Minimum information guideline for spectrophotometric and fluorometric methods to assess biofilm formation in microplates

Inhibitory effects of Trichoderma asperellum culture filtrates on pathogenic bacteria, Burkholderia pseudomallei

Background

Burkholderia pseudomallei is a soil- and water-dwelling bacterium that causes the life-threatening infection melioidosis. Patients typically acquire this infection through environmental exposure, so reducing B. pseudomallei levels in the environment could mitigate the risk of infection. Trichoderma asperellum is a biological control agent that synthesizes a diverse range of antimicrobial substances targeting other microorganisms. This study therefore examined the antibacterial and anti-biofilm activities of T. asperellum culture filtrate against B. pseudomallei.

Methods

The antibacterial activities of T. asperellum culture filtrates, collected at various time intervals, were assessed against B. pseudomallei using the agar well diffusion method. Subsequently, the minimum inhibitory concentrations (MICs), minimum bactericidal concentrations (MBCs), and anti-biofilm activities of the culture filtrate exhibiting the highest inhibitory effect were determined. Bactericidal efficacy was further evaluated via a time-kill assay. The mechanisms underlying inhibition were then investigated using scanning electron microscopy and crystal violet uptake assays.

Results

Filtrate collected from 7-day old cultures of T. asperellum (TD7) exhibited the strongest inhibitory effect on B. pseudomallei, with an inhibition zone of 30.33 ± 0.19 mm. The MIC of TD7 against B. pseudomallei was 7.81 ± 0.00 mg/mL and the MBC ranged from 7.81 ± 0.00 to 11.72 ± 1.75 mg/mL. Time-kill studies with TD7 confirmed its bactericidal activity, with complete elimination of B. pseudomallei occurring within 30 min treatment at 62.48 mg/mL (8xMIC) and 24 h treatment at 7.81 mg/mL (1xMIC). At a concentration of  7.81 mg/mL, TD7 also significantly reduced B. pseudomallei biofilm formation. Scanning electron microscopy revealed surface roughening and cell shrinkage of TD7-treated B. pseudomallei. TD7-treated bacteria were also found to absorb more crystal violet dye than untreated cells, indicating that TD7 might inhibit and kill B. pseudomallei by disrupting cell membrane permeability.

Conclusions

Our findings demonstrate that T. asperellum culture filtrates possess bactericidal activity and effectively disrupt biofilm formation by B. pseudomallei. This suggests that T. asperellum could potentially be used to reduce the presence of B. pseudomallei in the environment and, consequently, lower the incidence of melioidosis.

Anti-Biofilm Agents to Overcome Pseudomonas aeruginosa Antibiotic Resistance

Pseudomonas aeruginosa is one of world's most threatening bacteria. In addition to the emerging prevalence of multi-drug resistant (MDR) strains, the bacterium also possesses a wide variety of virulence traits that worsen the course of the infections. Particularly, its ability to form biofilms that protect colonies from antimicrobial agents is a major cause of chronic and hard-to-treat infections in immune-compromised patients. This protective barrier also ensures cell growth on abiotic surfaces and thus enables bacterial survival on medical devices. Hence, as the WHO alerted to the need to develop new treatments, the use of anti-biofilm agents (ABAs) appeared as a promising approach. Given the selection pressure imposed by conventional antibiotics, a new therapeutic strategy has emerged that aims at reducing bacterial virulence without inhibiting cell growth. So-called anti-virulence agents (AVAs) would then restore the efficacy of conventional antibiotics (ATBs) or potentiate the effectiveness of the immune system. The last decade has seen the development of ABAs as AVAs against P. aeruginosa. This review aims to highlight the design strategy and critical features of these molecules to pave the way for further discoveries of highly potent compounds.

Use of FISH-FLOW as a Method for the Identification and Quantification of Bacterial Populations

The gastrointestinal tract (GIT) harbors the largest group of microbiotas among the microbial communities of the human host. The resident organisms typical of a healthy gut are well adapted to the gastrointestinal environment while alteration of these populations can trigger disorders that may affect the health and well-being of the host. Various investigations have applied different tools to study bacterial communities in the gut and their correlation with gastrointestinal disorders such as inflammatory bowel disease (IBD), obesity, and diabetes. This study proposes fluorescent in situ hybridization, combined with flow cytometry (FISH-FLOW), as an alternative approach for phylum level identification of Firmicutes, Bacteroidetes, Actinobacteria, and Proteobacteria and quantification of target bacteria from the GIT based on analysis of fecal samples, where results are validated by quantitative polymerase chain reaction (qPCR) and 16S ribosomal ribonucleic acid (16s rRNA) sequencing. The results obtained via FISH-FLOW experimental approach show high specificity for the developed probes for hybridization with the target bacteria. The study, therefore, suggests the FISH-FLOW as a reliable method for studying bacterial communities in the gut with results correlating well with those of metagenomic investigations of the same fecal samples.

Characterization and biological activity of selenium nanoparticles biosynthesized by Yarrowia lipolytica

In this research, biogenic selenium nanoparticles were produced by the fungi Yarrowia lipolytica, and the biological activity of its nanoparticles was studied for the first time. The electron microscopy analyses showed the production of nanoparticles were intracellular and the resulting particles were extracted and characterized by XRD, zeta potential, FESEM, EDX, FTIR spectroscopy and DLS. These analyses showed amorphous spherical nanoparticles with an average size of 110 nm and a Zeta potential of -34.51 ± 2.41 mV. Signatures of lipids and proteins were present in the capping layer of biogenic selenium nanoparticles based on FTIR spectra. The antimicrobial properties of test strains showed that Serratia marcescens, Klebsiella pneumonia, Escherichia coli, Pseudomonas aeruginosa and Bacillus subtilis were inhibited at concentrations between 160 and 640 μg/mL, while the growth of Candida albicans was hindered by 80 μg/mL of biogenic selenium nanoparticles. At concentrations between 0.5 and 1.5 mg/mL of biogenic selenium nanoparticles inhibited up to 50% of biofilm formation of Klebsiella pneumonia, Acinetobacter baumannii, Staphylococcus aureus and Pseudomonas aeruginosa. Additionally, the concentration of 20-640 μg/mL of these bioSeNPs showed antioxidant activity. Evaluating the cytotoxicity of these nanoparticles on the HUVEC and HepG2 cell lines did not show any significant toxicity within MIC concentrations of SeNPs. This defines that Y. lipolytica synthesized SeNPs have strong potential to be exploited as antimicrobial agents against pathogens of WHO concern.

Formation of Single-Species and Multispecies Biofilm by Isolates from Septic Transfusion Reactions in Platelet Bag Model

During 2018-2021, eight septic transfusion reactions occurred from transfusion of platelet units contaminated with Acinetobacter spp., Staphylococcus saprophyticus, Leclercia adecarboxylata, or a combination of those environmental organisms. Whether biofilm formation contributed to evasion of bacterial risk mitigations, including bacterial culture, point-of-care testing, or pathogen-reduction technology, is unclear. We designed a 12-well plate-based method to evaluate environmental determinants of single-species and multispecies biofilm formation in platelets. We evaluated bacteria isolated from septic transfusion reactions for biofilm formation by using crystal violet staining and enumeration of adherent bacteria. Most combinations of bacteria had enhanced biofilm production compared with single bacteria. Combinations involving L. adecarboxylata had increased crystal violet biofilm production and adherent bacteria. This study demonstrates that transfusion-relevant bacteria can produce biofilms well together. More work is needed to clarify the effect of biofilms on platelet bacterial risk control strategies, but US Food and Drug Administration-recommended strategies remain acceptable.

The design and development of EcoBiomes: Multi-species synthetic microbial consortia inspired by natural desert microbiome to enhance the resilience of climate-sensitive ecosystems

Synthetic microbial communities, which simplify the complexity of natural ecosystems while retaining their key features, are gaining momentum in engineering and biotechnology applications. One potential application is the development of bioinoculants, offering an eco-friendly, sustainable solution to promote plant growth and increase resilience to abiotic stresses amidst climate change. A potential source for stress-tolerant microbes is those associated with desert plants, evolved and shaped by selective pressures to promote host health under harsh environmental conditions. In our research, we aim to design and develop synthetic microbial consortia inspired by the natural microbiota of four desert plants native to the Arabian Peninsula, inferred from our previous work identifying the structure and predicting the function of these microbial communities using high throughput eDNA barcoding. To obtain culturable microbes that are manageable and traceable yet still representative of natural microbial communities, we combined multiple experimental protocols coupled with compatibility and synergy assessments, along with in planta testing. We isolated a total of 75 bacteria and conducted detailed biological evaluations, revealing that an overwhelming majority (84 %) of all isolates produced indole acetic acid (IAA), with 73 % capable of solubilizing phosphate, 60 % producing siderophores, 47 % forming biofilms, and 35 % producing ACC deaminase, all contributing to plant growth and stress tolerance. We constructed four synthetic microbial consortia, named EcoBiomes, consisting of synergistic combinations of multiple species that can co-exist without significant antagonism. Our preliminary data indicate that EcoBiomes enhance the resilience of heterologous host plants under simulated environmental stresses, including drought, heat, and salinity. EcoBiomes offer a unique, sustainable, and eco-friendly solution to mitigate the impact of climate change on sensitive ecosystems, ultimately affecting global food security.

From 0D-complex to 3D-MOF: changing the antimicrobial activity of zinc(II) via reaction with aminocinnamic acids

Combining zinc nitrate with 3- and/or 4- aminocinnamic acid (3-ACA and 4-ACA, respectively) leads to the formation of the 0D complex [Zn(4-AC)2(H2O)2], the 1D coordination polymer [Zn(3-AC)(4-AC)], and the 2D and 3D MOFs [Zn(3-AC)2]∙2H2O and [Zn(4-AC)2]∙H2O, respectively. These compounds result from the deprotonation of the acid molecules, with the resulting 3- and 4-aminocinnamate anions serving as bidentate terminal or bridging ligands. All solids were fully characterized via single crystal and powder X-ray diffraction and thermal techniques. Given the mild antimicrobial properties of cinnamic acid derivatives and the antibacterial nature of the metal cation, these compounds were assessed and demonstrated very good planktonic cell killing as well as inhibition of biofilm growth against Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus.

A Comprehensive Review of Microbial Biofilms on Contact Lenses: Challenges and Solutions

Contact lenses (CL) have become an immensely popular means of vision correction, offering comfort to millions worldwide. However, the persistent issue of biofilm formation on lenses raises significant problems, leading to various ocular complications and discomfort. The aim of this review is to develop safer and more effective strategies for preventing and managing microbial biofilms on CL, improving the eye health and comfort of wearers. Taking these into consideration, the present study investigates the intricate mechanisms of biofilm formation, by exploring the interplay between microbial adhesion, the production of extracellular polymeric substances, and the properties of the lens material itself. Moreover, it emphasizes the diverse range of microorganisms involved, encompassing bacteria, fungi, and other opportunistic pathogens, elucidating their implications within lenses and other medical device-related infections and inflammatory responses. Going beyond the challenges posed by biofilms on CL, this work explores the advancements in biofilm detection techniques and their clinical relevance. It discusses diagnostic tools like confocal microscopy, genetic assays, and emerging technologies, assessing their capacity to identify and quantify biofilm-related infections. Finally, the paper delves into contemporary strategies and innovative approaches for managing and preventing biofilms development on CL. In Conclusion, this review provides insights for eye care practitioners, lens manufacturers, and microbiology researchers. It highlights the intricate interactions between biofilms and CL, serving as a foundation for the development of effective preventive measures and innovative solutions to enhance CL safety, comfort, and overall ocular health. Research into microbial biofilms on CL is continuously evolving, with several future directions being explored to address challenges and improve eye health outcomes as far as CL wearers are concerned.

Quorum-quenching enzyme Est816 assisted antibiotics against periodontitis induced by Aggregatibacter actinomycetemcomitans in rats

Introduction

Quorum-quenching enzyme Est816 hydrolyzes the lactone rings of N-acyl homoserine lactones, effectively blocking the biofilm formation and development of Gram-negative bacteria. However, its applications in the oral field is limited. This study aimed to evaluate the efficacy of enzyme Est816 in combination with antibiotics against periodontitis induced by Aggregatibacter actinomycetemcomitans in vitro and in vivo.

Methods

The antimicrobial efficacy of enzyme Est816 in combination with minocycline, metronidazole, and amoxicillin was determined using the minimum inhibitory concentration test. The anti-biofilm effect of enzyme Est816 was assessed using scanning electron microscopy, live/dead bacterial staining, crystal violet staining, and real-time quantitative PCR. Biocompatibility of enzyme Est816 was assessed in human gingival fibroblasts (HGF) by staining. A rat model of periodontitis was established to evaluate the effect of enzyme Est816 combined with minocycline using micro-computed tomography and histological staining.

Results

Compared to minocycline, metronidazole, and amoxicillin treatment alone, simultaneous treatment with enzyme Est816 increased the sensitivity of biofilm bacteria to antibiotics. Enzyme Est816 with minocycline exhibited the highest rate of biofilm clearance and high biocompatibility. Moreover, the combination of enzyme Est816 with antibiotics improved the antibiofilm effects of the antibiotics synergistically, reducing the expression of the virulence factor leukotoxin gene (ltxA) and fimbria-associated gene (rcpA). Likewise, the combination of enzyme Est816 with minocycline exhibited a remarkable inhibitory effect on bone resorption and inflammation damage in a rat model of periodontitis.

Discussion

The combination of enzyme Est816 with antibiotics represents a prospective anti-biofilm strategy with the potential to treat periodontitis.

Minimum Information for Conducting and Reporting In Vitro Intracellular Infection Assays

Bacterial pathogens are constantly evolving to outsmart the host immune system and antibiotics developed to eradicate them. One key strategy involves the ability of bacteria to survive and replicate within host cells, thereby causing intracellular infections. To address this unmet clinical need, researchers are adopting new approaches, such as the development of novel molecules that can penetrate host cells, thus exerting their antimicrobial activity intracellularly, or repurposing existing antibiotics using nanocarriers (i.e., nanoantibiotics) for site-specific delivery. However, inconsistency in information reported across published studies makes it challenging for scientific comparison and judgment of experiments for future direction by researchers. Together with the lack of reproducibility of experiments, these inconsistencies limit the translation of experimental results beyond pre-clinical evaluation. Minimum information guidelines have been instrumental in addressing such challenges in other fields of biomedical research. Guidelines and recommendations provided herein have been designed for researchers as essential parameters to be disclosed when publishing their methodology and results, divided into four main categories: (i) experimental design, (ii) establishing an in vitro model, (iii) assessment of efficacy of novel therapeutics, and (iv) statistical assessment. These guidelines have been designed with the intention to improve the reproducibility and rigor of future studies while enabling quantitative comparisons of published studies, ultimately facilitating translation of emerging antimicrobial technologies into clinically viable therapies that safely and effectively treat intracellular infections.

Evaluation of Novel HLM Peptide Activity and Toxicity against Planktonic and Biofilm Bacteria: Comparison to Standard Antibiotics

BACKGROUND

Antibiotic resistance is one of the main concerns of public health, and the whole world is trying to overcome such a challenge by finding novel therapeutic modalities and approaches. This study has applied the sequence hybridization approach to the original sequence of two cathelicidin natural parent peptides (BMAP-28 and LL-37) to design a novel HLM peptide with broad antimicrobial activity.

METHODS

The physicochemical characteristics of the newly designed peptide were determined. As well, the new peptide's antimicrobial activity (Minimum Inhibitory Concentration (MIC), Minimum Bacterial Eradication Concentration (MBEC), and antibiofilm activity) was tested on two control (Staphylococcus aureus ATCC 29213, Escherichia coli ATCC 25922) and two resistant (Methicillin-resistant Staphylococcus aureus (MRSA) ATCC BAA41, New Delhi metallo-beta- lactamase-1 Escherichia coli ATCC BAA-2452) bacterial strains. Furthermore, synergistic studies have been applied to HLM-hybridized peptides with five conventional antibiotics by checkerboard assays. Also, the toxicity of HLM-hybridized peptide was studied on Vero cell lines to obtain the IC50 value. Besides the percentage of hemolysis action, the peptide was tested in freshly heparinized blood.

RESULTS

The MIC values for the HLM peptide were obtained as 20, 10, 20, and 20 μM, respectively. Also, the results showed no hemolysis action, with low to slightly moderate toxicity action against mammalian cells, with an IC50 value of 10.06. The Biomatik corporate labs, where HLM was manufactured, determined the stability results of the product by Mass Spectrophotometry (MS) and High-performance Liquid Chromatography (HPLC) methods. The HLM-hybridized peptide exhibited a range of synergistic to additive antimicrobial activities upon combination with five commercially available different antibiotics. It has demonstrated the biofilm-killing effects in the same concentration required to eradicate the control strains.

CONCLUSION

The results indicated that HLM-hybridized peptide displayed a broad-spectrum activity toward different bacterial strains in planktonic and biofilm forms. It showed synergistic or additive antimicrobial activity upon combining with commercially available different antibiotics.

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.

A microtiter peg lid with ziggurat geometry for medium-throughput antibiotic testing and in situ imaging of biofilms

Bacteria biofilm responses to disinfectants and antibiotics are quantified and observed using multiple methods, though microscopy, particularly confocal laser scanning microscopy (CLSM) is preferred due to speed, a reduction in user error, and in situ analysis. CLSM can resolve biological and spatial heterogeneity of biofilms in 3D with limited throughput. The microplate peg-lid-based assay, described in ASTM E2799-22, is a medium-throughput method for testing biofilms but does not permit in situ imaging. Breaking off the peg, as recommended by the manufacturer, risks sample damage, and is limited to easily accessible pegs. Here we report modifications to the peg optimized for in situ visualization and visualization of all pegs. We report similar antibiotic challenge recovery via colony formation following the ASTM E2799-22 protocol and in situ imaging. We report novel quantifiable effects of antibiotics on biofilm morphologies, specifically biofilm streamers. The new design bridges the MBEC® assays design that selects for biofilm phenotypes with in situ imaging needs.

A Guideline for Assessment and Characterization of Bacterial Biofilm Formation in the Presence of Inhibitory Compounds

Campylobacter jejuni, a zoonotic foodborne pathogen, is the worldwide leading cause of acute human bacterial gastroenteritis. Biofilms are a significant reservoir for survival and transmission of this pathogen, contributing to its overall antimicrobial resistance. Natural compounds such as essential oils, phytochemicals, polyphenolic extracts, and D-amino acids have been shown to have the potential to control biofilms formed by bacteria, including Campylobacter spp. This work presents a proposed guideline for assessing and characterizing bacterial biofilm formation in the presence of naturally occurring inhibitory molecules using C. jejuni as a model. The following protocols describe: i) biofilm formation inhibition assay, designed to assess the ability of naturally occurring molecules to inhibit the formation of biofilms; ii) biofilm dispersal assay, to assess the ability of naturally occurring inhibitory molecules to eradicate established biofilms; iii) confocal laser scanning microscopy (CLSM), to evaluate bacterial viability in biofilms after treatment with naturally occurring inhibitory molecules and to study the structured appearance (or architecture) of biofilm before and after treatment.

A systematic review of the use of bacteriophages for in vitro biofilm control

Bacteriophages (phages) are very promising biological agents for the prevention and control of bacterial biofilms. However, little is known about the parameters that can influence the efficacy of phages on biofilms. This systematic review provides a summary and analysis of the published data about the use of phages to control pre-formed biofilms in vitro, suggesting recommendations for future experiments in this area. A total of 68 articles, containing data on 605 experiments addressing the efficacy of phages to control biofilms in vitro were included, after a search conducted in Web of Science, Embase, and Medline (PubMed). The data collected from each experiment included information about biofilm growth conditions, phage characteristics, treatment conditions and biofilm reduction. In most cases, biofilms were formed in the surface of microtiter plates (82.5%); the median time for biofilm formation was 24 h, as is the median treatment duration. Quantification of biofilm biomass (52.6%), viable cells (25.5%) and metabolic activity (17.9%) were the most common biofilm assessment methods. Correlation analysis revealed that some phage parameters can influence the treatment outcome: higher phage concentrations were strongly associated with improved biofilm control, leading to higher levels of biofilm reduction, and phages with higher burst sizes and shorter latent periods seem to be the best candidates to control biofilms in vitro. However, the great variability of the methodologies used prompts the need for the development of standardized in vitro methodologies to characterize phage/biofilm interactions and to assess the efficacy of phages to control biofilms.

Tools of the Trade: Image Analysis Programs for Confocal Laser-Scanning Microscopy Studies of Biofilms and Considerations for Their Use by Experimental Researchers

Confocal laser-scanning microscopy (CLSM) is the bedrock of the microscopic visualization of biofilms. Previous applications of CLSM in biofilm studies have largely focused on observations of bacterial or fungal elements of biofilms, often seen as aggregates or mats of cells. However, the field of biofilm research is moving beyond qualitative observations alone, toward the quantitative analysis of the structural and functional features of biofilms, across clinical, environmental, and laboratory conditions. In recent times, several image analysis programs have been developed to extract and quantify biofilm properties from confocal micrographs. These tools not only vary in their scope and relevance to the specific biofilm features under study but also with respect to the user interface, compatibility with operating systems, and raw image requirements. Understanding these considerations is important when selecting tools for quantitative biofilm analysis, including at the initial experimental stages of image acquisition. In this review, we provide an overview of image analysis programs for confocal micrographs of biofilms, with a focus on tool selection and image acquisition parameters that are relevant for experimental researchers to ensure reliability and compatibility with downstream image processing.

Interactions of microorganisms within a urinary catheter polymicrobial biofilm model

Biofilms are often polymicrobial in nature, which can impact their behavior and overall structure, often resulting in an increase in biomass and enhanced antimicrobial resistance. Using plate counts and locked nucleic acid/2'-O-methyl-RNA fluorescence in situ hybridization (LNA/2'OMe-FISH), we studied the interactions of four species commonly associated with catheter-associated urinary tract infections (CAUTI): Enterococcus faecalis, Escherichia coli, Candida albicans, and Proteus mirabilis. Eleven combinations of biofilms were grown on silicone coupons placed in 24-well plates for 24 h, 37°C, in artificial urine medium (AUM). Results showed that P. mirabilis was the dominant species and was able to inhibit both E. coli and C. albicans growth. In the absence of P. mirabilis, an antagonistic relationship between E. coli and C. albicans was observed, with the former being dominant. E. faecalis growth was not affected in any combination, showing a more mutualistic relationship with the other species. Imaging results correlated with the plate count data and provided visual verification of species undetected using the viable plate count. Moreover, the three bacterial species showed overall good repeatability SD (S_r ) values (0.1-0.54) in all combinations tested, whereas C. albicans had higher repeatability S_r values (0.36-1.18). The study showed the complexity of early-stage interactions in polymicrobial biofilms. These interactions could serve as a starting point when considering targets for preventing or treating CAUTI biofilms containing these species.

Lipid-Like Biofilm from a Clinical Brain Isolate of Aspergillus terreus: Quantification, Structural Characterization and Stages of the Formation Cycle

Invasive infections caused by filamentous fungi have increased considerably due to the alteration of the host's immune response. Aspergillus terreus is considered an emerging pathogen and has shown resistance to amphotericin B treatment, resulting in high mortality. The development of fungal biofilm is a virulence factor, and it has been described in some cases of invasive aspergillosis. In addition, although the general composition of fungal biofilms is known, findings related to biofilms of a lipid nature are rarely reported. In this study, we present the identification of a clinical strain of A. terreus by microbiological and molecular tools, also its in vitro biofilm development capacity: (i) Biofilm formation was quantified by Crystal Violet and reduction of tetrazolium salts assays, and simultaneously the stages of biofilm development were described by Scanning Electron Microscopy in High Resolution (SEM-HR). (ii) Characterization of the organizational structure of the biofilm was performed by SEM-HR. The hyphal networks developed on the surface, the abundant air channels created between the ECM (extracellular matrix) and the hyphae fused in anastomosis were described. Also, the presence of microhyphae is reported. (iii) The chemical composition of the ECM was analyzed by SEM-HR and CLSM (Confocal Laser Scanning Microscopy). Proteins, carbohydrates, nucleic acids and a relevant presence of lipid components were identified. Some structures of apparent waxy appearance were highlighted by SEM-HR and backscatter-electron diffraction, for which CLSM was previously performed. To our knowledge, this work is the first description of a lipid-type biofilm in filamentous fungi, specifically of the species A. terreus from a clinical isolate.

In vitro studies of biofilm-forming Bacillus strains, biocontrol agents isolated from the maize phyllosphere

We aimed to assess how biofilm formation by three Bacillus isolates was affected by changes in temperature, water potential, growth media, time, and the combinations between these factors. The strains had been selected as potential biological control agents (BCAs) in earlier studies, and they were identified as B. subtilis and B. velezensis spp. through 16 rRNA sequencing and MALDI-TOF MS. Maize leaves (ML) were used as one of the growth media, since they made it possible to simulate the nutrient content in the maize phyllosphere, from which the bacteria were originally isolated. The strains were able to form biofilm both in ML and biofilm-inducing MSgg after 24, 48, and 72 h. Biofilm development in the form of pellicles and architecturally complex colonies varied morphologically from one strain to another and depended on the conditions mentioned above. In all cases, colonies and pellicles were less complex when both temperature and water potential were lower. Scanning electron microscopy (SEM) revealed that changing levels of complexity in pellicles were correlated with those in colonies. Statistical analyses found that the quantification of biofilm produced by the isolates was influenced by all the conditions tested. In terms of motility (which may contribute to biofilm formation), swimming and swarming were possible for all strains in 0.3 and 0.7% agar, respectively. A more in-depth understanding of how abiotic factors influence biofilm formation can contribute to a more effective use of these biocontrol strains against pathogens in the maize phyllosphere.

Flexible biofilm monitoring device

Biofilms and their analysis are increasingly attracting the attention of the scientific community due to the immense importance and impact of biofilms in various natural, technical and medical fields. For these purposes, an optimized and extended antibiofilm assay system based on the Calgary Biofilm Device (MBEC Assay® system) consisting of microtiter plate and PCR tubes was established. Its implementation was used to study the growth characteristics of the sessile phenotype of Pseudomonas fluorescens exposed to antimicrobial peptides. Inhibitory effects of an antimicrobial peptide on P. fluorescens biofilm formation could be determined at a concentration of 250 μg/ml (biofilm prevention concentration (BPC)) using the modified biofilm assay. Similarly, the biofilm bactericidal concentration (BBC) at 125 μg/ml and the minimum biofilm elimination concentration to remove 90% of the total biofilm mass (MBEC90) were measured at a concentration range of 15.625-1.95 μg/ml. In conclusion, this optimized system provides a highly variable, simple, and cost-effective alternative to high-throughput screening based on the Calgary Biofilm Device (CBD).

Comparison of Antimicrobial and Antibiofilm Activity of Proflavine Co-crystallized with Silver, Copper, Zinc, and Gallium Salts

Here, we exploit our mechanochemical synthesis for co-crystallization of an organic antiseptic, proflavine, with metal-based antimicrobials (silver, copper, zinc, and gallium). Our previous studies have looked for general antimicrobial activity for the co-crystals: proflavine·AgNO3, proflavine·CuCl, ZnCl3[Proflavinium], [Proflavinium]2[ZnCl4]·H2O, and [Proflavinium]3[Ga(oxalate)3]·4H2O. Here, we explore and compare more precisely the bacteriostatic (minimal inhibitory concentrations) and antibiofilm (prevention of cell attachment and propagation) activities of the co-crystals. For this, we choose three prominent "ESKAPE" bacterial pathogens of Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus. The antimicrobial behavior of the co-crystals was compared to that of the separate components of the polycrystalline samples to ascertain whether the proflavine-metal complex association in the solid state provided effective antimicrobial performance. We were particularly interested to see if the co-crystals were effective in preventing bacteria from initiating and propagating the biofilm mode of growth, as this growth form provides high antimicrobial resistance properties. We found that for the planktonic lifestyle of growth of the three bacterial strains, different co-crystal formulations gave selectivity for best performance. For the biofilm state of growth, we see that the silver proflavine co-crystal has the best overall antibiofilm activity against all three organisms. However, other proflavine-metal co-crystals also show practical antimicrobial efficacy against E. coli and S. aureus. While not all proflavine-metal co-crystals demonstrated enhanced antimicrobial efficacy over their constituents alone, all possessed acceptable antimicrobial properties while trapped in the co-crystal form. We also demonstrate that the metal-proflavine crystals retain antimicrobial activity in storage. This work defines that co-crystallization of metal compounds and organic antimicrobials has a potential role in the quest for antimicrobials/antiseptics in the defense against bacteria in our antimicrobial resistance era.

Multi-Modal Imaging Monitored M2 Macrophage Targeting Sono-Responsive Nanoparticles to Combat MRSA Deep Infections

Background

MRSA with high morbidity and mortality is prone to cause serious infection, SDT has become a new antibiotic-free modality for bacterial infection treatment. Switching from proinflammatory M1 macrophages to anti-inflammatory M2 macrophages dominant could activate the immune system to generate an anti-infection immune response.

Methods

Herein, we developed M2 macrophages derived cell membranes coated PLGA nanoparticles with IR780 encapsulation (M2/IR780@PLGA) for antibacterial SDT and subsequent M2 macrophage polarization to enhance the therapeutic efficacy of MRSA myositis. For in situ visualization of antibacterial SDT, both diagnostic high-frequency US and magnetic resonance imaging (MRI) were introduced to monitor the sono-therapeutic progression of M2/IR780@PLGA nanoparticles in mice with bacterial myositis.

Results

Our developed M2/IR780@PLGA nanoparticles exhibited excellent antibacterial effects due to the IR780 under low-frequency US irradiation in vitro. In an MRSA-infected mice model, a great deal of M2/IR780@PLGA nanoparticles accumulated at the site of inflammation due to M2 macrophage coating. The infected legs in the M2/IR780@PLGA nanoparticles-based SDT group were significantly smaller, fewer blood flow signals, a slight muscular edema without obvious intermuscular abscesses under high-frequency US and MR images guidance. Histopathology proved the infected legs in the M2/IR780@PLGA nanoparticles-mediated SDT group had less clumped bacteria infiltration, more M2 macrophage expression and less M1 macrophage expression. The percentage of mature dendritic cells in spleens was much higher in the group of mice with M2/IR780@PLGA nanoparticles-based SDT.

Conclusion

This study provides a promising nanoparticles-based SDT anti-bacterial strategy, which could effectively enhance the antibacterial SDT and subsequent promote M2 macrophage polarization to boost the therapeutic efficacy of MRSA myositis.

Cell Viability Assays for Candida auris

Cell viability assays are useful for assessing the efficacy of antifungal therapeutics and disinfection strategies in vitro. In recent years these assays have been fundamental for the testing of conventional and novel therapies against the nosocomial fungal pathogen Candida auris. Here we provide detailed descriptions of methods for assessing cellular viability of Candida auris in vitro, such as metabolic assays (XTT and resazurin), colony-forming unit counting, live/dead quantitative PCR, and fluorescent staining for microscopic analyses.

A Critical Review of the Antimicrobial and Antibiofilm Activities of Green-Synthesized Plant-Based Metallic Nanoparticles

Metallic nanoparticles (MNPs) produced by green synthesis using plant extracts have attracted huge interest in the scientific community due to their excellent antibacterial, antifungal and antibiofilm activities. To evaluate these pharmacological properties, several methods or protocols have been successfully developed and implemented. Although these protocols were mostly inspired by the guidelines from national and international regulatory bodies, they suffer from a glaring absence of standardization of the experimental conditions. This situation leads to a lack of reproducibility and comparability of data from different study settings. To minimize these problems, guidelines for the antimicrobial and antibiofilm evaluation of MNPs should be developed by specialists in the field. Being aware of the immensity of the workload and the efforts required to achieve this, we set out to undertake a meticulous literature review of different experimental protocols and laboratory conditions used for the antimicrobial and antibiofilm evaluation of MNPs that could be used as a basis for future guidelines. This review also brings together all the discrepancies resulting from the different experimental designs and emphasizes their impact on the biological activities as well as their interpretation. Finally, the paper proposes a general overview that requires extensive experimental investigations to set the stage for the future development of effective antimicrobial MNPs using green synthesis.

A Microfluidic Chip for Studies of the Dynamics of Antibiotic Resistance Selection in Bacterial Biofilms

Biofilms are arguably the most important mode of growth of bacteria, but how antibiotic resistance emerges and is selected in biofilms remains poorly understood. Several models to study evolution of antibiotic resistance have been developed, however, their usability varies depending on the nature of the biological question. Here, we developed and validated a microfluidic chip (Brimor) for studying the dynamics of enrichment of antibiotic-resistant bacteria in biofilms using real-time monitoring with confocal microscopy. In situ extracellular cellulose staining and physical disruption of the biomass confirmed Escherichia coli growth as biofilms in the chip. We showed that seven generations of growth occur in 16 h when biofilms were established in the growth chambers of Brimor, and that bacterial death and growth rates could be estimated under these conditions using a plasmid with a conditional replication origin. Additionally, competition experiments between antibiotic-susceptible and -resistant bacteria at sub-inhibitory concentrations demonstrated that the antibiotic ciprofloxacin selected for antibiotic resistance in bacterial biofilms at concentrations 17-fold below the minimal inhibitory concentration of susceptible planktonic bacteria. Overall, the microfluidic chip is easy to use and a relevant model for studying the dynamics of selection of antibiotic resistance in bacterial biofilms and we anticipate that the Brimor chip will facilitate basic research in this area.

Tranexamic acid protects against implant-associated infection by reducing biofilm formation

Perioperative administration of tranexamic acid (TXA) is thought to be related to decreased postoperative implant-associated infection rates; however, the relationship remains unclear. We explored the inhibitory effect of TXA on infection both in vitro and in vivo. We investigated biofilm formation after TXA administration through different detection methods, all of which showed that TXA reduces biofilm formation in vitro and was further proven to be associated with decreased protein and polysaccharide contents in biofilms. We observed decreased biofilm on implants and decreased bacteria in the infection area with strengthened neutrophil accumulation in the mouse implant-associated infection model. Our results suggest that TXA protects against implant-associated infection by reducing biofilm formation in infected tissues.

Seaweed Extracts: A Promising Source of Antibiofilm Agents with Distinct Mechanisms of Action against Pseudomonas aeruginosa

The organization of bacteria in biofilms is one of the adaptive resistance mechanisms providing increased protection against conventional treatments. Thus, the search for new antibiofilm agents for medical purposes, especially of natural origin, is currently the object of much attention. The objective of the study presented here was to explore the potential of extracts derived from three seaweeds: the green Ulva lactuca, the brown Stypocaulon scoparium, and the red Pterocladiella capillacea, in terms of their antibiofilm activity against P. aeruginosa. After preparation of extracts by successive maceration in various solvents, their antibiofilm activity was evaluated on biofilm formation and on mature biofilms. Their inhibition and eradication abilities were determined using two complementary methods: crystal violet staining and quantification of adherent bacteria. The effect of active extracts on biofilm morphology was also investigated by epifluorescence microscopy. Results revealed a promising antibiofilm activity of two extracts (cyclohexane and ethyl acetate) derived from the green alga by exhibiting a distinct mechanism of action, which was supported by microscopic analyses. The ethyl acetate extract was further explored for its interaction with tobramycin and colistin. Interestingly, this extract showed a promising synergistic effect with tobramycin. First analyses of the chemical composition of extracts by GC-MS allowed for the identification of several molecules. Their implication in the interesting antibiofilm activity is discussed. These findings suggest the ability of the green alga U. lactuca to offer a promising source of bioactive candidates that could have both a preventive and a curative effect in the treatment of biofilms.

An In Vitro Evaluation of Denture Cleansing Regimens against a Polymicrobial Denture Biofilm Model

Denture stomatitis (DS) is an inflammatory disease resulting from a polymicrobial biofilm perturbation at the denture surface–palatal mucosa interface. Recommendations made by dental health care professionals often lack clarity for appropriate denture cleaning. This study investigated the efficacy of brushing with off-the-shelf denture cleanser (DC) tablets (Poligrip^®) vs. two toothpastes (Colgate^® and Crest^®) in alleviating the viable microorganisms (bacteria and fungi) in an in vitro denture biofilm model. Biofilms were grown on poly(methyl)methacrylate (PMMA) discs, then treated daily for 7 days with mechanical disruption (brushing), plus Poligrip^® DC, Colgate^® or Crest^® toothpastes. Weekly treatment with Poligrip^® DC on day 7 only was compared to daily modalities. All treatment parameters were processed to determine viable colony forming units for bacteria and fungi using the Miles and Misra technique, and imaged by confocal laser scanning microscopy (CLSM). Brushing with daily DC therapy was the most effective treatment in reducing the viable biofilm over 7 days of treatment. Brushing only was ineffective in controlling the viable bioburden, which was confirmed by CLSM imaging. This data indicates that regular cleansing of PMMA with DC was best for polymicrobial biofilms.

Non-destructive investigation of extracellular enzyme activities and kinetics in intact freshwater biofilms with mineral beads as carriers

Current procedures for fluorometric detection of extracellular hydrolytic enzyme activities in intact aquatic biofilms are very laborious and insufficiently standardized. To facilitate the direct determination of a multitude of enzymatic parameters without biofilm disintegration, a new approach was followed. Beads made of different mineral materials were subjected to biofilm growth in various aquatic environments. After biofilm coating, the beads were singly placed in microplate wells, containing the required liquid analytical medium and a fluorogenic substrate. Based on fluorometric detection of the enzymatically generated reaction products, enzyme activities and kinetics were determined. Mean enzymatic activities of ceramic bead-attached biofilms grown in a natural stream followed the decreasing sequence L-alanine aminopeptidase > L-leucine aminopeptidase > phosphomonoesterase > β-glucosidase > phosphodiesterase > α-glucosidase > sulfatase. After one week of exposure, the relative standard deviations of enzyme activities ranged from 21 to 67%. Sintered glass bead-associated biofilms displayed the lowest standard deviations ranging from 19 to 34% in all experiments. This material proved to be suitable for short-time experiments in stagnant media. Ceramic beads were stable during more than three weeks of exposure in a natural stream. Biofilm formation was inhomogeneous or poorly visible on glass and lava beads accompanied by high variations of enzyme activities. The applicability of the method to study enzyme inhibition reactions was successfully proven by the determination of inhibition effects of caffeine on biofilm-associated phosphodiesterase.Key points• Optimized method to determine enzymatic parameters in aquatic biofilms• Direct investigation of bead-bound biofilms without biofilm disintegration• Fluorometric detection offers high sensitivity and sample throughput.

Inhibition of d-alanylation of teichoic acids overcomes resistance of methicillin-resistant Staphylococcus aureus

Background

MRSA are high-priority multidrug-resistant pathogens. Although there are still some antibiotics active against MRSA, continuous efforts to discover new antibiotics and treatment strategies are needed because resistance to these new drugs has already been reported.

Objectives

Here we explore if d-alanylation of teichoic acids (TAs) mediated by the dlt operon gene products might be a druggable target to overcome β-lactam-resistance of MRSA.

Methods

MICs and bactericidal effects of several β-lactam antibiotics were monitored in a panel of clinical MRSA strains with genetic or chemically induced deficiency in d-alanylation of TAs. Efficiency of the chemical inhibitor to rescue MRSA-infected larvae of Galleria mellonella as well as its ability to prevent or eradicate biofilms of S. aureus were analysed.

Results

Genetic inactivation of the Dlt system or its chemical inhibition re-sensitizes MRSA to β-lactams. Among the 13 strains, the most pronounced effect was obtained using the inhibitor with imipenem, reducing the median MIC from 16 to 0.25 mg/L. This combination was also bactericidal in some strains and significantly protected G. mellonella larvae from lethal MRSA infections. Finally, inactivation of d-alanylation potentiated the effect of imipenem on inhibition and/or eradication of biofilm.

Conclusions

Our combined results show that highly efficient inhibitors of d-alanylation of TAs targeting enzymes of the Dlt system should be promising therapeutic adjuvants, especially in combination with carbapenems, for restoring the therapeutic efficacy of this class of antibiotics against MRSA.

N-Acetyl-l-cysteine-Loaded Nanosystems as a Promising Therapeutic Approach Toward the Eradication of Pseudomonas aeruginosa Biofilms

Bacterial biofilms are a major health concern, mainly due to their contribution to increased bacterial resistance to well-known antibiotics. The conventional treatment of biofilms represents a challenge, and frequently, eradication is not achieved with long-lasting administration of antibiotics. In this context, the present work proposes an innovative therapeutic approach that is focused on the encapsulation of N-acetyl-l-cysteine (NAC) into lipid nanoparticles (LNPs) functionalized with d-amino acids to target and disrupt bacterial biofilms. The optimized formulations presented a mean hydrodynamic diameter around 200 nm, a low polydispersity index, and a high loading capacity. These formulations were stable under storage conditions up to 6 months. In vitro biocompatibility studies showed a low cytotoxicity effect in fibroblasts and a low hemolytic activity in human red blood cells. Nevertheless, unloaded LNPs showed a higher hemolytic potential than NAC-loaded LNPs, which suggests a safer profile of the latter. The in vitro antibiofilm efficacy of the developed formulations was tested against Staphylococcus epidermidis (Gram-positive) and Pseudomonas aeruginosa (Gram-negative) mature biofilms. The results showed that the NAC-loaded LNPs were ineffective against S. epidermidis biofilms, while a significant reduction of biofilm biomass and bacterial viability in P. aeruginosa biofilms were observed. In a more complex therapeutic approach, the LNPs were further combined with moxifloxacin, revealing a beneficial effect between the LNPs and the antibiotic against P. aeruginosa biofilms. Both alone and in combination with moxifloxacin, unloaded and NAC-loaded LNPs functionalized with d-amino acids showed a great potential to reduce bacterial viability, with no significant differences in the presence or absence of NAC. However, the presence of NAC in NAC-loaded functionalized LNPs shows a safer profile than the unloaded LNPs, which is beneficial for an in vivo application. Overall, the developed formulations present a potential therapeutic approach against P. aeruginosa biofilms, alone or in combination with antibiotics.

Nitrate modulation of Bacillus sp. biofilm components: a proposed model for sustainable bioremediation

The presence of different pollutants in wastewater hinder microbial growth, compromise enzymatic activity or compete for electrons required for bioremediation pathway. Therefore, there is a need to use a single microorganism that is capable of tolerating different toxic compounds and can perform simultaneous bioremediation. In the present study, nitrate reducing bacteria capable of decolorizing azo dye was identified as Bacillus subtillis sp. DN using protein profiling, morphological and biochemical tests X-ray diffraction pattern, Raman spectroscopy and cyclic voltammetry confirm that the bacterium under study possesses membrane-bound nitrate reductase and that is capable of direct electron transfer. The addition of nitrate concentrations (0-50 mM) resulted in increased biofilm formation with variable exopolysaccharides, protein, and eDNA. Fourier Transform Infrared spectrum revealed the presence of a biopolymer at high nitrate concentrations. Effective capacitance and conductivity of the cells grown in different nitrate concentrations suggest changes in the relative position of polar groups, their relative orientation and permeability of cell membrane as detected by dielectric spectroscopy. The increase in biofilm shifted the removal of the azo dye from biodegradation to bioadsorption. Our results indicate that nitrate modulates biofilm components. Bacillus sp. DN granular biofilm can be used for simultaneous nitrate and azo dye removal from wastewater.

Microbial Warfare on Three Fronts: Mixed Biofilm of Aspergillus fumigatus and Staphylococcus aureus on Primary Cultures of Human Limbo-Corneal Fibroblasts

Background

Coinfections with fungi and bacteria in ocular pathologies are increasing at an alarming rate. Two of the main etiologic agents of infections on the corneal surface, such as Aspergillus fumigatus and Staphylococcus aureus, can form a biofilm. However, mixed fungal–bacterial biofilms are rarely reported in ocular infections. The implementation of cell cultures as a study model related to biofilm microbial keratitis will allow understanding the pathogenesis in the cornea. The cornea maintains a pathogen-free ocular surface in which human limbo-corneal fibroblast cells are part of its cell regeneration process. There are no reports of biofilm formation assays on limbo-corneal fibroblasts, as well as their behavior with a polymicrobial infection.

Objective

To determine the capacity of biofilm formation during this fungal–bacterial interaction on primary limbo-corneal fibroblast monolayers.

Results

The biofilm on the limbo-corneal fibroblast culture was analyzed by assessing biomass production and determining metabolic activity. Furthermore, the mixed biofilm effect on this cell culture was observed with several microscopy techniques. The single and mixed biofilm was higher on the limbo-corneal fibroblast monolayer than on abiotic surfaces. The A. fumigatus biofilm on the human limbo-corneal fibroblast culture showed a considerable decrease compared to the S. aureus biofilm on the limbo-corneal fibroblast monolayer. Moreover, the mixed biofilm had a lower density than that of the single biofilm. Antibiosis between A. fumigatus and S. aureus persisted during the challenge to limbo-corneal fibroblasts, but it seems that the fungus was more effectively inhibited.

Conclusion

This is the first report of mixed fungal–bacterial biofilm production and morphological characterization on the limbo-corneal fibroblast monolayer. Three antibiosis behaviors were observed between fungi, bacteria, and limbo-corneal fibroblasts. The mycophagy effect over A. fumigatus by S. aureus was exacerbated on the limbo-corneal fibroblast monolayer. During fungal–bacterial interactions, it appears that limbo-corneal fibroblasts showed some phagocytic activity, demonstrating tripartite relationships during coinfection.

Biofilm inhibition and bactericidal activity of NiTi alloy coated with graphene oxide/silver nanoparticles via electrophoretic deposition

Biofilm formation on medical devices can induce complications. Graphene oxide/silver nanoparticles (GO/AgNPs) coated nickel-titanium (NiTi) alloy has been successfully produced. Therefore, the aim of this study was to determine the anti-bacterial and anti-biofilm effects of a GO/AgNPs coated NiTi alloy prepared by Electrophoretic deposition (EPD). GO/AgNPs were coated on NiTi alloy using various coating times. The surface characteristics of the coated NiTi alloy substrates were investigated and its anti-biofilm and anti-bacterial effect on Streptococcus mutans biofilm were determined by measuring the biofilm mass and the number of viable cells using a crystal violet assay and colony counting assay, respectively. The results showed that although the surface roughness increased in a coating time-dependent manner, there was no positive correlation between the surface roughness and the total biofilm mass. However, increased GO/AgNPs deposition produced by the increased coating time significantly reduced the number of viable bacteria in the biofilm (p < 0.05). Therefore, the GO/AgNPs on NiTi alloy have an antibacterial effect on the S. mutans biofilm. However, the increased surface roughness does not influence total biofilm mass formation (p = 0.993). Modifying the NiTi alloy surface using GO/AgNPs can be a promising coating to reduce the consequences of biofilm formation.

Interlaboratory study for the evaluation of three microtiter plate-based biofilm quantification methods

Microtiter plate methods are commonly used for biofilm assessment. However, results obtained with these methods have often been difficult to reproduce. Hence, it is important to obtain a better understanding of the repeatability and reproducibility of these methods. An interlaboratory study was performed in five different laboratories to evaluate the reproducibility and responsiveness of three methods to quantify Staphylococcus aureus biofilm formation in 96-well microtiter plates: crystal violet, resazurin, and plate counts. An inter-lab protocol was developed for the study. The protocol was separated into three steps: biofilm growth, biofilm challenge, biofilm assessment. For control experiments participants performed the growth and assessment steps only. For treatment experiments, all three steps were performed and the efficacy of sodium hypochlorite (NaOCl) in killing S. aureus biofilms was evaluated. In control experiments, on the log₁₀-scale, the reproducibility SD (S_R) was 0.44 for crystal violet, 0.53 for resazurin, and 0.92 for the plate counts. In the treatment experiments, plate counts had the best responsiveness to different levels of efficacy and also the best reproducibility with respect to responsiveness (Slope/S_R = 1.02), making it the more reliable method to use in an antimicrobial efficacy test. This study showed that the microtiter plate is a versatile and easy-to-use biofilm reactor, which exhibits good repeatability and reproducibility for different types of assessment methods, as long as a suitable experimental design and statistical analysis is applied.

Incidence of Bacillus cereus, Bacillus sporothermodurans and Geobacillus stearothermophilus in ultra-high temperature milk and biofilm formation capacity of isolates

The presence of mesophilic and thermophilic spore-forming bacteria in UHT milk, as well as biofilm formation in dairy plants, are concerning. The current study explored the spore-forming bacilli diversity in 100 samples of UHT milk (skimmed and whole). Through this work, a total of 239 isolates from UHT milk samples were obtained. B. cereus s.s. was isolated from 7 samples, B. sporothermodurans from 19 and, G. stearothermophilus from 25 samples. Genes encoding hemolysin (HBL), and non-hemolytic (NHE) enterotoxins were detected in B. cereus s.s. isolates. All isolates of B. cereus s.s. (12) B. sporothermodurans (38), and G. stearothermophilus (47) were selected to verify the ability of biofilm formation in microtiter plates. The results showed all isolates could form biofilms. The OD₅₉₅ values of biofilm formation varied between 0.14 and 1.04 for B. cereus, 0.20 to 1.87 for B. sporothermodurans, and 0.49 to 2.77 for G. stearothermophilus. The data highlights that the dairy industry needs to reinforce control in the initial quality of the raw material and in CIP cleaning procedures; avoiding biofilm formation and consequently a persistent microbiota in processing plants, which can shelter pathogenic species such as B. cereus s.s.

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).

Biofilms vs. cities and humans vs. aliens - a tale of reproducibility in biofilms

Biofilms are complex and dynamic structures that include many more components than just viable cells. Therefore, the apparently simple goal of growing reproducible biofilms is often elusive. One of the challenges in defining reproducibility for biofilm research is that different research fields use a spectrum of parameters to define reproducibility for their particular application. For instance, is the researcher interested in achieving a similar population density, height of biofilm structures, or function of the biofilm in a certain ecosystem/industrial context? Within this article we categorize reproducibility into four different levels: level 1, no reproducibility; level 2, standard reproducibility; level 3, potential standard reproducibility; and level 4, total reproducibility. To better understand the need for these different levels of reproducibility, we expand on the 'cities of microbes' analogy for biofilms by imagining that a new civilization has reached the Earth's outskirts and starts studying the Earth's cities. This will provide a better sense of scale and illustrate how small details can impact profoundly on the growth and behavior of a biofilm and our understanding of reproducibility.

Bacterial cyclic diguanylate signaling networks sense temperature

Many bacteria use the second messenger cyclic diguanylate (c-di-GMP) to control motility, biofilm production and virulence. Here, we identify a thermosensory diguanylate cyclase (TdcA) that modulates temperature-dependent motility, biofilm development and virulence in the opportunistic pathogen Pseudomonas aeruginosa. TdcA synthesizes c-di-GMP with catalytic rates that increase more than a hundred-fold over a ten-degree Celsius change. Analyses using protein chimeras indicate that heat-sensing is mediated by a thermosensitive Per-Arnt-SIM (PAS) domain. TdcA homologs are widespread in sequence databases, and a distantly related, heterologously expressed homolog from the Betaproteobacteria order Gallionellales also displayed thermosensitive diguanylate cyclase activity. We propose, therefore, that thermotransduction is a conserved function of c-di-GMP signaling networks, and that thermosensitive catalysis of a second messenger constitutes a mechanism for thermal sensing in bacteria.

Use of Quorum Sensing Inhibition Strategies to Control Microfouling

Interfering with the quorum sensing bacterial communication systems has been proposed as a promising strategy to control bacterial biofilm formation, a key process in biofouling development. Appropriate in vitro biofilm-forming bacteria models are needed to establish screening methods for innovative anti-biofilm and anti-microfouling compounds. Four marine strains, two Pseudoalteromonas spp. and two Vibrio spp., were selected and studied with regard to their biofilm-forming capacity and sensitivity to quorum sensing (QS) inhibitors. Biofilm experiments were performed using two biofilm cultivation and quantification methods: the xCELLigence^® system, which allows online monitoring of biofilm formation, and the active attachment model, which allows refreshment of the culture medium to obtain a strong biofilm that can be quantified with standard staining methods. Although all selected strains produced acyl-homoserine-lactone (AHL) QS signals, only the P. flavipulchra biofilm, measured with both quantification systems, was significantly reduced with the addition of the AHL-lactonase Aii20J without a significant effect on planktonic growth. Two-species biofilms containing P. flavipulchra were also affected by the addition of Aii20J, indicating an influence on the target bacterial strain as well as an indirect effect on the co-cultured bacterium. The use of xCELLigence^® is proposed as a time-saving method to quantify biofilm formation and search for eco-friendly anti-microfouling compounds based on quorum sensing inhibition (QSI) strategies. The results obtained from these two in vitro biofilm formation methods revealed important differences in the response of biosensor bacteria to culture medium and conditions, indicating that several strains should be used simultaneously for screening purposes and the cultivation conditions should be carefully optimized for each specific purpose.

Candida albicans as an Essential "Keystone" Component within Polymicrobial Oral Biofilm Models?

Background: Existing standardized biofilm assays focus on simple mono-species or bacterial-only models. Incorporating Candida albicans into complex biofilm models can offer a more appropriate and relevant polymicrobial biofilm for the development of oral health products. Aims: This study aimed to assess the importance of interkingdom interactions in polymicrobial oral biofilm systems with or without C. albicans, and test how these models respond to oral therapeutic challenges in vitro. Materials and Methods: Polymicrobial biofilms (two models containing 5 and 10 bacterial species, respectively) were created in parallel in the presence and absence of C. albicans and challenged using clinically relevant antimicrobials. The metabolic profiles and biomasses of these complex biofilms were estimated using resazurin dye and crystal violet stain, respectively. Quantitative PCR was utilized to assess compositional changes in microbial load. Additional assays, for measurements of pH and lactate, were included to monitor fluctuations in virulence "biomarkers." Results: An increased level of metabolic activity and biomass in the presence of C. albicans was observed. Bacterial load was increased by more than a factor of 10 in the presence of C. albicans. Assays showed inclusion of C. albicans impacted the biofilm virulence profiles. C. albicans did not affect the biofilms' responses to the short-term incubations with different treatments. Conclusions: The interkingdom biofilms described herein are structurally robust and exhibit all the hallmarks of a reproducible model. To our knowledge, these data are the first to test the hypothesis that yeasts may act as potential "keystone" components of oral biofilms.

Filling the Void: An Optimized Polymicrobial Interkingdom Biofilm Model for Assessing Novel Antimicrobial Agents in Endodontic Infection

There is a growing realization that endodontic infections are often polymicrobial, and may contain Candida spp. Despite this understanding, the development of new endodontic irrigants and models of pathogenesis remains limited to mono-species biofilm models and is bacterially focused. The purpose of this study was to develop and optimize an interkingdom biofilm model of endodontic infection and use this to test suitable anti-biofilm actives. Biofilms containing Streptococcus gordonii, Fusobacterium nucleatum, Porphyromonas gingivalis, and Candida albicans were established from ontological analysis. Biofilms were optimized in different media and atmospheric conditions, prior to quantification and imaging, and subsequently treated with chlorhexidine, EDTA, and chitosan. These studies demonstrated that either media supplemented with serum were equally optimal for biofilm growth, which were dominated by S. gordonii, followed by C. albicans. Assessment of antimicrobial activity showed significant effectiveness of each antimicrobial, irrespective of serum. Chitosan was most effective (3 log reduction), and preferentially targeted C. albicans in both biofilm treatment and inhibition models. Chitosan was similarly effective at preventing biofilm growth on a dentine substrate. This study has shown that a reproducible and robust complex interkingdom model, which when tested with the antifungal chitosan, supports the notion of C. albicans as a key structural component.

From Treatise to Test: Evaluating Traditional Remedies for Anti-Biofilm Potential

Traditional plant-based remedies hold vast potential as novel antimicrobial agents, particularly for recalcitrant infection states such as biofilms. To explore their potential, it is important to bring these remedies out of historical treatises, and into present-day scientific evaluation. Using an example of Indian traditional medicine (Ayurveda), we present a perspective toward evaluating historical remedies for anti-biofilm potential. Across compendia, we identified three plant-based remedies (of Kalanchoe pinnata, Cynodon dactylon, and Ocimum tenuiflorum) recommended for wounds. The remedies were reconstituted in accordance with historical practices, and tested for their effects on biofilm formation and eradication assays of wound pathogens, Pseudomonas aeruginosa and Staphylococcus aureus. Based on our approach and the results obtained, we provide insights into the considerations and challenges related to identifying potential remedies in historical texts, and testing them in the laboratory with standard biofilm assays. We believe this will be relevant for future studies exploring anti-biofilm approaches at the interface of historical medicine and present-day scientific practices.

Current Knowledge and Future Directions in Developing Strategies to Combat Pseudomonas aeruginosa Infection

In the face of growing antimicrobial resistance, there is an urgent need for the development of effective strategies to target Pseudomonas aeruginosa. This metabolically versatile bacterium can cause a wide range of severe opportunistic infections in patients with serious underlying medical conditions, such as those with burns, surgical wounds or people with cystic fibrosis. Many of the key adaptations that arise in this organism during infection are centered on core metabolism and virulence factor synthesis. Interfering with these processes may provide a new strategy to combat infection which could be combined with conventional antibiotics. This review will provide an overview of the most recent work that has advanced our understanding of P. aeruginosa infection. Strategies that exploit this recent knowledge to combat infection will be highlighted alongside potential alternative therapeutic options and their limitations.

Chitosan Ameliorates Candida auris Virulence in a Galleria mellonella Infection Model

Candida auris has emerged as a multidrug-resistant nosocomial pathogen over the last decade. Outbreaks of the organism in health care facilities have resulted in life-threatening invasive candidiasis in over 40 countries worldwide. Resistance by C. auris to conventional antifungal drugs such as fluconazole and amphotericin B means that alternative therapeutics must be explored. As such, this study served to investigate the efficacy of a naturally derived polysaccharide called chitosan against aggregative (Agg) and nonaggregative (non-Agg) isolates of C. aurisin vitro and in vivo. In vitro results indicated that chitosan was effective against planktonic and sessile forms of Agg and non-Agg C. auris In a Galleria mellonella model to assess C. auris virulence, chitosan treatment was shown to ameliorate killing effects of both C. auris phenotypes (NCPF 8973 and NCPF 8978, respectively) in vivo Specifically, chitosan reduced the fungal load and increased survival rates of infected Galleria, while treatment alone was nontoxic to the larvae. Finally, chitosan treatment appeared to induce a stress-like gene expression response in NCPF 8973 in the larvae likely arising from a protective response by the organism to resist antifungal activity of the compound. Taken together, results from this study demonstrate that naturally derived compounds such as chitosan may be useful alternatives to conventional antifungals against C. auris.