Intrinsic Antibacterial Activity Research Articles

Simple synthesis of novel magnetic silver polymer nanocomposites with a good separation capacity and intrinsic antibacterial activities with high performance.

Two new coordination polymers namely, [(AgCN)4LS]n (1) and [(AgCN)3LN]n (2), were successfully synthesized by the reaction of AgNO3 and cyanide as a co-anion with LS[1,1'-(hexane-1,4-diyl)bis(3-methylimidazoline-2-thione] and LN[1,1,3,3-tetrakis(3,5-dimethyl-1-pyrazole)propane] ligands in order to use them for the preparation of magnetic nanocomposites with MnFe2O4 nanoparticles by an efficient and facile method. They were then well characterized via numerous techniques, including elemental analysis, FT-IR spectroscopy, TGA, PXRD, SEM, TEM, EDX, VSM, BET, ICP, and single-crystal X-ray diffraction. The considered polymers and their magnetic nanocomposites with nearly the same antibacterial activity demonstrated a highly inhibitive effect on the growth of Gram-negative (Escherichia coli, Pseudomonas aeruginosa) and Gram-positive (Staphylococcus aureus, Bacillus subtilis) bacteria. By considering the simple separation and recyclable characters of the magnetic nanocomposites, these materials are suitable to be used in biological applications.

Custom-design of intrinsically antimicrobial polyurethane hydrogels as multifunctional injectable delivery systems for mini-invasive wound treatment

• Infections represent the major obstacle hindering the healing of chronic wounds. • The development of polymers intrinsically antimicrobial reduces the need of antibiotics. • The chemical versatility of polyurethanes results in polymers with ad-hoc properties. • System thermosensitivity allows shape-adaptability and rapid post-injection gelation. • The micellar hydrogel network opens the way to versatile delivery carriers. Effective management of hard-to-close skin wounds is a challenging issue due to several co-morbidities in affected patients. Particularly, infections represent a major obstacle in wound healing. The design of efficient wound treatments thus represents an urgent need. Injectable drug delivery hydrogels with intrinsic antimicrobial and antifungal properties were herein designed for perspective application in the mini-invasive treatment of hard-to-close wounds. First, an amphiphilic polyurethane was synthesized from Poloxamer® 407 macrodiol and N-Boc diethanolamine chain extender (DHP407, M ¯ w =33 kDa). Chain-extension reaction step was optimized to maximize the formation of -NH groups along the polymer chains (4.5 × 10 20 ±1.8 × 10 19 –NH groups/g polymer ), after Boc-caging group removal (D-DHP407). DHP407 and D-DHP407 water-based solutions were thermosensitive with slightly different Critical Micellar Concentration (17.5 μg/mL vs . 19.7 μg/mL) and cluster hydrodynamic diameter (235.6 ± 19.9 nm vs . 260.1 ± 20.5 nm), and similar Critical Micellar Temperature (22.5 °C vs . 23.1 °C). A polyurethane solution concentration (15% w/V) was selected by tube-inverting test and rheological analysis showing injectability, as evidenced by sol-to-gel transition at 27.7 ± 0.6 °C for DHP407 and 29.7 ± 0.6 °C for D-DHP407, within few minutes, at similar gelation kinetics. DHP407 and D-DHP407 hydrogels showed controlled release of Bovine Serum Albumin (BSA) model protein (1 mg/mL), with no burst phenomena. BSA released from DHP407 and D-DHP407 hydrogels at 24 h was 33.7 ± 5.0% and 24.6 ± 1.2%, respectively. D-DHP407 hydrogel was biocompatible and able to support NIH-3T3 cell proliferation. Furthermore, D-DHP407 hydrogel showed intrinsic antifungal and antibacterial activity against C. albicans and Gram-positive S. aureus and Gram-negative E. coli bacteria, injectability and capability to retain shape post-injection, making it promising for future use in the management of hard-to-close skin wounds.

1447. Emergence of Avibactam Resistance in Multidrug-Resistant Enterobacteriaceae

BackgroundAvibactam (AVI) is a non-β-lactam β-lactamase inhibitor used clinically to inhibit bacterial β-lactamase activity against the β-lactam antibiotic ceftazidime. We previously observed intrinsic in vitro antibacterial activity of AVI against multidrug-resistant Enterobacteriaceae. Here we characterize the rapid emergence of AVI resistance following AVI exposure.MethodsWe grew two carbapenem- and colistin-resistant isolates (E. coli ARLG 2829/MCR1_NJ and Klebsiella pneumoniae AR-0636) in liquid culture containing 16x the AVI minimum inhibitory concentration (MIC) for 24 hours. We then tested the AVI MIC of each strain daily for 17 days following serial passage on antibiotic-free media. We also tested MICs of AVI and 6 β-lactam antibiotics against broadly susceptible E. coli and K. pneumoniae isolates following growth with AVI. Finally, we tested in vivo activity of AVI using a mouse thigh infection model in which groups of 5 mice infected with 1x108 CFU/thigh of AR-0636 were treated with AVI 250 mg/kg or saline every 8 hours for 24 hours.ResultsFollowing growth in AVI 128 μg/mL, the AVI MIC of both strains increased from 8 to > 256 μg/mL and remained ≥ 256 μg/mL for 17 days of serial passage on antibiotic-free media. Following AVI treatment, MICs were also elevated for mecillinam, which, like AVI, targets penicillin-binding protein 2 (PBP2), but not for drugs with different PBP affinities. In a mouse thigh infection model, AVI treatment resulted in an average 1.4 log10 decrease in CFU/thigh compared to placebo. AVI MICs in bacteria recovered from treated mouse thighs were unchanged from initial MIC.ConclusionAVI resistance emerged rapidly in vitro and persisted for over two weeks in the absence of selective pressure. The co-emergence of mecillinam resistance suggests that AVI resistance may reflect PBP2 alterations. Development of resistance was not observed in a mouse model. These results have important implications for new non-β-lactam β-lactamase inhibitors (nacubactam, zidebactam) with structural similarities to AVI and known intrinsic antibacterial activity that have recently completed Phase I trials in combination with β-lactam drugs and are likely to play an important future role in CRE treatment.Disclosures Thea Brennan-Krohn, MD, D(ABMM), Tecan (Other Financial or Material Support, HP D300 digital ​dispenser and its consumables were provided by Tecan. Tecan had no role in study design, data collection/interpretation, or poster preparation.) Shade Rodriguez, BA, Tecan (Other Financial or Material Support, HP D300 digital ​dispenser and its consumables were provided by Tecan. Tecan had no role in study design, data collection/interpretation, or poster preparation.) James Kirby, MD, D(ABMM), AstraDx (Advisor or Review Panel member, Other Financial or Material Support, Co-founder)First Light Biosciences (Advisor or Review Panel member)Tecan (Other Financial or Material Support, HP D300 digital ​dispenser and its consumables were provided by Tecan. Tecan had no role in study design, data collection/interpretation, or poster preparation.)

1254. In vitro activity of sulbactam-durlobactam against recent global clinical Acinetobacter baumannii-calcoaceticus complex isolates

Background Acinetobacter baumannii-calcoaceticus complex (ABC) causes severe infections that are difficult to treat due to increasing resistance to antibacterial therapy. Sulbactam (SUL) has intrinsic antibacterial activity against ABC, but its clinical utility has been compromised by the prevalence of serine β-lactamases. Durlobactam (DUR, previously ETX2514) is a diazabicyclooctenone β-lactamase inhibitor with potent activity against Ambler classes A, C and D serine β-lactamases that effectively restores SUL activity against ABC isolates. SUL-DUR is an antibiotic designed to treat serious infections caused by Acinetobacter, including multidrug-resistant strains, which is currently in Phase 3 clinical testing. The potency of SUL-DUR against geographically diverse ABC isolates collected in 2018 was measured.Methods929 ABC isolates, including 698 A. baumannii, 13 A. calcoaceticus, 54 A. nosocomialis, and 164 A. pittii, were collected in 2018 from geographically diverse medical centers in the United States, Europe, Latin America, Israel and the Asia-Pacific region. Susceptibility testing was performed according to CLSI guidelines. Data analysis was performed using CLSI and EUCAST breakpoint criteria where available. Select isolates were subjected to whole genome sequencing with an Illumina MiSeq V2 instrument and analysis using CLCBio Genomics Workbench v6.5.ResultsIn surveillance of 929 global isolates from 2018, the SUL-DUR MIC90 was 2 mg/L compared with 64 mg/L for SUL alone. This level of potency was consistent across species, regions, source of infection and subsets of resistance phenotypes. Fifty percent of the isolates were non-susceptible to carbapenems. Only 7 isolates (0.75%) had SUL-DUR MIC values >4 mg/L. Whole genome sequencing of these 7 isolates revealed that they either encoded the metallo-β-lactamase NDM-1, which DUR does not inhibit, or single amino acid substitutions near the active site of PBP3, the primary target of SUL.ConclusionSUL-DUR demonstrated potent antibacterial activity against recent, geographically diverse clinical isolates of ABC, including MDR isolates. These data support the potential utility of SUL-DUR for the treatment of antibiotic-resistant infections caused by ABC.DisclosuresSarah McLeod, PhD, Entasis Therapeutics (Employee) Samir Moussa, PhD, Entasis Therapeutics (Employee) Alita Miller, PhD, Entasis Therapeutics (Employee)

1293. Sulbactam-durlobactam is active against recent, multi-drug resistant Acinetobacter baumannii clinical isolates from the Middle East

BackgroundThe incidence of infections caused by multidrug-resistant (MDR) Acinetobacter baumannii (Ab) is increasing at an alarming rate in certain regions of the world, including the Middle East. Sulbactam (SUL) has intrinsic antibacterial activity against Ab; however, the prevalence of β-lactamases in Ab has limited its therapeutic utility. Durlobactam (DUR, formerly ETX2514) is a diazabicyclooctenone β-lactamase inhibitor with broad-spectrum activity against Ambler class A, C and D β-lactamases that restores SUL activity in vitro against MDR Ab. SUL-DUR is an antibiotic designed to treat serious infections caused by Acinetobacter, including multidrug-resistant strains, that is currently in Phase 3 clinical development. In global surveillance studies of >3600 isolates from 2012-2017, the MIC90 of SUL-DUR was 2 mg/L. Although surveillance systems to monitor MDR infections in the Middle East are currently being established, quantitative, prevalence-based data are not yet available. Therefore, the potency of SUL-DUR was determined against 190 recent, diverse Ab clinical isolates from this region.Methods190 Ab isolates were collected between 2016 - 2018 from medical centers located in Israel (N = 47), Jordan (N = 36), Qatar (N = 13), Kuwait (N = 42), Lebanon (N = 8), Saudi Arabia (N = 24) and United Arab Emirates (N = 20). Seventy-five percent and 20.5% of these isolates were from respiratory and blood stream infections, respectively. Susceptibility to SUL-DUR and comparator agents was performed according to CLSI guidelines, and data analysis was performed using CLSI and EUCAST breakpoint criteria where available.ResultsThis collection of isolates was 86% carbapenem-resistant and 90% sulbactam-resistant (based on a breakpoint of 4 mg/L). The addition of SUL-DUR (fixed at 4 mg/L) decreased the sulbactam MIC90 from 64 mg/L to 4 mg/L. Only 3 isolates (1.6%) had SUL-DUR MIC values of > 4 mg/L. This potency was consistent across countries, sources of infection and subsets of resistance phenotypes.ConclusionSUL-DUR demonstrated potent antibacterial activity against recent clinical isolates of Ab from the Middle East, including MDR isolates. These data support the global development of SUL-DUR for the treatment of MDR Ab infections.DisclosuresAlita Miller, PhD, Entasis Therapeutics (Employee) Sarah McLeod, PhD, Entasis Therapeutics (Employee) Samir Moussa, PhD, Entasis Therapeutics (Employee)

Polymerized ionic liquids‐based hydrogels with intrinsic antibacterial activity: Modern weapons against antibiotic‐resistant infections

AbstractIn this study, the inherent antibacterial activity of 11 different polymerized ionic liquids (PILs)‐based hydrogels as well as their corresponding monomers was examined in an extensive screening. The methicillin‐resistant Staphylococcus aureus Xen 30 (MRSA Xen 30) and Pseudomonas aeruginosa Xen 5 (P. aeruginosa Xen 5) were chosen as test microorganisms. Both are typical representatives of gram‐positive and gram‐negative bacteria, respectively. Six of the 11 tested monomers were able to eradicate more than 80% of P. aeruginosa Xen 5 cells in suspension. Unfortunately, the anionic, neutral and zwitterionic representatives lost their function after polymerization. However, the cationic gels retained their antibacterial activity with nearly 100% eradication of selected microorganisms ‐ even at the smallest amount tested. Bactericidal activity against gram‐positive MRSA Xen 30 was high when the bacteria were treated with the imidazolium‐based monomers. Five of the tested compounds showed rather limited bactericidal activity <50% killed bacteria. The weak antibacterial activities could be significantly increased by crosslinking them to three‐dimensional networks. As a result, all the hydrogels possessed strong killing efficiencies of at least 68% and were able to maintain this activity even at low hydrogel volume fractions. These findings are very promising for the development of new antibacterial materials for medical applications, for example, stent coatings.

MWCNT-oxazolidinone conjugates with antibacterial activity

In this work, two types of MWCNT-oxazolidinone conjugates were synthesized, by varying the quartz tube lengths in the reactor (40 cm and 60 cm), with the aim at evaluating and comparing their biological potential against nine bacterial strains. MWCNT-1 (40 cm) showed higher surface defects and lower crystallinity than MWCNT-2 (60 cm). During each step of chemical modification, the organic material incorporation onto the MWCNTs changed the surface defects, density, and thermic stability. Interestingly, due to the intrinsic antibacterial activity of the oxazolidinone compounds, oxazolidinone-conjugated nanomaterials f-MWCNT-Sn-Oxa were active against the evaluated strains, while none of pristine MWCNT, f-MWCNT, or f-MWCNT-Sn exhibited antibacterial activity. The results point out to f-MWCNT-S1-Oxa-1 as the best antibacterial nanomaterial because it was active against several bacterial strains. Antibacterial results obtained with the f-MWCNT-Sn-Oxa-1 series demonstrate a significant effect of the oligomethylene chain (Sn) length against Staphylococcus aureus clinically isolated strain.

Potentiation of Antibiotic Activity by a Meldrum's Acid Arylamino Methylene Derivative against Multidrug-Resistant Bacterial Strains.

This study aimed to evaluate the intrinsic antibacterial activity and antibiotic-enhancing effect of an arylamino methylene derivative (MAD) in association with fluoroquinolones. The antibacterial activity against multiresistant Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli was analyzed by determining the minimum inhibitory concentration (MIC) using the broth micro dilution method. A reduction in the MIC of the fluoroquinolones against strains treated simultaneously with the MAD was interpreted as an enhanced antibiotic activity. While the MAD exhibited no clinically effective action (MIC ≥ 1.024µg/mL), it was found to significantly potentiate the activity of norfloxacin, ofloxacin and lomefloxacin against all the strains, which may be related to structural similarities between the MAD and quinolones. Our findings suggest that Meldrum's acid arylamino derivatives may represent promising molecules in the elaboration of new drugs to reverse resistance to fluoroquinolones.

Development and Characterization of Clay-Nanocomposites for Water Purification.

In this work we propose a facile method of preparing cost-effective clay-metaloxide/metal (CuO/Ag and ZnO/Ag) composite pellets for an efficient water purification technique. Clay, with intrinsic antibacterial activity, served as a membrane support for different metaloxide/Ag nanoparticles (NPs) concentrations (2.5, 5 and 10 wt.%), as the active fillers. The effect of time (24 and 48 h) on the bactericidal activity of these pellets was also monitored. The clay–nanocomposite pellets were characterized using: X-ray diffraction, X-ray fluorescence, scanning electron microscopy, transmission electron microscopy, ultraviolet–visible (UV–Vis) spectrophotometry and nitrogen desorption analysis. The antibacterial activity performance was tested using E. coli and S. aureus strains of ATCC25922 and ATCC25923, respectively, in two aqueous media (nutrient broth and nutrient-free) by the colony-forming unit method. The results showed that the clay-CuO/Ag composite with a bandgap (1.24 eV) exhibited overall best performance under all conditions and time factors of ~100% efficiency in nutrient-free medium for all concentrations and times and 20–40% efficiency in nutrient broth for 24 h. The clay-ZnO/Ag with a bandgap of 2.88 eV showed no bactericidal activity in both media, except for that with 10 wt.% ZnO/Ag which showed 100% efficiency in nutrient-free medium after 24 h. All the synthesized composites showed 100% bactericidal efficiency in nutrient free medium after 48 h. These results indicate that, the clay/metaloxide/Ag could serve as efficient water purification technique, with a potential for large-scale commercialization.

Lysin LysMK34 of Acinetobacter baumannii Bacteriophage PMK34 Has a Turgor Pressure-Dependent Intrinsic Antibacterial Activity and Reverts Colistin Resistance.

The prevalence of extensively and pandrug-resistant strains of Acinetobacter baumannii leaves little or no therapeutic options for treatment for this bacterial pathogen. Bacteriophages and their lysins represent attractive alternative antibacterial strategies in this regard. We used the extensively drug-resistant A. baumannii strain MK34 to isolate the bacteriophage PMK34 (vB_AbaP_PMK34). This phage shows fast adsorption and lacks virulence genes; nonetheless, its narrow host spectrum based on capsule recognition limits broad application. PMK34 is a Fri1virus member of the Autographiviridae and has a 41.8-kb genome (50 open reading frames), encoding an endolysin (LysMK34) with potent muralytic activity (1,499.9 ± 131 U/μM), a typical mesophilic thermal stability up to 55°C, and a broad pH activity range (4 to 10). LysMK34 has an intrinsic antibacterial activity up to 4.8 and 2.4 log units for A. baumannii and Pseudomonas aeruginosa strains, respectively, but only when a high turgor pressure is present. The addition of 0.5 mM EDTA or application of an osmotic shock after treatment can compensate for the lack of a high turgor pressure. The combination of LysMK34 and colistin results in up to 32-fold reduction of the MIC of colistin, and colistin-resistant strains are resensitized in both Mueller-Hinton broth and 50% human serum. As such, LysMK34 may be used to safeguard the applicability of colistin as a last-resort antibiotic.IMPORTANCEA. baumannii is one of the most challenging pathogens for which development of new and effective antimicrobials is urgently needed. Colistin is a last-resort antibiotic, and even colistin-resistant A. baumannii strains exist. Here, we present a lysin that sensitizes A. baumannii for colistin and can revert colistin resistance to colistin susceptibility. The lysin also shows a strong, turgor pressure-dependent intrinsic antibacterial activity, providing new insights in the mode of action of lysins with intrinsic activity against Gram-negative bacteria.

Structural characterization, antibacterial activity and NorA efflux pump inhibition of flavonoid fisetinidol

Flavonoids belong to the extensive group of polyphenols and have several biological activities such as anti-inflammatory, anti-ulcer, anticancer, antiviral, antibacterial, and antispasmodic. These compounds can thus be explored as a tool against multidrug resistant bacteria, as nosocomial infections now constitute a major public health problem worldwide. We have carried out a structural characterization by nuclear magnetic resonance and FT-IR of fisetinidol, a flavonoid isolated from B. pentandra stems. In addition, this flavonoid was tested for antibacterial and modulatory activities, as well as inhibition of the NorA efflux pump. Fisetinidol has no intrinsic antibacterial activity. However, there is synergism in association with norfloxacin, with a two-fold decrease in MIC. When compared to chlorpromazine, a standard efflux pump inhibitor, a two-fold decrease in MIC was also verified when used against S. aureus SA-1199B, which over expresses the NorA gene encoding the NorA efflux protein. As such, it could become an alternative source to reverse the bacterial resistance if administered in association with antibiotics.

Drug-free and non-crosslinked chitosan scaffolds with efficient antibacterial activity against both Gram-negative and Gram-positive bacteria

Treatment of oral pathogens is important for both oral and systemic health. The antimicrobial activity of chitosan (CS)-based scaffolds either loading antibiotics or compositing with other agents are well documented. However, the intrinsic antibacterial activity of CS scaffolds alone has never been reported. Herein, we fabricated the non-crosslinked CS scaffold and investigated its antibacterial activity against typical oral pathogens, Gram-negative Porphyromonas gingivalis and Gram-positive Streptococcus mutans. We found both pathogens were completely killed by 1 mg CS scaffolds at 6 h, due largely to the CS-induced time-dependent bacteria clustering. Interestingly, β-glycerophosphate crosslinked scaffolds showed no antibacterial activity. In conclusion, the bactericidal activity of CS scaffolds alone is reported for the first time. Together with the biodegradability, physical stability, biocompatibility and great antibacterial activity, the non-crosslinked CS scaffolds may have great potentials not only in treating oral diseases but also in wound healing and tissue engineering.

Structure-Dependent Antibacterial Activity of Amino Acid-Based Supramolecular Hydrogels

Bacterial infections are currently a major concern to human health. Amino acid-based supramolecular polymer hydrogels, which boast intrinsic antibacterial activity, are an important solution due to their good biocompatibility, cost effectiveness, and tunable structural properties. Herein, we reported three types of transparent supramolecular hydrogel with intrinsic antibacterial activity from self-assembly of commercially available Fmoc-tryptophan (Fmoc-W), Fmoc-methionine (Fmoc-M), and Fmoc-tyrosine (Fmoc-Y). The resulting hydrogels selectively inhibited the growth of Gram-positive bacteria. Moreover, the order of antibacterial activity was Fmoc-W hydrogel > Fmoc-M hydrogel > Fmoc-Y hydrogel. The critical aggregation concentration (CAC) values were found at concentrations of approximately 0.0293, 0.1172, and 0.4688 mM for Fmoc-W, Fmoc-M, and Fmoc-Y, respectively. Transmission electron microscope (TEM) images revealed rigid and aligned nanofibers for Fmoc-W hydrogel, while flexible nanofibers for Fmoc-M hydrogel and Fmoc-Y hydrogel. The results indicated that stronger aggregation capability of the gelator and the synergistic nanostructural morphology with more rigid and aligned nanofibers can lead to higher antibacterial activity of its corresponding hydrogel. In addition, the molecular arrangements of Fmoc-amino acids in the hydrogels may also contribute to their antibacterial activity. These results can guide the rational design, fabrication, and future application of other self-assembled amino acid-based hydrogels with excellent antibacterial activity.

A potent enzybiotic against methicillin-resistant Staphylococcus aureus.

Staphylococcus aureus is one of the most dreadful infectious agents, responsible for high mortality and morbidity in both humans and animals. The increased prevalence of multidrug-resistant (MDR) Staphylococcus aureus strains has limited the number of available treatment options, which calls for the development of alternative and effective modalities against MDR S. aureus. Endolysins are bacteriophage-derived antibacterials, which attack essential conserved elements of peptidoglycan that are vital for bacterial survival, making them promising alternatives or complements to existing antibiotics for tackling such infections. For developing endolysin lysin-methicillin-resistant-5 (LysMR-5) as an effective antimicrobial agent, we evaluated its physical and chemical characteristics, and its intrinsic antibacterial activity against staphylococcal strains, including methicillin-resistant Staphylococcus aureus (MRSA). In this study, we cloned, expressed, and purified LysMR-5 from S. aureus phage MR-5. In silico analysis revealed that LysMR-5 harbors two catalytic and one cell wall-binding domain. Biochemical characterization and LC-MS analysis showed that both catalytic domains were active and had no dependence on divalent ions for their action, Zn2+ exerted a negative effect. The optimal lytic activity of the endolysin was at 37°C/pH 7.0 and in the presence of ≥ 300mM concentration of NaCl. Circular dichroism (CD) demonstrated a loss in secondary structure with an increase in temperature confirming the thermosensitive nature of endolysin. Antibacterial assays revealed that LysMR-5 was active against diverse clinical isolates of staphylococci. It showed high lytic efficacy against S. aureus ATCC 43300, as an endolysin concentration as low as 15µg/ml was sufficient to achieve maximum lytic activity within 30min and it was further confirmed by scanning electron microscopy. Our results indicate that rapid and strong bactericidal activity of LysMR-5 makes it a valuable candidate for eradicating multidrug-resistant S. aureus.

In Vitro Bactericidal Effects of Photodynamic Therapy Combined with Four Tetracyclines against Clostridioides difficile KCTC5009 in Planktonic Cultures.

Surface disinfection in health-care facilities is critical to prevent dissemination of Clostridioides difficile (C. difficile). Tetracyclines (TCs) are broad-spectrum antibiotics that are associated with a low risk of development of C. difficile infection (CDI) and are used as photosensitizers (PS) in photodynamic therapy (PDT). We evaluated whether TCs may be useful environmental cleansing agents. We compared the in vitro ability to kill C. difficile of four TCs (TC, doxycycline, minocycline, and tigecycline) combined with PDT using ultraviolet A (UVA). We included chitosan, a cationic material, as a booster to increase the photodynamic bactericidal efficacy of TCs. PDT-induced bactericidal effects were assessed by the number of viable cells and the degree of DNA damage and membrane integrity. To avoid the intrinsic antibacterial activity of TCs at high concentrations, we used low concentrations of TCs (0.05 and 0.1 mg/mL). The bactericidal effect of treatment with chitosan plus PDT was over 100 times higher than that with PDT alone for each of the four TCs. DNA damage measured by ethidium bromide monoazide and real-time quantitative polymerase chain reaction was also greater for PDT plus chitosan treatment than for PDT alone or under control conditions: the threshold cycle (Ct) values for the control, PDT, and PDT plus chitosan were 14.67 ± 0.22, 20.46 ± 0.12, and 25.54 ± 0.17, respectively. All four TCs caused similar levels of severe cell membrane damage during PDT compared with control conditions. These data suggest that PDT combined with any of the four TCs plus chitosan might be an available tool to kill efficiently planktonic form of C. difficile.

Facile preparation of a novel biogenic silver-loaded Nanofilm with intrinsic anti-bacterial and oxidant scavenging activities for wound healing

To eliminate the microbial infection from an injury site, various modalities have been developed such as dressings and human skin substitutes. However, the high amount of reactive oxygen species, microbial infection, and damaging extracellular matrix remain as the main challenges for the wound healing process. In this study, for the first time, green synthesized silver nanoparticles (AgNPs) using Teucrium polium extract were embedded in poly lactic acid/poly ethylene glycol (PLA/PEG) film to provide absorbable wound dressing, with antioxidant and antibacterial features. The physicochemical analysis demonstrated, production of AgNPs with size approximately 32.2 nm and confirmed the presence of phytoconstituents on their surface. The antibacterial assessments exhibited a concentration-dependent sensitivity of Staphylococcus aureus and Pseudomonas aeruginosa toward biosynthesized AgNPs, which showed a suitable safety profile in human macrophage cells. Furthermore, oxidant scavenging assays demonstrated exploitation of plant extract as a reducing agent, endows antioxidant activity to biogenic AgNPs. The formation of PLA/PEG nanofilm and entrapment of AgNPs into their matrix were clearly confirmed by scanning electron microscopy. More importantly, antibacterial examination demonstrated that the introduction of biogenic AgNPs into PLA/PEG nanofibers led to complete growth inhibition of P. aeruginosa and S. aureus. In summary, the simultaneous antioxidant activity and antimicrobial activity of the novel biogenic AgNPs/PLA/PEG nanofilm showed its potential for application as wound dressing.

Vanadium pentoxide nanoplates: Synthesis, characterization and unveiling the intrinsic anti-bacterial activity

This study reports the synthesis and characterization of vanadium pentoxide nanoplates (VnNp) with the unique shape. Electron microscopy identified morphological alterations on the bacterial surface of representative Gram-positive, Staphylococcus aureus and Gram-negative, Escherichia coli upon VnNp treatment. In addition, Raman spectral mapping also elucidated changes in the bio-molecular signals from these bacteria. Further, the study proved reactive oxygen species (ROS) generation in E. coli biofilms. Overall, the results envision the possible use of VnNp as a potential surface coating agent to impart antibacterial activity.

Evaluation of antibacterial and enhancement of antibiotic action by the flavonoid kaempferol 7-O-β-D-(6″-O-cumaroyl)-glucopyranoside isolated from Croton piauhiensis müll

There has been a rapid increase in the incidence and prevalence of opportunistic bacterial infections. Inappropriate use of current antibiotics has continuously contributed to the emergence of resistance to conventional antibiotic therapy. Therefore, the search for natural molecules that are able to combat infections is of great public interest, and many of these compounds with antimicrobial properties can be obtained from phytochemical studies of medicinal plants. In this context, this study reports the isolation and characterization of the flavonoid, kaempferol 7-O-β-D-(6″-O-cumaroyl)-glucopyranoside, from Croton piauhiensis leaves. Additionally, the intrinsic antimicrobial action of the compound and its enhancement against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus strains were assessed. The minimum inhibitory concentration (MIC) of the compound was determined using broth microdilution assays. To evaluate the modulatory effect of the flavonoid, the MIC of antibiotics amikacin and gentamicin, belonging to the class aminoglycosides was assessed, with and without the compound in sterile microplates. The results of intrinsic antibacterial activity tests revealed that the compound had no antibacterial activity against strains tested at concentrations <1024 μg/mL. The combination of the flavonoid at a concentration of 128 μg/mL with gentamicin presented synergistic effects against S. aureus 10 and E. coli 06, and also reduced the MIC from 16 μg/mL to 4 μg/mL and 8 μg/mL, respectively. Amikacin also showed synergistic effects against S. aureus 10 and E. coli 06. We also observed reduced MIC for both, from 128 μg/mL to 32 μg/mL; however, antagonism for P. aeruginosa increased the MIC from 16 μg/mL to 64 μg/mL. The combination of the flavonoid with the aminoglycosides may be an alternative to potentiate the expected results in treatment against S. aureus and E. coli, since their association leads to a synergistic effect, reducing the MIC of these drugs and decreasing the dose necessary for therapeutic success.

Polymyxin B-Polysaccharide Polyion Nanocomplex with Improved Biocompatibility and Unaffected Antibacterial Activity for Acute Lung Infection Management.

The decade-old antibiotic, polymyxin B (PMB), is regarded as the last line defense against gram-negative "superbug." However, the serious nephrotoxicity and neurotoxicity strongly obstruct further application of this highly effective antibiotic. Herein, a charge switchable polyion nanocomplex exhibiting pH-sensitive property is proposed to deliver PMB which is expected to improve the biosafety of PMB on the premise of retaining excellent antibacterial activity. The polyion nanocomplex is prepared through electrostatic interaction of positively charged PMB and negatively charged 2,3-dimethyl maleic anhydride (DA) grafted chitoligosaccharide (CS). The negative charge of CS-DA will convert to positive due to the hydrolysis of amide bonds in acidic infectious environment, leading to the disassembly of CS-DA/PMB nanocomplex and release of PMB. CS-DA/PMB nanocomplex does not show significant toxicity to mammalian cells while retaining excellent bactericidal capability equivalent to free PMB. The nephrotoxicity and neurotoxicity of CS-DA/PMB dramatically decrease compared to free PMB. Moreover, CS-DA/PMB nanocomplex exhibits superior bactericidal activity against Pseudomonas aeruginosa in an acute lung infection mouse model. The pH-sensitive polyion nanocomplexes may provide a new way to reduce the side effects of highly toxic antibiotics without reducing their intrinsic antibacterial activity, which is the key factor to achieve extensive in vivo clinical applications.

Poly(oxanorbornene)-Coated CdTe Quantum Dots as Antibacterial Agents.

In this study, synthetic mimics of antimicrobial peptides based on poly(oxanorbornene) molecules (or PONs) were used to coat CdTe quantum dots (QDs). These PONs-CdTe QDs were investigated for their activity against Escherichia coli, a bacterium with antibiotic resistant strains. At the same time, the antibacterial activity of the PONs-CdTe QDs was compared to the antibacterial activity of free PONs and free CdTe QDs. The observed antibacterial activity of the PONs-CdTe QDs was additive and concentration dependent. The conjugates had a significantly lower minimum inhibitory concentration (MIC) than the free PONs and QDs, particularly for PONs-CdTe QDs which contained PONs of high amine density. The maximum activity of PONs-CdTe QDs was not realized by conjugating PONs with the highest intrinsic antibacterial activity (i.e., the lowest MIC in solution as free PONs), indicating that the mechanism of action for free PONs and PONs-CdTe QDs is different. Equally important, conjugating PONs to CdTe QDs decreased their hemolytic activity against red blood cells compared to free PONs, lending to higher therapeutic indices against E. coli. This could potentially enable the use of higher, and therefore more effective, PONs-QDs concentrations when addressing bacterial contamination, without concerns of adverse impacts on mammalian cells and organisms.