Degradable Microneedle Patch with Photothermal-Promoted Bacteria-Infected Wound Healing and Microenvironment Remodeling.

Bacteria-infected wound healing is one of the most challenging issues in health management that is attracting worldwide concerns. Despite great achievements with antibiotics, emergence of antibiotic-resistance retarded the wound healing process and also led to severe outcomes. Exploration of novel antibiotics together with amelioration of wound healing efficacy is desirable. Herein, a degradable microneedle patch (AAZH@MNs) was fabricated through incorporating near-infrared light responsive photothermal agents for sustained bacteria killing and prevention of biofilm formation. In addition, the antibacterial microneedle patch could even remold the microenvironment of bacteria-infected wounds through an antibacterial effect, significantly facilitating the wound healing process.

Assessment of multispecies biofilm growth on root canal dentin under different radiation therapy regimens.

OBJECTIVES: To assess the growth of a multispecies biofilm on root canal dentin under different radiotherapy regimens. MATERIALS AND METHODS: Sixty-three human root dentin cylinders were distributed into six groups. In three groups, no biofilm was formed (n = 3): NoRT) non-irradiated dentin; RT55) 55 Gy; and RT70) 70 Gy. In the other three groups (n = 18), a 21-day multispecies biofilm (Enterococcus faecalis, Streptococcus mutans, and Candida albicans) was formed in the canal: NoRT + Bio) non-irradiated + biofilm; RT55 + Bio) 55 Gy + biofilm; and RT70 + Bio) 70 Gy + biofilm. The biofilm was quantified (CFUs/mL). Biofilm microstructure was assessed under SEM. Microbial penetration into dentinal tubules was assessed under CLSM. For the biofilm biomass and dentin microhardness pre- and after biofilm growth assessments, 45 bovine dentin specimens were distributed into three groups (n = 15): NoRT) non-irradiated + biofilm; RT55 + Bio) 55 Gy + biofilm; and RT70 + Bio) 70 Gy + biofilm. RESULTS: Irradiated specimens (70 Gy) had higher quantity of microorganisms than non-irradiated (p = .010). There was gradual increase in biofilm biomass from non-irradiated to 55 Gy and 70 Gy (p < .001). Irradiated specimens had greater reduction in microhardness after biofilm growth. Irradiated dentin led to the growth of a more complex and irregular biofilm. There was microbial penetration into the dentinal tubules, regardless of the radiation regimen. CONCLUSION: Radiotherapy increased the number of microorganisms and biofilm biomass and reduced dentin microhardness. Microbial penetration into dentinal tubules was noticeable. CLINICAL RELEVANCE: Cumulative and potentially irreversible side effects of radiotherapy affect biofilm growth on root dentin. These changes could compromise the success of endodontic treatment in oncological patients undergoing head and neck radiotherapy.

High-Intensity Blue Light (450-460 nm) Phototherapy for Pseudomonas aeruginosa-Infected Wounds.

Background: Nosocomial wound infection with Pseudomonas aeruginosa (PA) is a serious complication often responsible for the septic mortality of burn patients. Objective: High-intensity antimicrobial blue light (aBL) treatment may represent an alternative therapy for PA infections and will be investigated in this study. Methods: Antibacterial effects of a light-emitting diode array (450-460 nm; 300 mW/cm2; 15/30 min; 270/540 J/cm2) against PA were determined by suspension assay, biofilm assay, and a human skin wound model and compared with 15-min topically applied 3% citric acid (CA) and wound irrigation solution (Prontosan®; PRT). Results: aBL reduced the bacterial number [2.51-3.56 log10 colony-forming unit (CFU)/mL], whereas PRT or CA treatment achieved a 4.64 or 6.60 log10 CFU/mL reduction in suspension assays. aBL reduced biofilm formation by 60-66%. PRT or CA treatment showed reductions by 25% or 13%. Here, aBL reduced bacterial number in biofilms (1.30-1.64 log10 CFU), but to a lower extend than PRT (2.41 log10 CFU) or CA (2.48 log10 CFU). In the wound skin model, aBL (2.21-2.33 log10 CFU) showed a bacterial reduction of the same magnitude as PRT (2.26 log10 CFU) and CA (2.30 log10 CFU). Conclusions: aBL showed a significant antibacterial efficacy against PA and biofilm formation in a short time. However, a clinical application of aBL in wound therapy requires effective active skin cooling and eye protection, which in turn may limit clinical implementation.

Light over mechanics: microbial community structure and activity in simulated migrating bedforms are controlled by oscillating light rather than by mechanical forces.

Sandy sediments of lowland streams are transported as migrating ripples. Benthic microorganisms colonizing sandy grains are exposed to frequent moving-resting cycles and are believed to be shaped by two dominant environmental factors: mechanical stress during the moving phase causing biofilm abrasion, and alternating light-dark cycles during the resting phase. Our study consisted of two laboratory experiments and aimed to decipher which environmental factor causes the previously observed hampered sediment-associated microbial activity and altered community structure during ripple migration. The first experiment tested the effect of three different migration velocities under comparable light conditions. The second experiment compared migrating and stationary sediments under either constant light exposure or light oscillation. We hypothesized that microbial activity and community structure would be more strongly affected by (1) higher compared to lower migration velocities, and by (2) light oscillation compared to mechanical stress. Combining the results from both experiments, we observed lower microbial activity and an altered community structure in sediments exposed to light oscillation, whereas migration velocity had less impact on community activity and structure. Our findings indicate that light oscillation is the predominating environmental factor acting during ripple migration, resulting in an increased vulnerability of light-dependent photoautotrophs and a possible shift toward heterotrophy.

Photoactivated riboflavin inhibits planktonic and biofilm growth of Candida albicans and non-albicans Candida species.

Fungal infections caused by Candida species pose a serious threat to humankind. Antibiotics abuse and the ability of Candida species to form biofilm have escalated the emergence of drug resistance in clinical settings and hence, rendered it more difficult to treat Candida-related diseases. Lethal effects of Candida infection are often due to inefficacy of antimicrobial treatments and failure of host immune response to clear infections. Previous studies have shown that a combination of riboflavin with UVA (riboflavin/UVA) light demonstrate candidacidal activity albeit its mechanism of actions remain elusive. Thus, this study sought to investigate antifungal and antibiofilm properties by combining riboflavin with UVA against Candida albicans and non-albicans Candida species. The MIC20 for the fluconazole and riboflavin/UVA against the Candida species tested was within the range of 0.125-2 µg/mL while the SMIC50 was 32 µg/mL. Present findings indicate that the inhibitory activities exerted by riboflavin/UVA towards planktonic cells are slightly less effective as compared to controls. However, the efficacy of the combination towards Candida species biofilms showed otherwise. Inhibitory effects exerted by riboflavin/UVA towards most of the tested Candida species biofilms points towards a variation in mode of action that could make it an ideal alternative therapeutic for biofilm-related infections.

Photodynamic Therapy With Resveratrol and an Nd:YAG Laser for Enterococcus faecalis Elimination.

BACKGROUND/AIM: Enterococcus faecalis is the leading cause of endodontic treatment failures. Despite various conventional disinfection approaches, microorganisms often persist in root canals. Photodynamic therapy (PDT) is an adjunct antimicrobial strategy employing a nontoxic photosensitizer (PS) and light source. This study evaluated the antimicrobial effect of PDT using an Nd:YAG laser and resveratrol (RSV) with or without pigment, and confirmed that RSV is nontoxic as a PS. MATERIALS AND METHODS: We employed laser irradiation at a 3W output power, using RSV and red pigment as the PS, on an E. faecalis bacterial solution. Subsequently, colony-forming units were quantified. The impact of RSV on osteoblasts was measured using an MTT assay. RESULTS: E. faecalis counts declined after laser irradiation. The combined application of laser irradiation with RSV, red pigment, or both showed a reduction compared to no irradiation and control groups without RSV and red pigment. The 50% cytotoxic concentration against osteoblast cells from mice incubated with RSV for 48 h was 162 µM. The value with RSV and laser was 201 µM and that with RSV and red pigment was 199 µM. The value with RSV, laser and red pigment was 357 µM. CONCLUSION: The combination of Nd:YAG laser irradiation and RSV as the PS with pigment was efficacious for E. faecalis elimination without inducing any toxic effects on osteoblasts. This combination holds potential as a root canal irrigation strategy.

Photodynamic inactivation of bacteria: Why it is not enough to excite a photosensitizer.

BACKGROUND: The development of multidrug resistance (MDR) in infectious agents is one of the most serious global problems facing humanity. Antimicrobial photodynamic therapy (APDT) shows encouraging results in the fight against MDR pathogens, including those in biofilms. METHODS: Photosensitizers (PS), monocationic methylene blue, polycationic and polyanionic derivatives of phthalocyanines, electroneutral and polycationic derivatives of bacteriochlorin were used to study photodynamic inactivation of Gram-positive and Gram-negative planktonic bacteria and biofilms under LED irradiation. Zeta potential measurements, confocal fluorescence imaging, and coarse-grained modeling were used to evaluate the interactions of PS with bacteria. PS aggregation and photobleaching were studied using absorption and fluorescence spectroscopy. RESULTS: The main approaches to ensure high efficiency of bacteria photosensitization are analyzed. CONCLUSIONS: PS must maintain a delicate balance between binding to exocellular and external structures of bacterial cells and penetration through the cell wall so as not to get stuck on the way to photooxidation-sensitive structures of the bacterial cell.

Phenotypic and Transcriptional Responses of Pseudomonas aeruginosa Biofilms to UV-C Irradiation via Side-Emitting Optical Fibers: Implications for Biofouling Control.

Biofilms give rise to a range of issues, spanning from harboring pathogens to accelerating microbial-induced corrosion in pressurized water systems. Introducing germicidal UV-C (200-280 nm) irradiation from light-emitting diodes (LEDs) into flexible side-emitting optical fibers (SEOFs) presents a novel light delivery method to inhibit the accumulation of biofilms on surfaces found in small-diameter tubing or other intricate geometries. This work used surfaces fully submerged in flowing water that contained Pseudomonas aeruginosa, an opportunistic pathogen commonly found in water system biofilms. A SEOF delivered a UV-C gradient to the surface for biofilm inhibition. Biofilm growth over time was monitored in situ using optical conference tomography. Biofilm formation was effectively inhibited when the 275 nm UV-C irradiance was ≥8 µW/cm2. Biofilm samples were collected from several regions on the surface, representing low and high UV-C irradiance. RNA sequencing of these samples revealed that high UV-C irradiance inhibited the expression of functional genes related to energy metabolism, DNA repair, quorum sensing, polysaccharide production, and mobility. However, insufficient sublethal UV-C exposure led to upregulation genes for SOS response and quorum sensing as survival strategies against the UV-C stress. These results underscore the need to maintain minimum UV-C exposure on surfaces to effectively inhibit biofilm formation in water systems.

Antibacterial and antibiofilm performance of low-frequency ultrasound against Escherichia coli O157:H7 and its application in fresh produce.

Ultrasound technology has been focused on due to its unique advantages in biofilm removal compared with traditional antibacterial methods. Herein, the anti-biofilm properties of low-frequency ultrasound (LFUS) were studied against Enterohemorrhagic Escherichia coli O157: H7 (E. coli O157:H7). After ultrasonication (20 kHz, 300 W) for 5 min, the removal rate of biofilm from polystyrene sheets reached up to 99.999 %. However, the bacterial cells could not be inactivated completely even extending the duration of ultrasonic irradiation to 30 min. Fortunately, this study indicated that LFUS could efficiently weaken the metabolic capacity and biofilm-forming ability of bacterial cells separated from biofilm. It could be associated with the removal of cell surface appendages and damage to cell membrane induced by mechanical vibration and acoustic cavitation. Besides, the genetic analysis proved that the transcription level of genes involved in curli formation was significantly down-regulated during ultrasonic irradiation, thus impeding the process of irreversible adhesion and cells aggregation. Finally, the actual application effect of LFUS was also evaluated in different fresh produces model. The results of this study would provide a theoretical basis for the further application of ultrasound in the food preservation.

Dentin disinfection and adhesive bond strength using modified photoactivated carbon nanoparticles.

AIMS: The present study aimed to investigate the bond integrity and disinfection efficacy of Methylene blue(MB) alone, MB-PDT (Photodynamic therapy), MB@ carbon nanoparticles (CP)-PDT, and Cr, Cr: YSGG (ECL) against lactobacilli in Caries-affected dentin (CAD) MATERIAL AND METHODS: Methods consisted of Shear bond strength (SBS), Scanning electron microscopy (SEM), energy dispersive X-ray (EDX), methods of disinfection, and failure analysis. CAD samples were prepared and biofilm formed on the specimens randomly allocated into five groups based on disinfection. Group 1: CHX; Group 2: MB; Group 3: MB-PDT: group 4: MB@CP-PDT and group 5: ECL. After disinfection Colony forming units were measured and specimens were restored and positioned under a universal testing machine (UTM). Failure analysis was performed using a stereomicroscope. The difference in survival rate was assessed using the Kruskal-Walis test. Mean and standard deviation for bond values after different methods of disinfection was evaluated using analysis of variance (ANOVA) and Post Hoc Tukey. The significance level was p<0.05 RESULTS: Morphological analysis revealed that CPs under SEM are flat discs with edged irregular shapes. EDX analyses show a spike indicating carbon particles by more than 95%. MB@CP-PDT displayed the highest reduction in lactobacillus levels in comparison to the other disinfection methods. The highest SBS was exhibited by the CAD sample disinfected with ECL. The lowest SBS values in CAD specimens after cavity cleansing with MB alone. The predominant failure type in CAD disinfected with MB alone, ECL CHX, MB-PDT, and MB@CP-PDT was adhesive. CONCLUSION: The use of MB@CP-PDT showed high antibacterial potency against lactobacillus but demonstrated bond values similar to CHX. Use of Er, Cr: YSGG showed considerable effectiveness against lactobacillus along with the highest bond values.

Efficacy of a novel remotely-generated ultrasonic root canal irrigation system for removing biofilm-mimicking hydrogel from a simulated isthmus model.

AIM: To evaluate the efficacy of a novel ultrasonic irrigation device, remotely-generated irrigation with a non-invasive sound field enhancement (RINSE) system, in removing biofilm-mimicking hydrogel from a simulated isthmus model and compare it with sonically- and ultrasonically-activated irrigation systems. METHODOLOGY: A polycarbonate root canal model containing two standardized root canals (apical diameter of 0.20 mm, 4% taper, 18 mm long with a coronal reservoir) connected by three isthmuses (0.40 mm deep, 2 mm high, 4 mm long) was used as the test model. The isthmuses were filled with a hydroxyapatite powder-containing hydrogel. The canals were filled with irrigant, and the models were randomly assigned to the following activation groups (n = 15): EndoActivator (EA), ultrasonically activated irrigation (UAI), and RINSE system (RS). Syringe irrigation (SI) with a 30G needle served as the control. Standardized images of the isthmuses were taken before and after irrigation, and the amount of hydrogel removed was determined using image analysis software and compared across groups using anova (p < .05). RESULTS: Hydrogel removal was significantly higher with the RS (83.7%) than with UAI, EA, or SI (p ≤ .01). UAI (69.2%) removed significantly more hydrogel than SI and EA (p < .05), while there was no significant difference between SI (24.3%) and EA (25.7%) (p = .978). CONCLUSIONS: RINSE system resulted in the most hydrogel removal, performing better than UAI or EA. The effect of RS was also not reliant on the insert or tip entering the pulp chamber or root canal, making it particularly useful in conservative endodontics.

An in vitro study on the efficacy of hydrogen peroxide mediated high-power photodynamic therapy affecting Enterococcus faecalis biofilm formation and dispersal.

OBJECTIVE: Biofilms are involved in failure of root canal treatment due to their high resistance to antimicrobial agents, which make their removal as a big challenge. The present study aims at utilizing hydrogen peroxide (HP) plus high frequency laser reinforced antimicrobial photodynamic therapy (a-PDT) as a complementary therapy against Enterococcus faecalis (E. faecalis) at planktonic and biofilm stages. MATERIALS AND METHODS: E. faecalis at planktonic and biofilm stages was treated with the photosensitizer HP, followed by no irradiation or irradiation with a power of 2.5 W (ʎ = 980 nm). The cell viability, anti-biofilm, anti-metabolic potential, and temperature changes were evaluated. RESULTS: The combination of HP and 980 nm diode laser intensely boosted antibacterial and anti-biofilm efficacy compared with either component alone, affirming HP reinforcement as a bacteriostatic agent. The maximum effect on biofilm occurs in 5.25% sodium hypochlorite (NaOCl) group. During laser irradiations, the mean of temperature changes remains below 5.6 °C. CONCLUSIONS: It could be concluded that the HP could improve anti-biofilm efficacy as a photosensitizer in a-PDT.

Photothermally responsive chitosan-coated iron oxide nanoparticles for enhanced eradication of bacterial biofilms.

This work developed a pH/NIR responsive antibacterial agent (CS-FeNPs) composed of chitosan (CS) and Fe3O4 nanoparticles (FeNPs). CS triggers bacterial attraction through surface charge, while Fe acts as a photothermal agent (PTA). The CS-Fe NPs exhibited antibacterial and antibiofilm activity against both bacteria (G+/G-). However, higher activity was observed against bacteria (G-) due to electrostatic interactions. The CS-FeNPs bind with the bacterial membrane through electrostatic interactions and disturb bacterial cells. Later, in an acidic environment, CS-FeNPs bind with bacterial membrane, and NIR irradiation leads the antibacterial activity. CS-FeNPs exhibited a potential photothermal conversion efficiency (η) of 21.53 %. Thus, it converts NIR irradiation into heat to kill the bacterial pathogen. The CS-FeNPs were found to be less cytotoxic with great antibacterial efficiency on planktonic bacteria and their biofilm, which indicates that they deserve to develop potential and safe treatment strategies for the treatment of bacterial infections.

Influence of antimicrobial photodynamic therapy with different pre-irradiation times on children's dental biofilm: randomized clinical trial.

PURPOSE: Photodynamic therapy (PDT) is effective in reducing pathogenic microorganisms in the oral cavity and in preventing dental diseases. This study evaluated the pre-irradiation time using PDT (diode laser associated with 0.01% methylene blue) to decrease the number of microorganisms in the visible plaque in permanent teeth. METHODS: This randomized clinical trial included 108 homologous lower permanent first molars (36 and 46) with biofilm from 54 children aged six to 12 years. PDT was performed (0.01% methylene blue photosensitizer/therapeutic laser-InGaAIP), according to the following protocols: Group 1, biofilm collection of the distal area of the lingual surface of 36 µm before PDT; group 2, mesial area of the lingual surface of 36 µm 1 min after PDT; group 3, area of the lingual surface of 46 µm before PDT; and group 4, mesial area of the lingual surface of 46 µm 5 min after PDT. RESULTS: After statistical analysis, significant differences were observed between the groups (p = 0.000). In groups 2 and 4, the number of bacteria tended to decrease, with a more evident bacterial reduction in group 4. CONCLUSIONS: Pre-irradiation reduced the number of colony-forming units of mature bacterial biofilms in vivo. A time of 5 min resulted in a greater reduction in the number of colony-forming units. CLINICAL TRIAL REGISTRATION: ReBEC Identifier: RBR-6bqfp3; Date of Register: March 2nd, 2020. Retrospectively Registered.

Inactivation effect of low-energy X-ray irradiation against planktonic and biofilm Pseudomonas fluorescens and its antibacterial mechanism.

Pseudomonas fluorescens is a well-known biofilm former on food contact surfaces and can cause severe cross-contamination in food processing premises. This study aimed to determine the inactivation effect of low-energy X-ray on P. fluorescens planktonic cells in phosphate-buffered saline solution (PBS) and P. fluorescens biofilm cells on food-contact-surface (stainless steel). The results demonstrated that low-energy X-ray irradiation at 125 Gy inactivated 4.60 log CFU/mL and 4.21 log CFU/cm2 for P. fluorescens planktonic and biofilm cells, respectively. Based on Weibull model, low-energy X-ray achieved tR1 values of 14.8 Gy and 11.6 Gy for P. fluorescens planktonic and biofilm cells, respectively. Apart from cell inactivation, the irradiation also led to the destruction of extracellular polymeric substances (EPS) structure. Low-energy X-ray irradiation markedly damaged bacterial glucose uptake system and resulted in part loss of bacterial membrane potential and integrity. These results suggested the potential of the low-energy X-ray for inactivating P. fluorescens biofilm cells and removing EPS in food industry.

Shining light on multi-drug resistant Candida auris: Ultraviolet-C disinfection, wavelength sensitivity, and prevention of biofilm formation of an emerging yeast pathogen.

Candida auris is an emerging fungal superbug of worldwide interest. It is associated with high mortality rates and exhibits increased resistance to antifungals. Ultraviolet subtype C (UVC) light can be used to disinfect surfaces to mitigate its spread. The objectives of this study were (1) To investigate UVC disinfection performances and wavelength sensitivity of C. auris. (2) To evaluate the UVC dose required for the prevention of biofilm formation on stainless-steel, plastic (polystyrene), and poly-cotton fabric surfaces. C. auris was grown following standard procedures. The study utilized six different UVC LED arrays with wavelengths between 252 and 280 nm. Arrays were set at similar intensities, to obtain doses of 5-40 mJ cm-2 and similar irradiation time. Disinfection performance for each array was determined using log reduction value (LRV) and percentage reduction by comparing the controls against the irradiated treatments. Evaluation of the ability of 267 nm UVC LEDs to prevent C. auris biofilm formation was investigated using stainless-steel, plastic coupons, and poly-cotton fabric. Peak sensitivity to UVC disinfection was between 267 and 270 nm. With 20 mJ cm-2 , the study obtained ≥LRV3. On stainless-steel coupons, 30 mJ cm-2 was sufficient to prevent biofilm formation, while on plastic, this required 10 mJ cm-2 . A dose of 60 mJ cm-2 reduced biofilms on poly-cotton fabric significantly (R2 = 0.9750, p = 0.0002). The study may allow for the design and implementation of disinfection systems.

Organic Photo-antimicrobials: Principles, Molecule Design, and Applications.

The emergence of multi-drug-resistant pathogens threatens the healthcare systems world-wide. Recent advances in phototherapy (PT) approaches mediated by photo-antimicrobials (PAMs) provide new opportunities for the current serious antibiotic resistance. During the PT treatment, reactive oxygen species or heat produced by PAMs would react with the cell membrane, consequently leaking cytoplasm components and effectively eradicating different pathogens like bacteria, fungi, viruses, and even parasites. This Perspective will concentrate on the development of different organic photo-antimicrobials (OPAMs) and their application as practical therapeutic agents into therapy for local infections, wound dressings, and removal of biofilms from medical devices. We also discuss how to design highly efficient OPAMs by modifying the chemical structure or conjugating with a targeting component. Moreover, this Perspective provides a discussion of the general challenges and direction for OPAMs and what further needs to be done. It is hoped that through this overview, OPAMs can prosper and will be more widely used for microbial infections in the future, especially at a time when the global COVID-19 epidemic is getting more serious.

UV and bacteriophages as a chemical-free approach for cleaning membranes from anaerobic bioreactors.

Anaerobic membrane bioreactor (AnMBR) for wastewater treatment has attracted much interest due to its efficacy in providing high-quality effluent with minimal energy costs. However, membrane biofouling represents the main bottleneck for AnMBR because it diminishes flux and necessitates frequent replacement of membranes. In this study, we assessed the feasibility of combining bacteriophages and UV-C irradiation to provide a chemical-free approach to remove biofoulants on the membrane. The combination of bacteriophage and UV-C resulted in better log cells removal and ca. 2× higher extracellular polymeric substance (EPS) concentration reduction in mature biofoulants compared to either UV-C or bacteriophage alone. The cleaning mechanism behind this combined approach is by 1) reducing the relative abundance of Acinetobacter spp. and selected bacteria (e.g., Paludibacter, Pseudomonas, Cloacibacterium, and gram-positive Firmicutes) associated with the membrane biofilm and 2) forming cavities in the biofilm to maintain water flux through the membrane. When the combined treatment was further compared with the common chemical cleaning procedure, a similar reduction on the cell numbers was observed (1.4 log). However, the combined treatment was less effective in removing EPS compared with chemical cleaning. These results suggest that the combination of UV-C and bacteriophage have an additive effect in biofouling reduction, representing a potential chemical-free method to remove reversible biofoulants on membrane fitted to an AnMBR.

Low-energy X-ray inactivation of Listeria monocytogenes in mono-/co-culture biofilms with Pseudomonas fluorescens on food contact surfaces.

This study assessed the inactivation kinetics of 150 keV low-energy X-ray on mono-/co-culture biofilms of Listeria monocytogenes and Pseudomonas fluorescens on three different food-contact-surfaces (polyethylene, acrylic, and stainless steel). The results indicated that the level of biofilm formation of mono-/co-cultures of L. monocytogenes and P. fluorescens was the highest on acrylic. The mono-culture L. monocytogenes biofilm cells exhibited higher resistance to the low-energy X-rays than the corresponding mono-culture P. fluorescens biofilm cells, regardless of surface types. Furthermore, co-culture had enhanced the resistance of both P. fluorescens and L. monocytogenes biofilm cells to the low-energy X-ray. Two kinetic models for the inactivation process were investigated, including (i) Linear model and (ii) Weibull model. Based on R2, RMSE and AIC analysis, the Weibull model was superior in fitting the inactivation curves of low-energy X-ray on L. monocytogenes in mono-/co-culture biofilms with P. fluorescens. For mono-culture biofilms, the irradiation achieved the tR1 value (derived from the Weibull model, i.e., the dose required for the first 1-log reduction) of 46.36-50.81 Gy for L. monocytogenes and the tR1 value of 25.61-31.33 Gy for P. fluorescens. For co-culture biofilms, higher tR1 values for L. monocytogenes (59.54-70.77 Gy) and P. fluorescens (32.73-45.13 Gy) were yielded than those for their individual counterparts in mono-culture biofilm.

Alternating magnetic fields and antibiotics eradicate biofilm on metal in a synergistic fashion.

Hundreds of thousands of human implant procedures require surgical revision each year due to infection. Infections are difficult to treat with conventional antibiotics due to the formation of biofilm on the implant surface. We have developed a noninvasive method to eliminate biofilm on metal implants using heat generated by intermittent alternating magnetic fields (iAMF). Here, we demonstrate that heat and antibiotics are synergistic in biofilm elimination. For Pseudomonas aeruginosa biofilm, bacterial burden was reduced >3 log with iAMF and ciprofloxacin after 24 h compared with either treatment alone (p < 0.0001). This effect was not limited by pathogen or antibiotic as similar biofilm reductions were seen with iAMF and either linezolid or ceftriaxone in Staphylococcus aureus. iAMF and antibiotic efficacy was seen across various iAMF settings, including different iAMF target temperatures, dose durations, and dosing intervals. Initial mechanistic studies revealed membrane disruption as one factor important for AMF enhanced antibacterial activity in the biofilm setting. This study demonstrates the potential of utilizing a noninvasive approach to reduce biofilm off of metallic implants.