A self-assembling graphene oxide coating for enhanced bactericidal and osteogenic properties of poly-ether-ether-ketone

Poly-ether-ether-ketone (PEEK) is a biomedical plastic that can be used for orthopedic implants, but it offers poor antibacterial properties and bioactivity. In this study, PEEK was sulfonated with the obtained porous structure adsorbing graphene oxide (GO). The surface microstructures and properties of the original PEEK, sulfonated PEEK (SPEEK), and GO-grafted PEEK (GO-SPEEK) were characterized. The results revealed that the GO-SPEEK surface is a 3D porous structure exhibiting superior hydrophilicity to the original PEEK. Although SPEEK was shown to possess antimicrobial properties against both Escherichia coli and Staphylococcus aureus, the bactericidal effect was even more significant for GO-SPEEK, at about 86% and 94%, respectively. In addition, the in vitro simulated-body-fluid immersion and cell experiments indicated that GO-SPEEK had much better hydroxyapatite (HA)-precipitation induction capacity and cell-material interactions (e.g., cell adhesion, proliferation, osteodifferentiation, and extracellular matrix mineralization. The tensile test revealed that the mechanical properties of PEEK were maintained after surface modification, as GO-SPEEK has comparable values of elastic modulus and tensile strength to PEEK. Our investigation sought a method to simultaneously endow PEEK with both good antimicrobial properties and bioactivity as well as mechanical properties, providing a theoretical basis for developing high-performance orthopedic implants in the clinic.

Bactericidal Effect and Cytotoxicity of Graphene Oxide/Silver Nanocomposites

To tackle the proliferation of pathogenic microorganisms without relying on antibiotics, innovative materials boasting antimicrobial properties have been engineered. This study focuses on the development of graphene oxide/silver (GO/Ag) nanocomposites, derived from partially reduced graphene oxide adorned with silver nanoparticles. Various nanocomposites with different amounts of silver (GO/Ag-1, GO/Ag-2, GO/Ag-3, and GO/Ag-4) were synthesized, and their antibacterial efficacy was systematically studied. The silver nanoparticles were uniformly deposited on the partially reduced graphene oxide surface, exhibiting spherical morphologies with an average size of 25 nm. The nanocomposites displayed potent antibacterial properties against both gram-positive bacteria (S. aureus and B. subtilis) and gram-negative bacteria (E. coli and S. enterica) as confirmed by minimum inhibition concentration (MIC) studies and time-dependent experiments. The optimal MIC for Gram-positive bacteria was 62.5 μg/mL and for Gram-negative bacteria was 125 μg/mL for the GO/Ag nanocomposites. Bacterial cells that encountered the nanocomposite films exhibited significantly greater inhibitory effects compared to those exposed to conventional antibacterial materials. Furthermore, the cytotoxicity of these nanocomposites was assessed using human epithelial cells (HEC), revealing that GO/Ag-1 and GO/Ag-2 exhibited lower toxicity levels toward HEC and remained compatible even at higher dilution rates. This study underscores the potential of GO/Ag-based nanocomposites as versatile materials for antibacterial applications, particularly as biocompatible wound dressings, offering promising prospects for wound healing and infection control.

Activities of aztreonam in combination with several novel β-lactam-β-lactamase inhibitor combinations against carbapenem-resistant Klebsiella pneumoniae strains coproducing KPC and NDM

Isolates coproducing serine/metallo-carbapenems are a serious emerging public health threat, given their rapid dissemination and the limited number of treatment options. The purposes of this study were to evaluate the in vitro antibacterial activity of novel β-lactam-β-lactamase inhibitor combinations (BLBLIs) against carbapenem-resistant Klebsiella pneumoniae (CRKP) coproducing metallo-β-lactamase and serine-β-lactamase, and to explore their effects in combination with aztreonam, meropenem, or polymyxin in order to identify the best therapeutic options. Four CRKP isolates coproducing K. pneumoniae carbapenemase (KPC) and New Delhi metallo-β-lactamase (NDM) were selected, and a microdilution broth method was used to determine their susceptibility to antibiotics. Time-kill assay was used to detect the bactericidal effects of the combinations of antibiotics. The minimum inhibitory concentration (MIC) values for imipenem and meropenem in three isolates did not decrease after the addition of relebactam or varbobactam, but the addition of avibactam to aztreonam reduced the MIC by more than 64-fold. Time-kill assay demonstrated that imipenem-cilastatin/relebactam (ICR) alone exerted a bacteriostatic effect against three isolates (average reduction: 1.88 log10 CFU/mL) and ICR combined with aztreonam exerted an additive effect. Aztreonam combined with meropenem/varbobactam (MEV) or ceftazidime/avibactam (CZA) showed synergistic effects, while the effect of aztreonam combined with CZA was inferior to that of MEV. Compared with the same concentration of aztreonam plus CZA combination, aztreonam/avibactam had a better bactericidal effect (24 h bacterial count reduction >3 log10CFU/mL). These data indicate that the combination of ATM with several new BLBLIs exerts powerful bactericidal activity, which suggests that these double β-lactam combinations might provide potential alternative treatments for infections caused by pathogens coproducing-serine/metallo-carbapenems.

Inherent Antibacterial Properties of Biodegradable FeMnC(Cu) Alloys for Implant Application

Implant-related infections or inflammation are one of the main reasons for implant failure. Therefore, different concepts for prevention are needed, which strongly promote the development and validation of improved material designs. Besides modifying the implant surface by, for example, antibacterial coatings (also implying drugs) for deterring or eliminating harmful bacteria, it is a highly promising strategy to prevent such implant infections by antibacterial substrate materials. In this work, the inherent antibacterial behavior of the as-cast biodegradable Fe69Mn30C1 (FeMnC) alloy against Gram-negative Pseudomonas aeruginosa and Escherichia coli as well as Gram-positive Staphylococcus aureus is presented for the first time in comparison to the clinically applied, corrosion-resistant AISI 316L stainless steel. In the second step, 3.5 wt % Cu was added to the FeMnC reference alloy, and the microbial corrosion as well as the proliferation of the investigated bacterial strains is further strongly influenced. This leads for instance to enhanced antibacterial activity of the Cu-modified FeMnC-based alloy against the very aggressive, wild-type bacteria P. aeruginosa. For clarification of the bacterial test results, additional analyses were applied regarding the microstructure and elemental distribution as well as the initial corrosion behavior of the alloys. This was electrochemically investigated by a potentiodynamic polarization test. The initial degraded surface after immersion were analyzed by glow discharge optical emission spectrometry and transmission electron microscopy combined with energy-dispersive X-ray analysis, revealing an increase of degradation due to Cu alloying. Due to their antibacterial behavior, both investigated FeMnC-based alloys in this study are attractive as a temporary implant material.

Mechanism for transmission and pathogenesis of carbapenem-resistant Enterobacterales harboring the carbapenemase IMP and clinical countermeasures

Carbapenem-resistant Enterobacterales (CRE) are some of the most important pathogens causing infections, which can be challenging to treat. We identified four blaIMP-carrying CRE isolates and collected clinical data. The transferability and stability of the plasmid were verified by conjugation, successive passaging, and plasmid elimination assays. The IncC blaIMP-4-carrying pIMP4-ECL42 plasmid was successfully transferred into the recipient strain, and the high expression of traD may have facilitated the conjugation transfer of the plasmid. Interestingly, the plasmid showed strong stability in clinical isolates. Whole-genome sequencing was performed on all isolates. We assessed the sequence similarity of blaIMP -harboring plasmid from our institution and compared it to plasmids for which sequence data are publicly available. We found that four blaIMP-carrying CRE belonged to four different sequence types. The checkerboard technique and time-kill assays were used to investigate the best antimicrobial therapies for blaIMP-carrying CRE. The time-kill assay showed that the imipenem of 1× minimum inhibitory concentration (MIC) alone had the bactericidal or bacteriostatic effect against IMP-producing strains at 4-12 h in vitro. Moreover, the combination of tigecycline (0.5/1/2 × MIC) and imipenem (0.5/1 × MIC) showed a bactericidal effect against the blaIMP-26-carrying CRECL60 strain.IMPORTANCECarbapenem-resistant Enterobacterales (CRE) are an urgent public health threat, and infections caused by these microorganisms are often associated with high mortality and limited treatment options. This study aimed to determine the clinical features, molecular characteristics, and plasmid transmissible mechanisms of blaIMP carriage as well as to provide a potential treatment option. Here, we demonstrated that conjugated transfer of the IncC blaIMP-4-carrying plasmid promotes plasmid stability, so inhibition of conjugated transfer and enhanced plasmid loss may be potential ways to suppress the persistence of this plasmid. The imipenem alone or tigecycline-imipenem combination showed a good bactericidal effect against IMP-producing strains. In particular, our study revealed that imipenem alone or tigecycline-imipenem combination may be a potential therapeutic option for patients who are infected with IMP-producing strains. Our study supports further trials of appropriate antibiotics to determine optimal treatment and emphasizes the importance of continued monitoring of IMP-producing strains in the future.

Novel Antibacterial and Biocompatible Nanostructured Gels Based on One-step Synthesis as a Potential Disinfectant for Endodontic Infection Control

AIM

The objective of this study was to develop nanostructured gels as biocompatible intracanal disinfectants by one-step microwave radiation-assisted synthesis.

METHODS

Polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) were used as a support network, and polyethylene glycol (PEG) was used as a reducing agent. The gels were characterized by measuring the swelling ratio (SR) and rheological properties and by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The antibacterial effects of each gel were evaluated against the endodontic clinical strain Enterococcus faecalis. Then, the viability of the 21-day mature multispecies bacterial biofilm was assessed using confocal microscopy in an ex vivo model, where the biofilm was exposed to the mix of nanogels. The cell proliferation, viability, and morphology of human periodontal ligament (HPDL) cells were quantified using a real-time IncuCyte® S3 Live-Cell System. Viability was measured by confocal microscopy using an ex vivo model exposing a 21-day mature multispecies bacterial biofilm to the mix of nanogels.

RESULTS

The antibacterial activity of the gels coincided with the superficial characterization and the solubility of the gel in the growth medium. Gels with higher viscosity (327.85-980.58 Pa s), higher dissolution (42-70%SR), and lower porosity (no porosity and 611.63 nm) showed excellent antibacterial activity against E. faecalis. Despite their physicochemical characteristics, CuNPs gels showed greater effectiveness against E. faecalis.These nanostructured gels with high PVA concentrations promote HPDL cells proliferation while still exerting antibacterial properties. Mix of nanogels showed an increase non-viable cells biomass from at of application.

CONCLUSIONS

The use of biocompatible polymers influences the physicochemical, bactericidal, and cytotoxic response, making these materials potential disinfectant agents against resistant bacteria with good biocompatibility and improved HPDL cells proliferation.

Effect of plasma-activated organic acids on different chicken cuts inoculated with Salmonella Typhimurium and Campylobacter jejuni and their antioxidant activity

Lactic acid, gallic acid, and their mixture (1% each) were prepared (LA, GA, and LGA) and plasma-activated organic acids (PAOA) were produced through exposure to plasma for 1 h (PAL, PAG, and PLGA). Chicken breast and drumstick were immersed in the prepared solutions for 10 min and analyzed their antibacterial effect against Salmonella Typhimurium and Campylobacter jejuni and antioxidant activity during 12 d of storage. As a result, PAOA inactivated approximately 6.37 log CFU/mL against S. Typhimurium and 2.76, 1.86, and 3.04 log CFU/mL against C. jejuni (PAL, PAG, and PLGA, respectively). Moreover, PAOA had bactericidal effect in both chicken parts inoculated with pathogens, with PAL and PLGA displaying higher antibacterial activity compared to PAG. Meanwhile, PAOA inhibited lipid oxidation in chicken meats, and PAG and PLGA had higher oxidative stability during storage compared to PAL. This can be attributed to the superior antioxidant properties of GA and LGA, including higher total phenolic contents, ABTS+ reducing activity, and DPPH radical scavenging activity, when compared to LA. In particular, when combined with plasma treatment, LGA showed the greatest improvement in antioxidant activity compared to other organic acids. In summary, PLGA not only had a synergistic bactericidal effect against pathogens on chicken, but also improved oxidative stability during storage. Therefore, PLGA can be an effective method for controlling microorganisms without adverse effect on lipid oxidation for different chicken cuts.

Laser-Induced Transferred Antibacterial Nanoparticles for Mixed-Species Bacteria Biofilm Inactivation

In the present study, copper and silver nanoparticles with a concentration of 20 µg/cm² were synthesized using the method of laser-induced forward transfer (LIFT). The antibacterial activity of the nanoparticles was tested against bacterial biofilms that are common in nature, formed by several types of microorganisms (mixed-species bacteria biofilms): Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. The Cu nanoparticles showed complete inhibition of the bacteria biofilms used. In the course of the work, a high level of antibacterial activity was demonstrated by nanoparticles. This activity manifested in the complete suppression of the daily biofilm, with the number of bacteria decreasing by 5-8 orders of magnitude from the initial concentration. To confirm antibacterial activity, and determine reductions in cell viability, the Live/Dead Bacterial Viability Kit was used. FTIR spectroscopy revealed that after Cu NP treatment, there was in a slight shift in the region, which corresponded to fatty acids, indicating a decrease in the relative motional freedom of molecules.

The study on bactericidal effect and ultrastructural alterations of chlorocresol nanoemulsion disinfectant against Staphylococcus aureus

Chlorocresol nanoemulsion disinfectant (CND) is an environmental disinfectant prepared with nanoemulsion as its drug carrier. This study aimed to investigate the bactericidal effect of CND on Staphylococcus aureus ( S. aureus) and its effect on bacterial ultrastructure. The neutralizing effect of CND against S. aureus was first screened by suspension quantitative evaluation experiment procedure of neutralizer. Disinfection performance was evaluated by the determination of Minimal Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC), quantitative bactericidal experiment, and comparative experiment of disinfection performance between 0.1% CND and 0.1% chlorocresol aqueous solution. Meanwhile, the effect of CND on the ultrastructure of S. aureus was investigated with scanning electron microscope (SEM) and transmission electron microscope (TEM) to preliminarily explore the bactericidal mechanism. The results showed that 3% Tween-80 in PBS could be screened as the neutralizer of CND against S. aureus. MIC and MBC were 100 μg/mL and 200 μg/mL, respectively. The bactericidal rates were all 100% when 0.06% and 0.08% disinfectant acted for 15 and 5 min, respectively. Furthermore, compared with 0.1% chlorocresol aqueous solution, the bactericidal effect of 0.1% CND was significantly enhanced (p⟨0.01). After treatment with CND for 10 min, SEM observation showed that the morphology of S. aureus cells were changed and the integrity destroyed. TEM observation showed that the cell shape changed, and the structures of the cell wall, cell membrane and cytoplasm were damaged in varying degrees. CND showed the strong bactericidal effect on S. aureus and could cause ultrastructure alterations of S. aureus.

Effect of Heat Treatment on Osteoblast Performance and Bactericidal Behavior of Ti6Al4V(ELI)-3at.%Cu Fabricated by Laser Powder Bed Fusion

Cu addition to alloys for biomedical applications has been of great interest to reduce bacterial growth. In situ-alloyed Ti6Al4V(ELI)-3at.%Cu was successfully manufactured by laser powder bed fusion (L-PBF). Even so, post-heat treatments are required to avoid distortions and/or achieve required/desired mechanical and fatigue properties. The present study is focused on the investigation of microstructural changes in L-PBF Ti6Al4V(ELI)-3at.%Cu after stress relieving and annealing treatments, as well as their influence on osteoblast and bactericidal behavior. After the stress relieving treatment, a homogenously distributed β phase and CuTi₂ intermetallic precipitates were observed over the α' matrix. The annealing treatment led to the increase in amount and size of both types of precipitates, but also to phase redistribution along α lamellas. Although microstructural changes were not statistically significant, such increase in β and CuTi₂ content resulted in an increase in osteoblast proliferation after 14 days of cell culture. A significant bactericidal behavior of L-PBF Ti6Al4V(ELI)-3at.%Cu by means of ion release was found after the annealing treatment, provably due to the easier release of Cu ions from β phase. Biofilm formation was inhibited in all on Cu-alloyed specimens with stress relieving but also annealing treatment.

Surface Engineering of AgNPs-Decorated Polyetheretherketone

Metal nanostructure-treated polymers are widely recognized as the key material responsible for a specific antibacterial response in medical-based applications. However, the finding of an optimal bactericidal effect in combination with an acceptable level of cytotoxicity, which is typical for metal nanostructures, prevents their expansion from being more significant so far. This study explores the possibility of firmly anchoring silver nanoparticles (AgNPs) into polyetherether ketone (PEEK) with a tailored surface morphology that exhibits laser-induced periodic surface structures (LIPSS). We demonstrated that laser-induced forward transfer technology is a suitable tool, which, under specific conditions, enables uniform decoration of the PEEK surface with AgNPs, regardless of whether the surface is planar or LIPSS structured. The antibacterial test proved that AgNPs-decorated LIPSS represents a more effective bactericidal protection than their planar counterparts, even if they contain a lower concentration of immobilized particles. Nanostructured PEEK with embedded AgNPs may open up new possibilities in the production of templates for replication processes in the construction of functional bactericidal biopolymers or may be directly used in tissue engineering applications.

Evaluation of the effect of peptidoglycan-constituting components on photocatalytic bactericidal sterilization

Previous studies in our lab have shown that peptidoglycan (PG) enhances the photocatalytic bactericidal effect. Therefore, in this study, we focused on the PG-constituting components. The PG-constituting components were added to Mesoplasma florum with no cell wall, respectively, and their effects on photocatalytic sterilization were investigated. The PG-constituting components used were amino sugars, amino acids, L-Alanine-D-Glutamic Acid (L-Ala-D-Glu) dipeptide of diaminopimelic acid (DAP）-type crosslinking peptide, and Lysine (Lys）-type crosslinking peptide. We compared the survival rates of M. florum cells and PG-constituting components-added M. florum cells after 3 h of photocatalytic reaction. Consequently, the survival rates of the cells that were added N-acetylglucosamine (GlcNAc）, DAP, and L-Ala- D-Glu dipeptide were significantly lower than those of only the cells. Furthermore, the amounts of hydrogen peroxide (H2O2) generated by the photocatalytic reaction under the presence of these components were determined. The results showed that DAP, L-Ala- D-Glu dipeptide, and PG of DAP-type significantly increased the amount of H2O2 produced. From the above results, it is suggested that the presence of DAP and L-Ala- D-Glu dipeptide in the photocatalytic reaction boosts the production of H2O2 and enhances the bactericidal effect and that GlcNAc might produce reactive oxygen species other than H2O2.

Effectiveness of ozonized saline solution in the treatment of Proteus spp. bacterial cystitis

Bacterial cystitis is a common clinical problem among cats and dogs and is one of the main reasons for the administration of antimicrobials. This can cause serious damage to public and animal health, as this practice facilitates the selection of bacteria that are multidrug-resistant to antibiotics. In this context, it is urgent to understand and validate therapeutic modalities that complement antimicrobial treatment in cystitis cases. Ozone therapy has been proposed by scientists owing to the various mechanisms of action in a range of pathologies, both in human and animal medicine. This paper describes the bactericidal action of two different protocols of bladder irrigation with ozonized saline solution (59 μg/mL) in a paraplegic canine with recurrent bacterial cystitis caused by Proteus spp. In the first protocol, the bladder instillations were applied once a day for three consecutive days while in the second, successive lavages were performed throughout the day until a significant reduction in the presence of bacteria in the urine sediment. In this study, we were able to demonstrate that repeated bladder instillation within 24 hours was the most effective treatment for Proteus compared to a single instillation on successive days.

Additive Nanosecond Laser-Induced Forward Transfer of High Antibacterial Metal Nanoparticle Dose onto Foodborne Bacterial Biofilms

Additive laser-induced forward transfer (LIFT) of metal bactericidal nanoparticles from a polymer substrate directly onto food bacterial biofilms has demonstrated its unprecedented efficiency in combating pathogenic microorganisms. Here, a comprehensive study of laser fluence, metal (gold, silver and copper) film thickness, and the transfer distance effects on the antibacterial activity regarding biofilms of Gram-negative and Gram-positive food bacteria (Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Listeria monocytogenes, Salmonella spp.) indicated the optimal operation regimes of the versatile modality. LIFT-induced nanoparticle penetration into a biofilm was studied by energy-dispersion X-ray spectroscopy, which demonstrated that nanoparticles remained predominantly on the surface of the biofilm.

New Insights into the Antimicrobial Potential of Polyalthia longifolia-Antibiofilm Activity and Synergistic Effect in Combination with Penicillin against Staphylococcus aureus

Widespread antibiotic resistance has led to the urgent need for the identification of new antimicrobials. Plants are considered a valuable potential resource for new effective antimicrobial compounds. Therefore, in the present study, we focused on the antimicrobial activity of Polyalthia longifolia plants harvested from Cameroon using the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and time-kill assays. The mechanism of action was investigated by employing fluorescence and scanning electron microscopy. The anti-Staphylococcus aureus activity was studied using biofilm inhibition and checkerboard assays. Our results revealed that the tested extracts possess important antimicrobial activities, notably against Gram positive bacteria (MICs as low as 0.039 mg/mL). P. longifolia leaf extracts exhibited a significant bactericidal effect, with a total kill effect recorded after only 2 h of exposure at concentrations equivalent to MBC (0.078 and 0.156 mg/mL). The extracts showed a synergistic antibacterial activity in combination with penicillin against a MRSA clinical isolate and significantly inhibited S. aureus biofilm formation. The mechanism of action is related to the impairment of cell membrane integrity and cell lysis. All these findings suggest that P. longifolia could be an important source of reliable compounds used to develop new antimicrobials.

Ag2O Nanoparticles as a Candidate for Antimicrobial Compounds of the New Generation

Antibiotic resistance in microorganisms is an important problem of modern medicine which can be solved by searching for antimicrobial preparations of the new generation. Nanoparticles (NPs) of metals and their oxides are the most promising candidates for the role of such preparations. In the last few years, the number of studies devoted to the antimicrobial properties of silver oxide NPs have been actively growing. Although the total number of such studies is still not very high, it is quickly increasing. Advantages of silver oxide NPs are the relative easiness of production, low cost, high antibacterial and antifungal activities and low cytotoxicity to eukaryotic cells. This review intends to provide readers with the latest information about the antimicrobial properties of silver oxide NPs: sensitive organisms, mechanisms of action on microorganisms and further prospects for improving the antimicrobial properties.

The Effect of Gap Distance between a Pin and Water Surface on the Inactivation of Escherichia coli Using a Pin-to-Water Plasma

Atmospheric plasmas have been applied for the inactivation of microorganisms. Industrials demand to investigate the relation of the key reactive species induced by plasmas and the operating parameters including boundary conditions in order to control plasma treatment processes. In this study, we investigated the effect of gap distance between a pin-electrode and water surface on inactivation efficacy. When the gap distance decreased from 5 mm to 1 mm, the reduction of Escherichia coli (E. coli) was increased to more than 4 log CFU/mL. The reactive oxygen species measured optically and spectrophotometrically were influenced by gap distance. The results from electron spin resonance (ESR) analysis showed that the pin-to-water plasma generated hydroxyl radical (OH•) and singlet oxygen (¹O₂) in the water and superoxide radical (O₂⁻•) served as a precursor of OH•. The inactivation of E. coli was significantly alleviated by sodium azide (¹O₂ scavenger), indicating that ¹O₂ contributes the most to bacterial inactivation. These findings provide a potentially effective strategy for bacterial inactivation using a pin-to-water plasma.

Inactivation of Salmonella typhimurium SL1344 by Chlorogenic Acid and the Impairment of Cellular Integrity

Chlorogenic acid (CGA) is an antibacterial agent that can be isolated from Eucommia ulmoides Oliver, a Chinese medicinal and edible plant food. The inhibitory effect of CGA on bacterial growth and stiffness of the outer membrane (OM) had been reported, while more evidence were required to elucidate its impairment of cell wall. In this study, the morphological and physiochemical changes of Salmonella cells under CGA treatment were investigated. Firstly, the minimum inhibitory concentration (MIC) of CGA against Salmonella was assayed. Later, the permeability of OM and activity of the proteins released were measured and observed to reveal the alteration of OM characteristic and cellular morphology. Finally, reactive oxygen species and cell membrane fluidity were analyzed, respectively, to elucidate how CGA damaged cell surface. The results showed that MIC of CGA against Salmonella was 6.25 mg/L. Under sub-lethal doses of CGA, the OM permeability and the release of soluble proteins were enhanced evidently, and Salmonella cells showed more deformed and shrunken, confirming the impairment of cellular integrity under CGA. Finally, the possible cause of cell surface damage was investigated. the fluidity of the membrane was increased upon CGA treatment, which may the possible cause of OM by CGA.

Highly Active Small Aminated Quinolinequinones against Drug-Resistant Staphylococcus aureus and Candida albicans

Two subseries of aminated quinolinequinones (AQQs, AQQ1-16) containing electron-withdrawing group (EWG) or electron-donating group (EDG) in aryl amine moiety were successfully synthesized. Antimicrobial activity assessment indicates that some of the AQQs (AQQ8-10 and AQQ12-14) with an EDG in aryl amine exhibited strong antibacterial activity against Gram-positive bacterial strains, including Staphylococcus aureus (ATCC^® 29213) and Enterococcus faecalis (ATCC^® 29212). In contrast, AQQ4 with an EWG in aryl amine displayed excellent antifungal activity against fungi Candida albicans (ATCC^® 10231) with a MIC value of 1.22 μg/mL. To explore the mode of action, the selected AQQs (AQQ4 and AQQ9) were further evaluated in vitro to determine their antimicrobial activity against each of 20 clinically obtained resistant strains of Gram-positive bacteria by performing antibiofilm activity assay and time-kill curve assay. In addition, in silico studies were carried out to determine the possible mechanism of action observed in vitro. The data obtained from these experiments suggests that these molecules could be used to target pathogens in different modes of growth, such as planktonic and biofilm.

A Vehicle-Free Antimicrobial Polymer Hybrid Gold Nanoparticle as Synergistically Therapeutic Platforms for Staphylococcus aureus Infected Wound Healing

Pathogenic bacteria infection is a serious threat to human public health due to the high morbidity and mortality rates. Nano delivery system for delivering antibiotics provides an alternative option to improve the efficiency compared to conventional therapeutic agents. In addition to the drug loading capacity of nanocarriers, which is typically around 10%, further lowers the drug dose that pathological bacteria are exposed to. Moreover, nanocarriers that are not eliminated from the body may cause side effects. These limitations have motivated the development of self-delivery systems that are formed by the self-assembly of different therapeutic agents. In this study, a vehicle-free antimicrobial polymer polyhexamethylene biguanide (PHMB, with bactericidal and anti-biofilm functions) hybrid gold nanoparticle (Au NPs, with photothermal therapy (PTT)) platform (PHMB@Au NPs) is developed. This platform exhibits an excellent synergistic effect to enhance the photothermal bactericidal effect for Staphylococcus aureus under near-infrared irradiation. Furthermore, the results showed that PHMB@Au NPs inhibit the formation of biofilms, quickly remove bacteria to promote wound healing through PTT in infection model in vivo, and even mediate the transition of macrophages from M1 to M2 type, and accelerate tissue angiogenesis. PHMB@Au NPs will have promising value as highly effective antimicrobial agents for patient management.

Ionic and non-ionic intravenous X-ray contrast media: antibacterial agents?

X-ray contrast media have been reported to have inhibitory effects on bacterial growth. Despite its potentially beneficial effect on patients, these features of contrast media have received relatively little attention in the medical literature in the past decades. The aim of this review is to evaluate the literature concerning the bactericidal and bacteriostatic effects of X-ray contrast media, specifically if there is a known difference concerning these effects between ionic and non-ionic contrast media. Systematic literature review was performed for the years of publication between 1911 and 2019. Since the publication of Grossich in 1911, the effect of iodine on the treatment of superficial infections in surgical procedures has been established clinical knowledge. Bacteriostatic and bactericidal effects of ionic X-ray contrast media are well established. However, non-ionic contrast agents have been the subject of little research in this respect. In past decades, the hypothesis emerged in the literature that mainly the concentration of free iodine might be responsible for any bacteriostatic or bactericidal effect of ionic X-ray contrast media. Nowadays, however, only non-ionic contrast media are used. The question regarding the mechanism and magnitude of bacteriostatic or bactericidal effects of these, non-ionic contrast media, could not be answered conclusively from this review. Non-ionic contrast media could be used intentionally when a local antibacterial effect is intended (e.g. in percutaneous abscess drainage), as well as to reduce the overall dose of antibiotics administered to a patient. Thus, this question remains relevant and might constitute the area of future research.

Active Quinolinequinones against Methicillin-Resistant Staphylococcus spp

Serious bacterial infections could be caused by Gram-positive microorganisms, in particular methicillin-resistant Staphylococcus aureus and Staphylococcus epidermidis. Aiming to address this challenging issue by developing the potent and selective antimicrobial lead structures against methicillin-resistant Staphylococcus spp., herein, we report in vitro evaluation of quinolinequinones (QQ1-QQ10) against the Gram-negative and Gram-positive strains using the broth microdilution technique. The design principle of the quinolinequinones was based on the variation of the structures attached to the 1,4-quinone moiety and substituent(s) within amino phenyl moiety. A series of ten quinolinequinones displayed activity mainly against the Gram-positive strains with a minimal inhibitory concentration (MIC=1.22-1250 mg/L) within the Clinical and Laboratory Standards Institute (CLSI) levels. Interestingly, QQ3, QQ5, and QQ6 displayed equal antibacterial inhibitory activity against S. aureus (MIC=1.22 mg/L), respectively, to the standard positive control Cefuroxime-Na. QQ2, QQ3, and QQ5 had the best inhibitory activity with the MIC value of 1.22 mg/L (4-fold more potent compared reference standard Cefuroxime) against S. epidermidis. On the other hand, QQ3 was the most effective quinolinequinone against fungi, in particular C. albicans. The identified lead quinolinequinones (QQ3 and QQ5) with a comprehensive analysis of structure-activity relationships and further studies showed high activity against methicillin-resistant Staphylococcus spp. It is worth noting that the isopropyl group has importance for excellent bioactivity. Remarkably, the in vitro antibiofilm and bactericidal activities (each of 32 clinically obtained strains of Gram-positive bacteria) of the selected two quinolinequinones (QQ3 and QQ5) have been evaluated for the mode of action in addition to the time-kill curve study.

Bactericidal Effect of Pseudomonas oryziphila sp. nov., a Novel Pseudomonas Species Against Xanthomonas oryzae Reduces Disease Severity of Bacterial Leaf Streak of Rice

Pseudomonas is a diverse genus of Gammaproteobacteria with increasing novel species exhibiting versatile trains including antimicrobial and insecticidal activity, as well as plant growth-promoting, which make them well suited as biocontrol agents of some pathogens. Here we isolated strain 1257 that exhibited strong antagonistic activity against two pathovars of Xanthomonas oryzae, especially X. oryzae pv. oryzicola (Xoc) responsible for the bacterial leaf streak (BLS) in rice. The phylogenetic, genomic, physiological, and biochemical characteristics support that strain 1257 is a representative of a novel Pseudomonas species that is most closely related to the entomopathogenic bacterium Pseudomonas entomophila. We propose to name it Pseudomonas oryziphila sp. nov. Comparative genomics analyses showed that P. oryziphila 1257 possesses most of the central metabolic genes of two closely related strains P. entomophila L48 and Pseudomonas mosselii CFML 90-83, as well as a set of genes encoding the type IV pilus system, suggesting its versatile metabolism and motility properties. Some features, such as insecticidal toxins, phosphate solubilization, indole-3-acetic acid, and phenylacetic acid degradation, were disclosed. Genome-wide random mutagenesis revealed that the non-ribosomal peptide catalyzed by LgrD may be a major active compound of P. oryziphila 1257 against Xoc RS105, as well as the critical role of the carbamoyl phosphate and the pentose phosphate pathway that control the biosynthesis of this target compound. Our findings demonstrate that 1257 could effectively inhibit the growth and migration of Xoc in rice tissue to prevent the BLS disease. To our knowledge, this is the first report of a novel Pseudomonas species that displays a strong antibacterial activity against Xoc. The results suggest that the P. oryziphila strain could be a promising biological control agent for BLS.

Discovery and structure-activity relationships of the quinolinequinones: Promising antimicrobial agents and mode of action evaluation

In our pursuit of developing the novel, potent, and selective antimicrobial agents, we managed to obtain the quinolinequinone for their antimicrobial profile with minimal inhibitory concentrations (MICs) determined against a panel of seven bacterial strains (three gram-positive and four gram-negative bacteria) and three fungi. The structure-activity relationship (SAR) for the quinolinequinone class of antimicrobials was determined. Interestingly, QQ1, QQ4, QQ6-9, QQ12, and QQ13 displayed equal antibacterial potential against S. aureus (MIC = 1.22 mg/L), respectively, to the standard positive control Cefuroxime-Na. QQ10 had the best inhibitory activity with the MIC value of 1.22 mg/L (fourfold more potent compared to reference standard Clotrimazole) against Candida albicans. On the other hand, while QQ10 is not too effective against gram-positive bacteria as much as the other analogs, QQ10 was the most effective quinolinequinones against fungi. Selected quinolinequinones were further evaluated for the mode of action, using in vitro antibiofilm activity, bactericidal activity by using time-kill curve assay, antibiofilm activity, and potential antimicrobial activity against each of 32 clinically obtained resistant strains of Gram-positive Bacteria. The results also revealed that the QQ14 had specific antifungal activity against fungi in particular C. albicans. Our results clearly showed that quinolinequinones are much more active in the inhibition of the biofilm attachment process than the inhibition of mature biofilm formation. Thus, as treatment options are narrowing for Methicillin-resistant Staphylococcus spp., Vancomycin-resistant Staphylococcus spp. daily, the quinolinequinones reported herein display promise as the lead candidates for further clinical applications against serious infections.

Adding Two Antimicrobial Glasses to an Endodontic Sealer to Prevent Bacterial Root Canal Reinfection: An In Vivo Pilot Study in Dogs

Current endodontic procedures continue to be unsuccessful for completely removing pathogens present inside the root canal system, which can lead to recurrent infections. In this study, we aimed to assess the antimicrobial capacity and tissue response of two inorganic bactericidal additives incorporated into a paste root canal sealer on contaminated root dentin in vivo. An experimental study was performed in 30 teeth of five Beagle dogs. After inducing microbiological contamination, root canal systems were treated by randomly incorporating one of two antimicrobial additives into a commercial epoxy-amine resin sealer (AH Plus), i.e., G3T glass-ceramic (n = 10) and ZnO-enriched glass (n = 10); 10 samples were randomized as a control group. After having sacrificed the animals, microbiological, radiological, and histological analyses were performed, which were complemented with an in vitro bactericidal test and characterization by field emission scanning electron microscopy. The tested groups demonstrated a non-significant microbiological reduction in the postmortem periapical index values between the control group and the bactericidal glass-ceramic group (p = 0.885), and between the control group and the ZnO-enriched glass group (p = 0.169). The histological results showed low values of inflammatory infiltrate, and a healing pattern characterized by fibrosis in 44.4% of the G3T glass-ceramic and 60.0% of ZnO-enriched glass. Bactericidal glassy additives incorporated in this root canal sealer are safe and effective in bacterial reduction.

[The organization of pre-clinical studies of bactericidal and wound healing effects of the impulse photoherapy device "Zarya"]

The purpose of the study is to determine therapeutic effectiveness of the pulsed high intensity optical irradiation device "Zarya" exemplified by treatment of model wounds in laboratory animals and to compare with traditional methods of wound treatment. The prototype of "Zarya" device was used whose operating principle was based on pulsed irradiation of affected areas with high intensity optical radiation in continuous spectrum generated by pulsed xenon lamp. The therapeutic effect of the "Zarya" device was compared with effectiveness of the certified medical ultraviolet irradiator based on low-pressure mercury lamp and also with known wound-healing and antibacterial medication Levomekol ointment. The mature male rats of Wistar line were used in the study. The animals were distributed to 4 groups: group 1 was irradiated by "Zarya" device, group 2 was irradiated by low-pressure mercury lamp, group 3 was treated with Levomekol ointment and group 4 was exposed to no exposure. The linear wound was modeled according to the standard method under ether anesthesia. The therapeutic procedures were applied daily during 7 days. The bactericidal effect was studied on the basis of smears from wound onto flora on the 2nd, 5th and 7th day. On the 8th day the animals were subjected to euthanasia. It was established that "Zarya" device application permits to reduce considerably both duration of therapeutic procedures and therapy course in general and also to achieve more pronounced bactericidal effect. The obtained data is supposed to be used for development of program of clinical trials.

Prevention of pathogen microorganisms at indoor air ventilation system using synthesized copper nanoparticles

This article describes the impregnation of copper nanoparticles (CuNP) in a polyester fibre filter that can be used in solid–gas filtration to retain the spread of pathogen microorganisms in indoor environments. The impregnation of the CuNP was achieved by spraying the suspension on the surface of filter media. An acid pretreatment was also evaluated to increase the adhesion between fibre and nanoparticle. The synthesis of the CuNP was done by chemical reduction. The bacterial effect was measured through the contact method for Escherichia coli and Staphylococcus aureus, and we demonstrate that the presence of CuNP to filter media reduced up to 99.99% of gram‐negative and 99.98% of gram‐positive bacteria. The pretreatment with HCl was a good alternative to filter modification due to the higher adhesion between CuNP and the fibre while the high efficiency against pathogen microorganisms was kept. The modification of filters with CuNP can improve the air quality of indoor environments, vanishing the pathogen microorganisms circulating in the air.

Analysis of Genetic Diversity and Antibiotic Options for Clinical Listeria monocytogenes Infections in China

Background

The aim of this study was to investigate the mechanism of Listeria monocytogenes (Lm) pathogenicity and resistance. In addition, the effect of existing treatment options against Lm were systematically evaluated.

Methods

Six Lm isolates were collected and antimicrobial susceptibility testing of 15 antibiotics were done. Subsequently, whole genome sequencing and bioinformatics analysis were performed. Biofilm formation was evaluated by crystal violet staining. Furthermore, the effect of meropenem, linezolid, penicillin, vancomycin, and trimethoprim/sulfamethoxazole were determined using the time-kill assay.

Results

Four sequence types (STs) were identified (ST1, ST3, ST87, ST451). Multivirulence-locus sequence typing results classified ST87 isolates into cluster. All isolates were resistant to fosfomycin and daptomycin with fosX and mprF. In addition, a total of 80 virulence genes were detected and 72 genes were found in all 6 isolates. Seven genes associated with hemolysin were found in 26530 and 115423. However, due to lack of one genomic island including virulence genes related to flagellar synthesis, isolate 115423 produced less biofilm than 5 other isolates. Although all isolates were susceptible to vancomycin, the in vitro time-kill assay showed that vancomycin monotherapy resulted in less than 2 log₁₀ cerebrospinal fluid (CFU)/mL compared with the initial count. Trimethoprim/sulfamethoxazole at serum or CFU concentrations had bactericidal effect against tested Lm strains at 24 hours.

Conclusions

ST87 clone was a typical prevalent ST in clinical Lm isolates in China. Trimethoprim/sulfamethoxazole might be greater potential therapeutic option against Lm infections.

Induced Biological Response in Contact with Ag-and Cu-Doped Carbon Coatings for Potential Orthopedic Applications

Silver and copper as additives of various biomaterials have been reported as the potential solutions for biomedicine applications, mostly because of inducing bactericidal effects. The application of those admixtures in diamond-like carbon (DLC) coatings may be desirable for orthopedic implants. In the present manuscript, the biological effect of coatings with up to about 7 at.% and 14 at.% of, respectively, Cu and Ag is compared. The morphology, chemical structure, and composition of films deposited on AISI 316LVM and Ti6Al7Nb is characterized. The live/dead analysis conducted with Escherichia coli shows a higher bactericidal potential of silver than copper. Although the Cu-doped coatings can positively affect the proliferation of Saos-2 and EA.hy926 cell lines, the results of XTT test are on the verge of 70% of viability. Biological effect of silver on EA.hy926 cell lines is negative but that admixture ensures high proliferation of osteoblasts in contact with coatings deposited on titanium alloy (over 20% better than for substrate material). In that case, the viability is reaching about 85% for Ag-doped coatings on AISI 316LVM and 75% on Ti6Al7Nb. The results indicate that for the sake of bactericidal coatings that may promote osteointegration, the candidates are DLC with silver content no higher than 10 at.%.

A High-Throughput Screening System Based on Fluorescence-Activated Cell Sorting for the Directed Evolution of Chitinase A

Chitinases catalyze the degradation of chitin, a polymer of N-acetylglucosamine found in crustacean shells, insect cuticles, and fungal cell walls. There is great interest in the development of improved chitinases to address the environmental burden of chitin waste from the food processing industry as well as the potential medical, agricultural, and industrial uses of partially deacetylated chitin (chitosan) and its products (chito-oligosaccharides). The depolymerization of chitin can be achieved using chemical and physical treatments, but an enzymatic process would be more environmentally friendly and more sustainable. However, chitinases are slow-acting enzymes, limiting their biotechnological exploitation, although this can be overcome by molecular evolution approaches to enhance the features required for specific applications. The two main goals of this study were the development of a high-throughput screening system for chitinase activity (which could be extrapolated to other hydrolytic enzymes), and the deployment of this new method to select improved chitinase variants. We therefore cloned and expressed the Bacillus licheniformis DSM8785 chitinase A (chiA) gene in Escherichia coli BL21 (DE3) cells and generated a mutant library by error-prone PCR. We then developed a screening method based on fluorescence-activated cell sorting (FACS) using the model substrate 4-methylumbelliferyl β-d-N,N′,N″-triacetyl chitotrioside to identify improved enzymes. We prevented cross-talk between emulsion compartments caused by the hydrophobicity of 4-methylumbelliferone, the fluorescent product of the enzymatic reaction, by incorporating cyclodextrins into the aqueous phases. We also addressed the toxicity of long-term chiA expression in E. coli by limiting the reaction time. We identified 12 mutants containing 2–8 mutations per gene resulting in up to twofold higher activity than wild-type ChiA.

Influence of TiO2 Nanoparticles on the Resistance of Cementitious Composite Materials to the Action of Bacteria

The formation of biofilms on cementitious building surfaces can cause visible discoloration and premature deterioration, and it can also represent a potential health threat to building occupants. The use of embedded biofilm-resistant photoactivated TiO₂ nanoparticles at low concentrations in the cementitious composite matrix is an effective method to increase material durability and reduce maintenance costs. Zone of inhibition studies of TiO₂-infused cementitious samples showed efficacy toward both Gram-negative and Gram-positive bacteria.

Antibacterial Effect of Stainless Steel Surfaces Treated with a Nanotechnological Coating Approved for Food Contact

Stainless steel, widely present in the food industry, is frequently exposed to bacterial colonization with possible consequences on consumers' health. 288 stainless steel disks with different roughness (0.25, 0.5 and 1 μm) were challenged with four Gram-negative (Escherichia coli ATCC 25922, Salmonella typhimurium ATCC 1402, Yersinia enterocolitica ATCC 9610 and Pseudomonas aeruginosa ATCC 27588) and four Gram-positive bacteria (Staphylococcus aureus ATCC 6538, Enterococcus faecalis ATCC 29212, Bacillus cereus ATCC 14579 and Listeria monocytogenes NCTT 10888) and underwent three different sanitizing treatments (UVC, alcohol 70% v/v and Gold lotion). Moreover, the same procedure was carried out onto the same surfaces after a nanotechnological surface coating (nanoXHAM^® D). A significant bactericidal effect was exerted by all of the sanitizing treatments against all bacterial strains regardless of roughness and surface coating. The nanoXHAM^® D coating itself induced an overall bactericidal effect as well as in synergy with all sanitizing treatments regardless of roughness. Stainless steel surface roughness is poorly correlated with bacterial adhesion and only sanitizing treatments can exert significant bactericidal effects. Most of sanitizing treatments are toxic and corrosive causing the onset of crevices that are able to facilitate bacterial nesting and growth. This nanotechnological coating can reduce surface adhesion with consequent reduction of bacterial adhesion, nesting, and growth.

Development and characterization of a carvacrol nanoemulsion and evaluation of its antimicrobial activity against selected food-related pathogens

Carvacrol has been recognized as an efficient growth inhibitor of food pathogens. However, carvacrol oil is poorly water-soluble and can be oxidized, decomposed or evaporated when exposed to the air, light, or heat. To overcome these limitations, a carvacrol nanoemulsion was developed and its antimicrobial activity against food pathogens evaluated in this study. The nanoemulsion containing 3% carvacrol oil, 9% surfactants (HLB 11) and 88% water, presented good stability over a period of 90 days. In general, the carvacrol nanoemulsion (MIC: 256 µg ml^-1 for E. coli and Salmonella spp., 128 µg ml^-1 for Staphylococcus aureus and Pseudomonas aeruginosa) exhibited improved antimicrobial activity compared to the free oil. The carvacrol nanoemulsion additionally displayed bactericidal activity against Escherichia coli, P. aeruginosa and Salmonella spp. Therefore, the results of this study indicated that carvacrol oil nanoemulsions can potentially be incorporated into food formulations, wherein their efficacy for the prevention and control of microbial growth could be evaluated.

In Vitro Destruction of Pathogenic Bacterial Biofilms by Bactericidal Metallic Nanoparticles via Laser-Induced Forward Transfer

A novel, successful method of bactericidal treatment of pathogenic bacterial biofilms in vitro by laser-induced forward transfer of metallic nanoparticles from a polyethylene terephthalate polymeric substrate was suggested. Transferred nanoparticles were characterized by scanning and transmission electron microscopy, energy-dispersive X-ray and Raman spectroscopy. The antibacterial modality of the method was tested on Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas Aeruginosa) bacterial biofilms in vitro, revealing their complete destruction. The proposed simple, cost-effective and potentially mobile biofilm treatment method demonstrated its high and broad bactericidal efficiency.

Antibacterial Activity of Cinnamomum camphora Essential Oil on Escherichia coli During Planktonic Growth and Biofilm Formation

Bacterial biofilms are believed to be principal virulence factors for many localized chronic infectious diseases. Escherichia coli is one of the most common microbial pathogens and frequently causes biofilm-associated opportunistic infections, such as diarrhea, endometritis and mastitis. Cinnamomum camphora essential oil (CCEO) has shown potential in treating intractable chronic endometritis in dairy cows. There is little scientific evidence regarding the effect of CCEO on bacterial biofilms. The objective of this study was to investigate the effect of CCEO on E. coli biofilm formation and how CCEO affects E. coli in suspension and in a biofilm. CCEO killed all clinical E. coli strains in either planktonic or biofilm state isolated from dairy cows with clinical endometritis. The minimum inhibitory concentration (MIC) for 90% of the organisms was 4.297 μL/mL, the minimum bactericidal concentration for 90% of the organisms was 6.378 μL/mL, the minimum biofilm inhibitory concentration for 90% of the organisms was 6.850 μL/mL, and the minimum biofilm eradication concentration (MBEC) for 90% of the organisms was 8.467 μL/mL. The MBECs were generally two times higher than the MICs. Flow cytometry analysis confirmed that significant bacterial killing occurred during the first 1 h after exposure to subinhibitory concentrations of CCEO. In addition, CCEO exerted a significant inhibitory effect on E. coli biofilm formation, and bacterial killing occurred during the first 30 min of exposure to subinhibitory biofilm concentrations of CCEO. The biofilm yield of E. coli was significantly reduced after CCEO treatment, along with an increased dead/live microbial ratio in biofilms compared with that in the non-treated control, as confirmed by scanning electron microscopy images and confocal laser scanning microscopy images. These data revealed that CCEO efficiently kills E. coli during planktonic growth and biofilm formation.

Galectin-2 Has Bactericidal Effects against Helicobacter pylori in a β-galactoside-Dependent Manner

Helicobacter pylori is associated with the onset of gastritis, peptic ulcers, and gastric cancer. Galectins are a family of β-galactoside-binding proteins involved in diverse biological phenomena. Galectin-2 (Gal-2), a member of the galectin family, is predominantly expressed in the gastrointestinal tract. Although some galectin family proteins are involved in immunoreaction, the role of Gal-2 against H. pylori infection remains unclear. In this study, the effects of Gal-2 on H. pylori morphology and survival were examined. Gal-2 induced H. pylori aggregation depending on β-galactoside and demonstrated a bactericidal effect. Immunohistochemical staining of the gastric tissue indicated that Gal-2 existed in the gastric mucus, as well as mucosa. These results suggested that Gal-2 plays a role in innate immunity against H. pylori infection in gastric mucus.

Bactericidal effects of high intensity focused ultrasound on Bacillus Calmette-Guerin in vivo and in vitro

Purpose: The objective of this study was to investigate the bactericidal effects of high intensity focused ultrasound (HIFU) on Bacillus Calmette-Guerin (BCG, a substitute for Mycobacterium tuberculosis) in vitro and in vivo, and to explore the underlying mechanisms. Materials and methods: HIFU, at a fixed frequency of 1 MHz, was applied to both BCG culture suspensions and subcutaneous BCG abscesses in rats. Results: HIFU irradiation significantly reduced the bacterial survival rate and caused temperature elevations both in vitro and in vivo. Furthermore, BCG suspensions irradiated for 15 s at 3185 and 6369 W/cm² had increased cell wall damage, which resulted in morphological changes compared to the untreated control group. Additionally, we observed histological changes in the rat subcutaneous abscesses after HIFU ablation at 6369 W/cm². H&E staining of infected lesions showed coagulative necrosis with central nucleus dissolution and increased infiltration of inflammatory cells, as well as nuclear pyknosis and nuclear fragmentation in the periphery. The volumes of the subcutaneous abscesses in the HIFU-treated group were significantly lower than those in the sham-treated group. Conclusion: HIFU has the therapeutic potential to treat BCG-infected tissues in rats. We theorize that a combination of mechanical, cavitation, and thermal effects most efficiently inactivate BCG bacteria via HIFU. This study is expected to provide a bio-plausible basis for a noninvasive and effective treatment for tuberculosis.

Protective Effect of the Golden Staphyloxanthin Biosynthesis Pathway on Staphylococcus aureus under Cold Atmospheric Plasma Treatment

Staphylococcus aureus infection poses a serious threat to public health, and antibiotic resistance has complicated the clinical treatment and limited the solutions available to solve this problem. Cold atmospheric plasma (CAP) is a promising strategy for microorganism inactivation. However, the mechanisms of microbial inactivation or resistance remain unclear. In this study, we treated S. aureus strains with a self-assembled CAP device and found that CAP can kill S. aureus in an exposure time-dependent manner. In addition, the liquid environment can influence the survival rate of S. aureus post-CAP treatment. The S. aureus cells can be completely inactivated in normal saline and phosphate-buffered saline but not in tryptic soy broth culture medium. Scanning and transmission electron microscopy revealed that the CAP-treated S. aureus cells maintained integrated morphological structures, similar to the wild-type strain. Importantly, the CAP-treated S. aureus cells exhibited a reduced pigment phenotype. Deletion of the staphyloxanthin biosynthetic genes crtM and crtN deprived the pigmentation ability of S. aureus Newman. Both the Newman-ΔcrtM and Newman-ΔcrtN mutants presented high sensitivity to CAP treatment, whereas Newman-ΔcrtO exhibited a survival rate comparable to wild-type Newman after CAP treatment. Our data demonstrated that the yellow pigment intermediates of the staphyloxanthin biosynthetic pathway are responsible for the protection of S. aureus from CAP inactivation. The key enzymes, such as CrtM and CrtN, of the golden staphyloxanthin biosynthetic pathway could be important targets for the design of novel sterilization strategies against S. aureus infections.IMPORTANCEStaphylococcus aureus is an important pathogen that can be widely distributed in the community and clinical settings. The emergence of S. aureus with multiple-antibiotic resistance has complicated staphylococcal infection control. The development of alternative strategies with powerful bactericidal effects is urgently needed. Cold atmospheric plasma (CAP) is a promising strategy for microorganism inactivation. Nevertheless, the underlying mechanisms of microbial inactivation or resistance are not completely illustrated. In this study, we validated the bactericidal effects of CAP on S. aureus, including antibiotic-resistant strains. We also found that the golden staphyloxanthin, as well as its yellow pigment intermediates, protected S. aureus against CAP, and blocking the staphyloxanthin synthesis pathway at the early steps could strengthen the sensitivity of S. aureus to CAP treatment. These data provide insights into the germicidal mechanism of CAP from the aspect of bacteria and suggest new targets against S. aureus infections.

The Bactericidal Effect of a Combination of Food-Grade Compounds and their Application as Alternative Antibacterial Agents for Food Contact Surfaces

Chemical antibacterials are widely used to control microbial growth but have raised concerns about health risks. It is necessary to find alternative, non-toxic antibacterial agents for the inhibition of pathogens in foods or food contact surfaces. To develop a non-toxic and “green” food-grade alternative to chemical sanitizers, we formulated a multicomponent antibacterial mixture containing Rosmarinus officinalis L., Camellia sinensis L., citric acid, and ε-polylysine and evaluated its bactericidal efficacy against Staphylococcus aureus, Escherichia coli, Bacillus cereus, Salmonella Enteritidis, and Listeria monocytogenes on food contact surfaces. A combination of the agents allowed their use at levels lower than were effective when tested individually. At a concentration of 0.25%, the multicomponent mixture reduced viable cell count by more than 5 log CFU/area, with complete inactivation 24 h after treatment. The inhibitory efficacy of the chemical antibacterial agent (sodium hypochlorite, 200 ppm) and the multicomponent antibacterial mixture (0.25%) on utensil surfaces against S. aureus, E. coli, S. Enteritidis, and L. monocytogenes were similar, but the multicomponent system was more effective against B. cereus than sodium hypochlorite, with an immediate 99.999% reduction on knife and plastic basket surfaces, respectively, and within 2 h on cutting board surfaces after treatment. A combination of these food-grade antibacterials could be a useful strategy for inhibition of bacteria on food contact surfaces while allowing use of lower concentrations of its components than are effective individually. This multicomponent food-grade antibacterial mixture may be a suitable “green” alternative to chemical sanitizers.

Synergetic Effects of Combined Treatment of Colistin With Meropenem or Amikacin on Carbapenem-Resistant Klebsiella pneumoniae in vitro

The purpose of this study was to investigate the synergistic and bactericidal effects of combinations of colistin with meropenem or amikacin in vitro and provide laboratory data needed for development of therapeutic strategies for the treatment of carbapenem-resistant Klebsiella pneumoniae (CRKP) infection. We found that minimum inhibitory concentration (MIC) of colistin, meropenem and amikacin were 2~32, 4~256, and 1~16384 μg/ml, respectively. The minimum bactericidal concentration of the antibiotics was either 1× or 2×MIC. Treatments of 6 CRKP isolates at 1 μg/ml colistin completely killed 2 of them and suppressed 4 others growth. 4 CRKP isolates at 16 μg/ml meropenem or amikacin completely killed and suppressed 2 others growth. 2 CRKP isolates showed synergic effects in all colistin combination and 3 CRKP isolates showed synergic effects in part of colistin combination. Our data suggest that colistin in combination with either meropenem or amikacin could be a valid therapeutic option against colistin-resistant CRKP isolates. Moreover, the combination of colistin-amikacin is less expensive to treat CRKP infections in Eastern Heilongjiang Province.

Surface-Enhanced IR-Absorption Microscopy of Staphylococcus aureus Bacteria on Bactericidal Nanostructured Si Surfaces

Surface-enhanced IR absorption (SEIRA) microscopy was used to reveal main chemical and physical interactions between Staphylococcus aureus bacteria and different laser-nanostructured bactericidal Si surfaces via simultaneous chemical enhancement of the corresponding IR-absorption in the intact functional chemical groups. A cleaner, less passivated surface of Si nanoripples, laser-patterned in water, exhibits much stronger enhancement of SEIRA signals compared to the bare Si wafer, the surface coating of oxidized Si nanoparticles and oxidized/carbonized Si (nano) ripples, laser-patterned in air and water. Additional very strong bands emerge in the SEIRA spectra on the clean Si nanoripples, indicating the potential chemical modifications in the bacterial membrane and nucleic acids during the bactericidal effect.

Photothermal inactivation of methicillin-resistant Staphylococcus aureus: anti-biofilm mediated by a polypyrrole-carbon nanocomposite

Widespread resistance to antibiotics amongst pathogens has become a tremendous challenge of high morbidity and mortality rates which increases the needs to exploring novel methods of treatment. An efficient antimicrobial procedure to root out pathogenic bacteria is photothermal therapy. In this study, antimicrobial effects of a polypyrrole-carbon nanocomposite (PPy-C) upon laser irradiation in order to destroy the pathogenic gram-positive bacterium, methicillin-resistant Staphylococcus aureus (MRSA) were assessed. The bacterial cells were incubated with 500, 750 and 1000 μg ml-1 concentrations of PPy-C and irradiated with an 808-nm laser at a power density of 1.0 W cm-2. To indicate the biocompatibility and toxic effect of the nanocomposite without and with laser irradiation, the authors counted the number of CFUs and compared it to an untreated sample. Antibacterial mechanisms of PPy-C were assessed through temperature increment, reactive oxygen species production, and protein and DNA leakages. Photothermal heating assay showed that 26°C temperature increases in the presence of 1000 µg ml-1 PPy-C led to >98% killing of MRSA. Furthermore, 20 min radiation of near-infrared light to PPy-C in different concentrations indicated destruction and reduction in the MRSA biofilm formation. Therefore, PPy-C was introduced as a photothermal absorber with a bactericidal effect in MRSA.

Coordination-Assisted Self-Assembled Polypeptide Nanogels to Selectively Combat Bacterial Infection

In the present scenario, the invention of bacteria-selective antimicrobial agent comprising negligible toxicity and hemolytic effect is a great challenge. To surmount this challenge, here, a series of polypeptide nanogels (PNGs) have been fabricated by a coordination-assisted self-assembly of a mannose-conjugated antimicrobial polypeptide, poly(arginine-r-valine)-mannose (poly(Arg-r-Val)-M₂), with Zn²⁺ ions. The fabricated PNGs are spherical in shape with a unique structural appearance similar to that of Taxus baccata fruits. PNGs, with a unique structural arrangement and threshold surface charge density, selectively interact with the bacterial membrane and exhibit potent antimicrobial activity, as reflected in their lower minimum inhibitory concentration values (varies from 2 to 16 μg/mL). PNGs show a remarkably high binding constant, 6.02 × 105 M^-1 (from isothermal titration calorimetry, ITC), with the bacterial membrane which manifests its potent bactericidal effect. PNGs are nontoxic against mammalian and red blood cells as reflected from their higher cell viability and insignificant hemolytic effect. PNGs are taken up by the bacterial membrane and selectively undergo structural deformation (scrutinized by ITC) followed by an exposure of free poly(Arg-r-Val)-M₂ molecules. The free poly(Arg-r-Val)-M₂ molecules are enforced to lyse the bacterial membrane (visualized by cryo-transmission electron microscopy) followed by the diffusion of the cytoplasmic component out of the membrane which culminates in the final death of the bacterium.

Evaluation of essential oil obtained from Mentha×piperita L. against multidrug-resistant strains

Background

Bacterial multidrug resistance currently poses an increasingly serious threat, with important clinical consequences regarding treatment options. In 2017, the WHO released a global list of resistant bacteria, identifying multidrug-resistant (MDR) Gram-negative bacteria such as carbapenem-resistant Enterobacteriaceae, Pseudomonas aeruginosa or Acinetobacter baumannii, extended-spectrum cephalosporin-resistant Enterobacteriaceae as critical priorities for developing new strategies of treatment.

Purpose

The novelty presented in this study refers to the evaluation of the volatile oil obtained from the leaves of Mentha×piperita L., on MDR strains from hospitalized patients.

Material and methods

The essential oil was extracted by steam distillation and tested on six reference bacterial strains and also on the MDR strains collected from patients of the “Pius Brînzeu” Emergency Clinical County Hospital Timișoara. The in vitro antibacterial activity was evaluated by agar disk diffusion method and microdilution method.

Results

Testing the antibacterial activity of peppermint oil on both reference strains and isolated MDR strains from hospitalized patients demonstrated its bactericidal effect. Minimum inhibitory concentration (MIC) was lower (20 mg/mL) for Staphylococcus aureus, Escherichia coli and Proteus mirabilis and higher (40 mg/mL) for Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii strains. Minimum bactericidal concentration (MBC) was equal to MIC, with the exception of Pseudomonas aeruginosa strains, where MBC was the double of MIC.

Conclusion

The present study highlights the bactericidal activity of Mentha×piperita L. essential oil on all tested MDR or extensively drug-resistant Gram-positive and Gram-negative strains of Staphylococcus aureus, Escherichia coli, Klebsiellapneumoniae, Proteus mirabilis, Pseudomonas aeruginosa and Acinetobacter baumannii. This oil may be a therapeutic option in the near future for many infectious diseases produced by MDR bacteria.

[Do liquid wastes from automated instruments in medical laboratories have their proper microbicide effect?]

Liquid wastes from clinical biology automated systems are currently evacuated in the urban network after chemical treatment to eliminate a possible risk of infection. Since these wastes are ecotoxic because of the presence of numerous chemical reagents, we studied their intrinsic microbicidal power towards a selection of infectious agents widely found in clinical specimens. The objective was to determine if an additional anti-infectious treatment before elimination is necessary. Thus, we evaluated the bactericidal effect of liquid wastes of several automated systems towards four bacterial species (Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Enterococcus faecalis) and their virucidal activity against a non-enveloped virus, resistant in the environment (adenovirus). This effect was determined for different exposure times. Our results showed that the antibacterial activity was highly variable depending on the waste-bacteria pair considered (varying from no activity to complete sterilization of a strong bacterial inoculum). The liquid wastes were on the other hand globally inactive towards adenovirus.

Effects of Erbium:Yttrium-Aluminum-Garnet Laser Irradiation on Bovine Dentin Contaminated by Cariogenic Bacteria

Objective: This study was performed to determine the bactericidal effects of erbium:yttrium-aluminum-garnet (Er:YAG) laser irradiation and the morphological and chemical composition changes in bovine dentin. Methods: Dentin slabs were prepared from bovine incisors, and then cultured with Streptococcus mutans to produce bacteria-infected dentin samples. The samples were randomly divided into five groups with Er:YAG laser irradiation energy densities of 0, 6.37, 12.73, 19.11, and 25.47 J/cm². After irradiation, samples were stained and observed by confocal laser scanning microscopy. The bactericidal abilities were measured using live/dead staining. The morphology and chemical components were investigated by scanning electron microscopy and energy-dispersive spectrometry. Results: After irradiation, the elimination of bacteria and the smear layer were significantly better in the high energy density groups (19.11, 25.47 J/cm²) than in the low energy density groups (6.37, 12.73 J/cm²; p < 0.001). On morphological examination, the group with minimum energy density (6.37 J/cm²) showed superficial melting. In the high energy density groups (12.73, 19.11, and 25.47 J/cm²), laser-irradiated dentin showed a clean surface with open orifices. Significant increases were observed in the weight percentages of calcium (from 19.75 ± 0.69 to 34.47 ± 2.91, p < 0.001) and phosphate (from 8.58 ± 0.43 to 15.10 ± 1.81, p < 0.001), whereas significant decreases were observed for oxygen (from 49.84 ± 0.69 to 36.39 ± 2.86, p < 0.001) and carbon (from 26.06 ± 3.58 to 12.80 ± 2.26, p < 0.01) with increasing energy density. Conclusions: This study confirmed that Er:YAG laser irradiation has bactericidal and dentin conditioning effects.

Silver Nanoparticles with High Loading Capacity of Amphotericin B: Characterization, Bactericidal and Antifungal Effects

The purpose of this study was to evaluate the most appropriate conditions to generate silver nanoparticles (AgNPs) loaded with a potent antimycotic drug like amphotericin B (AmB), characterize the physicochemical properties, and to evaluate the cytotoxic effect and biological activity of these new nanostructures as a potential nanocarrier for hydrophobic drugs. It was determined that the optimal molar ratio between Ag and AmB is 1/1 given the uniformity of size around 170 nm of the nanoparticles generated as well as their strongly negative ζ potential of -35 mV, a condition that favors repulsions between AgNPs and inhibiting their aggregation. In this condition, only 0.8 mg.mL-1 of Ag is needed to solubilize 5 mg.mL-1 of AmB, a concentration currently used in commercial formulations. It is important to emphasize that the loading capacity (w/w) of this nanostructure is much higher than that of micellar and liposomal formulations. These AgNP-AmB nanoparticles retain both the bactericidal effect of silver and the cytotoxic and antifungal effect of AmB. However, it was shown that these nanoparticles are spontaneously associated with plasma lipoproteins (LDL and HDL), inhibiting their cytotoxic effects on red blood cells and on at least two cell lines, Vero and H1299 and slightly reducing its bactericidal effect on P. aeruginosa. In contrast, the antifungal effect of the formulation is maintained and is even higher than that when the nanoparticle is not associated with lipoproteins, indicating that this association is of the reversible type. The characterization of these nanoparticles is discussed as a potential new model formulation able to improve the antifungal therapeutic efficiency of AmB.

Evaluation of fast-acting bactericidal activity and substantivity of an antiseptic agent, olanexidine gluconate, using an ex vivo skin model

PURPOSE

We assessed the fast-acting bactericidal activity and substantivity of olanexidine gluconate (OLG) to investigate its remaining bactericidal activity on the skin after rinsing and drying by using an ex vivo Yucatan micropig (YMP) skin model.

METHODOLOGY

The fast-acting bactericidal activity was evaluated in pigskin models inoculated with methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis, vancomycin-resistant Enterococcus faecalis (VRE), Acinetobacter baumannii, Corynebacterium minutissimum and Cutibacterium acnes. To evaluate substantivity, the YMP skin piece first had 1.5 % OLG, chlorhexidine gluconate (CHG) formulations or 10 % povidone-iodine (PVP-I) applied to it, and was then rinsed with distilled water, incubated for 4, 6, 8 or 12 h and inoculated with the test bacteria (MRSA, S. epidermidis and VRE). The viable bacteria remaining at 1 min of exposure of bacteria were counted to measure the quantity of antiseptic molecules retaining bactericidal activity. To determine the factors contributing to the substantivity, the stratum corneum (SC) of the YMP skin that had had OLG or CHG applied to it was exfoliated using a tape-stripping method and the amount of antiseptic was quantitated.

RESULTS

OLG showed a fast-acting bactericidal activity that was similar to or stronger than that of CHG formulations up to a concentration of 1 % and PVP-I with a short exposure time of 30 s, and substantivity until 12 h after rinsing, whereas the other antiseptics hardly showed any substantivity. There was 2.8 times or more OLG in the SC than CHG.

CONCLUSION

OLG has fast-acting activity and substantivity, which are required properties for an antiseptic, and is useful for preventing infections.

Nano-encapsulated HHC10 host defense peptide (HDP) reduces the growth of Escherichia coli via multimodal mechanisms

The eradication of several pathogenic drug resistant "Superbug" such as Escherichia coli became difficult especially in chronic infections using existing antibiotics due to the emergence of antibiotic resistance. Owing to their unique antibacterial properties, host defense peptides (HDP) have gained significant attention to combat colonization of bacteria. This study aims designing delivery systems for HHC10 peptide to target bacteria inside the cells might be a promising approach by protecting from degradation, controlling the release, enhancing the susceptibility of target microbes and improving bioavailability. Nano-formulated HHC10 was evaluated for its efficacy (CFU assay) and possible mechanism of action (membrane interaction and apoptosis) against E. coli. Dose-dependent inhibition of E. coli growth is observed for nano-encapsulated and bare HHC10 and encapsulated form remain non-toxic to macrophage mouse cells (RAW264.6) up to 20 μM. Mechanistic analyses using transmission electron microscopy and flow cytometry techniques revealed that bactericidal activity of HHC10-NP progresses via a multimodal mechanism of bacterial cell death by cell-membrane lysis on direct interaction with bacteria while through induction of the apoptotic death pathway inside the host cells. These results offer an insight on future strategies for the development and application of antimicrobial peptides as antibacterial alternatives. Controlled delivery of HHC10 peptide from PLGA-NP kills bacteria by two different mechanism: (i) direct killing: HHC10 disintegrate the cell membrane of bacteria by electrostatic interactions and (ii) indirect killing: induction of apoptosis in bacteria infect cells.

Phenanthrene Antibiotic Targets Bacterial Membranes and Kills Staphylococcus aureus With a Low Propensity for Resistance Development

New classes of antibiotics with different mechanisms of action are urgently required for combating antimicrobial resistance. Blestriacin, a dihydro-biphenanthrene with significant antibacterial activity, was recently isolated from the fibrous roots of Bletilla striata. Here, we report the further characterization of the antimicrobial potential and mode of action of blestriacin. The phenanthrene compound inhibited the growth of all tested clinical isolates of Staphylococcus aureus including methicillin-resistant S. aureus (MRSA). The minimum inhibitory concentrations (MICs) of blestriacin against these pathogens ranged from 2 to 8 μg/mL. Minimum bactericidal concentration (MBC) tests were conducted, and the results demonstrated that blestriacin was bactericidal against S. aureus. This effect was confirmed by the time-kill assays. At bactericidal concentrations, blestriacin caused loss of membrane potential in B. subtilis and S. aureus and disrupted the bacterial membrane integrity of the two strains. The spontaneous mutation frequency of S. aureus to blestriacin was determined to be lower than 10^-9. The selection and whole genome sequencing of the blestriacin –resistant mutants of S. aureus indicated that the development of blestriacin resistance in S. aureus involves mutations in multi-genes. All these observations can be rationalized by the suggestion that membrane is a biological target of blestriacin.