Control of Biofilm Formation: Antibiotics and Beyond

Green nanotechnology in phytosynthesis and its efficiency in inhibiting bacterial biofilm formation: implications for medicine

Nanotechnology is used in several biomedical applications, including antimicrobial and antibiofilm applications using nanomaterials. Bacterial biofilm varies according to the strain; the matrix is very strong and resistant. In this sense, phytosynthesis is an important method for combating bacterial biofilms through the use of metallic nanoparticles (silver, gold, or copper) with increased marketing and technical-scientific potential. In this review, we seek to gather the leading publications on the use of phytosynthesized metallic nanoparticles against bacterial biofilms. Furthermore, this study aims to understand the main characteristics and parameters of these nanomaterials, their antibiofilm efficiency, and the presence or absence of cytotoxicity in these developed technologies.

Phenotypic and genotypic perspectives on detection methods for bacterial antimicrobial resistance in a One Health context: research progress and prospects

The widespread spread of bacterial antimicrobial resistance (AMR) and multidrug-resistant bacteria poses a significant threat to global public health. Traditional methods for detecting bacterial AMR are simple, reproducible, and intuitive, requiring long time incubation and high labor intensity. To quickly identify and detect bacterial AMR is urgent for clinical treatment to reduce mortality rate, and many new methods and technologies were required to be developed. This review summarizes the current phenotypic and genotypic detection methods for bacterial AMR. Phenotypic detection methods mainly include antimicrobial susceptibility tests, while genotypic detection methods have higher sensitivity and specificity and can detect known or even unknown drug resistance genes. However, most of the current tests are either genotypic or phenotypic and rarely combined. Combining the advantages of phenotypic and genotypic methods, combined with the joint application of multiple rapid detection methods may be the trend for future AMR testing. Driven by rapid diagnostic technology, big data analysis, and artificial intelligence, detection methods of bacterial AMR are expected to constantly develop and innovate. Adopting rational detection methods and scientific data analysis can better address the challenges of bacterial AMR and ensure human health and social well-being.

Advancing Antibiotic-Resistant Microbe Combat: Nanocarrier-Based Systems in Combination Therapy Targeting Quorum Sensing

The increase in antibiotic-resistant bacteria presents a significant risk to worldwide public health, emphasizing the necessity of novel approaches to address infections. Quorum sensing, an essential method of communication among bacteria, controls activities like the formation of biofilms, the production of virulence factors, and the synthesis of secondary metabolites according to the number of individuals in the population. Quorum quenching, which interferes with these processes, emerges as a vital approach to diminish bacterial virulence and prevent biofilm formation. Nanocarriers, characterized by their small size, high surface-area-to-volume ratio, and modifiable surface chemistry, offer a versatile platform for the disruption of bacterial communication by targeting various stages within the quorum sensing pathway. These features allow nanocarriers to infiltrate biofilms, disrupt cell membranes, and inhibit bacterial proliferation, presenting a promising alternative to traditional antibiotics. Integrating nanocarrier-based systems into combination therapies provides a multi-pronged approach to infection control, enhancing both the efficacy and specificity of treatment regimens. Nonetheless, challenges related to the stability, safety, and clinical effectiveness of nanomaterial-based antimicrobial treatments remain. Continued research and development are essential to overcoming these obstacles and fully harnessing the potential of nano-antimicrobial therapies. This review emphasizes the importance of quorum sensing in bacterial behavior and highlights the transformative potential of nanotechnology in advancing antimicrobial treatments, offering innovative solutions to combat antibiotic-resistant pathogens.

Current Strategies for Combating Biofilm-Forming Pathogens in Clinical Healthcare-Associated Infections

The biofilm formation by various pathogens causes chronic infections and poses severe threats to industry, healthcare, and society. They can form biofilm on surfaces of medical implants, heart valves, pacemakers, contact lenses, vascular grafts, urinary catheters, dialysis catheters, etc. These biofilms play a central role in bacterial persistence and antibiotic tolerance. Biofilm formation occurs in a series of steps, and any interference in these steps can prevent its formation. Therefore, the hunt to explore and develop effective anti-biofilm strategies became necessary to decrease the rate of biofilm-related infections. In this review, we highlighted and discussed the current therapeutic approaches to eradicate biofilm formation and combat drug resistance by anti-biofilm drugs, phytocompounds, antimicrobial peptides (AMPs), antimicrobial lipids (AMLs), matrix-degrading enzymes, nanoparticles, phagebiotics, surface coatings, photodynamic therapy (PDT), riboswitches, vaccines, and antibodies. The clinical validation of these findings will provide novel preventive and therapeutic strategies for biofilm-associated infections to the medical world.

Discovery and engineering of a novel peptide, Temporin-WY2, with enhanced in vitro and in vivo efficacy against multi-drug resistant bacteria

Infections by drug-resistant microorganisms are a threat to global health and antimicrobial peptides are considered to be a new hope for their treatment. Temporin-WY2 was identified from the cutaneous secretion of the Ranidae frog, Amolops wuyiensis. It presented with a potent anti-Gram-positive bacterial efficacy, but its activity against Gram-negative bacteria and cancer cell lines was unremarkable. Also, it produced a relatively high lytic effect on horse erythrocytes. For further improvement of its functions, a perfect amphipathic analogue, QUB-1426, and two lysine-clustered analogues, 6K-WY2 and 6K-1426, were synthesised and investigated. The modified peptides were found to be between 8- and 64-fold more potent against Gram-negative bacteria than the original peptide. Additionally, the 6K analogues showed a rapid killing rate. Also, their antiproliferation activities were more than 100-fold more potent than the parent peptide. All of the peptides that were examined demonstrated considerable biofilm inhibition activity. Moreover, QUB-1426, 6K-WY2 and 6K-1426, demonstrated in vivo antimicrobial activity against MRSA and E. coli in an insect larvae model. Despite observing a slight increase in the hemolytic activity and cytotoxicity of the modified peptides, they still demonstrated a improved therapeutic index. Overall, QUB-1426, 6K-WY2 and 6K-1426, with dual antimicrobial and anticancer functions, are proposed as putative drug candidates for the future.

Evaluation of the use of sonication combined with enzymatic treatment for biofilm removal in the microbiological diagnosis of prosthetic joint infection

Sonicating explanted prosthetic implants to physically remove biofilms is a recognized method for improving the microbiological diagnosis of prosthetic joint infection (PJI); however, chemical and enzymatic treatments have been investigated as alternative biofilm removal methods. We compared the biofilm dislodging efficacy of sonication followed by the addition of enzyme cocktails with different activity spectra in the diagnosis of PJI with that of the sonication of fluid cultures alone. Consecutive patients who underwent prosthesis explantation due to infection at our institution were prospectively enrolled for 1 year. The diagnostic procedure included the collection of five intraoperative tissue cultures, sonication of the removed devices, and conventional culture of the sonication fluid. The resulting sonication fluid was also treated with an enzyme cocktail consisting of homemade dispersin B (0.04 µg/mL) and proteinase K (Sigma; 100 µg/mL) for 45 minutes at 37°C. The resulting sonication (S) and sonication with subsequent enzymatic treatment (SE) fluids were plated for aerobic and anaerobic culture broth for 7 days (aerobic) or 14 days (anaerobic). Identification was performed by matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (Bruker). We included 107 patients from whom a prosthetic implant had been removed, among which PJI was diagnosed in 36 (34%). The sensitivity of S alone was significantly greater than that of SE alone (82% vs 71%; P < 0.05). Four patients with PJI were positive after sonication alone but negative after sonication plus enzymatic treatment. The four microorganisms missed after the addition of the enzyme cocktail were Staphylococcus aureus, two coagulase-negative Staphylococci, and Cutibacterium acnes. In conclusion, sonication alone was more sensitive than sonication followed by enzymatic treatment. The combination of these two methods had no synergistic effect; in contrast, the results suggest that the combination of both dislodgment methods affects the viability of gram-positive microorganisms.

IMPORTANCE

While the potential of sonication and enzymes as biofilm dispersal agents has been previously described, the originality of our work resides in the combination of both methods, which is hypothesized to enhance the ability to remove biofilm and, therefore, improve the microbiological diagnosis of PJI.

A 'rich-get-richer' mechanism drives patchy dynamics and resistance evolution in antibiotic-treated bacteria

Bacteria in nature often form surface-attached communities that initially comprise distinct subpopulations, or patches. For pathogens, these patches can form at infection sites, persist during antibiotic treatment, and develop into mature biofilms. Evidence suggests that patches can emerge due to heterogeneity in the growth environment and bacterial seeding, as well as cell-cell signaling. However, it is unclear how these factors contribute to patch formation and how patch formation might affect bacterial survival and evolution. Here, we demonstrate that a 'rich-get-richer' mechanism drives patch formation in bacteria exhibiting collective survival (CS) during antibiotic treatment. Modeling predicts that the seeding heterogeneity of these bacteria is amplified by local CS and global resource competition, leading to patch formation. Increasing the dose of a non-eradicating antibiotic treatment increases the degree of patchiness. Experimentally, we first demonstrated the mechanism using engineered Escherichia coli and then demonstrated its applicability to a pathogen, Pseudomonas aeruginosa. We further showed that the formation of P. aeruginosa patches promoted the evolution of antibiotic resistance. Our work provides new insights into population dynamics and resistance evolution during surface-attached bacterial growth.

Strategic Single-Residue Substitution in the Antimicrobial Peptide Esc(1-21) Confers Activity against Staphylococcus aureus, Including Drug-Resistant and Biofilm Phenotype

Staphylococcus aureus, a bacterium resistant to multiple drugs, is a significant cause of illness and death worldwide. Antimicrobial peptides (AMPs) provide an excellent potential strategy to cope with this threat. Recently, we characterized a derivative of the frog-skin AMP esculentin-1a, Esc(1-21) (1) that is endowed with potent activity against Gram-negative bacteria but poor efficacy against Gram-positive strains. In this study, three analogues of peptide 1 were designed by replacing Gly8 with α-aminoisobutyric acid (Aib), Pro, and dPro (2-4, respectively). The single substitution Gly8 → Aib8 in peptide 2 makes it active against the planktonic form of Gram-positive bacterial strains, especially Staphylococcus aureus, including multidrug-resistant clinical isolates, with an improved biostability without resulting in cytotoxicity to mammalian cells. Moreover, peptide 2 showed a higher antibiofilm activity than peptide 1 against both reference and clinical isolates of S. aureus. Peptide 2 was also able to induce rapid bacterial killing, suggesting a membrane-perturbing mechanism of action. Structural analysis of the most active peptide 2 evidenced that the improved biological activity of peptide 2 is the consequence of a combination of higher biostability, higher α helical content, and ability to reduce membrane fluidity and to adopt a distorted helix, bent in correspondence of Aib8. Overall, this study has shown how a strategic single amino acid substitution is sufficient to enlarge the spectrum of activity of the original peptide 1, and improve its biological properties for therapeutic purposes, thus paving the way to optimize AMPs for the development of new broad-spectrum anti-infective agents.

The Effect of Bovine Trypsin on the Adhesion and pH of Dental Plaque Biofilms: An In Vitro Study

OBJECTIVE

The aim of this study was to investigate the effect of bovine trypsin on the adhesion and pH of dental plaque biofilms.

METHODS

A multispecies dental plaque biofilm model and a single-species dental plaque biofilm model were established in vitro. Three groups were tested: (1) blank control group (aseptic ultrapure water); (2) negative control group (1M Tris-HCl buffer, pH = 7.4); and (3) experimental group (bovine trypsin). Adhesion ability was measured using an automatic microplate reader and visualised by confocal laser scanning microscopy (CLSM). The pH was measured using a pH meter. The expression of gtfB, gtfC, and gtfD was analysed using quantitative real-time polymerase chain reaction.

RESULTS

Adhesion ability in the experimental group was significantly lower than that in the blank group and the negative control group (P < .05); readhesion ability in the experimental group was inhibited for a certain period of time (24-hour multispecies biofilms were inhibited from 4 to 8 hours, and the 48- and 72-hour multispecies biofilms were inhibited from 2 to 6 hours; P < .05). The decrease in pH was inhibited for a certain period of time (24-hour multispecies biofilms were inhibited from 2 to 8 hours, and the 48- and 72-hour multispecies biofilms were inhibited from 1 to 8 hours; P < .05). Expression levels of gtfB, gtfC, gtfD, and ldh in the experimental group were significantly lower than those in the blank group (P < .05).

CONCLUSIONS

Bacterial adhesion, and readhesion, decreasd pH, and expression of adhesion- and acid-related genes by Streptococcus mutans in biofilms could be reduced by bovine trypsin for a certain period of time.

Tapping the biosynthetic potential of marine Bacillus licheniformis LHG166, a prolific sulphated exopolysaccharide producer: structural insights, bio-prospecting its antioxidant, antifungal, antibacterial and anti-biofilm potency as a novel anti-infective lead

The escalating global threat of antimicrobial resistance necessitates prospecting uncharted microbial biodiversity for novel therapeutic leads. This study mines the promising chemical richness of Bacillus licheniformis LHG166, a prolific exopolysaccharide (EPSR2-7.22 g/L). It comprised 5 different monosaccharides with 48.11% uronic acid, 17.40% sulfate groups, and 6.09% N-acetyl glucosamine residues. EPSR2 displayed potent antioxidant activity in DPPH and ABTS+, TAC and FRAP assays. Of all the fungi tested, the yeast Candida albicans displayed the highest susceptibility and antibiofilm inhibition. The fungi Aspergillus niger and Penicillium glabrum showed moderate EPSR2 susceptibility. In contrast, the fungi Mucor circinelloides and Trichoderma harzianum were resistant. Among G+ve tested bacteria, Enterococcus faecalis was the most susceptible, while Salmonella typhi was the most sensitive to G-ve pathogens. Encouragingly, EPSR2 predominantly demonstrated bactericidal effects against both bacterial classes based on MBC/MIC of either 1 or 2 superior Gentamicin. At 75% of MBC, EPSR2 displayed the highest anti-biofilm activity of 88.30% against B. subtilis, while for G-ve antibiofilm inhibition, At 75% of MBC, EPSR2 displayed the highest anti-biofilm activity of 96.63% against Escherichia coli, Even at the lowest dose of 25% MBC, EPSR2 reduced biofilm formation by 84.13% in E. coli, 61.46% in B. subtilis. The microbial metabolite EPSR2 from Bacillus licheniformis LHG166 shows promise as an eco-friendly natural antibiotic alternative for treating infections and oxidative stress.

A Comprehensive Review of Recent Research into the Effects of Antimicrobial Peptides on Biofilms-January 2020 to September 2023

Microbial biofilm formation creates a persistent and resistant environment in which microorganisms can survive, contributing to antibiotic resistance and chronic inflammatory diseases. Increasingly, biofilms are caused by multi-drug resistant microorganisms, which, coupled with a diminishing supply of effective antibiotics, is driving the search for new antibiotic therapies. In this respect, antimicrobial peptides (AMPs) are short, hydrophobic, and amphipathic peptides that show activity against multidrug-resistant bacteria and biofilm formation. They also possess broad-spectrum activity and diverse mechanisms of action. In this comprehensive review, 150 publications (from January 2020 to September 2023) were collected and categorized using the search terms 'polypeptide antibiotic agent', 'antimicrobial peptide', and 'biofilm'. During this period, a wide range of natural and synthetic AMPs were studied, of which LL-37, polymyxin B, GH12, and Nisin were the most frequently cited. Furthermore, although many microbes were studied, Staphylococcus aureus and Pseudomonas aeruginosa were the most popular. Publications also considered AMP combinations and the potential role of AMP delivery systems in increasing the efficacy of AMPs, including nanoparticle delivery. Relatively few publications focused on AMP resistance. This comprehensive review informs and guides researchers about the latest developments in AMP research, presenting promising evidence of the role of AMPs as effective antimicrobial agents.

CheV enhances the virulence of Salmonella Enteritidis, and the Chev-deleted Salmonella vaccine provides immunity in mice

BACKGROUND

Salmonella enteritidis (SE) is a major zoonotic pathogen and causes infections in a variety of hosts. The development of novel vaccines for SE is necessary to eradicate this pathogen. Genetically engineered attenuated live vaccines are more immunogenic and safer. Thus, to develop a live attenuated Salmonella vaccine, we constructed a cheV gene deletion strain of SE (named ΔcheV) and investigated the role of cheV in the virulence of SE. First, the ability to resist environmental stress in vitro, biofilm formation capacity, drug resistance and motility of ΔcheV were analyzed. Secondly, the bacterial adhesion, invasion, intracellular survival assays were performed by cell model. Using a mouse infection model, an in vivo virulence assessment was conducted. To further evaluate the mechanisms implicated by the reduced virulence, qPCR analysis was utilized to examine the expression of the strain's major virulence genes. Finally, the immune protection rate of ΔcheV was evaluated using a mouse model.

RESULTS

Compared to C50336, the ΔcheV had significantly reduced survival ability under acidic, alkaline and thermal stress conditions, but there was no significant difference in survival under oxidative stress conditions. There was also no significant change in biofilm formation ability, drug resistance and motility. It was found that the adhesion ability of ΔcheV to Caco-2 cells remained unchanged, but the invasion ability and survival rate in RAW264.7 cells were significantly reduced. The challenge assay results showed that the LD50 values of C50336 and ΔcheV were 6.3 × 105 CFU and 1.25 × 107 CFU, respectively. After the deletion of the cheV gene, the expression levels of fimD, flgG, csgA, csgD, hflK, lrp, sipA, sipB, pipB, invH, mgtC, sodC, rfbH, xthA and mrr1 genes were significantly reduced. The live attenuated ΔcheV provided 100% protection in mice against SE infection.

CONCLUSION

All the results confirmed that the deletion of the cheV gene reduces the virulence of SE and provides significant immune protection in mice, indicating that ΔcheV could be potential candidates to be explored as live-attenuated vaccines.

Implants coating strategies for antibacterial treatment in fracture and defect models: A systematic review of animal studies

Objective

Fracture-related infection (FRI) remains a major concern in orthopaedic trauma. Functionalizing implants with antibacterial coatings are a promising strategy in mitigating FRI. Numerous implant coatings have been reported but the preventive and therapeutic effects vary. This systematic review aimed to provide a comprehensive overview of current implant coating strategies to prevent and treat FRI in animal fracture and bone defect models.

Methods

A literature search was performed in three databases: PubMed, Web of Science and Embase, with predetermined keywords and criteria up to 28 February 2023. Preclinical studies on implant coatings in animal fracture or defect models that assessed antibacterial and bone healing effects were included.

Results

A total of 14 studies were included in this systematic review, seven of which used fracture models and seven used defect models. Passive coatings with bacteria adhesion resistance were investigated in two studies. Active coatings with bactericidal effects were investigated in 12 studies, four of which used metal ions including Ag+ and Cu2+; five studies used antibiotics including chlorhexidine, tigecycline, vancomycin, and gentamicin sulfate; and the other three studies used natural antibacterial materials including chitosan, antimicrobial peptides, and lysostaphin. Overall, these implant coatings exhibited promising efficacy in antibacterial effects and bone formation.

Conclusion

Antibacterial coating strategies reduced bacterial infections in animal models and favored bone healing in vivo. Future studies of implant coatings should focus on optimal biocompatibility, antibacterial effects against multi-drug resistant bacteria and polymicrobial infections, and osseointegration and osteogenesis promotion especially in osteoporotic bone by constructing multi-functional coatings for FRI therapy.

The translational potential of this paper

The clinical treatment of FRI is complex and challenging. This review summarizes novel orthopaedic implant coating strategies applied to FRI in preclinical studies, and offers a perspective on the future development of orthopaedic implant coatings, which can potentially contribute to alternative strategies in clinical practice.

Understanding the intricacies of microbial biofilm formation and its endurance in chronic infections: a key to advancing biofilm-targeted therapeutic strategies

Bacterial biofilms can adhere to various surfaces in the environment with human beings being no exception. Enclosed in a self-secreted matrix which contains extracellular polymeric substances, biofilms are intricate communities of bacteria that play a significant role across various sectors and raise concerns for public health, medicine and industries. These complex structures allow free-floating planktonic cells to adopt multicellular mode of growth which leads to persistent infections. This is of great concern as biofilms can withstand external attacks which include antibiotics and immune responses. A more comprehensive and innovative approach to therapy is needed in view of the increasing issue of bacterial resistance brought on by the overuse of conventional antimicrobial medications. Thus, to oppose the challenges posed by biofilm-related infections, innovative therapeutic strategies are being explored which include targeting extracellular polymeric substances, quorum sensing, and persister cells. Biofilm-responsive nanoparticles show promising results by improving drug delivery and reducing the side effects. This review comprehensively examines the factors influencing biofilm formation, host immune defence mechanisms, infections caused by biofilms, diagnostic approaches, and biofilm-targeted therapies.

A nanocomposite hydrogel for co-delivery of multiple anti-biofilm therapeutics to enhance the treatment of bacterial biofilm-related infections

The characteristics of biofilms have exacerbated the issue of clinical antibiotic resistance, rendering it a pressing challenge in need of resolution. The combination of biofilm-dispersing agents and antibiotics can eliminate biofilms and promote healing synergistically in infected wounds. In this study, we developed a novel nanocomposite hydrogel (NC gel) comprised of the poly(lactic acid)-hyperbranched polyglycerol (PLA-HPG) based bioadhesive nanoparticles (BNPs) and a hydrophilic carboxymethyl chitosan (CS) network. The NC gel was designed to co-deliver two biofilm-dispersing agents (an NO-donor SNO, and an α-amylase Am) and an antibiotic, cefepime (Cef), utilizing a synergistic anti-biofilm mechanism in which Am loosens the matrix structure and NO promotes the release of biofilm bacteria via quorum sensing, and Cef kills bacteria. The drug-loaded NC gel (SNO/BNP/CS@Am-Cef) demonstrated sustained drug release, minimal cytotoxicity, and increased drug-bacterial interactions at the site of infection. When applied to mice infected with methicillin-resistant Staphylococcus aureus (MRSA) biofilms in vivo, SNO/BNP/CS@Am-Cef enhanced biofilm elimination and promoted wound healing compared to traditional antibiotic treatments. Our work demonstrates the feasibility of the co-delivery of biofilm-dispersing agents and antibiotics using the NC gel and presents a promising approach for the polytherapy of bacterial biofilm-related infections.

Antibacterial micro/nanomotors: current research progress, challenges, and opportunities

Bacterial infections remain a formidable threat to human health, a situation exacerbated by the escalating problem of antibiotic resistance. While alternative antibacterial strategies such as oxidants, heat treatments, and metal nanoparticles (NPs) have shown potential, they come with significant drawbacks, ranging from non-specificity to potential environmental concerns. In the face of these challenges, the rapid evolution of micro/nanomotors (MNMs) stands out as a revolutionary development in the antimicrobial arena. MNMs harness various forms of energy and convert it into a substantial driving force, offering bright prospects for combating microbial threats. MNMs' mobility allows for swift and targeted interaction with bacteria, which not only improves the carrying potential of therapeutic agents but also narrows the required activation range for non-drug antimicrobial interventions like photothermal and photodynamic therapies, substantially improving their bacterial clearance rates. In this review, we summarized the diverse propulsion mechanisms of MNMs employed in antimicrobial applications and articulated their multiple functions, which include direct bactericidal action, capture and removal of microorganisms, detoxification processes, and the innovative detection of bacteria and associated toxins. Despite MNMs' potential to revolutionize antibacterial research, the translation from laboratory to clinical use remains challenging. Based on the current research status, we summarized the potential challenges and possible solutions and also prospected several key directions for future studies of MNMs for antimicrobial purposes. Collectively, by highlighting the important knowns and unknowns of antimicrobial MNMs, our present review would help to light the way forward for the field of antimicrobial MNMs and prevent unnecessary blindness and detours.

Electrochemical Deposition of Copper on Bioactive Porous Titanium Dioxide Layer: Antibacterial and Pro-Osteogenic Activities

Ti surfaces must exhibit antibacterial activity without cytotoxicity to promote bone reconstruction and prevent infection simultaneously. In this study, we employed a two-step electrochemical treatment process, namely, microarc oxidation (MAO) and cathodic electrochemical deposition (CED), to modify Ti surfaces. During the MAO step, a porous TiO2 (pTiO2) layer with a surface roughness of approximately 2.0 μm was generated on the Ti surface, and in the CED step, Cu was deposited onto the pTiO2 layer on the Ti surface, forming Cu@pTiO2. Cu@pTiO2 exhibited a similar structure, adhesion strength, and crystal phase to pTiO2. Moreover, X-ray photoelectron spectroscopy (XPS) confirmed the presence of Cu in Cu@pTiO2 at an approximate concentration of 1.0 atom %. Cu@pTiO2 demonstrated a sustained release of Cu ions for a minimum of 28 days in a simulated in vivo environment. In vitro experiments revealed that Cu@pTiO2 effectively eradicated approximately 99% of Staphylococcus aureus and Escherichia coli and inhibited biofilm formation, in contrast to the Ti and pTiO2 surfaces. Moreover, Cu@pTiO2 supported the proliferation of osteoblast-like cells at a rate comparable to that observed on the Ti and pTiO2 surfaces. Similar to pTiO2, Cu@pTiO2 promoted the calcification of osteoblast-like cells compared with Ti. In summary, we successfully conferred antibacterial and pro-osteogenic activities to Ti surfaces without inducing cytotoxic effects or structural and mechanical alterations in pTiO2 through the application of MAO and CED processes. Moreover, we found that the pTiO2 layer promoted bacterial growth and biofilm formation more effectively than the Ti surface, highlighting the potential drawbacks of rough and porous surfaces. Our findings provide fundamental insights into the surface design of Ti-based medical devices for bone reconstruction and infection prevention.

Glycosyl hydrolase from Pseudomonas fluorescens inhibits the biofilm formation of Pseudomonads

Biofilms are complex microbial communities embedded in extracellular matrix. Pathogens within the biofilm become more resistant to the antibiotics than planktonic counterparts. Novel strategies are required to encounter biofilms. Exopolysaccharides are one of the major components of biofilm matrix and play a vital role in biofilm architecture. In previous studies, a glycosyl hydrolase, PslGPA, from Pseudomonas aeruginosa was found to be able to inhibit biofilm formation by disintegrating exopolysaccharide in biofilms. Here, we investigate the potential spectrum of PslG homologous protein with anti-biofilm activity. One glycosyl hydrolase from Pseudomonas fluorescens, PslGPF, exhibits anti-biofilm activities and the key catalytic residues of PslGPF are conserved with those of PslGPA. PslGPF at concentrations as low as 50 nM efficiently inhibits the biofilm formation of P. aeruginosa and disassemble its preformed biofilm. Furthermore, PslGPF exhibits anti-biofilm activity on a series of Pseudomonads, including P. fluorescens, Pseudomonas stutzeri and Pseudomonas syringae pv. phaseolicola. PslGPF stays active under various temperatures. Our findings suggest that P. fluorescens glycosyl hydrolase PslGPF has potential to be a broad spectrum inhibitor on biofilm formation of a wide range of Pseudomonads.

Synergistic Potential of α-Melanocyte Stimulating Hormone Based Analogues with Conventional Antibiotic against Planktonic, Biofilm-Embedded, and Systemic Infection Model of MRSA

The repotentiation of the existing antibiotics by exploiting the combinatorial potential of antimicrobial peptides (AMPs) with them is a promising approach to address the challenges of slow antibiotic development and rising antimicrobial resistance. In the current study, we explored the ability of lead second generation Ana-peptides viz. Ana-9 and Ana-10, derived from Alpha-Melanocyte Stimulating Hormone (α-MSH), to act synergistically with different classes of conventional antibiotics against methicillin-resistant Staphylococcus aureus (MRSA). The peptides exhibited prominent synergy with β-lactam antibiotics, namely, oxacillin, ampicillin, and cephalothin, against planktonic MRSA. Furthermore, the lead combination of Ana-9/Ana-10 with oxacillin provided synergistic activity against clinical MRSA isolates. Though the treatment of MRSA is complicated by biofilms, the lead combinations successfully inhibited biofilm formation and also demonstrated biofilm disruption potential. Encouragingly, the peptides alone and in combination were able to elicit in vivo anti-MRSA activity and reduce the bacterial load in the liver and kidney of immune-compromised mice. Importantly, the presence of Ana-peptides at sub-MIC doses slowed the resistance development against oxacillin in MRSA cells. Thus, this study highlights the synergistic activity of Ana-peptides with oxacillin advocating for the potential of Ana-peptides as an alternative therapeutic and could pave the way for the reintroduction of less potent conventional antibiotics into clinical use against MRSA infections.

Novel marine metalloprotease-new approaches for inhibition of biofilm formation of Stenotrophomonas maltophilia

Many marine organisms produce bioactive molecules with unique characteristics to survive in their ecological niches. These enzymes can be applied in biotechnological processes and in the medical sector to replace aggressive chemicals that are harmful to the environment. Especially in the human health sector, there is a need for new approaches to fight against pathogens like Stenotrophomonas maltophilia which forms thick biofilms on artificial joints or catheters and causes serious diseases. Our approach was to use enrichment cultures of five marine resources that underwent sequence-based screenings in combination with deep omics analyses in order to identify enzymes with antibiofilm characteristics. Especially the supernatant of the enrichment culture of a stony coral caused a 40% reduction of S. maltophilia biofilm formation. In the presence of the supernatant, our transcriptome dataset showed a clear stress response (upregulation of transcripts for metal resistance, antitoxins, transporter, and iron acquisition) to the treatment. Further investigation of the enrichment culture metagenome and proteome indicated a series of potential antimicrobial enzymes. We found an impressive group of metalloproteases in the proteome of the supernatant that is responsible for the detected anti-biofilm effect against S. maltophilia. KEY POINTS: • Omics-based discovery of novel marine-derived antimicrobials for human health management by inhibition of S. maltophilia • Up to 40% reduction of S. maltophilia biofilm formation by the use of marine-derived samples • Metalloprotease candidates prevent biofilm formation of S. maltophilia K279a by up to 20.

Synergistic effect of doxycycline and aqueous extract of irradiated khella on structure of nanobacteria isolated from kidney stones: In vitro and in vivo studies

Kidney stones have been associated with an increased risk of chronic kidney diseases, end-stage renal failure. This study is devoted to isolate nanobacteria from patients with active urolithiasis and investigate the in vitro and in vivo antinanobacterial activity of some antibiotics alone or in combination with extracts of irradiated herbs from certain medicinal plants. Nanobacteria were detected using scanning (SEM) and transmission (TEM) electron microscopy, protein electrophoresis (SDS-PAGE) and DNA profile. The antimicrobial susceptibility of some biofilm-producing nanobacterial isolates was evaluated. The effect of medicinal plant extracts on growth was tested. A combination treatment between the most potent extracts and antibiotics was tested on biofilm production, protein profile, release of 260 nm absorbing material, protein content, and ultrastructure of the strongest biofilm producers. In vivo study of nanobacteria and its treatment by the most potent agents was evaluated on male rats. Renal function was measured in serum; histological examination and oxidative stress parameters were determined in kidney tissues. Results showed that streptomycin, trimethoprim/sulfamethoxazole, doxycycline, and water extracts of irradiated khella at 6 kGy had antinanobacterial activity. Meanwhile, the synergistic effect of the aqueous extract of irradiated Khella and doxycycline showed higher inhibition activity on microbial growth and biofilm production. They affected dramatically the strength of its cell membrane and subsequently its ultrastructure. Moreover, these results are confirmed by ameliorations in renal function and histological alterations. It could be concluded that the combination of DO and an aqueous extract of irradiated khella has an antinephrotoxic effect against nanobacteria-induced renal toxicity.

Effect of silver sulfadiazine on mature mixed bacterial biofilms on voice prostheses

BACKGROUND

Biofilm formation on voice prostheses disrupts the function and limits the lifespan of voice prostheses. There is still no effective clinical strategy for inhibiting or removing these biofilms. Silver sulfadiazine (SSD), as an exogenous antibacterial agent, has been widely used in the prevention and treatment of infection, however, its effect on voice prosthesis biofilms is unknown. The purpose of this study was to explore the effect of SSD on the mature mixed bacterial biofilms present on voice prostheses.

METHODS

Quantitative and qualitative methods, including the plate counting method, real-time fluorescence quantitative PCR, crystal violet staining, the 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide) (XTT) reduction assay, scanning electron microscopy, and laser confocal microscopy, were used to determine the effect of SSD on the number of bacterial colonies, biofilm formation ability, metabolic activity, and ultrastructure of biofilms in a mature mixed bacterial (Staphylococcus aureus, Streptococcus faecalis and Candida albicans) voice prosthesis biofilm model. The results were verified in vitro on mature mixed bacterial voice prosthesis biofilms from patients, and the possible mechanism of action was explored.

RESULTS

Silver sulfadiazine decreased the number of bacterial colonies on mature mixed bacterial voice prosthesis biofilm, significantly inhibited the biofilm formation ability and metabolic activity of mature voice prosthesis biofilms, inhibited the formation of the complex spatial structure of voice prosthesis biofilms, and inhibited the synthesis of polysaccharides and proteins in the biofilm extracellular matrix. The degree of inhibition and removal effect increased with SSD concentration.

CONCLUSIONS

Silver sulfadiazine can effectively inhibit and remove mature mixed bacterial voice prosthesis biofilms and decrease biofilm formation ability and metabolic activity; SSD may exert these effects by inhibiting the synthesis of polysaccharides and proteins among the extracellular polymeric substances of voice prosthesis biofilms.

Incorporation of collagen into Pseudomonas aeruginosa and Staphylococcus aureus biofilms impedes phagocytosis by neutrophils

Biofilms are communities of microbes embedded in a matrix of extracellular polymeric substances (EPS). Matrix components can be produced by biofilm organisms and can also originate from the environment and then be incorporated into the biofilm. For example, we have recently shown that collagen, a host-produced protein that is abundant in many different infection sites, can be taken up into the biofilm matrix, altering biofilm mechanics. The biofilm matrix protects bacteria from clearance by the immune system, and some of that protection likely arises from the mechanical properties of the biofilm. Pseudomonas aeruginosa and Staphylococcus aureus are common human pathogens notable for forming biofilm infections in anatomical sites rich in collagen. Here, we show that the incorporation of Type I collagen into P. aeruginosa and S. aureus biofilms significantly hinders phagocytosis of biofilm bacteria by human neutrophils. However, enzymatic treatment with collagenase, which breaks down collagen, can partly or entirely negate the protective effect of collagen and restore the ability of neutrophils to engulf biofilm bacteria. From these findings, we suggest that enzymatic degradation of host materials may be a potential way to compromise biofilm infections and enhance the efficacy of the host immune response without promoting antibiotic resistance. Such an approach might be beneficial both in cases where the infecting species is known and also in cases wherein biofilm components are not readily known, such as multispecies infections or infections by unknown species.

Effects of Flavonoids and Antibiotics Combination on Preformed Biofilms and Small RNA of Staphylococcus aureus

Antibiotic resistance of Staphylococcus aureus has considerably increased among non-clinical or asymptomatic individuals. The formation of biofilms denies antimicrobial access to its targets present on the surface and inside the cell. The present study tested the effect of the combination of flavonoids and antibiotics over the preformed biofilms of S. aureus. The eradication of the preformed biofilms was analyzed using the crystal violet method. It has shown that 2500 µg mL-1 Rutin and 100 µg mL-1 Erythromycin (MIC Concentration) combination efficiently reduced the growth of the cells, which were adhered to the surfaces forming the biofilms. Fluorescence microscopic analysis indicated that the Rutin and Erythromycin (MIC value) combinations could eradicate the preformed biofilm cells more efficiently than other combinations. We found that the flavonoids and antibiotics with MIC concentration show a significant effect over the preformed biofilms cells of S. aureus. In addition, the semi-quantitative real-time PCR analysis for the sRNAs under the treatment of Rutin and Erythromycin combinations showed that few small RNAs expression (SprF, SprG, ArtR, Teg49, Teg41, and RNAIII) are getting downregulated upon the treatment; but again recovers with the incubation time interval increases. Combinations have a significant effect on Teg49 where there is a very faint intensity of the band, but for other small RNAs, there is an irregular pattern on the gel image. It has been concluded that at the initial period of incubation, the combinations have an effect on all the sRNAs but once the incubation increases, the effects have been slowly decreasing. It has been concluded that the combination has been able to reduce the doubling time of S. aureus upon treatment. Whereas, the small RNAs used in the study can be further evaluated for expression profiling through qRT-PCT.

Graphical abstract

Facile fabrication of Nishamalaki churna mediated silver nanoparticles with antibacterial application

Antimicrobial resistance (AMR) is one of the most serious threats to today's healthcare system. The prime factor behind increasing AMR is the formation of complex bacterial biofilms which acts as the protective shield between the bacterial cell and the antimicrobial drugs. Among various nanoformulations, green synthesized metallic silver nanoparticles are currently gaining research focus in safely breaking bacterial biofilms due to the inherent antimicrobial property of silver. In the current work, the aqueous extract of the ayurvedic formulation Nishamalaki churna is used to exhibit one pot green synthesis of silver nanoparticles. The physicochemical characteristics of Nishamalaki churna extract mediated AgNPs were evaluated using various analytical techniques, like UV-Visible spectrophotometer, FT-IR spectroscopy, SEM, XRD, DLS-Zeta potential analyzer etc. The synthesized spherical AgNPs were well formed within the size range of 30 nm to 80 nm. Furthermore, the synthesized AgNPs showed potent antibacterial effects against two primary AMR-causing bacterial species like Staphylococcus aureus and Pseudomonas aeruginosa with the successful destruction of their biofilm formation. Additionally, these AgNPs have shown profound antioxidant and anti-inflammatory activities as desirable add-on effects required by a prospective antibacterial agent.

The pharmacokinetic-pharmacodynamic modelling framework as a tool to predict drug resistance evolution

Pharmacokinetic-pharmacodynamic (PKPD) models, which describe how drug concentrations change over time and how that affects pathogen growth, have proven highly valuable in designing optimal drug treatments aimed at bacterial eradication. However, the fast rise of antimicrobial resistance calls for increased focus on an additional treatment optimization criterion: avoidance of resistance evolution. We demonstrate here how coupling PKPD and population genetics models can be used to determine treatment regimens that minimize the potential for antimicrobial resistance evolution. Importantly, the resulting modelling framework enables the assessment of resistance evolution in response to dynamic selection pressures, including changes in antimicrobial concentration and the emergence of adaptive phenotypes. Using antibiotics and antimicrobial peptides as an example, we discuss the empirical evidence and intuition behind individual model parameters. We further suggest several extensions of this framework that allow a more comprehensive and realistic prediction of bacterial escape from antimicrobials through various phenotypic and genetic mechanisms.

Antibacterial Films of Silver Nanoparticles Embedded into Carboxymethylcellulose/Chitosan Multilayers on Nanoporous Silicon: A Layer-by-Layer Assembly Approach Comparing Dip and Spin Coating

The design and engineering of antibacterial materials are key for preventing bacterial adherence and proliferation in biomedical and household instruments. Silver nanoparticles (AgNPs) and chitosan (CHI) are broad-spectrum antibacterial materials with different properties whose combined application is currently under optimization. This study proposes the formation of antibacterial films with AgNPs embedded in carboxymethylcellulose/chitosan multilayers by the layer-by-layer (LbL) method. The films were deposited onto nanoporous silicon (nPSi), an ideal platform for bioengineering applications due to its biocompatibility, biodegradability, and bioresorbability. We focused on two alternative multilayer deposition processes: cyclic dip coating (CDC) and cyclic spin coating (CSC). The physicochemical properties of the films were the subject of microscopic, microstructural, and surface-interface analyses. The antibacterial activity of each film was investigated against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) bacteria strains as model microorganisms. According to the findings, the CDC technique produced multilayer films with higher antibacterial activity for both bacteria compared to the CSC method. Bacteria adhesion inhibition was observed from only three cycles. The developed AgNPs-multilayer composite film offers advantageous antibacterial properties for biomedical applications.

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.

Essential oils to contrast biodeterioration of the external marble of Florence Cathedral

The search for more sustainable strategies to contrast biodeterioration of stone cultural heritage has been developing in recent years to find alternatives to synthetic biocides, since their toxicity and potential impact on the environment and health. In this study, the application of the oregano and thyme essential oils (EOs) was tested to control microbial growth on the external marble of Florence Cathedral affected by extended darkening. Before in situ application, preliminary tests were carried out to evaluate the interference of the EOs with marble (colorimetric and water absorption assays on marble specimens) and their efficacy in inhibiting marble microbiota (sensitivity test on nutrient media). EOs inhibited the whole cultivable microbiota sampled from the Cathedral marble at a very low concentration, while they did not interfere with colour and water absorption capability of uncolonised marble samples when applied as a 2 % solution. Then the two EOs and the commercial biocide Biotin T were used in in situ trials on marble in two outdoor study sites of Florence Cathedral. The effectiveness of the treatments was assessed through short- and mid-term evaluation by multidisciplinary in situ non-invasive (colorimetric and ATP assays, microscopy) and ex situ (microbial viable titer) tests. Concerning results, we found a good correspondence between parameters for evaluation of viability (bacterial and fungi viable titer) and activity (ATP determination) and some correspondence among these and microscopy and colorimetry. Considering the whole data, treatments with oregano and thyme EOs were effective against microbial community, in more cases comparably to the commercial biocide. Some differences found, particularly by viable titer, in the two study sites or in bacterial and fungal components of the microbiota can be partly attributed to differences in structure and colonization pattern of the microbial community due to the peculiar climatic conditions of the differently exposed study areas.

Characterization of the Community of Black Meristematic Fungi Inhabiting the External White Marble of the Florence Cathedral

Meristematic black fungi are a highly damaging group of microorganisms responsible for the deterioration of outdoor exposed monuments. Their resilience to various stresses poses significant challenges for removal efforts. This study focuses on the community of meristematic fungi inhabiting the external white marble of the Cathedral of Santa Maria del Fiore, where they contribute to its darkening. Twenty-four strains were isolated from two differently exposed sites of the Cathedral, and their characterization was conducted. Phylogenetic analysis using ITS and LSU rDNA regions revealed a wide diversity of rock-inhabiting fungal strains within the sampled areas. Eight strains, belonging to different genera, were also tested for thermal preferences, salt tolerance, and acid production to investigate their tolerance to environmental stressors and their interaction with stone. All tested strains were able to grow in the range of 5-30 °C, in the presence 5% NaCl, and seven out of eight strains were positive for the production of acid. Their sensitivities to essential oils of thyme and oregano and to the commercial biocide Biotin T were also tested. The essential oils were found to be the most effective against black fungi growth, indicating the possibility of developing a treatment with a low environmental impact.

Multimodal-Driven Magnetic Microrobots with Enhanced Bactericidal Activity for Biofilm Eradication and Removal from Titanium Mesh

Modern micro/nanorobots can perform multiple tasks for biomedical and environmental applications. Particularly, magnetic microrobots can be completely controlled by a rotating magnetic field and their motion powered and controlled without the use of toxic fuels, which makes them most promising for biomedical application. Moreover, they are able to form swarms, allowing them to perform specific tasks at a larger scale than a single microrobot. In this work, they developed magnetic microrobots composed of halloysite nanotubes as backbone and iron oxide (Fe₃ O₄ ) nanoparticles as magnetic material allowing magnetic propulsion and covered these with polyethylenimine to load ampicillin and prevent the microrobots from disassembling. These microrobots exhibit multimodal motion as single robots as well as in swarms. In addition, they can transform from tumbling to spinning motion and vice-versa, and when in swarm mode they can change their motion from vortex to ribbon and back again. Finally, the vortex motion mode is used to penetrate and disrupt the extracellular matrix of Staphylococcus aureus biofilm colonized on titanium mesh used for bone restoration, which improves the effect of the antibiotic's activity. Such magnetic microrobots for biofilm removal from medical implants could reduce implant rejection and improve patients' well-being.

Hydrogel Delivery of DNase I and Liposomal Vancomycin to Eradicate Fracture-related Methicillin-resistant Staphylococcus aureus Infection and Support Osteoporotic Fracture Healing

Fracture-related infection (FRI) is a devastating complication in orthopedic surgery. A recent study showed that FRI causes more severe infection and further delays healing in osteoporotic bone. Moreover, bacterial biofilm formed on implants cannot be eradicated by systemic antibiotics, warranting novel treatments. Here, we developed a DNase I and Vancomycin hydrogel delivery vehicle to eradicate Methicillin-resistant Staphylococcus aureus (MRSA) infection in vivo. Vancomycin was encapsulated in liposomes, and DNase I and Vancomycin/liposomal-Vancomycin was loaded on thermosensitive hydrogel. In vitro drug release test showed a burst release of DNase I (77.2%) within 72 hours and sustained release of Vancomycin (82.6%) up to day 14. The in vivo efficacy was evaluated in a clinically relevant ovariectomy (OVX) induced osteoporotic metaphyseal fracture model with MRSA infection, and a total of 120 Sprague Dawley rats were used. In the OVX with infection group, biofilm development caused a drastic inflammatory response, trabecular bone destruction, and non-union. In the DNase I and Vancomycin co-delivery hydrogel group (OVX-Inf-DVG), bacteria on bone and implant were eradicated. X-ray and micro-CT showed preservation of trabecular bone and bone union. HE staining showed the absence of inflammatory necrosis, and fracture healing was restored. The local elevation of TNF-α and IL-6 and increased number of osteoclasts were prevented in the OVX-Inf-DVG group. Our findings suggest that dual release of DNase I and Vancomycin initially followed by Vancomycin only later up to 14 days effectively eliminates MRSA infection, prevents biofilm development and provides a sterile environment to promote fracture healing in osteoporotic bone with FRI. STATEMENT OF SIGNIFICANCE: The biofilm formation on the implant is difficult to eradicate, causing recurrent infection and non-union in fracture-related infection (FRI). Here we developed a hydrogel therapy with high in vivo efficacy to eliminate MRSA biofilm infection in a clinically-relevant FRI model in osteoporotic bone. By loading DNase I and vancomycin/liposomal-vancomycin on thermosensitive poly-(DL-lactic acidco-glycolic acid) (PLGA)-polyethylene glycol (PEG)-PLGA hydrogel, a dual release of DNase I and Vancomycin was achieved whilst preserving enzyme activity. In this model, the progressive development of infection caused a drastic inflammatory response, osteoclastogenesis, trabecular bone destruction, and non-union of fracture. These pathological changes were successfully prevented by the dual delivery of DNase I and vancomycin. Our findings provide a promising strategy for FRI in osteoporotic bone.

Biofilm control strategies in the light of biofilm-forming microorganisms

Biofilm is a complex consortium of microorganisms attached to biotic or abiotic surfaces and live in self-produced or acquired extracellular polymeric substances (EPSs). EPSs are mainly formed by lipids, polysaccharides, proteins, and extracellular DNAs. The adherence to the surface of microbial communities is seen in food, medical, dental, industrial, and environmental fields. Biofilm development in food processing areas challenges food hygiene, and human health. In addition, bacterial attachment and biofilm formation on medical implants inside human tissue can cause multiple critical chronic infections. More than 30 years of international research on the mechanisms of biofilm formation have been underway to address concerns about bacterial biofilm infections. Antibiofilm strategies contain cold atmospheric plasma, nanotechnological, phage-based, antimicrobial peptides, and quorum sensing inhibition. In the last years, the studies on environmentally-friendly techniques such as essential oils and bacteriophages have been intensified to reduce microbial growth. However, the mechanisms of the biofilm matrix formation are still unclear. This review aims to discuss the latest antibiofilm therapeutic strategies against biofilm-forming bacteria.

Characterization, genome analysis and antibiofilm efficacy of lytic Proteus phages RP6 and RP7 isolated from university hospital sewage

The crystalline formation of biofilms by Proteus blocks the urine flow which often complicates the health care of catheterized patients. Bacteriophages has been highlighted as a promising tool to control biofilm-mediated bacterial infections. Here, we isolated and characterized two newly isolated lytic phages capable of infecting clinical isolates of P. mirabilis and P. vulgaris. Moreover, insights regarding the biological and molecular characterization were analysed. Both RP6 and RP7 phages showed a Proteus-genus-specific profile, administering no lytic activity against other family of Enterobacteriaceae. The optimal MOI value of the RP6 and RP7 phages were determined as 0.1 and 0.01, respectively. The one-step growth curve showed that RP6 and RP7 phages have a short latent period of 20 min and large burst size of 220-371 PFU/ML per infected host cell. Bacteria growth was reduced immediately after the phages were added, which is shown by the optical density (OD) measurement after 24 hr. Proteus phage RP6 and RP7 were found to eradicate both the planktonic and mature biofilms produced by the Proteus isolates tested. Genome sequence of Proteus phage RP6 was found to be 58,619 bp, and a G-C content of 47%. Also, Proteus phage RP7 genome size was 103,593 bp with G-C ratio of 38.45%. A total of 70 and 172 open reading frame (ORF) was encoded in RP6 and RP7 phage genomes, respectively. Interestingly, there were no tRNA encoded by Proteus phage RP6 genome even though there is a significant G-C content difference between the phage and its host. Additionally, the exhibition of highly lytic activity and absence of virulence and antibiotic-resistant genes in both Proteus RP6 and RP7 phages emphasized that this newly isolated phages are promising for potential therapeutic phages.

Natural Medicine a Promising Candidate in Combating Microbial Biofilm

Studies on biofilm-related infections are gaining prominence owing to their involvement in most clinical infections and seriously threatening global public health. A biofilm is a natural form of bacterial growth ubiquitous in ecological niches, considered to be a generic survival mechanism adopted by both pathogenic and non-pathogenic microorganisms and entailing heterogeneous cell development within the matrix. In the ecological niche, quorum sensing is a communication channel that is crucial to developing biofilms. Biofilm formation leads to increased resistance to unfavourable ecological effects, comprising resistance to antibiotics and antimicrobial agents. Biofilms are frequently combated with modern conventional medicines such as antibiotics, but at present, they are considered inadequate for the treatment of multi-drug resistance; therefore, it is vital to discover some new antimicrobial agents that can prevent the production and growth of biofilm, in addition to minimizing the side effects of such therapies. In the search for some alternative and safe therapies, natural plant-derived phytomedicines are gaining popularity among the research community. Phytomedicines are natural agents derived from natural plants. These plant-derived agents may include flavonoids, terpenoids, lectins, alkaloids, polypeptides, polyacetylenes, phenolics, and essential oils. Since they are natural agents, they cause minimal side effects, so could be administered with dose flexibility. It is vital to discover some new antimicrobial agents that can control the production and growth of biofilms. This review summarizes and analyzes the efficacy characteristics and corresponding mechanisms of natural-product-based antibiofilm agents, i.e., phytochemicals, biosurfactants, antimicrobial peptides, and their sources, along with their mechanism, quorum sensing signalling pathways, disrupting extracellular matrix adhesion. The review also provides some other strategies to inhibit biofilm-related illness. The prepared list of newly discovered natural antibiofilm agents could help in devising novel strategies for biofilm-associated infections.

Comparative Study of Effects of Endophytic Fungal Silver Nanoparticles and Nanoemulsion on Escherichia coli

Green nanotechnology, a branch of nanotechnology, makes use of extract from plants or microorganisms to synthesize nanoparticles. This approach is eco-friendlier and more cost-effective than conventional methods of nanoparticle synthesis. Silver nanoparticles have interested researchers because several studies suggest that they have a wide range of applications in the field of medicine; it is known to serve as a good antimicrobial agent. This study concentrated on the synthesis of silver nanoparticles and nanoemulsion from the extract of an endophytic fungi-Lasiodiplodia theobromae. Nanoemulsion was prepared using an essential oil-tea tree oil from Melaleuca alternifolia (commonly known as tea tree). The nanoparticles were characterized using UV-visible spectra, SEM, FESEM, EDAX, XRD, and FTIR analysis. A comparative antimicrobial study was carried out between endophytic fungal extract-derived nanoparticles (EFNP) and nanoemulsion (EFNE) against two strains of Escherichia coli, through various experimental assays including Agar well diffusion method and assays that determined the minimum inhibitory concentration, minimum bactericidal concentration, and biofilm formation. From the results obtained, it was evident that both EFNP and EFNE had antibacterial activity and that the EFNE worked better than the former. This study suggested that EFNE was a good antibiotic alternative, and further in vivo studies must be done to check the efficacy.

DNase I and chitosan enhance efficacy of ceftazidime to eradicate Burkholderia pseudomallei biofilm cells

Biofilm-associated Burkholderia pseudomallei infection contributes to antibiotic resistance and relapse of melioidosis. Burkholderia pseudomallei biofilm matrix contains extracellular DNA (eDNA) that is crucial for biofilm establishment. However, the contribution of eDNA to antibiotic resistance by B. pseudomallei remains unclear. In this study, we first demonstrated in vitro that DNase I with the administration of ceftazidime (CAZ) at 24 h considerably inhibited the 2-day biofilm formation and reduced the number of viable biofilm cells of clinical B. pseudomallei isolates compared to biofilm treated with CAZ alone. A 3-4 log reduction in numbers of viable cells embedded in the 2-day biofilm was observed when CAZ was combined with DNase I. Confocal laser-scanning microscope visualization emphasized the competence of DNase I followed by CAZ supplementation to significantly limit B. pseudomallei biofilm development and to eradicate viable embedded B. pseudomallei biofilm cells. Furthermore, DNase I supplemented with chitosan (CS) linked with CAZ (CS/CAZ) significantly eradicated shedding planktonic and biofilm cells. These findings indicated that DNase I effectively degraded eDNA leading to biofilm inhibition and dispersion, subsequently allowing CAZ and CS/CAZ to eradicate both shedding planktonic and embedded biofilm cells. These findings provide efficient strategies to interrupt biofilm formation and improve antibiotic susceptibility of biofilm-associated infections.

Marine bioactive compounds as antibiofilm agent: a metabolomic approach

The ocean is a treasure trove of both living and nonliving creatures, harboring incredibly diverse group of organisms. A plethora of marine sourced bioactive compounds are discovered over the past few decades, many of which are found to show antibiofilm activity. These are of immense clinical significance since the formation of microbial biofilm is associated with the development of high antibiotic resistance. Biofilms are also responsible to bring about problems associated with industries. In fact, the toilets and wash-basins also show degradation due to development of biofilm on their surfaces. Antimicrobial resistance exhibited by the biofilm can be a potent threat not only for the health care unit along with industries and daily utilities. Various recent studies have shown that the marine members of various kingdom are capable of producing antibiofilm compounds. Many such compounds are with unique structural features and metabolomics approaches are essential to study such large sets of metabolites. Associating holobiome metabolomics with analysis of their chemical attribute may bring new insights on their antibiofilm effect and their applicability as a substitute for conventional antibiotics. The application of computer-aided drug design/discovery (CADD) techniques including neural network approaches and structured-based virtual screening, ligand-based virtual screening in combination with experimental validation techniques may help in the identification of these molecules and evaluation of their drug like properties.

Inhibition and Removal of Mature Mixed-Bacteria Biofilms on Voice Prostheses by Sodium Selenite

Purpose

Biofilms on voice prostheses are important factors shortening their service life. Sodium selenite has been used to prevent and treat various diseases. Whether sodium selenite can inhibit and remove mature biofilms on voice prostheses is still unknown.

Methods

To verify the effects of sodium selenite on mature mixed-bacteria biofilms (Staphylococcus aureus, Candida albicans, and Streptococcus faecalis) on voice prostheses, we used quantitative and qualitative methods, eg, real-time fluorescence quantitative PCR, crystal violet staining, 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide) (XTT) reduction assays, and scanning electron microscopy, to measure the effects of sodium selenite on the number of bacterial colonies, biofilm formation ability, metabolic activity, and ultrastructure in a model of mature mixed-bacteria biofilms on voice prostheses and validated the effects in vitro on mature biofilms on voice prostheses from patients.

Results

When exploring the possible mechanism of biofilm inhibition and removal by sodium selenite, we found that it significantly inhibited and removed biofilms on voice prostheses and effectively destroyed the spatial structure of the biofilms. The inhibition and removal effects became more significant with increasing sodium selenite concentrations.

Conclusion

We demonstrated that sodium selenite can inhibit and remove biofilms of mature mixed strains on voice prostheses, providing a novel basis for treating patients' voice prosthesis biofilms.

Synthesis and Antimicrobial Evaluation of New Cephalosporin Derivatives Containing Cyclic Disulfide Moieties

Due to a steady increase in microbial resistance, there is a need to increase the effectiveness of antibiotic performance by involving additional mechanisms of their penetration or retention for their better action. Cephalosporins are a successful group of antibiotics to combat pathogenic microorganisms, including drug-resistant strains. In this study, we investigated the effect of newly synthesized cephalosporin derivatives with cyclic disulfide modifications against several Gram-positive and Gram-negative strains as well as against biofilm formation. The incorporation of asparagusic acid was found to be effective in improving the activity of the drug against Gram-negative strains compared to the all carbon-control compounds. Furthermore, we could demonstrate the successful reduction of biofilm formation for Staphylococcus aureus and Pseudomonas aeruginosa at similar concentrations as obtained against planktonic cells. We propose that the incorporation of cyclic disulfides is one additional strategy to improve antibiotic activity and to combat bacterial infections.

Reverse effects of Streptococcus mutans physiological states on neutrophil extracellular traps formation as a strategy to escape neutrophil killing

Bacteria in nature are present in different lifestyles with distinct characteristics. Streptococcus mutans is the etiologic pathogen of dental caries and could easily gain access into the bloodstream after oral surgery and adopt a biofilm lifestyle, resulting in infective endocarditis. A growing amount of evidence have revealed that the large web-like structure composed of extracellular DNA and antimicrobial proteins released by neutrophils, named Neutrophil Extracellular Traps (NETs), play an active role in the defense against bacterial invasion. The present study demonstrated that NETs formation was discriminatively affected by S. mutans biofilm and its planktonic counterpart. The free-floating planktonic S. mutans exhibited an active NETs response, whereas the biofilm community exhibited a reverse negative NETs response. Besides, impaired biofilm killing correlated with the decrease in NETs production. Unlike planktonic cells, biofilm avoided the burst of reactive oxygen species (ROS) when co-culture with neutrophils, and the NADPH-oxidase pathway was partially involved. A mice infection model also supported the distinguishing response of neutrophils challenged by different lifestyles of S. mutans. In conclusion, different bacterial physiological states can affect the distinct response of the host-microbe interaction, thus contributing to the anti-pathogen immune response activation and immune surveillance survival.

Potential functions and applications of diverse microbial exopolysaccharides in marine environments

Exopolysaccharides (EPSs) from microorganisms are essential harmless natural biopolymers used in applications including medications, nutraceuticals and functional foods, cosmetics, and insecticides. Several microbes can synthesize and excrete EPSs with chemical properties and structures that make them suitable for several important applications. Microbes secrete EPSs outside their cell walls, as slime or as a "jelly" into the extracellular medium. These EPS-producing microbes are ubiquitous and can be isolated from aquatic and terrestrial environments, such as freshwater, marine water, wastewater, and soils. They have also been isolated from extreme niches like hot springs, cold waters, halophilic environments, and salt marshes. Recently, microbial EPSs have attracted interest for their applications such as environmental bio-flocculants because they are degradable and nontoxic. However, further efforts are required for the cost-effective and industrial-scale commercial production of microbial EPSs. This review focuses on the exopolysaccharides obtained from several extremophilic microorganisms, their synthesis, and manufacturing optimization for better cost and productivity. We also explored their role and applications in interactions between several organisms.

Therapeutic Potential of Antimicrobial Peptide PN5 against Multidrug-Resistant E. coli and Anti-Inflammatory Activity in a Septic Mouse Model

Antibiotic-resistant bacteria have become a public health problem. Thus, antimicrobial peptides (AMPs) have been evaluated as substitutes for antibiotics. Herein, we investigated PN5 derived from Pinus densiflora (pine needle). PN5 exhibited antimicrobial activity without causing cytotoxic effects. Based on these results, we examined the mode of action of PN5 against Gram-negative and -positive bacteria. PN5 exhibited membrane permeabilization ability, had antimicrobial stability in the presence of elastase, a proteolytic enzyme, and did not induce resistance in bacteria. Bacterial lipopolysaccharide (LPS) induces an inflammatory response in RAW 264.7 macrophages. PN5 suppressed proinflammatory cytokines mediated by NF-κB and mitogen-activated protein kinase signaling. In C57BL/6J mice treated with LPS and d-galactosamine, PN5 exhibited anti-inflammatory activity in inflamed mouse livers. Our results indicate that PN5 has antimicrobial and anti-inflammatory activities and thus may be useful as an antimicrobial agent to treat septic shock caused by multidrug-resistant (MDR) Escherichia coli without causing further resistance. IMPORTANCE Antibiotic-resistant bacteria are a global health concern. There is no effective treatment for antibiotic-resistant bacteria, and new alternatives are being suggested. The present study found antibacterial and anti-inflammatory activities of PN5 derived from Pinus densiflora (pine needle), and further investigated the therapeutic effect in a mouse septic model. As a mechanism of antibacterial activity, PN5 exhibited the membrane permeabilization ability of the toroidal model, and treated strains did not develop drug resistance during serial passages. PN5 showed immunomodulatory properties of neutralizing LPS in a mouse septic model. These results indicate that PN5 could be a new and promising therapeutic agent for bacterial infectious disease caused by antibiotic-resistant strains.

Anti-quorum sensing and cytotoxic activity of elemi essential oil

Essential oils have several biological activities such as antimicrobial, antioxidant, proliferative, and anti-inflammatory. This study aimed identification of bioactive compounds found in Elemi essential oil (EO) and to determine the anti-quorum sensing and cytotoxic activities of EO. In this study, bioactive compounds of EO were analyzed using GC-MS, and the antibacterial activity of elemi was screened against Staphylococcus aureus ATCC 25923, Methicillin-Resistant Staphylococcus aureus ATCC 43300, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Pseudomonas aeruginosa PAO1. Anti-biofilm activity and pyocyanin production on P. aeruginosa PAO1 were also investigated. The effect of EO on cell viability was also analyzed by thiazolyl blue tetrazolium bromide (MTT) and neutral red uptake (NR) assay in fibroblast cells. According to GC results, the major component of EO was determined as limonene (55%). A sub-MIC of elemi essential oil inhibited biofilm formation and pyocyanin production by 43% and 56%, respectively. On the other hand, EO also had an acute effect on the mitochondrial and lysosomal activities of fibroblast cell lines. Mitochondrial and lysosomal activities were significantly decreased when EO concentrations were applied for 24 and 48 hours (p&lt;0.05). In conclusion, EO has inhibitory activity on biofilm formation and pyocyanin production, and also the lower doses of oil have no toxic effects on fibroblast cells. However, higher doses of EO have more cytotoxic effects on mitochondrial activity rather than the lysosomal activity of fibroblast cell lines. It is thought that EO exhibits these activities due to the amount of limonene in its content. 

Multidrug-Resistant Biofilm, Quorum Sensing, Quorum Quenching, and Antibacterial Activities of Indole Derivatives as Potential Eradication Approaches

Challenges encountered in relapse of illness caused by resistance of microorganisms to antimicrobial agents (drugs) are due to factors of severe stress initiated by random use of antibiotics and insufficient beneficial approaches. These challenges have resulted to multiple drug resistance (MDR) and, subsequently, biofilm formation. A type of intercellular communication signal called quorum sensing (QS) has been studied to cause the spread of resistance, thereby enabling a formation of stable community for microorganisms. The QS could be inhibited using QS inhibitors (QSIs) called quorum-quenching (QQ). The QQ is an antibiofilm agent. Indole derivatives from plant sources can serve as quorum-quenching eradication approach for biofilm, as well as a promising nontoxic antibiofilm agent. In other words, phytochemicals in plants help to control and prevent biofilm formation. It could be recommended that combination strategies of these indoles' derivatives with antibiotics would yield enhanced results.

Guaiacol augments quorum quenching potential of Ciprofloxacin against Pseudomonas aeruginosa

AIM

The present study aims to investigate the antimicrobial as well as antivirulence potential and the principle mechanism of action of guaiacol against Pseudomonas aeruginosa.

METHODS AND RESULTS

Quorum sensing inhibition and membrane disruption studies were performed to check effect of guaiacol on the virulence of P. aeruginosa. Production of various virulence factors and biofilm formation were studied at sub-MIC concentration of guaiacol alone (1/8 MIC) and in combination with ciprofloxacin (1/2 FIC). Guaiacol exhibited synergistic interactions with ciprofloxacin and further reduced production of all virulence factors and biofilm formation. Using crystal violet (CV) assay and quantification of exopolysaccharide we observed weak biofilm formation, together with reduced motilities at sub MIC which was further visualized by confocal laser microscopy and Field Emission Scanning Electron Microscopy (FESEM).The antibacterial activity of guaiacol against P. aeruginosa upon 2×MIC exposure coincided with enhanced membrane permeability leading to disruption and release of cellular material as quantified by CV uptake assay and Sodium dodecyl suphate-polyacrylamide gel electrophoresis (SDS-PAGE). The results demonstrated that sub MICs of guaiacol in combination with ciprofloxacin can act as a potent alternate compound for attenuation of quorum sensing in P. aeruginosa.

CONCLUSION

Study reports that guaiacol in combination with ciprofloxacin at 1/2 FIC significantly compromised the bacterial growth and motilities alongside inducing quorum quenching potential. This was accompanied by inhibition of biofilm which subsequently decreased EPS production at sub MIC concentration. Furthermore, guaiacol in combination displayed a severe detrimental effect on bacterial membrane disruption, thereby enhancing cellular material release.

SIGNIFICANCE AND IMPACT OF STUDY

For the first time, the potential of guaiacol in combination with ciprofloxacin in attenuation of virulence factors and biofilm formation in P. aeruginosa were described. Results corroborate on how plant bioactive in synergism with antibiotics can act as alternate treatment regime to tackle the menace of drug resistance.

An Overview of Biofilm Formation-Combating Strategies and Mechanisms of Action of Antibiofilm Agents

Biofilm formation on surfaces via microbial colonization causes infections and has become a major health issue globally. The biofilm lifestyle provides resistance to environmental stresses and antimicrobial therapies. Biofilms can cause several chronic conditions, and effective treatment has become a challenge due to increased antimicrobial resistance. Antibiotics available for treating biofilm-associated infections are generally not very effective and require high doses that may cause toxicity in the host. Therefore, it is essential to study and develop efficient anti-biofilm strategies that can significantly reduce the rate of biofilm-associated healthcare problems. In this context, some effective combating strategies with potential anti-biofilm agents, including plant extracts, peptides, enzymes, lantibiotics, chelating agents, biosurfactants, polysaccharides, organic, inorganic, and metal nanoparticles, etc., have been reviewed to overcome biofilm-associated healthcare problems. From their extensive literature survey, it can be concluded that these molecules with considerable structural alterations might be applied to the treatment of biofilm-associated infections, by evaluating their significant delivery to the target site of the host. To design effective anti-biofilm molecules, it must be assured that the minimum inhibitory concentrations of these anti-biofilm compounds can eradicate biofilm-associated infections without causing toxic effects at a significant rate.

Cytocompatible Amphipathic Carbon Quantum Dots as Potent Membrane-Active Antibacterial Agents with Low Drug Resistance and Effective Inhibition of Biofilm Formation

It is very challenging to design nanomaterials with both excellent antibacterial activity and cytocompatibility when facing bacterial infection. Here, inspired by antimicrobial peptides (AMPs), we fabricate carbon quantum dots (CQDs) derived from hydrophobic tryptophan and hydrophilic lysine or arginine (Lys/Trp-CQDs and Arg/Trp-CQDs), which possess amphipathic properties. These CQDs could effectively destroy bacterial membranes without developing resistance, inhibit biofilms formed by Staphylococcus aureus, and exhibit good in vitro biocompatibility. The antibacterial activities are caused by not only surface cationic structures and excess intracellular reactive oxygen species (ROS) generated by the CQDs but also the effects of the surface hydrophobic groups. These combined mechanisms of actions lead to bacterial membrane disruption, which raises the hope for combating bacterial infection without concern about drug resistance. What's more, the effect of amphiphilicity on balancing sterilization with biocompatibility expands the research ideas for developing available antibacterial nanomaterials.

In vitro anti-clostridial action and potential of the spice herbs essential oils to prevent biofilm formation of hypervirulent Clostridioides difficile strains isolated from hospitalized patients with CDI

BACKGROUND

Clostridioides difficile is the most common causative agent of antibiotic-acquired diarrhea in hospitalized patients associated with substantial morbidity and mortality. The global epidemic of CDI (Clostridioides difficile infection) began in the early 20th century with the emergence of the hypervirulent and resistant ribotype 027 strains, and requires an urgent search for new therapeutic agents.

OBJECTIVE

The aim of this study is to investigate the antibacterial activity of the three essential oils isolated from spice herbs (wild oregano, garlic and black pepper) against C. difficile clinical isolates belonging to 6 different PCR ribotypes and their potential inhibitory effect on the biofilm production in in vitro conditions.

RESULTS

Wild oregano essential oil showed strong inhibitory activity in concentrations 0.02-1.25 mg/mL and bactericidal activity in concentrations from 0.08 to 10 mg/mL. Garlic essential oil was effective in the concentration range of 0.02-40 mg/mL, and 0.16 - > 40 mg/mL. MIC and MBC for black pepper oil ranged from 0.04 to 40 mg/mL, and 0.08 - > 40 mg/mL, respectively. All the tested oils reduced in vitro biofilm production, with the best activity of oregano oil.

CONCLUSION

Essential oils of wild oregano, black pepper and garlic are candidates for adjunctive therapeutics in the treatment of CDI. Oregano oil should certainly be preferred due to the lack of selectivity of action in relation to the ribotype, the strength of the produced biofilm and/or antibiotic-susceptibility patterns.

Clinical Escherichia coli: From Biofilm Formation to New Antibiofilm Strategies

Escherichia coli is one of the species most frequently involved in biofilm-related diseases, being especially important in urinary tract infections, causing relapses or chronic infections. Compared to their planktonic analogues, biofilms confer to the bacteria the capacity to be up to 1000-fold more resistant to antibiotics and to evade the action of the host’s immune system. For this reason, biofilm-related infections are very difficult to treat. To develop new strategies against biofilms, it is important to know the mechanisms involved in their formation. In this review, the different steps of biofilm formation in E. coli, the mechanisms of tolerance to antimicrobials and new compounds and strategies to combat biofilms are discussed.