepime against MRSA strains. The Leu10-teixobactin and cefepime combination exerted synergism against most strains tested in broth microdilution assay. Time-kill profiles showed that both Leu10-teixobactin and cefepime predominantly exhibited synergistic activity, with > 2.0-log10CFU decrease compared to monotherapy at 24 h. Moreover, biofilm assays revealed a significant inhibition of biofilm production in ATCC™43300 cells treated with sub-MICs of Leu10-teixobactin and cefepime. Subsequent electron microscopy studies showed more extensive damage with the combination therapy compared to monotherapies, including aberrant bacterial morphology, vesicle formation and substantial lysis, indicating combined damage to the cell wall. Quantitative real-time PCR revealed marked perturbation of genes mecA, sarA, atlA, and icaA, substantiating the apparent mode of combined antibacterial action of both antibiotics against peptidoglycan synthesis and initial biofilm production. Hence, the study highlights the prospective utility of the Leu10-teixobactin-cefepime combination in treating MRSA infections via β-lactam potentiation.

FengycinA-M3 Inhibits Listeria monocytogenes by Binding to Penicillin-Binding Protein 2B Targets to Disrupt Cell Structure

The contamination of food with Listeria monocytogenes threatens food safety and human health, and developing a novel, green, and safe antimicrobial substance will offer a new food preservation strategy. FengycinA-M3 is a novel lipid peptide with low cytotoxicity and resistance and has effective antibacterial activity against L. monocytogenes with a minimum inhibitory concentration (MIC) of 4 µg/mL. Further combined transcriptomics and proteomics analysis yielded 20 differentially expressed genes (DEGs). The MICs of the combined use of FengycinA-M3 and Cefalexin on L. monocytogenes were further determined as FengycinA-M3 (2 µg/mL) and Cefalexin (8 µg/mL) using the checkerboard method. In addition, FengycinA-M3 was found to play a role in delaying pork deterioration. This study explored the inhibitory effect of FengycinA-M3 on L. monocytogenes and its mechanism of action. FengycinA-M3 interacted with penicillin-binding protein 2B on the cell membrane of L. monocytogenes, destroying the permeability of the membrane, causing cell membrane rupture, thereby inhibiting the growth of L. monocytogenes. Overall, FengycinA-M3 is a promising candidate for preventing the emergence and spread of L. monocytogenes with potential applications in food processing.

Design, synthesis of griseofamine A derivatives and development of potent antibacterial agents against MRSA

The prevalence of methicillin-resistant Staphylococcus aureus (MRSA), one of the most important multidrug-resistant bacteria in clinic, has become a serious global health issue. In this study, we designed and synthesized a series of griseofamine A derivatives and evaluated their antibacterial profiles. In vitro assays found that compound 9o10 showed a remarkable improvement of antibacterial activity toward MRSA (MIC = 0.0625 μg/mL), compared with griseofamine A (MIC = 8 μg/mL) and vancomycin (MIC = 0.5 μg/mL) with low hemolysis and cytotoxicity. Its rapid bactericidal property was also confirmed by time-kill curve assay. Furthermore, compound 9o10 displayed weak drug resistance frequency. In in vivo experiment, compound 9o10 exhibited more potent antibacterial efficacy than vancomycin and excellent biosafety (LD50 > 2 g/kg). Preliminary mechanism study revealed compound 9o10 might involve antibacterial mechanisms contributing to membrane damage. Taken together, compound 9o10 possessed excellent inhibitory activity against MRSA in vitro and in vivo with low toxicity and drug resistance frequency, making it a promising hit compound for further development against MRSA infections.

Prevalence and types of methicillin-resistant Staphylococcus aureus (MRSA) in meat and meat products from retail outlets and in samples of animal origin collected in farms, slaughterhouses and meat processing facilities. A review

Methicillin-resistant Staphylococcus aureus (MRSA) is a frequent cause of nosocomial and community infections, in some cases severe and difficult to treat. In addition, there are strains of MRSA that are specifically associated with food-producing animals. For this reason, in recent years special attention has been paid to the role played by foodstuffs of animal origin in infections by this microorganism. With the aim of gaining knowledge on the prevalence and types of MRSA in meat and meat products, a review was undertaken of work published on this topic since 2001, a total of 259 publications, 185 relating to meat samples from retail outlets and 74 to samples of animal origin collected in farms, slaughterhouses and meat processing facilities. Strains of MRSA were detected in 84.3% reports (156 out of 185) from retail outlets and 86.5% reports (64 out of 74) from farms, slaughterhouses and meat processing facilities, although in most of the research this microorganism was detected in under 20% of samples from retail outlets, and under 10% in those from farms, slaughterhouses and meat processing facilities. The meat and meat products most often contaminated with MRSA were pork and chicken. In addition to the mecA gene, it is crucial to take into consideration the mecB and mecC genes, so as to avoid misidentification of strains as MSSA (methicillin-susceptible Staphylococcus aureus). The great variety of methods used for the determination of MRSA highlights the need to develop a standardized protocol for the study of this microorganism in foods.

An Overview of Naphthylimide as Specific Scaffold for New Drug Discovery

Naphthylimides play a pivotal role as aromatic heterocyclic compounds, serving as the foundational structures for numerous pharmacologically significant drugs. These drugs encompass antibacterial, antifungal, anticancer, antimalarial, antiviral, anti-inflammatory, antithrombotic, and antiprotozoal agents. The planar and heteroaromatic characteristics of naphthylimides grant them a strong ability to intercalate into DNA. This intercalation property renders naphthylimide derivatives highly valuable for various biological activities. The advantageous pharmacological activity and ease of synthesis associated with naphthylimides and their derivatives provide significant benefits in the design and development of new compounds within this class. Currently, only a few such molecules are undergoing preclinical and clinical evaluations. In this paper, we have compiled the literature on naphthylimides reported by researchers from 2006 to 2024. Our focus lies on exploring the pharmacological activities of their analogues from a drug development and discovery perspective, while examining their structure-activity relationship and mechanisms of action.

Ultrasonic nanotechnology for the effective management of Staphylococcus aureus skin infections: an update

Ultrasonic nanotechnology represents a groundbreaking advancement in the management of Staphylococcus aureus skin infections, addressing the significant limitations of conventional treatments. S. aureus poses substantial challenges, including antibiotic resistance and biofilm formation, necessitating novel and effective approaches. By harnessing the power of ultrasonic waves and nanostructures, this technology offers a precise mechanism to disrupt bacterial cells, enhancing antibiotic susceptibility and facilitating the eradication of bacterial colonies. This innovative approach not only improves treatment outcomes, but also offers a non-invasive and highly efficient alternative to traditional methods. Recent studies have demonstrated the remarkable efficacy of ultrasonic nanotechnology, showcasing its ability to revolutionize the treatment paradigm for S. aureus infections. Ongoing research is dedicated to refining treatment protocols, developing new nanostructures, and assessing clinical applicability, with a focus on overcoming challenges such as scalability and long-term effectiveness. This review provides a comprehensive overview of the current state of ultrasonic nanotechnology in combating S. aureus skin infections, detailing its mechanism of action, summarizing key research findings, and highlighting its superiority over conventional modalities. Accumulating evidence underscores its potential as a pivotal development in modern science and technology, promising significant advancements in infection management strategies. As research continues to evolve, the optimization of protocols, exploration of innovative applications, and translation into clinical practice are poised to further solidify the transformative impact of ultrasonic nanotechnology in the medical field.

Prevalence and molecular characterization of multidrug-resistant coagulase negative staphylococci from urban wastewater in Delhi-NCR, India

Antimicrobial resistance (AMR) is global health concern escalating rapidly in both clinical settings and environment. The effluent from pharmaceuticals and hospitals may contain diverse antibiotics, exerting selective pressure to develop AMR. To study the aquatic prevalence of drug-resistant staphylococci, sampling was done from river Yamuna (3 sites) and wastewater (7 sites) near pharmaceutical industries in Delhi-NCR, India. 59.25% (224/378) were considered presumptive staphylococci while, methicillin resistance was noted in 25% (56/224) isolates. Further, 23 methicillin-resistant coagulase negative staphylococci (MR-CoNS) of 8 different species were identified via 16S rRNA gene sequencing. Multidrug resistance (MDR) was noted in 60.87% (14/23) isolates. PCR based detection of antibiotic resistance genes revealed the number of isolates containing mecA (7/23), blaZ (6/23), msrA (10/23), aac(6')aph (2") (2/23), aph(3')-IIIa (2/23), ant(4')-Ia (1/23), dfrG (4/23), dfrA(drfS1) (3/23), tetK (1/23) and tetM (1/23). The current research highlights the concerning prevalence of MDR-CoNS in aquatic environment in Delhi.

Design, Synthesis and Biological Evaluation of C3‐Indolyl/(3‐chloro‐indolyl)‐C4‐aryl/heteroaryl‐azetidin‐2‐ones

Herein, trans‐ and cis‐azetidin‐2‐ones 3–6 were strategically synthesized, capitalizing on the bioactivity of azetidin‐2‐ones and indole pharmacophore, followed by a comprehensive characterization using a diverse array of spectroscopic techniques. The sixteen azetidin‐2‐ones were examined for antimicrobial activities against both Gram‐negative (P. aeruginosa, E. coli, A. baumannii) and Gram‐positive bacteria (S. aureus, E. faecium, B. cereus), as well as against C. albicans and C. tropicalis fungal strains. The highly potent compounds (5 a, 6 b, 6 d) demonstrated maximum inhibition against all multidrug‐resistant strains, with minimum inhibitory concentrations ranging from 0.97–3.9 μg/mL, surpassing the potency of standard ampicillin (MIC: 3.12–50 μg/mL). Moreover, 6 b and 6 d exhibited significant inhibitory effects on C. albicans (MIC: 0.97 μg/mL), comparable to fluconazole. The presence of C3‐(3‐chloro‐indolyl) scaffold, combined with diverse electronic effects at N1/C4‐centers, particularly the inclusion of thiophen‐2‐yl motif, greatly influenced the activity of target compounds. Assessment of 4 d, 4 i–k and 6 d on THLE‐2 cell lines revealed their preferential safety. Molecular docking studies revealed seven compounds with active dual targeting of DNA GyrB and PBP2a proteins, demonstrating a potent broad‐spectrum antibacterial effect. In silico ADME analysis affirms positive drug‐likeness and favorable pharmacokinetic characteristics of indole‐derived hybrids, indicating a promising potential for addressing challenges in evolving multidrug resistance.

In silico exploration of 4(α-l-rhamnosyloxy)-benzyl isothiocyanate: A promising phytochemical-based drug discovery approach for combating multi-drug resistant Staphylococcus aureus

Multidrug-resistant (MDR) Staphylococcus aureus infections significantly threaten global health. With rising resistance to current antibiotics and limited solutions, the urgent discovery of new, effective, and affordable antibacterials with low toxicity is imperative to combat diverse MDR S. aureus strains. Hence, in this study, we introduce an in silico phytochemical-based approach for discovering novel antibacterial agents, underscoring the potential of computational approaches in therapeutic discovery. Glucomoringin Isothiocyanate (GMG-ITC) from Moringa oleifera Lam. is one of the phytochemical compounds with several biological activities, including antimicrobial, anti-inflammatory, and antioxidant activities, and is also effective against S. aureus. This study focuses on screening GMG-ITC as a potential drug candidate to combat MDR S. aureus infections through a molecular docking approach. Moreover, interaction amino acid analysis, in silico pharmacokinetics, compound target prediction, pathway enrichment analysis and molecular dynamics (MD) simulations were conducted for further investigation. Molecular docking and interaction analysis showed strong binding affinity towards S. aureus lipase, dihydrofolate reductase, and other MDR S. aureus proteins, including penicillin-binding protein 2a, MepR, D-Ala:D-Ala ligase, and RPP TetM, through hydrophilic and hydrophobic interactions. GMG-ITC also showed a strong binding affinity to cyclooxygenase-2 and FAD-dependent NAD(P)H oxidase, suggesting that it is a potential anti-inflammatory and antioxidant candidate that may eliminate inflammation and oxidative stress associated with S. aureus infections. MD simulations validated the stability of the GMG-ITC molecular interactions determined by molecular docking. In silico pharmacokinetic analysis highlights its potency as a drug candidate, showing strong absorption, distribution, and excretion properties in combination with low toxicity. It acts as an active protease and enzyme inhibitor with moderate activity against GPCR ligands, ion channels, nuclear receptor ligands, and kinases. Enrichment analysis further elucidated its involvement in important biological, molecular, and cellular functions with potential therapeutic applications in diseases like cancer, hepatitis B, and influenza. Results suggest that GMG-ITC is an effective antibacterial agent that could treat MDR S. aureus-associated infections.

The relationship between resistance evolution and carbon metabolism in Staphylococcus xylosus under ceftiofur sodium stress

Staphylococcus xylosus has emerged as a bovine mastitis pathogen with increasing drug resistance, resulting in substantial economic impacts. This study utilized iTRAQ analysis to investigate the mechanisms driving resistance evolution in S. xylosus under ceftiofur sodium stress. Findings revealed notable variations in the expression of 143 proteins, particularly glycolysis-related proteins (TpiA, Eno, GlpD, Ldh) and peptidoglycan (PG) hydrolase Atl. Following the induction of ceftiofur sodium resistance in S. xylosus, the emergence of resistant strains displaying characteristics of small colony variants (SCVs) was observed. The transcript levels of TpiA, Eno, GlpD and Ldh were up-regulated, TCA cycle proteins (ICDH, MDH) and Atl were down-regulated, lactate content was increased, and NADH concentration was decreased in SCV compared to the wild strain. That indicates a potential role of carbon metabolism, specifically PG hydrolysis, glycolysis, and the TCA cycle, in the development of resistance to ceftiofur sodium in S. xylosus.

Susceptibility of Staphylococcus aureus to Anti-Inflammatory Drugs with a Focus on the Combinatory Effect of Celecoxib with Oxacillin In Vitro

Musculoskeletal infections (MIs) are among the most difficult-to-treat staphylococcal diseases due to antibiotic resistance. This has encouraged the development of innovative strategies, such as combination therapy, to combat MI. The aim of this study was to investigate the in vitro antistaphylococcal activity of anti-inflammatory drugs and the combined antimicrobial effect of celecoxib and oxacillin. The minimum inhibitory concentrations (MICs) of 17 anti-inflammatory drugs against standard strains and clinical isolates of S. aureus, including methicillin-resistant strains (MRSAs), were determined using the broth microdilution method. The fractional inhibitory concentration indices (FICIs) were evaluated using checkerboard assays. Celecoxib produced the most potent antistaphylococcal effect against all tested strains (MICs ranging from 32 to 64 mg/L), followed by that of diacerein against MRSA3 and MRSA ATCC 33592 (MIC 64 mg/L). Several synergistic effects were observed against the tested S. aureus strains, including MRSA (FICI ranging from 0.087 to 0.471). The strongest synergistic interaction (FICI 0.087) was against MRSA ATCC 33592 at a celecoxib concentration of 2 mg/L, with a 19-fold oxacillin MIC reduction (from 512 to 26.888 mg/L). This is the first report on the combined antistaphylococcal effect of celecoxib and oxacillin. These findings suggest celecoxib and its combination with oxacillin as perspective agents for research focused on the development of novel therapies for MI caused by S. aureus. This study further indicates that celecoxib could resensitize certain MRSA strains, in some cases, to be susceptible to β-lactams (e.g., oxacillin) that were not previously tested. It is essential to mention that the in vitro concentrations of anti-inflammatory drugs are higher than those typically obtained in patients. Therefore, an alternative option for its administration could be the use of a drug delivery system for the controlled slow release from an implant at the infection site.

A sandwich-structured multifunctional platform based on self-assembled Ti3C2Tx@Au NPs films, antibiotics, and silent region SERS probe for the capture, determination, and drug resistance analysis of Gram-positive bacteria

A multifunctional surface-enhanced Raman scattering (SERS) platform integrating sensitive detection and drug resistance analysis was developed for Gram-positive bacteria. The substrate was based on self-assembled Ti3C2Tx@Au NPs films and capture molecule phytic acid (IP6) to achieve specific capture of Gram-positive bacteria and different bacteria were analyzed by fingerprint signal. It had advantages of good stability and homogeneity (RSD = 8.88%). The detection limit (LOD) was 102 CFU/mL for Staphylococcus aureus and 103 CFU/mL for MRSA, respectively. A sandwich structure was formed on the capture substrate by signal labels prepared by antibiotics (penicillin G and vancomycin) and non-interference SERS probe molecules (4-mercaptobenzonitrile (2223 cm-1) and 2-amino-4-cyanopyridine (2240 cm-1)) to improve sensitivity. The LOD of Au NPs@4-MBN@PG to S. aureus and Au NPs@AMCP@Van to MRSA and S. aureus were all improved to 10 CFU/mL, with a wide dynamic linear range from 108 to 10 CFU/mL (R2 ≥ 0.992). The SERS platform can analyze the drug resistance of drug-resistant bacteria. Au NPs@4-MBN@PG was added to the substrate and captured MRSA to compare the SERS spectra of 4-MBN. The intensity inhomogeneity of 4-MBN at the same concentrations of MRSA and the nonlinearity at the different concentrations of MRSA revealed that MRSA was resistant to PG. Finally, the SERS platform achieved the determination of MRSA in blood. Therefore, this SERS platform has great significance for the determination and analysis of Gram-positive bacteria.

Predicting S. aureus antimicrobial resistance with interpretable genomic space maps

Increasing antimicrobial resistance (AMR) represents a global healthcare threat. To decrease the spread of AMR and associated mortality, methods for rapid selection of optimal antibiotic treatment are urgently needed. Machine learning (ML) models based on genomic data to predict resistant phenotypes can serve as a fast screening tool prior to phenotypic testing. Nonetheless, many existing ML methods lack interpretability. Therefore, we present a methodology for visualization of sequence space and AMR prediction based on the non-linear dimensionality reduction method - generative topographic mapping (GTM). This approach, applied to AMR data of >5000 S. aureus isolates retrieved from the PATRIC database, yielded GTM models with reasonable accuracy for all drugs (balanced accuracy values ≥0.75). The Generative Topographic Maps (GTMs) represent data in the form of illustrative maps of the genomic space and allow for antibiotic-wise comparison of resistant phenotypes. The maps were also found to be useful for the analysis of genetic determinants responsible for drug resistance. Overall, the GTM-based methodology is a useful tool for both the illustrative exploration of the genomic sequence space and AMR prediction.

A novel extraction-free dual HiFi-LAMP assay for detection of methicillin-sensitive and methicillin-resistant Staphylococcus aureus

Staphylococcus aureus (S. aureus) is a leading cause of bacteremia and blood stream infections. Methicillin-resistant S. aureus (MRSA) that first appeared in 1961 often caused hospital-acquired infections (HAIs) and community-acquired infections (CAIs) and was associated with high mortality rate. Accurate and rapid point-of-care testing (POCT) of MRSA is crucial for clinical management and treatment of MRSA infections, as well as the prevention and control of HAIs and CAIs. Here, we reported a novel extraction-free dual HiFi-LAMP assay for discriminative detection of methicillin-susceptible S. aureus and MRSA. The dual HiFi-LAMP assay can detect 30 copies/reaction of nuc and mecA genes with detection limits of 147 and 158 copies per 25 µL reaction, respectively. A retrospective clinical evaluation with 107 clinical S. aureus isolates showed both sensitivity and specificity of 100%. A prospective clinical evaluation with 35 clinical samples revealed a specificity of 100% and a sensitivity of 92.3%. The dual HiFi-LAMP assay can detect almost all S. aureus samples (141/142; 99.3%) within 20 min, implying that the entire HiFi-LAMP assay (including sample process) can be completed within 40 min, extremely significantly shorter than 3-5 days by the traditional clinical microbial culture and antibiotic susceptibility testing. The novel extraction-free dual HiFi-LAMP assay can be used as a robust POCT tool to promote precise diagnosis and treatment of MRSA infections in hospitals and to facilitate surveillance of MRSA at hospital and community settings.IMPORTANCEMethicillin-resistant Staphylococcus aureus (MRSA) was associated with high mortality rate and listed as a "priority pathogen" by the World Health Organization. Accurate and rapid point-of-care testing (POCT) of MRSA is critically required for clinical management and treatment of MRSA infections. Some previous LAMP-based POCT assays for MRSA might be questionable due to their low specificity and the lack of appropriate evaluation directly using clinical samples. Furthermore, they are relatively tedious and time-consuming because they require DNA extraction and lack multiplex detection capacity. Here, we reported a novel extraction-free dual HiFi-LAMP assay for discriminative detection of MRSA and methicillin-susceptible S. aureus. The assay has high specificity and sensitivity and can be completed within 40 min. Clinical evaluation with real clinical samples and clinical isolates showed excellent performance with 100% specificity and 92.3%-100% sensitivity. The novel extraction-free assay may be a robust POCT tool to promote precise diagnosis of MRSA infections and facilitate surveillance of MRSA at hospital and community settings.

Interaction of zincite, alpha-terpineol, geranyl acetate, linalool, myrcenol, terpinolene, and thymol with virulence factors of Escherichia coli, Mycobacterium tuberculosis, Pseudomonas aeruginosa, and Staphylococcus aureus

BACKGROUND

Based on gas chromatography - mass spectrometry (GC-MS) results of a previous study, six metabolites including alpha-terpineol, geranyl acetate, linalool, myrcenol, terpinolene, and thymol showed significantly higher amounts relative to other metabolites.

METHODS

A continuation of the previous study, the interaction of these metabolites with the main virulence factors of P. aeruginosa (pseudomonas elastase and exotoxin A), Staphylococcus aureus (alpha-hemolysin and protein 2a), Mycobacterium tuberculosis (ESX-secreted protein B and the serine/threonine protein kinase), and Escherichia coli (heat-labile enterotoxin and Shiga toxin) were evaluated by molecular docking study and molecular simulation.

RESULTS

In the case of Shiga toxin, higher and lower binding affinities were related to alpha-terpinolene and zincite with values of -5.8 and -2.6 kcal/mol, respectively. For alpha-hemolysin, terpinolene and alpha-terpinolene demonstrated higher binding affinities with similar energies of -5.9 kcal/mol. Thymol and geranyl acetate showed lower binding energy of -5.7 kcal/mol toward protein 2a. Furthermore, thymol had a higher binding affinity toward heat-labile enterotoxin and ESX-secreted protein B with values of -5.9 and -6.1 kcal/mol, respectively.

CONCLUSIONS

It is concluded that the availability of secondary metabolites of A. haussknechtii surrounding zinc oxide (ZnO) NPs can hinder P. aeruginosa by inactivating Pseudomonas elastase and exotoxin.

Green and sustainable approaches for the Friedel-Crafts reaction between aldehydes and indoles

The synthesis of indoles and their derivatives, more specifically bis(indolyl)methanes (BIMs), has been an area of great interest in organic chemistry, since these compounds exhibit a range of interesting biological and pharmacological properties. BIMs are naturally found in cruciferous vegetables and have been shown to be effective antifungal, antibacterial, anti-inflammatory, and even anticancer agents. Traditionally, the synthesis of BIMs has been achieved upon the acidic condensation of an aldehyde with indole, utilizing a variety of protic or Lewis acids. However, due to the increased environmental awareness of our society, the focus has shifted towards the development of greener synthetic technologies, like photocatalysis, organocatalysis, the use of nanocatalysts, microwave irradiation, ball milling, continuous flow, and many more. Thus, in this review, we summarize the medicinal properties of BIMs and the developed BIM synthetic protocols, utilizing the reaction between aldehydes with indoles, while focusing on the more environmentally friendly methods developed over the years.

Synergistic effect of secondary metabolites isolated from Pestalotiopsis sp. FKR-0115 in overcoming β-lactam resistance in MRSA

Six aromatic secondary metabolites, pestalone (1), emodin (2), phomopsilactone (3), pestalachlorides B (4), C (5), and D (6), were isolated from Pestalotiopsis sp. FKR-0115, a filamentous fungus collected from white moulds growing on dead branches in Minami Daito Island. The efficacy of these secondary metabolites against methicillin-resistant Staphylococcus aureus (MRSA) with and without meropenem (β-lactam antibiotic) was evaluated using the paper disc method and broth microdilution method. The chemical structures of the isolated compounds (1-6) were characterised using spectroscopic methods, including nuclear magnetic resonance and mass spectrometry. All six isolated compounds exhibited synergistic activity with meropenem against MRSA. Among the six secondary metabolites, pestalone (1) overcame bacterial resistance in MRSA to the greatest extent.

Structural Insights into the Penicillin-Binding Protein 4 (DacB) from Mycobacterium tuberculosis

Mycobacterium tuberculosis, a major cause of mortality from a single infectious agent, possesses a remarkable mycobacterial cell envelope. Penicillin-Binding Proteins (PBPs) are a family of bacterial enzymes involved in the biosynthesis of peptidoglycan. PBP4 (DacB) from M. tuberculosis (MtbPBP4) has been known to function as a carboxypeptidase, and the role and significance of carboxypeptidases as targets for anti-tuberculosis drugs or antibiotics have been extensively investigated over the past decade. However, their precise involvement remains incompletely understood. In this study, we employed predictive modeling and analyzed the three-dimensional structure of MtbPBP4. Interestingly, MtbPBP4 displayed a distinct domain structure compared to its homologs. Docking studies with meropenem verified the presence of active site residues conserved in PBPs. These findings establish a structural foundation for comprehending the molecular function of MtbPBP4 and offer a platform for the exploration of novel antibiotics.

Unraveling the mechanism of ceftaroline-induced allosteric regulation in penicillin-binding protein 2a: insights for novel antibiotic development against methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) acquires high-level resistance against β-lactam antibiotics by expressing penicillin-binding protein 2a (PBP2a). PBP2a is a cell wall-synthesizing protein whose closed active site exhibits a reduced binding affinity toward β-lactam antibiotics. Ceftaroline (CFT), a fifth-generation cephalosporin, can effectively inhibit the PBP2a activity by binding to an allosteric site to trigger the active site opening, allowing a second CFT to access the active site. However, the essential mechanism behind the allosteric behavior of PBP2a remains unclear. Herein, computational simulations are employed to elucidate how CFT allosterically regulates the conformation and dynamics of the active site of PBP2a. While CFT stabilizes the allosteric domain surrounding it, it simultaneously enhances the dynamics of the catalytic domain. Specifically, the study successfully captured the opening process of the active pocket in the allosteric CFT-bound systems and discovered that CFT alters the potential signal-propagating pathways from the allosteric site to the active site. These findings reveal the implied mechanism of the CFT-mediated allostery in PBP2a and provide new insights into dual-site drug design or combination therapy against MRSA targeting PBP2a.

The Role of Five-Membered Heterocycles in the Molecular Structure of Antibacterial Drugs Used in Therapy

Five-membered heterocycles are essential structural components in various antibacterial drugs; the physicochemical properties of a five-membered heterocycle can play a crucial role in determining the biological activity of an antibacterial drug. These properties can affect the drug's activity spectrum, potency, and pharmacokinetic and toxicological properties. Using scientific databases, we identified and discussed the antibacterials used in therapy, containing five-membered heterocycles in their molecular structure. The identified five-membered heterocycles used in antibacterial design contain one to four heteroatoms (nitrogen, oxygen, and sulfur). Antibacterials containing five-membered heterocycles were discussed, highlighting the biological properties imprinted by the targeted heterocycle. In some antibacterials, heterocycles with five atoms are pharmacophores responsible for their specific antibacterial activity. As pharmacophores, these heterocycles help design new medicinal molecules, improving their potency and selectivity and comprehending the structure-activity relationship of antibiotics. Unfortunately, particular heterocycles can also affect the drug's potential toxicity. The review extensively presents the most successful five-atom heterocycles used to design antibacterial essential medicines. Understanding and optimizing the intrinsic characteristics of a five-membered heterocycle can help the development of antibacterial drugs with improved activity, pharmacokinetic profile, and safety.

A Review on Five and Six-Membered Heterocyclic Compounds Targeting the Penicillin-Binding Protein 2 (PBP2A) of Methicillin-Resistant Staphylococcus aureus (MRSA)

Staphylococcus aureus is a common human pathogen. Methicillin-resistant Staphylococcus aureus (MRSA) infections pose significant and challenging therapeutic difficulties. MRSA often acquires the non-native gene PBP2a, which results in reduced susceptibility to β-lactam antibiotics, thus conferring resistance. PBP2a has a lower affinity for methicillin, allowing bacteria to maintain peptidoglycan biosynthesis, a core component of the bacterial cell wall. Consequently, even in the presence of methicillin or other antibiotics, bacteria can develop resistance. Due to genes responsible for resistance, S. aureus becomes MRSA. The fundamental premise of this resistance mechanism is well-understood. Given the therapeutic concerns posed by resistant microorganisms, there is a legitimate demand for novel antibiotics. This review primarily focuses on PBP2a scaffolds and the various screening approaches used to identify PBP2a inhibitors. The following classes of compounds and their biological activities are discussed: Penicillin, Cephalosporins, Pyrazole-Benzimidazole-based derivatives, Oxadiazole-containing derivatives, non-β-lactam allosteric inhibitors, 4-(3H)-Quinazolinones, Pyrrolylated chalcone, Bis-2-Oxoazetidinyl macrocycles (β-lactam antibiotics with 1,3-Bridges), Macrocycle-embedded β-lactams as novel inhibitors, Pyridine-Coupled Pyrimidinones, novel Naphthalimide corbelled aminothiazoximes, non-covalent inhibitors, Investigational-β-lactam antibiotics, Carbapenem, novel Benzoxazole derivatives, Pyrazolylpyridine analogues, and other miscellaneous classes of scaffolds for PBP2a. Additionally, we discuss the penicillin-binding protein, a crucial target in the MRSA cell wall. Various aspects of PBP2a, bacterial cell walls, peptidoglycans, different crystal structures of PBP2a, synthetic routes for PBP2a inhibitors, and future perspectives on MRSA inhibitors are also explored.

Reverse vaccinology & immunoinformatics approach to design a multiepitope vaccine (CV3Ag-antiMRSA) against methicillin resistant Staphylococcus aureus (MRSA) - a pathogen affecting both human and animal health

Infections caused by drug resistant bacteria is a silent detrimental pandemic affecting the global health care profoundly. Methicillin resistant Staphylococcus aureus (MRSA) is a pathogen that causes serious infections in different settings (community, hospital & veterinary) whose treatment remains highly challenging due to its powerful characteristics (antibiotic resistance strategies, virulence factors). In this study, we used reverse vaccinology (RV) approach and designed an immunogenic multi epitope vaccine (CV3Ag-antiMRSA) targeting three potential antigen candidates viz., mecA encoding transpeptidase (PBP2a) protein responsible for conferring methicillin resistance and two virulence determinants - hlgA encoding gamma-hemolysin component A (a pore forming toxin) and isdB encoding iron regulated surface determinant B (heme transport component that allows S. aureus to scavenge iron from host hemoglobin and myoglobin). We employed an array of immunoinformatic tools/server to identify and use immunogenic epitopes (B cell and MHC class) to develop the chimeric subunit vaccine V4 (CV3Ag-antiMRSA) with immune modulating adjuvant and linkers. Based on different parameters, the vaccine construct V4 (CV3Ag-antiMRSA) was determined to be suitable vaccine (antigenic and non-allergen). Molecular docking and simulation of CV3Ag-antiMRSA with Toll Like Receptor (TLR2) predicted its immuno-stimulating potential. Finally, in silico cloning of CV3Ag-antiMRSA construct into pet28a and pet30 vector displayed its feasibility for the heterologous expression in the E. coli expression system. This vaccine candidate (CV3Ag-antiMRSA) designed based on the MRSA genomes obtained from both animal and human hosts can be experimentally validated and thereby contribute to vaccine development to impart protection to both animal and human health.Communicated by Ramaswamy H. Sarma.

The depsidones from marine sponge-derived fungus Aspergillus unguis IB151 as an anti-MRSA agent: Molecular docking, pharmacokinetics analysis, and molecular dynamic simulation studies

Methicillin-resistant Staphylococcus aureus (MRSA) is an emerging nosocomial pathogen among hospitalized patients, with high morbidity and mortality rates. The discovery of a novel antibacterial is urgently needed to address this resistance problem. The present study aims to explore the antibacterial potential of three depsidone compounds: 2-clorounguinol (1), unguinol (2), and nidulin (3), isolated from the marine sponge-derived fungus Aspergillus unguis IB1, both in vitro and in silico. The antibacterial activity of all compounds was evaluated by calculating the Minimum inhibitory concentration (MIC) and Minimum bactericidal concentration (MBC) against MRSA using agar diffusion and total plate count methods, respectively. Bacterial cell morphology changes were  studied for the first time using scanning electron microscopy (SEM). Molecular docking, pharmacokinetics analysis, and molecular dynamics simulation were performed to determine possible protein-ligand interactions and the stability of the targeting penicillin-binding protein 2a (PBP2a) against 2-clorounguinol (1). The research findings indicated that compounds 1 to 3 exhibited MIC and MBC values of 2 µg/mL and 16 µg/mL against MRSA, respectively. MRSA cells displayed a distinct shape after the addition of the depsidone compound, as observed in SEM. According to the in silico study, 2-chlorounguinol exhibited the highest binding-free energy (BFE) with PBP2a (-6.7 kcal/mol). For comparison, (E)-3-(2-(4-cyanostyryl)-4-oxoquinazolin-3(4H)-yl) benzoic acid inhibits PBP2a with a BFE less than -6.6 kcal/mol. Based on the Lipinski's rule of 5, depsidone compounds constitute a class of compounds with good pharmacokinetic properties, being easily absorbed and permeable. These findings suggest that 2-chlorounguinol possesses potential antibacterial activity and could be developed as an antibiotic adjuvant to reduce antimicrobial resistance.

Synthesis, nanostructuring and in silico studies of a new imine bond containing a macroheterocycle as a promising PBP-2a non-β-lactam inhibitor

This study is devoted to the synthesis of a 40-membered macroheterocycle with its further nanostructuring by magnetite nanoparticles. The mentioned macroheterocycle was synthesized by the [2+2] cyclocondensation of the oxygen-containing diamine with an aromatic dialdehyde in a non-catalytic medium and with no work-up procedure. The structure of the obtained macroheterocycle was studied by 1H and 13C nuclear magnetic resonance spectroscopy and matrix-assisted laser desorption/ionization-time of flight mass spectrometry. Furthermore, the nanosupramolecular complex of macroheterocycles with magnetite nanoparticles was obtained and investigated by Fourier-transform infrared and ultraviolet-visible spectroscopy methods. Shifts in the infrared spectra of the nanosupramolecular complex indicate the interaction through metal-aromatic ring non-covalent bonding. The shift is also observed for the C-O-C stretching band of ether bonds. The loading rate of macroheterocycles on magnetite nanoparticles was 18.6%. The morphology of the ensemble was studied by transmission electron microscopy, which confirmed the synthesis of nanospherical particles with a diameter range of 10-20 nm. Powder X-ray diffraction analysis showed patterns of cubic Fe3O4 nanoparticles with a crystallite size equal to 9.1 nm. The macroheterocycle and its nanosupramolecular complex were tested against Klebsiella pneumoniae, Pseudomonas aeruginosa and Staphylococcus aureus. The results have shown that the created complex has shown 64 times better activity against Staphylococcus aureus in comparison with the individual macroheterocycle and 32 times better activity in comparison with the pristine antibiotic Ampicillin as a control. In addition, computational analysis of the macroheterocycle was performed at the B3LYP/6-31G level in water. Molecular docking analyses for the macroheterocycle revealed Penicillin-binding protein PBP2a (5M18) from the transpeptidase family as a target protein in Staphylococcus aureus.

Molecular basis of β-lactam antibiotic resistance of ESKAPE bacterium E. faecium Penicillin Binding Protein PBP5

Penicillin-binding proteins (PBPs) are essential for the formation of the bacterial cell wall. They are also the targets of β-lactam antibiotics. In Enterococcus faecium, high levels of resistance to β-lactams are associated with the expression of PBP5, with higher levels of resistance associated with distinct PBP5 variants. To define the molecular mechanism of PBP5-mediated resistance we leveraged biomolecular NMR spectroscopy of PBP5 - due to its size (>70 kDa) a challenging NMR target. Our data show that resistant PBP5 variants show significantly increased dynamics either alone or upon formation of the acyl-enzyme inhibitor complex. Furthermore, these variants also exhibit increased acyl-enzyme hydrolysis. Thus, reducing sidechain bulkiness and expanding surface loops results in increased dynamics that facilitates acyl-enzyme hydrolysis and, via increased β-lactam antibiotic turnover, facilitates β-lactam resistance. Together, these data provide the molecular basis of resistance of clinical E. faecium PBP5 variants, results that are likely applicable to the PBP family.

Novel Thiazolylketenyl Quinazolinones as Potential Anti-MRSA Agents and Allosteric Modulator for PBP2a

Bacterial infections caused by methicillin-resistant Staphylococcus aureus have seriously threatened public health. There is an urgent need to propose an existing regimen to overcome multidrug resistance of MRSA. A unique class of novel anti-MRSA thiazolylketenyl quinazolinones (TQs) and their analogs were developed. Some synthesized compounds showed good bacteriostatic potency. Especially TQ 4 was found to exhibit excellent inhibition against MRSA with a low MIC of 0.5 μg/mL, which was 8-fold more effective than norfloxacin. The combination of TQ 4 with cefdinir showed stronger antibacterial potency. Further investigation revealed that TQ 4, with low hemolytic toxicity and low drug resistance, was not only able to inhibit biofilm formation but also could reduce MRSA metabolic activity and showed good drug-likeness. Mechanistic explorations revealed that TQ 4 could cause leakage of proteins by disrupting membrane integrity and block DNA replication by intercalated DNA. Furthermore, the synergistic antibacterial effect with cefdinir might be attributed to TQ 4 with the ability to induce PBP2a allosteric regulation of MRSA and further trigger the opening of the active site to promote the binding of cefdinir to the active site, thus inhibiting the expression of PBP2a, thereby overcoming MRSA resistance and significantly enhancing the anti-MRSA activity of cefdinir. A new strategy provided by these findings was that TQ 4, possessing both excellent anti-MRSA activity and allosteric effect of PBP2a, merited further development as a novel class of antibacterial agents to overcome increasingly severe MRSA infections.

Chemical Profile, Antibacterial, Antibiofilm, and Antiviral Activities of Pulicaria crispa Most Potent Fraction: An In Vitro and In Silico Study

Infectious diseases caused by viruses and bacteria are a major public health concern worldwide, with the emergence of antibiotic resistance, biofilm-forming bacteria, viral epidemics, and the lack of effective antibacterial and antiviral agents exacerbating the problem. In an effort to search for new antimicrobial agents, this study aimed to screen antibacterial and antiviral activity of the total methanol extract and its various fractions of Pulicaria crispa (P. crispa) aerial parts. The P. crispa hexane fraction (HF) was found to have the strongest antibacterial effect against both Gram-positive and Gram-negative bacteria, including biofilm producers. The HF fraction reduced the expression levels of penicillin binding protein (PBP2A) and DNA gyrase B enzymes in Staphylococcus aureus and Pseudomonas aeruginosa, respectively. Additionally, the HF fraction displayed the most potent antiviral activity, especially against influenza A virus, affecting different stages of the virus lifecycle. Gas chromatography/mass spectrometry (GC/MS) analysis of the HF fraction identified 27 compounds, mainly belonging to the sterol class, with β-sitosterol, phytol, stigmasterol, and lupeol as the most abundant compounds. The in silico study revealed that these compounds were active against influenza A nucleoprotein and polymerase, PBP2A, and DNA gyrase B. Overall, this study provides valuable insights into the chemical composition and mechanism of action of the P. crispa HF fraction, which may lead to the development of more effective treatments for bacterial and viral infections.

Drug Repurposing Approach in Developing New Furosemide Analogs as Antimicrobial Candidates and Anti-PBP: Design, Synthesis, and Molecular Docking

Multidrug-resistant microorganisms have become a global health problem, prompting research into new antimicrobials. Drug repurposing is a new technique in drug discovery used to improve drug development success. As a well-studied medication with a sulfonamide moiety, furosemide was chosen to study its antimicrobial effect on different microbial strains. In addition, a new family of furosemide analogs was investigated for their antimicrobial efficacy. According to the obtained results, the majority of the examined molecules exhibited potential antimicrobial activity. Compounds 3b and 4a had the best anti-MRSA results, with an MIC = 7.81 µg/mL. They also demonstrated potent anti-gram-negative activity against E. coli (MIC = 1.95 µg/mL and 3.91 µg/mL, respectively). A time-killing kinetics study against E. coli and MRSA showed bactericidal actions of 3b and 4a within 120-150 min. Moreover, an anti-PBP activity and an in vitro cytotoxicity evaluation were performed. Furosemide decreased the PBP2a levels in MRSA by 21.5% compared to the control. However, the furosemide analogs 3b and 4a demonstrated superior anti-PBP activity (55.9 and 57.1 % reduction in the expression of PBP2a, respectively). In addition, compound 4a was nearly nontoxic to normal WI-38 cells (IC₅₀ = 248.60 μg /mL) indicating its high safety profile. Finally, the ability of furosemide and compounds 3b and 4a to bind to the target PBP2a enzyme has also been supported by molecular docking research.

Activity of Patchouli and Tea Tree Essential Oils against Staphylococci Isolated from Pyoderma in Dogs and Their Synergistic Potential with Gentamicin and Enrofloxacin

In this paper, we show the effect of some essential oils (EOs) on staphylococci, including multidrug-resistant strains isolated from pyoderma in dogs. A total of 13 Staphylococcus pseudintermedius and 8 Staphylococcus aureus strains were studied. To assess the sensitivity of each strain to the antimicrobial agents, two commercial EOs from patchouli (Pogostemon cablin; PcEO) and tea tree (Melaleuca alternifolia; MaEO) as well as two antibiotics (gentamicin and enrofloxacin) were used. The minimum inhibitory concentration (MIC) followed by checkerboards in the combination of EO-antibiotic were performed. Finally, fractional inhibitory concentrations were calculated to determine possible interactions between these antimicrobial agents. PcEO MIC ranged from 0.125 to 0.5 % v/v (1.2-4.8 mg/mL), whereas MaEO MIC was tenfold higher (0.625-5% v/v or 5.6-44.8 mg/mL). Gentamicin appeared to be highly prone to interacting with EOs. Dual synergy (38.1% of cases) and PcEO additive/MaEO synergism (53.4%) were predominantly observed. On the contrary, usually, no interactions between enrofloxacin and EOs were observed (57.1%). Both commercial EOs were characterized by natural composition without artificial adulteration. Patchouli and tea tree oils can be good alternatives for treating severe cases of pyoderma in dogs, especially when dealing with multidrug-resistant strains.

The Synergistic Antimicrobial Effect and Mechanism of Nisin and Oxacillin against Methicillin-Resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is responsible for skin and soft tissue infections with multi-resistance to many antibiotics. It is thus imperative to explore alternative antimicrobial treatments to ensure future treatment options. Nisin (NIS), an antibacterial peptide produced by Lactococcus lactis, was selected to combine with Oxacillin (OX), to evaluate the antimicrobial effect and potential mechanism against MRSA. The synergistic antimicrobial effect of OX and NIS was verified by Minimal Inhibitory Concentration (MIC) assays, checkerboard analysis, time-kill curve, biofilm producing ability, and mice skin infection model in vivo. For the potential synergistic antimicrobial mechanism, the microstructure and integrity change of MRSA cells were determined by Scanning and Transmission Electron Microscope (SEM and TEM), intracellular alkaline phosphatase activity and propidium iodide staining were assayed; And transcription of mecA, main gene of MRSA resistant to OX, were detected by qRT-PCR. The results showed NIS could restore the sensitivity of MRSA to OX and inhibit biofilm production; OX + NIS can make MRSA cell deform; NIS may recover OX sensitivity by inhibiting the transcription of mecA. In vivo, mice skin infection models indicate that OX + NIS can substantially alleviate MRSA infections. As a safe commercially available biological compound, NIS and the combination of antibiotics are worth developing as new anti-MRSA biomaterials.

Computational Screening of Approved Drugs for Inhibition of the Antibiotic Resistance Gene mecA in Methicillin-Resistant Staphylococcus aureus (MRSA) Strains

Antibiotic resistance is a critical problem that results in a high morbidity and mortality rate. The process of discovering new chemotherapy and antibiotics is challenging, expensive, and time-consuming, with only a few getting approved for clinical use. Therefore, screening already-approved drugs to combat pathogens such as bacteria that cause serious infections in humans and animals is highly encouraged. In this work, we aim to identify approved antibiotics that can inhibit the mecA antibiotic resistance gene found in methicillin-resistant Staphylococcus aureus (MRSA) strains. The MecA protein sequence was utilized to perform a BLAST search against a drug database containing 4302 approved drugs. The results revealed that 50 medications, including known antibiotics for other bacterial strains, targeted the mecA antibiotic resistance gene. In addition, a structural similarity approach was employed to identify existing antibiotics for S. aureus, followed by molecular docking. The results of the docking experiment indicated that six drugs had a high binding affinity to the mecA antibiotic resistance gene. Furthermore, using the structural similarity strategy, it was discovered that afamelanotide, an approved drug with unclear antibiotic activity, had a strong binding affinity to the MRSA-MecA protein. These findings suggest that certain already-approved drugs have potential in chemotherapy against drug-resistant pathogenic bacteria, such as MRSA.

Investigating the antibacterial mechanism of Ampelopsis cantoniensis extracts against methicillin-resistant Staphylococcus aureus via in vitro and in silico analysis

Methicillin-resistant Staphylococcus aureus (MRSA) is a critical pathogen responsible for a wide variety of serious infectious diseases in humans. The accelerated phenomena of drug tolerance, drug resistance, and dysbacteriosis provoked by antibiotic misuse are impeding the effectiveness of contemporary antibiotic therapies primarily used to treat this common worldwide pathogen. In this study, the antibacterial activity of 70% ethanol extract and multiple polar solvents of Ampelopsis cantoniensis were measured against the clinical MRSA isolate. The agar diffusion technique was employed to determine the zone of inhibition (ZOI), accompanied by the use of a microdilution series to identify the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC). Our results revealed that the ethyl acetate fraction exhibited the most significant antibacterial activity, which was determined to be bacteriostatic based on the MBC/MIC ratio 8. A list of compounds isolated from A. cantoniensis was computationally studied to further investigate the mechanism of action with the bacterial membrane protein PBP2a. The combination of molecular docking and molecular dynamics methods showed that the main compound, dihydromyricetin (DHM), is expected to bind to PBP2a at allosteric site. In addition, DHM was identified as the major compound of ethyl acetate fraction, which accounts for 77.03 ± 2.44% by high performance liquid chromatography (HPLC) analysis. As a concluding remark, our study addressed the antibacterial mechanism and suggested the prioritization of natural products derived from A. cantoniensis as a potential therapy for MRSA.Communicated by Ramaswamy H. Sarma.

Success stories of natural product-derived compounds from plants as multidrug resistance modulators in microorganisms

Microorganisms evolve resistance to antibiotics as a function of evolution. Antibiotics have accelerated bacterial resistance through mutations and acquired resistance through a combination of factors. In some cases, multiple antibiotic-resistant determinants are encoded in these genes, immediately making the recipient organism a "superbug". Current antimicrobials are no longer effective against infections caused by pathogens that have developed antimicrobial resistance (AMR), and the problem has become a crisis. Microorganisms that acquire resistance to chemotherapy (multidrug resistance) are a major obstacle for successful treatments. Pharmaceutical industries should be highly interested in natural product-derived compounds, as they offer new sources of chemical entities for the development of new drugs. Phytochemical research and recent experimental advances are discussed in this review in relation to the antimicrobial efficacy of selected natural product-derived compounds as well as details of synergistic mechanisms and structures. The present review recognizesand amplifies the importance of compounds with natural origins, which can be used to create safer and more effective antimicrobial drugs by combating microorganisms that are resistant to multiple types of drugs.

Synergistic Combinations of FDA-Approved Drugs with Ceftobiprole against Methicillin-Resistant Staphylococcus aureus

New strategies are urgently needed to address the public health threat of antimicrobial resistance. Synergistic agent combinations provide one possible pathway toward addressing this need and are also of fundamental mechanistic interest. Effective methods for comprehensively identifying synergistic agent combinations are required for such efforts. In this study, an FDA-approved drug library was screened against methicillin-resistant Staphylococcus aureus (MRSA) (ATCC 43300) in the absence and presence of sub-MIC levels of ceftobiprole, a PBP2a-targeted anti-MRSA β-lactam. This screening identified numerous potential synergistic agent combinations, which were then confirmed and characterized for synergy using checkerboard analyses. The initial group of synergistic agents (sum of the minimum fractional inhibitory concentration ∑FIC_min ≤0.5) were all β-lactamase-resistant β-lactams (cloxacillin, dicloxacillin, flucloxacillin, oxacillin, nafcillin, and cefotaxime). Cloxacillin-the agent with the greatest synergy with ceftobiprole-is also highly synergistic with ceftaroline, another PBP2a-targeted β-lactam. Further follow-up studies revealed a range of ceftobiprole synergies with other β-lactams, including with imipenem, meropenem, piperacillin, tazobactam, and cefoxitin. Interestingly, given that essentially all other ceftobiprole-β-lactam combinations showed synergy, ceftaroline and ceftobiprole showed no synergy. Modest to no synergy (0.5 < ∑FIC_min ≤ 1.0) was observed for several non-β-lactam agents, including vancomycin, daptomycin, balofloxacin, and floxuridine. Mupirocin had antagonistic activity with ceftobiprole. Flucloxacillin appeared particularly promising, with both a low intrinsic MIC and good synergy with ceftobiprole. That so many β-lactam combinations with ceftobiprole show synergy suggests that β-lactam combinations can generally increase β-lactam effectiveness and may also be useful in reducing resistance emergence and spread in MRSA. IMPORTANCE Antimicrobial resistance represents a serious threat to public health. Antibacterial agent combinations provide a potential approach to combating this problem, and synergistic agent combinations-in which each agent enhances the antimicrobial activity of the other-are particularly valuable in this regard. Ceftobiprole is a late-generation β-lactam antibiotic developed for MRSA infections. Resistance has emerged to ceftobiprole, jeopardizing this agent's effectiveness. To identify synergistic agent combinations with ceftobiprole, an FDA-approved drug library was screened for potential synergistic combinations with ceftobiprole. This screening and follow-up studies identified numerous β-lactams with ceftobiprole synergy.

In Vitro and In Vivo Antibacterial Activity, Toxicity and Resistance Analysis of Pleuromutilin Derivative Z33 against Methicillin-Resistant Staphylococcus aureus

The novel pleuromutilin derivative, which showed excellent in vitro antibacterial activity against MRSA, 22-(2-(2-(4-((4-(4-nitrophenyl)piperazin-1-yl)methyl)-1H-1,2,3-triazol-1-yl)acetamido)phenyl)thioacety-l-yl-22-deoxypleuromutilin (Z33), was synthesized and characterized in our previous work. In this study, the preliminary pharmacodynamics and safety of Z33 were further evaluated. In in vitro antibacterial activity assays, Z33 was found to be a potent bactericidal antibiotic against MRSA that induced dose-dependent growth inhibition and long-term post-antibiotic effect (PAE). The drug-resistance test demonstrated that Z33 possessed a narrow mutant selection window and lower propensities to select resistance than that of tiamulin. Cytochrome P450 (CYP450) inhibition assay determined that the inhibitory effect of Z33 was similar to that of tiamulin against the activity of CYP3A4, and was lower than that of tiamulin on the activity of CYP2E1. Toxicity determination showed that both Z33 and tiamulin displayed low cytotoxicity of RAW264.7 cells. Furthermore, Z33 was found to be a high-security compound with a 50% lethal dose (LD₅₀) above 5000 mg/kg in the acute oral toxicity test in mice. In an in vivo antibacterial activity test, Z33 displayed better therapeutic effectiveness than tiamulin in the neutropenic mouse thigh infection model. In summary, Z33 was worthy of further development as a highly effective and safe antibiotic agent against MRSA infection.