Intracellular Staphylococcus aureus persisters upon antibiotic exposure

Unraveling persistent bacteria: Formation, niches, and eradication strategies

Persistent bacteria (persisters) are phenotypic variants that emerge either randomly or in response to a range of adverse environmental conditions. Persistence represents a state whereby a subpopulation of microorganisms can spontaneously enter a "dormant" state in response to environmental factors, while simultaneously exhibiting elevated tolerance to antimicrobial agents. This review provides the current definition of bacterial persistence and summarizes the mechanisms of persisters formation as well as the various niches of bacterial persistence encountered in clinical practice. Strategies targeting persisters are outlined, including but not limited to direct killing, awakening of persistent bacteria, combined clearance, and inhibition of persistence formation, and we conclude by proposing challenges and solutions for addressing bacterial persistence in current clinical practice.

Important Role of Triphenylamine in Modulating the Antibacterial Performance Relationships of Antimicrobial Peptide Mimics by Alkyl Chain Engineering

Multidrug resistance (MDR) bacteria pose a serious threat to human health, and the development of effective antimicrobial drugs is urgent. Herein, we used alkyl chain engineering to design and synthesize two series of antimicrobial peptide mimics with distinct cores: triphenylamine quaternary ammonium derivatives (TPQs) and diphenylethene quaternary ammonium derivatives (BPQs), and we investigated the effect of varying the alkyl chain lengths on antibacterial activity. We found that the introduction of a triphenylamine group significantly enhances the antibacterial activity of short-chain dimethyl quaternary ammonium derivatives while maintaining their excellent biocompatibility. Most notably, TPQ-1 exhibited negligible invasiveness toward living cells and possesses good antimicrobial activities, with good efficacy against biofilms and persisters. Moreover, TPQ-1 exhibited good antimicrobial effects in vivo and significantly accelerated the healing process of methicillin-resistant Staphylococcus aureus-infected wounds. This work promotes the practical application of antimicrobial peptide mimics and triphenylamine derivatives.

Effect of host microenvironment and bacterial lifestyles on antimicrobial sensitivity and implications for susceptibility testing

Bacterial infections remain a major global health issue, with antimicrobial resistance (AMR) worsening the crisis. However, treatment failure can occur even when bacteria show antibiotic susceptibility in diagnostic tests. We explore factors such as phenotypic resilience, bacterial lifestyles such as biofilms, and differences between laboratory tests and real infection sites, highlighting the need for improved platforms to better predict treatment outcomes, and reviewing emerging technologies aimed at improving susceptibility testing.

Antibacterial Peptides-Produced Cell Hydrogel Eliminates Intracellular Pathogens and Remodels Immune Microenvironment for Osteomyelitis Therapy

Featuring bacterial invasion and colonization within cells, chronic infection-induced immune suppression, and inflammatory cell infiltration, osteomyelitis is currently an intractable and recurrent bone disease. In this study, an injectable hydrogel that gels in situ and is loaded with engineered antimicrobial cells (LL37-MSC@OCAHM) is developed. This anti-inflammatory hydrogel not only maintains cell activity in the inflammatory environment but also releases magnesium ions (Mg2+) to promote the differentiation of MSCs into bone-forming cells, contributing to bone mass formation, enhancing bone repair, and accelerating bone healing. The engineered cells continuously produce antimicrobial peptides of LL37, which effectively kill both extracellular and intracellular bacteria at the osteomyelitis site. Additionally, cell hydrogel also modulates the immune response by shifting the osteomyelitis environment from pro-inflammatory to anti-inflammatory, reducing the infiltration of immune cells and myeloid-derived suppressor cells (MDSCs). We also demonstrated its ability to activate immune responses and generate immune memory, thereby preventing the recurrence of secondary infections. This study introduces an engineered cell-based approach that combines active antimicrobial effect, immune modulation, and bone repair, for effectively eliminating osteomyelitis infections and preventing recurrence.

Sulfamethoxazole-trimethoprim plus rifampicin combination therapy for methicillin-resistant Staphylococcus aureus infection: An in vitro study

Methicillin-resistant Staphylococcus aureus (MRSA) is highly drug-resistant. The current Japanese guidelines (2019 edition) for managing and treating MRSA infections mention alternative anti-MRSA agents, including sulfamethoxazole-trimethoprim (ST) and rifampicin (RFP). Both ST and RFP are oral drugs and are expected to be effective alternatives to anti-MRSA drugs in clinical cases where anti-MRSA drugs are not indicated. Although guidelines for treating MRSA infections describe the efficacy of ST-RFP combination therapy and although it is used in clinical practice, only a limited number of in vitro studies have demonstrated its efficacy in pharmacokinetic/pharmacodynamic models. This study aimed to investigate the efficacy of the combination therapy of ST-RFP against MRSA in some in vitro models, including a pharmacokinetic/pharmacodynamic model. The MRSA strains obtained were subjected to antibiotic susceptibility tests. A checkerboard assay for drug combination synergy of ST-RFP was performed. Furthermore, a chemostat model was used to validate the combination therapy of ST-RFP as an in vitro pharmacokinetic/pharmacodynamic model. Viable cell counts and antibiotic concentrations were measured. The checkerboard assay showed that the ST-RFP combination had an additive effect on all strains (the lowest fractional inhibitory concentration index ranged from 0.63 to 1.00). The in vitro chemostat model demonstrated the usefulness of the combination of ST-RFP against MRSA, especially in ST-resistant strains. Regrowth of MRSA was observed in RFP monotherapy but not in the ST-RFP combination therapy. This study demonstrated the potential effectiveness of the ST-RFP combination against ST-resistant MRSA, providing important foundational data that may support future clinical investigations.

Disrupting cross-adaptation in high-risk MRSA: Sanguinarine as a multi-effective stress sensitizer for environmental and food safety

Methicillin-resistant Staphylococcus aureus (MRSA) represents a significant public health concern owing to its formidable antibiotic resistance and robust capacity for biofilm formation. The cross-adaptation mechanism enables MRSA to develop tolerance to environmental stressors such as antibiotics, acid, heat and osmotic pressure, leading to the persistence infections and environmental contamination. The cross-adaptation mechanism enables MRSA to develop tolerance to environmental stressors, such as antibiotics, acid, heat and osmotic pressure, leading to the persistence infections and environmental contamination. Here, we identified 261 strains of S. aureus and 9 high-risk MRSA from the environment of dairy farms and raw milk. The natural product Sanguinarine (SAN), derived from feed additives, exhibits effective anti-MRSA and anti-biofilm activity. Notably, SAN enhances the sensitivity of MRSA to antibiotics, acid, heat, and osmotic pressure by disrupting the cross-adaptation mechanism. Mechanistic investigations revealed that SAN significantly reduces the transcriptional level of type I (dnaK, groEL, etc.) and type III (clpB, clpP, etc.) heat stress response genes while markedly upregulating type II (σB) gene. Furthermore, SAN upregulates Na+/H+ antiporters activity, F0F1-ATPase activity and purine metabolism, while broadly downregulating DNA damage repair genes and disrupting ribosomal function. Additionally, SAN induces non-synonymous mutations in key stress response factors ClpB/L, leading to a loss of conformational homeostasis. SAN elicits a distinct stress response compared to environmental stressors, weakening MRSA's resilience and demonstrating promising capabilities for MRSA clearance and biofilm inhibition. Overall, SAN provides an effective strategy for the clearance of high-risk MRSA and the assurance of public health security.

Artesunate Perturbs GTP Binding of the Conserved GTPase Obg Thereby Alleviating Antibiotic Resistance in Methicillin-Resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is an important nosocomial pathogen that causes various secondary infections among hospital-associated patients. The pathogen is challenging to treat due to its resistance to a wide spectrum of antibiotics, including the last-resort antibiotic vancomycin and newly developed drugs, such as linezolid and daptomycin. While the invention of entirely new drugs to combat MRSA infection seems almost impossible, potentiating the efficacy of conventional antibiotics is critical. Our article explores the novel application of the antimalarial drug artesunate, which enhances the efficacy of vancomycin and cefoxitin in treating MRSA infections. We focused on ObgSa, a conserved GTPase in MRSA, and found that artesunate selectively binds to its GTP-binding pocket. We further evaluated the GTP-binding activity and metal dependence (specifically, Mg2+) of this conserved GTPase. In silico analysis identified several threonine residues essential for GTP binding, which were subsequently mutated to assess their role in GTP binding. As shown in the analysis, these mutations significantly impacted both the GTP binding and hydrolysis functions of ObgSa. Notably, these threonine residues were also crucial for artesunate binding within the GTP-binding domain. When the effect of artesunate was assessed, the drug competitively inhibited GTP binding and hydrolysis of the GTPase. This result was manifested as reduced antibiotic tolerance, disruption of biofilms, and a decrease in persister cells─critical factors in chronic infections. In summary, our research presents an innovative strategy to combat antimicrobial resistance through artesunate, highlighting its potential effectiveness in eradicating infections.

Mixed Infections in the Female Lower Genital Tract: Unlocking the Current Landscape and Future Directions

Understanding mixed infections in the female lower genital tract is a critical challenge in modern infection research. The interplay of multiple pathogens complicates disease progression, often resulting in treatment failure, recurrent infections, and significant public health and economic burdens. These infections are further exacerbated by disrupted host immune responses, which hinder the recovery of the vaginal microecosystem. Additionally, microbial biofilms-a fundamental mode of pathogen coexistence-contribute to the persistence and drug resistance of these infections, complicating management strategies. This review examines the pathogenesis, diagnosis, and treatment of mixed infections in the female lower genital tract while exploring potential avenues for future research. These findings emphasize the need for greater focus on these infections and offer insights to enhance further research in this area.

Antibiotic-recalcitrant Salmonella during infection

Antibiotic-recalcitrant infections, defined as the prolonged carriage of pathogenic bacteria even in the presence of antibiotics, are often caused by bacteria that are genetically susceptible to the drug. These recalcitrant bacteria fail to proliferate in the presence of antibiotics but remain viable such that they may recolonize their niche following antibiotic withdrawal. Significant progress has been made in our understanding of antibiotic-recalcitrant Salmonella, which are thought to be the source of infection relapse. In recent years, it has been shown that recalcitrant bacteria manipulate host immune defences and could directly contribute to the spread of antimicrobial resistance. In this Review, we provide an overview of what is currently known about the antibiotic recalcitrance of Salmonella during infection and highlight knowledge gaps requiring additional research in the future.

Disruption of sulfur transferase complex increases bacterial intramacrophage persistence

Bacterial persisters contribute significantly to clinical treatment failure and relapse. These cells could resist antibiotic treatment via transient phenotypic and gene expression alterations. We conducted a high-throughput screening of Salmonella Typhimurium transposon mutants to identify key genes for intramacrophage antibiotic persistence. The results show that a sulfur transferase complex encoded by yheM, yheL, yheN, trmU and yhhP are involved in bacterial intramacrophage antibiotic persistence. Salmonella could persist in macrophages by downregulating the expression of the sulfur transferase complex during exposure to high concentrations of antibiotics, and even in a persistent infection mouse model. Mechanistically, deletion of yheM increases reactive nitrogen species (RNS) in the exponential phase, which inhibits bacterial respiration and ATP generation. In contrast, absence of yheM promotes persister formation by elevating (p)ppGpp levels in the stationary phase. Taken together, our data demonstrate that bacteria use the sulfur transferase to coordinate intramacrophage replication and persistence for adaptation to various environmental stresses. These findings reveal the role of the sulfur transferase complex in bacterial intramacrophage persistence and provide a promising target for antibacterial infection therapy.

Halogen anion modulated metal-organic frameworks with enhanced nanozyme activities for bacterial biofilm disruption

There is an urgent need to develop new nanozymes with enhanced catalytic activities to combat bacterial infections, which have become increasingly challenging due to the misuse of antibiotics and the difficulties of new antibiotic discovery. Here, we employed a new strategy against bacterial biofilms by introducing halide anions to modulate the crystal facets of ZIF-L metal-organic frameworks (MOFs) and then loading chloroquine to form Ch@ZIF-L. The modulation of crystal facets significantly enhanced the oxidase activities of ZIF-L, which can be significantly changed by modulation of its crystal facets, with the hexagonal ZIF-L (ZIF-L-H-Cl) structure showing the highest oxidase activity. At pH 6.0, over 80% of chloroquine was released from Ch@ZIF-L-H-Cl within 8 hours, altering the DNA conformation of bacterial biofilms and disrupting the extracellular polymeric substances (EPSs). The generation of singlet oxygen catalyzed by ZIF-L-H-Cl can effectively kill bacteria at the infected wound site. The composite nanozyme of Ch@ZIF-L-H-Cl, when treated at 100 μg mL-1, exhibited no adverse effects on normal cell growth or hemolysis. Our in vivo experiments demonstrated an 85% reduction of the wound area by day 8 and a rapid recovery of body weight in mice with wounds infected with Staphylococcus aureus (S. aureus) biofilms. Furthermore, substantial reductions in bacterial counts were observed in both wounds and blood samples in the mice, highlighting the great potential of Ch@ZIF-L-H-Cl in combating bacterial biofilm infections.

Tissue geometry spatiotemporally drives bacterial infections

Epithelial tissues serve as the first line of host against bacterial infections. The self-organization of epithelial tissues continuously adapts to the architecture and mechanics of microenvironments, thereby dynamically impacting the initial niche of infections. However, the mechanism by which tissue geometry regulates bacterial infection remains poorly understood. Here, we showed geometry-guided infection patterns of bacteria in epithelial tissues using bioengineering strategies. We discovered that cellular traction forces play a crucial role in the regulation of bacterial invasive sites and marginal infection patterns in epithelial monolayers through triggering co-localization of mechanosensitive ion channel protein Piezo1 with bacteria. Further, we developed precise mechanobiology-based strategies to potentiate the antibacterial efficacy in animal models of wound and intestinal infection. Our findings demonstrate that tissue geometry exerts a key impact on mediating spatiotemporal infections of bacteria, which has important implications for the discovery and development of alternative strategies against bacterial infections.

Broad-spectrum antimicrobial activity and in vivo efficacy of SK1260 against bacterial pathogens

Introduction

Antimicrobial resistance (AMR) is a growing global health concern, necessitating the development of novel therapeutic agents. Antimicrobial peptides (AMPs) have emerged as promising candidates due to their broad-spectrum activity and lower resistance potential. SK1260 is a newly developed AMP evaluated for its efficacy against Gram-positive and Gram-negative pathogens, including multidrug-resistant strains.

Methods

The antimicrobial activity of SK1260 was assessed through minimum inhibitory concentration (MIC) assays against clinical and reference strains of Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Time-kill kinetics were performed to evaluate bactericidal activity over time. In vivo efficacy was determined using murine infection models, where bacterial burden, tissue pathology, and survival rates were assessed following peptide administration.

Results

SK1260 exhibited potent antibacterial activity, with MIC values ranging from 3.13 to 12.5 µg/mL. Time-kill studies demonstrated dose- and time-dependent bactericidal effects, achieving complete bacterial clearance at concentrations ≥1× MIC, comparable to ciprofloxacin. In vivo studies revealed significant reductions in bacterial loads in vital organs, reduced histopathological damage, and improved survival in treated mice. Peptide treatment restored normal tissue architecture and showed efficacy equivalent to standard antibiotic therapy.

Discussion

The study establishes SK1260 as a promising broad-spectrum antimicrobial agent with efficacy against drug-resistant pathogens. Its ability to reduce bacterial burden and protect tissue integrity in vivo highlights its therapeutic potential. Further preclinical development and clinical trials are warranted to explore SK1260 as a viable alternative in the fight against AMR.

Methicillin-sensitive Staphylococcus aureus lineages contribute towards poor patient outcomes in orthopaedic device-related infections

Staphylococci are the most common cause of orthopaedic device-related infections (ODRIs), with Staphylococcus aureus responsible for a third or more of cases. This prospective clinical and laboratory study investigated the association of genomic and phenotypic variation with treatment outcomes in ODRI isolates. Eighty-six invasive S. aureus isolates were collected from patients with ODRI, and clinical outcome was assessed after a follow-up examination of 24 months. Each patient was then considered to have been 'cured' or 'not cured' based on predefined clinical criteria. Whole-genome sequencing and molecular characterization identified isolates belonging to globally circulating community- and hospital-acquired lineages. Most isolates were phenotypically susceptible to methicillin and lacked the staphylococcal cassette chromosome mec cassette [methicillin-susceptible S. aureus (MSSA); 94%] but contained several virulence genes, including toxins and biofilm genes. Whilst recognizing the role of the host immune response, we identified genetic variance, which could be associated with the infection severity or clinical outcome. Whilst this and several other studies reinforce the role antibiotic resistance [e.g. methicillin-resistant S. aureus (MRSA) infection] has on treatment failure, it is important not to overlook MSSA that can cause equally destructive infections and lead to poor patient outcomes.

Alternative approaches to antibiotics in the control of mastitis in dairy cows: a review

Bovine mastitis is the most widespread and economically burdensome condition affecting dairy herds worldwide, causing substantial financial losses in the livestock and dairy sectors. The main approach to treating mastitis in dairy cows is based on the administration of antibiotics. However, their widespread use has led to the emergence of antibiotic-resistant pathogens, and thus to numerous food safety problems. Consequently, a growing body of scientific research has been directed towards exploring new and effective therapeutic alternatives for the management of bovine mastitis, which could replace conventional antibiotic therapy. This review surveys the various alternative strategies employed in the prevention and treatment of mastitis in dairy cattle. These strategies include nanoparticle therapy, bacteriophage therapy, vaccination, phytotherapy, the use of animal proteins, probiotics and bacteriocins. In addition, the potential synergistic effects resulting from the combination of these treatments has shown real benefits that will be highlighted.

A hollow fiber infection model to study intracellular and extracellular antibiotic activity against Staphylococcus aureus

Antibiotic activity against intracellular pathogens is commonly evaluated in static models that do not reproduce plasma concentration fluctuations. However, efficacy is influenced by exposure conditions, related to drug pharmacokinetic profile. This study developed and validated an intracellular pharmacodynamic model using the hollow fiber system, the gold standard for evaluating extracellular antibiotic activity. The activity of fluoroquinolones, i.e., bactericidal antibiotics with intracellular tropism, was studied against intracellular Staphylococcus aureus, involved in persistence/recurrence of infections. In this model, moxifloxacin was more effective than in static conditions (0.87 log10 killing gain), while ciprofloxacin kill rate was slower (18 vs. 12 h to achieve 1 log10 killing). These differences were linked to the Cmax/MIC ratio, which was 2.5-fold higher for moxifloxacin but 3.4-fold lower for ciprofloxacin in dynamic vs. static conditions. This model could be applied to other drugs, cell types, or pathogens, offering a tool for optimizing dosing schemes and considering intracellular reservoirs.

Investigation and Analysis of Staphylococcus aureus Contamination in Food in Yantai City, China: Based on a 14-Year Continuous Monitoring

Staphylococcus aureus is a foodborne zoonotic pathogen that threatens food safety and public health. However, few people have conducted long-term and systematic studies on S. aureus contamination in food in Yantai City. To investigate the contamination situation of S. aureus in food and improve the ability of early warning and control of foodborne diseases, a total of 2384 samples from 17 categories were collected from 13 monitoring points in Yantai City, from 2010 to 2023. Forty-four samples were positively detected for S. aureus, with a detection rate of 1.85% (44/2384). The detection rate of S. aureus was highest in Zhifu District (4.12%), followed by Penglai District (2.45%), Zhaoyuan District (2.37%), Kaifa District (2.19%), and Longkou District (1.98%). Positive detection rates were higher in frozen rice and flour products at 8.82% (6/68), quick-frozen dishes at 5.56% (1/18), aquatic products at 4.05% (3/74), and meat and meat products at 3.55% (27/760). Positive detection rates in samples from the first, second, third, and fourth quarters were 0% (0/44), 2.21% (20/906), 2.13% (22/1033), and 0.50% (2/401), respectively. Positive detection rates in bulk and prepackaged samples were 2.33% (36/1546) and 0.95% (8/838), respectively, with statistically significant differences (χ2 = 5.66, p < 0.05). Positive detection rates were significantly different for samples collected from different sampling stages, of which at production and processing stages was 7.78% (20/257), catering stages 1.38% (10/727), and distribution stages 1% (14/1400) (χ2 = 56.41, p < 0.05). Frozen rice and flour products, quick-frozen dishes, aquatic products, and meat and meat products are the main food products contaminated with S. aureus, and the resulting secondary contamination is a hidden danger for the occurrence of foodborne diseases, which should be given sufficient attention.

Piceatannol and its analogues alleviate Staphylococcus aureus pathogenesis by targeting β-lactamase biofilms and α-hemolysin

β-Lactamases, biofilms and toxins pose challenges for combating S. aureus infection. Thus, identifying inhibitors that can restore bacterial sensitivity to antibiotics, destroy biofilms, and antitoxins is a promising way to develop alternative agents. In this study, we found that piceatannol (pit), along with its analogues resveratrol (ret) and pterostilbene (pts) bind with β-lactamase to inhibit its activity, and 96TYR, 58ILE and 66LYS were identified as the critical binding residues. Pit and pts reduced the ampicillin (Amp) and gentamicin (Gm) MICs against S. aureus and enhanced the bactericidal ability of Amp. Pit and its analogues inhibited the formation of S. aureus USA300. In addition, the pit analogues bound with α-hemolysin and suppressed the hemolysis activity of the bacterial culture supernatant. The mechanism analysis revealed that pit exhibited multiple potential binding modes with α-hemolysin. Pit significantly decreased the cytotoxicity and the adherence effect mediated by S. aureus and increased the survival rate of Galleria mellonella that infected with S. aureus, the pathological tissue damage of Galleria mellonella was alleviated by treatment with pit alone or in combination with Amp. Taken together, our findings identify promising compounds for the development of S. aureus infection inhibitors.

Metal Ion and Antibiotic Co-loaded Nanoparticles for Combating Methicillin-Rresistant Staphylococcus aureus-Induced Osteomyelitis

Methicillin-resistant Staphylococcus aureus (MRSA) causes osteomyelitis (OM), which seriously threatens public health due to its antimicrobial resistance. To increase the sensitivity of antibiotics and eradicate intracellular bacteria, a Zn2+ and vancomycin (Van) codelivered nanotherapeutic (named Man-Zn2+/Van NPs) was fabricated and characterized via mannose (Man) modification. Man-Zn2+/Van NPs exhibit significant inhibitory activity against extra- and intracellular MRSA and obviously decrease the minimum inhibitory concentration of Van. Man-Zn2+/Van NPs can be easily internalized by MRSA-infected macrophages and significantly accumulated in infected bone via Man-mediated targeting. In vivo experiments in a mouse OM model verified that Man-Zn2+/Van NPs significantly reduce the extra- and intracellular MRSA burden, improve gait patterns, increase bone mass, and decrease inflammatory cytokine expression. The antibacterial mechanism of Man-Zn2+/Van NPs includes destruction of the MRSA membrane, degeneration of intracellular proteins and DNA, inhibition of MRSA glycolysis, and intervention in the energy metabolism of bacteria. Overall, this metal-antibiotic nanotherapeutics strategy provides new insight for combating extra- and intracellular infections caused by MRSA-induced OM.

Biofilm Resilience: Molecular Mechanisms Driving Antibiotic Resistance in Clinical Contexts

Healthcare-associated infections pose a significant global health challenge, negatively impacting patient outcomes and burdening healthcare systems. A major contributing factor to healthcare-associated infections is the formation of biofilms, structured microbial communities encased in a self-produced extracellular polymeric substance matrix. Biofilms are critical in disease etiology and antibiotic resistance, complicating treatment and infection control efforts. Their inherent resistance mechanisms enable them to withstand antibiotic therapies, leading to recurrent infections and increased morbidity. This review explores the development of biofilms and their dual roles in health and disease. It highlights the structural and protective functions of the EPS matrix, which shields microbial populations from immune responses and antimicrobial agents. Key molecular mechanisms of biofilm resistance, including restricted antibiotic penetration, persister cell dormancy, and genetic adaptations, are identified as significant barriers to effective management. Biofilms are implicated in various clinical contexts, including chronic wounds, medical device-associated infections, oral health complications, and surgical site infections. Their prevalence in hospital environments exacerbates infection control challenges and underscores the urgent need for innovative preventive and therapeutic strategies. This review evaluates cutting-edge approaches such as DNase-mediated biofilm disruption, RNAIII-inhibiting peptides, DNABII proteins, bacteriophage therapies, antimicrobial peptides, nanoparticle-based solutions, antimicrobial coatings, and antimicrobial lock therapies. It also examines critical challenges associated with biofilm-related healthcare-associated infections, including diagnostic difficulties, disinfectant resistance, and economic implications. This review emphasizes the need for a multidisciplinary approach and underscores the importance of understanding biofilm dynamics, their role in disease pathogenesis, and the advancements in therapeutic strategies to combat biofilm-associated infections effectively in clinical settings. These insights aim to enhance treatment outcomes and reduce the burden of biofilm-related diseases.

Staphylococcus aureus induces mitophagy via the HDAC11/IL10 pathway to sustain intracellular survival

BACKGROUND

The immune evasion and prolonged survival of Staphylococcus aureus (S. aureus) within macrophages are key factors contributing to the difficulty in curing osteomyelitis. Although macrophages play a vital role as innate immune cells, the mechanisms by which S. aureus survives within them and suppresses host immune functions remain incompletely understood.

METHODS

This study employed confocal microscopy, flow cytometry, ELISA, and siRNA technology to assess the survival capacity of S. aureus within macrophages and the impact of inflammatory cytokines on its persistence. Proteomics was used to investigate the potential mechanisms and differential proteins involved in S. aureus intracellular survival. Additionally, confocal microscopy, flow cytometry, Mdivi-1 intervention, and Western blot were utilized to validate the role of mitophagy in supporting S. aureus survival. The study further explored how the HDAC11/IL10 axis enhances mitophagy to promote intracellular S. aureus survival by using HDAC11 overexpression, siRNA, and rapamycin intervention combined with confocal microscopy and flow cytometry.

RESULTS

The findings demonstrated that IL10 promotes mitophagy to clear mitochondrial reactive oxygen species (mtROS), thereby enhancing the intracellular survival of S. aureus within macrophages. Additionally, we discovered that the transcriptional repressor of IL10, HDAC11, was significantly downregulated during S. aureus infection. Overexpression of HDAC11 and the use of the autophagy activator rapamycin further validated that the HDAC11/IL10 axis regulates mitophagy via the mTOR pathway, which is essential for supporting S. aureus intracellular survival.

CONCLUSION

This study reveals that S. aureus enhances IL10 production by inhibiting HDAC11, thereby promoting mitophagy and mtROS clearance, which supports its survival within macrophages. These findings offer new insights into the intracellular survival mechanisms of S. aureus and provide potential therapeutic approaches for the clinical management of osteomyelitis.

Antimicrobial activity of octyl gallate nanoemulsion combined with photodynamic technology and its effect on food preservation

Photodynamic inactivation, as a safe and effective antimicrobial technology that does not damage the organoleptic properties of the food itself, decreases the use of preservatives and is gradually gaining attention in the food industry. This study selected octyl gallate (OG) as an antimicrobial photosensitizer with eucalyptus oil as the oil phase and prepared it as an octyl gallate nanoemulsion (OG-NE) to ensure the delivery of the photosensitizer. Escherichia coli and Staphylococcus aureus inactivation with the OG-NE combined with photodynamic technology, as well as the effect on the quality of food products, was investigated. The results showed the successful preparation and homogeneous distribution of the OG-NE with an encapsulation rate of 85.18 %. The OG-NE's ability to produce single oxygen (1O2) was significantly higher, as shown by 1O2 production. The OG-NE combined photodynamic technique confirmed the effectiveness of microbial removal, demonstrating a significant increase in reactive oxygen species (ROS) and the permeability of the cell membrane. The effect of the OG-NE combined photodynamic technology on perch (microbiology, pH, whiteness, water holding capacity, TVB-N and TBA) and litchi (weight loss, titratable acid and sugar content) preservation was assessed. Food preservation experiments revealed that the OG-NE combined photodynamic technology exhibited a positive effect on food quality. The results indicated that the combination of the OG-NE and photodynamic technology provided a new alternative strategy for the food industry in antimicrobial and preservation.

Hinokitiol potentiates antimicrobial activity of bismuth drugs: a combination therapy for overcoming antimicrobial resistance

Antimicrobial resistance (AMR) poses a significant global health threat, rendering many infections untreatable. To combat AMR, repurposing approved drugs has emerged as a cost-effective strategy. Bismuth drugs, when combined with antibiotics, have been proven to be effective against Helicobacter pylori, including antibiotic-resistant strains. However, bismuth drugs alone exhibit limited antimicrobial activity against a narrow spectrum of pathogens. Therefore, a novel approach to enhance the efficacy and broaden the antimicrobial spectrum of bismuth drugs is highly desirable. Herein, we show that a naturally occurring monoterpenoid, hinokitiol, could potentiate the antimicrobial activity of bismuth drugs. We demonstrate a strong synergy between hinokitiol and colloidal bismuth subcitrate (CBS) against various Gram-positive and Gram-negative bacterial strains, including methicillin-resistant Staphylococcus aureus (MRSA). Moreover, the combination of hinokitiol and CBS exhibits anti-biofilm activity by preventing biofilm formation and eliminating S. aureus persister cells. Importantly, the combination therapy demonstrates promising antimicrobial efficacy in murine infection models including skin wound, gastrointestinal and blood infections. Mechanistic studies reveal that hinokitiol enhances bismuth ion (Bi(iii)) accumulation and reduces intracellular iron levels. By using thermal proteome profiling combined with dynamic quantitative proteomics analysis, we demonstrate that the bismuth-hinokitiol combination propagated the bismuth binding and interfered with ribosome synthesis, the glycolysis process, impaired bacterial cell wall synthesis and pathogenesis in MRSA. Our finding highlights the potential of combinatorial hinokitiol and bismuth drugs in the fight against AMR.

Implant-Derived S. aureus Isolates Drive Strain-Specific Invasion Dynamics and Bioenergetic Alterations in Osteoblasts

Background: Implants are integral to modern orthopedic surgery. The outcomes are good, but infections remain a serious issue. Staphylococcus aureus (S. aureus), along with Staphylococcus epidermidis, are predominant pathogens responsible for implant-associated infections, as conventional antibiotic treatments often fail due to biofilm formation or the pathogens' ability to invade cells and to persist intracellularly. Objectives: This study therefore focused on interactions of S. aureus isolates from infected implants with MG63 and SaOS2 osteoblasts by investigating the adhesion, invasion, and the impact on the bioenergetics of osteoblasts. Methods and Results: We found that the ability of S. aureus to adhere to osteoblasts depends on the isolate and was not associated with a single gene or expression pattern of characteristic adhesion proteins, and further, was not correlated with invasion. However, analysis of invasion capabilities identified better invasion conditions for S. aureus isolates with the SaOS2 osteoblastic cells. Interestingly, metabolic activity of osteoblasts remained unaffected by S. aureus infection, indicating cell survival. In contrast, respiration assays revealed an altered mitochondrial bioenergetic turnover in infected cells. While basal as well as maximal respiration in MG63 osteoblasts were not influenced statistically by S. aureus infections, we found increased non-mitochondrial respiration and enhanced glycolytic activity in the osteoblasts, which was again, more pronounced in the SaOS2 osteoblastic cells. Conclusions: Our findings highlight the complexity of S. aureus-host interactions, where both the pathogen and the host cell contribute to intracellular persistence and survival, representing a major factor for therapeutic failures.

K+-Responsive Nanoparticles with Charge Reversal and Gating Synergistic Effects for Targeted Intracellular Bacteria Eradication

Intracellular bacteria can evade the attack of the immune system and the bactericidal effects of most antibiotics due to the protective effect of the host cells. Herein, inspired by the stimuli-responsive behaviors of biological ion channels, a kind of synergistic cascade potassium ion (K+)-responsive nanoparticles gated with K+-responsive polymers is ingeniously designed to target intracellular bacteria and then control drug release. Due to the cooperative interaction of host-guest complexation and conformational transition of K+-responsive polymers, the grafted gates based on these polymers could recognize high K+ concentration to reverse the negatively charged nanoparticles into positively charged ones for targeting bacteria and subsequently inducing a switch from the hydrophobic shrinking "off" state to the hydrophilic stretching "on" state for drug release. The K+-responsive nanoparticles can effectively load antibiotics and be endocytosed into the infected cells, and K+-responsive gates can be actuated by a high intracellular K+ concentration. With the efficient synergistic cascade strategy, these K+-responsive nanocarriers can deliver antibiotics to the subcellular region where intracellular bacteria reside and show superior elimination efficiencies in vitro and in vivo than the free drug in delivering vancomycin. The K+-responsive nanocarriers are expected to improve the bioavailability of drugs and enhance their antibacterial efficacy.

Maltodextrin-derived nanoparticles resensitize intracellular dormant Staphylococcus aureus to rifampicin

Intracellular bacteria are recognized as a crucial factor in the persistence and recurrence of infections. The efficacy of current antibiotic treatments faces substantial challenges due to the dormant state formation of intracellular bacteria. In this study, we devised a strategy aimed at reverting intracellular dormant bacteria to a metabolically active state, thereby increasing their vulnerability to antibiotics. We found that oligosaccharides, especially maltodextrin (MD), can be absorbed by dormant S. aureus, leading to their revival and restoration of sensitivity to rifampicin (Rif). We then synthesized a reactive oxygen species (ROS)-responsive MD-prodrug by covalently binding MD with 4-(hydroxymethyl) phenylboronic acid pinacol ester (MD-PBAP) and prepared a ROS-responsive nanoparticles (MDNP) using a nanoprecipitation and self-assembly method. Once internalized by host cells, MDNP was degraded to MD, reactivating dormant S. aureus, and enhancing their susceptibility to Rif. More importantly, MDNP treatment restored the sensitivity of intracellular persistent S. aureus to Rif in both a reservoir transfer model and whole-body infection model. Additionally, MDNP have demonstrated excellent biocompatibility in both in vitro and in vivo settings. These results offer a promising therapeutic avenue for managing persistent intracellular bacterial infections by reviving and resensitizing intracellular dormant bacteria to conventional antibiotics.

Harnessing light-activated gallium porphyrins to combat intracellular Staphylococcus aureus using an in vitro keratinocyte infection model

Staphylococcus aureus (S. aureus) can survive inside nonprofessional phagocytes such as keratinocytes, enabling it to evade antibiotics and cause recurrent infections once treatment stops. New antibacterial strategies to eliminate intracellular, multidrug-resistant bacteria are needed. This study used a keratinocyte model infected with methicillin-resistant S. aureus (MRSA) to test light-activated compounds, specifically heme-mimetic gallium (III) porphyrin (Ga3+CHP) and visible light, known as antimicrobial photodynamic inactivation (aPDI), for eliminating intracellular MRSA. Ga3+CHP was found to accumulate more in infected cells, particularly within lysosomal structures where MRSA resides. Flow cytometry and fluorescence microscopy revealed significant colocalization of MRSA and Ga3+CHP. Under aPDI, MRSA showed reduced adhesion to host cells and a 70% reduction in the GFP signal from intracellular bacteria. Additionally, light-activated Ga3+CHP significantly decreased the number of extracellular bacteria, reducing the potential for further infection. This study is the first to analyze aPDI toxicity in real time within an infection model, demonstrating that this method is neither cytotoxic nor phototoxic.

A prophage competition element protects Salmonella from lysis

Most bacteria are polylysogens that carry multiple prophages integrated into the chromosome. These prophages confer advantages to their bacterial host, yet also pose a lethal threat as they can reactivate and enter a lytic cycle. DNA damage of the bacterial host is a common trigger of prophage lytic cycles. Because DNA damage is frequently experienced by bacterial pathogens exposed to host immune defenses, prophage activation may be common during infection. Investigating the consequences of prophage induction in Salmonella, we discover a prophage competition element in the Gifsy-1 prophage that we name ribonuclease effector module with ATPase, inhibitor, and nuclease (RemAIN) because it blocks the lytic cycles and release of viral particles of co-resident prophages. Intramacrophage Salmonella persisters, a subpopulation that incurs DNA damage, experience prophage reactivation and subsequent RemAIN activation, which influences Salmonella persisters and macrophage response to infection. Our findings reveal a multi-layered host-pathogen arms race in which prophage-prophage competition influences bacterial persistence and the mammalian immune response.

Metabolites augment oxidative stress to sensitize antibiotic-tolerant Staphylococcus aureus to fluoroquinolones

If left unchecked, infections involving antibiotic-refractory bacteria are expected to cause millions of deaths per year in the coming decades. Beyond genetically resistant bacteria, persisters, which are genetically susceptible cells that survive antibiotic doses that kill the rest of the clonal population, can potentially contribute to treatment failure and infection relapse. Stationary-phase bacterial cultures are enriched with persisters, and it has been shown that stimulating these populations with exogenous nutrients can reduce persistence to different classes of antibiotics, including topoisomerase-targeting fluoroquinolones (FQs). In this study, we show that adding glucose and amino acids to nutrient-starved Staphylococcus aureus cultures enhanced their sensitivity to FQs, including delafloxacin (Dela)-a drug that was recently approved for treating staphylococcal infections. We found that while the added nutrients increased nucleic acid synthesis, this increase was not required to sensitize S. aureus to FQs. We further demonstrate that addition of these nutrients increases membrane potential and the ability to generate harmful reactive oxygen species (ROS) during FQ treatment. Chelating iron, scavenging hydroxyl radicals, and limiting oxygenation during FQ treatment and during recovery following FQ treatment rescued nutrient-stimulated S. aureus. In all, our data suggest that while nutrient stimulation increases the activity of FQ targets in stationary-phase S. aureus, the resulting generation of ROS, presumably made possible through metabolic upregulation, is the primary driver of increased sensitivity to these drugs.IMPORTANCEStaphylococcus aureus causes many chronic and relapsing infections because of its ability to endure host immunity and antibiotic therapy. While several studies have focused on the nutrient requirements for the formation and maintenance of staphylococcal infections, the effects of the nutrient environment on bacterial responses to antibiotic treatment remain understudied. Here, we show that adding nutrients to starved S. aureus activates biosynthetic processes, including DNA synthesis, but it is the generation of harmful reactive oxidants that sensitizes S. aureus to DNA topoisomerase-targeting FQs. Our results suggest that the development of approaches aimed at perturbing metabolism and increasing oxidative stress can potentiate the bactericidal activity of FQs against antibiotic-tolerant S. aureus.

Inducing programmed cell death trough MazEF system to combat Staphylococcus aureus: A non-antibiotic treatment candidate

The aim of the present study was to evaluate the role of extracellular death factor (EDF) derived from Escherichia coli in the induction of programmed cell death (PCD) in methicillin-resistant and -susceptible Staphylococcus aureus (MRSA and MSSA). The confirmation of bacterial strains as well as the minimum inhibitory concentration (MIC) test were performed according to CLSI, 2022. The extraction and efficacy determination of EDF as well as the CFU assessment were done. The expression of mazE and mazF gens in different conditions was evaluated by Real-time PCR. The likely formation of persister cells from MRSA and MSSA, and the possible synthesis of EDF in old cultures of these pathogens was evaluated, as well. The combination of EDF of two E. coli strains and sub-MIC rifampin reduced the CFUs of MRSA and MSSA strains in mid-logarithmic growth phase while increased the expression of mazF several times more than mazE gene. The expression of these genes in different conditions were unlike. EDF was produced in the old cultures of MRSA and MSSA. The supernatant of E. coli 25922 was more powerful than the clinical strain ones to decrease the CFUs of the MRSA and MSSA. The EDF derived from E. coli in combination with sub-MIC rifampin could induce PCD in MRSA and MSSA through activation of the MazEF system. This phenomenon could be exploited as a non-antibiotic treatment candidate to combat the infections caused by the antibiotic-resistant pathogens. However, more studies should be performed in this regard.

Doxifluridine effectively kills antibiotic-resistant Staphylococcus aureus in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a leading cause of morbidity and mortality globally, often exacerbated by infections such as methicillin-resistant Staphylococcus aureus (MRSA). The rise in antibiotic-resistant strains complicates treatment and underscores the need for novel therapeutic drugs. In this paper, we further investigated the antimicrobial potential of a fluoropyrimidine anticancer drug doxifluridine against multidrug-resistant S. aureus. Determination of minimum inhibitory concentration (MIC) or minimum bactericidal concentration (MBC), monitoring of growth curve, time-kill assays, biofilm bactericidal assays, and chequerboard studies were conducted to evaluate the antibacterial efficacy of doxifluridine. Safety was assessed via hemolysis and cytotoxicity assays, and an in vivo Galleria mellonella larvae model was employed to test protective effects. Doxifluridine demonstrated significant antibacterial activity against clinical multidrug resistance (MDR) S. aureus isolates, with MIC and MBC values ranging from 0.5 to 2 µg/mL and 1 to 4 µg/mL, respectively. The results revealed doxifluridine's potent bactericidal effects within 8 hours. Moreover, doxifluridine-treated bacteria showed a substantial reduction in biofilm mass and viability. Furthermore, chequerboard assays indicated synergistic interactions between doxifluridine and other antibiotics, reducing MIC values by two- to eightfold. More importantly, safety evaluations confirmed that doxifluridine did not exhibit hemolytic toxicity or cytotoxicity. Finally, doxifluridine significantly increased the survival rate of MRSA-infected G. mellonella larvae in vivo. In brief, doxifluridine exhibited promising in vitro and in vivo antibacterial activity against MRSA, suggesting its potential as a repurposed drug for treating resistant bacterial infections in COPD patients.IMPORTANCEThe study provides robust evidence for the antibacterial efficacy of doxifluridine against Methicillin-resistant Staphylococcus aureus in chronic obstructive pulmonary disease (COPD) patients. Its rapid action, ability to disrupt biofilms, and synergistic effects with other antibiotics, combined with a favorable safety profile, highlight its potential as a repurposed therapeutic agent. Future clinical trials will be essential to confirm these findings and pave the way for its integration into clinical practice. This work not only provides candidate for tackling the management of bacterial infections in COPD but also exemplifies the potential of drug repurposing in combating antibiotic-resistant infections.

Tetracycline and Oxacillin Act Synergistically on Biofilms and Display Increased Efficacy In Vivo Against Staphylococcus aureus

Oxacillin (bactericidal) and tetracycline (bacteriostatic) are clinically relevant antibiotics that are routinely prescribed to treat Staphylococcus aureus infections but not conventionally used in combination. There is an urgent need for treatment regimens that can act upon biofilms during infection, associated with chronic infections on indwelling devices, as well as acute planktonic (systemic) infection. Here we show that in an in vitro model oxacillin and tetracycline act synergistically against S. aureus UAMS-1 biofilms, reducing the concentration of both antibiotics necessary to eradicate an established biofilm. Using an in vivo zebrafish larval infection model with S. aureus NewHG, they display improved bacterial clearance compared to each drug alone and can counteract a loss of host phagocytes, an important innate defence against S. aureus. In these cases, the bacteriostatic nature of tetracycline enhances rather than dampens the bactericidal action of oxacillin, although an exact mechanism remains to be elucidated. We suggest a dual therapy could be of clinical use against biofilm-forming S. aureus and has a potential use in patients with a compromised immune system.

Discovery of novel dihydropyrrolidone-thiadiazole compound crosstalk between the YycG/F two-component regulatory pathway and cell membrane homeostasis to combat methicillin-resistant Staphylococcus aureus

The rapid emergence and spread of multidrug-resistant (MDR) Gram-positive pathogens present a significant challenge to global healthcare. Methicillin-resistant Staphylococcus aureus (MRSA) is a particular concern because of its high resistance to most antibiotics. Based on our previously reported chemical structure of compound 62, a series of novel derivatives were synthesized and evaluated for their antibacterial activities. We found that some of these derivatives displayed effective antibacterial activity against Gram-positive pathogens, with minimal cytotoxicity (CC50>100 μM) and hemolytic activity (HC50>200 μM). Among these derivatives, the minimum inhibitory concentration (MIC) of 62-7c against Gram-positive bacterial isolates ranged from 6.25 to 25 μM. This derivative also exhibited significant synergistic antibacterial effects with daptomycin both in vitro and in vivo, with an ability to eradicate planktonic and persister cells of MRSA. Additionally, 62-7c inhibited biofilm formation and eradicated mature biofilms of MRSA. Mechanistic studies revealed that 62-7c inhibited the YycG kinase activity and disrupted the cell membrane by binding to cardiolipin (CL), leading to cell death. Importantly, no development of drug resistance was observed even after 20 serial passages. Furthermore, 62-7c exhibited high biosafety and potent effectiveness in combating infections in both mouse pneumonia and mouse wound models infected with MRSA. Thus, our study revealed that 62-7c has the potential to serve as a novel antibacterial agent for treating MRSA infections.

Proton motive force and antibiotic tolerance in bacteria

Bacterial antibiotic tolerance is a decades-old phenomenon in which a bacterial sub-population, commonly known as persisters, does not respond to antibiotics and remains viable upon prolonged antimicrobial treatment. Persisters are detectable in populations of bacterial strains that are not antibiotic-resistant and are known to be responsible for treatment failure and the occurrence of chronic and recurrent infection. The clinical significance of antibiotic tolerance is increasingly being recognized and comparable to antibiotic resistance. To eradicate persisters, it is necessary to understand the cellular mechanisms underlying tolerance development. Previous works showed that bacterial antibiotic tolerance was attributed to the reduction in metabolic activities and activation of the stringent response, SOS response and the toxin-antitoxin system which down-regulates transcription functions. The latest research findings, however, showed that decreased metabolic activities alone do not confer a long-lasting tolerance phenotype in persisters, and that active defence mechanisms such as efflux and DNA repair are required for the long-term maintenance of phenotypic tolerance. As such active tolerance-maintenance mechanisms are energy-demanding, persisters need to generate and maintain the transmembrane proton motive force (PMF) for oxidative phosphorylation. This minireview summarizes the current understanding of cellular mechanisms essential for prolonged expression of phenotypic antibiotic tolerance in bacteria, with an emphasis on the importance of generation and maintenance of PMF in enabling proper functioning of the active tolerance mechanisms in persisters. How such mechanisms can be utilized as targets for the development of anti-persister strategies will be discussed.

Phenotypic Heterogeneity in Pathogens

Pathogen diversity within an infected organism has traditionally been explored through the lens of genetic heterogeneity. Hallmark studies have characterized how genetic diversity within pathogen subpopulations contributes to treatment escape and infectious disease progression. However, recent studies have begun to reveal the mechanisms by which phenotypic heterogeneity is established within genetically identical populations of invading pathogens. Furthermore, exciting new work highlights how these phenotypically heterogeneous subpopulations contribute to a pathogen population better equipped to handle the complex and fluctuating environment of a host organism. In this review, we focus on how bacterial pathogens, including Staphylococcus aureus, Salmonella typhimurium, Pseudomonas aeruginosa, and Mycobacterium tuberculosis, establish and maintain phenotypic heterogeneity, and we explore recent work demonstrating causative links between this heterogeneity and infection outcome.

Antibody-antibiotic conjugate targeted therapy for orthopedic implant-associated intracellular S. aureus infections

INTRODUCTION

Treating orthopedic implant-associated infections, especially those caused by Staphylococcus aureus (S. aureus), remains a significant challenge. S. aureus has the ability to invade host cells, enabling it to evade both antibiotics and immune responses during infection, which may result in clinical treatment failures. Therefore, it is critical to identify the host cell type of implant-associated intracellular S. aureus infections and to develop a strategy for highly targeted delivery of antibiotics to the host cells.

OBJECTIVES

Introduced an antibody-antibiotic conjugate (AAC) for the targeted elimination of intracellular S. aureus.

METHODS

The AAC comprises of a human monoclonal antibody (M0662) directly recognizes the surface antigen of S. aureus, Staphylococcus protein A, which is conjugated with vancomycin through cathepsin-sensitive linkers that are cleavable in the proteolytic environment of the intracellular phagolysosome. AAC, vancomycin and vancomycin combined with AAC were used in vitro intracellular infection and mice implant infection models. We then tested the effect of AAC in vivo and in vivo by fluorescence imaging, in vivo imaging, bacterial quantitative analysis and bacterial biofilm imaging.

RESULTS

In vitro, it was observed that AAC captured extracellular S. aureus and co-entered the cells, and subsequently released vancomycin to induce rapid elimination of intracellular S. aureus. In the implant infection model, AAC significantly improved the bactericidal effect of vancomycin. Scanning electron microscopy showed that the application of AAC effectively blocked the formation of bacterial biofilm. Further histochemical and micro-CT analysis showed AAC significantly reduced the level of bone marrow density (BMD) and bone volume fraction (BV/TV) reduction caused by bacterial infection in the distal femur of mice compared to vancomycin treatment alone.

CONCLUSIONS

The application of AAC in an implant infection model showed that it significantly improved the bactericidal effects of vancomycin and effectively blocked the formation of bacterial biofilms, without apparent toxicity to the host.

A natural killer cell mimic against intracellular pathogen infections

In the competition between the pathogen infection and the host defense, infectious microorganisms may enter the host cells by evading host defense mechanisms and use the intracellular biomolecules as replication nutrient. Among them, intracellular Staphylococcus aureus relies on the host cells to protect itself from the attacks by antibiotics or immune system to achieve long-term colonization in the host, and the consequent clinical therapeutic failures and relapses after antibiotic treatment. Here, we demonstrate that intracellular S. aureus surviving well even in the presence of vancomycin can be effectively eliminated using an emerging cell-mimicking therapeutic strategy. These cell mimics with natural killer cell-like activity (NKMs) are composed of a redox-responsive degradable carrier, and perforin and granzyme B within the carrier. NKMs perform far more effectivly than clinical antibiotics in treating intracellular bacterial infections, providing a direct evidence of the NK cell-mimicking immune mechanism in the treatment of intracellular S. aureus.

A host-directed adjuvant resuscitates and sensitizes intracellular bacterial persisters to antibiotics

There are two major problems in the field of antimicrobial chemotherapy-antibiotic resistance and antibiotic tolerance. In the case of antibiotic tolerance, antibiotics fail to kill the bacteria as their phenotypic state affords them protection from the bactericidal activity of the antibiotic. Antibiotic tolerance can affect an entire bacterial population, or a subset of cells known as persister cells. Interaction with the host induces the formation of persister cells in numerous pathogens, with reactive oxygen and nitrogen species production being heavily implicated in the collapse of bacterial energy levels and entrance into an antibiotic tolerant state. Here, we developed a high-throughput screen to identify energy modulators for intracellular Staphylococcus aureus . The identified compound, KL1 , increases intracellular bacterial energy and sensitizes the persister population to antibiotics, without causing cytotoxicity or bacterial outgrowth. We demonstrate that KL1 exhibits adjuvant activity in a murine model of S. aureus bacteremia and intracellular infection of Salmonella Typhimurium . Transcriptomic analysis and further studies on its mechanism of action reveal that KL1 modulates host immune response genes and suppresses the production of reactive species in host macrophages, alleviating one of the major stressors that induce antibiotic tolerance. Our findings highlight the potential to target intracellular persister cells by stimulating their metabolism and encourage larger efforts to address antibiotic tolerance at the host-pathogen interface, particularly within the intracellular milieu.

Tracking the progeny of bacterial persisters using a CRISPR-based genomic recorder

The rise of antimicrobial failure is a global emergency, and causes beyond typical genetic resistance must be determined. One probable factor is the existence of subpopulations of transiently growth-arrested bacteria, persisters, that endure antibiotic treatment despite genetic susceptibility to the drug. The presence of persisters in infected hosts has been successfully established, notably through the development of fluorescent reporters. It is proposed that infection relapse is caused by persisters resuming growth after cessation of the antibiotic treatment, but to date, there is no direct evidence for this. This is because no tool or reporter currently exists to track the extent to which infection relapse is initiated by regrowth of persisters in the host. Indeed, once they have transitioned out of the persister state, the progeny of persisters are genetically and phenotypically identical to susceptible bacteria in the population, making it virtually impossible to ascertain the source of relapse. We designed pSCRATCH (plasmid for Selective CRISPR Array expansion To Check Heritage), a molecular tool that functions to record the state of antibiotic persistence in the genome of Salmonella persisters. We show that pSCRATCH successfully marks persisters by adding spacers in their CRISPR arrays and the genomic label is stable in persister progeny after exit from persistence. We further show that in a Salmonella infection model the system enables the discrimination of treatment failure originating from persistence versus resistance. Thus, pSCRATCH provides proof of principle for stable marking of persisters and a prototype for applications to more complex infection models and other pathogens.

The macrophage-bacterium mismatch in persister formation

Many pathogens are hard to eradicate, even in the absence of genetically detectable antimicrobial resistance mechanisms and despite proven antibiotic susceptibility. The fraction of clonal bacteria that temporarily elude effective antibiotic treatments is commonly known as 'antibiotic persisters.' Over the past decade, there has been a growing body of research highlighting the pivotal role played by the cellular host in the development of persisters. In parallel, this research has also sought to elucidate the molecular mechanisms underlying the formation of intracellular antibiotic persisters and has demonstrated a prominent role for the bacterial stress response. However, questions remain regarding the conditions leading to the formation of stress-induced persisters among a clonal population of intracellular bacteria and despite an ostensibly uniform environment. In this opinion, following a brief review of the current state of knowledge regarding intracellular antibiotic persisters, we explore the ways in which macrophage functional heterogeneity and bacterial phenotypic heterogeneity may contribute to the emergence of these persisters. We propose that the degree of mismatch between the macrophage permissiveness and the bacterial preparedness to invade and thrive intracellularly may explain the formation of stress-induced nonreplicating intracellular persisters.

Single-cell phenotypic profiling and backtracing exposes and predicts clinically relevant subpopulations in isogenic Staphylococcus aureus communities

Isogenic bacterial cell populations are phenotypically heterogenous and may include subpopulations of antibiotic tolerant or heteroresistant cells. The reversibility of these phenotypes and lack of biomarkers to differentiate functionally different, but morphologically identical cells is a challenge for research and clinical detection. To overcome this, we present ´Cellular Phenotypic Profiling and backTracing (CPPT)´, a fluorescence-activated cell sorting platform that uses fluorescent probes to visualize and quantify cellular traits and connects this phenotypic profile with a cell´s experimentally determined fate in single cell-derived growth and antibiotic susceptibility analysis. By applying CPPT on Staphylococcus aureus we phenotypically characterized dormant cells, exposed bimodal growth patterns in colony-derived cells and revealed different culturability of single cells on solid compared to liquid media. We demonstrate that a fluorescent vancomycin conjugate marks cellular subpopulations of vancomycin-intermediate S. aureus with increased likelihood to survive antibiotic exposure, showcasing the value of CPPT for discovery of clinically relevant biomarkers.

Marine-derived bioactive materials as antibiofilm and antivirulence agents

Microbial infections are major human health issues, and, recently, the mortality rate owing to bacterial and fungal infections has been increasing. In addition to intrinsic and extrinsic antimicrobial resistance mechanisms, biofilm formation is a key adaptive resistance mechanism. Several bioactive compounds from marine organisms have been identified for use in biofilm therapy owing to their structural complexity, biocompatibility, and economic viability. In this review, we discuss recent trends in the application of marine natural compounds, marine-bioinspired nanomaterials, and marine polymer conjugates as possible therapeutic agents for controlling biofilms and virulence factors. We also comprehensively discuss the mechanisms underlying biofilm formation and inhibition of virulence factors by marine-derived materials and propose possible applications of novel and effective antibiofilm and antivirulence agents.

Itaconate induces tolerance of Staphylococcus aureus to aminoglycoside antibiotics

INTRODUCTION

Staphylococcus aureus is one of the chief pathogens that cause chronic and recurrent infections. Failure of the antibiotics to curb the infections contributes to relapse and is an important reason for the high mortality rate. Treatment failure may also be due to antibiotic tolerance. Accumulating evidence suggests that t the host immune environment plays an important role in inducing antibiotic tolerance of S. aureus, but research in this area has been limited.

METHODS

In this study,the minimum inhibitory concentration (MIC) of the antibiotics against S. aureus was determined using the standard broth microdilution method.The study evaluated whether itaconate induces antibiotic tolerance in S. aureus through an antibiotic bactericidal activity assay.The effect of itaconate on the growth of S. aureus was evaluated by monitoring the growth of S. aureus in medium supplemented with itaconate. Additionally, RNA sequencing and metabolomics analyses were used to determine transcriptional and metabolic changes in S. aureus when exposed to itaconate.

RESULTS AND DISCUSSION

According to the study,we found that the immune metabolite itaconate can induce tolerance in both methicillin-resistant and -susceptible S. aureus to aminoglycosides. When S. aureus was exposed to itaconate, its growth slowed down and transcriptomic and metabolomic alterations associated with decreased energy metabolism, including the tricarboxylate cycle, glycolysis, pyruvate metabolism, and arginine biosynthesis, were observed. These changes are associated with aminoglycoside tolerance. This study highlights the role of immune signaling metabolites in bacterial antibiotic tolerance and suggests new strategies to improve antibiotic treatment by modulating the host immune response and stimulating the metabolism of bacteria.

Staphylococcus aureus Co-Infection in COVID-19 Patients: Virulence Genes and Their Influence on Respiratory Epithelial Cells in Light of Risk of Severe Secondary Infection

Pandemics from viral respiratory tract infections in the 20th and early 21st centuries were associated with high mortality, which was not always caused by a primary viral infection. It has been observed that severe course of infection, complications and mortality were often the result of co-infection with other pathogens, especially Staphylococcus aureus. During the COVID-19 pandemic, it was also noticed that patients infected with S. aureus had a significantly higher mortality rate (61.7%) compared to patients infected with SARS-CoV-2 alone. Our previous studies have shown that S. aureus strains isolated from patients with COVID-19 had a different protein profile than the strains in non-COVID-19 patients. Therefore, this study aims to analyze S. aureus strains isolated from COVID-19 patients in terms of their pathogenicity by analyzing their virulence genes, adhesion, cytotoxicity and penetration to the human pulmonary epithelial cell line A549. We have observed that half of the tested S. aureus strains isolated from patients with COVID-19 had a necrotizing effect on the A549 cells. The strains also showed greater variability in terms of their adhesion to the human cells than their non-COVID-19 counterparts.

A Rhein-Based Derivative Targets Staphylococcus aureus

The rise in antibiotic-resistant bacteria highlights the need for novel antimicrobial agents. This study presents the design and synthesis of a series of rhein (RH)-derived compounds with improved antimicrobial properties. The lead compound, RH17, exhibited a potent antibacterial activity against Staphylococcus aureus (S. aureus) isolates, with minimum inhibitory concentrations (MICs) ranging from 8 to 16 μg/mL. RH17 disrupted bacterial membrane stability, hindered metabolic processes, and led to an increase in reactive oxygen species (ROS) production. These mechanisms were confirmed through bacterial growth inhibition assays, membrane function assessments, and ROS detection. Notably, RH17 outperformed the parent compound RH and demonstrated bactericidal effects in S. aureus. The findings suggest that RH17 is a promising candidate for further development as an antimicrobial agent against Gram-positive pathogens, addressing the urgent need for new therapies.

A rare biofilm dispersion strategy demonstrated by Staphylococcus aureus under oxacillin stress

Staphylococcus aureus (S. aureus), a versatile Gram-positive bacterium, is implicated in a spectrum of infections, and its resilience is often attributed to biofilm formation. This study investigates the effect of sub-inhibitory doses of oxacillin on biofilm formation by methicillin-resistant S. aureus (MRSA). Specifically, it examines how these doses influence biofilms' development, maturation, and dispersal. The biofilm's zenith reached 48 h of incubation, followed by a noteworthy decline at 96 h and a distinctive clearance zone around biofilm-positive cells exposed to oxacillin. Scanning electron micrographs unveiled an intriguing active biofilm dispersal mechanism, a rarity in this species. Among 180 isolates, only three carrying the elusive icaD gene exhibited this phenomenon. icaD gene was absent in their counterparts. Notably, the icaD gene emerges as a distinctive marker, crucial in regulating biofilm dispersion and setting these isolates apart. The captivating interplay of oxacillin, biofilm dynamics, and genetic signatures disintegrate novel dimensions in understanding MRSA's adaptive strategies and underscores the importance of the icaD gene in engineering biofilm resilience.

Staphylococcus aureus SOS response: Activation, impact, and drug targets

Staphylococcus aureus is a common cause of diverse infections, ranging from superficial to invasive, affecting both humans and animals. The widespread use of antibiotics in clinical treatments has led to the emergence of antibiotic-resistant strains and small colony variants. This surge presents a significant challenge in eliminating infections and undermines the efficacy of available treatments. The bacterial Save Our Souls (SOS) response, triggered by genotoxic stressors, encompasses host immune defenses and antibiotics, playing a crucial role in bacterial survival, invasiveness, virulence, and drug resistance. Accumulating evidence underscores the pivotal role of the SOS response system in the pathogenicity of S. aureus. Inhibiting this system offers a promising approach for effective bactericidal treatments and curbing the evolution of antimicrobial resistance. Here, we provide a comprehensive review of the activation, impact, and key proteins associated with the SOS response in S. aureus. Additionally, perspectives on therapeutic strategies targeting the SOS response for S. aureus, both individually and in combination with traditional antibiotics are proposed.

Current advances in black phosphorus-based antibacterial nanoplatform for infection therpy

Black phosphorus (BP) has attracted much attention due to its excellent physiochemical properties. However, due to its biodegradability and simple antibacterial mechanism, using only BP nanomaterials to combat bacterial infections caused by drug-resistant pathogens remains a significant challenge. In order to improve the antibacterial efficiency and avoid the emergence of drug resistance, BP nanomaterials have been combined with other functional materials to form black phosphorus-based antibacterial nanoplatform (BPANP), which provides unprecedented opportunities for the treatment of drug-resistant infections. This article reviews the performance of BPANP and its multiple antibacterial mechanisms while emphatically introducing its design direction and latest application progress in antibacterial fields. Moreover, this paper additionally summarizes and discusses the current challenges and inadequacies of BPANP that need to be improved in future research. We believe that this review will provide researchers with an up-to-date and multifaceted reference, and provide new ideas for designing effective strategies against drug-resistant bacteria.

Unraveling the role of toxin-antitoxin systems in Burkholderia pseudomallei: exploring bacterial pathogenesis and interactions within the HigBA families

Burkholderia pseudomallei (Bpm) is a Gram-negative intracellular pathogen that causes melioidosis in humans, a neglected, underreported, and lethal disease that can reach a fatal outcome in over 50% of the cases. It can produce both acute and chronic infections, the latter being particularly challenging to eliminate because of the intracellular life cycle of the bacteria and its ability to generate a "persister" dormant state. The molecular mechanism that allows the switch between growing and persister phenotypes is not well understood but it is hypothesized to be due at least in part to the participation of toxin-antitoxin (TA) systems. We have previously studied the link between one of those systems (defined as HigBA) with specific expression patterns associated with levofloxacin antibiotic exposure. Through in silico methods, we predicted the presence of another three pairs of genes encoding for additional putative HigBA systems. Therefore, our main goal was to establish which mechanisms are conserved as well as which pathways are specific among different Bpm TA systems from the same family. We hypothesize that the high prevalence, and sometimes even redundancy of these systems in the Bpm chromosomes indicates that they can interact with each other and not function as only individual systems, as it was traditionally thought, and might be playing an undefined role in Bpm lifecycle. Here, we show that both the toxin and the antitoxin of the different systems contribute to bacterial survival and that toxins from the same family can have a cumulative effect under environmental stressful conditions.

IMPORTANCE

Toxin-antitoxin (TA) systems play a significant role in bacterial persistence, a phenomenon where bacterial cells enter a dormant or slow-growing state to survive adverse conditions such as nutrient deprivation, antibiotic exposure, or host immune responses. By studying TA systems in Burkholderia pseudomallei, we can gain insights into how this pathogen survives and persists in the host environment, contributing to its virulence and ability to cause melioidosis chronic infections.

Pyridine-2,6-Dicarboxamide Proligands and their Cu(II)/Zn(II) Complexes Targeting Staphylococcus Aureus for the Attenuation of In Vivo Dental Biofilm

In the pursuit to combat stubborn bacterial infections, particularly those stemming from gram-positive bacteria, this study is an attempt to craft a precision-driven platform characterized by unparalleled selectivity, specificity, and synergistic antimicrobial mechanisms. Leveraging remarkable potential of metalloantibiotics in antimicrobial applications, herein, this work rationally designs, synthesizes, and characterizes a new library of Pyridine-2,6-dicarboxamide ligands and their corresponding transition metal Cu(II)/Zn(II) complexes. The lead compound L11 demonstrates robust antibacterial properties against Staphylococcus aureus (Minimum Inhibitory Concentration (MIC) = 2-16 µg mL-1), methicillin and vancomycin-resistant S. aureus (MIC = 2-4 µg mL-1) and exhibit superior antibacterial activity when compared to FDA-approved vancomycin, the drug of last resort. Additionally, the compound exhibits notable antimicrobial efficacy against resistant enterococcus strains (MIC = 2-8 µg mL-1). To unravel mechanistic profile, advanced imaging techniques including SEM and AFM are harnessed, collectively suggesting a mechanistic pathway involving cell wall disruption. Live/dead fluorescence studies further confirm efficacy of L11 and its complexes against S. aureus membranes. This translational exploration extends to a rat model, indicating promising in vivo therapeutic potential. Thus, this comprehensive research initiative has capabilities to transcends the confines of this laboratory, heralding a pivotal step toward combatting antibiotic-resistant pathogens and advancing the frontiers of metalloantibiotics-based therapy with a profound clinical implication.