Reduction In Bacterial Viability Research Articles

Antibiofilm Efficacy of Silver Nanoparticles Alone or Mixed with Calcium Hydroxide as Intracanal Medicaments: An Ex-Vivo Analysis

IntroductionThis study aimed to determine the most effective antibiofilm concentration of silver nanoparticles (AgNPs) alone or in combination with calcium hydroxide (Ca[OH]2) against Fusobacterium nucleatum biofilm. MethodsThe minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of AgNPs alone or with Ca(OH)2 were determined. Dentin slices were sterilized and inoculated with F. nucleatum for 3 weeks to establish a biofilm. Samples were randomly assigned to determine the MIC and MBC for AgNPs alone or mixed with Ca(OH)2. A higher concentration of AgNPs for both preparations was also used. Triple antibiotic paste, Ca(OH)2, and saline were used as controls. Specimens in each group were subdivided over 2 observation periods: 7 and 14 days. At the end of each period, specimens were analyzed with 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) to determine the metabolic activity. Also, samples from each group were assessed by scanning electron microscopy. ResultsThe MIC and MBC of AgNPs alone against F. nucleatum coincided at 0.04%. The combination of AgNPs + Ca(OH)2 exhibited a lower MIC and MBC of 0.03%. MTT analysis showed a significant reduction in bacterial viability in all groups compared with negative controls (P < .05). A more substantial reduction in bacterial cells was observed with increasing concentrations of AgNPs at both periods. The combination (AgNPs [0.06%] + Ca[OH]2) was the most potent against F. nucleatum. ConclusionsThe findings demonstrated that combining AgNPs with Ca(OH)2 was more effective on the F. nucleatum biofilm than either material alone, suggesting a combined effect.

Photodynamic antimicrobial chemotherapy coupled with the use of the photosensitizers methylene blue and temoporfin as a potential novel treatment for Staphylococcus aureus in burn infections.

Photodynamic antimicrobial chemotherapy (PACT) is a novel alternative antimicrobial therapy that elicits a broad mechanism of action and therefore has a low probability of generating resistance. Such properties make PACT ideally suited for utilization in localized applications such as burn wounds. The aim of this study was to determine the antimicrobial activity of MB and temoporfin against both a S. aureus isolate and a P. aeruginosa isolate in light (640 nm) and dark conditions at a range of time points (0–20 min). A Staphylococcus aureus isolate and a Pseudomonas aeruginosa isolate were treated in vitro with methylene blue (MB) and temoporfin under different conditions following exposure to light at 640 nm and in no-light (dark) conditions. Bacterial cell viability [colony-forming units (c.f.u.) ml−1] was then calculated. Against P. aeruginosa , when MB was used as the photosensitizer, no phototoxic effect was observed in either light or dark conditions. After treatment with temoporfin, a reduction of less than one log (7.00×107 c.f.u. ml−1) was observed in the light after 20 min of exposure. However, temoporfin completely eradicated S. aureus in both light and dark conditions after 1 min (where a seven log reduction in c.f.u. ml−1 was observed). Methylene blue resulted in a loss of S. aureus viability, with a two log reduction in bacterial viability (c.f.u. ml−1) reported in both light and dark conditions after 20 min exposure time. Temoporfin demonstrated greater antimicrobial efficacy than MB against both the S. aureus and P. aeruginosa isolates tested. At 12.5 µM temoporfin resulted in complete eradication of S. aureus . In light of this study, further research into the validity of PACT, coupled with the photosensitizers (such as temoporfin), should be conducted in order to potentially develop alternative antimicrobial treatment regimes for burn wounds.

A traditional Ugandan Ficus natalensis bark cloth exhibits antimicrobial activity against methicillin-resistant Staphylococcus aureus.

Surgical site, soft tissue and wound infections are some of the most prominent causes of healthcare-associated infections (HCAIs). Developing novel antimicrobial textiles and wound dressings may help alleviate the risk of developing HCAIs. We aimed to determine the antimicrobial efficacy of natural Ugandan bark cloth derived exclusively from the Ficus natalensis tree. Antimicrobial contact and disc diffusion assays, coupled with time-kill kinetic assays, demonstrated that bark cloth inhibited the growth of a clinically relevant methicillin-resistant Staphylococcus aureus (MRSA) strain and acted as a bactericidal agent causing a seven-log reduction in bacterial viability. Scanning electron microscopy was used to reveal morphological changes in the bacterial cell ultrastructure when exposed to bark cloth, which supported a proposed mechanism of antimicrobial activity. The observed antimicrobial properties, combined with the physical characteristics elicited by bark cloth, suggest this product is ideally suited for wound and other skin care applications. This is the first report where a whole bark cloth product made by traditional methods has been employed as an antimicrobial fabric against MRSA. Bark cloth is a highly sustainable and renewable product and this study presents a major advance in the search for natural fabrics which could be deployed for healthcare applications.

Is a reduction in viability enough to determine biofilm susceptibility to a biocide?

The abundance and prevalence of dry-surface biofilms (DSBs) in hospitals constitute an emerging problem, yet studies rarely report the cleaning and disinfection efficacy against DSBs. Here, the combined impact of treatments on viability, transferability, and recovery of bacteria from DSBs has been investigated for the first time. Staphylococcus aureus DSBs were produced in alternating 48-hour wet-dry cycles for 12 days on AISI 430 stainless steel discs. The efficacy of 11 commercially available disinfectants, 4 detergents, and 2 contactless interventions were tested using a modified standardized product test. Reduction in viability, direct transferability, cross transmission (via glove intermediate), and DSB recovery after treatment were measured. Of 11 disinfectants, 9 were effective in killing and removing bacteria from S. aureus DSBs with >4 log10 reduction. Only 2 disinfectants, sodium dichloroisocyanurate 1,000 ppm and peracetic acid 3,500 ppm, were able to lower both direct and cross transmission of bacteria (<2 compression contacts positive for bacterial growth). Of 11 disinfectants, 8 could not prevent DSB recovery for >2 days. Treatments not involving mechanical action (vaporized hydrogen peroxide and cold atmospheric plasma) were ineffective, producing <1 log10 reduction in viability, DSB regrowth within 1 day, and 100% transferability of DSB after treatment. Reduction in bacterial viability alone does not determine product performance against biofilm and might give a false sense of security to consumers, manufacturers and regulators. The ability to prevent bacterial transfer and biofilm recovery after treatment requires a better understanding of the effectiveness of biocidal products.

A bilayered skin substitute developed using an eggshell membrane crosslinked gelatin-chitosan cryogel.

Commercially available allografts and xenografts pose problems such as high cost, risk of infection transmission and immune rejection of grafts. Thus, bioengineered skin substitutes fabricated from natural biomaterials or synthetic polymers are currently the focus of skin tissue engineering. In this study, eggshell membrane (ESM) powder was used to crosslink a gelatin-chitosan cryogel thereby replacing glutaraldehyde, a known cytotoxic chemical crosslinker. The resultant ESM-crosslinked macroporous cryogel with a pore size ranging between 10 and 350 μm has improved flexibility, biodegradability and biocompatibility compared to a glutaraldehyde-crosslinked cryogel. For healing of large and deep wounds, bilayered scaffolds which exhibit key aspects of skin physiology are being explored. Hence, we fabricated a bilayered substitute by coupling the ESM-crosslinked cryogel (dermal equivalent) to a non-porous, physically-crosslinked gelatin-chitosan film (epidermal equivalent). The epidermal layer provides the requisite barrier properties while the dermal layer facilitates cell attachment and migration for optimal wound healing. Further, chitosan confers antibacterial properties to the cryogel with almost 50% reduction in bacterial viability. Animal studies confirm that the developed bilayered skin substitute is non-allergic, aids wound healing by improving re-epithelialization within 14 days and supports the formation of skin appendages. This system presents a new and alternative treatment option for burn and chronic wounds.

Interaction of the surface bound antimicrobial peptides melimine and Mel4 with Staphylococcus aureus

Melimine and Mel4 are cationic antimicrobial peptides which can resist biofilm development once bound to biomaterials. The aim of the current study was to determine the mode of action of bound melimine and Mel4 against S. aureus. The peptides were covalently attached to glass using an azidobenzoic acid linker. The amount of attached peptides was confirmed by XPS and amino acid analysis and their covalent attachment by SDS extraction. The release of autolysins after interaction of S. aureus with immobilized peptides was determined in cell free supernatants. The interaction of immobilized peptides with lipoteichoic acid was confirmed by ELISA. Membrane damage by surface bound peptides was assessed using DiSC(3)-5 (membrane potential sensitive), Syto-9 (membrane permeable) and PI (membrane impermeable) dyes with fluorescence microscopy. Release of ATP and nucleic acids (DNA/RNA) was measured in the surrounding fluid. Attachment of the peptides resulted in increased N% for melimine (5.4 ± 1.8%) and for Mel4 (4.8 ± 1.8%). The concentrations of immobilised amino acids were 0.297 nmole for melimine and 0.358 nmole for Mel4. SDS extraction released < 15% of peptides from the glass. The immobilized peptides bound ≥ 4 times more LTA than control surfaces. More autolysins (8 ± 2%; p = 0.026) were released from Mel4 than melimine or control surfaces. Membrane depolarization occurred at 15 min and was associated with a reduction in bacterial viability ≥ 37% for both peptides (p < 0.001). Disruption of the membrane potential resulted in loss of ATP from melimine (0.9 ± 0.4 nM) or Mel4 (0.6 ± 0.3 nM) coated surfaces compared to control (p < 0.001). Melimine coatings yielded 27 ± 11% (p = 0.026) and Mel4 gave 17 ± 12% (p = 0.150) PI stained cells after 4 h. DNA/RNA was released only by melimine coatings (2.1 ± 0.1 times; p = 0.011) compared to process control at 6 h. Both bound peptides resulted in the release of ATP, but only melimine released DNA/RNA while Mel4-coating resulted in the release of autolysins. Since the mode of action of melimine and Mel4 relate to the cell surface, they have potential for the development of infection-resistant implants.

Electrospun Bioabsorbable Fibers Containing S-Nitrosoglutathione for Tissue Engineering Applications.

Blended and coaxial fibers comprising polycaprolactone and gelatin, containing the endogenous nitric oxide (NO) donor S-nitrosoglutathione (GSNO), were electrospun. Both types of fibers had their NO release profiles tested under physiological conditions to examine their potential applications as biomedical scaffolds. The coaxial fibers exhibited a prolonged and consistent release of NO over the course of 4 d from the core-encapsulated GSNO, while the blended fibers had a large initial release and leaching of GSNO that was exhausted over a shorter period of time. Bacterial testing of both fiber scaffolds was conducted over a 24 h period against Staphylococcus aureus (S. aureus) and demonstrated a 3-log reduction in bacterial viability. In addition, no cytotoxic response was reported when the material was tested on mouse fibroblast cells in vitro. These fibrous matrices were also shown to support cell growth, attachment, and overall activity of fibroblasts when exposed to NO, especially when GSNO was encapsulated within coaxial fibers. From an application point of view, these NO-releasing fibers offer great potential in tissue engineering and biomedical applications because of the crucial role of NO in regulating a variety of biological processes in humans such as angiogenesis, tissue remodeling, and eliminating foreign pathogens.

Unravelling the antimicrobial action of antidepressants on gut commensal microbes

Over the past decade, there has been increasing evidence highlighting the implication of the gut microbiota in a variety of brain disorders such as depression, anxiety, and schizophrenia. Studies have shown that depression affects the stability of gut microbiota, but the impact of antidepressant treatments on microbiota structure and metabolism remains underexplored. In this study, we investigated the in vitro antimicrobial activity of antidepressants from different therapeutic classes against representative strains of human gut microbiota. Six different antidepressants: phenelzine, venlafaxine, desipramine, bupropion, aripiprazole and (S)-citalopram have been tested for their antimicrobial activity against 12 commensal bacterial strains using agar well diffusion, microbroth dilution method, and colony counting. The data revealed an important antimicrobial activity (bacteriostatic or bactericidal) of different antidepressants against the tested strains, with desipramine and aripiprazole being the most inhibitory. Strains affiliating to most dominant phyla of human microbiota such as Akkermansia muciniphila, Bifidobacterium animalis and Bacteroides fragilis were significantly altered, with minimum inhibitory concentrations (MICs) ranged from 75 to 800 μg/mL. A significant reduction in bacterial viability was observed, reaching 5 logs cycle reductions with tested MICs ranged from 400 to 600 μg/mL. Our findings demonstrate that gut microbiota could be altered in response to antidepressant drugs.

Multifunctional Response of Piezoelectric Sodium Potassium Niobate (NKN)-Toughened Hydroxyapatite-Based Biocomposites

In this study, hydroxyapatite (HA)-sodium potassium niobate (NKN) composites with varying concentrations of NKN (10, 20, and 30 wt %) were optimally developed at 1075 °C for 2 h. Detailed microstructural analyses have been performed by means of scanning and transmission electron microscopy. The maximum fracture toughness, hardness, and compressive and flexural strengths were obtained to be ∼209, ∼93, ∼112, and ∼88%, respectively, for the HA-30 wt % NKN composite compared to monolithic HA. The antibacterial tests revealed the significant reduction in bacterial viability on poled (@ 20 kV for 30 min at 500 °C) HA-NKN composite samples while cultured with Staphylococcus aureus and Escherichia coli bacteria. The cytocompatibility tests revealed the significantly enhanced MG63 cell proliferation for electrical stimulation-treated negatively charged HA and H30N composite samples.

Vinegar inhibits the formation of oral biofilm in situ

BackgroundVinegar has been recognized as an effective antimicrobial agent for long. This study intended to elucidate the effect of commercially available vinegar on in situ pellicle formation and existing 24-h biofilms.MethodsIn situ biofilm formation took place on bovine enamel slabs mounted in individual splints and exposed intraorally over 3 min and 24 h, respectively. After 5 s rinsing with vinegar, all samples were analyzed via fluorescence microscopy (FM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In addition, salivary samples were collected and analyzed via FM. Samples with water rinsing served as controls.ResultsVinegar caused destruction of the pellicle. Compared to the control group, vinegar rinsing reduced the outer globular layer of the pellicle (p < 0.001), and resulted in formation of subsurface pellicle. Also, vinegar rinsing could reduce bacterial viability and disrupt the 24-h biofilm. Total bacteria amount of saliva samples decreased remarkably (p < 0.001) after vinegar rinsing within 30 min. Reduction of bacterial viability was observed even 120 min after vinegar rinsing in both biofilm and saliva sample (p < 0.001).ConclusionThis in situ study reveals that rinsing with vinegar for only 5 s alters the pellicle layer resulting in subsurface pellicle formation. Furthermore, vinegar rinsing will destruct mature (24-h) biofilms, and significantly reduce the viability of planktonic microbes in saliva, thereby decreasing biofilm formation.

Susceptibility of monomicrobial or polymicrobial biofilms derived from infected diabetic foot ulcers to topical or systemic antibiotics in vitro.

Diabetic foot ulcers can become chronic and non-healing despite systemic antibiotic treatment. The penetration of systematically-administered antibiotics to the site of infection is uncertain, as is the effectiveness of such levels against polymicrobial biofilms. We have developed an in vitro model to study the effectiveness of different treatments for infected diabetic foot ulcers in a wound-like environment and compared the activity of systemic levels of antibiotics with that for topically applied antibiotics released from calcium sulfate beads. This is the first study that has harvested bacteria from diabetic foot infections and recreated similar polymicrobial biofilms to those present in vivo for individual subjects. After treatment with levels of gentamicin attained in serum after systemic administration (higher than corresponding tissues concentrations) we measured a 0–2 log reduction in bacterial viability of P. aeruginosa, S. aureus or a polymicrobial biofilm. Conversely, addition of gentamicin loaded calcium sulfate beads resulted in 5–9 log reductions in P. aeruginosa, S aureus and polymicrobial biofilms derived from three subjects. We conclude that systemically administered antibiotics are likely to be inadequate for successfully treating these infections, especially given the vastly increased concentrations required to inhibit cells in a biofilm, and that topical antibiotics provide a more effective alternative.

Mechanism of Action of Surface Immobilized Antimicrobial Peptides Against Pseudomonas aeruginosa.

Bacterial colonization and biofilm development on medical devices can lead to infection. Antimicrobial peptide-coated surfaces may prevent such infections. Melimine and Mel4 are chimeric cationic peptides showing broad-spectrum antimicrobial activity once attached to biomaterials and are highly biocompatible in animal models and have been tested in Phase I and II/III human clinical trials. These peptides were covalently attached to glass using an azidobenzoic acid linker. Peptide attachment was confirmed using X-ray photoelectron spectroscopy and amino acid analysis. Mel4 when bound to glass was able to adopt a more ordered structure in the presence of bacterial membrane mimetic lipids. The ability of surface bound peptides to neutralize endotoxin was measured along with their interactions with the bacterial cytoplasmic membrane which were analyzed using DiSC(3)-5 and Sytox green, Syto-9, and PI dyes with fluorescence microscopy. Leakage of ATP and nucleic acids from cells were determined by analyzing the surrounding fluid. Attachment of the peptides resulted in increases in the percentage of nitrogen by 3.0% and 2.4%, and amino acid concentrations to 0.237 nmole and 0.298 nmole per coverslip on melimine and Mel4 coated surfaces, respectively. The immobilized peptides bound lipopolysaccharide and disrupted the cytoplasmic membrane potential of Pseudomonas aeruginosa within 15 min. Membrane depolarization was associated with a reduction in bacterial viability by 82% and 63% for coatings melimine and Mel4, respectively (p < 0.001). Disruption of membrane potential was followed by leakage of ATP from melimine (1.5 ± 0.4 nM) or Mel4 (1.3 ± 0.2 nM) coated surfaces compared to uncoated glass after 2 h (p < 0.001). Sytox green influx started after 3 h incubation with either peptide. Melimine coatings yielded 59% and Mel4 gave 36% PI stained cells after 4 h. Release of the larger molecules (DNA/RNA) commenced after 4 h for melimine (1.8 ± 0.9 times more than control; p = 0.008) and after 6 h with Mel4 (2.1 ± 0.2 times more than control; p < 0.001). The mechanism of action of surface bound melimine and Mel4 was similar to that of the peptides in solution, however, their immobilization resulted in much slower (approximately 30 times) kinetics.

Chitosan-based nitric oxide-releasing dressing for anti-biofilm and in vivo healing activities in MRSA biofilm-infected wounds

Bacterial biofilms on wounds impair the healing process and often lead to chronic wounds. Chitosan is a well-known biopolymer with antimicrobial and anti-biofilm effects. S-nitrosoglutathione (GSNO) has been identified as a promising nitric oxide (NO) donor to defend against pathogenic biofilms and enhance wound healing activities. In this study, we prepared NO-releasing chitosan film (CS/NO film) and evaluated its anti-biofilm activity and in vivo wound healing efficacy against methicillin-resistant Staphylococcus aureus (MRSA) biofilm-infected wounds in diabetic mice. The in vitro release study showed sustained release of NO over 3 days in simulated wound fluid. The CS/NO film significantly enhanced antibacterial activity against MRSA by > 3 logs reduction in bacterial viability. Moreover, CS/NO film exhibited a 3-fold higher anti-biofilm activity than the control and CS film. In in vivo MRSA biofilm-infected wounds, the CS/NO film-treated group showed faster biofilm dispersal, wound size reduction, epithelialization rates, and collagen deposition than the untreated and CS film-treated groups. Therefore, the CS/NO film investigated in this study could be a promising approach for the treatment of MRSA biofilm-infected wounds.

Trans,trans-farnesol, an antimicrobial natural compound, improves glass ionomer cement properties.

A series of experiments were conducted to characterize a novel restorative material. We explored the effect on biological, physical and chemical properties of glass ionomer cement (GIC) adding-the naturally occurring tt-farnesol (900 mM). Two groups were accomplished for all assays: GIC+tt-farnesol and GIC (control). Biological assays: 1) agar diffusion against some cariogenic bacteria; 2) S. mutans biofilm formation and confocal laser scanning microscopy-CLSM. 3) gtfB, gtfC, gtfD, gbpB, vicR, and covR expression; 4) MTT and microscopic morphology. Physical properties assays: 1) roughness; 2) hardness; 3) compressive strength and 4) diametral tensile strength. Chemical assay: Raman spectroscopy. The adding of tt-farnesol to GIC led to larger zones of inhibition (p<0.05), biofilms with a short-term reduction in bacterial viability but similar biomass (p>0.05). Polysaccharides levels increased over time, similarly over groups (p>0.05). Viable and non-viable S. mutans were seen on the specimens’ surface by CLSM but their virulence was not modulated by tt-farnesol. The tt-farnesol increased the HaCaT cell viability without impact on compressive and diametral tensile strength and roughness although the hardness was positively affected (p<0.05). Raman confirmed the presence of tt-farnesol. The incorporation of tt-farnesol into GIC inhibited the growth of cariogenic bacteria but had a little effect on the composition, structure and physiology of the biofilm matrices. Also, the tt-farnesol increased the hardness and the biocompatibility of the GIC, not influencing negatively other physical properties of the restorative material.

In Vivo Antibacterial Efficacy of Nitric Oxide-Releasing Hyperbranched Polymers against Porphyromonas gingivalis.

The in vivo antibacterial activity of NO-releasing hyperbranched polymers was evaluated against Porphyromonas gingivalis, a key oral pathogen associated with periodontitis, using a murine subcutaneous chamber model. Escalating doses of NO-releasing polymers (1.5, 7.5, and 37.5 mg/kg) were administered into a P. gingivalis-infected chamber once a day for 3 days. Chamber fluids were collected on day 4, with microbiological evaluation indicating a dose-dependent bactericidal action. In particular, NO-releasing polymers at 37.5 mg/kg (1170 μg of NO/kg) achieved complete bacterial eradication (>6-log reduction in bacterial viability), demonstrating greater efficacy than amoxicillin (∼4-log reduction in bacterial viability), a commonly used antibiotic. Time-kill assays further revealed that largest dose (37.5 mg/kg; 1170 μg of NO/kg) resulted in ∼3-log killing of P. gingivalis after only a single dose. Based on these results, the potential clinical utility of NO-releasing hyperbranched polymers appears promising, particularly for oral health applications.

Sodium Hyaluronate Nanocomposite Respirable Microparticles to Tackle Antibiotic Resistance with Potential Application in Treatment of Mycobacterial Pulmonary Infections.

Tuberculosis resistant cases have been estimated to grow every year. Besides Mycobacterium tuberculosis, other mycobacterial species are responsible for an increasing number of difficult-to-treat infections. To increase efficacy of pulmonary treatment of mycobacterial infections an inhalable antibiotic powder targeting infected alveolar macrophages (AMs) and including an efflux pump inhibitor was developed. Low molecular weight sodium hyaluronate sub-micron particles were efficiently loaded with rifampicin, isoniazid and verapamil, and transformed in highly respirable microparticles (mean volume diameter: 1 μm) by spray drying. These particles were able to regenerate their original size upon contact with aqueous environment with mechanical stirring or sonication. The in vitro drugs release profile from the powder was characterized by a slow release rate, favorable to maintain a high drug level inside AMs. In vitro antimicrobial activity and ex vivo macrophage infection assays employing susceptible and drug resistant strains were carried out. No significant differences were observed when the powder, which did not compromise the AMs viability after a five-day exposure, was compared to the same formulation without verapamil. However, both preparations achieved more than 80% reduction in bacterial viability irrespective of the drug resistance profile. This approach can be considered appropriate to treat mycobacterial respiratory infections, regardless the level of drug resistance.

Evaluating the Potential for Resistance Development to Antimicrobial Blue Light (at 405 nm) in Gram-Negative Bacteria: In vitro and in vivo Studies.

Antimicrobial resistance is a threat to public health that requires our immediate attention. With increasing numbers of microbes that are becoming resistant to routinely used antimicrobials, it is vital that we look to other, non-traditional therapies for the treatment of infections. Antimicrobial blue light (aBL) is an innovative approach that has demonstrated efficacy for the inactivation of an array of microbial pathogens. In the present study, we investigated the potential for resistance development to aBL in Gram-negative pathogenic bacteria by carrying out multiple aBL exposures on bacteria. In the first aBL exposure, clinical isolates of Pseudomonas aeruginosa, Acinetobacter baumannii, and uropathogenic Escherichia coli [107 colony forming units/mL (CFU/mL)] were irradiated in phosphate-buffered saline with aBL at 405 nm until a >99.99% reduction in bacterial viability was achieved. Irradiation was then repeated for each bacterial species over 20 cycles of aBL exposure. The potential for resistance development to aBL was also investigated in vivo, in superficial mouse wounds infected with a bioluminescent strain of P. aeruginosa (PAO1; 108 CFU) and irradiated with a sub-curative radiant exposures of 108 or 216 J/cm2 aBL over 5 cycles of treatment (over 5 days) prior to bacterial isolation from the animal tissue. PAO1 isolated from infected tissue were treated with aBL at 216 J/cm2, in vitro, in parallel with unexposed PAO1 or PAO1 isolates from mouse wound infections not treated with aBL. No statistically significant correlation was found between the aBL-susceptibility of bacteria in vitro and the number of cycles of aBL exposure any bacterial species (P ≥ 0.26). In addition, serial exposure of infected mouse wounds to aBL did not result in any change in the susceptibility to aBL of PAO1 (P = 0.97). In conclusion, it is unlikely that sequential exposure to aBL will result in aBL-resistance in Gram-negative bacteria. Also, multiple aBL treatments may potentially be administered to an infected wound without resistance development becoming a concern.

Antimicrobial photodynamic therapy alone or in combination with antibiotic local administration against biofilms of Fusobacterium nucleatum and Porphyromonas gingivalis

Antimicrobial photodynamic therapy (aPDT) kills several planktonic pathogens. However, the susceptibility of biofilm-derived anaerobic bacteria to aPDT is poorly characterized. Here, we evaluated the effect of Photodithazine (PDZ)-mediated aPDT on Fusobacterium nucleatum and Porphyromonas gingivalis biofilms. In addition, aPDT was tested with metronidazole (MTZ) to explore the potential antimicrobial effect of the treatment. The minimum inhibitory concentration (MIC) of MTZ was defined for each bacterial species. Single-species biofilms of each species were grown on polystyrene plates under anaerobic conditions for five days. aPDT was performed by applying PDZ at concentrations of 50, 75 and 100 mg/L, followed by exposure to 50 J/cm2 LED light (660 nm) with or without MTZ. aPDT exhibited a significant reduction in bacterial viability at a PDZ concentration of 100 mg/L, with 1.12 log10 and 2.66 log10 reductions for F. nucleatum and P. gingivalis in biofilms, respectively. However, the antimicrobial effect against F. nucleatum was achieved only when aPDT was combined with MTZ at 100× MIC. Regarding P. gingivalis, the combination of PDZ-mediated aPDT at 100 mg/L with MTZ 100× MIC resulted in a 5 log10 reduction in the bacterial population. The potential antimicrobial effects of aPDT in combination with MTZ for both single pathogenic biofilms were confirmed by live/dead staining. These results suggest that localized antibiotic administration may be an adjuvant to aPDT to control F. nucleatum and P. gingivalis biofilms.

A Novel Silver Bioactive Glass Elicits Antimicrobial Efficacy Against Pseudomonas aeruginosa and Staphylococcus aureus in an ex Vivo Skin Wound Biofilm Model.

Biofilm infection is now understood to be a potent contributor to the recalcitrant nature of chronic wounds. Bacterial biofilms evade the host immune response and show increased resistance to antibiotics. Along with improvements in antibiotic stewardship, effective new anti-biofilm therapies are urgently needed for effective wound management. Previous studies have shown that bioactive glass (Bg) is able to promote healing with moderate bactericidal activity. Here we tested the antimicrobial efficacy of a novel BG incorporating silver (BgAg), against both planktonic and biofilm forms of the wound-relevant bacteria Pseudomonas aeruginosa and Staphylococcus aureus. BgAg was stable, long lasting, and potently effective against planktonic bacteria in time-kill assays (6-log reduction in bacterial viability within 2 h) and in agar diffusion assays. BgAg reduced bacterial load in a physiologically relevant ex vivo porcine wound biofilm model; P. aeruginosa (2-log reduction) and S. aureus (3-log reduction). BgAg also conferred strong effects against P. aeruginosa biofilm virulence, reducing both protease activity and virulence gene expression. Co-culture biofilms appeared more resistant to BgAg, where a selective reduction in S. aureus was observed. Finally, BgAg was shown to benefit the host response to biofilm infection, directly reducing host tissue cell death. Taken together, the findings provide evidence that BgAg elicits potent antimicrobial effects against planktonic and single-species biofilms, with beneficial effects on the host tissue response. Further investigations are required to elucidate the specific consequences of BG administration on polymicrobial biofilms, and further explore the effects on host–microbe interactions.

New sol–gel synthesis of NiO antibacterial nano-pigment and its application as healthcare coating

This report deals with the fabrication of NiO nanoparticle (NiO Nps) dispersed alkyd coating and its antimicrobial activity. NiO Nps is prepared by novel sol–gel technique using pectic polysaccharides as a gelling agent. The gelling agent converts the hydroxo-metal network into a gel within 4 h of time. After calcination, the FESEM and TEM micrograph of the obtained NiO Nps shows cubic and irregular shaped structures with size ranging from 30 to 200 nm. The structural characterizations have been evaluated through XRD, FTIR, UV–vis and VSM studies. The antimicrobial activity of NiO Nps has been carried out against both gram negative and gram positive bacteria namely Escherichia coli, Klebsiella pneumonia and Proteus vulgaris, Streptococcus mutans, Bacillus subtilis, and Staphylococcus aureus. The findings of the present study indicate that the NiO Nps permeate the bacterial cell wall, accumulated inside thereby facilitating the synergistic impact against the growth of bacterial strains. The experimental outcomes suggest the potential use of NiO as pigments in the alkyd coating. Alkyd coating consisting of NiO Nps exhibits considerable reduction in bacterial viability when it comes in contact against microbial strains, proving the efficacy of the coating.