Intracellular Penetration and Effects of Antibiotics on Staphylococcus aureus Inside Human Neutrophils: A Comprehensive Review

Potassium-Doped MnO2 Nanoparticles Reprogram Neutrophil Calcium Signaling to Accelerate Healing of Methicillin-Resistant Staphylococcus aureus-Infected Diabetic Wounds

Neutrophils, as first-line immune cells, typically lose their edge within the diabetic wounds accompanied by methicillin-resistant Staphylococcus aureus (MRSA) infections (the D/M setting), playing the role of "more foe than friend" during the healing process. Specifically, reduced influx of calcium ions (Ca2+) and impaired calcium homeostasis yield the dysfunction of neutrophil sequential behaviors in pathogen killing and wound healing, manifesting as suppressed chemotaxis, decreased intracellular reactive oxygen species (ROS) generation, prolonged apoptosis, and retention of neutrophil extracellular traps (NETs). To address this challenge, this study fabricated potassium (K)-doped manganese dioxide nanoparticles (MnO2 NPs), which activated transmembrane Ca2+ channels by inducing neutrophil depolarization via electron transfer. Subsequently, this contributed to the initial Ca2+ influx and reprogrammed Ca2+-dependent behaviors of impaired neutrophils. Also, the potential antimicrobial capacity of K-MnO2 NPs created a favorable extracellular environment that restored calcium homeostasis, enabling apoptotic neutrophils to be removed timely. Therefore, the wounds treated with K-MnO2 NPs in the D/M setting exhibited potent resistance to MRSA and rapid healing, which could be attributed to the synergistic effects of K-MnO2 NPs in leveraging Ca2+ influx and maintaining calcium homeostasis. In brief, K-MnO2 NPs constitute an effective strategy to resist MRSA and rapid wound healing in the D/M setting.

Exploring the Therapeutic Potential of Antibiotics in Hyperglycemia-Induced Macrophage Dysfunctions

Background: Diabetes mellitus exacerbates immune dysfunction, leading to higher susceptibility to infections. This study investigated the effects of antibiotics on macrophage functions under high glucose conditions to mimic a diabetic context. Methods: Using murine macrophage cell line RAW 264.7, the present study evaluated the cytotoxicity, phagocytosis, bactericidal activity, and pro-inflammatory cytokine production after treatment with four antibiotics: oxytetracycline, ciprofloxacin, sulfamethoxazole-trimethoprim, and cefotaxime. Results: All antibiotics demonstrated no cytotoxicity across 1×-8× MIC concentrations. Hyperglycemia significantly impaired macrophage phagocytosis and bactericidal activity while inducing pro-inflammatory mediator markers, IL-1, IL-6, TNF-α, and iNOS. Only ciprofloxacin significantly improved phagocytic achieving levels comparable to the low glucose control. Treatments with ciprofloxacin, sulfamethoxazole-trimethoprim, and cefotaxime significantly enhanced bactericidal activity without altering the pro-inflammatory cytokine profile. Conclusions: These findings underscore the negative effect of high glucose on macrophage functions and suggest that ciprofloxacin may be a potential therapeutic option for diabetes-associated infections.

The antivirulent Staphylococcal sRNA SprC regulates CzrB efflux pump to adapt its response to zinc toxicity

Bacterial regulatory RNAs (sRNAs) are important players to control gene expression. In Staphylococcus aureus, SprC is an antivirulent trans-acting sRNA known to base-pair with the major autolysin atl mRNA, preventing its translation. Using MS2-affinity purification coupled with RNA sequencing, we looked for its sRNA-RNA interactome and identified 14 novel mRNA targets. In vitro biochemical investigations revealed that SprC binds two of them, czrB and deoD, and uses a single accessible region to regulate its targets, including Atl translation. Unlike Atl regulation, the characterization of the SprC-czrB interaction pinpointed a destabilization of the czrAB cotranscript, leading to a decrease of the mRNA level that impaired CzrB zinc efflux pump expression. On a physiological standpoint, we showed that SprC expression is detrimental to combat against zinc toxicity. In addition, phagocyctosis assays revealed a significant, but moderate, increase of czrB mRNA levels in a sprC-deleted mutant, indicating a functional link between SprC and czrB upon internalization in macrophages, and suggesting a role in resistance to both oxidative and zinc bursts. Altogether, our data uncover a novel pathway in which SprC is implicated, highlighting the multiple strategies used by S. aureus to balance virulence using an RNA regulator.

Therapies in preclinical and in early clinical development for the treatment of urinary tract infections: from pathogens to therapies

INTRODUCTION

Urinary tract infections (UTIs) are a prevalent health challenge characterized by the invasion and multiplication of microorganisms in the urinary system. The continuous exploration of novel therapeutic interventions is imperative. Advances in research offer hope for revolutionizing the management of UTIs and improving the overall health outcomes for individuals affected by these infections.

AREAS COVERED

This review aimed to provide an overview of existing treatments for UTIs, highlighting their strengths and limitations. Moreover, we explored and analyzed the latest therapeutic modalities under clinical development. Finally, the review offered a picture into the potential implications of these therapies on the future landscape of UTIs treatment, discussing possible advancements and challenges for further research.

EXPERT OPINION

Comprehensions into the pathogenesis of UTIs have been gleaned from foundational basic science studies, laying the groundwork for the exploration of novel therapeutic interventions. The primary source of evidence originates predominantly from animal studies conducted on murine models. Nevertheless, the lack of clinical trials interferes the acquisition of robust evidence in humans. The challenges presented by the heterogeneity and virulence of uropathogens add an additional layer of complexity, posing an obstacle that scientists and clinicians are actively grappling with in their pursuit of effective solutions.

Deciphering the Drug Delivery Potential of Milk Exosome Nanovesicles for Aminobenzylpenicillin Therapeutic Efficacy against Contagious Staphylococcus Aureus in Bovine Mastitis

The emergence of antimicrobial resistance and failure of antibiotic treatment are challenging tasks for managing bovine mastitis, which is mainly caused by the contagious Staphylococcus aureus (S. aureus).To overcome these difficulties, there is an urgent need for a novel drug system. In the present study, the aim is to develop next-generation therapeutics against S. aureus by harnessing the drug delivery potential of milk nanovesicles called milk exosomes (mENs). In the present work, a drug system is developed by encapsulating aminobenzylpenicillin (AMP) in mENs (mENs-AMP). Electron microscopy and zeta-sizer results indicate that the size of mENs-AMP ranged from 55.79 ± 2.8 to 85.53 ± 7.4 nm. The AMP loading efficiency in mENs is 88.61% with its sustained release. Fluorescence spectroscopy results indicated that mENs are biocompatible with mammary epithelial cells. In vitro studies show that the antibacterial activity and the minimum inhibitory concentrations of mENs-AMP are eleven times greater and four times lower than that of unencapsulated AMP, respectively. The mENs-AMP exhibit significantly higher therapeutic efficacy than AMP at the same dosage and treatment frequency. Validation of this approach is demonstrated in mastitis-affected animals through an observation in the reduction of somatic cell counts and bacterial loads in the milk of treated animals.

Host cell environments and antibiotic efficacy in tuberculosis

The aetiologic agent of tuberculosis (TB), Mycobacterium tuberculosis (Mtb), can survive, persist, and proliferate in a variety of heterogeneous subcellular compartments. Therefore, TB chemotherapy requires antibiotics crossing multiple biological membranes to reach distinct subcellular compartments and target these bacterial populations. These compartments are also dynamic, and our understanding of intracellular pharmacokinetics (PK) often represents a challenge for antitubercular drug development. In recent years, the development of high-resolution imaging approaches in the context of host-pathogen interactions has revealed the intracellular distribution of antibiotics at a new level, yielding discoveries with important clinical implications. In this review, we describe the current knowledge regarding cellular PK of antibiotics and the complexity of drug distribution within the context of TB. We also discuss the recent advances in quantitative imaging and highlight their applications for drug development in the context of how intracellular environments and microbial localisation affect TB treatment efficacy.

Staphylococcus aureus suppresses the pentose phosphate pathway in human neutrophils via the adenosine receptor A2aR to enhance intracellular survival

IMPORTANCE

Staphylococcus aureus is one of the leading causes of antimicrobial-resistant infections whose success as a pathogen is facilitated by its massive array of immune evasion tactics, including intracellular survival within critical immune cells such as neutrophils, the immune system's first line of defense. In this study, we describe a novel pathway by which intracellular S. aureus can suppress the antimicrobial capabilities of human neutrophils by using the anti-inflammatory adenosine receptor, adora2a (A2aR). We show that signaling through A2aR suppresses the pentose phosphate pathway, a metabolic pathway used to fuel the antimicrobial NADPH oxidase complex that generates reactive oxygen species (ROS). As such, neutrophils show enhanced ROS production and reduced intracellular S. aureus when treated with an A2aR inhibitor. Taken together, we identify A2aR as a potential therapeutic target for combatting intracellular S. aureus infection.

Periprosthetic joint infection and immunity: Current understanding of host-microbe interplay

Periprosthetic joint infection (PJI) is a major complication of total joint arthroplasty. Even with current treatments, failure rates are unacceptably high with a 5-year mortality rate of 26%. Majority of the literature in the field has focused on development of better biomarkers for diagnostics and treatment strategies including innovate antibiotic delivery systems, antibiofilm agents, and bacteriophages. Nevertheless, the role of the immune system, our first line of defense during PJI, is not well understood. Evidence of infection in PJI patients is found within circulation, synovial fluid, and tissue and include numerous cytokines, metabolites, antimicrobial peptides, and soluble receptors that are part of the PJI diagnosis workup. Macrophages, neutrophils, and myeloid-derived suppressor cells (MDSCs) are initially recruited into the joint by chemokines and cytokines produced by immune cells and bacteria and are activated by pathogen-associated molecular patterns. While these cells are efficient killers of planktonic bacteria by phagocytosis, opsonization, degranulation, and recruitment of adaptive immune cells, biofilm-associated bacteria are troublesome. Biofilm is not only a physical barrier for the immune system but also elicits effector functions. Additionally, bacteria have developed mechanisms to evade the immune system by inactivating effector molecules, promoting killing or anti-inflammatory effector cell phenotypes, and intracellular persistence and dissemination. Understanding these shortcomings and the mechanisms by which bacteria can subvert the immune system may open new approaches to better prepare our own immune system to combat PJI. Furthermore, preoperative immune system assessment and screening for dysregulation may aid in developing preventative interventions to decrease PJI incidence.

Whole genomic sequencing of Staphylococcus aureus strain RMI-014804 isolated from pulmonary patient sputum via next-generation sequencing technology

Nosocomial infections, commonly referred to as healthcare-associated infections, are illnesses that patients get while hospitalized and are typically either not yet manifest or may develop. One of the most prevalent nosocomial diseases in hospitalized patients is pneumonia, among the leading causes of mortality and morbidity. Viral, bacterial, and fungal pathogens cause pneumonia. More severe introductions commonly included Staphylococcus aureus, which is at the top of bacterial infections, per World Health Organization reports. The staphylococci, S. aureus, strain RMI-014804, mesophile, on-sporulating, and non-motile bacterium, was isolated from the sputum of a pulmonary patient in Pakistan. Many characteristics of S. aureus strain RMI-014804 have been revealed in this paper, with complete genome sequence and annotation. Our findings indicate that the genome is a single circular 2.82 Mbp long genome with 1,962 protein-coding genes, 15 rRNA, 49 tRNA, 62 pseudogenes, and a GC content of 28.76%. As a result of this genome sequencing analysis, researchers will fully understand the genetic and molecular basis of the virulence of the S. aureus bacteria, which could help prevent the spread of nosocomial infections like pneumonia. Genome analysis of this strain was necessary to identify the specific genes and molecular mechanisms that contribute to its pathogenicity, antibiotic resistance, and genetic diversity, allowing for a more in-depth investigation of its pathogenesis to develop new treatments and preventive measures against infections caused by this bacterium.

SK-03-92 Drug Kills Intracellular Mycobacterium tuberculosis

BACKGROUND

Tuberculosis affects millions of people worldwide. The emergence of drug-resistant Mycobacterium tuberculosis strains has made treatment more difficult. A drug discovery project initiated to screen natural products identified a lead stilbene compound, and structure function analysis of hundreds of analogs led to the discovery of the SK-03-92 stilbene lead compound with activity against several non-tuberculoid mycobacteria.

METHODS

For this study, an MIC analysis and intracellular killing assay were performed to test SK-03-92 against M. tuberculosis grown in vitro as well as within murine macrophage cells.

RESULTS

The MIC analysis showed that SK-03-92 had activity against M. tuberculosis in the range of 0.39 to 6.25 μg/mL, including activity against single-drug-resistant strains. Further, an intracellular kill assay demonstrated that the SK-03-92 lead compound killed M. tuberculosis cells within murine macrophage cells.

CONCLUSION

Together, the data show the SK-03-92 lead compound can kill M. tuberculosis bacteria within mammalian macrophages.

Formate Metabolism in Shigella flexneri and Its Effect on HeLa Cells at Different Stages during the Infectious Process

Shigellosis caused by Shigella is one of the most important foodborne illnesses in global health, but little is known about the metabolic cross talk between this bacterial pathogen and its host cells during the different stages of the infection process. A detailed understanding of the metabolism can potentially lead to new drug targets remedying the pressing problem of antibiotic resistance. Here, we use stable isotope-resolved metabolomics as an unbiased and fast method to investigate how Shigella metabolizes 13C-glucose in three different environments: inside the host cells, adhering to the host cells, and alone in suspension. We find that especially formate metabolism by bacteria is sensitive to these different environments. The role of formate in pathogen metabolism is sparsely described in the literature compared to the roles of acetate and butyrate. However, its metabolic pathway is regarded as a potential drug target due to its production in microorganisms and its absence in humans. Our study provides new knowledge about the regulatory effect of formate. Bacterial metabolism of formate is pH dependent when studied alone in culture medium, whereas this effect is less pronounced when the bacteria adhere to the host cells. Once the bacteria are inside the host cells, we find that formate accumulation is reduced. Formate also affects the host cells resulting in a reduced infection rate. This was correlated to an increased immune response. Thus, intriguingly formate plays a double role in pathogenesis by increasing the virulence of Shigella and at the same time stimulating the immune response of the host. IMPORTANCE Bacterial infection is a pressing societal concern due to development of resistance toward known antibiotics. Central carbon metabolism has been suggested as a potential new target for drug development, but metabolic changes upon infection remain incompletely understood. Here, we used a cellular infection model to study how the bacterial pathogen Shigella adapts its metabolism depending on the environment starting from the extracellular medium until Shigella successfully invaded and proliferated inside host cells. The mixed-acid fermentation of Shigella was the major metabolic pathway during the infectious process, and the glucose-derived metabolite formate surprisingly played a divergent role in the pathogen and in the host cell. Our data show reduced infection rate when both host cells and bacteria were treated with formate, which correlated with an upregulated immune response in the host cells. The formate metabolism in Shigella thus potentially provides a route toward alternative treatment strategies for Shigella prevention.

Glycopeptide Antibiotics Impair Neutrophil Effector Functions

INTRODUCTION

Neutrophilic granulocytes represent the first line of defense against microorganisms. Granulocytes phagocytose microorganisms and specifically synthesize oxygen radicals against them, which eventually kills the invaders.

METHODS

Neutrophilic granulocytes were isolated from peripheral blood of healthy volunteer donors. Putative interference of new-generation antibiotics with neutrophil function was tested using a collection of granulocyte-stimulating agents and Amplex™ Red-based plate assay and flow cytometry-based respiratory burst assays. In addition, phagocytosis of E. coli, IL-8 production, bactericidal activity, and CD62L expression of granulocytes were evaluated.

RESULTS

Of note, we found that the two glycopeptide antibiotics dalbavancin and teicoplanin inhibited ROS production upon granulocyte activation via different signaling pathways in a dose-dependent manner. Dalbavancin also blocked the PMA-induced shedding of CD62L. In contrast, the oxazolidinone antibiotics tedizolid and linezolid had no effect on neutrophil function, while the combination of ceftazidime/avibactam dose dependently inhibited the fMLP/Cytochalasin B-induced granulocyte burst in a dose-dependent manner. Additionally, we showed that dalbavancin and teicoplanin as well as sulfametrole/trimethoprim and ceftazidime/avibactam inhibited baseline and PMA-induced IL-8 production by neutrophilic granulocytes. Moreover, dalbavancin impaired the bactericidal activity of neutrophilic granulocytes.

CONCLUSION

We here identified hitherto unknown inhibitory effects of several classes of antibiotics on the effector functions of neutrophilic granulocytes.

Staphylococcus aureus Infection Induces the Production of the Neutrophil Chemoattractants CXCL1, CXCL2, CXCL3, CXCL5, CCL3, and CCL7 by Murine Osteoblasts

Staphylococcus aureus is the principal causative agent of osteomyelitis, a serious bacterial infection of bone that is associated with progressive inflammatory damage. Bone-forming osteoblasts have increasingly been recognized to play an important role in the initiation and progression of detrimental inflammation at sites of infection and have been demonstrated to release an array of inflammatory mediators and factors that promote osteoclastogenesis and leukocyte recruitment following bacterial challenge. In the present study, we describe elevated bone tissue levels of the potent neutrophil-attracting chemokines CXCL1, CXCL2, CXCL3, CXCL5, CCL3, and CCL7 in a murine model of posttraumatic staphylococcal osteomyelitis. RNA sequencing (RNA-Seq) gene ontology analysis of isolated primary murine osteoblasts showed enrichment in differentially expressed genes involved in cell migration and chemokine receptor binding and chemokine activity following S. aureus infection, and a rapid increase in the expression of mRNA encoding CXCL1, CXCL2, CXCL3, CXCL5, CCL3, and CCL7, in these cells. Importantly, we have confirmed that such upregulated gene expression results in protein production with the demonstration that S. aureus challenge elicits the rapid and robust release of these chemokines by osteoblasts and does so in a bacterial dose-dependent manner. Furthermore, we have confirmed the ability of soluble osteoblast-derived chemokines to elicit the migration of a neutrophil-like cell line. As such, these studies demonstrate the robust production of CXCL1, CXCL2, CXCL3, CXCL5, CCL3, and CCL7 by osteoblasts in response to S. aureus infection, and the release of such neutrophil-attracting chemokines provides an additional mechanism by which osteoblasts could drive the inflammatory bone loss associated with staphylococcal osteomyelitis.

Mesoporous Organosilica Nanoparticles to Fight Intracellular Staphylococcal Aureus Infections in Macrophages

Intracellular bacteria are inaccessible and highly tolerant to antibiotics, hence are a major contributor to the global challenge of antibiotic resistance and recalcitrant clinical infections. This, in tandem with stagnant antibacterial discovery, highlights an unmet need for new delivery technologies to treat intracellular infections more effectively. Here, we compare the uptake, delivery, and efficacy of rifampicin (Rif)-loaded mesoporous silica nanoparticles (MSN) and organo-modified (ethylene-bridged) MSN (MON) as an antibiotic treatment against small colony variants (SCV) Staphylococcus aureus (SA) in murine macrophages (RAW 264.7). Macrophage uptake of MON was five-fold that of equivalent sized MSN and without significant cytotoxicity on human embryonic kidney cells (HEK 293T) or RAW 264.7 cells. MON also facilitated increased Rif loading with sustained release, and seven-fold increased Rif delivery to infected macrophages. The combined effects of increased uptake and intracellular delivery of Rif by MON reduced the colony forming units of intracellular SCV-SA 28 times and 65 times compared to MSN-Rif and non-encapsulated Rif, respectively (at a dose of 5 µg/mL). Conclusively, the organic framework of MON offers significant advantages and opportunities over MSN for the treatment of intracellular infections.

Genomic and phenotypic profiling of Staphylococcus aureus isolates from bovine mastitis for antibiotic resistance and intestinal infectivity

BACKGROUND

Staphylococcus aureus is one of the prevalent etiological agents of contagious bovine mastitis, causing a significant economic burden on the global dairy industry. Given the emergence of antibiotic resistance (ABR) and possible zoonotic spillovers, S aureus from mastitic cattle pose threat to both veterinary and public health. Therefore, assessment of their ABR status and pathogenic translation in human infection models is crucial.

RESULTS

In this study, 43 S. aureus isolates associated with bovine mastitis obtained from four different Canadian provinces (Alberta, Ontario, Quebec, and Atlantic provinces) were tested for ABR and virulence through phenotypic and genotypic profiling. All 43 isolates exhibited crucial virulence characteristics such as hemolysis, and biofilm formation, and six isolates from ST151, ST352, and ST8 categories showed ABR. Genes associated with ABR (tetK, tetM, aac6', norA, norB, lmrS, blaR, blaZ, etc.), toxin production (hla, hlab, lukD, etc.), adherence (fmbA, fnbB, clfA, clfB, icaABCD, etc.), and host immune invasion (spa, sbi, cap, adsA, etc.) were identified by analyzing whole-genome sequences. Although none of the isolates possessed human adaptation genes, both groups of ABR and antibiotic-susceptible isolates demonstrated intracellular invasion, colonization, infection, and death of human intestinal epithelial cells (Caco-2), and Caenorhabditis elegans. Notably, the susceptibilities of S. aureus towards antibiotics such as streptomycin, kanamycin, and ampicillin were altered when the bacteria were internalized in Caco-2 cells and C. elegans. Meanwhile, tetracycline, chloramphenicol, and ceftiofur were comparatively more effective with ≤ 2.5 log₁₀ reductions of intracellular S. aureus.

CONCLUSIONS

This study demonstrated the potential of S. aureus isolated from mastitis cows to possess virulence characteristics enabling invasion of intestinal cells thus calling for developing therapeutics capable of targeting drug-resistant intracellular pathogens for effective disease management.

Intracellular Experimental Evolution of Francisella tularensis Subsp. holarctica Live Vaccine Strain (LVS) to Antimicrobial Resistance

In vitro experimental evolution has complemented clinical studies as an excellent tool to identify genetic changes responsible for the de novo evolution of antimicrobial resistance. However, the in vivo context for adaptation contributes to the success of particular evolutionary trajectories, especially in intracellular niches where the adaptive landscape of virulence and resistance are strongly coupled. In this work, we designed an ex vivo evolution approach to identify evolutionary trajectories responsible for antibiotic resistance in the Live Vaccine Strain (LVS) of Francisella tularensis subsp. holarctica while being passaged to increasing ciprofloxacin (CIP) and doxycycline (DOX) concentrations within macrophages. Overall, adaptation within macrophages advanced much slower when compared to previous in vitro evolution studies reflecting a limiting capacity for the expansion of adaptive mutations within the macrophage. Longitudinal genomic analysis identified resistance conferring gyrase mutations outside the Quinolone Resistance Determining Region. Strikingly, FupA/B mutations that are uniquely associated with in vitro CIP resistance in Francisella were not observed ex vivo, reflecting the coupling of intracellular survival and resistance during intracellular adaptation. To our knowledge, this is the first experimental study demonstrating the ability to conduct experimental evolution to antimicrobial resistance within macrophages. The results provide evidence of differences in mutational profiles of populations adapted to the same antibiotic in different environments/cellular compartments and underscore the significance of host mediated stress during resistance evolution.

Dalbavancin Boosts the Ability of Neutrophils to Fight Methicillin-Resistant Staphylococcus aureus

Polymorphonuclear leukocytes (PMNs) are the most important cell type involved in the early nonspecific host response to bacterial pathogens. Staphylococcus aureus has evolved mechanisms to evade immune responses that contribute to its persistence in PMNs, and acquired resistance to several antimicrobials. Additionally, methicillin-resistant S. aureus (MRSA) is one of the most common causes of acute bacterial skin and skin-structure infections (ABSSSIs). Dalbavancin (DBV), a lipoglycopeptide, is indicated for the treatment of ABSSSIs, and has a broad spectrum of action against most microorganisms. Here, we sought to determine the effect of DBV on the neutrophil killing of MRSA and its potential immunomodulating activity. Our results revealed that DBV boosts MRSA killing by acting on both bacteria and PMNs. DBV pre-treatment of PMNs did not change the respiratory burst or degranulation, while an increased trend in neutrophil extracellular traps-associated elastase and in the production of TNFα and CXCL8 was revealed. In parallel, DBV caused a delay in the apoptosis of MRSA-infected neutrophils. In conclusion, we demonstrated a cooperative effect between the antimicrobial properties of PMNs and DBV, thus owing to their immunomodulatory activity. In the choice of the treatment management of serious S. aureus infections, DBV should be considered as an outstanding option since it reinforces PMNs pathogen clearance capability by exerting its effect directly, not only on MRSA but also on neutrophils.

Characterization, Quantification, and Visualization of Neutrophil Extracellular Traps

Following the discovery of neutrophil extracellular traps (NETs) in 2004 by Brinkmann and colleagues, there has been extensive research into the role of NETs in a number of inflammatory diseases, including periodontitis. This chapter describes the current methods for the isolation of peripheral blood neutrophils as well as of oral neutrophils for subsequent NET experiments, including approaches to quantify and visualize NET production, the ability of NETs to entrap and kill bacteria, and the removal of NETs by nuclease-containing plasma.

Antibody-Antimicrobial Conjugates for Combating Antibiotic Resistance

As the development of new antibiotics lags far behind the emergence of drug-resistant bacteria, alternative strategies to resolve this dilemma are urgently required. Antibody-drug conjugate is a promising therapeutic platform to delivering cytotoxic payloads precisely to target cells for efficient disease treatment. Antibody-antimicrobial conjugates (AACs) have recently attracted considerable interest from researchers as they can target bacteria in the target sites and improve the effectiveness of drugs (i.e., reduced drug dosage and adverse effects), abating the upsurge of antimicrobial resistance. In this review, the selection and progress of three essential blocks that compose the AACs: antibodies, antimicrobial payloads, and linkers are discussed. The commonly used conjugation strategies and the latest applications of AACs in recent years are also summarized. The challenges and opportunities of this booming technology are also discussed at the end of this review.

Immunomodulatory Effects of Macrolides Considering Evidence from Human and Veterinary Medicine

Macrolide antimicrobial agents have been in clinical use for more than 60 years in both human and veterinary medicine. The discovery of the non-antimicrobial properties of macrolides and the effect of immunomodulation of the inflammatory response has benefited patients with chronic airway diseases and impacted morbidity and mortality. This review examines the evidence of antimicrobial and non-antimicrobial properties of macrolides in human and veterinary medicine with a focus toward veterinary macrolides but including important and relevant evidence from the human literature. The complete story for these complex and important molecules is continuing to be written.

Longitudinal assessment of the inflammatory response: The next step in personalized medicine after severe trauma

Infections in trauma patients are an increasing and substantial cause of morbidity, contributing to a mortality rate of 5-8% after trauma. With increased early survival rates, up to 30-50% of multitrauma patients develop an infectious complication. Trauma leads to a complex inflammatory cascade, in which neutrophils play a key role. Understanding the functions and characteristics of these cells is important for the understanding of their involvement in the development of infectious complications. Recently, analysis of neutrophil phenotype and function as complex biomarkers, has become accessible for point-of-care decision making after trauma. There is an intriguing relation between the neutrophil functional phenotype on admission, and the clinical course (e.g., infectious complications) of trauma patients. Potential neutrophil based cellular diagnostics include subsets based on neutrophil receptor expression, responsiveness of neutrophils to formyl-peptides and FcγRI (CD64) expression representing the infectious state of a patient. It is now possible to recognize patients at risk for infectious complications when presented at the trauma bay. These patients display increased numbers of neutrophil subsets, decreased responsiveness to fMLF and/or increased CD64 expression. The next step is to measure these biomarkers over time in trauma patients at risk for infectious complications, to guide decision making regarding timing and extent of surgery and administration of (preventive) antibiotics.

pH-Responsive Hyperbranched Polymer Nanoparticles to Combat Intracellular Infection by Disrupting Bacterial Wall and Regulating Macrophage Polarization

Intracellular bacterial infections pose a serious threat to public health. Macrophages are a heterogeneous population of immune cells that play a vital role in intracellular bacterial infection. However, bacteria that survive inside macrophages could subvert the cell signaling and eventually reduce the antimicrobial activity of macrophages. Herein, dual pH-responsive polymer (poly[(3-phenylprop-2-ene-1,1-diyl)bis(oxy)bis(enthane-2,1-diyl)diacrylate-co-N-aminoethylpiperazine] (PCA)) nanoparticles were developed to clear intracellular bacteria by activating macrophages and destructing bacterial walls. The presence of acid-labile acetal linkages and tertiary amine groups in the polymer's backbone endow hyperbranched PCA dual pH-response activity that shows acid-induced positive charge increase and cinnamaldehyde release properties. The biodegraded PCA nanoparticles could significantly inhibit the growth of bacteria by damaging the bacterial walls. Meanwhile, PCA nanoparticles could uptake by macrophages, generate reactive oxygen species (ROS), and remodel the immune response by upregulating M1 polarization, leading to the reinforced antimicrobial capacity. Furthermore, PCA nanoparticles could promote bacteria-infected wound healing in vivo. Therefore, these dual pH-responsive PCA nanoparticles enabling bacteria-killing and macrophage activation provide a novel outlook for treating intracellular infection.

The mysteries of target site concentrations of antibiotics in bone and joint infections: what is known? A narrative review

INTRODUCTION

Currently, antibiotic treatment is often a standard dosing regimen in bone and joint infections (BJI). However, it remains unknown if exposure at the target-site is adequate. The aim of this review is to gain more insight in the relationship between the target site concentration of antibiotic and the minimal inhibitory concentration to target the bacteria in bone and joint infections (BJI).

AREAS COVERED

A literature search was performed by Erasmus MC Medical library. Bone, bone tissue and synovial concentration of antibiotics were covered in humans. In addition, we reported number of patients, dose, sampling method, analytical method and tissue and plasma concentrations. We used the epidemiological cut-off value (ECOFF) values of the targeted micro-organisms. If more than 3 publications were available on the antibiotic, we graphically presented ECOFFS values against reported antibiotic concentrations.

EXPERT OPINION

For most antibiotics the literature is sparse. In addition, a lot of variable and total antibiotic concentrations are published. Ciprofloxacin, cefazolin, cefuroxime, vancomycin and linezolid seem to have adequate average exposure if correlating total concentration to ECOFF, when standard dosing is used. With regards to other antibiotics, results are inconclusive. More extensive pharmacokinetic/pharmacodynamic modeling in BJI is needed.

Can intracellular Staphylococcus aureus in osteomyelitis be treated using current antibiotics? A systematic review and narrative synthesis

Approximately 40% of treatments of chronic and recurrent osteomyelitis fail in part due to bacterial persistence. Staphylococcus aureus, the predominant pathogen in human osteomyelitis, is known to persist by phenotypic adaptation as small-colony variants (SCVs) and by formation of intracellular reservoirs, including those in major bone cell types, reducing susceptibility to antibiotics. Intracellular infections with S. aureus are difficult to treat; however, there are no evidence-based clinical guidelines addressing these infections in osteomyelitis. We conducted a systematic review of the literature to determine the demonstrated efficacy of all antibiotics against intracellular S. aureus relevant to osteomyelitis, including protein biosynthesis inhibitors (lincosamides, streptogramins, macrolides, oxazolidines, tetracyclines, fusidic acid, and aminoglycosides), enzyme inhibitors (fluoroquinolones and ansamycines), and cell wall inhibitors (beta-lactam inhibitors, glycopeptides, fosfomycin, and lipopeptides). The PubMed and Embase databases were screened for articles related to intracellular S. aureus infections that compared the effectiveness of multiple antibiotics or a single antibiotic together with another treatment, which resulted in 34 full-text articles fitting the inclusion criteria. The combined findings of these studies were largely inconclusive, most likely due to the plethora of methodologies utilized. Therefore, the reported findings in the context of the models employed and possible solutions for improved understanding are explored here. While rifampicin, oritavancin, linezolid, moxifloxacin and oxacillin were identified as the most effective potential intracellular treatments, the scientific evidence for these is still relatively weak. We advocate for more standardized research on determining the intracellular effectiveness of antibiotics in S. aureus osteomyelitis to improve treatments and patient outcomes.

The unforeseen intracellular lifestyle of Enterococcus faecalis in hepatocytes

Enterococcus faecalis is a bacterial species present at a subdominant level in the human gut microbiota. This commensal turns into an opportunistic pathogen under specific conditions involving dysbiosis and host immune deficiency. E. faecalis is one of the rare pathobionts identified to date as contributing to liver damage in alcoholic liver disease. We have previously observed that E. faecalis is internalized in hepatocytes. Here, the survival and fate of E. faecalis was examined in hepatocytes, the main epithelial cell type in the liver. Although referred to as an extracellular pathogen, we demonstrate that E. faecalis is able to survive and divide in hepatocytes, and form intracellular clusters in two distinct hepatocyte cell lines, in primary mouse hepatocytes, as well as in vivo. This novel process extends to kidney cells. Unraveling the intracellular lifestyle of E. faecalis, our findings contribute to the understanding of pathobiont-driven diseases.

A Human Osteocyte Cell Line Model for Studying Staphylococcus aureus Persistence in Osteomyelitis

Infectious osteomyelitis associated with periprosthetic joint infections is often recalcitrant to treatment and has a high rate of recurrence. In the case of Staphylococcus aureus, the most common pathogen in all forms of osteomyelitis, this may be attributed in part to residual intracellular infection of host cells, yet this is not generally considered in the treatment strategy. Osteocytes represent a unique cell type in this context due to their abundance, their formation of a syncytium throughout the bone that could facilitate bacterial spread and their relative inaccessibility to professional immune cells. As such, there is potential value in studying the host-pathogen interactions in the context of this cell type in a replicable and scalable in vitro model. Here, we examined the utility of the human osteosarcoma cell line SaOS2 differentiated to an osteocyte-like stage (SaOS2-OY) as an intracellular infection model for S. aureus. We demonstrate that S. aureus is capable of generating stable intracellular infections in SaOS2-OY cells but not in undifferentiated, osteoblast-like SaOS2 cells (SaOS2-OB). In SaOS2-OY cells, S. aureus transitioned towards a quasi-dormant small colony variant (SCV) growth phenotype over a 15-day post-infection period. The infected cells exhibited changes in the expression of key immunomodulatory mediators that are consistent with the infection response of primary osteocytes. Thus, SaOS2-OY is an appropriate cell line model that may be predictive of the interactions between S. aureus and human osteocytes, and this will be useful for studying mechanisms of persistence and for testing the efficacy of potential antimicrobial strategies.

Uropathogenic Escherichia coli Shows Antibiotic Tolerance and Growth Heterogeneity in an In Vitro Model of Intracellular Infection

Uropathogenic Escherichia coli (UPEC), the major causative agent of urinary tract infections, can invade different types of host cells. To compare the pharmacodynamic properties of antibiotics against intra- and extracellular UPEC, an in vitro model of intracellular infection was established in J774 mouse macrophages infected by the UPEC strain CFT073. We tested antibiotics commonly prescribed against urinary tract infections (gentamicin, ampicillin, nitrofurantoin, trimethoprim, sulfamethoxazole, and ciprofloxacin) and the investigational fluoroquinolone finafloxacin. The metabolic activity of individual bacteria was assessed by expressing the fluorescent reporter protein TIMERbac within CFT073. Concentration-response experiments revealed that all tested antibiotics were much less effective against intracellular bacteria than extracellular ones. Most antibiotics, except fluoroquinolones, were unable to reach a bactericidal effect intracellularly at clinically achievable concentrations. Ciprofloxacin and finafloxacin killed 99.9% of extracellular bacteria at concentrations around the MIC, while for intracellular bacteria, concentrations more than 100× over the MIC were required to achieve a bactericidal effect. Time-kill curves showed that finafloxacin was more rapidly bactericidal in acidic medium than at neutral pH, while the reverse observation was made for ciprofloxacin. Intracellularly, kill curves showed biphasic kinetics for both fluoroquinolones, suggesting the presence of drug-tolerant subpopulations. Flow cytometry analysis of TIMERbac fluorescence revealed a marked heterogeneity in intracellular growth of individual bacteria, suggesting that the presence of subpopulations reaching a state of metabolic dormancy was the main reason for increased antibiotic tolerance of intracellular UPEC.

Formulation strategies for bacteriophages to target intracellular bacterial pathogens

Bacteriophages (Phages) are antibacterial viruses that are unaffected by antibiotic drug resistance. Many Phase I and Phase II phage therapy clinical trials have shown acceptable safety profiles. However, none of the completed trials could yield data supporting the promising observations noted in the experimental phage therapy. These trials have mainly focused on phage suspensions without enough attention paid to the stability of phage during processing, storage, and administration. This is important because in vivo studies have shown that the effectiveness of phage therapy greatly depends on the ratio of phage to bacterial concentrations (multiplicity of infection) at the infection site. Additionally, bacteria can evade phages through the development of phage-resistance and intracellular residence. This review focuses on the use of phage therapy against bacteria that survive within the intracellular niches. Recent research on phage behavior reveals that some phage can directly interact with, get internalized into, and get transcytosed across mammalian cells, prompting further research on the governing mechanisms of these interactions and the feasibility of harnessing therapeutic phage to target intracellular bacteria. Advances to improve the capability of phage attacking intracellular bacteria using formulation approaches such as encapsulating/conjugating phages into/with vector carriers via liposomes, polymeric particles, inorganic nanoparticles, and cell penetrating peptides, are summarized. While promising progress has been achieved, research in this area is still in its infancy and warrants further attention.

Repurposing of the Fasciolicide Triclabendazole to Treat Infections Caused by Staphylococcus spp. and Vancomycin-Resistant Enterococci

One approach to combat the increasing incidence of multidrug-resistant (MDR) bacterial pathogens involves repurposing existing compounds with known safety and development pathways as new antibacterial classes with potentially novel mechanisms of action. Here, triclabendazole (TCBZ), a drug originally developed to treat Fasciola hepatica (liver fluke) in sheep and cattle, and later in humans, was evaluated as an antibacterial alone or in combination with sub-inhibitory concentrations of polymyxin B (PMB) against clinical isolates and reference strains of key Gram-positive and Gram-negative bacteria. We show for the first time that in vitro, TCBZ selectively kills methicillin-sensitive and methicillin-resistant Staphylococcus aureus and Staphylococcus pseudintermedius at a minimum inhibitory concentration (MIC) range of 2–4 µg/mL, and vancomycin-resistant enterococci at a MIC range of 4–8 µg/mL. TCBZ also inhibited key Gram-negative bacteria in the presence of sub-inhibitory concentrations of PMB, returning MIC₉₀ values of 1 µg/mL for Escherichia coli, 8 µg/mL for Klebsiella pneumoniae, 2 µg/mL for Acinetobacter baumannii and 4 µg/mL for Pseudomonasaeruginosa. Interestingly, TCBZ was found to be bacteriostatic against intracellular S. aureus but bactericidal against intracellular S. pseudintermedius. Additionally, TCBZ’s favourable pharmacokinetic (PK) and pharmacodynamic (PD) profile was further explored by in vivo safety and efficacy studies using a bioluminescent mouse model of S. aureus sepsis. We show that repeated four-hourly oral treatment of mice with 50 mg/kg TCBZ after systemic S. aureus challenge resulted in a significant reduction in S. aureus populations in the blood to 18 h post-infection (compared to untreated mice) but did not clear the bacterial infection from the bloodstream, consistent with in vivo bacteriostatic activity. These results indicate that additional pharmaceutical development of TCBZ may enhance its PK/PD, allowing it to be an appropriate candidate for the treatment of serious MDR bacterial pathogens.

Clindamycin as an Alternative Option in Optimizing Periodontal Therapy

Periodontal disease is an oral infectious and inflammatory disease caused by microorganisms that determine the host-mediated destruction of soft and hard periodontal tissues, which ultimately leads to tooth loss. Periodontitis affects a large part of the population, with various degrees of severity. Treatment consists of etiologic therapy: the removal of biofilm through mechanical debridement plus microbial elimination by supplementary measures. Antibiotic administration, either systemically or through local delivery, has been shown to improve clinical outcomes after mechanical periodontal treatment. Clindamycin is a lincosamide with a broad spectrum, being active against aerobic, anaerobic, and β-lactamase-producing bacteria. This antibiotic offers several advantages and some disadvantages and has been used in periodontal treatment both systemically and locally with various degrees of success. Among the properties that recommend it for periodontal treatment is the bacteriostatic effect, the inhibition of bacterial proteins synthesis, the enhancement of neutrophil chemotaxis, phagocytosis and the oxidative burst–oxidative stress storm. Furthermore, it is easily absorbed at the level of oral tissues in a considerable amount. This substantial tissue penetration, especially inside the bone, is synergistic with a stimulating effect on the host immune system. The aim of this review is to explore the applicability of this antibiotic agent and to evaluate its antimicrobial potential and limitations at the level of the oral biofilm associated with periodontal disease.

Dual therapeutic targeting of intra-articular inflammation and intracellular bacteria enhances chondroprotection in septic arthritis

Bacterial infections involving joints and vital organs represent a challenging clinical problem because of the two concurrent therapeutic goals of bacterial eradication and tissue preservation. In the case of septic arthritis, permanent destruction of articular cartilage by intense host inflammation is commonly seen even after successful treatment of bacterial infection. Here, we provide scientific evidence of a novel treatment modality that can protect articular cartilage and enhanced eradication of causative bacteria in septic arthritis. Locally delivered cell-penetrating antibiotics such as rifampicin effectively eradicate intracellular reservoirs of methicillin-resistant Staphylococcus aureus within joint cells. Furthermore, mitigation of intra-articular inflammation by targeting the NLRP3 (nucleotide-binding oligomerization domain-, leucine-rich repeat- and pyrin domain-containing 3) inflammasome protects articular cartilage from damage in a murine model of knee septic arthritis. Together, concurrent mitigation of intra-articular inflammation and local adjuvant targeting of intracellular bacteria represents a promising new therapeutic strategy for septic arthritis.

Legionella antibiotic susceptibility testing: is it time for international standardization and evidence-based guidance?

Legionella pneumophila, a Gram-negative bacillus, is the causative agent of Legionnaire's disease, a form of severe community-acquired pneumonia. Infection can have high morbidity, with a high proportion of patients requiring ICU admission, and up to 10% mortality, which is exacerbated by the lack of efficacy of typical empirical antibiotic therapy against Legionella spp. The fastidious nature of the entire Legionellaceae family historically required inclusion of activated charcoal in the solid medium to remove growth inhibitors, which inherently interferes with accurate antimicrobial susceptibility determination, an acknowledged methodological shortfall, now rectified by a new solid medium that gives results comparable to those of microbroth dilution. Here, as an international Legionella community (with authors representing various international reference laboratories, countries and clinical stakeholders for diagnosis and treatment of legionellosis), we set out recommendations for the standardization of antimicrobial susceptibility testing methods, guidelines and reference strains to facilitate an improved era of antibiotic resistance determination.

The clinical path to deliver encapsulated phages and lysins

The global emergence of multidrug-resistant pathogens is shaping the current dogma regarding the use of antibiotherapy. Many bacteria have evolved to become resistant to conventional antibiotherapy, representing a health and economic burden for those afflicted. The search for alternative and complementary therapeutic approaches has intensified and revived phage therapy. In recent decades, the exogenous use of lysins, encoded in phage genomes, has shown encouraging effectiveness. These two antimicrobial agents reduce bacterial populations; however, many barriers challenge their prompt delivery at the infection site. Encapsulation in delivery vehicles provides targeted therapy with a controlled compound delivery, surpassing chemical, physical and immunological barriers that can inactivate and eliminate them. This review explores phages and lysins' current use to resolve bacterial infections in the respiratory, digestive, and integumentary systems. We also highlight the different challenges they face in each of the three systems and discuss the advances towards a more expansive use of delivery vehicles.

Recalcitrant Staphylococcus aureus Infections: Obstacles and Solutions

Antibiotic treatment failure of Staphylococcus aureus infections is very common. In addition to genetically encoded mechanisms of antibiotic resistance, numerous additional factors limit the efficacy of antibiotics in vivo Identifying and removing the barriers to antibiotic efficacy are of major importance, as even if new antibiotics become available, they will likely face the same barriers to efficacy as their predecessors. One major obstacle to antibiotic efficacy is the proficiency of S. aureus to enter a physiological state that is incompatible with antibiotic killing. Multiple pathways leading to antibiotic tolerance and the formation of tolerant subpopulations called persister cells have been described for S. aureus Additionally, S. aureus is a versatile pathogen that can infect numerous tissues and invade a variety of cell types, of which some are poorly penetrable to antibiotics. It is therefore unlikely that there will be a single solution to the problem of recalcitrant S. aureus infection. Instead, specific approaches may be required for targeting tolerant cells within different niches, be it through direct targeting of persister cells, sensitization of persisters to conventional antibiotics, improved penetration of antibiotics to particular niches, or any combination thereof. Here, we examine two well-described reservoirs of antibiotic-tolerant S. aureus, the biofilm and the macrophage, the barriers these environments present to antibiotic efficacy, and potential solutions to the problem.

Nano-fats for bugs: the benefits of lipid nanoparticles for antimicrobial therapy

Bacterial infections are an imminent global healthcare threat evolving from rapidly advancing bacterial defence mechanisms that antibiotics fail to overcome. Antibiotics have been designed for systemic administration to target planktonic bacteria, leading to difficulties in reaching the site of localized bacterial infection and an inability to overcome the biological, chemical and physical barriers of bacteria, including biofilms, intracellular infections and antimicrobial resistance. The amphiphilic, biomimetic and antimicrobial properties of lipids provide a promising toolbox to innovate and advance antimicrobial therapies, overcoming the barriers presented by bacteria in order to directly and effectively treat recalcitrant infections. Nanoparticulate lipid-based drug delivery systems can enhance antibiotic permeation through the chemical and physical barriers of bacterial infections, as well as fuse with bacterial cell membranes, release antibiotics in response to bacteria and act synergistically with loaded antibiotics to enhance the total antimicrobial efficacy. This review explores the barriers presented by bacterial infections that pose bio-pharmaceutical challenges to antibiotics and how different structural and functional mechanisms of lipids can enhance antimicrobial therapies. Different nanoparticulate lipid-based systems are presented as valuable drug delivery systems to advance the efficacy of antibiotics, including liposomes, liquid crystalline nanoparticles, solid lipid nanoparticles, nanostructured lipid carriers and lipid nanocarriers. In summary, liquid crystalline nanoparticles are emerging with the greatest potential for clinical applications and commercial success as an "all-rounder" advanced lipid-based antimicrobial therapy that overcomes the multiple biological, chemical and physical barriers of bacteria.

Antimicrobial Peptides and Cell-Penetrating Peptides for Treating Intracellular Bacterial Infections

Bacterial infections caused by intracellular pathogens are difficult to control. Conventional antibiotic therapies are often ineffective, as high doses are needed to increase the number of antibiotics that will cross the host cell membrane to act on the intracellular bacterium. Moreover, higher doses of antibiotics may lead to elevated severe toxic effects against host cells. In this context, antimicrobial peptides (AMPs) and cell-penetrating peptides (CPPs) have shown great potential to treat such infections by acting directly on the intracellular pathogenic bacterium or performing the delivery of cargos with antibacterial activities. Therefore, in this mini-review, we cover the main AMPs and CPPs described to date, aiming at intracellular bacterial infection treatment. Moreover, we discuss some of the proposed mechanisms of action for these peptide classes and their conjugation with other antimicrobials.

Locally delivered adjuvant biofilm-penetrating antibiotics rescue impaired endochondral fracture healing caused by MRSA infection

Infection is a devastating complication following an open fracture. We investigated whether local rifampin-loaded hydrogel can combat infection and improve healing in a murine model of methicillin-resistant Staphylococcus aureus (MRSA) osteomyelitis. A transverse fracture was made at the tibia midshaft of C57BL/6J mice aged 10-12 weeks and stabilized with an intramedullary pin. A total of 1 × 106 colony-forming units (CFU) of MRSA was inoculated. A collagen-based hydrogel containing low-dose (60 μg) and high-dose (300 μg) rifampin was applied before closure. Postoperative treatment response was assessed through bacterial CFU counts from tissue and hardware, tibial radiographs and microcomputed tomography (μCT), immunohistochemistry, and histological analyses. All untreated MRSA-infected fractures progressed to nonunion by 28 days with profuse MRSA colonization. Infected fractures demonstrated decreased soft callus formation on safranin O stain compared to controls. Areas of dense interleukin-1β stain were associated with poor callus formation. High-dose rifampin hydrogels reduced the average MRSA load in tissue (p < 0.0001) and implants (p = 0.041). Low-dose rifampin hydrogels reduced tissue bacterial load by 50% (p = 0.021). Among sterile models, 88% achieved union compared to 0% of those infected. Mean radiographic union scale in tibia scores improved from 6 to 8.7 with high-dose rifampin hydrogel (p = 0.024) and to 10 with combination local/systemic rifampin therapy (p < 0.0001). μCT demonstrated reactive bone formation in MRSA infection. Histology demonstrated restored fracture healing with bacterial elimination. Rifampin-loaded hydrogels suppressed osteomyelitis, prevented implant colonization, and improved healing. Systemic rifampin was more effective at eliminating infection and improving fracture healing. Further investigation into rifampin-loaded hydrogels is required to correlate these findings with clinical efficacy.

Immunomodulatory gene expression analysis in LPS-stimulated human polymorphonuclear leukocytes treated with antibiotics commonly used for multidrug-resistant strains

Conventional antibiotics used for the treatment of severe infections such as sepsis and septic shock confer immunomodulatory benefits. However, the growing problem of multidrug resistant infections has led to an increase in the administration of non-conventional last-resort antibiotics, including quinolones, aminoglycosides, and polypeptides, and the effects of these drugs on immunomodulatory gene expression in activated human polymorphonuclear leukocytes (PMNs) have not been reported. In this study, lipopolysaccharide-stimulated PMNs were incubated with piperacillin, rifampicin, fosfomycin (FOM), levofloxacin (LVFX), minocycline (MINO), colistin, tigecycline, or amikacin, and the mRNA expression levels of pattern recognition receptors (TLR2, TLR4, and CD14), inflammatory cytokines (TNFα and IL6), and chemokine receptors (IL8Rs and ITGAM) in these cells were quantitated using real-time qPCR. Many of the tested antibiotics altered the expression of the investigated cytokines. Notably, FOM, LVFX, and MINO significantly downregulated the expression of IL6, which is associated with pro- and anti-inflammatory defense mechanisms. Treatment of FOM and LVFX reduced IL-6 production as well as observed for IL6 gene expression. These findings indicated transcription and translation cooperation under the used experimental conditions. Therefore, our findings suggest that administration of these antibiotics suppresses the host anti-inflammatory response.

Differential effects of antibiotics on neutrophils exposed to lipoteichoic acid derived from Staphylococcus aureus

BACKGROUND

Persistent bacteremia occurs in at least 30% of patients with Staphylococcus aureus bloodstream infection (SAB) and may be attributable to a dysregulated host immune response. Neutrophils interact with a variety of S. aureus microbial factors, including lipoteichoic acid (LTA), to activate phagocytic function in a concentration-dependent manner. Antibiotics have been shown to exert both direct antimicrobial action as well as immunomodulatory effects. In this study, we compared the effects of different anti-staphylococcal antibiotics on LTA-mediated immune activation of neutrophils.

METHODS

Neutrophils obtained from healthy volunteers were exposed to two levels of LTA (1 and 10 μg/ml) with or without addition of antibiotics from different pharmacologic classes (vancomycin, daptomycin, ceftaroline). Neutrophil function was assessed by examining phagocytic response, activation (CD11b, CD62L expression), Toll-like receptor-2 expression, cell survival and apoptosis, and CXCL8 release.

RESULTS

Differential LTA-mediated antibiotic effects on neutrophil function were observed primarily at the high LTA exposure level. Ceftaroline in the presence of 10 μg/ml LTA had the most prominent effects on phagocytosis and CD11b and CD62L expression, with trends towards increased neutrophil survival and preservation of CXCL8 release when compared to daptomycin and vancomycin with the latter significantly dampening PMN CXCL8 release.

CONCLUSIONS

Select antimicrobial agents, such as ceftaroline, exert immunostimulatory effects on neutrophils exposed to S. aureus LTA, which when confirmed in vivo, could be leveraged for its dual immunomodulatory and antibacterial actions for the treatment of persistent SAB mediated by a dysregulated host response.

Pharmacokinetic/pharmacodynamic considerations for new and current therapeutic drugs for uncomplicated gonorrhoea-challenges and opportunities

BACKGROUND

Increasing multidrug resistance rates in Neisseria gonorrhoeae have raised concerns and an urgent call for new antibiotics for treatment of gonorrhoea. Several decades of subdued drug development in this field and the recent failures of two new antibiotics to show non-inferiority compared with the current first-line antibiotics ceftriaxone plus azithromycin highlight the need for improved preclinical tools to predict clinical outcome of new drugs in the development process.

OBJECTIVES

To summarize current pharmacokinetic/pharmacodynamic (PK/PD) knowledge and dose-finding strategies for antibiotics against gonorrhoea.

SOURCES

Literature review of published papers and discussions by global experts at a special workshop on this topic.

CONTENT

We review current knowledge of gonococcal specific PK/PD principles and provide an update on new in vitro and in vivo models to correlate drug exposure with clinical outcome, and identify challenges and gaps in gonococcal therapeutic research.

IMPLICATIONS

Identifying the ideal antimicrobial agent and dose for treating uncomplicated urogenital and pharyngeal gonococcal disease requires appropriate validated non-clinical PK/PD models. Recent advances in adapting in vitro and in vivo models for use in gonorrhoea are an important step for enabling the development of new drugs with reduced risk of failure in Phase 3 clinical development and diminish the risk of emergence of resistance.

Biodistribution and intracellular localization of hyaluronan and its nanogels. A strategy to target intracellular S. aureus in persistent skin infections

Intracellular pathogens are a critical challenge for antimicrobial therapies. Staphylococcus aureus (S. aureus) causes approximately 85% of all skin and soft tissue infections in humans worldwide and more than 30% of patients develop chronic or recurrent infections within three months, even after appropriate antibacterial therapies. S. aureus is also one of the most common bacteria found in chronic wounds. Recent evidences suggest that S. aureus is able to persist within phagolysosomes of skin cells (i.e. keratinocytes, phagocytic cells), being protected from both the immune system and a number of antimicrobials. To overcome these limits, nano-formulations that enable targeted therapies against intracellular S. aureus might be developed. Herein, the biodistribution and intracellular localisation of hyaluronan (HA) and HA-based nanoparticles (nanogels, NHs) are investigated, both after intravenous (i.v.) injections (in mice) and topical administrations (in ex vivo human skin). Results indicate HA and NHs accumulate especially in skin and liver of mice after i.v. injection. After topical application on human skin explants, no penetration of both HA and NHs was detected in skin with intact stratum corneum. By contrast, in barrier-disrupted human skin (with partial removal and loosening of stratum corneum), HA and NHs penetrate to the viable epidermis and are taken up by keratinocytes. In mechanically produced wounds (skin without epidermis) they accumulate in wound tissue and are taken up by dermis cells, e.g. fibroblasts and phagocytic cells. Interestingly, in all cases, the cellular uptake is CD44-mediated. In vitro studies confirmed that after CD44-mediated uptake, both HA and NHs accumulate in lysosomes of dermal fibroblasts and macrophages, as previously reported for keratinocytes. Finally, the colocalisation between intracellular S. aureus and HA or NHs is demonstrated, in macrophages. Altogether, for the first time, these results strongly suggest that HA and HA-based NHs can provide a targeted therapy to intracellular S. aureus, in persistent skin or wound infections.

Critical Role for the NLRP3 Inflammasome in Mediating IL-1β Production in Shigella sonnei-Infected Macrophages

Shigella is one of the leading bacterial causes of diarrhea worldwide, affecting more than 165 million people annually. Among the serotypes of Shigella, Shigella sonnei is physiologically unique and endemic in human immunodeficiency virus-infected men who have sex with men. The NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome, a protein complex composed of NLRP3, apoptosis-associated speck-like protein, and caspase-1, recognizes, and responds to pathogen infection and diverse sterile host-derived or environmental danger signals to induce IL-1β and IL-18 production. Although the Shigella flexneri-mediated activation of the NLRP3 inflammasome has been reported, the effect of S. sonnei on NLRP3 inflammasome activation remains unclear. We found that S. sonnei induced IL-1β production through NLRP3-dependent pathways in lipopolysaccharide-primed macrophages. A mechanistic study revealed that S. sonnei induced IL-1β production through P₂X₇ receptor-mediated potassium efflux, reactive oxygen species generation, lysosomal acidification, and mitochondrial damage. In addition, the phagocytosis of viable S. sonnei was important for IL-1β production. Furthermore, we demonstrated that NLRP3 negatively regulated phagocytosis and the bactericidal activity of macrophages against S. sonnei. These findings provide mechanistic insight into the activation of the NLRP3 inflammasome by S. sonnei in macrophages.

An alternative penicillin-binding protein involved in Salmonella relapses following ceftriaxone therapy

Background

Salmonella causes intracellular infections in humans. Besides quinolones, third generation cephalosporins are first line drugs used for salmonellosis therapy. An unresolved anomaly of this practice involves high relapse rates associated to quinolone- or cephalosporin-susceptible Salmonella isolates in patients that are discharged clinically following initial recovery. Reduced drug accessibility to intracellular locations has been hypothesized to impair pathogen eradication although supporting evidence is lacking in vivo. Here, we uncover a novel penicillin-binding protein as the first Salmonella factor likely contributing to relapse following beta-lactam, mainly ceftriaxone, therapy.

Methods

We used Salmonella enterica serovar Typhimurium mutants lacking the alternative penicillin-binding proteins PBP2_SAL or PBP3_SAL. Affinity of PBP2_SAL and PBP3_SAL for beta-lactam antibiotics was tested. Relapse after ceftriaxone therapy was analysed in the murine typhoid model.

Findings

S. Typhimurium does not express PBP2_SAL or PBP3_SAL in the Mueller-Hinton medium used for susceptibility testing. The pathogen produces these PBPs in response to acidic pH and nutrient limitation, conditions found in phagosomes of mammalian cells. PBP3_SAL has low affinity for beta-lactams, even at acidic pH. In vitro susceptibility to ceftriaxone at low pH is strongly reduced. S. Typhimurium lacking PBP3_SAL was unable to cause relapse in mice following ceftriaxone therapy.

Interpretation

The reduced capacity of ceftriaxone to clear S. Typhimurium in vivo is favoured by a switch in beta-lactam targets. This switch, involving production of the less-susceptible PBP3_SAL, remains invisible for standard procedures used in clinical therapy. We conclude that eradication of salmonellosis will be possible only upon targeting of PBP3_SAL with novel drugs.

New automated analysis to monitor neutrophil function point-of-care in the intensive care unit after trauma

BACKGROUND

Patients often develop infectious complications after severe trauma. No biomarkers exist that enable early identification of patients who are at risk. Neutrophils are important immune cells that combat these infections by phagocytosis and killing of pathogens. Analysis of neutrophil function used to be laborious and was therefore not applicable in routine diagnostics. Hence, we developed a quick and point-of-care method to assess a critical part of neutrophil function, neutrophil phagosomal acidification. The aim of this study was to investigate whether this method was able to analyze neutrophil functionality in severely injured patients and whether a relation with the development of infectious complications was present.

RESULTS

Fifteen severely injured patients (median ISS of 33) were included, of whom 6 developed an infection between day 4 and day 9 after trauma. The injury severity score did not significantly differ between patients who developed an infection and patients who did not (p = 0.529). Patients who developed an infection showed increased acidification immediately after trauma (p = 0.006) and after 3 days (p = 0.026) and a decrease in the days thereafter to levels in the lower normal range. In contrast, patients who did not develop infectious complications showed high-normal acidification within the first days and increased tasset to identify patients at risk for infections after trauma and to monitor the inflammatory state of these trauma patients.

CONCLUSION

Neutrophil function can be measured in the ICU setting by rapid point-of-care analysis of phagosomal acidification. This analysis differed between trauma patients who developed infectious complications and trauma patients who did not. Therefore, this assay might prove a valuable asset to identify patients at risk for infections after trauma and to monitor the inflammatory state of these trauma patients.

TRIAL REGISTRATION

Central Committee on Research Involving Human Subjects, NL43279.041.13. Registered 14 February 2014. https://www.toetsingonline.nl/to/ccmo_search.nsf/Searchform?OpenForm.

Myxobacteria-Derived Outer Membrane Vesicles: Potential Applicability Against Intracellular Infections

In 2019, it was estimated that 2.5 million people die from lower tract respiratory infections annually. One of the main causes of these infections is Staphylococcus aureus, a bacterium that can invade and survive within mammalian cells. S. aureus intracellular infections are difficult to treat because several classes of antibiotics are unable to permeate through the cell wall and reach the pathogen. This condition increases the need for new therapeutic avenues, able to deliver antibiotics efficiently. In this work, we obtained outer membrane vesicles (OMVs) derived from the myxobacteria Cystobacter velatus strain Cbv34 and Cystobacter ferrugineus strain Cbfe23, that are naturally antimicrobial, to target intracellular infections, and investigated how they can affect the viability of epithelial and macrophage cell lines. We evaluated by cytometric bead array whether they induce the expression of proinflammatory cytokines in blood immune cells. Using confocal laser scanning microscopy and flow cytometry, we also investigated their interaction and uptake into mammalian cells. Finally, we studied the effect of OMVs on planktonic and intracellular S. aureus. We found that while Cbv34 OMVs were not cytotoxic to cells at any concentration tested, Cbfe23 OMVs affected the viability of macrophages, leading to a 50% decrease at a concentration of 125,000 OMVs/cell. We observed only little to moderate stimulation of release of TNF-alpha, IL-8, IL-6 and IL-1beta by both OMVs. Cbfe23 OMVs have better interaction with the cells than Cbv34 OMVs, being taken up faster by them, but both seem to remain mostly on the cell surface after 24 h of incubation. This, however, did not impair their bacteriostatic activity against intracellular S. aureus. In this study, we provide an important basis for implementing OMVs in the treatment of intracellular infections.

Staphylococcus aureus Internalized by Skin Keratinocytes Evade Antibiotic Killing

Staphylococcus aureus causes the majority of skin and soft tissue infections. Half of patients treated for primary skin infections suffer recurrences within 6 months despite appropriate antibiotic sensitivities and infection control measures. We investigated whether S. aureus internalized by human skin keratinocytes are effectively eradicated by standard anti-staphylococcal antibiotics. S. aureus, but not S. epidermidis, were internalized and survive within keratinocytes without inducing cytotoxicity or releasing the IL-33 danger signal. Except for rifampicin, anti-staphylococcal antibiotics in regular clinical use, including flucloxacillin, teicoplanin, clindamycin, and linezolid, did not kill internalized S. aureus, even at 20-fold their standard minimal inhibitory concentration. We conclude that internalization of S. aureus by human skin keratinocytes allows the bacteria to evade killing by most anti-staphylococcal antibiotics. Antimicrobial strategies, including antibiotic combinations better able to penetrate into mammalian cells are required if intracellular S. aureus are to be effectively eradicated and recurrent infections prevented.

Anti-Mycoplasma Activity of Daptomycin and Its Use for Mycoplasma Elimination in Cell Cultures of Rickettsiae

Mycoplasma contamination detrimentally affects cellular functions and the growth of intracellular pathogens in cell cultures. Although several mycoplasmacidal agents are commercially available for sterile cell cultures, they are not applicable to rickettsia-infected cells. In our attempt to find an anti-mycoplasma drug for contaminated rickettsial cultures, we determined the susceptibilities of three common Mycoplasma species to daptomycin. Mycoplasma orale and M. arginini showed low-level resistance to daptomycin (minimum inhibitory concentration, MIC = 2 mg/L), whereas M. hyorhinis was high-level resistant (MIC = 32 mg/L). However, some Mycoplasma isolates developed higher resistance to daptomycin after failed treatments with inadequate doses or durations. An aminoglycoside (gentamicin) was still active against M. hyorhinis and could be used in Orientia cultures. For complete eradication of mycoplasmas in Rickettsia cultures, we recommend a 3-week treatment with daptomycin at 256 mg/L. In contaminated Orientia cultures, daptomycin at 32 mg/L was effective in eradicating M. orale, whereas either gentamicin or amikacin (100 mg/L) was effective in eradicating M. hyorhinis. Unlike each drug alone, the combinations of daptomycin plus clindamycin and/or quinupristin/dalfopristin proved effective in eradicating M. hyorhinis. In summary, our study demonstrated the in vitro anti-mycoplasma activity of daptomycin and its application as a new mycoplasma decontamination method for Rickettsia and Orientia cultures.