Untangling the Diverse and Redundant Mechanisms of Staphylococcus aureus Biofilm Formation

Early fibrin biofilm development in cardiovascular infections

The single most common microbe causing cardiovascular infections is Staphylococcus aureus (S. aureus). S. aureus produces coagulase that converts fibrinogen to fibrin, which is incorporated into biofilms. This process aids in adherence to intravascular structures, defense against the host immune system, and resistance to antimicrobial treatment. Despite its significance, fibrin formation in S. aureus biofilms remains poorly understood. Therefore, this study aimed to elucidate the early development of cardiovascular biofilms. Clinically isolated coagulase-positive S. aureus and coagulase-negative Staphylococcus lugdunensis (S. lugdunensis) from patients with cardiovascular infections, and a coagulase mutant S. aureus Δcoa, were grown in tryptic soy broth (TSB), Iscove's Modified Dulbecco's Medium (IMDM), and pooled human plasma, with or without porcine heart valves. Bacterial growth, metabolic activity, and bacterial fibrinogen utilization were measured over 24 h at 37 °C. Time-lapse confocal microscopy was used to visualize and track biofilm development. S. aureus exhibited more growth in TSB and human plasma than S. lugdunensis and S. aureus Δcoa, but showed similar growth in IMDM after 24 h. Peak metabolic activity for all isolates was highest in TSB and lowest in human plasma. The presence of porcine valves caused strain-dependent alterations in time to peak metabolic activity. Confocal imaging revealed fibrin-based biofilm development exclusively in the coagulase-producing S. aureus strains. Between 2 and 6 h of biofilm development, 74.9 % (p = 0.034) of the fibrinogen from the medium was converted to fibrin. Variations in fibrin network porosity and density were observed among different coagulase-producing S. aureus strains. Fibrin formation is mediated by S. aureus coagulase and first strands occurred within 3 h for clinical strains after exposure to human plasma. This study stresses the importance of experimental design given the bacterial changes due to different media and substrates and provides insights into the early pathogenesis of S. aureus cardiovascular biofilms.

Not All Antiseptic Solutions Are Equivalent in Removing Biofilm: A Comparison Across Different Orthopaedic Surfaces

BACKGROUND

Antiseptic solutions are commonly utilized during total joint arthroplasty (TJA) to prevent and treat periprosthetic joint infection (PJI). The purpose of this study was to investigate which antiseptic solution is most effective against methicillin-sensitive Staphylococcus aureus (MSSA) and Escherichia coli biofilms established in vitro on orthopaedic surfaces commonly utilized in total knee arthroplasty: cobalt-chromium (CC), oxidized zirconium (OxZr), and polymethylmethacrylate (PMMA).

METHODS

MSSA and E. coli biofilms were grown on CC, OxZr, and PMMA discs for 24 and 72 hours. Biofilm-coated discs were treated with control or various antiseptic solutions for 3 minutes. Solutions included 10% povidone-iodine, a 1:1 mixture of 10% povidone-iodine plus 3% hydrogen peroxide, diluted povidone-iodine, 0.05% chlorhexidine gluconate, and a surfactant-based formulation of ethanol, acetic acid, sodium acetate, benzalkonium chloride, and water. Following treatment, discs were sonicated to quantify adherent bacteria or underwent imaging with scanning electron microscopy to identify biofilm. Antiseptic solutions were considered efficacious if they produced a 3-log (1,000-fold) reduction in colony-forming units compared with controls.

RESULTS

On both OxZr and CC, 10% povidone-iodine with hydrogen peroxide eradicated all MSSA, and it achieved clinical efficacy on PMMA at both 24-hour MSSA biofilm (p < 0.0002) and 72-hour MSSA biofilm (p = 0.002). On 72-hour MSSA biofilm, 10% povidone-iodine eradicated all bacteria on OxZr and CC, and it achieved clinical efficacy on PMMA (p = 0.04). On 24-hour MSSA biofilm, 10% povidone-iodine achieved efficacy on all surfaces (all p < 0.01). The surfactant-based formulation only achieved clinical efficacy on 72-hour MSSA biofilms on CC (p = 0.04) and OxZr (p = 0.07). On 72-hour E. coli biofilm, 10% povidone-iodine with or without hydrogen peroxide achieved clinical efficacy on all surfaces. No other solution achieved clinical efficacy on either MSSA or E. coli.

CONCLUSIONS

Antiseptic solutions vary considerably in efficacy against bacterial biofilm. The 10% povidone-iodine solution with or without hydrogen peroxide consistently removed MSSA and E. coli biofilms on multiple orthopaedic surfaces and should be considered for clinical use.

CLINICAL RELEVANCE

Clinicians should be aware of the differences in the efficacy of antiseptic solutions on different orthopaedic surfaces when treating MSSA or E. coli biofilms.

Therapeutic efficacy of chitosan-based hybrid nanomaterials to treat microbial biofilms and their infections - A review

Antimicrobial resistance, the biggest issue facing the global healthcare sector, quickly emerged and spread due to the frequent use of antibiotics in regular treatments. The investigation of polymer-based nanomaterials as possible antibiofilm treatment agents is prompted by the growing ineffectiveness of conventional therapeutic techniques against these resistant bacteria species. So far, several articles have been published on microbial biofilm eradication using various polymer-based nanomaterials due to their therapeutic efficacy and biocompatibility nature. Despite their potential, a comprehensive review of the chitosan-based hybrid nanomaterials to treat microbial biofilms and their infections is lacking. This review provides a comprehensive investigation of the current state of therapeutic efficacy, various nanoformulations, advantages, limitations, and regulations of chitosan-based hybrid nanomaterials for biofilm treatment. Special attention is given to the application of chitosan-based nanomaterials in wound care, urinary tract infections, and dental biofilms are discussed, highlighting their role in managing biofilm-associated complications. Researchers will be better able to comprehend and develop unique, marketable chitosan-based nanomaterials with increased activity to treat biofilm infections in near future with the aid of this review.

Fighting fibrin with fibrin: Vancomycin delivery into coagulase-mediated Staphylococcus aureus biofilms via fibrin-based nanoparticle binding

Staphylococcus aureus skin and soft tissue infection is a common ailment placing a large burden upon global healthcare infrastructure. These bacteria are growing increasingly recalcitrant to frontline antimicrobial therapeutics like vancomycin due to the prevalence of variant populations such as methicillin-resistant and vancomycin-resistant strains, and there is currently a dearth of novel antibiotics in production. Additionally, S. aureus has the capacity to hijack the host clotting machinery to generate fibrin-based biofilms that confer protection from host antimicrobial mechanisms and antibiotic-based therapies, enabling immune system evasion and significantly reducing antimicrobial efficacy. Emphasis is being placed on improving the effectiveness of therapeutics that are already commercially available through various means. Fibrin-based nanoparticles (FBNs) were developed and found to interact with S. aureus through the clumping factor A (ClfA) fibrinogen receptor and directly integrate into the biofilm matrix. FBNs loaded with antimicrobials such as vancomycin enabled a targeted and sustained release of antibiotic that increased drug contact time and reduced the therapeutic dose required for eradicating the bacteria, both in vitro and in vivo. Collectively, these findings suggest that FBN-antibiotic delivery may be a novel and potent therapeutic tool for the treatment of S. aureus biofilm infections.

Emerging Strategies to Prevent Bacterial Infections on Titanium-Based Implants

Titanium and titanium alloys remain the gold standard for dental and orthopedic implants. These materials are heavily used because of their bioinert nature, robust mechanical properties, and seamless integration with bone. However, implant-associated infections (IAIs) remain one of the leading causes of implant failure. Eradicating an IAI can be difficult since bacteria can form biofilms on the medical implant, protecting the bacterial cells against systemic antibiotics and the host's immune system. If the infection is not treated promptly and aggressively, device failure is inevitable, leading to costly multi-step revision surgeries. To circumvent this dire situation, scientists and engineers continue to develop novel strategies to protect the surface of medical implants from bacteria. In this review, details on emerging strategies to prevent infection in titanium implants are reported. These strategies include anti-adhesion properties provided by polymers, superhydrophobic, superhydrophilic, and liquid-infused surface coatings, as well as strategies and coatings employed to lyse the bacteria. Additionally, commercially available technologies and those under preclinical trials are examined while discussing current and future trends.

Mechanisms of antimicrobial resistance in biofilms

Most bacteria in nature exist in aggregated communities known as biofilms, and cells within a biofilm demonstrate major physiological changes compared to their planktonic counterparts. Biofilms are associated with many different types of infections which can have severe impacts on patients. Infections involving a biofilm component are often chronic and highly recalcitrant to antibiotic therapy as a result of intrinsic physical factors including extracellular matrix production, low growth rates, altered antibiotic target production and efficient exchange of resistance genes. This review describes the biofilm lifecycle, phenotypic characteristics of a biofilm, and contribution of matrix and persister cells to biofilms intrinsic tolerance to antimicrobials. We also describe how biofilms can evolve antibiotic resistance and transfer resistance genes within biofilms. Multispecies biofilms and the impacts of various interactions, including cooperation and competition, between species on tolerance to antimicrobials in polymicrobial biofilm communities are also discussed.

Sensitizing methicillin-resistant Staphylococcus aureus (MRSA) to cefuroxime: the synergic effect of bicarbonate and the wall teichoic acid inhibitor ticlopidine

Methicillin-resistant Staphylococcus aureus (MRSA) strains are a major challenge for clinicians due, in part, to their resistance to most β-lactams, the first-line treatment for methicillin-susceptible S. aureus. A phenotype termed "NaHCO3-responsiveness" has been identified, wherein many clinical MRSA isolates are rendered susceptible to standard-of-care β-lactams in the presence of physiologically relevant concentrations of NaHCO3, in vitro and ex vivo; moreover, such "NaHCO3-responsive" isolates can be effectively cleared by β-lactams from target tissues in experimental infective endocarditis (IE). One mechanistic impact of NaHCO3 exposure on NaHCO3-responsive MRSA is to repress WTA synthesis. This NaHCO3 effect mimics the phenotype of tarO-deficient MRSA, including sensitization to the PBP2-targeting β-lactam, cefuroxime (CFX). Herein, we further investigated the impacts of NaHCO3 exposure on CFX susceptibility in the presence and absence of a WTA synthesis inhibitor, ticlopidine (TCP), in a collection of clinical MRSA isolates from skin and soft tissue infections (SSTI) and bloodstream infections (BSI). NaHCO3 and/or TCP enhanced susceptibility to CFX in vitro, by both minimum inhibitor concentration (MIC) and time-kill assays, as well as in an ex vivo simulated endocarditis vegetations (SEV) model, in NaHCO3-responsive MRSA. Furthermore, in experimental IE (presumably in the presence of endogenous NaHCO3), pre-exposure to TCP prior to infection sensitized the NaHCO3-responsive MRSA strain (but not the non-responsive strain) to enhanced clearances by CFX in target tissues. These data support the notion that NaHCO3 is acting similarly to WTA synthesis inhibitors, and that such inhibitors have potential translational applications in the treatment of certain MRSA strains in conjunction with specific β-lactam agents.

Characteristics of Staphylococcus aureus biofilm matured in tryptic soy broth, low-fat milk, or whole milk samples along with inactivation by 405 nm light combined with folic acid

In the present study, the characteristics of Staphylococcus aureus biofilms matured in tryptic soy broth (TSB), low-fat milk, or whole milk samples were identified along with their resistance to 405 nm light with or without folic acid. Phenotypic properties of carbohydrate and protein contents in extracellular polymeric substance (EPS) of S. aureus biofilms matured in different conditions were identified. The carbohydrate content was higher in the biofilm matured in low-fat milk (1.27) than the samples matured in whole milk (0.58) and TSB (0.10). Protein content in the EPS of biofilm was higher in the sample matured in whole milk (6.59) than the samples matured in low-fat milk (3.24) and TSB (2.08). Moreover, the maturation condition had a significant effect on the membrane lipid composition of the biofilm, producing more unsaturated fatty acids in biofilm matured in milk samples. These changes in biofilm matured in milk samples increased the resistance of S. aureus to 405 nm light in the presence of folic acid (LFA). Additionally, transcriptomic analysis was conducted to identify the response of S. aureus biofilm to LFA treatment. Several genes related to DNA and protein protection from oxidative stress along with biofilm accumulation were overexpressed in the LFA-treated biofilms. These results indicate the maturation of S. aureus biofilm in various samples and the biofilms responses to bactericidal treatments.

Hydrogel Coating versus Calcium Sulphate Beads as a Local Antibiotic Carrier for Debridement Procedures in Acute Periprosthetic Joint Infection: A Preliminary Study

Periprosthetic joint infections (PJI) are among the most difficult complications to treat in orthopaedic surgery. Debridement, antibiotics, and implant retention (DAIR) represent an efficient strategy for acute PJI, especially when resorbable local antibiotic carriers and coatings are used. The aim of this pilot study was to evaluate the difference between using antibiotic-loaded hydrogel (ALH) and calcium sulphate (CS) beads in the DAIR procedure. We analysed 16 patients who had been treated since 2018 for acute PJI, namely eight patients with knee PJI (50%), seven with hip PJI (43.7%), and one with shoulder PJI (6.2%). Nine patients were treated with the Debridement, Antibiotic Coating and Retention of the Implant (DACRI) method, while seven were treated with the Debridement, Antibiotic Pearls, Retention of the Implant (DAPRI) method. We found no significant differences between the two groups in terms of age, sex, the American Society of Anesthesiologists risk score, Charlson Comorbidity Index, localisation, days from onset to diagnosis and pathogenesis. Furthermore, no differences were found between the DACRI and DAPRI groups in terms of infection control (15 patients, 93.75% with p = 0.36) and last C-Reactive Protein values (p = 0.26), with a mean follow-up of 26.1 ± 7.7 months. Treatment for one patient affected by knee Candida albicans PJI in the DACRI group was not successful. In conclusion, DAPRI and DACRI appear to be safe and effective treatments for PJIs. This evidence will encourage the development of new clinical research into local carriers and coatings for use in acute implant-associated infections.

Combining the dual antibacterial and regenerative activities of platelet-rich plasma with β-lactams to mitigate MRSA-infected skin wounds

The emergence of multidrug-resistant bacteria contributes to the necessity of developing novel infection treatment approaches. This study was designed to evaluate the antimicrobial and wound healing activities of platelet-rich plasma (PRP) in combination with β-lactams (ampicillin and/or oxacillin) for the application on methicillin-resistant Staphylococcus aureus (MRSA)-infected skin. PRP was collected from the peripheral blood of healthy donors. The anti-MRSA activity was tested through a growth inhibition curve, colony-forming unit (CFU), and SYTO 9 assay. The PRP incorporation lowered the minimum inhibitory concentration (MIC) of ampicillin and oxacillin against MRSA. The combination of β-lactams together with PRP showed a three-log CFU reduction of MRSA. The major components of PRP for eliminating MRSA were found to be the complement system and iron sequestration proteins, according to the proteomic analysis. The adhesive bacterial colony in the microplate was decreased from 2.9 × 107 to 7.3 × 105 CFU after the treatment of cocktails containing β-lactams and PRP. The cell-based study indicated that keratinocyte proliferation was stimulated by PRP. The in vitro scratch and transwell experiments revealed that PRP improved keratinocyte migration. In the MRSA-infected mouse skin model, PRP appeared to show a synergistic effect for wound area reduction by 39% when combined with β-lactams. The MRSA burden in the infected area was lessened two-fold after topical administration of the combined β-lactams and PRP. PRP inhibited macrophage infiltration in the wound site to shorten the inflammatory phase and accelerate the initiation of the proliferative phase. No skin irritation was detected with the topical delivery of this combination. Our findings suggested that β-lactams plus PRP was applicable to alleviate the problems associated with MRSA via dual antibacterial and regenerative activities.

Antimicrobial Peptides and Small Molecules Targeting the Cell Membrane of Staphylococcus aureus

Clinical management of Staphylococcus aureus infections presents a challenge due to the high incidence, considerable virulence, and emergence of drug resistance mechanisms. The treatment of drug-resistant strains, such as methicillin-resistant S. aureus (MRSA), is further complicated by the development of tolerance and persistence to antimicrobial agents in clinical use. To address these challenges, membrane disruptors, that are not generally considered during drug discovery for agents against S. aureus, should be explored. The cell membrane protects S. aureus from external stresses and antimicrobial agents, but membrane-targeting antimicrobial agents are probably less likely to promote bacterial resistance. Nontypical linear cationic antimicrobial peptides (AMPs), highly modified AMPs such as daptomycin (lipopeptide), bacitracin (cyclic peptide), and gramicidin S (cyclic peptide), are currently in clinical use. Recent studies have demonstrated that AMPs and small molecules can penetrate the cell membrane of S. aureus, inhibit phospholipid biosynthesis, or block the passage of solutes between the periplasm and the exterior of the cell. In addition to their primary mechanism of action (MOA) that targets the bacterial membrane, AMPs and small molecules may also impact bacteria through secondary mechanisms such as targeting the biofilm, and downregulating virulence genes of S. aureus. In this review, we discuss the current state of research into cell membrane-targeting AMPs and small molecules and their potential mechanisms of action against drug-resistant physiological forms of S. aureus, including persister cells and biofilms.

Secreted mammalian DNases protect against systemic bacterial infection by digesting biofilms

Extracellular DNase DNASE1L3 maintains tolerance to self-DNA in humans and mice, whereas the role of its homolog DNASE1 remains controversial, and the overall function of secreted DNases in immunity is unclear. We report that deletion of murine DNASE1 neither caused autoreactivity in isolation nor exacerbated lupus-like disease in DNASE1L3-deficient mice. However, combined deficiency of DNASE1 and DNASE1L3 rendered mice susceptible to bloodstream infection with Staphylococcus aureus. DNASE1/DNASE1L3 double-deficient mice mounted a normal innate response to S. aureus and did not accumulate neutrophil extracellular traps (NETs). However, their kidneys manifested severe pathology, increased bacterial burden, and biofilm-like bacterial lesions that contained bacterial DNA and excluded neutrophils. Furthermore, systemic administration of recombinant DNASE1 protein during S. aureus infection rescued the mortality of DNase-deficient mice and ameliorated the disease in wild-type mice. Thus, DNASE1 and DNASE1L3 jointly facilitate the control of bacterial infection by digesting extracellular microbial DNA in biofilms, suggesting the original evolutionary function of secreted DNases as antimicrobial agents.

Approaching prosthesis infection environment: Development of an innovative in vitro Staphylococcus aureus biofilm model

The major role and implication of bacterial biofilms in the case of bone and prosthesis infections have been highlighted and often linked to implant colonization. Management strategies of these difficult-to-treat infections consist in surgeries and antibiotic treatment, but the rate of relapse remains high, especially if Staphylococcus aureus, a high-virulent pathogen, is involved. Therapeutic approaches are not adapted to the specific features of biofilm in bone context whereas infectious environment is known to importantly influence biofilm structure. In the present study, we aim to characterize S. aureus SH1000 (methicillin-sensitive strain, MSSA) and USA300 (methicillin-resistant strain, MRSA) biofilm on different surfaces mimicking the periprosthetic environment. As expected, protein adsorption on titanium enhanced the number of adherent bacteria for both strains. On bone explant, USA300 adhered more than SH1000. The simultaneous presence of two different surfaces was also found to change the bacterial behaviour. Thus, proteins adsorption on titanium and bone samples (from bank or directly recovered after an arthroplasty) were found to be key parameters that influence S. aureus biofilm formation: adhesion, matrix production and biofilm-related gene regulation. These results highlighted the need for new biofilm models, more relevant with the infectious environment by using adapted culture medium and presence of surfaces that are representative of in situ conditions to better evaluate therapeutic strategies against biofilm.

An Explorative Review on Advanced Approaches to Overcome Bacterial Resistance by Curbing Bacterial Biofilm Formation

The continuous emergence of multidrug-resistant pathogens evoked the development of innovative approaches targeting virulence factors unique to their pathogenic cascade. These approaches aimed to explore anti-virulence or anti-infective therapies. There are evident concerns regarding the bacterial ability to create a superstructure, the biofilm. Biofilm formation is a crucial virulence factor causing difficult-to-treat, localized, and systemic infections. The microenvironments of bacterial biofilm reduce the efficacy of antibiotics and evade the host's immunity. Producing a biofilm is not limited to a specific group of bacteria; however, Pseudomonas aeruginosa, Acinetobacter baumannii, and Staphylococcus aureus biofilms are exemplary models. This review discusses biofilm formation as a virulence factor and the link to antimicrobial resistance. In addition, it explores insights into innovative multi-targeted approaches and their physiological mechanisms to combat biofilms, including natural compounds, phages, antimicrobial photodynamic therapy (aPDT), CRISPR-Cas gene editing, and nano-mediated techniques.

Is biofilm formation intrinsic to the origin of life?

Biofilms are multicellular, often surface-associated, communities of autonomous cells. Their formation is the natural mode of growth of up to 80% of microorganisms living on this planet. Biofilms refractory towards antimicrobial agents and the actions of the immune system due to their tolerance against multiple environmental stresses. But how did biofilm formation arise? Here, I argue that the biofilm lifestyle has its foundation already in the fundamental, surface-triggered chemical reactions and energy preserving mechanisms that enabled the development of life on earth. Subsequently, prototypical biofilm formation has evolved and diversified concomitantly in composition, cell morphology and regulation with the expansion of prokaryotic organisms and their radiation by occupation of diverse ecological niches. This ancient origin of biofilm formation thus mirrors the harnessing environmental conditions that have been the rule rather than the exception in microbial life. The subsequent emergence of the association of microbes, including recent human pathogens, with higher organisms can be considered as the entry into a nutritional and largely stress-protecting heaven. Nevertheless, basic mechanisms of biofilm formation have surprisingly been conserved and refunctionalized to promote sustained survival in new environments.

Staphylococcal Enterotoxins Enhance Biofilm Formation by Staphylococcus aureus in Platelet Concentrates

Biofilm formation and slow growth by Staphylococcus aureus in platelet concentrates (PCs) cause missed detection of this bacterium during routine PC screening with automated culture systems. This heightens the chances of false-negative screening transfusions and pre-disposes transfusion patients to an elevated risk of sepsis due to secretion of staphylococcal enterotoxins (SEs) in PCs. A hybrid approach of comparative RNAseq analyses and CRISPR mutagenesis of SE genes was employed to investigate the effect of SEs in S. aureus growth and biofilm formation in PCs. RNAseq data showed no differential expression for key biofilm genes, whereas SE genes were upregulated (>0.5- to 3.6-fold change) in PCs compared to trypticase soy broth (TSB). Remarkably, growth and biofilm formation assays revealed increased growth for the S. aureus SE mutants, while their ability to form biofilms was significantly impaired (−6.8- to −2.4-fold change) in comparison to the wild type strain, in both PCs and TSB. Through the well-established superantigen mechanism of SEs, we propose three roles for SEs during biofilm development in PCs: (1) provide a scaffold for biofilm matrix, (2) mediate cell-to-cell aggregation, and (3) guarantee biofilm survival. Furthermore, SE contribution to both growth and biofilm development seems to be centrally regulated by agr via quorum sensing and by saeSR and sigB. This study reveals new roles for SEs, which enforce their relevance in ensuring PC safety for transfusion patients. It further deciphers the underlying reasons for failed S. aureus detection in PCs during screening with automated culture systems.

Innovative Strategies to Overcome Antimicrobial Resistance and Tolerance

Antimicrobial resistance and tolerance are natural phenomena that arose due to evolutionary adaptation of microorganisms against various xenobiotic agents. These adaptation mechanisms make the current treatment options challenging as it is increasingly difficult to treat a broad range of infections, associated biofilm formation, intracellular and host adapted microbes, as well as persister cells and microbes in protected niches. Therefore, novel strategies are needed to identify the most promising drug targets to overcome the existing hurdles in the treatment of infectious diseases. Furthermore, discovery of novel drug candidates is also much needed, as few novel antimicrobial drugs have been introduced in the last two decades. In this review, we focus on the strategies that may help in the development of innovative small molecules which can interfere with microbial resistance mechanisms. We also highlight the recent advances in optimization of growth media which mimic host conditions and genome scale molecular analyses of microbial response against antimicrobial agents. Furthermore, we discuss the identification of antibiofilm molecules and their mechanisms of action in the light of the distinct physiology and metabolism of biofilm cells. This review thus provides the most recent advances in host mimicking growth media for effective drug discovery and development of antimicrobial and antibiofilm agents.

Evaluation of three Staphylococcus aureus proteins involved in the adhesion process as antigens for the detection of bovine intramammary infections

Introduction. Fast and accurate diagnosis is one of the key strategies in the successful control of intramammary infections caused by Staphylococcus aureus. Immunoassays are one of the diagnostic tools that have been proposed for the detection of S. aureus infection because they offer an advantage in terms of cost and are fast and easy to use compared to other diagnostic tests.Gap statement. The main challenge of the immunoassays is to identify antigens or serological markers that allow accurate discrimination between infected and uninfected cows with S. aureus, since this bacterium can naturally colonize different areas of the animal body.Aim. To evaluate three S. aureus proteins (IsdA, ClfA, SdrD) involved in the adhesion process as antigens to detect indicator antibodies of bovine intramammary infections.Methodology. Ninety-six cows in lactation and not vaccinated against S. aureus were included. Forty-eight of these cows were infected with S. aureus, while the rest (n=48 cows) were uninfected. Blood and milk samples were collected from each animal to recover serum and whey. IgG titres against the three proteins individually and combined (Mix) were measured in each sample using an enzyme-linked immunosorbent assay (ELISA) test.Results. Significant differences in the IgG response against the proteins evaluated were observed, highlighting the antigenic potential of IsdA and demonstrating that some antigens can detect specific antibodies of infection better than others. According to receiver operating characteristic (ROC) curve analysis, the combined proteins showed the most remarkable capacity (sensitivity of 79 % and specificity of 77 %) to differentiate between infected and uninfected cows when blood samples were used. In addition, the combined proteins also showed the highest specificity (94 %) when using milk samples.Conclusion. Our findings provide information on the usefulness of three adhesion-associated S. aureus proteins in detecting serological markers of intramammary infections in bovines.

Current therapeutic interventions combating biofilm-related infections in orthopaedics : a systematic review of in vivo animal studies

Aims

Biofilm-related infection is a major complication that occurs in orthopaedic surgery. Various treatments are available but efficacy to eradicate infections varies significantly. A systematic review was performed to evaluate therapeutic interventions combating biofilm-related infections on in vivo animal models.

Methods

Literature research was performed on PubMed and Embase databases. Keywords used for search criteria were “bone AND biofilm”. Information on the species of the animal model, bacterial strain, evaluation of biofilm and bone infection, complications, key findings on observations, prevention, and treatment of biofilm were extracted.

Results

A total of 43 studies were included. Animal models used included fracture-related infections (ten studies), periprosthetic joint infections (five studies), spinal infections (three studies), other implant-associated infections, and osteomyelitis. The most common bacteria were Staphylococcus species. Biofilm was most often observed with scanning electron microscopy. The natural history of biofilm revealed that the process of bacteria attachment, proliferation, maturation, and dispersal would take 14 days. For systemic mono-antibiotic therapy, only two of six studies using vancomycin reported significant biofilm reduction, and none reported eradication. Ten studies showed that combined systemic and topical antibiotics are needed to achieve higher biofilm reduction or eradication, and the effect is decreased with delayed treatment. Overall, 13 studies showed promising therapeutic potential with surface coating and antibiotic loading techniques.

Conclusion

Combined topical and systemic application of antimicrobial agents effectively reduces biofilm at early stages. Future studies with sustained release of antimicrobial and biofilm-dispersing agents tailored to specific pathogens are warranted to achieve biofilm eradication.

Cite this article: Bone Joint Res 2022;11(10):700–714.

The effects of rotating magnetic field and antiseptic on in vitro pathogenic biofilm and its milieu

The application of various magnetic fields for boosting the efficacy of different antimicrobial molecules or in the character of a self-reliant antimicrobial agent is considered a promising approach to eradicating bacterial biofilm-related infections. The purpose of this study was to analyze the phenomenon of increased activity of octenidine dihydrochloride-based antiseptic (OCT) against Staphylococcus aureus and Pseudomonas aeruginosa biofilms in the presence of the rotating magnetic field (RMF) of two frequencies, 5 and 50 Hz, in the in vitro model consisting of stacked agar discs, placed in increasing distance from the source of the antiseptic solution. The biofilm-forming cells' viability and morphology as well as biofilm matrix structure and composition were analyzed. Also, octenidine dihydrochloride permeability through biofilm and porous agar obstacles was determined for the RMF-exposed versus unexposed settings. The exposure to RMF or OCT apart did not lead to biofilm destruction, contrary to the setting in which these two agents were used together. The performed analyses revealed the effect of RMF not only on biofilms (weakening of cell wall/membranes, disturbed morphology of cells, altered biofilm matrix porosity, and composition) but also on its milieu (altered penetrability of octenidine dihydrochloride through biofilm/agar obstacles). Our results suggest that the combination of RMF and OCT can be particularly promising in eradicating biofilms located in such areas as wound pockets, where physical obstacles limit antiseptic activity.

Linezolid decreases Staphylococcus aureus biofilm formation by affecting the IcaA and IcaB proteins

Background

The ica gene of Staphylococcus aureus (S. aureus) plays a vital role in its growth and biofilm formation. Among them, IcaA and IcaB are critical proteins for synthesizing extracellular polysaccharides and biofilms in S. aureus. To investigate whether the formation of S. aureus biofilms can be inhibited through the IcaA and IcaB proteins by the presence of linezolid.

Methods

The icaA and icaB genes of S. aureus ATCC 25923 were silenced by homologous recombination. The critical roles of icaA and icaB in S. aureus were analysed by observing the growth curve and biofilm formation after linezolid treatment. Then, the effect of linezolid on the morphology of S. aureus was observed by scanning electron microscopy. Finally, the potential binding ability of linezolid to Ica proteins was predicted by molecular docking.

Results

The icaA- and icaB-silenced strains were successfully constructed, and the sensitivity of S. aureus to linezolid was decreased after icaA and icaB silencing. Scanning electron microscopy showed that linezolid caused invagination of the S. aureus surface and reduced the production of biofilms. Molecular docking results showed that linezolid could bind to IcaA and IcaB proteins.

Conclusion

IcaA and IcaB are potential targets of linezolid in inhibiting the biofilm formation of S. aureus (ATCC 25923).

Lung-adapted Staphylococcus aureus isolates with dysfunctional agr system trigger a proinflammatory response

BACKGROUND

Staphylococcus aureus (Sa) dominates the lung microbiota of Cystic Fibrosis (CF) children and persistent clones are able to establish chronic infection for years, having a direct deleterious impact on lung function. However, in this context, the exact contribution of Sa to the decline in respiratory function in CF children is not elucidated.

METHODS

To investigate the contribution of persistent S. aureus clones in CF disease, we undertook the analysis of sequential isogenic isolates recovered from 15 young CF patients.

RESULTS

Using an Air-Liquid infection model, we observed a strong correlation between Sa adaption in the lung (late isolates), low toxicity and pro-inflammatory cytokine secretion. Conversely, early isolates appeared to be highly cytotoxic but did not promote cytokine secretion. We found that cytokine secretion was dependent on Staphylococcal protein A (Spa), which was selectively expressed in late compared to early isolates as a consequence of dysfunctional agr quorum-sensing system. Finally, we demonstrated the involvement of TNF-α receptor 1 signaling in the inflammatory response of airway epithelial cells to these lung-adapted Sa isolates.

CONCLUSION

Our results suggest an unexpected direct role of bacterial lung adaptation in the progression of chronic lung disease by promoting a pro-inflammatory response through acquired agr dysfunction.

Enhancing osseointegration and mitigating bacterial biofilms on medical-grade titanium with chitosan-conjugated liquid-infused coatings

Titanium alloys, in particular, medical-grade Ti-6Al-4 V, are heavily used in orthopaedic applications due to their high moduli, strength, and biocompatibility. Implant infection can result in biofilm formation and failure of prosthesis. The formation of a biofilm on implants protects bacteria from antibiotics and the immune response, resulting in the propagation of the infection and ultimately resulting in device failure. Recently, slippery liquid-infused surfaces (LIS) have been investigated for their stable liquid interface, which provides excellent repellent properties to suppress biofilm formation. One of the current limitations of LIS coatings lies in the indistinctive repellency of bone cells in orthopaedic applications, resulting in poor tissue integration and bone ingrowth with the implant. Here, we report a chitosan impregnated LIS coating that facilitates cell adhesion while preventing biofilm formation. The fabricated coating displayed high contact angles (108.2 ± 5.2°) and low sliding angles (3.56 ± 4.3°). Elemental analysis obtained using X-ray photoelectron spectroscopy (XPS) confirmed the availability of fluorine and nitrogen, indicating the presence of fluorosilane and chitosan in the final coating. Furthermore, our results suggest that chitosan-conjugated LIS increased cell adhesion of osteoblast-like SaOS-2 cells and significantly promoted proliferation (a fourfold increase at 7-day incubation) compared to conventional titanium liquid-infused surfaces. Furthermore, the chitosan conjugated LIS significantly reduced biofilm formation of methicillin-resistant Staphylococcus aureus (MRSA) by up to 50% and 75% when compared to untreated titanium and chitosan-coated titanium, respectively. The engineered coating can be easily modified with other biopolymers or capture molecules to be applied to other biomaterials where tissue integration and biofilm prevention are needed.

Imaging and characterization of transitions in biofilm morphology via anomalous diffusion following environmental perturbation

Microorganisms form macroscopic structures for the purpose of environmental adaptation. Sudden environmental perturbations induce dynamics that cause bacterial biofilm morphology to transit to another equilibrium state, thought to be related to anomalous diffusion processes. Here, detecting the super-diffusion characteristics would offer a long-sought goal for a rapid detection method of biofilm phenotypes based on their dynamics, such as growth or dispersal. In this paper, phase-sensitive Doppler optical coherence tomography (OCT) and dynamic light scattering (DLS) are combined to demonstrate wide field-of-view and label-free internal dynamic imaging of biofilms. The probability density functions (PDFs) of phase displacement of the backscattered light and the dynamic characteristics of the PDFs are estimated by a simplified mixed Cauchy and Gaussian model. This model can quantify the super-diffusion state and estimate the dynamic characteristics and macroscopic responses in biofilms that may further describe dispersion and growth in biofilm models.

Tylosin Inhibits Streptococcus suis Biofilm Formation by Interacting With the O-acetylserine (thiol)-lyase B CysM

Streptococcus suis (S. suis) can decrease its virulence or modify local conditions through biofilm formation, which promotes infection persistence in vivo. Biofilm formation is an important cause of chronic drug-resistant S. suis infection. The aim of this study was to evaluate whether tylosin effectively inhibits S. suis biofilm formation by interacting with O-acetylserine (thiol)-lyase B (CysM), a key enzymatic regulator of cysteine synthesis. Biofilm formation of the mutant (ΔcysM) strain was significantly lower compared to the wild-type ATCC 700794 strain. Tylosin inhibited cysM gene expression, decreased extracellular matrix contents, and reduced cysteine, homocysteine, and S-adenosylmethionine levels, indicating its potential value as an effective inhibitor of S. suis biofilm formation. Furthermore, using biolayer interferometry technology and fourier-transform infrared spectroscopy, we found that tylosin and CysM could be combined directly. Overall, these results provide evidence that tylosin inhibits S. suis biofilm formation by interacting with CysM.

A quorum-based fluorescent probe for imaging pathogenic bacteria

Imaging of bacterial infections can be used for a wide range of investigations, including diagnosis and pathogenesis of infections, and molecular probes targeting biological processes during infection have been used...

Two-Step Approach Using Degradable Magnesium to Inhibit Surface Biofilm and Subsequently Kill Planktonic Bacteria

Bacterial infection remains a great risk in medical implantation surgery. In this paper, we found that degradable metals may be a feasible alternative option of antibacterial implantation materials. It is known that the spalling mechanism of magnesium (Mg) during degradation leads to Mg ions-induced alkaline environment, which is harmful to planktonic bacteria. In this study, we showed that alkaline pH environment is almost harmless to those adhesive bacteria protected in well-formed biofilms. Moreover, experimental results demonstrated that the biofilm formed in the place where Mg spalls are destroyed, releasing the covered bacteria to be planktonic in the alkaline environment. As a result, the colonization of biofilms continues to shrink during the degradation of Mg. It implies that if degradable metal is employed as implantation material, even if bacterial infection occurs, it may be possibly cured without second surgery.

Aerosolized Hypertonic Saline Hinders Biofilm Formation to Enhance Antibiotic Susceptibility of Multidrug-Resistant Acinetobacter baumannii

Limited therapeutic options are available for multidrug-resistant Acinetobacter baumannii (MDR-AB), and the development of effective treatments is urgently needed. The efficacy of four aerosolized antibiotics (gentamicin, amikacin, imipenem, and meropenem) on three different MDR-AB strains was evaluated using hypertonic saline (HS, 7 g/100 mL) as the aerosol carrier. HS aerosol effectively hindered biofilm formation by specific MDR-AB strains. It could also interrupt the swarming dynamics of MDR-AB and the production of extracellular polymeric substances, which are essential for biofilm progression. Biofilms protect the microorganisms from antibiotics. The use of HS aerosol as a carrier resulted in a decreased tolerance to gentamicin and amikacin in the biofilm-rich MDR-AB. Moreover, we tested the aerosol characteristics of antibiotics mixed with HS and saline, and results showed that HS enhanced the inhaled delivery dose with a smaller particle size distribution of the four antibiotics. Our findings demonstrate the potential of using “old” antibiotics with our “new” aerosol carrier, and potentiate an alternative therapeutic strategy to eliminate MDR-AB infections from a biofilm-disruption perspective.

Bacterial Biofilms and Their Implications in Pathogenesis and Food Safety

Biofilm formation is an integral part of the microbial life cycle in nature. In food processing environments, bacterial transmissions occur primarily through raw or undercooked foods and by cross-contamination during unsanitary food preparation practices. Foodborne pathogens form biofilms as a survival strategy in various unfavorable environments, which also become a frequent source of recurrent contamination and outbreaks of foodborne illness. Instead of focusing on bacterial biofilm formation and their pathogenicity individually, this review discusses on a molecular level how these two physiological processes are connected in several common foodborne pathogens such as Listeria monocytogenes, Staphylococcus aureus, Salmonella enterica and Escherichia coli. In addition, biofilm formation by Pseudomonas aeruginosa is discussed because it aids the persistence of many foodborne pathogens forming polymicrobial biofilms on food contact surfaces, thus significantly elevating food safety and public health concerns. Furthermore, in-depth analyses of several bacterial molecules with dual functions in biofilm formation and pathogenicity are highlighted.

Non-Antimicrobial Adjuvant Strategies to Tackle Biofilm-Related Staphylococcus aureus Prosthetic Joint Infections

Staphylococcus aureus frequently causes community- and hospital-acquired infections. S. aureus attachment followed by biofilm formation on tissues and medical devices plays a significant role in the establishment of chronic infections. Staphylococcal biofilms encase bacteria in a matrix and protect the cells from antimicrobials and the immune system, resulting in infections that are highly resistant to treatment. The biology of biofilms is complex and varies between organisms. In this review, we focus our discussion on S. aureus biofilms and describe the stages of their formation. We particularly emphasize genetic and biochemical processes that may be vulnerable to novel treatment approaches. Against this background, we discuss treatment strategies that have been successful in animal models of S. aureus biofilm-related infection and consider their possible use for the prevention and eradication of biofilm-related S. aureus prosthetic joint infection.

Antibiotic-Impregnated Liquid-Infused Coatings Suppress the Formation of Methicillin-Resistant Staphylococcus aureus Biofilms

Medical device-associated infections are an ongoing problem. Once an implant is infected, bacteria create a complex community on the surface known as a biofilm, protecting the bacterial cells against antibiotics and the immune system. To prevent biofilm formation, several coatings have been engineered to hinder bacterial adhesion or viability. In recent years, liquid-infused surfaces (LISs) have been shown to be effective in repelling bacteria due to the presence of a tethered liquid interface. However, local lubricant loss or temporary local displacement can lead to bacteria penetrating the lubrication layer, which can then attach to the surface, proliferate, and form a biofilm. Biofilm formation on biomedical devices can subsequently disrupt the chemistry tethering the slippery liquid interface, causing the LIS coating to fail completely. To address this concern, we developed a "fail-proof" multifunctional coating through the combination of a LIS with tethered antibiotics. The coatings were tested on a medical-grade stainless steel using contact angle, sliding angle, and Fourier transform infrared spectroscopy. The results confirm the presence of antibiotics while maintaining a stable and slippery liquid interface. The antibiotic liquid-infused surface significantly reduced biofilm formation (97% reduction compared to the control) and was tested against two strains of Staphylococcus aureus, including a methicillin-resistant strain. We also demonstrated that antibiotics remain active and reduce bacteria proliferation after subsequent coating modifications. This multifunctional approach can be applied to other biomaterials and provide not only a fail-safe but a fail-proof strategy for preventing bacteria-associated infections.

Insight on the Structure-to-Activity of Carbosilane Metallodendrimers in the Fight against Staphylococcus aureus Biofilms

Biofilm formation is a critical health concern, involved in most human bacterial infections. Combatting this mechanism, which increases resistance to traditional antibiotics and host immune defences, requires novel therapeutic approaches. The remarkable biocide activity and the monodispersity of carbosilane metallodendrimers make them excellent platforms to evaluate the impact of different structural parameters on the biological activity. In this work, we explore the influence of iminopyridine ring substituents on the antibacterial activity against planktonic and biofilm Staphylococcus aureus. New families of first-generation Ru(II) and Cu(II) metallodendrimers were synthesised and analysed, in comparison to the non-substituted counterparts. The results showed that the presence of methyl or methoxy groups in meta position to the imine bond decreased the overall positive charge on the metal ion and, subsequently, the activity against planktonic bacteria. However, it seemed a relevant parameter to consider for the prevention of biofilm formation, if they contribute to increasing the overall lipophilicity. An optimum balance of the charge and lipophilicity of the metallodrug, accomplished through structural design, will provide effective biocide agents against bacteria biofilms.

Recent Innovations in Bacterial Infection Detection and Treatment

Bacterial infections are a major threat to human health, exacerbated by increasing antibiotic resistance. These infections can result in tremendous morbidity and mortality, emphasizing the need to identify and treat pathogenic bacteria quickly and effectively. Recent developments in detection methods have focused on electrochemical, optical, and mass-based biosensors. Advances in these systems include implementing multifunctional materials, microfluidic sampling, and portable data-processing to improve sensitivity, specificity, and ease of operation. Concurrently, advances in antibacterial treatment have largely focused on targeted and responsive delivery for both antibiotics and antibiotic alternatives. Antibiotic alternatives described here include repurposed drugs, antimicrobial peptides and polymers, nucleic acids, small molecules, living systems, and bacteriophages. Finally, closed-loop therapies are combining advances in the fields of both detection and treatment. This review provides a comprehensive summary of the current trends in detection and treatment systems for bacterial infections.

Improved diagnostic prediction of the pathogenicity of bloodstream isolates of Staphylococcus epidermidis

With an estimated 440,000 active cases occurring each year, medical device associated infections pose a significant burden on the US healthcare system, costing about $9.8 billion in 2013. Staphylococcus epidermidis is the most common cause of these device-associated infections, which typically involve isolates that are multi-drug resistant and possess multiple virulence factors. S. epidermidis is also frequently a benign contaminant of otherwise sterile blood cultures. Therefore, tests that distinguish pathogenic from non-pathogenic isolates would improve the accuracy of diagnosis and prevent overuse/misuse of antibiotics. Attempts to use multi-locus sequence typing (MLST) with machine learning for this purpose had poor accuracy (~73%). In this study we sought to improve the diagnostic accuracy of predicting pathogenicity by focusing on phenotypic markers (i.e., antibiotic resistance, growth fitness in human plasma, and biofilm forming capacity) and the presence of specific virulence genes (i.e., mecA, ses1, and sdrF). Commensal isolates from healthy individuals (n = 23), blood culture contaminants (n = 21), and pathogenic isolates considered true bacteremia (n = 54) were used. Multiple machine learning approaches were applied to characterize strains as pathogenic vs non-pathogenic. The combination of phenotypic markers and virulence genes improved the diagnostic accuracy to 82.4% (sensitivity: 84.9% and specificity: 80.9%). Oxacillin resistance was the most important variable followed by growth rate in plasma. This work shows promise for the addition of phenotypic testing in clinical diagnostic applications.

Increased Incidence and Plasma-Biofilm Formation Ability of SCCmec Type IV Methicillin-Resistant Staphylococcus aureus (MRSA) Isolated From Patients With Bacteremia

In Japan, Staphylococcal cassette chromosome mec (SCCmec) type IV methicillin-resistant Staphylococcus aureus (MRSA) is an increasingly prominent cause of bacteremia, but the virulence of most of these strains is unclear. We aimed to investigate the relationship between the molecular characteristics and the ability to form biofilms in the presence of blood plasma (plasma-biofilms) of MRSA strains isolated from bloodstream infections. In this study, the molecular characteristics and biofilms of MRSA strains isolated from blood cultures between 2015 and 2017 were analyzed by PCR-based assays, crystal violet staining, and confocal reflection microscopy methods. Among the 90 MRSA isolates, the detection rate of SCCmec type II clones decreased from 60.7 to 20.6%. The SCCmec type IV clone replaced the SCCmec type II clone as the dominant clone, with a detection rate increasing from 32.1 to 73.5%. The plasma-biofilm formation ability of the SCCmec type IV clone was higher than the SCCmec type II clone and even higher in strains harboring the cna or arcA genes. Plasma-biofilms, mainly composed of proteins, were formed quickly and strongly. Our study demonstrated the increased plasma-biofilm formation ability of SCCmec type IV strains.

Enzyme-Functionalized Mesoporous Silica Nanoparticles to Target Staphylococcus aureus and Disperse Biofilms

BACKGROUND

Staphylococcus aureus biofilms pose a unique challenge in healthcare due to their tolerance to a wide range of antimicrobial agents. The high cost and lengthy timeline to develop novel therapeutic agents have pushed researchers to investigate the use of nanomaterials to deliver antibiofilm agents and target biofilm infections more efficiently. Previous studies have concentrated on improving the efficacy of antibiotics by deploying nanoparticles as nanocarriers. However, the dispersal of the extracellular polymeric substance (EPS) matrix in biofilm-associated infections is also critical to the development of novel nanoparticle-based therapies.

METHODS

This study evaluated the efficacy of enzyme-functionalized mesoporous silica nanoparticles (MSNs) against methicillin-resistant S. aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) biofilms. MSNs were functionalized with the enzyme lysostaphin, which causes cell lysis of S. aureus bacteria. This was combined with two other enzyme functionalized MSNs, serrapeptase and DNase I which will degrade protein and eDNA in the EPS matrix, to enhance eradication of the biofilm. Cell viability after treatment with enzyme-functionalized MSNs was assessed using a MTT assay and CLSM, while crystal violet staining was used to assess EPS removal.

RESULTS

The efficacy of all three enzymes against S. aureus cells and biofilms was significantly improved when they were immobilized onto MSNs. Treatment efficacy was further enhanced when the three enzymes were used in combination against both MRSA and MSSA. Regardless of biofilm maturity (24 or 48 h), near-complete dispersal and killing of MRSA biofilms were observed after treatment with the enzyme-functionalized MSNs. Disruption of mature MSSA biofilms with a polysaccharide EPS was less efficient, but cell viability was significantly reduced.

CONCLUSION

The combination of these three enzymes and their functionalization onto nanoparticles might extend the therapeutic options for the treatment of S. aureus infections, particularly those with a biofilm component.

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.

An Evaluation of the Antibacterial Properties of Tormentic Acid Congener and Extracts From Callistemon viminalis on Selected ESKAPE Pathogens and Effects on Biofilm Formation

ESKAPE pathogens, namely, Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species, are responsible for a majority of all healthcare-acquired infections (HAI). The bacteria cause nosocomial infections in immunocompromised patients. Extracts from Callistemon viminalis have been shown to have antibacterial, antifungal, and anti-inflammatory activities. Tormentic acid congener, a pentacyclic triterpene saponin, was isolated from C. viminalis leaves. This study aimed to investigate the antibacterial effects of tormentic acid congener and leaf extracts on biofilm formation by A. baumannii, S. aureus, S. pyogenes, and P. aeruginosa. The antibacterial effects were determined by the microbroth dilution method, and ciprofloxacin was used as the standard antibacterial drug. Biofilm formation and detachment assays were performed using crystal violet staining. Production of extracellular polymeric DNA and polysaccharides from biofilms was also determined. Tormentic acid congener showed time-dependent antibacterial activity against P. aeruginosa with a MIC of 100 µg/ml and caused significant protein leakage. Antibacterial activity was found when tormentic acid congener was tested against both S. aureus and P. aeruginosa. The MICs were found to be 25 µg/ml and 12.5 µg/ml for P. aeruginosa and S. aureus cells, respectively. S. pyogenes was found to be susceptible to tormentic acid congener and the hydroethanolic extract with an MIC of 100 µg/ml and 25 µg/ml, respectively. A. baumannii was found not to be susceptible to the compound or the extracts. The compound and the extracts caused a significant decrease in the biofilm extracellular polysaccharide content of S. pyogenes. The extracts and tormentic acid congener caused detachment of biofilms and decreased the release of extracellular DNA and capsular polysaccharides from biofilms of P. aeruginosa and S. aureus. Tormentic acid congener and extracts, thus, have significant antibacterial and antibiofilm activities on these selected ESKAPE bacteria and can act as source lead compounds for the development of antibacterial triterpenoids.

Phenotypic Characterization and Whole Genome Analysis of a Strong Biofilm-Forming Staphylococcus aureus Strain Associated With Subclinical Bovine Mastitis in Colombia

Staphylococcus aureus represent a serious threat to public health due to food safety, antibiotic resistance, and the potential zoonotic transmission of strains between dairy cattle and humans. Biofilm formation by S. aureus results in chronicity of the infections which confers protection against the immune response and antibiotics. Likewise, biofilm allows the exchange of mobile genetic material among different strains through microbial interactions inside the matrix. In Colombia, where S. aureus continues to be one of the main pathogens isolated from bovine intramammary infections and where milking by hand is highly frequent, there are knowledge gaps on the zoonotic potential of the strains. Therefore, the aim of this work was to characterize genotypically and phenotypically the S. aureus Sa1FB strain with strong biofilm production and to perform genomic and phenotypic comparisons with other relevant S. aureus strains (native and references strains). These results show a highly productive strain of biofilm and a low ability of cell invasion compared to the other two native strains. In addition, high genomic similarity between S. aureus Sa1FB and the reference strains was observed, despite of the differences reported at the clinical level. However, Sa1FB exhibited special features in terms of mobile genetic elements, highlighting its ability to accept foreign genetic material. Indeed, this could increase mutation, pathogenesis, and adaptability to new hosts, representing a risk for people in contact with the milk obtained from animals infected with these strains. These results present the relevance of surveillance for early detection of emergent clones with zoonotic potential, which reduces the risk of occupational exposure and their spread in the community.

Biological role of EPS from Pseudomonas syringae pv. syringae UMAF0158 extracellular matrix, focusing on a Psl-like polysaccharide

Pseudomonas syringae is a phytopathogenic model bacterium that is used worldwide to study plant-bacteria interactions and biofilm formation in association with a plant host. Within this species, the syringae pathovar is the most studied due to its wide host range, affecting both, woody and herbaceous plants. In particular, Pseudomonas syringae pv. syringae (Pss) has been previously described as the causal agent of bacterial apical necrosis on mango trees. Pss exhibits major epiphytic traits and virulence factors that improve its epiphytic survival and pathogenicity in mango trees. The cellulose exopolysaccharide has been described as a key component in the development of the biofilm lifestyle of the P. syringae pv. syringae UMAF0158 strain (PssUMAF0158). PssUMAF0158 contains two additional genomic regions that putatively encode for exopolysaccharides such as alginate and a Psl-like polysaccharide. To date, the Psl polysaccharide has only been studied in Pseudomonas aeruginosa, in which it plays an important role during biofilm development. However, its function in plant-associated bacteria is still unknown. To understand how these exopolysaccharides contribute to the biofilm matrix of PssUMAF0158, knockout mutants of genes encoding these putative exopolysaccharides were constructed. Flow-cell chamber experiments revealed that cellulose and the Psl-like polysaccharide constitute a basic scaffold for biofilm architecture in this bacterium. Curiously, the Psl-like polysaccharide of PssUMAF0158 plays a role in virulence similar to what has been described for cellulose. Finally, the impaired swarming motility of the Psl-like exopolysaccharide mutant suggests that this exopolysaccharide may play a role in the motility of PssUMAF0158 over the mango plant surface.

A Trimeric Autotransporter Enhances Biofilm Cohesiveness in Yersinia pseudotuberculosis but Not in Yersinia pestis

Cohesion of biofilms made by Yersinia pestis and Yersinia pseudotuberculosis has been attributed solely to an extracellular polysaccharide matrix encoded by the hms genes (Hms-dependent extracellular matrix [Hms-ECM]). However, mutations in the Y. pseudotuberculosis BarA/UvrY/CsrB regulatory cascade enhance biofilm stability without dramatically increasing Hms-ECM production. We found that treatment with proteinase K enzyme effectively destabilized Y. pseudotuberculosis csrB mutant biofilms, suggesting that cell-cell interactions might be mediated by protein adhesins or extracellular matrix proteins. We identified an uncharacterized trimeric autotransporter lipoprotein (YPTB2394), repressed by csrB, which has been referred to as YadE. Biofilms made by a ΔyadE mutant strain were extremely sensitive to mechanical disruption. Overexpression of yadE in wild-type Y. pseudotuberculosis increased biofilm cohesion, similar to biofilms made by csrB or uvrY mutants. We found that the Rcs signaling cascade, which represses Hms-ECM production, activated expression of yadE The yadE gene appears to be functional in Y. pseudotuberculosis but is a pseudogene in modern Y. pestis strains. Expression of functional yadE in Y. pestis KIM6+ weakened biofilms made by these bacteria. This suggests that although the YadE autotransporter protein increases Y. pseudotuberculosis biofilm stability, it may be incompatible with the Hms-ECM production that is essential for Y. pestis biofilm production in fleas. Inactivation of yadE in Y. pestis may be another instance of selective gene loss in the evolution of flea-borne transmission by this species.IMPORTANCE The evolution of Yersinia pestis from its Y. pseudotuberculosis ancestor involved gene acquisition and gene losses, leading to differences in biofilm production. Characterizing the unique biofilm features of both species may provide better understanding of how each adapts to its specific niches. This study identifies a trimeric autotransporter, YadE, that promotes biofilm stability of Y. pseudotuberculosis but which has been inactivated in Y. pestis, perhaps because it is not compatible with the Hms polysaccharide that is crucial for biofilms inside fleas. We also reveal that the Rcs signaling cascade, which represses Hms expression, activates YadE in Y. pseudotuberculosis The ability of Y. pseudotuberculosis to use polysaccharide or YadE protein for cell-cell adhesion may help it produce biofilms in different environments.

Nanomechanical properties of zirconium anodized in a mixture of electrolytes with fluoride ions

The present work introduces nanostructured Zr as a possible choice of metallic implant biomaterial in competition with titanium and its new alloys. The paper reports on the preparation of anodized zirconium in a mixture of electrolytes with fluoride ions, 1 M (NH₄)2SO₄ + 0.15 M NH₄F + distilled water, at 20 V. The obtained nanostructures were investigated by SEM, EDX, XRD and AFM techniques. The SEM - EDX longitudinal and cross sectional analysis revealed the morphology of the formed oxide layers and their thicknesses, which were found to be 7.45 ± 0.18 μm. The mean nanopores' diameter was calculated as 15.8 ± 3.3 nm. The XRD investigations enabled the evaluation of crystallite sizes and texture coefficients for zirconium and zirconium oxide containing samples. The inhibition effect against Escherichia coli and Streptococcus Aureus bacteria was evaluated and discussed as well. The AFM studies revealed that the nano-porous Zr has similar hardness parameter as the uncoated Zr, but lower surface adhesion force that could be translated into improved properties in terms of antimicrobial effects, as confirmed by its inhibition index, which makes it a very promising material for bio-medical applications.

Does fibrinogen serve the host or the microbe in Staphylococcus infection?

PURPOSE OF REVIEW

Fibrin(ogen) is a multifunctional clotting protein that not only has critical roles in hemostasis but is also important in inflammatory processes that control bacterial infection. As a provisional extracellular matrix protein, fibrin(ogen) functions as a physical barrier, a scaffold for immune cell migration, or as a spatially-defined cue to drive inflammatory cell activation. These mechanisms contribute to overall host antimicrobial defense against infection. However, numerous bacterial species have evolved mechanisms to manipulate host fibrin(ogen) to promote microbial virulence and survival. Staphylococcal species, in particular, express numerous virulence factors capable of engaging fibrin(ogen), promoting fibrin formation, and driving the dissolution of fibrin matrices.

RECENT FINDINGS

Recent studies have highlighted both new insights into the molecular mechanisms involved in fibrin(ogen)-mediated host defense and pathogen-driven virulence. Of particular interest is the role of fibrin(ogen) in forming host protective biofilms versus pathogen protective barriers and biofilms as well as the role of fibrin(ogen) in mediating direct host antimicrobial responses.

SUMMARY

Current data suggest that the role of fibrin(ogen) in staphylococcal infection is highly context-dependent and that better defining the precise cellular and molecular pathways activated will provide unique opportunities of therapeutic intervention to better treat Staphylococcal disease.

Chronic Staphylococcus aureus Lung Infection Correlates With Proteogenomic and Metabolic Adaptations Leading to an Increased Intracellular Persistence

BACKGROUND

Chronic lung infection in cystic fibrosis (CF) patients by Staphylococcus aureus is a well-established epidemiological fact. Indeed, S. aureus is the most commonly identified pathogen in the lungs of CF patients. Improving our understanding of the mechanisms associated with the persistence of S. aureus is therefore an important issue.

METHODS

We selected pairs of sequential S. aureus isolates from 3 patients with CF and from 1 patient with non-CF chronic lung disease. We used a combination of genomic, proteomic, and metabolomic approaches with functional assays for in-depth characterization of S. aureus long-term persistence.

RESULTS

In this study, we show that late S. aureus isolates from CF patients have an increased ability for intracellular survival in CF bronchial epithelial-F508del cells compared to ancestral early isolates. Importantly, the increased ability to persist intracellularly was confirmed for S. aureus isolates within the own-patient F508del epithelial cells. An increased ability to form biofilm was also demonstrated. Furthermore, we identified the underlying genetic modifications that induce altered protein expression profiles and notable metabolic changes. These modifications affect several metabolic pathways and virulence regulators that could constitute therapeutic targets.

CONCLUSIONS

Our results strongly suggest that the intracellular environment might constitute an important niche of persistence and relapse necessitating adapted antibiotic treatments.

Adhesin genes and biofilm formation among pediatric Staphylococcus aureus isolates from implant-associated infections

BACKGROUND

Microbial surface component recognizing adhesive matrix molecules (MSCRAMMs) facilitate Staphylococcus aureus adherence to host tissue. We hypothesized that S. aureus isolates from implant-associated infections (IAIs) would differ in MSCRAMM profile and biofilm formation in vitro compared to skin and soft tissue infection (SSTI) isolates.

METHODS

Pediatric patients and their isolates were identified retrospectively. IAI and SSTI isolates were matched (1:4). Pulsed field gel electrophoresis was performed to group isolates as USA300 vs. non-USA300. Whole genome sequencing was performed and raw sequence data were interrogated for presence of MSCRAMMs (clfA, clfB, cna, ebh, efb, fnbpA, fnbpB, isdA, isdB, sdrC, sdrD, sdrE), biofilm-associated (icaA,D,B,C), and Panton-Valentine leukocidin (lukSF-PV) genes, accessory gene regulator group, and multilocus sequence types. In vitro biofilm formation was assessed for 47 IAI and 47 SSTI isolates using a microtiter plate assay. Conditional logistic regression was performed for analysis of matched data (STATA11, College Station, TX).

RESULTS

Forty-seven IAI and 188 SSTI isolates were studied. IAI isolates were more often methicillin susceptible S. aureus and non-USA300 vs. SSTI isolates [34 (72%) vs. 79 (42%), p = 0.001 and 38 (81%) vs. 57 (30%) p <0.001, respectively]. Greater than 98% of isolates carried clfA, clfB, efb, isdA, isdB, and icaA,D,B,C while cna was more frequently found among IAI vs. SSTI isolates (p = 0.003). Most isolates were strong biofilm producers.

CONCLUSIONS

S. aureus IAI isolates were significantly more likely to be MSSA and non-USA300 than SSTI isolates. Carriage of MSCRAMMs and biofilm formation did not differ significantly between isolates. Evaluation of genetic polymorphisms and gene expression profiles are needed to further delineate the role of adhesins in the pathogenesis of IAIs.

Tailoring Nanoparticle-Biofilm Interactions to Increase the Efficacy of Antimicrobial Agents Against Staphylococcus aureus

Background

Considering the timeline required for the development of novel antimicrobial drugs, increased attention should be given to repurposing old drugs and improving antimicrobial efficacy, particularly for chronic infections associated with biofilms. Methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) are common causes of biofilm-associated infections but produce different biofilm matrices. MSSA biofilm cells are typically embedded in an extracellular polysaccharide matrix, whereas MRSA biofilms comprise predominantly of surface proteins and extracellular DNA (eDNA). Nanoparticles (NPs) have the potential to enhance the delivery of antimicrobial agents into biofilms. However, the mechanisms which influence the interactions between NPs and the biofilm matrix are not yet fully understood.

Methods

To investigate the influence of NPs surface chemistry on vancomycin (VAN) encapsulation and NP entrapment in MRSA and MSSA biofilms, mesoporous silica nanoparticles (MSNs) with different surface functionalization (bare-B, amine-D, carboxyl-C, aromatic-A) were synthesised using an adapted Stöber method. The antibacterial efficacy of VAN-loaded MSNs was assessed against MRSA and MSSA biofilms.

Results

The two negatively charged MSNs (MSN-B and MSN-C) showed a higher VAN loading in comparison to the positively charged MSNs (MSN-D and MSN-A). Cellular binding with MSN suspensions (0.25 mg mL⁻¹) correlated with the reduced viability of both MSSA and MRSA biofilm cells. This allowed the administration of low MSNs concentrations while maintaining a high local concentration of the antibiotic surrounding the bacterial cells.

Conclusion

Our data suggest that by tailoring the surface functionalization of MSNs, enhanced bacterial cell targeting can be achieved, leading to a novel treatment strategy for biofilm infections.

A new coumarin compound DCH combats methicillin-resistant Staphylococcus aureus biofilm by targeting arginine repressor

Staphylococcus aureus infection is difficult to eradicate because of biofilm formation and antibiotic resistance. The increasing prevalence of methicillin-resistant Staphylococcus aureus (MRSA) infection necessitates the development of a new agent against bacterial biofilms. We report a new coumarin compound, termed DCH, that effectively combats MRSA in vitro and in vivo and exhibits potent antibiofilm activity without detectable resistance. Cellular proteome analysis suggests that the molecular mechanism of action of DCH involves the arginine catabolic pathway. Using molecular docking and binding affinity assays of DCH, and comparison of the properties of wild-type and ArgR-deficient MRSA strains, we demonstrate that the arginine repressor ArgR, an essential regulator of the arginine catabolic pathway, is the target of DCH. These findings indicate that DCH is a promising lead compound and validate bacterial ArgR as a potential target in the development of new drugs against MRSA biofilms.

Adhesin genes and biofilm formation among pediatric Staphylococcus aureus isolates from implant-associated infections

Background

Microbial surface component recognizing adhesive matrix molecules (MSCRAMMs) facilitate Staphylococcus aureus adherence to host tissue. We hypothesized that S. aureus isolates from implant-associated infections (IAIs) would differ in MSCRAMM profile and biofilm formation in vitro compared to skin and soft tissue infection (SSTI) isolates.

Methods

Pediatric patients and their isolates were identified retrospectively. IAI and SSTI isolates were matched (1:4). Pulsed field gel electrophoresis was performed to group isolates as USA300 vs. non-USA300. Whole genome sequencing was performed and raw sequence data were interrogated for presence of MSCRAMMs (clfA, clfB, cna, ebh, efb, fnbpA, fnbpB, isdA, isdB, sdrC, sdrD, sdrE), biofilm-associated (icaA,D,B,C), and Panton-Valentine leukocidin (lukSF-PV) genes, accessory gene regulator group, and multilocus sequence types. In vitro biofilm formation was assessed for 47 IAI and 47 SSTI isolates using a microtiter plate assay. Conditional logistic regression was performed for analysis of matched data (STATA11, College Station, TX).

Results

Forty-seven IAI and 188 SSTI isolates were studied. IAI isolates were more often methicillin susceptible S. aureus and non-USA300 vs. SSTI isolates [34 (72%) vs. 79 (42%), p = 0.001 and 38 (81%) vs. 57 (30%) p <0.001, respectively]. Greater than 98% of isolates carried clfA, clfB, efb, isdA, isdB, and icaA,D,B,C while cna was more frequently found among IAI vs. SSTI isolates (p = 0.003). Most isolates were strong biofilm producers.

Conclusions

S. aureus IAI isolates were significantly more likely to be MSSA and non-USA300 than SSTI isolates. Carriage of MSCRAMMs and biofilm formation did not differ significantly between isolates. Evaluation of genetic polymorphisms and gene expression profiles are needed to further delineate the role of adhesins in the pathogenesis of IAIs.