An improved medium for growing Staphylococcus aureus biofilm

Surfactants' Interplay with Biofilm Development in Staphylococcus and Candida

The capacity of micro-organisms to form biofilms is a pervasive trait in the microbial realm. For pathogens, biofilm formation serves as a virulence factor facilitating successful host colonization. Simultaneously, infections stemming from biofilm-forming micro-organisms pose significant treatment challenges due to their heightened resistance to antimicrobial agents. Hence, the quest for active compounds capable of impeding microbial biofilm development stands as a pivotal pursuit in biomedical research. This study presents findings concerning the impact of three surfactants, namely, polysorbate 20 (T20), polysorbate 80 (T80), and sodium dodecyl sulfate (SDS), on the initial stage of biofilm development in both Staphylococcus aureus and Candida dubliniensis. In contrast to previous investigations, we conducted a comparative assessment of the biofilm development capacity of these two taxonomically distant groups, predicated on their shared ability to reduce TTC. The common metabolic trait shared by S. aureus and C. dubliniensis in reducing TTC to formazan facilitated a simultaneous evaluation of biofilm development under the influence of surfactants across both groups. Our results revealed that surfactants could impede the development of biofilms in both species by disrupting the initial cell attachment step. The observed effect was contingent upon the concentration and type of compound, with a higher inhibition observed in culture media supplemented with SDS. At maximum concentrations (5%), T20 and T80 significantly curtailed the formation and viability of S. aureus and C. dubliniensis biofilms. Specifically, T20 inhibited biofilm development by 75.36% in S. aureus and 71.18% in C. dubliniensis, while T80 exhibited a slightly lower inhibitory effect, with values ranging between 66.68% (C. dubliniensis) and 65.54% (S. aureus) compared to the controls. Incorporating these two non-toxic surfactants into pharmaceutical formulations could potentially enhance the inhibitory efficacy of selected antimicrobial agents, particularly in external topical applications.

Biosynthesis of Ag2Se nanoparticles as a broad-spectrum antimicrobial agent with excellent biocompatibility

Silver (Ag)-containing nanomaterials have emerged as promising alternatives or adjuvants to antibiotics. Ongoing research is dedicated to enhance their antimicrobial efficacy, stability, biocompatibility, and environmental sustainability. Microorganism-synthesized Ag-containing nanomaterials offer distinct advantages, especially for various surface modification, which potentially fulfill these objectives. In this study, we present the synthesis of silver-selenium (Bio-Ag2Se) nanoparticles using a yeast strain, Rhodotorula mucilaginosa PA-1. These Bio-Ag2Se nanoparticles have small size with a narrow size distribution (12.3 ± 2.9 nm) and long-term stability. They demonstrate a broad antimicrobial spectrum and high antimicrobial efficacy at very low concentrations, effectively targeting microorganisms including Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, Staphylococcus aureus, as well as pathogenic fungus Candida albicans. Furthermore, Bio-Ag2Se nanoparticles exhibit excellent efficacy to inhibit and eliminate biofilms formed by notorious pathogen S. aureus. In contrast, Bio-Ag2Se nanoparticles at effective antibacterial concentrations demonstrate favorable biocompatibility and do not show obvious cytotoxic effects on human and plant cells. To elucidate the antibacterial mechanisms of Bio-Ag2Se nanoparticles against S. aureus and E. coli, transcriptomic analysis and phenotypic examination were employed. The results reveal significant and broad up-regulation in carbon metabolism pathways in both S. aureus and E. coli, suggesting it as one of the major antibacterial mechanisms of Bio-Ag2Se. This study presents a green synthesis strategy for Ag-containing nanoparticles with promising applications.

Biofilm antimicrobial susceptibility testing: where are we and where could we be going?

Our knowledge about the fundamental aspects of biofilm biology, including the mechanisms behind the reduced antimicrobial susceptibility of biofilms, has increased drastically over the last decades. However, this knowledge has so far not been translated into major changes in clinical practice. While the biofilm concept is increasingly on the radar of clinical microbiologists, physicians, and healthcare professionals in general, the standardized tools to study biofilms in the clinical microbiology laboratory are still lacking; one area in which this is particularly obvious is that of antimicrobial susceptibility testing (AST). It is generally accepted that the biofilm lifestyle has a tremendous impact on antibiotic susceptibility, yet AST is typically still carried out with planktonic cells. On top of that, the microenvironment at the site of infection is an important driver for microbial physiology and hence susceptibility; but this is poorly reflected in current AST methods. The goal of this review is to provide an overview of the state of the art concerning biofilm AST and highlight the knowledge gaps in this area. Subsequently, potential ways to improve biofilm-based AST will be discussed. Finally, bottlenecks currently preventing the use of biofilm AST in clinical practice, as well as the steps needed to get past these bottlenecks, will be discussed.

Gene expression and cell culture assays reveal cheese isolate Lactococcus lactis MC5 may influence the virulence of Staphylococcus aureus

Staphylococcus aureus (SA) can thrive in a wide variety of hosts and environments, causing clinical infections and foodborne intoxications. In Brazil, SA is commonly isolated from traditional soft cheeses, especially those prepared from unpasteurized milk. In this research, the isolate S. aureus SABRC1 was evaluated for virulence traits under different conditions, including co-inoculation with Lactococcus lactis MC5 (isolated from "Fresh Minas Cheese"), which produces antibacterial peptides. Results from experiments with Caco-2 culture indicated S. aureus SABRC1 was able to adhere (42.83 ± 1.79%) and to invade (48.57 ± 0.41%) the intestinal cells. On the other hand, L. lactis MC5 presented anti-staphylococcal activity as indicated by agar assays, and it was also able to antagonize intestinal cell invasion by S. aureus. Moreover, Reverse Transcriptase-PCR experiments showed virulence genes of S. aureus SABRC1 (hla, icaA and sea) were differentially expressed under diverse culture conditions, which included Brain Heart Infusion modified or not by the addition of glucose, sodium chloride, milk or cheese. This suggests the virulence of S. aureus SABRC1 is influenced by compounds commonly found in daily diets, and not only by its genetic repertoire, adding a novel level of complexity for controlling infection by this pathogen.

Inhibition of Acinetobacter baumannii Biofilm Formation Using Different Treatments of Silica Nanoparticles

There exists a multitude of pathogens that pose a threat to human and public healthcare, collectively referred to as ESKAPE pathogens. These pathogens are capable of producing biofilm, which proves to be quite resistant to elimination. Strains of A. baumannii, identified by the "A" in the acronym ESKAPE, exhibit significant resistance to amoxicillin in vivo due to their ability to form biofilm. This study aims to inhibit bacterial biofilm formation, evaluate novel silica nanoparticles' effectiveness in inhibiting biofilm, and compare their effectiveness. Amoxicillin was utilized as a positive control, with a concentration exceeding twice that when combined with silica NPs. Treatments included pure silica NPs, silica NPs modified with copper oxide (CuO.SiO2), sodium hydroxide (NaOH.SiO2), and phosphoric acid (H3PO4.SiO2). The characterization of NPs was conducted using scanning electron microscopy (SEM), while safety testing against normal fibroblast cells was employed by MTT assay. The microtiter plate biofilm formation assay was utilized to construct biofilm, with evaluations conducted using three broth media types: brain heart infusion (BHI) with 2% glucose and 2% sucrose, Loria broth (LB) with and without glucose and sucrose, and Dulbecco's modified eagle medium/nutrient (DMEN/M). Concentrations ranging from 1.0 mg/mL to 0.06 µg/mL were tested using a microdilution assay. Results from SEM showed that pure silica NPs were mesoporous, but in the amorphous shape of the CuO and NaOH treatments, these pores were disrupted, while H3PO4 was composed of sheets. Silica NPs were able to target Acinetobacter biofilms without harming normal cells, with viability rates ranging from 61-73%. The best biofilm formation was achieved using a BHI medium with sugar supplementation, with an absorbance value of 0.35. Biofilms treated with 5.0 mg/mL of amoxicillin as a positive control alongside 1.0 mg/mL of each of the four silica treatments in isolation, resulting in the inhibition of absorbance values of 0.04, 0.13, 0.07, 0.09, and 0.08, for SiO2, CuO.SiO2, NaOH.SiO2 and H3PO4.SiO2, respectively. When amoxicillin was combined, inhibition increased from 0.3 to 0.04; NaOH with amoxicillin resulted in the lowest minimum biofilm inhibitory concentration (MBIC), 0.25 µg/mL, compared to all treatments and amoxicillin, whereas pure silica and composite had the highest MBIC, even when combined with amoxicillin, compared to all treatments, but performed better than that of the amoxicillin alone which gave the MBIC at 625 µg/mL. The absorbance values of MBIC of each treatment showed no significant differences in relation to amoxicillin absorbance value and relation to each other. Our study showed that smaller amoxicillin doses combined with the novel silica nanoparticles may reduce toxic side effects and inhibit biofilm formation, making them viable alternatives to high-concentration dosages. Further investigation is needed to evaluate in vivo activity.

Staphylococcus epidermidis Pathogenesis: Interplay of icaADBC Operon and MSCRAMMs in Biofilm Formation of Isolates from Pediatric Bacteremia in Peshawar, Pakistan

Background and Objective: Staphylococcus epidermidis is an opportunistic pathogen from pediatric bacteremia that is commonly isolated. Biofilm is the major virulence factor of S. epidermidis; however, the role of biofilm determinants in biofilm formation is highly contradictory and diverse. The current study aimed to investigate the role of polysaccharide-dependent and polysaccharide-independent pathogenic determinants in biofilm formation under physiological stress conditions. Materials and Methods: The isolates (n = 75) were identified and screened for the icaADBC operon, IS256, and an array of MSCRAMMs (Microbial Surface Component Recognizing Adhesive Matrix Molecules) through PCR analysis. The activity of the icaADBC operon was detected by Congo red assay, and the biofilm formation was analyzed through microtiter plate assay. Results: S. epidermidis isolates produced biofilm (n = 65; 86.6%) frequently. The icaA was the major representative module of the actively expressing icaADBC operon (n = 21; 80.7% sensitivity). The MSCRAMMs, including fbe (n = 59; 90.7%; p = 0.007), and embp (n = 57; 87.6%; p = 0.026), were highly prevalent and associated with biofilm positive S. epidermidis. The prevalence of icaADBC operon in biofilm positive and negative S. epidermidis was not significant (n = 41; 63%; p = 0.429). No significant association was found between IS256 and actively complete icaADBC operon (n = 10; 47.6%; p = 0.294). In the presence of 5% human plasma and glucose stress, S. epidermidis produced a strong biofilm (n = 55; 84.6%). Conclusion: The polysaccharide-dependent biofilm formation is significantly replaced (n = 21; 28%; p = 0.149) by a polysaccharide-independent mechanism (n = 59; 90.7%; p = 0.007), in which the MSCRAMMs might actively play their role. The fibrinogen-binding protein and extracellular matrix-binding protein might be potential anti-biofilm drug targets, markers of rapid diagnosis, and potential vaccine candidates of S. epidermidis involved in pediatric bacteremia.

The Innate Immune Protein Calprotectin Interacts With and Encases Biofilm Communities of Pseudomonas aeruginosa and Staphylococcus aureus

Calprotectin is a transition metal chelating protein of the innate immune response known to exert nutritional immunity upon microbial infection. It is abundantly released during inflammation and is therefore found at sites occupied by pathogens such as Pseudomonas aeruginosa and Staphylococcus aureus. The metal limitation induced by this protein has previously been shown to mediate P. aeruginosa and S. aureus co-culture. In addition to the transition metal sequestration role of calprotectin, it has also been shown to have metal-independent antimicrobial activity via direct cell contact. Therefore, we sought to assess the impact of this protein on the biofilm architecture of P. aeruginosa and S. aureus in monomicrobial and polymicrobial culture. The experiments described in this report reveal novel aspects of calprotectin's interaction with biofilm communities of P. aeruginosa and S. aureus discovered using scanning electron microscopy and confocal laser scanning microscopy. Our results indicate that calprotectin can interact with microbial cells by stimulating encapsulation in mesh-like structures. This physical interaction leads to compositional changes in the biofilm extracellular polymeric substance (EPS) in both P. aeruginosa and S. aureus.

Hijacking host components for bacterial biofilm formation: An advanced mechanism

Biofilm is a community of bacteria embedded in the extracellular matrix that accounts for 80% of bacterial infections. Biofilm enables bacterial cells to provide particular conditions and produce virulence determinants in response to the unavailability of micronutrients and local oxygen, resulting in their resistance to various antibacterial agents. Besides, the human immune reactions are not completely competent in the elimination of biofilm. Most importantly, the growing body of evidence shows that some bacterial spp. use a variety of mechanisms by which hijack the host components to form biofilm. In this regard, host components, such as DNA, hyaluronan, collagen, fibronectin, mucin, oligosaccharide moieties, filamentous polymers (F-actin), plasma, platelets, keratin, sialic acid, laminin, vitronectin, C3- and C4- binding proteins, antibody, proteases, factor I, factor H, and acidic proline-rich proteins have been reviewed. Hence, the characterization of interactions between bacterial biofilm and the host would be critical to effectively address biofilm-associated infections. In this paper, we review the latest information on the hijacking of host factors by bacteria to form biofilm.

Quantitative flow chamber system for evaluating in vitro biofilms and the kinetics of S. aureus biofilm formation in human plasma media

Background

It has been well established that biofilm formation on orthopaedic implants is a critical event in the pathogenesis of orthopaedic infections, yet the natural history of this process with respect to bacterial adhesion, proliferation, and glycocalyx matrix production remains poorly understood. Moreover, there are no quantitative methods yet available to assess the differences in biofilm formation between different bacterial strains or implant materials. Consequently, this study aimed to investigate the natural history of S. aureus in in vitro biofilm formation in human plasma media using a flow chamber system. Bioluminescent S. aureus strains were used to better understand the bacterial growth and biofilm formation on orthopaedic materials. Also, the effects of human plasma media were assessed by loading the chamber with Tryptic Soy Broth with 10% human plasma (TSB + HP).

Results

Scanning electron microscopy (SEM) was utilized to assess the morphological appearance of the biofilms, revealing that S. aureus inoculation was required for biofilm formation, and that the phenotypes of biofilm production after 24 h inoculation with three tested strains (SH1000, UAMS-1, and USA300) were markedly different depending on the culture medium. Time course study of the bioluminescence intensity (BLI) and biofilm production on the implants due to the UAMS-1 and USA300 strains revealed different characteristics, whereby UAMS-1 showed increasing BLI and biofilm growth until peaking at 9 h, while USA300 showed a rapid increase in BLI and biofilm formation at 6 h. The kinetics of biofilm formation for both UAMS-1 and USA300 were also supported and confirmed by qRT-PCR analysis of the 16S rRNA gene. Biofilms grown in our flow chamber in the plasma media were also demonstrated to involve an upregulation of the biofilm-forming-related genes icaA, fnbA, and alt. The BLI and SEM results from K-wire experiments revealed that the in vitro growth and biofilm formation by UAMS-1 and USA300 on stainless-steel and titanium surfaces were virtually identical.

Conclusion

We demonstrated a novel in vitro model for S. aureus biofilm formation with quantitative BLI and SEM outcome measures, and then used this model to demonstrate the presence of strain-specific phenotypes and its potential use to evaluate anti-microbial surfaces.

Searching for the Secret of Stickiness: How Biofilms Adhere to Surfaces

Bacterial biofilms are communities of cells enclosed in an extracellular polymeric matrix in which cells adhere to each other and to foreign surfaces. The development of a biofilm is a dynamic process that involves multiple steps, including cell-surface attachment, matrix production, and population expansion. Increasing evidence indicates that biofilm adhesion is one of the main factors contributing to biofilm-associated infections in clinics and biofouling in industrial settings. This review focuses on describing biofilm adhesion strategies among different bacteria, including Vibrio cholerae, Pseudomonas aeruginosa, and Staphylococcus aureus. Techniques used to characterize biofilm adhesion are also reviewed. An understanding of biofilm adhesion strategies can guide the development of novel approaches to inhibit or manipulate biofilm adhesion and growth.

Study of the impact of cultivation conditions and peg surface modification on the in vitro biofilm formation of Staphylococcus aureus and Staphylococcus epidermidis in a system analogous to the Calgary biofilm device

Introduction. Staphylococcus aureus (SA) and Staphylococcus epidermidis (SE) are the most common pathogens from the genus Staphylococcus causing biofilm-associated infections. Generally, biofilm-associated infections represent a clinical challenge. Bacteria in biofilms are difficult to eradicate due to their resistance and serve as a reservoir for recurring persistent infections.Gap Statement. A variety of protocols for in vitro drug activity testing against staphylococcal biofilms have been introduced. However, there are often fundamental differences. All these differences in methodical approaches can then be reflected in the form of discrepancies between results.Aim. In this study, we aimed to develop optimal conditions for staphylococcal biofilm formation on pegs. The impact of peg surface modification was also studied.Methodology. The impact of tryptic soy broth alone or supplemented with foetal bovine serum (FBS) or human plasma (HP), together with the impact of the inoculum density of bacterial suspensions and the shaking versus the static mode of cultivation, on total biofilm biomass production in SA and SE reference strains was studied. The surface of pegs was modified with FBS, HP, or poly-l-lysine (PLL). The impact on total biofilm biomass was evaluated using the crystal violet staining method and statistical data analysis.Results. Tryptic soy broth supplemented with HP together with the shaking mode led to crucial potentiation of biofilm formation on pegs in SA strains. The SE strain did not produce biofilm biomass under the same conditions on pegs. Preconditioning of peg surfaces with FBS and HP led to a statistically significant increase in biofilm biomass formation in the SE strain.Conclusion. Optimal cultivation conditions for robust staphylococcal biofilm formation in vitro might differ among different bacterial strains and methodical approaches. The shaking mode and supplementation of cultivation medium with HP was beneficial for biofilm formation on pegs for SA (ATCC 29213) and methicillin-resistant SA (ATCC 43300). Peg conditioning with HP and PLL had no impact on biofilm formation in either of these strains. Peg coating with FBS showed an adverse effect on the biofilm formation of these strains. By contrast, there was a statistically significant increase in biofilm biomass production on pegs coated with FBS and HP for SE (ATCC 35983).

Assessing biofilm inhibition and immunomodulatory activity of small amounts of synthetic host defense peptides synthesized using SPOT-array technology

Peptides are promising drug candidates because of their diversity, biocompatibility and spectrum of activities. Here, we describe a protocol for high-throughput screening of SPOT-peptide arrays to assess the antibiofilm, antimicrobial and immunomodulatory activities of synthetic peptides. It is a Protocol Extension of our previous Nature Protocols article, which describes the synthesis of SPOT-peptide arrays and assays for screening antimicrobial activity. This latest protocol allows the simultaneous assessment of hundreds of synthetic host defense peptides to define their overall activity profiles and identify candidate sequences that are suitable for further characterization and development as anti-infectives. When coupled with the SPOT-array technology for peptide synthesis, the described procedures are rapid, inexpensive and straightforward for peptide library screening. The protocols can be implemented in most microbiology or immunology research laboratories without the need for specialists. The time to complete each step ranges between 1 and 4 h with overnight pauses, and datasets related to the antibiofilm and immunomodulatory activities of a large set of peptide sequences can be generated in a few days.

Paracetamol modulates biofilm formation in Staphylococcus aureus clonal complex 8 strains

Staphylococcus aureus biofilms are a major problem in modern healthcare due to their resistance to immune system defenses and antibiotic treatments. Certain analgesic agents are able to modulate S. aureus biofilm formation, but currently no evidence exists if paracetamol, often combined with antibiotic treatment, also has this effect. Therefore, we aimed to investigate if paracetamol can modulate S. aureus biofilm formation. Considering that certain regulatory pathways for biofilm formation and virulence factor production by S. aureus are linked, we further investigated the effect of paracetamol on immune modulator production. The in vitro biofilm mass of 21 S. aureus strains from 9 genetic backgrounds was measured in the presence of paracetamol. Based on biofilm mass quantity, we further investigated paracetamol-induced biofilm alterations using a bacterial viability assay combined with N-Acetylglucosamine staining. Isothermal microcalorimetry was used to monitor the effect of paracetamol on bacterial metabolism within biofilms and green fluorescent protein (GFP) promoter fusion technology for transcription of staphylococcal complement inhibitor (SCIN). Clinically relevant concentrations of paracetamol enhanced biofilm formation particularly among strains belonging to clonal complex 8 (CC8), but had minimal effect on S. aureus planktonic growth. The increase of biofilm mass can be attributed to the marked increase of N-Acetylglucosamine containing components of the extracellular matrix, presumably polysaccharide intercellular adhesion. Biofilms of RN6390A (CC8) showed a significant increase in the immune modulator SCIN transcription during co-incubation with low concentrations of paracetamol. Our data indicate that paracetamol can enhance biofilm formation. The clinical relevance needs to be further investigated.

Staphylococcus aureus impairs cutaneous wound healing by activating the expression of a gap junction protein, connexin-43 in keratinocytes

Chronic wounds have been considered as major medical problems that may result in expensive healthcare. One of the common causes of chronic wounds is bacterial contamination that leads to persistent inflammation and unbalanced host cell immune responses. Among the bacterial strains that have been identified from chronic wounds, Staphylococcus aureus is the most common strain. We previously observed that S. aureus impaired mouse cutaneous wound healing by delaying re-epithelialization. Here, we investigated the mechanism of delayed re-epithelialization caused by S. aureus infection. With the presence of S. aureus exudate, the migration of in vitro cultured human keratinocytes was significantly inhibited and connexin-43 (Cx43) was upregulated. Inhibition of keratinocyte migration by S. aureus exudate disappeared in keratinocytes where the expression of Cx43 knocked down. Protein kinase phosphorylation array showed that phosphorylation of Akt-S473 was upregulated by S. aureus exudate. In vivo study of Cx43 in S. aureus-infected murine splinted cutaneous wound model showed upregulation of Cx43 in the migrating epithelial edge by S. aureus infection. Treatment with a PI3K/Akt inhibitor reduced Cx43 expression and overcame the wound closure impairment by S. aureus infection in the mouse model. This may contribute to the development of treatment to bacterium-infected wounds.

Concerted dispersion of Staphylococcus aureus biofilm by bacteriophage and 'green synthesized' silver nanoparticles

Staphylococcal biofilms predominantly cause persistent nosocomial infections. The widespread antibiotic resistance followed by its ability to form biofilm in biological and inert surfaces often contributes to major complications in patients and veterinary animals. Strategic importance of bacteriophage therapy against critical staphylococcal infections had been predicted ever since the advent of antibiotic resistant staphylococcal strains. The significance of metal nanoparticles in quenching biofilm associated bacteria was previously reported. In this study, we demonstrate a concerted action of ‘green synthesized’ silver nanoparticles and bacteriophages in removing pre-formed Staphylococcus aureus biofilms from an inert glass surface in a time dependent manner. Our results demonstrate, for the first time, the rapid co-operative dispersion of the bacterial biofilm. In addition, the synergistic activity of the nanoparticles and bacteriophages causes the loss of viability of the biofilm entrapped bacterial cells thus preventing establishment of a new infection and subsequent colonization. This work further opens up a platform for the combinational therapeutic approach with a variety of nanoparticles and bacteriophages against mono or poly bacterial biofilm in environmental, industrial or clinical settings.

Formation of biofilm by Staphylococcus aureus ‘Rumba’ on untreated glass surface and a concerted disruption of the biofilm by silver nanoparticle and phage ϕ44AHJD.

Environmental factors modulate biofilm formation by Staphylococcus aureus

Biofilm formation on indwelling medical devices represents an exclusive evasion mechanism for many pathogenic bacteria to establish chronic infections. Staphylococcus aureus is one of the major bacterial pathogens that are able to induce both animal and human infections. The continued emergence of multiple drug-resistant S. aureus, especially methicillin-resistant S. aureus, is problematic due to limited treatment options. Biofilm formation by S. aureus complicates the treatment of methicillin-resistant S. aureus infections. Therefore, elucidating the mechanisms of biofilm formation in this pathogen is important for the development of alternative therapeutic strategies. Various environmental and genetic factors contribute to biofilm formation. In this review, we address the environmental factors and discuss how they affect biofilm formation by S. aureus.

Influence of Laboratory Culture Media on in vitro Growth, Adhesion, and Biofilm Formation of Pseudomonas aeruginosa and Staphylococcus aureus

OBJECTIVE

Pseudomonas aeruginosa and Staphylococcus aureus dual-species biofilm infections are notoriously difficult to manage. This study aimed at investigating the influence of four different culture media on the planktonic growth, adhesion, and biofilm formation of P. aeruginosa and S. aureus.

MATERIALS AND METHODS

We monitored four different culture media including Nutrient Broth, Brain Heart Infusion (BHI) broth, Luria-Bertani broth, and RPMI 1640 medium on the planktonic growth, adhesion, and biofilm formation of P. aeruginosa (ATCC 27853) and S. aureus (ATCC 25923) using MTT assay and scanning electron microscopy (SEM).

RESULTS

The most robust growth of the mono- and dual-species cultures was noted in BHI broth. On the contrary, RPMI 1640 medium promoted maximal initial adhesion of both the mono- and dual-species, but BHI broth fostered the maximal biofilm growth. SEM images showed profuse extracellular polysaccharide production in biofilms, particularly in coculture, in BHI medium.

CONCLUSION

Our data demonstrate that BHI broth, relative to the other tested media, is the most conducive for in vitro evaluation of biofilm and planktonic growth kinetics of these two pathogens, both in mono- and coculture.

Characterization of Biofilms Formed by Foodborne Methicillin-Resistant Staphylococcus aureus

The objective of this study was to evaluate the capacity of 49 methicillin resistant Staphylococcus aureus (MRSA) from foods of animal origin (42 from dairy products and 7 from meat and meat products) to form biofilms. Overall, a higher biofilm biomass was observed for those MRSA strains harboring SCCmec type IV, while 8 MRSA strains (5 from dairy products and 3 from meat and meat products) were classified as strong biofilm formers in standard Tryptic Soy Broth medium. When a prolonged incubation period (48 h) was applied for those 8 MRSA strains, an increased biofilm biomass accumulation was observed during the time course, whereas the number of viable cells within the biofilms decreased as the biomass increased. The capacity of biofilm production correlated pretty well between the experiments using polystyrene microtiter plates and stainless steel micro-well plates, and significant higher values were observed in stainless steel when glucose was added to TSB during the enrichment. Biofilms were further characterized by confocal laser scanning microscope (CLSM), confirming that proteins and α-polysaccharides were the predominant components inside the extracellular polymeric matrix of biofilms formed by MRSA strains. In conclusion, our results confirm that MRSA isolates from foods of animal origin have significant capacity for forming biofilms with a high protein content, which can play a key role for the successful dissemination of MRSA lineages via food. Knowledge of the capacity of MRSA strains to produce biofilms, as well as characterization of the main MRSA biofilms matrix components, can help both to counteract the mechanisms involved in biofilm formation and resistance and to define more rational control strategies by using tailor-made cleaning agents.

Antimicrobial ceragenins inhibit biofilms and affect mammalian cell viability and migration in vitro

The healing of burn wounds is often hampered by bacterial infection and the formation of biofilms. Antimicrobial peptides (AMPs) are effective in promoting wound healing, but are susceptible to degradation. We have tested the ability of ceragenins (CSAs), mimics of antimicrobial peptides, to mitigate preformed biofilms and stimulate wound healing in vitro. Potent CSAs (MICs < 10 μg·mL⁻¹) were tested against biofilms formed from a mixture of Pseudomonas aeruginosa and Staphylococcus aureus grown for 22 h and subjected to 20 h treatment. Many CSAs showed more potent anti‐biofilm activity than the endogenous AMP LL‐37, and CSA‐13 and CSA‐90 decreased the amount of biofilm matrix substances detected by SYPRO Ruby stain. Effects on mammalian cells were measured by viability, migration, and tube formation assays in vitro. Although CSAs were toxic to immortalized human keratinocytes (HaCaTs) at higher concentrations (>10 μg·mL⁻¹), lower concentrations of CSA‐13 and CSA‐192 stimulated cell migration. CSA‐13, CSA‐90, and CSA‐142 also stimulated tube formation in an in vitro angiogenesis model. An inhibitor of vascular endothelial growth factor receptor 2 (VEGFR2) blocked tube formation stimulated by CSA‐13, suggesting that CSA‐13 signals through this receptor. Ceragenins display anti‐biofilm activity and stimulate migration and tube formation in vitro. This work suggests that ceragenins have the potential to be both topical antimicrobials and wound‐healing adjunct therapeutics.

Detection of Biofilms in Biopsies from Chronic Rhinosinusitis Patients: In Vitro Biofilm Forming Ability and Antimicrobial Susceptibility Testing in Biofilm Mode of Growth of Isolated Bacteria

Chronic rhinosinusitis (CRS) is the most common illness among chronic disorders that remains poorly understood from a pathogenic standpoint and has a significant impact on patient quality of life, as well as healthcare costs. Despite being widespread, little is known about the etiology of the CRS. Recent evidence, showing the presence of biofilms within the paranasal sinuses, suggests a role for biofilm in the pathogenesis. To elucidate the role of biofilm in the pathogenesis of CRS, we assessed the presence of biofilm at the infection site and the ability of the aerobic flora isolated from CRS patients to form biofilm in vitro. For selected bacterial strains the susceptibility profiles to antibiotics in biofilm condition was also evaluated.Staphylococci represented the majority of the isolates obtained from the infection site, with S. epidermidis being the most frequently isolated species. Other isolates were represented by Enterobacteriaceae or by species present in the oral flora. Confocal laser scanning microscopy (CLSM) of the mucosal biopsies taken from patients with CRS revealed the presence of biofilm in the majority of the samples. Strains isolated from the specific infection site of the CRS patients were able to form biofilm in vitro at moderate or high levels, when tested in optimized conditions. No biofilm was observed by CLSM in the biopsies from control patients, although the same biopsies were positive for staphylococci in microbiological culture analysis. Drug-susceptibility tests demonstrated that the susceptibility profile of planktonic bacteria differs from that of sessile bacteria in biofilms.

Screening a Commercial Library of Pharmacologically Active Small Molecules against Staphylococcus aureus Biofilms

It is now well established that bacterial infections are often associated with biofilm phenotypes that demonstrate increased resistance to common antimicrobials. Further, due to the collective attrition of new antibiotic development programs by the pharmaceutical industries, drug repurposing is an attractive alternative. In this work, we screened 1,280 existing commercially available drugs in the Prestwick Chemical Library, some with previously unknown antimicrobial activity, against Staphylococcus aureus, one of the commonly encountered causative pathogens of burn and wound infections. From the primary screen of the entire Prestwick Chemical Library at a fixed concentration of 10 μM, 104 drugs were found to be effective against planktonic S. aureus strains, and not surprisingly, these were mostly antimicrobials and antiseptics. The activity of 18 selected repurposing candidates, that is, drugs that show antimicrobial activity that are not already considered antimicrobials, observed in the primary screen was confirmed in dose-response experiments. Finally, a subset of nine of these drug candidates was tested against preformed biofilms of S. aureus We found that three of these drugs, niclosamide, carmofur, and auranofin, possessed antimicrobial activity against preformed biofilms, making them attractive candidates for repurposing as novel antibiofilm therapies.

Enzymatic degradation of in vitro Staphylococcus aureus biofilms supplemented with human plasma

Enzymatic debridement is a therapeutic strategy used clinically to remove necrotic tissue from wounds. Some of the enzymes utilized for debridement have been tested against bacterial pathogens, but the effectiveness of these agents in dispersing clinically relevant biofilms has not been fully characterized. Here, we developed an in vitro Staphylococcus aureus biofilm model that mimics wound-like conditions and employed this model to investigate the antibiofilm activity of four enzymatic compounds. Human plasma at concentrations of 0%–50% was supplemented into growth media and used to evaluate biofilm biomass accumulation over 24 hours and 48 hours in one methicillin-sensitive and five methicillin-resistant strains of S. aureus. Supplementation of media with 10% human plasma resulted in the most robust biofilms in all six strains. The enzymes α-amylase, bromelain, lysostaphin, and papain were then tested against S. aureus biofilms cultured in 10% human plasma. Quantification of biofilms after 2 hours and 24 hours of treatment using the crystal violet assay revealed that lysostaphin decreased biomass by up to 76%, whereas α-amylase, bromelain, and papain reduced biomass by up to 97%, 98%, and 98%, respectively. Scanning electron microscopy confirmed that the dispersal agents detached the biofilm exopolysaccharide matrix and bacteria from the growth surface. Lysostaphin caused less visible dispersal of the biofilms, but unlike the other enzymes, induced morphological changes indicative of bacterial cell damage. Overall, our results indicate that use of enzymes may be an effective means of eradicating biofilms and a promising strategy to improve treatment of multidrug-resistant bacterial infections.

Rifampicin-containing combinations are superior to combinations of vancomycin, linezolid and daptomycin against Staphylococcus aureus biofilm infection in vivo and in vitro

Susceptibility to antibiotics is dramatically reduced when bacteria form biofilms. In clinical settings this has a profound impact on treatment of implant-associated infections, as these are characterized by biofilm formation. Current routine susceptibility testing of microorganisms from infected implants does not reflect the actual susceptibility, and the optimal antibiotic strategy for treating implant-associated infections is not established. In this study of biofilm formation in implant-associated osteomyelitis, we compared thein vitroandin vivoefficacy of selected antibiotics alone and in combination againstStaphylococcus aureus.We tested vancomycin, linezolid, daptomycin and tigecycline alone and in combination with rifampicin, vancomycin, linezolid and daptomycin againstS. aureusIn vitro, biofilm formation dramatically reduced susceptibility by a factor of 500-2000.In vivo, antibiotic combinations were tested in a murine model of implant-associated osteomyelitis. Mice were infected by inserting implants colonized withS. aureustrough their tibia. After 11 days, the animals were divided into different groups (five animals/group) and given 14 days of antibiotic therapy. All antibiotics resulted in a reduced bacterial load in the infected bone surrounding the implant. Overall, the most effective antibiotic combinations contained rifampicin. Combinations containing two non-rifampicin antibiotics were not more active than single drugs.

Development of a hematogenous implant-related infection in a rat model

Background

Implant-related osteomyelitis is a major complication that requires immediate treatment, often involving removal of the implant, prolonging patient recovery and inflating expenses. Current research involving interventions to diminish the prevalence of such measures include investigating prophylactic and therapeutic remedies. A proper and accurate animal model is needed to thoroughly investigate such treatments. The scope of this project was to develop an animal model in which a consistent and measurable infection can be formed on an orthopedic implant when bacteria is introduced via a hematogenous source.

Methods

Titanium Kirschner-wires were implanted into the intramedullary canals of both femurs. Staphylococcus aureus, ranging from10⁴ to 10⁹ colony forming units, was injected into a tail vessel. After a designated time (3, 7, 14, or 42 days) the femurs were harvested and bacterial numbers determined for both the femur and the implanted K-wire. In addition, histology and micro-computed tomography were used as subjective tools to further characterize the infection.

Results

Consistent infection, that is infection of ≥75 % of the femurs, wasn’t achieved until 10⁷ CFU S. aureus was injected. At 10⁷ CFU, the femurs contained 4.6x10⁶ CFU/g bone tissue at day 3 and 4.8×10⁸ CFU/g bone tissue by day 14. The wire showed comparable contamination with 4.8×10⁴ CFU/mm² at day 3 and 3.7×10⁵/mm² by day 14. After 42 days, the bacteria number decreased but was still occupying at 1.9×10⁵ CFU/g bone tissue. There were morphological changes to the bone as well. At day 42, there were signs of osteonecrosis and active bone formation when compared to control animals that received a K-wire but were inoculated with saline.

Conclusions

A model for hematogenous osteomyelitis, a common complication associated with implants, has been introduced. A reproducible, preclinical model is essential to evaluate future methods used to mitigate blood-borne bacteria hardware and bone infections.

A novel bacteriophage cocktail reduces and disperses Pseudomonas aeruginosa biofilms under static and flow conditions

Pseudomonas aeruginosa is an opportunistic human pathogen that forms highly stable communities - biofilms, which contribute to the establishment and maintenance of infections. The biofilm state and intrinsic/acquired bacterial resistance mechanisms contribute to resistance/tolerance to antibiotics that is frequently observed in P. aeruginosa isolates. Here we describe the isolation and characterization of six novel lytic bacteriophages: viruses that infect bacteria, which together efficiently infect and kill a wide range of P. aeruginosa clinical isolates. The phages were used to formulate a cocktail with the potential to eliminate P. aeruginosa PAO1 planktonic cultures. Two biofilm models were studied, one static and one dynamic, and the phage cocktail was assessed for its ability to reduce and disperse the biofilm biomass. For the static model, after 4 h of contact with the phage suspension (MOI 10) more than 95% of biofilm biomass was eliminated. In the flow biofilm model, a slower rate of activity by the phage was observed, but 48 h after addition of the phage cocktail the biofilm was dispersed, with most cells eliminated (> 4 logs) comparing with the control. This cocktail has the potential for development as a therapeutic to control P. aeruginosa infections, which are predominantly biofilm centred.

Quantifying the natural history of biofilm formation in vivo during the establishment of chronic implant-associated Staphylococcus aureus osteomyelitis in mice to identify critical pathogen and host factors

While it is well known that Staphylococcus aureus establishes chronic implant-associated osteomyelitis by generating and persisting in biofilm, research to elucidate pathogen, and host specific factors controlling this process has been limited due to the absence of a quantitative in vivo model. To address this, we developed a murine tibia implant model with ex vivo region of interest (ROI) imaging analysis by scanning electron microscopy (SEM). Implants were coated with Staphylococcus aureus strains (SH1000, UAMS-1, USA300LAC) with distinct in vitro biofilm phenotypes, were used to infect C57BL/6 or Balb/c mice. In contrast to their in vitro biofilm phenotype, results from all bacteria strains in vivo were similar, and demonstrated that biofilm on the implant is established within the first day, followed by a robust proliferation phase peaking on Day 3 in Balb/c mice, and persisting until Day 7 in C57BL/6 mice, as detected by SEM and bioluminescent imaging. Biofilm formation peaked at Day 14, covering ∼40% of the ROI coincident with massive agr-dependent bacterial emigration, as evidenced by large numbers of empty lacunae with few residual bacteria, which were largely culture negative (80%) and PCR positive (87.5%), supporting the clinical relevance of this implant model.

Prostaglandin E2 from Candida albicans Stimulates the Growth of Staphylococcus aureus in Mixed Biofilms

BACKGROUND

Previous studies showed that Staphylococcus aureus and Candida albicans interact synergistically in dual species biofilms resulting in enhanced mortality in animal models.

METHODOLOGY/PRINCIPAL FINDINGS

The aim of the current study was to test possible candidate molecules which might mediate this synergistic interaction in an in vitro model of mixed biofilms, such as farnesol, tyrosol and prostaglandin (PG) E2. In mono-microbial and dual biofilms of C.albicans wild type strains PGE2 levels between 25 and 250 pg/mL were measured. Similar concentrations of purified PGE2 significantly enhanced S.aureus biofilm formation in a mode comparable to that observed in dual species biofilms. Supernatants of the null mutant deficient in PGE2 production did not stimulate the proliferation of S.aureus and the addition of the cyclooxygenase inhibitor indomethacin blocked the S.aureus biofilm formation in a dose-dependent manner. Additionally, S. aureus biofilm formation was boosted by low and inhibited by high farnesol concentrations. Supernatants of the farnesol-deficient C. albicans ATCC10231 strain significantly enhanced the biofilm formation of S. aureus but at a lower level than the farnesol producer SC5314. However, C. albicans ATCC10231 also produced PGE2 but amounts were significantly lower compared to SC5314.

CONCLUSION/SIGNIFICANCE

In conclision, we identified C. albicans PGE2 as a key molecule stimulating the growth and biofilm formation of S. aureus in dual S. aureus/C. albicans biofilms, although C. albicans derived farnesol, but not tyrosol, may also contribute to this effect but to a lesser extent.

Biofilm formation by Staphylococcus aureus isolates from skin and soft tissue infections

Many diseases caused by Staphylococcus aureus are associated with biofilm formation. However, the ability of S. aureus isolates from skin and soft tissue infections to form biofilms has not yet been investigated. We tested 160 isolates from patients with various skin infections for biofilm-forming capacity in different growth media. All the isolates formed biofilms, the extent of which depended on the type of growth medium. The thickest biofilms were formed when both plasma and glucose were present in the broth; in this case, S. aureus incorporated host fibrin into the biofilm's matrix. There were no differences in the biofilm formation between isolates from different types of skin infections, except for a particularly good biofilm formation by isolates from diabetic wounds and a weaker biofilm formation by isolates from impetigo. In conclusion, biofilm formation is a universal behavior of S. aureus isolates from skin infections. In some cases, such as in diabetic wounds, a particularly strong biofilm formation most likely contributes to the chronic and recurrent character of the infection. Additionally, as S. aureus apparently uses host fibrin as part of the biofilm structure, we suggest that plasma should be included more frequently in in vitro biofilm studies.

Biofilm formation by clinical isolates and its relevance to clinical infections

Reports of biofilms have increased exponentially in the scientific literature over the past two decades, yet the vast majority of these are basic science investigations with limited clinical relevance. Biofilm studies involving clinical isolates are most often surveys of isolate collections, but suffer from lack of standardization in methodologies for producing and assessing biofilms. In contrast, more informative clinical studies correlating biofilm formation to patient data have infrequently been reported. In this chapter, biofilm surveys of clinical isolates of aerobic and anaerobic bacteria, mycobacteria, and Candida are reviewed, as well as those pertaining to the unique situation of cystic fibrosis. In addition, the influence of host components on in vitro biofilm formation, as well as published studies documenting the clinical impact of biofilms in human infections, are presented.

Human plasma enhances the expression of Staphylococcal microbial surface components recognizing adhesive matrix molecules promoting biofilm formation and increases antimicrobial tolerance In Vitro

Background

Microbial biofilms have been associated with the development of chronic human infections and represent a clinical challenge given their increased antimicrobial tolerance. Staphylococcus aureus is a major human pathogen causing a diverse range of diseases, of which biofilms are often involved. Staphylococcal attachment and the formation of biofilms have been shown to be facilitated by host factors that accumulate on surfaces. To better understand how host factors enhance staphylococcal biofilm formation, we evaluated the effect of whole human plasma on biofilm formation in clinical isolates of S. aureus and the expression of seven microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) known to be involved in biofilm formation by quantitative real-time PCR. We also evaluated whether plasma augmented changes in S. aureus biofilm morphology and antimicrobial resistance.

Results

Exposure of clinical isolates of S. aureus to human plasma (10%) within media, and to a lesser extent when coated onto plates, significantly enhanced biofilm formation in all of the clinical isolates tested. Compared to biofilms grown under non-supplemented conditions, plasma-augmented biofilms displayed significant changes in both the biofilm phenotype and cell morphology as determined by confocal scanning laser microscopy (CLSM) and scanning electron microscopy (SEM), respectively. Exposure of bacteria to plasma resulted in a significant fold-increase in MSCRAMM expression in both a time and isolate-dependent manner. Additionally, plasma-augmented biofilms displayed an increased tolerance to vancomycin compared to biofilms grown in non-supplemented media.

Conclusions

Collectively, these studies support previous findings demonstrating a role for host factors in biofilm formation and provide further insight into how plasma, a preferred growth medium for staphylococcal biofilm formation enhances as well as augments other intrinsic properties of S. aureus biofilms. Consequently, these findings indicate that incorporation of host factors may be necessary to better replicate in vivo conditions and for the best utility of a clinical biofilm assay to evaluate the process of biofilm formation and treatments.

Filaments in curved streamlines: Rapid formation of Staphylococcus aureus biofilm streamers

Biofilms are surface-associated conglomerates of bacteria that are highly resistant to antibiotics. These bacterial communities can cause chronic infections in humans by colonizing, for example, medical implants, heart valves, or lungs. Staphylococcus aureus, a notorious human pathogen, causes some of the most common biofilm-related infections. Despite the clinical importance of S. aureus biofilms, it remains mostly unknown how physical effects, in particular flow, and surface structure influence biofilm dynamics. Here we use model microfluidic systems to investigate how environmental factors, such as surface geometry, surface chemistry, and fluid flow affect biofilm development in S. aureus. We discovered that S. aureus rapidly forms flow-induced, filamentous biofilm streamers, and furthermore if surfaces are coated with human blood plasma, streamers appear within minutes and clog the channels more rapidly than if the channels are uncoated. To understand how biofilm streamer filaments reorient in flows with curved streamlines to bridge the distances between corners, we developed a mathematical model based on resistive force theory of slender filaments. Understanding physical aspects of biofilm formation in S. aureus may lead to new approaches for interrupting biofilm formation of this pathogen.