eDNA Inactivation and Biofilm Inhibition by the PolymericBiocide Polyhexamethylene Guanidine Hydrochloride (PHMG-Cl)

Metal-based nanoparticles: an alternative treatment for biofilm infection in hard-to-heal wounds

Metal-based nanoparticles (MNPs) are promoted as effective compounds in the treatment of bacterial infections and as possible alternatives to antibiotics. These MNPs are known to affect a broad spectrum of microorganisms using a multitude of strategies, including the induction of reactive oxygen species and interaction with the inner structures of the bacterial cells. The aim of this review was to summarise the latest studies about the effect of metal-based nanoparticles on pathogenic bacterial biofilm formed in wounds, using the examples of Gram-positive bacterium Staphylococcus aureus and Gram-negative bacterium Pseudomonas aeruginosa, as well as provide an overview of possible clinical applications.

Synthesis and antimicrobial properties of guanidine-functionalized labdane type diterpenoids

The occurrence of increased antibiotic resistance has reduced the availability of drugs effective in the control of infectious diseases, especially those caused by various combinations of bacteria and/or fungi that are often associated with poorer patient outcomes. In the hunt for novel antibiotics of interest to treat polymicrobial diseases, molecules bearing guanidine moieties have recently come to the fore in designing and optimizing antimicrobial agents. Due to their remarkable antibacterial and antifungal activities, labdane diterpenes are also attracting increasing interest in antimicrobial drug discovery. In this study, six different guanidines prenylated with labdanic fragments were synthesized and evaluated for their antimicrobial properties. Assays were carried out against both non-resistant and antibiotic-resistant bacteria strains, while their possible antifungal activities have been tested on the yeast Candida albicans. Two of the synthesized compounds, namely labdan-8,13(R)-epoxy-15-oyl guanidine and labdan-8,13(S)-epoxy-15-oyl guanidine, were finally selected as the best candidates for further developments in drug discovery, due to their antimicrobial effects on both Gram-negative and Gram-positive bacterial strains, their fungicide action, and their moderate toxicity in vivo on zebrafish embryos. The study also provides insights into the structure-activity relationships of the guanidine-functionalized labdane-type diterpenoids.

Polyhexamethylene guanidine hydrochloride as promising active ingredient for oral antiseptic products to eliminate microorganisms threatening the health of endangered wild cats: a comparative study with chlorhexidine digluconate

The aim of this study was to evaluate the antimicrobial efficacy of polyhexamethylene hydrochloride guanidine (PHMGH) compared to chlorhexidine digluconate (CLX) for use as an oral antiseptic during dental procedures in wild cats. This research is crucial due to limited information on the diversity of oral microorganisms in wild cats and the detrimental local and systemic effects of oral diseases, which highlights the importance of improving prevention and treatment strategies. Samples were collected from the oral cavities of four Puma concolor, one Panthera onca, and one Panthera leo, and the number of colony-forming units per milliliter (CFU/mL) was counted and semi-automatically identified. The antimicrobial susceptibility profile of bacterial isolates was determined using minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and time-kill kinetics of PHMGH and CLX. A total of 16 bacterial isolates were identified, consisting of six Gram-positive and 10 Gram-negative. PHMGH displayed MIC and MBC from 0.24 to 125.00 μg/mL, lower than those of CLX against three isolates. Time-kill kinetics showed that PHMGH reduced the microbial load by over 90% for all microorganisms within 30 min, whereas CLX did not. Only two Gram-positive isolates exposed to the polymer showed incomplete elimination after 60 min of contact. The results could aid in the development of effective prevention and treatment strategies for oral diseases in large felids. PHMGH showed promising potential at low concentrations and short contact times compared to the commercial product CLX, making it a possible active ingredient in oral antiseptic products for veterinary use in the future.

Femtosecond laser modified metal surfaces alter biofilm architecture and reduce bacterial biofilm formation

Biofilm formation, or microfouling, is a basic strategy of bacteria to colonise a surface and may happen on surfaces of any nature whenever bacteria are present. Biofilms are hard to eradicate due to the matrix in which the bacteria reside, consisting of strong, adhesive and adaptive self-produced polymers such as eDNA and functional amyloids. Targeting a biofilm matrix may be a promising strategy to prevent biofilm formation. Here, femtosecond laser irradiation was used to modify the stainless steel surface in order to introduce either conical spike or conical groove textures. The resulting topography consists of hierarchical nano-microstructures which substantially increase roughness. The biofilms of two model bacterial strains, P. aeruginosa PA01 and S. aureus ATCC29423, formed on such nanotextured metal surfaces, were considerably modified due to a substantial reduction in amyloid production and due to changes in eDNA surface adhesion, leading to significant reduction in biofilm biomass. Altering the topography of the metal surface, therefore, radically diminishes biofilm development solely by altering biofilm architecture. At the same time, growth and colonisation of the surface by eukaryotic adipose tissue-derived stem cells were apparently enhanced, leading to possible further advantages in controlling eukaryotic growth while suppressing prokaryotic contamination. The obtained results are important for developing anti-bacterial surfaces for numerous applications.

Antimicrobial polymer-loaded hydrogels for the topical treatment of multidrug-resistant wound biofilm infections

Integration of antimicrobial polymeric nanoparticles into hydrogel materials presents a promising strategy to address multidrug-resistant biofilm infections. Here we report an injectable hydrogel loaded with engineered cationic antimicrobial polymeric nanoparticles (PNPs) for the effective topical treatment of severe wound biofilm infections. The PNPs demonstrated biofilm penetration and disruption, resulting in the eradication of resistant and persister cells that reside within the biofilm. Significantly, PNPs did not elicit resistance development even after multiple exposures to sub-therapeutic doses. In vitro studies showed PNPs significantly reduced prolonged inflammation due to infection and promoted fibroblast migration. These PNPs were then incorporated into Poloxamer 407 (P407) hydrogels and utilized as an inert carrier for PNPs to provide a controlled and sustained topical release of the antimicrobial nanoparticles at the wound area. In vivo studies using a mature (4-day) wound biofilm infection in a murine model mimicking severe human wound infections demonstrated provided 99% bacterial biofilm clearance and significantly enhanced wound healing. Overall, this work demonstrated the efficacy and selectivity of the antimicrobial polymer-loaded hydrogel platform as a topical treatment for difficult-to-treat wound biofilm infections.

Anti-virulence prospects of Metformin against Pseudomonas aeruginosa: A new dimension to a multifaceted drug

Metformin (MeT) is an FDA-approved drug with a myriad of health benefits. Besides being used as an anti-diabetic drug, MeT is also effective against various cancers, liver-, cardiovascular-, and renal diseases. This study was undertaken to examine its unique potential as an anti-virulence drug against an opportunistic bacterial pathogen, Pseudomonas aeruginosa. Due to the menace of multidrug resistance in pathogenic microorganisms, many novel or repurposed drugs with anti-virulence prospects are emerging as next-generation therapies with the aim to overshadow the application of existing antimicrobial regimens. The quorum sensing (QS) mechanisms of P. aeruginosa are an attractive drug target for attenuating bacterial virulence. In this context, the anti-QS potential of MeT was scrutinized using biosensor assays. MeT was comprehensively evaluated for its effects on different motility phenotypes, virulence factor production (phenotypic and genotypic expression) along with biofilm development in P. aeruginosa in vitro. At sub-lethal concentrations, MeT displayed prolific quorum quenching (QQ) ability and remarkably inhibited AHL biosynthesis in P. aeruginosa. Moreover, MeT (1/8 MIC) effectively downregulated the expression levels of various QS- and virulence genes in P. aeruginosa, which coincided with a notable reduction in the levels of alginate, hemolysin, pyocyanin, pyochelin, elastase, and protease production. In silico analysis through molecular docking also predicted strong associations between MeT and QS receptors of P. aeruginosa. MeT also compromised the motility phenotypes and successfully abrogated biofilm formation by inhibiting EPS production in P. aeruginosa. Hence, MeT may be repurposed as an anti-virulence drug against P. aeruginosa in clinical settings.

K6[P2Mo18O62] as DNase-Mimetic Artificial Nucleases to Promote Extracellular Deoxyribonucleic Acid Degradation in Bacterial Biofilms

In the current study, the DNase-like activity of the Dawson-type polyoxometalate K6[P2Mo18O62] was explored. The obtained findings demonstrated that K6[P2Mo18O62] could effectively cleave phosphoester bonds in the DNA model substrate (4-nitrophenyl phosphate) and result in the degradation of plasmid DNA. Moreover, the application potential of this Dawson-type polyoxometalate as a DNase-mimetic artificial enzyme to degrade extracellular DNA (eDNA) in Escherichia coli (E. coli) bacterial biofilm was explored. The results demonstrated that K6[P2Mo18O62] exhibited high cleavage ability toward eDNA secreted by E. coli and thus eradicated the bacterial biofilm. In conclusion, Dawson-type polyoxometalate K6[P2Mo18O62] possessed desirable DNase-like activity, which could serve as a bacterial biofilm eradication agent by cleaving and degrading eDNA molecules.

α-Terpineol synergizes with gentamicin to rescue Caenorhabditis elegans from Pseudomonas aeruginosa infection by attenuating quorum sensing-regulated virulence

AIMS

This study scrutinized α-Terpineol (α-T) for its anti-virulence and anti-fouling potential against P. aeruginosa PAO1 in conjunction with gentamicin (GeN) using in-vitro, in-silico, and in-vivo approaches.

MAIN METHODS

The quorum quenching (QQ) potential of the drug combination was studied using a quorum sensing (QS) biosensor strain and tested for synergy using chequerboard and time-kill kinetics assays. The effect of α-T and GeN on bacterial motility, QS-regulated virulence factor production, and biofilm formation was assessed in P. aeruginosa PAO1 along with molecular docking analysis. The protective effects of α-T-GeN combination were also examined in a Caenorhabditis elegans infection model through slow-killing (SK) assays.

KEY FINDINGS

The drug combination displayed synergy, enhanced QQ activity, and suppressed AHL production in PAO1. At sub-inhibitory concentrations, the drug combination suppressed the expression of genes regulating QS and pseudomonal virulence, thereby inhibiting the production of virulence factors in PAO1. The drug combination compromised all forms of pseudomonal motility, strongly inhibited biofilm formation, and successfully eradicated preformed biofilms. Based on these findings, it is concluded that GeN (alone) does not harbor any QQ properties, but enhances the QQ potential of α-T. Moreover, combinational treatment protected C. elegans from pseudomonal infection and improved survival rates by 73 % at 96 h.

SIGNIFICANCE

For the first time, the molecular mechanism responsible for the anti-QS activity of α-T was unraveled through a comprehensive investigation, thereby asserting its potential as an anti-virulent drug against P. aeruginosa.

A combination therapy strategy for treating antibiotic resistant biofilm infection using a guanidinium derivative and nanoparticulate Ag(0) derived hybrid gel conjugate

Bacteria organized in biofilms show significant tolerance to conventional antibiotics compared to their planktonic counterparts and form the basis for chronic infections. Biofilms are composites of different types of extracellular polymeric substances that help in resisting several host-defense measures, including phagocytosis. These are increasingly being recognized as a passive virulence factor that enables many infectious diseases to proliferate and an essential contributing facet to anti-microbial resistance. Thus, inhibition and dispersion of biofilms are linked to addressing the issues associated with therapeutic challenges imposed by biofilms. This report is to address this complex issue using a self-assembled guanidinium-Ag(0) nanoparticle (AD-L@Ag(0)) hybrid gel composite for executing a combination therapy strategy for six difficult to treat biofilm-forming and multidrug-resistant bacteria. Improved efficacy was achieved primarily through effective biofilm inhibition and dispersion by the cationic guanidinium ion derivative, while Ag(0) contributes to the subsequent bactericidal activity on planktonic bacteria. Minimum Inhibitory Concentration (MIC) of the AD-L@Ag(0) formulation was tested against Acinetobacter baumannii (25 μg mL-1), Pseudomonas aeruginosa (0.78 μg mL-1), Staphylococcus aureus (0.19 μg mL-1), Klebsiella pneumoniae (0.78 μg mL-1), Escherichia coli (clinical isolate (6.25 μg mL-1)), Klebsiella pneumoniae (clinical isolate (50 μg mL-1)), Shigella flexneri (clinical isolate (0.39 μg mL-1)) and Streptococcus pneumoniae (6.25 μg mL-1). Minimum bactericidal concentration, and MBIC50 and MBIC90 (Minimum Biofilm Inhibitory Concentration at 50% and 90% reduction, respectively) were evaluated for these pathogens. All these results confirmed the efficacy of the formulation AD-L@Ag(0). Minimum Biofilm Eradication Concentration (MBEC) for the respective pathogens was examined by following the exopolysaccharide quantification method to establish its potency in inhibition of biofilm formation, as well as eradication of mature biofilms. These effects were attributed to the bactericidal effect of AD-L@Ag(0) on biofilm mass-associated bacteria. The observed efficacy of this non-cytotoxic therapeutic combination (AD-L@Ag(0)) was found to be better than that reported in the existing literature for treating extremely drug-resistant bacterial strains, as well as for reducing the bacterial infection load at a surgical site in a small animal BALB/c model. Thus, AD-L@Ag(0) could be a promising candidate for anti-microbial coatings on surgical instruments, wound dressing, tissue engineering, and medical implants.

Biocides as Biomedicines against Foodborne Pathogenic Bacteria

Biocides are currently considered the first line of defense against foodborne pathogens in hospitals or food processing facilities due to the versatility and efficiency of their chemical active ingredients. Understanding the biological mechanisms responsible for their increased efficiency, especially when used against foodborne pathogens on contaminated surfaces and materials, represents an essential first step in the implementation of efficient strategies for disinfection as choosing an unsuitable product can lead to antibiocide resistance or antibiotic–biocide cross-resistance. This review describes these biological mechanisms for the most common foodborne pathogens and focuses mainly on the antipathogen effect, highlighting the latest developments based on in vitro and in vivo studies. We focus on biocides with inhibitory effects against foodborne bacteria (e.g., Escherichia spp., Klebsiella spp., Staphylococcus spp., Listeria spp., Campylobacter spp.), aiming to understand their biological mechanisms of action by looking at the most recent scientific evidence in the field.