Convergence of Staphylococcus aureus Persister and Biofilm Research: Can Biofilms Be Defined as Communities of Adherent Persister Cells?

Adjunctive Rifampicin Increases Antibiotic Efficacy in Group A Streptococcal Tissue Infection Models

Biofilm has recently been highlighted as a complicating feature of necrotizing soft tissue infections (NSTI) caused by Streptococcus pyogenes (i.e., group A Streptococcus [GAS]) contributing to a persistence of bacteria in tissue despite prolonged antibiotic therapy. Here, we assessed the standard treatment of benzylpenicillin and clindamycin with or without rifampin in a tissue-like setting. Antibiotic efficacy was evaluated by CFU determination in a human organotypic skin model infected for 24 or 48 h with GAS strains isolated from NSTI patients. Antibiotic effect was also evaluated by microcalorimetric metabolic assessment in in vitro infections of cellular monolayers providing continuous measurements over time. Adjunctive rifampin resulted in enhanced antibiotic efficacy of bacterial clearance in an organotypic skin tissue model, 97.5% versus 93.9% (P = 0.006). Through microcalorimetric measurements, adjunctive rifampin resulted in decreased metabolic activity and extended lag phase for all clinical GAS strains tested (P < 0.05). In addition, a case report is presented of adjunctive rifampin treatment in an NSTI case with persistent GAS tissue infection. The findings of this study demonstrate that adjunctive rifampin enhances clearance of GAS biofilm in an in vitro tissue infection model.

Novel strategies to diagnose prosthetic or native bone and joint infections

INTRODUCTION

Bone and Joint Infections (BJI) are medically important, costly and occur in native and prosthetic joints. Arthroplasties will increase significantly in absolute numbers over time as well as the incidence of Prosthetic Joint Infections (PJI). Diagnosis of BJI and PJI is sub-optimal. The available diagnostic tests have variable effectiveness, are often below standard in sensitivity and/or specificity, and carry significant contamination risks during the collection of clinical samples. Improvement of diagnostics is urgently needed.

AREAS COVERED

We provide a narrative review on current and future diagnostic microbiology technologies. Pathogen identification, antibiotic resistance detection, and assessment of the epidemiology of infections via bacterial typing are considered useful for improved patient management. We confirm the continuing importance of culture methods and successful introduction of molecular, mass spectrometry-mediated and next-generation genome sequencing technologies. The diagnostic algorithms for BJI must be better defined, especially in the context of diversity of both disease phenotypes and clinical specimens rendered available.

EXPERT OPINION

Whether interventions in BJI or PJI are surgical or chemo-therapeutic (antibiotics and bacteriophages included), prior sensitive and specific pathogen detection remains a therapy-substantiating necessity. Innovative tests for earlier and more sensitive and specific detection of bacterial pathogens in BJI are urgently needed.

A scoping review protocol to identify clinical signs, symptoms and biomarkers indicative of biofilm presence in chronic wounds

Introduction: Wound healing is characterised by haemostatic, inflammatory, proliferative and remodelling phases. In the presence of comorbidities such as diabetes, healing can stall and chronic wounds may result. Infection is detrimental to these wounds and associated with poor outcomes. Wounds are contaminated with microbes and debris, and factors such as host resistance, bacterial virulence, species synergy and bioburden determine whether a wound will deteriorate to critically colonised/infected states. Biofilms are sessile microbial communities, exhibiting high-level antibiotic tolerance and resistance to host defences. Biofilm in critically colonised wounds can contribute to delayed healing. Little is known about clinical presentation and diagnosis of wound biofilms. Objective: To identify from the literature clinical signs, symptoms and biomarkers that may indicate biofilm in chronic wounds. Methods: This review will be guided by the Preferred Reporting Items for Systematic Reviews extension for Scoping Reviews (PRISMA-ScR), and the Joanna Briggs Institute Manual for Evidence Synthesis. Studies of any design in any language recruiting adult patients with  venous, diabetic, pressure or mixed arterial-venous ulcers and reporting data on clinical signs/symptoms of biofilm are eligible. Searches of Medline, Embase, CINAHL, Cochrane Central, Scopus, Web of Science, Google scholar and BASE will be conducted from inception to present. Reference scanning and contact with content experts will be employed. Title/abstract screening and full text selection will be executed by two reviewers independently. Discrepancies will be resolved by discussion between reviewers or through third party intervention. Data will be extracted by a single reviewer and verified by a second. Clinical signs and symptoms data will be presented in terms of study design, setting and participant demographic data. Discussion: Understanding biofilm impact on chronic wounds is inconsistent and based largely on in vitro research. This work will consolidate clinical signs, symptoms and biomarkers of biofilm in chronic wounds reported in the literature.

Eco-friendly Mycogenic Synthesis of ZnO and CuO Nanoparticles for In Vitro Antibacterial, Antibiofilm, and Antifungal Applications

Mycogenic synthesis of medically applied zinc oxide (ZnO) and copper oxide (CuO) nanoparticles (NPs) were exploited using Penicillium chrysogenum. The biogenesis and capping processes of the produced nano-metals were conducted by functional fungal extracellular enzymes and proteins. The obtained ZnO-NPs and CuO-NPs were characterized. Also, the antibacterial activity and minimum inhibitory concentration (MIC) values of ZnO-NPs and CuO-NPs were determined. Also, antibiofilm and antifungal activities were investigated. Results have demonstrated the ability of the bio-secreted proteins to cape and reduce ZnO and CuO to hexagonal and spherical ZnO-NPs and CuO-NPs with particle size at 9.0-35.0 nm and 10.5-59.7 nm, respectively. Both ZnO-NPs and CuO-NPs showed high antimicrobial activities not only against Gram-positive and Gram-negative bacteria but also against some phytopathogenic fungal strains. Besides this, those NPs showed varied antibiofilm effects against different microorganisms. Quantitative and qualitative analyses indicated that CuO-NPs had an effective antibiofilm activity against Staphylococcus aureus and therefore can be applied in diverse medical devices. Thus, the mycogenic green synthesized ZnO-NPs and CuO-NPs have the potential as smart nano-materials to be used in the medical field to limit the spread of some pathogenic microbes.

Antibacterial, Antibiofilm, and Antioxidant Activity of Polysaccharides Obtained from Fresh Sarcotesta of Ginkgo biloba: Bioactive Polysaccharide that Can Be Exploited as a Novel Biocontrol Agent

Staphylococcus aureus (S. aureus) biofilm plays an important role in the persistence of chronic infection due to its resistance to antibiotics. Because of their functional diversity, active polysaccharide is increasingly being applied as a biocontrol agent to inhibit the formation of biofilm by pathogens. In this study, a new polysaccharide, GBSPII-1, isolated from the fresh sarcotesta of Ginkgo biloba L. (G. biloba) was characterized and its effect on antibiofilm formation of S. aureus was examined in vitro. High-Performance Liquid Chromatography (HPLC) analysis showed that GBSPII-1 is an acidic heteropolysaccharide composed of mannose, rhamnose, glucose, glucuronic acid, and galacturonic acid. GBSPII-1 demonstrated a molecular weight of 34 kDa and may affect the accumulation of polysaccharide intercellular adhesion (PIA) by inhibiting icaA, icaB, icaC, and icaD gene expression at subinhibitory concentrations. Under 10 g/L, GBSPII-1 showed an antioxidant effect on the inhibition rate of H₂O₂-induced erythrocyte hemolysis and the scavenging rate of DPPH radicals was 76.5 ± 0.5% and 89.2 ± 0.26%, respectively. The findings obtained in this study indicate that GBSPII-1 has antibacterial effect, is a possible source of natural antioxidants, and may be a potential biocontrol agent for the design of new therapeutic strategies for biofilm-related S. aureus infections.

Harnessing ultrasound-stimulated phase change contrast agents to improve antibiotic efficacy against methicillin-resistant Staphylococcus aureus biofilms

Bacterial biofilms, often associated with chronic infections, respond poorly to antibiotic therapy and frequently require surgical intervention. Biofilms harbor persister cells, metabolically indolent cells, which are tolerant to most conventional antibiotics. In addition, the biofilm matrix can act as a physical barrier, impeding diffusion of antibiotics. Novel therapeutic approaches frequently improve biofilm killing, but usually fail to achieve eradication. Failure to eradicate the biofilm leads to chronic and relapsing infection, is associated with major financial healthcare costs and significant morbidity and mortality. We address this problem with a two-pronged strategy using 1) antibiotics that target persister cells and 2) ultrasound-stimulated phase-change contrast agents (US-PCCA), which improve antibiotic penetration.

We previously demonstrated that rhamnolipids, produced by Pseudomonas aeruginosa, could induce aminoglycoside uptake in gram-positive organisms, leading to persister cell death. We have also shown that US-PCCA can transiently disrupt biological barriers to improve penetration of therapeutic macromolecules. We hypothesized that combining antibiotics which target persister cells with US-PCCA to improve drug penetration could improve treatment of methicillin resistant S. aureus (MRSA) biofilms. Aminoglycosides alone or in combination with US-PCCA displayed limited efficacy against MRSA biofilms. In contrast, the anti-persister combination of rhamnolipids and aminoglycosides combined with US-PCCA dramatically improved biofilm killing. This novel treatment strategy has the potential for rapid clinical translation as the PCCA formulation is a variant of FDA-approved ultrasound contrast agents that are already in clinical practice and the low-pressure ultrasound settings used in our study can be achieved with existing ultrasound hardware at pressures below the FDA set limits for diagnostic imaging.

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.

Development of Antimicrobial Phototreatment Tolerance: Why the Methodology Matters

Due to rapidly growing antimicrobial resistance, there is an urgent need to develop alternative, non-antibiotic strategies. Recently, numerous light-based approaches, demonstrating killing efficacy regardless of microbial drug resistance, have gained wide attention and are considered some of the most promising antimicrobial modalities. These light-based therapies include five treatments for which high bactericidal activity was demonstrated using numerous in vitro and in vivo studies: antimicrobial blue light (aBL), antimicrobial photodynamic inactivation (aPDI), pulsed light (PL), cold atmospheric plasma (CAP), and ultraviolet (UV) light. Based on their multitarget activity leading to deleterious effects to numerous cell structures-i.e., cell envelopes, proteins, lipids, and genetic material-light-based treatments are considered to have a low risk for the development of tolerance and/or resistance. Nevertheless, the most recent studies indicate that repetitive sublethal phototreatment may provoke tolerance development, but there is no standard methodology for the proper evaluation of this phenomenon. The statement concerning the lack of development of resistance to these modalities seem to be justified; however, the most significant motivation for this review paper was to critically discuss existing dogma concerning the lack of tolerance development, indicating that its assessment is more complex and requires better terminology and methodology.

Identification of Eltrombopag as a Repurposing Drug Against Staphylococcus epidermidis and its Biofilms

Staphylococcus epidermidis is a common cause of nosocomial infections, and readily adheres to medical apparatus to form biofilms consisting of highly resistant persister cells. Owing to the refractory infections caused by S. epidermidis biofilms and persisters in immunosuppressed patients, it is crucial to develop new antimicrobials. In the present study, we analyzed the antimicrobial effects of the thrombopoietin receptor agonist eltrombopag (EP) against S. epidermidis planktonic cells, biofilms, and persister cells. EP was significantly toxic to S. epidermidis with the minimal inhibitory concentration of 8 μg/ml, and effectively inhibited the biofilms and persisters in a strain-dependent manner. In addition, EP was only mildly toxic to mammalian cells after 12 to 24 h treatment. It also partially synergized with vancomycin against S. epidermidis, which enhanced its antimicrobial effects and reduced its toxicity to mammalian cells. Taken together, EP is a potential antibiotic for treating refractory infections caused by S. epidermidis.

Mechanisms of Antibiotic Failure During Staphylococcus aureus Osteomyelitis

Staphylococcus aureus is a highly successful Gram-positive pathogen capable of causing both superficial and invasive, life-threatening diseases. Of the invasive disease manifestations, osteomyelitis or infection of bone, is one of the most prevalent, with S. aureus serving as the most common etiologic agent. Treatment of osteomyelitis is arduous, and is made more difficult by the widespread emergence of antimicrobial resistant strains, the capacity of staphylococci to exhibit tolerance to antibiotics despite originating from a genetically susceptible background, and the significant bone remodeling and destruction that accompanies infection. As a result, there is a need for a better understanding of the factors that lead to antibiotic failure in invasive staphylococcal infections such as osteomyelitis. In this review article, we discuss the different non-resistance mechanisms of antibiotic failure in S. aureus. We focus on how bacterial niche and destructive tissue remodeling impact antibiotic efficacy, the significance of biofilm formation in promoting antibiotic tolerance and persister cell formation, metabolically quiescent small colony variants (SCVs), and potential antibiotic-protected reservoirs within the substructure of bone.

Ecofriendly novel synthesis of tertiary composite based on cellulose and myco-synthesized selenium nanoparticles: Characterization, antibiofilm and biocompatibility

Microbial infections are considered common and dangerous for humans among other infections; therefore the synthesis of high efficacy antimicrobial and anti-biofilm composites is continuous to fight microbial resistance. In our study, a new and novel tertiary composite (TC) was synthesized, it composed of TEMPO cellulose (TOC), chitosan, starch, and myco-synthesized Se-NPs. Myco-synthesized Se-NPs and TC were fully characterized using UV, FT-IR, XRD, SEM with EDX, particle distribution, and mapping. The antimicrobial and anti-biofilm properties of selenium nanoparticles (Se-NPs) were effectively established for Pseudomonas aeruginosa and Staphylococcus aureus biofilms. The possible impact of myco-synthesized novel cellulose-based selenium nanoparticles tertiary composite on the biofilm formation of P. aeruginosa, S. aureus, and Candida albicans was evaluated in this study. TC exhibited constant biofilm inhibition against P. aeruginosa, S. aureus, and C. albicans, while the results obtained from cytotoxicity of Se-NPs and TC showed that, alteration occurred in the normal cell line of lung fibroblast cells (Wi-38) was shown as loss of their typical cell shape, granulation, loss of monolayer, shrinking or rounding of Wi-38 cell with an IC₅₀ value of where 461 and 550 ppm respectively.

Staphylococcal Biofilms: Challenges and Novel Therapeutic Perspectives

Staphylococci, like Staphylococcus aureus and S. epidermidis, are common colonizers of the human microbiota. While being harmless in many cases, many virulence factors result in them being opportunistic pathogens and one of the major causes of hospital-acquired infections worldwide. One of these virulence factors is the ability to form biofilms-three-dimensional communities of microorganisms embedded in an extracellular polymeric matrix (EPS). The EPS is composed of polysaccharides, proteins and extracellular DNA, and is finely regulated in response to environmental conditions. This structured environment protects the embedded bacteria from the human immune system and decreases their susceptibility to antimicrobials, making infections caused by staphylococci particularly difficult to treat. With the rise of antibiotic-resistant staphylococci, together with difficulty in removing biofilms, there is a great need for new treatment strategies. The purpose of this review is to provide an overview of our current knowledge of the stages of biofilm development and what difficulties may arise when trying to eradicate staphylococcal biofilms. Furthermore, we look into promising targets and therapeutic methods, including bacteriocins and phage-derived antibiofilm approaches.

Nanotheranostics: A Possible Solution for Drug-Resistant Staphylococcus aureus and their Biofilms?

Staphylococcus aureus is a notorious pathogen that colonizes implants (orthopedic and breast implants) and wounds with a vicious resistance to antibiotic therapy. Methicillin-resistant S. aureus (MRSA) is a catastrophe mainly restricted to hospitals and emerged to community reservoirs, acquiring resistance and forming biofilms. Treating biofilms is problematic except via implant removal or wound debridement. Nanoparticles (NPs) and nanofibers could combat superbugs and biofilms and rapidly diagnose MRSA. Nanotheranostics combine diagnostics and therapeutics into a single agent. This comprehensive review is interpretative, utilizing mainly recent literature (since 2016) besides the older remarkable studies sourced via Google Scholar and PubMed. We unravel the molecular S. aureus resistance and complex biofilm. The diagnostic properties and detailed antibacterial and antibiofilm NP mechanisms are elucidated in exciting stories. We highlight the challenges of bacterial infections nanotheranostics. Finally, we discuss the literature and provide "three action appraisals". (i) The first appraisal consists of preventive actions (two wings), avoiding unnecessary hospital visits, hand hygiene, and legislations against over-the-counter antibiotics as the general preventive wing. Our second recommended preventive wing includes preventing the adverse side effects of the NPs from resistance and toxicity by establishing standard testing procedures. These standard procedures should provide breakpoints of bacteria's susceptibility to NPs and a thorough toxicological examination of every single batch of synthesized NPs. (ii) The second appraisal includes theranostic actions, using nanotheranostics to diagnose and treat MRSA, such as what we call "multifunctional theranostic nanofibers. (iii) The third action appraisal consists of collaborative actions.

Pulse Dosing of Antibiotic Enhances Killing of a Staphylococcus aureus Biofilm

Biofilms are highly tolerant to antibiotics and underlie the recalcitrance of many chronic infections. We demonstrate that mature Staphylococcus aureus biofilms can be substantially sensitized to the treatment by pulse dosing of an antibiotic – in this case, oxacillin. Pulse (periodic) dosing was compared to continuous application of antibiotic and was studied in a novel in vitro flow system which allowed for robust biofilm growth and tractable pharmacokinetics of dosing regimens. Our results highlight that a subpopulation of the biofilm survives antibiotic without becoming resistant, a population we refer to as persister bacteria. When oxacillin was continuously present the persister level did not decline, but, importantly, providing correctly timed periodic breaks decreased the surviving population. We found that the length of the periodic break impacted efficacy, and there was an optimal length that sensitized the biofilm to repeat treatment without allowing resistance expansion. Periodic dosing provides a potential simple solution to a complicated problem.

Structural Basis for the Inhibitor and Substrate Specificity of the Unique Fph Serine Hydrolases of Staphylococcus aureus

Staphylococcus aureus is a prevalent bacterial pathogen in both community and hospital settings, and its treatment is made particularly difficult by resilience within biofilms. Within this niche, serine hydrolase enzymes play a key role in generating and maintaining the biofilm matrix. Activity-based profiling has previously identified a family of serine hydrolases, designated fluorophosphonate-binding hydrolases (Fph's), some of which contribute to the virulence of S. aureus in vivo. These 10 Fph proteins have limited annotation and have few, if any, characterized bacterial or mammalian homologues. This suggests unique hydrolase functions even within bacterial species. Here we report structures of one of the most abundant Fph family members, FphF. Our structures capture FphF alone, covalently bound to a substrate analogue and bound to small molecule inhibitors that occupy the hydrophobic substrate-binding pocket. In line with these findings, we show that FphF has promiscuous esterase activity toward hydrophobic lipid substrates. We present docking studies that characterize interactions of inhibitors and substrates within the active site environment, which can be extended to other Fph family members. Comparison of FphF to other esterases and the wider Fph protein family suggest that FphF forms a new esterase subfamily. Our data suggest that other Fph enzymes, including the virulence factor FphB, are likely to have more restricted substrate profiles than FphF. This work demonstrates a clear molecular rationale for the specificity of fluorophosphonate probes that target FphF and provides a structural template for the design of enhanced probes and inhibitors of the Fph family of serine hydrolases.

In Vitro Activity of Carbosilane Cationic Dendritic Molecules on Prevention and Treatment of Candida Albicans Biofilms

Candida spp. are one of the most common fungal pathogens. Biofilms formed by Candidaalbicans offer resistance mechanisms against most antifungal agents. Therefore, development of new molecules effective against these microorganisms, alone or in combination with antifungal drugs, is extremely necessary. In the present work, we carried out a screening process of different cationic carbosilane dendritic molecules against C. albicans. In vitro activity against biofilm formation and biofilms was tested in both Colección Española de Cultivos Tipo (CECT) 1002 and clinical C. albicans strains. Cytotoxicity was studied in human cell lines, and biofilm alterations were observed by scanning electron microscopy (SEM). Antifungal activity of the carbosilane dendritic molecules was assessed by monitoring cell viability using both established and novel cell viability assays. One out of 14 dendritic molecules tested, named BDSQ024, showed the highest activity with a minimum biofilm inhibitory concentration (MBIC) for biofilm formation and a minimum biofilm damaging concentration (MBDC) for existing biofilm of 16-32 and 16 mg/L, respectively. Synergy with amphotericin (AmB) and caspofungin (CSF) at non-cytotoxic concentrations was found. Therefore, dendritic compounds are exciting new antifungals effective at preventing Candida biofilm formation and represent a potential novel therapeutic agent for treatment of C. albicans infection in combination with existing clinical antifungals.

Small Alarmone Synthetases RelP and RelQ of Staphylococcus aureus Are Involved in Biofilm Formation and Maintenance Under Cell Wall Stress Conditions

The stringent response is characterized by the synthesis of the alarmone (p)ppGpp. The phenotypic consequences resulting from (p)ppGpp accumulation vary among species, and for several pathogenic bacteria, it has been shown that the activation of the stringent response strongly affects biofilm formation and maintenance. In Staphylococcus aureus, (p)ppGpp can be synthesized by the RelA/SpoT homolog Rel upon amino acid deprivation or by the two small alarmone synthetases RelP and RelQ under cell wall stress. We found that relP and relQ increase biofilm formation under cell wall stress conditions induced by a subinhibitory vancomycin concentration. However, the effect of (p)ppGpp on biofilm formation is independent of the regulators CodY and Agr. Biofilms formed by the strain HG001 or its (p)ppGpp-defective mutants are mainly composed of extracellular DNA and proteins. Furthermore, the induction of the RelPQ-mediated stringent response contributes to biofilm-related antibiotic tolerance. The proposed (p)ppGpp-inhibiting peptide DJK-5 shows bactericidal and biofilm-inhibitory activity. However, a non-(p)ppGpp-producing strain is even more vulnerable to DJK-5. This strongly argues against the assumption that DJK-5 acts via (p)ppGpp inhibition. In summary, RelP and RelQ play a major role in biofilm formation and maintenance under cell wall stress conditions.

Impact of bacterial persisters on their host

The rise of antibiotic failure poses a severe threat to global health. There is growing concern that this failure is not solely driven by stable antibiotic resistance but also by a subpopulation of transiently non-growing, antibiotic tolerant bacteria. These 'persisters' have been proposed to seed relapsing infections, an important clinical outcome of treatment failure - although definitive evidence for this direct link remains elusive. Recent advances in the field have revealed the complex nature of intra-host persisters which drive their high adaptability through biosynthetic activity. These features of persisters contribute to evolution of antimicrobial resistance and modulation of host immune responses, despite clinically efficacious treatment.

Antibiotic Tolerance of Staphylococcus aureus Biofilm in Periprosthetic Joint Infections and Antibiofilm Strategies

The need for bone and joint prostheses is currently growing due to population aging, leading to an increase in prosthetic joint infection cases. Biofilms represent an adaptive and quite common bacterial response to several stress factors which confer an important protection to bacteria. Biofilm formation starts with bacterial adhesion on a surface, such as an orthopedic prosthesis, further reinforced by matrix synthesis. The biofilm formation and structure depend on the immediate environment of the bacteria. In the case of infection, the periprosthetic joint environment represents a particular interface between bacteria, host cells, and the implant, favoring biofilm initiation and maturation. Treating such an infection represents a huge challenge because of the biofilm-specific high tolerance to antibiotics and its ability to evade the immune system. It is crucial to understand these mechanisms in order to find new and adapted strategies to prevent and eradicate implant-associated infections. Therefore, adapted models mimicking the infectious site are of utmost importance to recreate a relevant environment in order to test potential antibiofilm molecules. In periprosthetic joint infections, Staphylococcus aureus is mainly involved because of its high adaptation to the human physiology. The current review deals with the mechanisms involved in the antibiotic resistance and tolerance of Staphylococcus aureus in the particular periprosthetic joint infection context, and exposes different strategies to manage these infections.

Short-Chain Fatty Acids Promote Mycobacterium avium subsp. hominissuis Growth in Nutrient-Limited Environments and Influence Susceptibility to Antibiotics

Mycobacterium avium subsp. hominissuis (MAH) is a common intracellular pathogen that infects immunocompromised individuals and patients with pre-existing chronic lung diseases, such as cystic fibrosis, who develop chronic and persistent pulmonary infections. The metabolic remodeling of MAH in response to host environmental stresses or within biofilms formed in bronchial airways plays an important role in development of the persistence phenotype contributing to the pathogen’s tolerance to antibiotic treatment. Recent studies suggest a direct relationship between bacterial metabolic state and antimicrobial susceptibility, and improved antibiotic efficacy has been associated with the enhanced metabolism in bacteria. In the current study, we tested approximately 200 exogenous carbon source-dependent metabolites and identified short-chain fatty acid (SCFA) substrates (propionic, butyric and caproic acids) that MAH can utilize in different physiological states. Selected SCFA enhanced MAH metabolic activity in planktonic and sessile states as well as in the static and established biofilms during nutrient-limited condition. The increased bacterial growth was observed in all conditions except in established biofilms. We also evaluated the influence of SCFA on MAH susceptibility to clinically used antibiotics in established biofilms and during infection of macrophages and found significant reduction in viable bacterial counts in vitro and in cultured macrophages, suggesting improved antibiotic effectiveness against persistent forms of MAH.

Staphylococcal Biofilm Development: Structure, Regulation, and Treatment Strategies

In many natural and clinical settings, bacteria are associated with some type of biotic or abiotic surface that enables them to form biofilms, a multicellular lifestyle with bacteria embedded in an extracellular matrix. Staphylococcus aureus and Staphylococcus epidermidis, the most frequent causes of biofilm-associated infections on indwelling medical devices, can switch between an existence as single free-floating cells and multicellular biofilms. During biofilm formation, cells first attach to a surface and then multiply to form microcolonies. They subsequently produce the extracellular matrix, a hallmark of biofilm formation, which consists of polysaccharides, proteins, and extracellular DNA. After biofilm maturation into three-dimensional structures, the biofilm community undergoes a disassembly process that leads to the dissemination of staphylococcal cells. As biofilms are dynamic and complex biological systems, staphylococci have evolved a vast network of regulatory mechanisms to modify and fine-tune biofilm development upon changes in environmental conditions. Thus, biofilm formation is used as a strategy for survival and persistence in the human host and can serve as a reservoir for spreading to new infection sites. Moreover, staphylococcal biofilms provide enhanced resilience toward antibiotics and the immune response and impose remarkable therapeutic challenges in clinics worldwide. This review provides an overview and an updated perspective on staphylococcal biofilms, describing the characteristic features of biofilm formation, the structural and functional properties of the biofilm matrix, and the most important mechanisms involved in the regulation of staphylococcal biofilm formation. Finally, we highlight promising strategies and technologies, including multitargeted or combinational therapies, to eradicate staphylococcal biofilms.

Selective Eradication of Staphylococcus aureus by the Designer Genetically Programmed Yeast Biocontrol Agent

Staphylococcus aureus is a common human pathogen that is particularly often associated with antibiotic resistance. The eradication of this ubiquitous infectious agent from its ecological niches and contaminated surfaces is especially complicated by excessive biofilm formation and persisting cells, which evade the antibacterial activity of conventional antibiotics. Here, we present an alternative view of the problem of specific S. aureus eradication. The constitutive heterologous production of highly specific bacteriolytic protease lysostaphin in yeast Pichia pastoris provides an efficient biocontrol agent, specifically killing S. aureus in coculture. A yeast-based anti-S. aureus probiotic was efficient in a high range of temperatures and target-to-effector ratios, indicating its robustness and versatility in eliminating S. aureus cells. The efficient eradication of S. aureus by live lysostaphin-producing P. pastoris was achieved at high scales, providing a simple, biocompatible and cost-effective strategy for S. aureus lysis in bioproduction and surface decontamination. Future biomedical applications based on designer yeast biocontrol agents require evaluation in in vivo models. However, we believe that this strategy is very promising since it provides highly safe, efficient and selective genetically programmed probiotics and targeted biocontrol agents.

Staphylococcal Biofilm Development: Structure, Regulation, and Treatment Strategies

In many natural and clinical settings, bacteria are associated with some type of biotic or abiotic surface that enables them to form biofilms, a multicellular lifestyle with bacteria embedded in an extracellular matrix. Staphylococcus aureus and Staphylococcus epidermidis, the most frequent causes of biofilm-associated infections on indwelling medical devices, can switch between an existence as single free-floating cells and multicellular biofilms. During biofilm formation, cells first attach to a surface and then multiply to form microcolonies. They subsequently produce the extracellular matrix, a hallmark of biofilm formation, which consists of polysaccharides, proteins, and extracellular DNA. After biofilm maturation into three-dimensional structures, the biofilm community undergoes a disassembly process that leads to the dissemination of staphylococcal cells. As biofilms are dynamic and complex biological systems, staphylococci have evolved a vast network of regulatory mechanisms to modify and fine-tune biofilm development upon changes in environmental conditions. Thus, biofilm formation is used as a strategy for survival and persistence in the human host and can serve as a reservoir for spreading to new infection sites. Moreover, staphylococcal biofilms provide enhanced resilience toward antibiotics and the immune response and impose remarkable therapeutic challenges in clinics worldwide. This review provides an overview and an updated perspective on staphylococcal biofilms, describing the characteristic features of biofilm formation, the structural and functional properties of the biofilm matrix, and the most important mechanisms involved in the regulation of staphylococcal biofilm formation. Finally, we highlight promising strategies and technologies, including multitargeted or combinational therapies, to eradicate staphylococcal biofilms.

Antimicrobial Susceptibility Testing of Antimicrobial Peptides to Better Predict Efficacy

During the development of antimicrobial peptides (AMP) as potential therapeutics, antimicrobial susceptibility testing (AST) stands as an essential part of the process in identification and optimisation of candidate AMP. Standard methods for AST, developed almost 60 years ago for testing conventional antibiotics, are not necessarily fit for purpose when it comes to determining the susceptibility of microorganisms to AMP. Without careful consideration of the parameters comprising AST there is a risk of failing to identify novel antimicrobials at a time when antimicrobial resistance (AMR) is leading the planet toward a post-antibiotic era. More physiologically/clinically relevant AST will allow better determination of the preclinical activity of drug candidates and allow the identification of lead compounds. An important consideration is the efficacy of AMP in biological matrices replicating sites of infection, e.g., blood/plasma/serum, lung bronchiolar lavage fluid/sputum, urine, biofilms, etc., as this will likely be more predictive of clinical efficacy. Additionally, specific AST for different target microorganisms may help to better predict efficacy of AMP in specific infections. In this manuscript, we describe what we believe are the key considerations for AST of AMP and hope that this information can better guide the preclinical development of AMP toward becoming a new generation of urgently needed antimicrobials.

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

Staphylococcus aureus is a pathogen that causes critical diseases, such as pneumonia, endocarditis, and bacteremia, upon gaining access to the bloodstream of the host. Because host innate immunity alone cannot fight against this rapidly expanding pathogen, the use of antibiotic agents is necessary to clear out S. aureus. However, sub-populations of S. aureus fail to respond to the antibiotics resulting in ineffective clearance of the bacteria. One mechanism by which S. aureus does not respond to the antibiotics is by developing resistance through alterations in its genetic makeup, and genetic studies have revealed a major portion of mechanisms that are responsible for the rise of these antibiotic-resistant strains. Another sub-population that fails to respond to the antibiotics is called persister cells. There is a mounting clinical evidence that these persister cells significantly contribute to the antibiotic failure and persistent infection, but a clear mechanistic picture of the formation of the S. aureus persister cells is unavailable. This review focuses on drawing out a mechanistic map of factors that contribute to the formation of S. aureus persister cells. Understanding the mechanism will provide future direction for the development of novel antibiotic strategies to more efficiently tackle infections caused by S. aureus.

Genetic and Biochemical Analysis of CodY-Mediated Cell Aggregation in Staphylococcus aureus Reveals an Interaction between Extracellular DNA and Polysaccharide in the Extracellular Matrix

The global regulator CodY links nutrient availability to the regulation of virulence factor gene expression in Staphylococcus aureus, including many genes whose products affect biofilm formation. Antithetical phenotypes of both biofilm deficiency and accumulation have been reported for codY-null mutants; thus, the role of CodY in biofilm development remains unclear. codY mutant cells of a strain producing a robust biofilm elaborate proaggregation surface-associated features not present on codY mutant cells that do not produce a robust biofilm. Biochemical analysis of the clinical isolate SA564, which aggregates when deficient for CodY, revealed that these features are sensitive to nuclease treatment and are resistant to protease exposure. Genetic analyses revealed that disrupting lgt (the diacylglycerol transferase gene) in codY mutant cells severely weakened aggregation, indicating a role for lipoproteins in the attachment of the biofilm matrix to the cell surface. An additional and critical role of IcaB in producing functional poly-N-acetylglucosamine (PIA) polysaccharide in extracellular DNA (eDNA)-dependent biofilm formation was shown. Moreover, overproducing PIA is sufficient to promote aggregation in a DNA-dependent manner regardless of source of nucleic acids. Taken together, our results point to PIA synthesis as the primary determinant of biofilm formation when CodY activity is reduced and suggest a modified electrostatic net model for matrix attachment whereby PIA associates with eDNA, which interacts with the cell surface via covalently attached membrane lipoproteins. This work counters the prevailing view that polysaccharide- and eDNA/protein-based biofilms are mutually exclusive. Rather, we demonstrate that eDNA and PIA can work synergistically to form a biofilm.IMPORTANCEStaphylococcus aureus remains a global health concern and exemplifies the ability of an opportunistic pathogen to adapt and persist within multiple environments, including host tissue. Not only does biofilm contribute to persistence and immune evasion in the host environment, it also may aid in the transition to invasive disease. Thus, understanding how biofilms form is critical for developing strategies for dispersing biofilms and improving biofilm disease-related outcomes. Using biochemical, genetic, and cell biology approaches, we reveal a synergistic interaction between PIA and eDNA that promotes cell aggregation and biofilm formation in a CodY-dependent manner in S. aureus We also reveal that envelope-associated lipoproteins mediate attachment of the biofilm matrix to the cell surface.

Structure-Activity Relationship and Anticancer Profile of Second-Generation Anti-MRSA Synthetic Retinoids

We previously reported the antibacterial activity of CD437, a known antitumor compound. It proved to be a potent antimicrobial agent effective against both growing and persister cells of methicillin-resistant Staphylococcus aureus (MRSA). Herein, we report the synthesis of a panel of analogs and their effect on both MRSA and cancer cells. The hydrophobic group of the parent compound was varied in steric bulk, and lipid-mimicking analogs were tested. Biological assessment confirmed that the adamantane moiety is the most effective substitution for antibacterial activity, and some preferential action in cancer over MRSA was achieved.

Repurposing human kinase inhibitors to create an antibiotic active against drug-resistant Staphylococcus aureus, persisters and biofilms

New drugs are desperately needed to combat methicillin-resistant Staphylococcus aureus (MRSA) infections. Here, we report screening commercial kinase inhibitors for antibacterial activity and found the anticancer drug sorafenib as major hit that effectively kills MRSA strains. Varying the key structural features led to the identification of a potent analogue, PK150, that showed antibacterial activity against several pathogenic strains at submicromolar concentrations. Furthermore, this antibiotic eliminated challenging persisters as well as established biofilms. PK150 holds promising therapeutic potential as it did not induce in vitro resistance, and shows oral bioavailability and in vivo efficacy. Analysis of the mode of action using chemical proteomics revealed several targets, which included interference with menaquinone biosynthesis by inhibiting demethylmenaquinone methyltransferase and the stimulation of protein secretion by altering the activity of signal peptidase IB. Reduced endogenous menaquinone levels along with enhanced levels of extracellular proteins of PK150-treated bacteria support this target hypothesis. The associated antibiotic effects, especially the lack of resistance development, probably stem from the compound's polypharmacology.

Virulence factors and antimicrobial resistance of Staphylococcus aureus isolated from the production process of Minas artisanal cheese from the region of Campo das Vertentes, Brazil

Staphylococcus aureus is one of the main pathogens found in cheeses produced with raw milk, including Minas artisanal cheese from Brazil. However, information about S. aureus isolated from artisanal cheeses and its sources of production in small-scale dairies is very limited. We aimed to characterize the virulence factors of S. aureus isolated from raw milk, endogenous starter culture, Minas artisanal cheese, and cheese handlers from the region of Campo das Vertentes, Minas Gerais, Brazil. We identified the staphylococcal isolates by MALDI-TOF mass spectrometry. We evaluated biofilm production on Congo red agar and polystyrene plates. We used PCR to detect icaA, icaB, icaC, sea, seb, sec, sed, see, tsst-1, agr, and mecA. We evaluated the expression of staphylococcal toxin genes in PCR-positive staphylococcal isolates using quantitative reverse-transcription PCR, and we evaluated the production of these toxins and their hemolytic activity in vitro. We also evaluated the antimicrobial resistance profile of the staphylococcal isolates. For statistical analysis, we used cluster analysis, χ² tests, and correspondence tests. We analyzed 76 staphylococcal isolates. According to PCR, 18.42, 18.42, 2.63, and 77.63% were positive for sea, tsst-1, sec, and agr, respectively. We found low expression of staphylococcal toxin genes according to quantitative reverse-transcription PCR, and only 2 staphylococcal isolates produced toxic shock syndrome toxins. A total of 43 staphylococcal isolates (56.58%) had hemolytic activity; 53 were biofilm-forming on Congo red agar (69.73%), and 62 on polystyrene plates (81.58%). None of the staphylococcal isolates expressed the mecA gene, and none presented a multi-drug resistance pattern. The highest resistance was observed for penicillin G (67.11%) in 51 isolates and for tetracycline (27.63%) in 21 isolates. The staphylococcal isolates we evaluated had toxigenic potential, with a higher prevalence of sea and tsst-1. Biofilm production was the main virulence factor of the studied bacteria. Six clusters were formed whose distribution frequencies differed for hemolytic activity, biofilm formation (qualitative and quantitative analyses), and resistance to penicillin, tetracycline, and erythromycin. These findings emphasize the need for effective measures to prevent staphylococcal food poisoning by limiting S. aureus growth and enterotoxin formation throughout the food production chain and the final product.

Growth Mode and Physiological State of Cells Prior to Biofilm Formation Affect Immune Evasion and Persistence of Staphylococcus aureus

The present study investigated Staphylococcus aureus ATCC25923 surfaceomes (cell surface proteins) during prolonged growth by subjecting planktonic and biofilm cultures (initiated from exponential or stationary cells) to label-free quantitative surfaceomics and phenotypic confirmations. The abundance of adhesion, autolytic, hemolytic, and lipolytic proteins decreased over time in both growth modes, while an opposite trend was detected for many tricarboxylic acid (TCA) cycle, reactive oxygen species (ROS) scavenging, Fe-S repair, and peptidolytic moonlighters. In planktonic cells, these changes were accompanied by decreasing and increasing adherence to hydrophobic surface and fibronectin, respectively. Specific RNA/DNA binding (cold-shock protein CspD and ribosomal proteins) and the immune evasion (SpA, ClfA, and IsaB) proteins were notably more abundant on fully mature biofilms initiated with stationary-phase cells (SDBF) compared to biofilms derived from exponential cells (EDBF) or equivalent planktonic cells. The fully matured SDBF cells demonstrated higher viability in THP-1 monocyte/macrophage cells compared to the EDBF cells. Peptidoglycan strengthening, specific urea-cycle, and detoxification enzymes were more abundant on planktonic than biofilm cells, indicating the activation of growth-mode specific pathways during prolonged cultivation. Thus, we show that S. aureus shapes its surfaceome in a growth mode-dependent manner to reach high levofloxacin tolerance (>200-times the minimum biofilm inhibitory concentration). This study also demonstrates that the phenotypic state of the cells prior to biofilm formation affects the immune-evasion and persistence-related traits of S. aureus.

5-Benzylidene-4-Oxazolidinones Are Synergistic with Antibiotics for the Treatment of Staphylococcus aureus Biofilms

The failure of frontline antibiotics in the clinic is one of the most serious threats to human health and requires a multitude of novel therapeutics and innovative approaches to treatment so as to curtail the growing crisis. In addition to traditional resistance mechanisms resulting in the lack of efficacy of many antibiotics, most chronic and recurring infections are further made tolerant to antibiotic action by the presence of biofilms. Herein, we report an expanded set of 5-benzylidene-4-oxazolidinones that are able to inhibit the formation of Staphylococcus aureus biofilms, disperse preformed biofilms, and, in combination with common antibiotics, are able to significantly reduce the bacterial load in a robust collagen-matrix model of biofilm infection.

Surviving as a Community: Antibiotic Tolerance and Persistence in Bacterial Biofilms

Biofilms are surface-associated bacterial communities that play both beneficial and harmful roles in nature, medicine, and industry. Tolerant and persister cells are thought to underlie biofilm-related bacterial recurrence in medical and industrial contexts. Here, we review recent progress aimed at understanding the mechanical features that drive biofilm resilience and the biofilm formation process at single-cell resolution. We discuss findings regarding mechanisms underlying bacterial tolerance and persistence in biofilms and how these phenotypes are linked to antibiotic resistance. New strategies for combatting tolerance and persistence in biofilms and possible methods for biofilm eradication are highlighted to inspire future development.

Chemical Induction of Aminoglycoside Uptake Overcomes Antibiotic Tolerance and Resistance in Staphylococcus aureus

Aminoglycoside antibiotics require proton motive force (PMF) for bacterial internalization. In non-respiring populations, PMF drops below the level required for drug influx, limiting the utility of aminoglycosides against strict and facultative anaerobes. We recently demonstrated that rhamnolipids (RLs), biosurfactant molecules produced by Pseudomonas aeruginosa, potentiate aminoglycoside activity against Staphylococcus aureus. Here, we demonstrate that RLs induce PMF-independent aminoglycoside uptake to restore sensitivity to otherwise tolerant persister, biofilm, small colony variant, and anaerobic populations of S. aureus. Furthermore, we show that this approach represses the rise of resistance, restores sensitivity to highly resistant clinical isolates, and is effective against other Gram-positive pathogens. Finally, while other membrane-acting agents can synergize with aminoglycosides, induction of PMF-independent uptake is uncommon, and distinct to RLs among several compounds tested. In all, small-molecule induction of PMF-independent aminoglycoside uptake circumvents phenotypic tolerance, overcomes genotypic resistance, and expands the utility of aminoglycosides against intrinsically recalcitrant bacterial populations.

5-Dodecanolide interferes with biofilm formation and reduces the virulence of Methicillin-resistant Staphylococcus aureus (MRSA) through up regulation of agr system

Methicillin resistant Staphylococcus aureus (MRSA) is a predominant human pathogen with high morbidity that is listed in the WHO high priority pathogen list. Being a primary cause of persistent human infections, biofilm forming ability of S. aureus plays a pivotal role in the development of antibiotic resistance. Hence, targeting biofilm is an alternative strategy to fight bacterial infections. The present study for the first time demonstrates the non-antibacterial biofilm inhibitory efficacy of 5-Dodecanolide (DD) against ATCC strain and clinical isolates of S. aureus. In addition, DD is able to inhibit adherence of MRSA on human plasma coated Titanium surface. Further, treatment with DD significantly reduced the eDNA synthesis, autoaggregation, staphyloxanthin biosynthesis and ring biofilm formation. Reduction in staphyloxanthin in turn increased the susceptibility of MRSA to healthy human blood and H2O2 exposure. Quantitative PCR analysis revealed the induced expression of agrA and agrC upon DD treatment. This resulted down regulation of genes involved in biofilm formation such as fnbA and fnbB and up regulation of RNAIII, hld, psmα and genes involved in biofilm matrix degradation such as aur and nuc. Inefficacy of DD on the biofilm formation of agr mutant further validated the agr mediated antibiofilm potential of DD. Notably, DD was efficient in reducing the in vivo colonization of MRSA in Caenorhabditis elegans. Results of gene expression studies and physiological assays unveiled the agr mediated antibiofilm efficacy of DD.

Understanding Multicellularity: The Functional Organization of the Intercellular Space

The aim of this paper is to provide a theoretical framework to understand how multicellular systems realize functionally integrated physiological entities by organizing their intercellular space. From a perspective centered on physiology and integration, biological systems are often characterized as organized in such a way that they realize metabolic self-production and self-maintenance. The existence and activity of their components rely on the network they realize and on the continuous management of the exchange of matter and energy with their environment. One of the virtues of the organismic approach focused on organization is that it can provide an understanding of how biological systems are functionally integrated into coherent wholes. Organismic frameworks have been primarily developed by focusing on unicellular life. Multicellularity, however, presents additional challenges to our understanding of biological systems, related to how cells are capable to live together in higher-order entities, in such a way that some of their features and behaviors are constrained and controlled by the system they realize. Whereas most accounts of multicellularity focus on cell differentiation and increase in size as the main elements to understand biological systems at this level of organization, we argue that these factors are insufficient to provide an understanding of how cells are physically and functionally integrated in a coherent system. In this paper, we provide a new theoretical framework to understand multicellularity, capable to overcome these issues. Our thesis is that one of the fundamental theoretical principles to understand multicellularity, which is missing or underdeveloped in current accounts, is the functional organization of the intercellular space. In our view, the capability to be organized in space plays a central role in this context, as it enables (and allows to exploit all the implications of) cell differentiation and increase in size, and even specialized functions such as immunity. We argue that the extracellular matrix plays a crucial active role in this respect, as an evolutionary ancient and specific (non-cellular) control subsystem that contributes as a key actor to the functional specification of the multicellular space and to modulate cell fate and behavior. We also analyze how multicellular systems exert control upon internal movement and communication. Finally, we show how the organization of space is involved in some of the failures of multicellular organization, such as aging and cancer.

Characterization and Antibiofilm Activity of Mannitol-Chitosan-Blended Paste for Local Antibiotic Delivery System

Mannitol, a polyalcohol bacterial metabolite, has been shown to activate dormant persister cells within bacterial biofilm. This study sought to evaluate an injectable blend of mannitol, chitosan, and polyethylene glycol for delivery of antibiotics and mannitol for eradication of Staphylococcal biofilm. Mannitol blends were injectable and had decreased dissociation and degradation in the enzyme lysozyme compared to blends without mannitol. Vancomycin and amikacin eluted in a burst response, with active concentrations extended to seven days compared to five days for blends without mannitol. Mannitol eluted from the paste in a burst the first day and continued through Day 4. Eluates from the mannitol pastes with and without antibiotics decreased viability of established S. aureus biofilm by up to 95.5% compared to blends without mannitol, which only decreased biofilm when loaded with antibiotics. Cytocompatibility tests indicated no adverse effects on viability of fibroblasts. In vivo evaluation of inflammatory response revealed mannitol blends scored within the 2–4 range at Week 1 (2.6 ± 1.1) and at Week 4 (3.0 ± 0.8), indicative of moderate inflammation and comparable to non-mannitol pastes (p = 0.065). Clinically, this paste could be loaded with clinician-selected antibiotics and used as an adjunctive therapy for musculoskeletal infection prevention and treatment.

Antimicrobial Treatment of Staphylococcus aureus in Patients With Cystic Fibrosis

Staphylococcus aureus is a ubiquitous human commensal pathogen. It is commonly isolated in cystic fibrosis (CF) patients and is considered one of the main causes of the recurrent acute pulmonary infections and progressive decline in lung function that characterize this inherited life-threatening multisystem disorder. However, the true role of S. aureus in CF patients is not completely understood. The main aim of this narrative review is to discuss the present knowledge of the role of S. aureus in CF patients. Literature review showed that despite the fact that the availability and use of drugs effective against S. aureus have coincided with a significant improvement in the prognosis of lung disease in CF patients, clearly evidencing the importance of S. aureus therapy, how to use old and new drugs to obtain the maximal effectiveness has not been precisely defined. The most important problem remains that the high frequency with which S. aureus is carried in healthy subjects prevents the differentiation of simple colonization from infection. Moreover, although experts recommend antibiotic administration in CF patients with symptoms and in those with persistent detection of S. aureus, the best antibiotic approach has not been defined. All these problems are complicated by the evidence that the most effective antibiotic against methicillin-resistant S. aureus (MRSA) cannot be used in patients with CF with the same schedules used in patients without CF. Further studies are needed to solve these problems and to assure CF patients the highest level of care.

Interaction Between Staphylococcal Biofilm and Bone: How Does the Presence of Biofilm Promote Prosthesis Loosening?

With the aging of population, the number of indications for total joint replacement is continuously increasing. However, prosthesis loosening can happen and is related to two major mechanisms: (1) aseptic loosening due to prosthesis micromotion and/or corrosion and release of wear particles from the different components of the implanted material and (2) septic loosening due to chronic prosthetic joint infection (PJI). The “aseptic” character of prosthesis loosening has been challenged over the years, especially considering that bacteria can persist in biofilms and be overlooked during diagnosis. Histological studies on periprosthetic tissue samples reported that macrophages are the principle cells associated with aseptic loosening due to wear debris. They produce cytokines and favor an inflammatory environment that induces formation and activation of osteoclasts, leading to bone resorption and periprosthetic osteolysis. In PJIs, the presence of infiltrates of polymorphonuclear neutrophils is a major criterion for histological diagnosis. Neutrophils are colocalized with osteoclasts and zones of osteolysis. A similar inflammatory environment also develops, leading to bone resorption through osteoclasts. Staphylococcus aureus, Staphylococcus epidermidis, and Staphylococcus lugdunensis are the main staphylococci observed in PJIs. They share the common feature to form biofilm. For S. aureus and S. epidermidis, the interaction between biofilm and immunes cells (macrophages and polymorphonuclear neutrophils) differs regarding the species. Indeed, the composition of extracellular matrix of biofilm seems to impact the interaction with immune cells. Recent papers also reported the major role of myeloid-derived suppressor cells in biofilm-associated PJIs with S. aureus. These cells prevent lymphocyte infiltration and facilitate biofilm persistence. Moreover, the role of T lymphocytes is still unclear and potentially underestimates. In this review, after introducing the cellular mechanism of aseptic and septic loosening, we will focus on the interrelationships between staphylococcal biofilm, immune cells, and bone cells.

Large variations in clinical antibiotic activity against Staphylococcus aureus biofilms of periprosthetic joint infection isolates

Staphylococcus aureus biofilms have a high tolerance to antibiotics, making the treatment of periprosthetic joint infection (PJI) challenging. From a clinical perspective, bacteria from surgical specimens are cultured in a planktonic state to determine antibiotic sensitivity. However, S. aureus exists primarily as established biofilms in PJI. To address this dichotomy, we developed a prospective registry of total knee and hip arthroplasty PJI S. aureus isolates to quantify the activity of clinically important antibiotics against isolates grown as biofilms. S. aureus planktonic minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were assessed using clinical laboratory standard index assays for 10 antibiotics (cefazolin, clindamycin, vancomycin, rifampin, linezolid, nafcillin, gentamicin, trimethoprim/sulfamethoxazole, doxycycline, and daptomycin). Mature biofilms of each strain were grown in vitro, after which biofilm MIC (MBIC) and biofilm MBC (MBBC) were determined. Overall, isolates grown as biofilms displayed larger variations in antibiotic MICs as compared to planktonic MIC values. Only rifampin, doxycycline, and daptomycin had measurable biofilm MIC values across all S. aureus isolates tested. Biofilm MBC observations complemented biofilm MIC observations; rifampin, doxycycline, and daptomycin were the only antibiotics with measurable biofilm MBC values. 90% of S. aureus biofilms could be killed by rifampin, 50% by doxycycline, and only 15% by daptomycin. Biofilm formation increased bacterial antibiotic tolerance nonspecifically across all antibiotics, in both MSSA and MRSA samples. Rifampin and doxycycline were the most effective antibiotics at killing established S. aureus biofilms. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1604-1609, 2019.

Studying Biofilm and Clinical Issues in Orthopedics

The association between biofilm-forming microorganisms and prosthetic joint infection influences all aspect of management including approaches to diagnosis, management and prevention. This article will provide an overview of new anti-biofilm strategies for management of prosthetic joint infection.

A Dual-Function Antibiotic-Transporter Conjugate Exhibits Superior Activity in Sterilizing MRSA Biofilms and Killing Persister Cells

New strategies are urgently needed to target MRSA, a major global health problem and the leading cause of mortality from antibiotic-resistant infections in many countries. Here, we report a general approach to this problem exemplified by the design and synthesis of a vancomycin-d-octaarginine conjugate (V-r8) and investigation of its efficacy in addressing antibiotic-insensitive bacterial populations. V-r8 eradicated MRSA biofilm and persister cells in vitro, outperforming vancomycin by orders of magnitude. It also eliminated 97% of biofilm-associated MRSA in a murine wound infection model and displayed no acute dermal toxicity. This new dual-function conjugate displays enhanced cellular accumulation and membrane perturbation as compared to vancomycin. Based on its rapid and potent activity against biofilm and persister cells, V-r8 is a promising agent against clinical MRSA infections.

Biofilm Producing Clinical Staphylococcus aureus Isolates Augmented Prevalence of Antibiotic Resistant Cases in Tertiary Care Hospitals of Nepal

Staphylococcus aureus, a notorious human pathogen, is a major cause of the community as well as healthcare associated infections. It can cause a diversity of recalcitrant infections mainly due to the acquisition of resistance to multiple drugs, its diverse range of virulence factors, and the ability to produce biofilm in indwelling medical devices. Such biofilm associated chronic infections often lead to increase in morbidity and mortality posing a high socio-economic burden, especially in developing countries. Since biofilm formation and antibiotic resistance function dependent on each other, detection of biofilm expression in clinical isolates would be advantageous in treatment decision. In this premise, we attempt to investigate the biofilm formation and its association with antibiotic resistance in clinical isolates from the patients visiting tertiary health care hospitals in Nepal. Bacterial cells isolated from clinical samples identified as S. aureus were examined for in-vitro biofilm production using both phenotypic and genotypic assays. The S. aureus isolates were also examined for susceptibility patterns of clinically relevant antibiotics as well as inducible clindamycin resistance using standard microbiological techniques and D-test, respectively. Among 161 S. aureus isolates, 131 (81.4%) were methicillin resistant S. aureus (MRSA) and 30 (18.6%) were methicillin sensitive S. aureus (MSSA) strains. Although a majority of MRSA strains (69.6%) showed inducible clindamycin resistance, almost all isolates (97% and 94%) were sensitive toward chloramphenicol and tetracycline, respectively. Detection of in vitro production of biofilm revealed the association of biofilm with methicillin as well as inducible clindamycin resistance among the clinical S. aureus isolates.

Targeting the Bacterial Protective Armour; Challenges and Novel Strategies in the Treatment of Microbial Biofilm

Infectious disease caused by pathogenic bacteria continues to be the primary challenge to humanity. Antimicrobial resistance and microbial biofilm formation in part, lead to treatment failures. The formation of biofilms by nosocomial pathogens such as Staphylococcus aureus (S. aureus), Pseudomonas aeruginosa (P. aeruginosa), and Klebsiella pneumoniae (K. pneumoniae) on medical devices and on the surfaces of infected sites bring additional hurdles to existing therapies. In this review, we discuss the challenges encountered by conventional treatment strategies in the clinic. We also provide updates on current on-going research related to the development of novel anti-biofilm technologies. We intend for this review to provide understanding to readers on the current problem in health-care settings and propose new ideas for new intervention strategies to reduce the burden related to microbial infections.

Linking toxin-antitoxin systems with phenotypes: A Staphylococcus aureus viewpoint

Toxin-antitoxin systems (TAS) are genetic modules controlling different aspects of bacterial physiology. They operate with versatility in an incredibly wide range of mechanisms. New TA modules with unexpected functions are continuously emerging from genome sequencing projects. Their discovery and functional studies have shed light on different characteristics of bacterial metabolism that are now applied to understanding clinically relevant questions and even proposed as antimicrobial treatment. Our main source of knowledge of TA systems derives from Gram-negative bacterial studies, but studies in Gram-positives are becoming more prevalent and provide new insights to TA functional mechanisms. In this review, we present an overview of the present knowledge of TA systems in the clinical pathogen Staphylococcus aureus, their implications in bacterial physiology and discuss relevant aspects that are driving TAS research. "This article is part of a Special Issue entitled: Dynamic gene expression, edited by Prof. Patrick Viollier".

Strategies against methicillin-resistant Staphylococcus aureus persisters

Chronic Staphylococcus aureus infections are complicated by frequent relapses not only from the development of drug resistance to conventional antibiotics, but also through the formation of persister bacterial cells. Bacterial persisters are in a transient, metabolically inactive state, making conventional antibiotics that target essential cellular growth processes ineffective, resulting in high clinical failure rates of antibiotic chemotherapy. The development of new antibiotics against persistent S. aureus is an urgent issue. Over the last decade, new strategies to identify S. aureus persister-active compounds have been proposed. This review summarizes the proposed targets, antipersister compounds and innovative methods that may augment conventional antibiotics against S. aureus persisters. The reviewed antipersister strategies can be summarized as two broad categories; directly targeting growth-independent targets and potentiating existing, ineffective antibiotics by aiding uptake or accessibility.

Targeting fundamental pathways to disrupt Staphylococcus aureus survival: clinical implications of recent discoveries

The emergence of community-associated methicillin-resistant Staphylococcus aureus during the past decade along with an impending shortage of effective antistaphylococcal antibiotics have fueled impressive advances in our understanding of how S. aureus overcomes the host environment to establish infection. Backed by recent technologic advances, studies have uncovered elaborate metabolic, nutritional, and virulence strategies deployed by S. aureus to survive the restrictive and hostile environment imposed by the host, leading to a plethora of promising antimicrobial approaches that have potential to remedy the antibiotic resistance crisis. In this Review, we highlight some of the critical and recently elucidated bacterial strategies that are potentially amenable to intervention, discuss their relevance to human diseases, and address the translational challenges posed by current animal models.

Quorum Sensing-Regulated Phenol-Soluble Modulins Limit Persister Cell Populations in Staphylococcus aureus

Incomplete killing of bacterial pathogens by antibiotics is an underlying cause of treatment failure and accompanying complications. Among those avoiding chemotherapy are persisters being individual cells in a population that for extended periods of time survive high antibiotic concentrations proposedly by being in a quiescent state refractory to antibiotic killing. While investigating the human pathogen Staphylococcus aureus and the influence of growth phase on persister formation, we noted that spent supernatants of stationary phase cultures of S. aureus or S. epidermidis, but not of distantly related bacteria, significantly reduced the persister cell frequency upon ciprofloxacin challenge when added to exponentially growing and stationary phase S. aureus cells. Curiously, the persister reducing activity of S. aureus supernatants was also effective against persisters formed by either S. carnosus or Listeria monocytogenes. The persister reducing component, which resisted heat but not proteases and was produced in the late growth phase in an agr quorum-sensing dependent manner, was identified to be the phenol-soluble modulin (PSM) toxins. S. aureus express several PSMs, each with distinct cytolytic and antimicrobial properties; however, the persister reducing activity was specifically linked to synthesis of the PSMα family. Correspondingly, a high-persister phenotype of a PSMα mutant was observed upon fluoroquinolone or aminoglycoside challenge, demonstrating that the persister reducing activity of PSMs can be endogenously synthesized or extrinsically added. Given that PSMs have been associated with lytic activity against bacterial membranes we propose that PSM toxins increase the susceptibility of persister cells to killing by intracellularly acting antibiotics and that chronic and re-occurring infections with quorum sensing, agr negative mutants may be difficult to treat with antibiotics because of persister cells formed in the absence of PSM toxins.

Therapeutic Targeting of the Staphylococcus aureus Accessory Gene Regulator (agr) System

Staphylococcus aureus can cause numerous different diseases, which has been attributed to its large repertoire of virulence factors, many of which are under the control of the accessory gene regulator (agr) quorum sensing system. Under conditions of high cell density, agr increases the production of many virulence factors, decreases expression of several colonization factors, and is intimately associated with the pathogenesis and biofilm formation of S. aureus. This review summarizes our current understanding of the molecular mechanisms underlying agr quorum sensing and the regulation of agr expression. The discussion also examines subgroups of agr and their association with different diseases, and concludes with an analysis of strategies for designing drugs and vaccines that target agr to combat S. aureus infections.

Novel Miniature Membrane Active Lipopeptidomimetics against Planktonic and Biofilm Embedded Methicillin-Resistant Staphylococcus aureus

Escalating multidrug resistance and highly evolved virulence mechanisms have aggravated the clinical menace of methicillin-resistant Staphylococcus aureus (MRSA) infections. Towards development of economically viable staphylocidal agents here we report eight structurally novel tryptophan-arginine template based peptidomimetics. Out of the designed molecules, three lipopeptidomimetics (S-6, S-7 and S-8) containing 12-amino dodecanoic acid exhibited cell selectivity and good to potent activity against clinically relevant pathogens MRSA, methicillin-resistant Staphylococcus epidermidis and vancomycin-resistant Enterococcus faecium (MIC: 1.4–22.7 μg/mL). Mechanistically, the active peptidomimetics dissipated membrane potential and caused massive permeabilization on MRSA concomitant with loss of viability. Against stationary phase MRSA under nutrient-depleted conditions, active peptidomimetics S-7 and S-8 achieved > 6 log reduction in viability upon 24 h incubation while both S-7 (at 226 μg/mL) and S-8 (at 28 μg/mL) also destroyed 48 h mature MRSA biofilm causing significant decrease in viability (p < 0.05). Encouragingly, most active peptidomimetic S-8 maintained efficacy against MRSA in presence of serum/plasma while exhibiting no increase in MIC over 17 serial passages at sub-MIC concentrations implying resistance development to be less likely. Therefore, we envisage that the current template warrants further optimization towards the development of cell selective peptidomimetics for the treatment of device associated MRSA infections.