Biofilms: survival mechanisms of clinically relevant microorganisms

Characterization of a novel polyextremotolerant fungus, Exophiala viscosa, with insights into its melanin regulation and ecological niche

Black yeasts are polyextremotolerant fungi that contain high amounts of melanin in their cell wall and maintain a primar yeast form. These fungi grow in xeric, nutrient depletes environments which implies that they require highly flexible metabolisms and have been suggested to contain the ability to form lichen-like mutualisms with nearby algae and bacteria. However, the exact ecological niche and interactions between these fungi and their surrounding community are not well understood. We have isolated 2 novel black yeasts from the genus Exophiala that were recovered from dryland biological soil crusts. Despite notable differences in colony and cellular morphology, both fungi appear to be members of the same species, which has been named Exophiala viscosa (i.e. E. viscosa JF 03-3 Goopy and E. viscosa JF 03-4F Slimy). A combination of whole genome sequencing, phenotypic experiments, and melanin regulation experiments have been performed on these isolates to fully characterize these fungi and help decipher their fundamental niche within the biological soil crust consortium. Our results reveal that E. viscosa is capable of utilizing a wide variety of carbon and nitrogen sources potentially derived from symbiotic microbes, can withstand many forms of abiotic stresses, and excretes melanin which can potentially provide ultraviolet resistance to the biological soil crust community. Besides the identification of a novel species within the genus Exophiala, our study also provides new insight into the regulation of melanin production in polyextremotolerant fungi.

Biofilm modifiers: The disparity in paradigm of oral biofilm ecosystem

A biofilm is a population of sessile microorganisms that has a distinct organized structure and characteristics like channels and projections. Good oral hygiene and reduction in the prevalence of periodontal diseases arise from minimal biofilm accumulation in the mouth, however, studies focusing on modifying the ecology of oral biofilms have not yet been consistently effective. The self-produced matrix of extracellular polymeric substances and greater antibiotic resistance make it difficult to target and eliminate biofilm infections, which lead to serious clinical consequences that are often lethal. Therefore, a better understanding is required to target and modify the ecology of biofilms in order to eradicate the infection, not only in instances of oral disorders but also in terms of nosocomial infections. The review focuses on several biofilm ecology modifiers to prevent biofilm infections, as well as the involvement of biofilm in antibiotic resistance, implants or in-dwelling device contamination, dental caries, and other periodontal disorders. It also discusses recent advances in nanotechnology that may lead to novel strategies for preventing and treating infections caused by biofilms as well as a novel outlook to infection control.

Resistance and Biofilm Production Profile of Potential Isolated from Kpètè-Kpètè Used to Produce Traditional Fermented Beer

This study aimed to characterize the pathogenicity of bacteria isolated from the starter of two traditional beers produced and consumed in Benin. After standard microbial identification, species were identified by specific biochemical tests such as catalase, coagulase, and API 20 E. Antibiotic sensitivity was tested according to the French Society of Microbiology Antibiogram Committee. The crystal violet microplate technique evaluated the biofilm production and conventional PCR was used to identify genes encoding virulence and macrolide resistance. According to our data, the traditional starter known as kpètè-kpètè that is used to produce beer is contaminated by Enterobacteriaceae and staphylococci species. Thus, 28.43% of the isolated bacteria were coagulase-negative staphylococci (CNS), and 10.93% coagulase-positive staphylococci (CPS). Six species such as Klebsiella terrigena (1.38%), Enterobacter aerogens (4.14%), Providencia rettgeri (5.51%), Chryseomonas luteola (6.89%), Serratia rubidae (15.16%), and Enterobacter cloacae (27.56%) were identified among Enterobacteriaceae. Those bacterial strains are multi-resistant to conventional antibiotics. The hight capability of produced biofilms was recorded with Enterobacter aerogens, Klebsiella terrigena (100%), Providencia rettgeri (75%), and Staphylococcus spp (60%). Enterobacter cloacae (4%) and coagulase-negative Staphylococcus (5.55%) harbor the macrolide resistance gene. For other strains, these genes were not detected. Foods contaminated with bacteria resistant to antibiotics and carrying a virulence gene could constitute a potential public health problem. There is a need to increase awareness campaigns on hygiene rules in preparing and selling these traditional beers.

Antimicrobial Susceptibility of Staphylococcus aureus Strains and Effect of Phloretin on Biofilm Formation

Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) are known to be responsible of various infections, including biofilm-associated diseases. The aim of this study was to analyze 19 strains of S. aureus from orthopedic sites in terms of phenotypic antimicrobial susceptibility against 13 selected antibiotics, slime/biofilm formation, molecular analysis of specific antibiotic resistance genes (mecA, cfr, rpoB), and biofilm-associated genes (icaADBC operon). Furthermore, the effect of phloretin on the production of biofilm was evaluated on 8 chosen isolates. The susceptibility test confirmed almost all strains were resistant to cefoxitin and oxacillin. Most strains possess the mecA, whereas none of the strains had the cfr gene. Four strains (1, 7, 10, and 24) presented single-nucleotide polymorphisms (SNPs) in rpoB, which confer rifampicin resistance. IcaD was detected in all tested strains, whereas icaR was only found in two strains (24 and 30). Phloretin had a dose-dependent effect on biofilm production. Specifically, 0.5 × MIC determined biofilm inhibition in 5 out of 8 strains (8, 24, 25, 27, 30), whereas an increase in biofilm production was detected with phloretin at the 0.125 × MIC across all tested strains. These data are useful to potentially develop novel compounds against antibiotic-resistant S. aureus.

Emerging evidence-based innovative approaches to control catheter-associated urinary tract infection: a review

Healthcare settings have dramatically advanced the latest medical devices, such as urinary catheters (UC) for infection, prevention, and control (IPC). The continuous or intermittent flow of a warm and conducive (urine) medium in the medical device, the urinary catheter, promotes the formation of biofilms and encrustations, thereby leading to the incidence of CAUTI. Additionally, the absence of an innate immune host response in and around the lumen of the catheter reduces microbial phagocytosis and drug action. Hence, the review comprehensively overviews the challenges posed by CAUTI and associated risks in patients' morbidity and mortality. Also, detailed, up-to-date information on the various strategies that blended/tailored the surface properties of UC to have anti-fouling, biocidal, and anti-adhesive properties to provide an outlook on how they can be better managed with futuristic solutions.

Antimicrobial and Apoptotic Efficacy of Plant-Mediated Silver Nanoparticles

Phytogenically synthesised nanoparticle (NP)-based drug delivery systems have promising potential in the field of biopharmaceuticals. From the point of view of biomedical applications, such systems offer the small size, high surface area, and possible synergistic effects of NPs with embedded biomolecules. This article describes the synthesis of silver nanoparticles (Ag-NPs) using extracts from the flowers and leaves of tansy (Tanacetum vulgare L.), which is known as a remedy for many health problems, including cancer. The reducing power of the extracts was confirmed by total phenolic and flavonoid content and antioxidant tests. The Ag-NPs were characterised by various analytical techniques including UV-vis spectroscopy, scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), Fourier transform infrared (FT-IR) spectroscopy, and a dynamic light scattering (DLS) system. The obtained Ag-NPs showed higher cytotoxic activity than the initial extracts against both human cervical cancer cell lines HeLa (ATCC CCL-2) and human melanoma cell lines A375 and SK-MEL-3 by MTT assay. However, the high toxicity to Vero cell culture (ATCC CCL-81) and human fibroblast cell line WS-1 rules out the possibility of their use as anticancer agents. The plant-mediated Ag-NPs were mostly bactericidal against tested strains with MBC/MIC index ≤4. Antifungal bioactivity (C. albicans, C. glabrata, and C. parapsilosis) was not observed for aqueous extracts (MIC > 8000 mg L^-1), but Ag-NPs synthesised using both the flowers and leaves of tansy were very potent against Candida spp., with MIC 15.6 and 7.8 µg mL^-1, respectively.

Staphylococcus aureus in Polymicrobial Skinand Soft Tissue Infections: Impact of Inter-Species Interactionsin Disease Outcome

Polymicrobial biofilms provide a complex environment where co-infecting microorganisms can behave antagonistically, additively, or synergistically to alter the disease outcome compared to monomicrobial infections. Staphylococcus aureus skin and soft tissue infections (Sa-SSTIs) are frequently reported in healthcare and community settings, and they can also involve other bacterial and fungal microorganisms. This polymicrobial aetiology is usually found in chronic wounds, such as diabetic foot ulcers, pressure ulcers, and burn wounds, where the establishment of multi-species biofilms in chronic wounds has been extensively described. This review article explores the recent updates on the microorganisms commonly found together with S. aureus in SSTIs, such as Pseudomonas aeruginosa, Escherichia coli, Enterococcus spp., Acinetobacter baumannii, and Candida albicans, among others. The molecular mechanisms behind these polymicrobial interactions in the context of infected wounds and their impact on pathogenesis and antimicrobial susceptibility are also revised.

Selecting a high-dose antibiotic-laden cement knee spacer

Prosthetic joint infection [PJI] after total knee arthroplasty (TKA) remains a common and challenging problem for joint replacement surgeons and patients. Once the diagnosis of PJI has been made, patient goals and characteristics as well as the infection timeline dictate treatment. Most commonly, this involves a two-stage procedure with the removal of all implants, debridement, and placement of a static or dynamic antibiotic spacer. Static spacers are commonly indicated for older, less healthy patients that would benefit from soft tissue rest after initial debridement. Mobile spacers are typically used in younger, healthier patients to improve quality of life and reduce soft-tissue contractures during antibiotic spacer treatment. Spacers are highly customizable with regard to antibiotic choice, cement variety, and spacer design, each with reported advantages, drawbacks, and indications that will be covered in this article. While no spacer is superior to any other, the modern arthroplasty surgeon must be familiar with the available modalities to optimize treatment for each patient. Here we propose a treatment algorithm to assist surgeons in deciding on treatment for PJI after TKA.

A pig model of tunneled dialysis catheter (TDC) infection and dysfunction: Opportunities for therapeutic innovation

BACKGROUND

Although tunneled dialysis catheters (TDC) are far from ideal, they still represent the main form of vascular access for most patients beginning dialysis. Catheters are easy to place and allow patients instant access to dialysis, but regardless of these benefits, catheters are associated with a high incidence of significant complications like bloodstream infections, central venous stenosis, thrombosis, and dysfunction. In the present study, we aim to describe and characterize a swine model of catheter dysfunction and bloodstream infection, that recreates the clinical scenario, to help to serve as a platform to develop therapeutic innovations for this important clinical problem.

METHODS

Six Yorkshire cross pigs were used in this study. Non-coated commercial catheters were implanted in the external jugular recreating the main features of common clinical practice. Catheters were aseptically accessed twice a week for a mock dialysis procedure (flushing in and out) to assess for and identify catheter dysfunction. Animals were monitored daily for infections; once detected, blood samples were collected for bacterial culture and antibiograms. Study animals were euthanized when nonresponsive to treatment. Tissue samples were collected in a standardized fashion for macroscopic inspection and histological analysis.

RESULTS

The data analysis revealed an early onset of infection with a median time to infection of 9 days, 40% of the isolates were polymicrobial, and the average time to euthanasia was 20.16 ± 7.3 days. Median time to catheter dysfunction onset was 6 days post-implantation. Postmortem dissection revealed external fibrin sheath and internal thrombosis as the main causes of catheter dysfunction. There was also evidence of central venous stenosis with positive cells for αSMA, CD68, Ki67, Smoothelin, and Vimentin within the venous neointima.

CONCLUSIONS

The described model represents a reliable and reproducible large animal model of catheter dysfunction and bloodstream infection, which recreates all the main complications of TDC's and so could be used as a validated large animal model to develop new therapies for TDC related infection, thrombosis/dysfunction and central venous stenosis.

Recent Strategies and Future Recommendations for the Fabrication of Antimicrobial, Antibiofilm, and Antibiofouling Biomaterials

Biomaterials and biomedical devices induced life-threatening bacterial infections and other biological adverse effects such as thrombosis and fibrosis have posed a significant threat to global healthcare. Bacterial infections and adverse biological effects are often caused by the formation of microbial biofilms and the adherence of various biomacromolecules, such as platelets, proteins, fibroblasts, and immune cells, to the surfaces of biomaterials and biomedical devices. Due to the programmed interconnected networking of bacteria in microbial biofilms, they are challenging to treat and can withstand several doses of antibiotics. Additionally, antibiotics can kill bacteria but do not prevent the adsorption of biomacromolecules from physiological fluids or implanting sites, which generates a conditioning layer that promotes bacteria's reattachment, development, and eventual biofilm formation. In these viewpoints, we highlighted the magnitude of biomaterials and biomedical device-induced infections, the role of biofilm formation, and biomacromolecule adhesion in human pathogenesis. We then discussed the solutions practiced in healthcare systems for curing biomaterials and biomedical device-induced infections and their limitations. Moreover, this review comprehensively elaborated on the recent advances in designing and fabricating biomaterials and biomedical devices with these three properties: antibacterial (bacterial killing), antibiofilm (biofilm inhibition/prevention), and antibiofouling (biofouling inhibition/prevention) against microbial species and against the adhesion of other biomacromolecules. Besides we also recommended potential directions for further investigations.

Polymyxin B complexation enhances the antimicrobial potential of graphene oxide

Introduction

The antibacterial activity of graphene oxide (GO) has been widely explored and tested against various pathogenic bacterial strains. Although antimicrobial activity of GO against planktonic bacterial cells was demonstrated, its bacteriostatic and bactericidal effect alone is not sufficient to damage sedentary and well protected bacterial cells inside biofilms. Thus, to be utilized as an effective antibacterial agent, it is necessary to improve the antibacterial activity of GO either by integration with other nanomaterials or by attachment of antimicrobial agents. In this study, antimicrobial peptide polymyxin B (PMB) was adsorbed onto the surface of pristine GO and GO functionalized with triethylene glycol.

Methods

The antibacterial effects of the resulting materials were examined by evaluating minimum inhibitory concentration, minimum bactericidal concentration, time kill assay, live/dead viability staining and scanning electron microscopy.

Results and discussion

PMB adsorption significantly enhanced the bacteriostatic and bactericidal activity of GO against both planktonic cells and bacterial cells in biofilms. Furthermore, the coatings of PMB-adsorbed GO applied to catheter tubes strongly mitigated biofilm formation, by preventing bacterial adhesion and killing the bacterial cells that managed to attach. The presented results suggest that antibacterial peptide absorption can significantly enhance the antibacterial activity of GO and the resulting material can be effectively used not only against planktonic bacteria but also against infectious biofilms.

Nitric Oxide-Releasing Hemodialysis Catheter Lock Solutions

In an attempt to address the significant morbidity, mortality, and economic cost associated with tunneled dialysis catheter (TDC) dysfunction, we report the development of nitric oxide-releasing dialysis catheter lock solutions. Catheter lock solutions with a range of NO payloads and release kinetics were prepared using low-molecular-weight N-diazeniumdiolate nitric oxide donors. Nitric oxide released through the catheter surface as a dissolved gas was maintained at therapeutically relevant levels for at least 72 h, supporting clinical translatability (interdialytic period). Slow, sustained NO release from the catheter surface prevented bacterial adhesion in vitro by 88.9 and 99.7% for Pseudomonas aeruginosa and Staphylococcus epidermidis, respectively, outperforming a burst NO-release profile. Furthermore, bacteria adhered to the catheter surface in vitro prior to lock solution use was reduced by 98.7 and 99.2% for P. aeruginosa and S. epidermidis, respectively, when using a slow releasing NO donor, demonstrating both preventative and treatment potential. The adhesion of proteins to the catheter surface, a process often preceding biofilm formation and thrombosis, was also lessened by 60-65% by sustained NO release. In vitro cytotoxicity of catheter extract solutions to mammalian cells was minimal, supporting the non-toxic nature of the NO-releasing lock solutions. The use of the NO-releasing lock solution in an in vivo TDC porcine model demonstrated decreased infection and thrombosis, enhanced catheter functionality, and improved outcome (i.e., likelihood of survival) as a result of catheter use.

Microbial Biofilm: A Review on Formation, Infection, Antibiotic Resistance, Control Measures, and Innovative Treatment

Biofilm is complex and consists of bacterial colonies that reside in an exopolysaccharide matrix that attaches to foreign surfaces in a living organism. Biofilm frequently leads to nosocomial, chronic infections in clinical settings. Since the bacteria in the biofilm have developed antibiotic resistance, using antibiotics alone to treat infections brought on by biofilm is ineffective. This review provides a succinct summary of the theories behind the composition of, formation of, and drug-resistant infections attributed to biofilm and cutting-edge curative approaches to counteract and treat biofilm. The high frequency of medical device-induced infections due to biofilm warrants the application of innovative technologies to manage the complexities presented by biofilm.

OpaR Exerts a Dynamic Control over c-di-GMP Homeostasis and cpsA Expression in Vibrio parahaemolyticus through Its Regulation of ScrC and the Trigger Phosphodiesterase TpdA

The second messenger cyclic dimeric GMP (c-di-GMP) plays a central role in controlling decision-making processes that are vitally important for the environmental survival of the human pathogen Vibrio parahaemolyticus. The mechanisms by which c-di-GMP levels and biofilm formation are dynamically controlled in V. parahaemolyticus are poorly understood. Here, we report the involvement of OpaR in controlling c-di-GMP metabolism and its effects on the expression of the trigger phosphodiesterase (PDE) TpdA and the biofilm-matrix related gene cpsA. Our results revealed that OpaR negatively modulates the expression of tpdA by maintaining a baseline level of c-di-GMP. The OpaR-regulated PDEs ScrC, ScrG, and VP0117 enable the upregulation of tpdA, to different degrees, in the absence of OpaR. We also found that TpdA plays the dominant role in c-di-GMP degradation under planktonic conditions compared to the other OpaR-regulated PDEs. In cells growing on solid medium, we observed that the role of the dominant c-di-GMP degrader alternates between ScrC and TpdA. We also report contrasting effects of the absence of OpaR on cpsA expression in cells growing on solid media compared to cells forming biofilms over glass. These results suggest that OpaR can act as a double-edged sword to control cpsA expression and perhaps biofilm development in response to poorly understood environmental factors. Finally, using an in-silico analysis, we indicate outlets of the OpaR regulatory module that can impact decision making during the motile-to-sessile transition in V. parahaemolyticus. IMPORTANCE The second messenger c-di-GMP is extensively used by bacterial cells to control crucial social adaptations such as biofilm formation. Here, we explore the role of the quorum-sensing regulator OpaR, from the human pathogen V. parahaemolyticus, on the dynamic control of c-di-GMP signaling and biofilm-matrix production. We found that OpaR is crucial to c-di-GMP homeostasis in cells growing on Lysogeny Broth agar and that the OpaR-regulated PDEs TpdA and ScrC alternate in the dominant role over time. Furthermore, OpaR plays contrasting roles in controlling the expression of the biofilm-related gene cpsA on different surfaces and growth conditions. This dual role has not been reported for orthologues of OpaR, such as HapR from Vibrio cholerae. It is important to investigate the origins and consequences of the differences in c-di-GMP signaling between closely and distantly related pathogens to better understand pathogenic bacterial behavior and its evolution.

Eradication of Staphylococcus epidermidis within Biofilms: Comparison of Systemic versus Supratherapeutic Concentrations of Antibiotics

Biofilm-forming bacterial infections result in clinical failure, recurring infections, and high health care costs. The antibiotic concentrations needed to eradicate biofilm require further research. We aimed to model an in vitro prosthetic joint infection (PJI) to elucidate the activity of traditional systemic concentrations versus supratherapeutic concentrations to eradicate a Staphylococcus epidermidis biofilm PJI. We evaluated S. epidermidis high-biofilm-forming (ATCC 35984) and low-biofilm-forming (ATCC 12228) isolates in an in vitro pharmacodynamic biofilm reactor model with chromium cobalt coupons to simulate prosthetic joint infection. Vancomycin, daptomycin, levofloxacin, and minocycline were used alone and combined with rifampin to evaluate the effect of biofilm eradication. We simulated three exposures: (i) humanized systemic dosing alone, (ii) supratherapeutic doses (1,000× MIC), and (iii) and dosing in combination with rifampin. Resistance development was monitored throughout the study. Simulated humanized systemic doses of a lipoglycopeptide (daptomycin), a fluoroquinolone (levofloxacin), a tetracycline (minocycline), and a glycopeptide (vancomycin) alone failed to eradicate a formed S. epidermidis biofilm. Supratherapeutic doses of vancomycin (2,000 μg/mL) and minocycline (15 μg/mL) with or without rifampin (15 μg/mL) failed to eradicate biofilms. However, a levofloxacin supratherapeutic dose (125 μg/mL) with rifampin eradicated the high-biofilm-producing isolate by 48 h. Interestingly, supratherapeutic-dose exposures of daptomycin (500 μg/mL) alone eradicated high- and low-biofilm-forming isolates in established biofilms. The concentrations needed to eradicate biofilms on foreign materials are not obtained with systemic dosing regimens. The failure of systemic dosing regimens to eradicate biofilms validates clinical findings with recurring infections. The addition of rifampin to supratherapeutic dosing regimens does not result in synergy. Supratherapeutic daptomycin dosing may be effective at the site of action to eradicate biofilms. Further studies are needed.

In Vitro Antibacterial Activity of Silver Nanoparticles Conjugated with Amikacin and Combined with Hyperthermia against Drug-Resistant and Biofilm-Producing Strains

In view of the current increase and spread of antimicrobial resistance (AMR), there is an urgent need to find new strategies to combat it. This study had two aims. First, we synthesized highly monodispersed silver nanoparticles (AgNPs) of approximately 17 nm, and we functionalized them with mercaptopoly(ethylene glycol) carboxylic acid (mPEG-COOH) and amikacin (AK). Second, we evaluated the antibacterial activity of this treatment (AgNPs_mPEG_AK) alone and in combination with hyperthermia against planktonic and biofilm-growing strains. AgNPs, AgNPs_mPEG, and AgNPs_mPEG_AK were characterized using a suite of spectroscopy and microscopy methods. Susceptibility to these treatments and AK was determined after 24 h and over time against 12 clinical multidrug-resistant (MDR)/extensively drug-resistant (XDR) isolates of Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. The efficacy of the treatments alone and in combination with hyperthermia (1, 2, and 3 pulses at 41°C to 42°C for 15 min) was tested against the same planktonic strains using quantitative culture and against one P. aeruginosa strain growing on silicone disks using confocal laser scanning microscopy. The susceptibility studies showed that AgNPs_mPEG_AK was 10-fold more effective than AK alone, and bactericidal efficacy after 4, 8, 24, or 48 h was observed against 100% of the tested strains. The combination of AgNPs_mPEG_AK and hyperthermia eradicated 75% of the planktonic strains and exhibited significant reductions in biofilm formation by P. aeruginosa in comparison with the other treatments tested, except for AgNPs_mPEG_AK without hyperthermia. In conclusion, the combination of AgNPs_mPEG_AK and hyperthermia may be a promising therapy against MDR/XDR and biofilm-producing strains. IMPORTANCE Antimicrobial resistance (AMR) is one of the greatest public health challenges, accounting for 1.27 million deaths worldwide in 2019. Biofilms, a complex microbial community, directly contribute to increased AMR. Therefore, new strategies are urgently required to combat infections caused by AMR and biofilm-producing strains. Silver nanoparticles (AgNPs) exhibit antimicrobial activity and can be functionalized with antibiotics. Although AgNPs are very promising, their effectiveness in complex biological environments still falls below the concentrations at which AgNPs are stable in terms of aggregation. Thus, improving the antibacterial effectiveness of AgNPs by functionalizing them with antibiotics may be a significant change to consolidate AgNPs as an alternative to antibiotics. It has been reported that hyperthermia has a large effect on the growth of planktonic and biofilm-producing strains. Therefore, we propose a new strategy based on AgNPs functionalized with amikacin and combined with hyperthermia (41°C to 42°C) to treat AMR and biofilm-related infections.

Nanoarchitectonics of nitric oxide releasing supramolecular structures for enhanced antibacterial efficacy under visible light irradiation

Light-controlled therapies offer a promising strategy to prevent and suppress infections caused by numerous bacterial pathogens. Excitation of exogenously supplied photosensitizers (PS) at specific wavelengths elicits levels of reactive oxygen intermediates toxic to bacteria. Porphyrin-based supramolecular nanostructure frameworks (SNF) are effective PS with unique physicochemical properties that have led to their widespread use in photomedicine. Herein, we developed a nitric oxide (NO) releasing, biocompatible, and stable porphyrin-based SNF (SNF-NO), which was achieved through a confined noncovalent self-assembly process based on π-π stacking. Characterization of the SNFs via scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis showed the formation of three-dimensional, well-defined octahedral structures. These SNF-NO were shown to exhibit a red shift due to the noncovalent self-assembly of porphyrins, which also show extended light absorption to broadly cover the entire visible light spectrum to enhance photodynamic therapy (PDT). Under visible light irradiation (46 J cm-2), the SNF generates high yields of singlet oxygen (1O2) radicals, hydroxyl radicals (HO), superoxide radicals (O2), and peroxynitrite (ONOO-) radicals that have shown potential to enhance antimicrobial photodynamic therapy (APDT) against Gram-positive methicillin-resistant Staphylococcus aureus (MRSA) and Gram-negative Escherichia coli (E. coli). The resulting SNFs also exhibit significant biofilm dispersion and a decrease in biomass production. The combination of robust photosensitizer SNFs with nitric oxide-releasing capabilities is dynamic in its ability to target pathogenic infections while remaining nontoxic to mammalian cells. The engineered SNFs have enormous potential for treating and managing microbial infections.

Vibrio Phage VMJ710 Can Prevent and Treat Disease Caused by Pathogenic MDR V. cholerae O1 in an Infant Mouse Model

Cholera, a disease of antiquity, is still festering in developing countries that lack safe drinking water and sewage disposal. Vibrio cholerae, the causative agent of cholera, has developed multi-drug resistance to many antimicrobial agents. In aquatic habitats, phages are known to influence the occurrence and dispersion of pathogenic V. cholerae. We isolated Vibrio phage VMJ710 from a community sewage water sample of Manimajra, Chandigarh, in 2015 during an outbreak of cholera. It lysed 46% of multidrug-resistant V. cholerae O1 strains. It had significantly reduced the bacterial density within the first 4-6 h of treatment at the three multiplicity of infection (MOI 0.01, 0.1, and 1.0) values used. No bacterial resistance was observed against phage VMJ710 for 20 h in the time-kill assay. It is nearest to an ICP1 phage, i.e., Vibrio phage ICP1_2012 (MH310936.1), belonging to the class Caudoviricetes. ICP1 phages have been the dominant bacteriophages found in cholera patients' stools since 2001. Comparative genome analysis of phage VMJ710 and related phages indicated a high level of genetic conservation. The phage was stable over a wide range of temperatures and pH, which will be an advantage for applications in different environmental settings. The phage VMJ710 showed a reduction in biofilm mass growth, bacterial dispersal, and a clear disruption of bacterial biofilm structure. We further tested the phage VMJ710 for its potential therapeutic and prophylactic properties using infant BALB/c mice. Bacterial counts were reduced significantly when phages were administered before and after the challenge of orogastric inoculation with V. cholerae serotype O1. A comprehensive whole genome study revealed no indication of lysogenic genes, genes associated with possible virulence factors, or antibiotic resistance. Based on all these properties, phage VMJ710 can be a suitable candidate for oral phage administration and could be a viable method of combatting cholera infection caused by MDR V. cholerae pathogenic strains.

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.

The Antibiofilm Effects of Antimony Tin Oxide Nanoparticles against Polymicrobial Biofilms of Uropathogenic Escherichia coli and Staphylococcus aureus

Biofilms are responsible for persistent or recurring microbial infections. Polymicrobial biofilms are prevalent in environmental and medical niches. Dual-species biofilms formed by Gram-negative uropathogenic Escherichia coli (UPEC) and Gram-positive Staphylococcus aureus are commonly found in urinary tract infection sites. Metal oxide nanoparticles (NPs) are widely studied for their antimicrobial and antibiofilm properties. We hypothesized that antimony-doped tin (IV) oxide (ATO) NPs, which contain a combination of antimony (Sb) and tin (Sn) oxides, are good antimicrobial candidates due to their large surface area. Thus, we investigated the antibiofilm and antivirulence properties of ATO NPs against single- and dual-species biofilms formed by UPEC and S. aureus. ATO NPs at 1 mg/mL significantly inhibited biofilm formation by UPEC, S. aureus, and dual-species biofilms and reduced their main virulence attributes, such as the cell surface hydrophobicity of UPEC and hemolysis of S. aureus and dual-species biofilms. Gene expression studies showed ATO NPs downregulated the hla gene in S. aureus, which is essential for hemolysin production and biofilm formation. Furthermore, toxicity assays with seed germination and Caenorhabditis elegans models confirmed the non-toxic nature of ATO NPs. These results suggest that ATO nanoparticles and their composites could be used to control persistent UPEC and S. aureus infections.

In vitro evaluation of biofilm formation by Candida parapsilosis and Enterobacter cloacae. Scanning electron microscopy and efficacy of antimicrobial combinations study

Fungal-bacterial infections are being increasingly recognized in clinical settings, and the interaction between these species in polymicrobial biofilms often lead to infections that are highly resistant to treatment. In this in vitro study, we analyzed the formation of mixed biofilms using clinically isolated Candida parapsilosis and Enterobacter cloacae. Additionally, we assessed the potential of conventional antimicrobials, both alone and in combination, for treating polymicrobial biofilms built by these human pathogens. Our results demonstrate that C. parapsilosis and E. cloacae are capable of forming mixed biofilms, as confirmed by scanning electron microscopy. Interestingly, we found that colistin alone or in combination with antifungal drugs was highly effective reducing up to 80% of the total biomass of polymicrobial biofilms.

Using SMART Magnetic Fluids and Gels for Prevention and Destruction of Bacterial Biofilms

Biofouling is a major problem in all natural and artificial settings where solid surfaces meet liquids in the presence of living microorganisms. Microbes attach to the surface and form a multidimensional slime that protects them from unfavorable environments. These structures, known as biofilms, are detrimental and very hard to remove. Here, we used SMART magnetic fluids [ferrofluids (FFs), magnetorheological fluids (MRFs), and ferrogels (FGs) containing iron oxide nano/microparticles] and magnetic fields to remove bacterial biofilms from culture tubes, glass slides, multiwell plates, flow cells, and catheters. We compared the ability of different SMART fluids to remove biofilms and found that commercially available, as well as homemade, FFs, MRFs, and FGs can successfully remove biofilm more efficiently than traditional mechanical methods, especially from textured surfaces. In tested conditions, SMARTFs reduced bacterial biofilms by five orders of magnitude. The ability to remove biofilm increased with the amount of magnetic particles; therefore, MRFs, FG, and homemade FFs with high amounts of iron oxide were the most efficient. We showed also that SMART fluid deposition can protect a surface from bacterial attachment and biofilm formation. Possible applications of these technologies are discussed.

Combating Bacterial Biofilms: Current and Emerging Antibiofilm Strategies for Treating Persistent Infections

Biofilms are intricate multicellular structures created by microorganisms on living (biotic) or nonliving (abiotic) surfaces. Medically, biofilms often lead to persistent infections, increased antibiotic resistance, and recurrence of infections. In this review, we highlighted the clinical problem associated with biofilm infections and focused on current and emerging antibiofilm strategies. These strategies are often directed at disrupting quorum sensing, which is crucial for biofilm formation, preventing bacterial adhesion to surfaces, impeding bacterial aggregation in viscous mucus layers, degrading the extracellular polymeric matrix, and developing nanoparticle-based antimicrobial drug complexes which target persistent cells within the biofilm core. It is important to acknowledge, however, that the use of antibiofilm agents faces obstacles, such as limited effectiveness in vivo, potential cytotoxicity to host cells, and propensity to elicit resistance in targeted biofilm-forming microbes. Emerging next generation antibiofilm strategies, which rely on multipronged approaches, were highlighted, and these benefit from current advances in nanotechnology, synthetic biology, and antimicrobial drug discovery. The assessment of current antibiofilm mitigation approaches, as presented here, could guide future initiatives toward innovative antibiofilm therapeutic strategies. Enhancing the efficacy and specificity of some emerging antibiofilm strategies via careful investigations, under conditions that closely mimic biofilm characteristics within the human body, could bridge the gap between laboratory research and practical application.

Investigation of the cleaning performance of commercial orthodontic cleaning tablets regarding biofilm removal on PMMA test specimens : An ex vivo study

PURPOSE

The purpose of this ex vivo study was to compare the cleaning performance of three commercially available orthodontic cleaners on polymethyl methacrylate (PMMA) test specimens covered with biofilm.

METHODS

Twenty subjects wore an individually manufactured vacuum-formed maxillary splint with four integrated PMMA test specimens for 7 days. The four test specimens were located on the buccal surfaces of the maxillary molars. After a 7-day wearing period, the PMMA test specimens colonized by biofilm were divided into two halves. One half was placed in 150 ml of tap water or in 150 ml of cleaning solution of the cleaners Retainer Brite® (Dentsply International Raintree Essix, Sarasota, FL, USA), Kukis® Xpress (Reckitt Benckiser, Heidelberg, Germany) or Dontodent (Propack, Heidelberg, Germany) while the other half remained uncleaned. The modified o‑phthaldialdehyde (OPA) method was used to determine the amount of protein on both halves of the test specimens. The difference was tested for significance as a measure of the cleaning effect using a paired sample t‑test.

RESULTS

The cleaning performance of the three orthodontic cleaners was higher than the cleaning performance of tap water (mean 25.9 ± 6.5%). While Retainer Brite® (mean 54.5 ± 7.1%) removed significantly more biofilm than Dontodent (mean 41.5 ± 9.2%, p < 0.001) and Kukis® Xpress (mean 39.9 ± 11.5%, p < 0.001), there was no significant difference in the cleaning performance between Kukis® Xpress and Dontodent (p = 1).

CONCLUSION

Seven-day-old biofilm is only removed partially by the investigated orthodontic cleaners, so that they are not suitable as the only measure for removing established biofilms.

Robotic-assisted knee replacement surgery & infection: A historical foundation, systematic review and meta-analysis

Background

An increasing proportion of Knee arthroplasty is performed using robotic-assisted surgical techniques. This study sought to use a meta-analytical approach to establish summary rates of surgical site infection in robotic-assisted procedures and compare the rate of deep infections to those seen in conventional knee arthroplasty.

Methods

This study performed a literature search across four online databases to establish a summary rate of surgical site infection across two categories: deep infection and superficial and pin-site infections. This was processed with the aid of a bespoke data-extraction tool. Risk of Bias analysis was performed using the Cochrane RoB2 tool. Meta-analysis was then performed with tests for heterogeneity and a DerSimonian-Laird random effects model.

Results

A total of 17 studies were identified as appropriate for inclusion in the meta-analysis. The summary rate of overall surgical site infections within one year of robotic knee arthroplasty was found to be 0.568% (SE = 0.183, 95% CI = 0.209-0.927). Deep infections fell to 0.154% (SE = 0.069, 95% CI = 0.018-0.290) and to 0.347% (SE = 0.109, 95% CI = 0.133-0.561) in superficial and pin-site infections.

Conclusion

The surgical site infection rates were found to be low across robotic knee arthroplasty. Further research is required to prove its superiority compared to the conventional, non-robotic technique.

Characterization of a soluble library of the Pseudomonas aeruginosa PAO1 membrane proteome with emphasis on c-di-GMP turnover enzymes

Studies of protein-protein interactions in membranes are very important to fully understand the biological function of a cell. The extraction of proteins from the native membrane environment is a critical step in the preparation of membrane proteins that might affect the stability of protein complexes. In this work, we used the amphiphilic diisobutylene/maleic acid copolymer to extract the membrane proteome of the opportunistic pathogen Pseudomonas aeruginosa, thereby creating a soluble membrane-protein library within a native-like lipid-bilayer environment. Size fractionation of nanodisc-embedded proteins and subsequent mass spectrometry enabled the identification of 3358 proteins. The native membrane-protein library showed a very good overall coverage compared to previous proteome data. The pattern of size fractionation indicated that protein complexes were preserved in the library. More than 20 previously described complexes, e.g. the SecYEG and Pili complexes, were identified and analyzed for coelution. Although the mass-spectrometric dataset alone did not reveal new protein complexes, combining pulldown assays with mass spectrometry was successful in identifying new protein interactions in the native membrane-protein library. Thus, we identified several candidate proteins for interactions with the membrane phosphodiesterase NbdA, a member of the c-di-GMP network. We confirmed the candidate proteins CzcR, PA4200, SadC, and PilB as novel interaction partners of NbdA using the bacterial adenylate cyclase two-hybrid assay. Taken together, this work demonstrates the usefulness of the native membrane-protein library of P. aeruginosa for the investigation of protein interactions and membrane-protein complexes. Data are available via ProteomeXchange with identifiers PXD039702 and PXD039700.

Imaging biofilms using fluorescence in situ hybridization: seeing is believing

Biofilms are complex structures with an intricate relationship between the resident microorganisms, the extracellular matrix, and the surrounding environment. Interest in biofilms is growing exponentially given its ubiquity in so diverse fields such as healthcare, environmental and industry. Molecular techniques (e.g., next-generation sequencing, RNA-seq) have been used to study biofilm properties. However, these techniques disrupt the spatial structure of biofilms; therefore, they do not allow to observe the location/position of biofilm components (e.g., cells, genes, metabolites), which is particularly relevant to explore and study the interactions and functions of microorganisms. Fluorescence in situ hybridization (FISH) has been arguably the most widely used method for an in situ analysis of spatial distribution of biofilms. In this review, an overview on different FISH variants already applied on biofilm studies (e.g., CLASI-FISH, BONCAT-FISH, HiPR-FISH, seq-FISH) will be explored. In combination with confocal laser scanning microscopy, these variants emerged as a powerful approach to visualize, quantify and locate microorganisms, genes, and metabolites inside biofilms. Finally, we discuss new possible research directions for the development of robust and accurate FISH-based approaches that will allow to dig deeper into the biofilm structure and function.

Advances in cholera research: from molecular biology to public health initiatives

The aquatic bacterium Vibrio cholerae is the etiological agent of the diarrheal disease cholera, which has plagued the world for centuries. This pathogen has been the subject of studies in a vast array of fields, from molecular biology to animal models for virulence activity to epidemiological disease transmission modeling. V. cholerae genetics and the activity of virulence genes determine the pathogenic potential of different strains, as well as provide a model for genomic evolution in the natural environment. While animal models for V. cholerae infection have been used for decades, recent advances in this area provide a well-rounded picture of nearly all aspects of V. cholerae interaction with both mammalian and non-mammalian hosts, encompassing colonization dynamics, pathogenesis, immunological responses, and transmission to naïve populations. Microbiome studies have become increasingly common as access and affordability of sequencing has improved, and these studies have revealed key factors in V. cholerae communication and competition with members of the gut microbiota. Despite a wealth of knowledge surrounding V. cholerae, the pathogen remains endemic in numerous countries and causes sporadic outbreaks elsewhere. Public health initiatives aim to prevent cholera outbreaks and provide prompt, effective relief in cases where prevention is not feasible. In this review, we describe recent advancements in cholera research in these areas to provide a more complete illustration of V. cholerae evolution as a microbe and significant global health threat, as well as how researchers are working to improve understanding and minimize impact of this pathogen on vulnerable populations.

The potency of bacteriophages isolated from chicken intestine and beef tribe to control biofilm-forming bacteria, Bacillus subtilis

Biofilm becomes one of the crucial food safety problems in the food industry as the formation of biofilm can be a source of contamination. To deal with the problem, an industry generally employs physical and chemical methods including sanitizers, disinfectants, and antimicrobials to remove biofilm. However, the use of these methods may bring about new problems, which are bacterial resistance in the biofilm and the risk for product contamination. New strategies to deal with bacterial biofilms are needed. Bacteriophages (phages), as a green alternative to chemical, have re-emerged as a promising approach to treat bacterial biofilm. In the present study, the potential of lytic phages which have antibiofilm activity on biofilm-forming bacteria (Bacillus subtilis), were isolated from chicken intestines and beef tripe obtained from Indonesian traditional markets using host cells obtained isolated from these samples. Phages isolation was conducted by using double layer agar technique. A lytic test of phages was administered on biofilm-forming bacteria. The difference of turbidity level between control (which were not infected by phages) and the test tubes containing host bacteria infected by phages was investigated. The infection time for the production of phages was determined based on the level of clarity of the media in the test tube with a longer lysate addition time. Three phages were isolated namely: ϕBS6, ϕBS8, and ϕUA7. It showed the ability to inhibit B. subtilis as biofilm-forming spoilage bacteria. The best inhibition results were obtained from ϕBS6. Infection with ϕBS6 in B. subtilis lead to 0.5 log cycle decreased in bacterial cells. This study showed that isolated phages might be used as a potential approach for handling the problem of biofilm formation by B. subtilis.

Antibiotics Resistance and Adhesive Properties of Clinical Staphylococcus aureus Isolated from Wound Infections

Staphylococcus aureus (S. aureus) is a ubiquitous pathogen responsible for several severe infections. This study aimed to investigate the adhesive properties and antibiotic resistance among clinical S. aureus isolated from Hail Hospital Province, Kingdom of Saudi Arabia (KSA), using molecular approaches. This study was conducted according to the ethical committee at Hail's guidelines on twenty-four S. aureus isolates. A polymerase chain reaction (PCR) was performed to identify genes encoding the β-lactamase resistance (blaZ), methicillin resistance (mecA), fluoroquinolone resistance (norA), nitric oxide reductase (norB), fibronectin (fnbA and fnbB), clumping factor (clfA) and intracellular adhesion factors (icaA and icaD). This qualitative study tested adhesion based on exopolysaccharide production on Congo red agar (CRA) medium and biofilm formation on polystyrene by S. aureus strains. Among 24 isolates, the cna and blaz were the most prevalent (70.8%), followed by norB (54.1%), clfA (50.0%), norA (41.6%), mecA and fnbB (37.5%) and fnbA (33.3%). The presence of icaA/icaD genes was demonstrated in almost all tested strains in comparison to the reference strain, S. aureus ATCC 43300. The phenotypic study of adhesion showed that all tested strains had moderate biofilm-forming capacity on polystyrene and represented different morphotypes on a CRA medium. Five strains among the twenty-four harbored the four genes of resistance to antibiotics (mecA, norA, norB and blaz). Considering the genes of adhesion (cna, clfA, fnbA and fnbB), these genes were present in 25% of the tested isolates. Regarding the adhesive properties, the clinical isolates of S. aureus formed biofilm on polystyrene, and only one strain (S17) produced exopolysaccharides on Congo red agar. All these results contribute to an understanding that the pathogenesis of clinical S. aureus isolates is due to their antibiotic resistance and adhesion to medical material.

Resistance, Tolerance, Virulence and Bacterial Pathogen Fitness-Current State and Envisioned Solutions for the Near Future

The current antibiotic crisis and the global phenomena of bacterial resistance, inherited and non-inherited, and tolerance-associated with biofilm formation-are prompting dire predictions of a post-antibiotic era in the near future. These predictions refer to increases in morbidity and mortality rates as a consequence of infections with multidrug-resistant or pandrug-resistant microbial strains. In this context, we aimed to highlight the current status of the antibiotic resistance phenomenon and the significance of bacterial virulence properties/fitness for human health and to review the main strategies alternative or complementary to antibiotic therapy, some of them being already clinically applied or in clinical trials, others only foreseen and in the research phase.

Antibiotic treatment can exacerbate biofilm-associated infection by promoting quorum cheater development

Quorum cheating, a socio-microbiological process that is based on mutations in cell density-sensing (quorum-sensing) systems, has emerged as an important contributor to biofilm-associated infection in the leading human pathogen Staphylococcus aureus. This is because inactivation of the staphylococcal Agr quorum-sensing system leads to pronounced biofilm formation, increasing resistance to antibiotics and immune defense mechanisms. Since biofilm infections in the clinic usually progress under antibiotic treatment, we here investigated whether such treatment promotes biofilm infection via the promotion of quorum cheating. Quorum cheater development was stimulated by several antibiotics used in the treatment of staphylococcal biofilm infections more strongly in biofilm than in the planktonic mode of growth. Sub-inhibitory concentrations of levofloxacin and vancomycin were investigated for their impact on biofilm-associated (subcutaneous catheter-associated and prosthetic joint-associated infection), where in contrast to a non-biofilm-associated subcutaneous skin infection model, a significant increase of the bacterial load and development of agr mutants was observed. Our results directly demonstrate the development of Agr dysfunctionality in animal biofilm-associated infection models and reveal that inappropriate antibiotic treatment can be counterproductive for such infections as it promotes quorum cheating and the associated development of biofilms.

Biofilm growth monitoring using guided wave ultralong-range Surface Plasmon Resonance: A proof of concept

Unwelcomed biofilms are problematic in food industries, surgical devices, marine applications, and wastewater treatment plants, essentially everywhere where there is moisture. Very recently, label-free advanced sensors such as localized and extended surface plasmon resonance (SPR) have been explored as tools for monitoring biofilm formation. However, conventional noble metal SPR substrates suffer from low penetration depth (100-300 nm) into the dielectric medium above the surface, preventing the reliable detection of large entities of single or multi-layered cell assemblies like biofilms which can grow up to a few micrometers or more. In this study, we propose using a plasmonic insulator-metal-insulator (IMI) structure (SiO₂-Ag-SiO₂) with a higher penetration depth based on a diverging beam single wavelength format of Kretschmann configuration in a portable SPR device. An SPR line detection algorithm for locating the reflectance minimum of the device helps to view changes in refractive index and accumulation of the biofilm in real-time down to 10^-7 RIU precision. The optimized IMI structure exhibits strong penetration dependence on wavelength and incidence angle. Within the plasmonic resonance, different angles penetrate different depths, showing a maximum near the critical angle. At the wavelength of 635 nm, a high penetration depth of more than 4 μm was obtained. Compared to a thin gold film substrate, for which the penetration depth is only ∼200 nm, the IMI substrate provides more reliable results. The average thickness of the biofilm after 24 h of growth was found to be between 6 and 7 μm with ∼63% live cell volume, as estimated from confocal microscopic images using an image processing tool. To explain this saturation thickness, a graded index biofilm structure is proposed in which the refractive index decreases with the distance from the interface. Furthermore, when plasma-assisted degeneration of biofilms was studied in a semi-real-time format, there was almost no effect on the IMI substrate compared to the gold substrate. The growth rate over the SiO₂ surface was higher than on gold, possibly due to differences between surface charge effects. On the gold, the excited plasmon generates an oscillating cloud of electrons, while for the SiO₂ case, this does not happen. This methodology can be utilized to detect and characterize biofilms with better signal reliability with respect to concentration and size dependence.

Using Genomics to Decipher the Enigmatic Properties and Survival Adaptation of Candidate Phyla Radiation

Microbial ecology is a critical field for understanding the composition, diversity, and functions of microorganisms in various environmental and health-related processes. The discovery of Candidate Phyla Radiation (CPR) through culture-independent methods has introduced a new division of microbes characterized by a symbiotic/parasitic lifestyle, small cell size, and small genome. Despite being poorly understood, CPRs have garnered significant attention in recent years due to their widespread detection in a variety of environmental and clinical samples. These microorganisms have been found to exhibit a high degree of genetic diversity compared to other microbes. Several studies have shed light on their potential importance in global biogeochemical cycles and their impact on various human activities. In this review, we provide a systematic overview of the discovery of CPRs. We then focus on describing how the genomic characteristics of CPRs have helped them interact with and adapt to other microbes in different ecological niches. Future works should focus on discovering the metabolic capacities of CPRs and, if possible, isolating them to obtain a better understanding of these microorganisms.

Synergistic Antifungal Interaction between Pseudomonas aeruginosa LV Strain Metabolites and Biogenic Silver Nanoparticles against Candida auris

Candida auris has been found to be a persistent colonizer of human skin and a successful pathogen capable of causing potentially fatal infection, especially in immunocompromised individuals. This fungal species is usually resistant to most antifungal agents and has the ability to form biofilms on different surfaces, representing a significant therapeutic challenge. Herein, the effect of metabolites of Pseudomonas aeruginosa LV strain, alone and combined with biologically synthesized silver nanoparticles (bioAgNP), was evaluated in planktonic and sessile (biofilm) cells of C. auris. First, the minimal inhibitory and fungicidal concentration values of 3.12 and 6.25 μg/mL, respectively, were determined for F4a, a semi-purified bacterial fraction. Fluopsin C and indolin-3-one seem to be the active components of F4a. Like the semi-purified fraction, they showed a time- and dose-dependent fungicidal activity. F4a and bioAgNP caused severe changes in the morphology and ultrastructure of fungal cells. F4a and indolin-3-one combined with bioAgNP exhibited synergistic fungicidal activity against planktonic cells. F4a, alone or combined with bioAgNP, also caused a significant decrease in the number of viable cells within the biofilms. No cytotoxicity to mammalian cells was detected for bacterial metabolites combined with bioAgNP at synergistic concentrations that presented antifungal activity. These results indicate the potential of F4a combined with bioAgNP as a new strategy for controlling C. auris infections.

Interspecies interactions in mixed-species biofilms formed by Enterococcus faecalis and gram-negative bacteria isolated from polymicrobial diabetic foot ulcers

Diabetic foot ulcers (DFU) are exacerbated by bacterial colonisation. Here, a high prevalence of Enterococcus faecalis was observed in DFU patients from an Argentinean hospital. E. faecalis was frequently co-isolated with Escherichia coli, Morganella morganii, and Pseudomonas aeruginosa. The effect of interspecies interactions on bacterial growth was investigated in mixed-species macrocolony biofilms developed in Lubbock-Glc-agar. Similar cell counts were found for E. faecalis and M. morganii growing in mixed and single-species biofilms. An E. faecalis strain showed 1 Log higher cell counts in mixed biofilms with E. coli. Remarkably, E. faecalis strains showed 2 to 4 Log higher cell counts in mixed biofilms with P. aeruginosa. This effect was not observed in planktonic growth or biofilms developed in tryptic soy agar. The present findings reveal bacterial interactions that benefit E. faecalis in mixed-species biofilms, mainly with P. aeruginosa, in a medium that partially mimics the nutrients found in DFU.

Antibacterial and Antibiofilm Activity of Different Species of Fabiana sp. Extract Obtained via Maceration and Ultrasound-Assisted Extraction against Staphylococcus epidermidis

Staphylococcus epidermidis is an opportunistic pathogen that, under certain conditions, can induce aggravated infectious processes, mainly in immunosuppressed patients. Moreover, S. epidermidis is one of the leading causes of medical device- and implant-associated infections and is also recognized as a canonical biofilm producer. Fabiana punensis, F. densa and F. patagonica are three medicinal plants that grow in arid environments in Argentina (Altoandina, Puna, Prepuna and Monte regions). In this work, we studied the antimicrobial activity of alcoholic extracts of these plant species obtained via maceration (M) and ultrasound-assisted extraction (UAE) against S. epidermidis. In addition, the antibiofilm activity of the F. densa extract was also evaluated. It was found that the extracts obtained via M did not present differences with those obtained via UAE regarding the chemical profile. F. densa showed the lowest minimum inhibitory concentration (MIC) value (75 µg GAE/mL). At concentrations higher than the MIC, the extract induced the release of cellular constituents. At the concentration of 1/8× MIC, the extract inhibited biofilm formation by 78%, reducing metabolic activity by 67%. On the other hand, it presented a low percentage of preformed biofilm removal. In all assays, gallic acid (GA) has been used as a reference antimicrobial compound. Finally, it was shown via microscopy visualization that the extract reduces adhesion to hydrophobic and hydrophilic surfaces. Thus, F. densa extracts could potentially be used for the antibiotic treatment of infections produced by S. epidermidis or as an inhibitor agent of production biofilm, avoiding infections caused by medical devices.

Ultrasonic irradiation enhanced the efficacy of antimicrobial photodynamic therapy against methicillin-resistant Staphylococcus aureus biofilm

Antimicrobial photodynamic therapy (aPDT) is a non-pharmacological antimicrobial regimen based on light, photosensitizer and oxygen. It has become a potential method to inactivate multidrug-resistant bacteria. However, limited by the delivery of photosensitizer (PS) in biofilm, eradicating biofilm-associated infections by aPDT remains challenging. This study aimed to explore the feasibility of combining ultrasonic irradiation with aPDT to enhance the efficacy of aPDT against methicillin-resistant staphylococcus aureus (MRSA) biofilm. A cationic benzylidene cyclopentanone photosensitizer with much higher selectivity to bacterial cells than mammalian cells were applied at the concentration of 10 μM. 532 nm laser (40 mW/cm², 10 min) and 1 MHz ultrasound (500 mW/cm², 10 min, simultaneously with aPDT) were employed against MRSA biofilms in vitro. In addition to combined with ultrasonic irradiation and aPDT, MRSA biofilms were treated with laser irradiation only, photosensitizer only, ultrasonic irradiation only, ultrasonic irradiation and photosensitizer, and aPDT respectively. The antibacterial efficacy was determined by XTT assay, and the penetration depth of PS in biofilm was observed using a photoluminescence spectrometer and a confocal laser scanning microscopy (CLSM). In addition, the viability of human dermal fibroblasts (WS-1 cells) after the same treatments mentioned above and the uptake of P3 by WS-1 cells after ultrasonic irradiation were detected by CCK-8 and CLSM in vitro. Results showed that the percent decrease in metabolic activity resulting from the US + aPDT group (75.76%) was higher than the sum of the aPDT group (44.14%) and the US group (9.88%), suggesting synergistic effects. Meanwhile, the diffusion of PS in the biofilm of MRSA was significantly increased by 1 MHz ultrasonic irradiation. Ultrasonic irradiation neither induced the PS uptake by WS-1 cells nor reduced the viability of WS-1 cells. These results suggested that 1 MHz ultrasonic irradiation significantly enhanced the efficacy of aPDT against MRSA biofilm by increasing the penetration depth of PS. In addition, the antibacterial efficacy of aPDT can be enhanced by ultrasonic irradiation, the US + aPDT treatment demonstrated encouraging in vivo antibacterial efficacy (1.73 log₁₀ CFU/mL reduction). In conclusion, the combination of aPDT and 1 MHz ultrasound is a potential and promising strategy to eradicate biofilm-associated infections of MRSA.

Effect of gentamicin on CD3+ T-lymphocyte proliferation for treatment of equine recurrent uveitis: An in vitro study

OBJECTIVE

The objective of the study was to determine the effect of gentamicin on CD3+ T-lymphocyte proliferation and cell viability using an in vitro cell culture model as a means of investigating the mechanism of action of low-dose intravitreal gentamicin injection.

ANIMALS STUDIED

Three adult horses with no evidence of ophthalmic or systemic disease.

PROCEDURE

Peripheral blood lymphocytes were treated with gentamicin at concentrations 37.5 μg/mL, 112.5 μg/mL, 187 μg/mL, 375 μg/mL, or 750 μg/mL then stimulated to proliferate with concanavalin A (ConA). 4',6-diamidino-2-phenylindole (DAPI) and carboxyfluoroscein succinimidyl ester (CSFE) were used as markers of cell viability and cell proliferation, respectively. Following 5-day culture, live cell counts and CSFE fluorescent intensity data were collected via automated cell count and flow cytometry. The experimental design was duplicated using preservative-free gentamicin and a proprietary brand formulation. Statistical analysis was performed using two-way ANOVA with Tukey's multiple comparison test.

RESULTS

No statistically significant comparisons in CD3+ T-lymphocyte live cell counts and geometric mean fluorescent intensity of CSFE were identified between gentamicin concentrations or formulations.

CONCLUSIONS

Gentamicin had no effect on equine peripheral blood CD3+ T-lymphocyte cell viability and proliferation in concentrations ranging from "safe" to "retinotoxic" in relation to intravitreal injection volumes. Low-dose intravitreal gentamicin may not suppress the Th1- and Th17-mediated immune response.

Antibiotic Susceptibility Profiling of Human Pathogenic Staphylococcus aureus Strains Using Whole Genome Sequencing and Genome-Scale Annotation Approaches

Staphylococcus species are major pathogens with increasing importance due to the rise in antibiotic resistance. Whole genome sequencing and genome-scale annotation are promising approaches to study the pathogenicity and dissemination of virulence factors in nosocomial methicillin-resistant and multidrug-resistant bacteria in intensive care units. Draft genome sequences of eight clinical S. aureus strains were assembled and annotated for the prediction of antimicrobial resistance genes, virulence factors, and phylogenetic analysis. Most of the studied S. aureus strains displayed multi-resistance toward the tested drugs, reaching more than seven drugs up to 12 in isolate S22. The mecA gene was detected in three isolates (S14, S21, and S23), mecC was identified in S8 and S9, and blaZ was commonly identified in all isolates except strain S23. Additionally, two complete mobile genomic islands coding for methicillin resistance SCCmec Iva (2B) were identified in strains S21 and S23. Numerous antimicrobial resistance genes (norA, norC, MgrA, tet(45), APH(3')-IIIa, and AAC(6')-APH(2″)) were identified in chromosomes of different strains. Plasmid analysis revealed the presence of blaZ, tetK, and ermC in different plasmid types, located in gene cassettes containing plasmid replicons (rep) and insertion sequences (IS). Additionally, the aminoglycoside-resistant determinants were identified in S1 (APH(3')-IIIa), while AAC(6)-APH(2″) was detected in strains S8 and S14. The trimethoprim (dfrC) resistance gene was detected in S. aureus S21, and the fosfomycin (fosB) resistance gene was detected only in S. aureus S14. We also noted that S. aureus S1 belongs to ST1-t127, which has been reported as one of the most frequent human pathogen types. Additionally, we noted the presence of rare plasmid-mediated mecC-MRSA in some of our isolates.

Collective protection against the type VI secretion system in bacteria

Bacteria commonly face attacks from other strains using the type VI secretion system (T6SS), which acts like a molecular speargun to stab and intoxicate competitors. Here we show how bacteria can work together to collectively defend themselves against these attacks. This project began with an outreach activity: while developing an online computer game of bacterial warfare, we noticed that one strategist ("Slimy") that made extracellular polymeric substances (EPS) was able to resist attacks from another strategist that employed the T6SS ("Stabby"). This observation motivated us to model this scenario more formally, using dedicated agent-based simulations. The model predicts that EPS production can serve as a collective defence mechanism, which protects both producing cells and neighbouring cells that do not make EPS. We then tested our model with a synthetic community that contains a T6SS-wielding attacker (Acinetobacter baylyi), and two T6SS-sensitive target strains (Escherichia coli) that either secrete EPS, or not. As predicted by our modelling, we find that the production of EPS leads to collective protection against T6SS attacks, where EPS producers protect each other and nearby non-producers. We identify two processes that explain this protection: EPS sharing between cells and a second general mechanism whereby groups of resistant cells shield susceptible cells, which we call "flank protection". Our work shows how EPS-producing bacteria can work together to defend themselves from the type VI secretion system.

Biofilm Production by Critical Antibiotic-Resistant Pathogens from an Equine Wound

As in human medicine, in veterinary medicine, chronic wounds are often related to polymicrobial infections and the presence of a biofilm, which compromises the effectiveness of therapeutic approaches. In this study, a Lusitano mare presented a 21-day-old chronic wound that was only being treated with an antiseptic. A swab sample was collected, and three isolates of Staphylococcus aureus and one of Pseudomonas aeruginosa were isolated. S. aureus did not show resistance to a panel of antibiotics. However, the P. aeruginosa isolate showed a resistance profile to carbapenems and fluoroquinolones, which may suggest a cross-resistance between antiseptic and antibiotics, given that no antibiotic therapy was applied to the wound or the mare in the previous year. Further experiments were conducted to assess the ability of the isolates to form biofilms, and to ascertain their susceptibility to gentamicin. The results demonstrated that the isolates produced biofilms. Gentamicin at the minimum inhibitory concentration (MIC) and 10× MIC caused biofilm removal between 59.3% and 85.7%, with the highest removal percentage being obtained for the P. aeruginosa isolate (at 10× MIC concentration). This study reveals that an equine wound was colonized by antibiotic resistant bacteria, and that all the wound colonizers could form biofilms, demonstrating the relevance of an adequate diagnosis and treatment when there is a suspicion of a biofilm-infected wound. It also highlights the possibility of resistance transmission between animals, animals and humans, or animals and the environment.

Role of Microbial Interactions across Food-Related Bacteria on Biofilm Population and Biofilm Decontamination by a TiO2-Nanoparticle-Based Surfactant

Microbial interactions play an important role in initial cell adhesion and the endurance of biofilm toward disinfectant stresses. The present study aimed to evaluate the effect of microbial interactions on biofilm formation and the disinfecting activity of an innovative photocatalytic surfactant based on TiO₂ nanoparticles. Listeria monocytogenes, Salmonella Enteritidis, Escherichia coli, Leuconostoc spp., Latilactobacillus sakei, Serratia liquefaciens, Serratia proteomaculans, Citrobacter freundii, Hafnia alvei, Proteus vulgaris, Pseudomonas fragi, and Brochothrix thermosphacta left to form mono- or dual-species biofilms on stainless steel (SS) coupons. The effectiveness of the photocatalytic disinfectant after 2 h of exposure under UV light on biofilm decontamination was evaluated. The effect of one parameter i.e., exposure to UV or disinfectant, was also determined. According to the obtained results, the microbial load of a mature biofilm depended on the different species or dual species that had adhered to the surface, while the presence of other species could affect the biofilm population of a specific microbe (p < 0.05). The disinfectant strengthened the antimicrobial activity of UV, as, in most cases, the remaining biofilm population was below the detection limit of the method. Moreover, the presence of more than one species affected the resistance of the biofilm cells to UV and the disinfectant (p < 0.05). In conclusion, this study confirms that microbial interactions affected biofilm formation and decontamination, and it demonstrates the effectiveness of the surfactant with the photocatalytic TiO₂ agent, suggesting that it could be an alternative agent with which to disinfect contaminated surfaces.

Dead space management strategies in the treatment of chronic osteomyelitis: a retrospective review

PURPOSE

Dead space management is critically important during the treatment of chronic osteomyelitis. Many dead space management strategies are available, each with their respective advantages and shortcomings. This study aims to present the outcomes and complications of dead space management strategies employed in the treatment of chronic osteomyelitis at a single tertiary level musculoskeletal unit.

METHODS

A retrospective review of dead space management strategies employed at a tertiary-level musculoskeletal infection unit was conducted. Patients of any age treated for chronic osteomyelitis of the appendicular skeleton with a minimum follow-up of 6 months were included in the study. Data were collected regarding patient demographics, aetiology and site of infection, dead space management strategy employed, follow-up period and outcome in terms of resolution of infection.

RESULTS

A final cohort of 132 patients underwent surgical treatment with a dedicated dead space management strategy for chronic osteomyelitis of the appendicular skeleton. Eleven patients (8%) experienced a recurrence of infection. Seven patients (63%) with recurrence were type B hosts, while four patients (37%) were type A hosts.

CONCLUSION

Dead space management is an integral part of treating chronic osteomyelitis; however, no guidelines currently exist regarding the most appropriate strategy. Favourable results are achievable in low to middle-income countries, and it is evident that no dead space management strategy is superior to another. The pursuit for the ideal void filler is ongoing.

LEVEL OF EVIDENCE

III.

Exploring the oral microbiome: an updated multidisciplinary oral healthcare perspective

The oral cavity is home to diverse microbial content, collectively called as the oral microbiome. The latest technological advancements have unraveled the intricacies of the oral microbiome.  It can be of great importance for oral health care givers to know the fundamentals and latest developments in the field of the oral microbiome, as oral dysbiosis is associated with many common diseases frequently seen and managed by them. These diseases include dental caries, periodontitis, mucosal diseases (such as oral leukoplakia, oral lichen planus, and systemic lupus erythematosus), oral cancers, and even co-infections related to the current COVID-19 pandemic. The emergence of new genomic and molecular biology methodologies has been pivotal for understanding the role of the human microbiome in health and disease. The current review compiles oral microbiome in health and disease with a multidisciplinary dental approach. The insight into the oral microbiome, which is provided dental specialty wise in the current article will initiate and guide researchers of various disciplines in developing microbiome-based therapeutic or prophylactic management strategies, managing public health challenges by microbiome-based boarder interventions and divert resources for preserving and achieving a balanced oral microbiome.

Food-grade titanium dioxide can affect microbiota physiology, adhesion capability, and interbacterial interactions: A study onL. rhamnosus and E. faecium

Food-grade titanium dioxide (TiO₂-FG) is a widespread metal oxide used in the food industries. Recently, the European Food Safety Authority concluded that TiO₂-FG cannot be considered safe for consumption due to its genotoxicity; however, its effect on the gut microbiota has not yet been completely unraveled. We studied the effects of TiO₂-FG (0.125 mg/mL) on Lactobacillus rhamnosus GG (LGG) and Enterococcus faecium NCIMB10415 (Ent), in particular some physiological and phenotypic traits (growth kinetics, bile salts, and ampicillin resistance) and their interactions with the host (auto-aggregation, biofilm formation, and adhesion on Caco-2/TC7 monolayers) and other gut microorganisms (antimicrobial activity towards pathogens). The results obtained revealed that TiO₂-FG alters both LGG and Ent growth and lowers bile resistance (62 and 34.5%, respectively) and adhesion on Caco-2/TC7 monolayers (34.8 and 14.16%, respectively). The other outcomes were strictly species-specific: Ent showed a lower ampicillin sensitivity (14.48%) and auto-aggregation (38.1%), while LGG showed a reduced biofilm formation (37%) and antimicrobial activity towards Staphylococcus aureus (35.73%). Overall, these results suggest an adverse effect of TiO₂-FG on both the endogenous and exogenously administered probiotics, contributing to the argument against using TiO₂-FG as a food additive.

Role of Metabolic Adaptation of Streptococcus suis to Host Niches in Bacterial Fitness and Virulence

Streptococcus suis, both a common colonizer of the porcine upper respiratory tract and an invasive pig pathogen, successfully adapts to different host environments encountered during infection. Whereas the initial infection mainly occurs via the respiratory tract, in a second step, the pathogen can breach the epithelial barrier and disseminate within the whole body. Thereby, the pathogen reaches other organs such as the heart, the joints, or the brain. In this review, we focus on the role of S. suis metabolism for adaptation to these different in vivo host niches to encounter changes in nutrient availability, host defense mechanisms and competing microbiota. Furthermore, we highlight the close link between S. suis metabolism and virulence. Mutants deficient in metabolic regulators often show an attenuation in infection experiments possibly due to downregulation of virulence factors, reduced resistance to nutritive or oxidative stress and to phagocytic activity. Finally, metabolic pathways as potential targets for new therapeutic strategies are discussed. As antimicrobial resistance in S. suis isolates has increased over the last years, the development of new antibiotics is of utmost importance to successfully fight infections in the future.

Enterobacteria Survival, Percolation, and Leaching on Soil Fertilized with Swine Manure

Swine manure has a high load of pathogens, which can pose a risk to human and environmental health. In Brazil, studies evaluating the survival of pathogens in soil are scarce. Therefore, this study aimed to evaluate the survival, percolation, and leaching of enterobacteria in clayey soil after fertilization with swine manure. For this purpose, soil columns were fertilized with manure spiked with enterobacteria. The microorganisms' behavior was monitored in terms of survival, percolation, and leaching with and without rain. Soil samples were collected, and Escherichia coli and Salmonella enterica serovar Senftemberg were quantified. The results indicated that E. coli survived for a longer period (43 days) than S. senftemberg (14 days). E. coli percolated quickly through the soil, leaching 60 cm in less than 5 min during rainy events and remaining viable for up to 24 h after the rain. The results show the importance of treating manure effectively before being added to the soil. An efficient treatment could be anaerobic digestion, followed by a pond system. Considering the characteristics of swine-producing regions, the load of effluents applied to the soil may percolate, leach, or run off and consequently contaminate water bodies with pathogens.

Flufenamic Acid, a Promising Agent for the Sensitization of Colistin-Resistant Gram-Negative Bacteria to Colistin

The continuous development of multidrug-resistant (MDR) Gram-negative bacteria poses a serious risk to public health on a worldwide scale. Colistin is used as the last-line antibiotic for the treatment of MDR pathogens, and colistin-resistant (COL-R) bacterial emergence thus has the potential to have a severe adverse impact on patient outcomes. In this study, synergistic activity was observed when colistin and flufenamic acid (FFA) were combined and used for the in vitro treatment of clinical COL-R Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, and Acinetobacter baumannii strains, as shown by checkerboard and time-kill assays. Crystal violet staining and scanning electron microscopy revealed the synergistic action of colistin-FFA against biofilms. When used to treat murine RAW264.7 macrophages, this combination did not induce any adverse toxicity. Strikingly, the survival rates of bacterially infected Galleria mellonella larvae were improved by such combination treatment, which was also sufficient to reduce the measured bacterial loads in a murine thigh infection model. Mechanistic propidium iodide (PI) staining analysis further demonstrated the ability of these agents to alter bacterial permeability in a manner that enhanced the efficacy of colistin treatment. Together, these data thus demonstrate that colistin and FFA can be synergistically combined to combat the spread of COL-R Gram-negative bacteria, providing a promising therapeutic tool with the potential to protect against COL-R bacterial infections and improve patient outcomes. IMPORTANCE Colistin is a last-line antibiotic used for the treatment of MDR Gram-negative bacterial infections. However, increasing resistance to it has been observed during clinical treatment. In this work, we assessed the efficacy of the combination of colistin and FFA for the treatment of COL-R bacterial isolates, demonstrating that the combined treatment has effective antibacterial and antibiofilm activities. Due to its low cytotoxicity and good therapeutic effects in vitro, the colistin-FFA combination may be a potential candidate for research into a resistance-modifying agent to combat infections caused by COL-R Gram-negative bacteria.