Killing Of Bacterial Cells Research Articles

In vitro antimicrobial and antibiofilm activity of ursolic acid and its amide derivatives against Acinetobacter baumannii

Background: Nosocomial infections due to biofilm-producing ESKAPE pathogens have raised globally. Acinetobacter baumannii is one of the members of ESKAPE pathogens and it's spreading widely and becomes more problematic to treat and managed in health care settings and in the community due to multidrug resistance. WHO categorizes A. baumannii among the pathogens for which new pharmacophores required on an urgent basis. Compounds from medicinal plants can be a source to developed novel antimicrobial agents against high-risk A.baumannii infections. Ursolic acid and its synthetic amide derivatives emerge as a new class of antimicrobial agents for treating multi drug-resistant infections. Methods and materials: To find out the antimicrobial and antibiofilm activity, we used the standard culture of A.baumannii (ATCC: 19606) and its colistin resistance strains. The antimicrobial and biofilm inhibiting activity of these compounds was evaluated by using the microdilution method, crystal violet assay, time-kill assays, post antimicrobial assays, cytotoxic activity, microscopic (light & Atomic force microscope) evaluation, and gene expression analysis. Results: The selected compound possesses antimicrobial and antibiofilm activity against the standard and colistin-resistant clinical isolates of A.baumannii. At MIC (77.87 μg/ml) of compound, it inhibits more than 65% of biofilm formation and eradicates more than 63% of pre-form biofilm. Amide derivate of ursolic acid effectively inhibits the biofilm formation as well as eradicated the preformed biofilms by killing bacterial cells. Furthermore, atomic force microscopy showed the disruption of cell membrane which might be the reason for antimicrobial activity. Gene expression analysis showed the significant downregulation of biofilm-forming genes (abaR and bap). Conclusion: So, ursolic acid and its amide derivative might be used to tackle Acinetobacter baumannii related nosocomial infections and further evaluated as a drug candidate.

Antibacterial Action of Nanoparticles by Lethal Stretching of Bacterial Cell Membranes.

It is commonly accepted that nanoparticles (NPs) can kill bacteria; however, the mechanism of antimicrobial action remains obscure for large NPs that cannot translocate the bacterial cell wall. It is demonstrated that the increase in membrane tension caused by the adsorption of NPs is responsible for mechanical deformation, leading to cell rupture and death. A biophysical model of the NP-membrane interactions is presented which suggests that adsorbed NPs cause membrane stretching and squeezing. This general phenomenon is demonstrated experimentally using both model membranes and Pseudomonas aeruginosa and Staphylococcus aureus, representing Gram-positive and Gram-negative bacteria. Hydrophilic and hydrophobic quasi-spherical and star-shaped gold (Au)NPs are synthesized to explore the antibacterial mechanism of non-translocating AuNPs. Direct observation of nanoparticle-induced membrane tension and squeezing is demonstrated using a custom-designed microfluidic device, which relieves contraction of the model membrane surface area and eventual lipid bilayer collapse. Quasi-spherical nanoparticles exhibit a greater bactericidal action due to a higher interactive affinity, resulting in greater membrane stretching and rupturing, corroborating the theoretical model. Electron microscopy techniques are used to characterize the NP-bacterial-membrane interactions. This combination of experimental and theoretical results confirm the proposed mechanism of membrane-tension-induced (mechanical) killing of bacterial cells by non-translocating NPs.

Activity of Cinnamaldehyde on Quorum Sensing and Biofilm Susceptibility to Antibiotics in Pseudomonas aeruginosa.

Quorum sensing (QS) plays an important role during infection for the opportunistic human pathogen Pseudomonas aeruginosa. Quorum sensing inhibition (QSI) can disrupt this initial event of infection without killing bacterial cells, and thus QS inhibitors have been suggested as novel approaches for anti-infective therapy. Cinnamaldehyde (CAD) is a P. aeruginosa biofilm inhibitor and disperser of preformed biofilms. In this study, the combined use of CAD and colistin (COL) revealed a synergistic activity, but this was not the case for CAD combined with carbenicillin, tobramycin (TOB), or erythromycin in checkerboard assays for P. aeruginosa. CAD demonstrated QSI activity by repression of the expression of lasB, rhlA and pqsA in GFP reporter assays. Approximately 70% reduction in GFP production was observed with the highest CAD concentration tested in all the QS reporter strains. TOB also showed strong QSI when combined with CAD in reporter assays. Combination treatments revealed an additive activity of CAD with COL and TOB in biofilm inhibition (75.2% and 83.9%, respectively) and preformed biofilm dispersion (~90% for both) when compared to the individual treatments. Therefore, a proposed method to mitigate P. aeruginosa infection is a combination therapy of CAD with COL or CAD with TOB as alternatives to current individual drug therapies.

Antimicrobial effectiveness of etidronate powder (Dual Rinse® HEDP) and two EDTA preparations against Enterococcus faecalis: a preliminary laboratory study.

This study aimed to evaluate the antimicrobial and antibiofilm activity of two chelating agents: ethylenediaminetetraacetic acid (EDTA) combined or not with detergents, and etidronic acid combined with sterile saline. The bacterial inhibitory and bactericidal concentrations (MIC and MBC, respectively) were determined on Enterococcus faecalis ATCC 4083 strain. Antimicrobial tests were performed on a biofilm model after treatment with the chelating agents at different times (1, 3, and 5min) using a biofilm eradication concentration (MBEC) and confocal laser scanning microscope (CLSM) assays. Quantification of cell biomass and percentage of live and dead cells in the biomass was assessed for each group. The normality of the distributions for each variable was assessed using the D'Agostino and Pearson's omnibus normality test. The comparison of bacterial viability among groups and between any two groups was performed using the non-parametric Kruskal-Wallis one-way analysis of variance and the Dunn's test, respectively. No significant between-group difference was observed regarding biomass reduction. On the other hand, EDTA combined with detergents displayed a substantial increase of the dead bacteria ranging between 35 and 43%; whereas, the number of cells killed in the control group and in the other treated groups always ranged between 1 and 6%, at all experimental times. The addition of detergents to EDTA can improve its anti-biofilm activity by reducing EPS production and enhancing the killing of sessile bacterial cells. Clinical relevance EDTA presents a relevant antimicrobial activity when combined with surface-active agents.

Photodynamic therapy in wound healing in vivo: a systematic review

Wounds constitute severe problems in public health. Inappropriate manipulation to promote wound healing and indiscriminate use of antibiotics may contribute to failure in wound treatment, leading to bacterial growth and resistance. Appropriate and correct approaches to wound treatment are crucially important. Further, the development of new and effective treatment modalities is important to decrease infection-related mortality and to reduce patient suffering and side effects. Photodynamic therapy (PDT) could be a promising approach to ameliorate this global health problem. We researched articles that used PDT in wound healing in vivo. The systematic review included articles that investigated the effect of PDT on wound healing in animals, published from May 2008 through 2018, in the databases PubMed and Web of Science. The main types of wounds described in the selected articles were burns, abrasions, and excisional wounds. Most of the studies tested PDT in wounds infected by methicillin-resistant Staphylococcus aureus, S. aureus standard strain, or Pseudomonas aeruginosa. The studies demonstrated that PDT contributes in several ways to the wound healing process, such as killing bacterial cells and stimulating the proliferation of fibroblasts and consequently of collagen and elastin. Based on these studies, PDT provided excellent results for the wound healing process, acting in several steps and accelerating tissue repair. PDT has proven to be a promising therapeutic modality, able to inhibit bacterial regrowth or kill bacteria, contributing significantly to accelerate the wound healing process.

Silver nanoparticle impregnated polyethersulfone ultrafiltration membrane: Optimization of degree of grafting of acrylic acid for biofouling prevention and improved water permeability

Membrane biofouling limits its lifetime and application. Our objective is to optimize surface modification and subsequent silver nanoparticle impregnation on polyethersulfone (PES) membrane for biofouling prevention. For this, silver nanoparticles were selectively impregnated on the PES membrane, via carbonyl group attachment on membrane surface by acrylic acid grafting. Based on mechanical property and silver loading, three different membranes (AA-Ag-PES-25, AA-Ag-PES-62 and AA-Ag-PES-185 with acrylic acid grafting of 25, 62 and 185 μg cm−2, respectively, and having resultant silver loading of 4.4, 9.06 and 16.94 wt%, respectively) were screened for further testing. Performance of the AA-Ag-PES-62 membrane was best, with least reduction of permeate flux at steady state (12.69%), signifying biofouling prevention, compared to only PES membrane (62.2% permeate flux reduction); the latter due to attached live E. coli cells, in absence of silver nanoparticles. For AA-Ag-PES-25 with a lower silver loading, bacterial cell killing was slower, with resultant permeate flux-drop at steady state (19.7%) being more than the optimum AA-Ag-PES-62 membrane. In contrast, for the higher silver loaded AA-Ag-PES-185, silver nanoparticles formed a surface layer, which resulted in partial pore-blockage with higher permeate flux reduction (27.28%). Regarding long-term performance, for AA-Ag-PES-62, there was neither flux-drop nor bacterial growth till 48 h, whereas, due to low silver content in AA-Ag-PES-25, bacteria re-grew after 24 h, which reflected into permeate flux-drop. AA-Ag-PES-62 membrane provides optimum performance in terms of E. coli killing and anti-biofouling effect, maintaining silver concentration in permeate (29.8 ppb), well within the permissible 100 ppb limit.

P-Coumaric acid quantum dots inhibit beta lactam resistant foodborne microorganisms

Foodborne diarrhoeal diseases are linked to the deaths of over 1.8 million people annually. The antimicrobial activity of p-coumaric acid was reported, however the application was limited due to poor water solubility. Quantum dot technology can be applied to overcome these limitations. Thus, we aimed to synthesize and characterize p-coumaric acid quantum dot by wet milling technique. Besides, the antimicrobial efficiency of the quantum dots was also tested on foodborne pathogens. The spherical shaped quantum dots were successfully synthesized. The average size of the quantum dots was 8.9 ± 3.7 nm with a zeta potential of −3.73 mV. The synthesis of quantum dot also increased the water solubility of p-coumaric acid to 1.98%. On disc diffusion assay, p-coumaric acid quantum dot exhibited significant inhibitory on various beta-lactam resistant test bacteria. The quantum dots inhibited the growth of all Gram- positive test bacteria, 5 Gram negative bacteria and 1 yeast. The antimicrobial performance was significantly better compared to free p-coumaric acid. The activity of p-coumaric acid quantum dot was microbicidal with a wide range of minimal inhibitory concentrations (31.25–500.00 µg/ml). On time kill analysis, p-coumaric acid quantum dots displayed concentration dependent killing capacity on Staphylococcus aureus and Proteus mirabilis. At concentration of minimal lethality concentration, 99.9% killing of bacterial cells were observed throughout the experimental period. A significantly lower bacterial growth was observed relative to control. In conclusion, p-coumaric acid quantum dots were successfully synthesized. The quantum dots exhibited significant antimicrobial activity on wide spectrum of foodborne microorganisms. The study suggested that the application of p-coumaric acid quantum dots in food system may be effective in inhibiting the growth of foodborne microorganisms.

Synthesis of curcumin quantum dots and their antimicrobial activity on necrotizing fasciitis causing bacteria

Necrotizing fasciitis is defined as an infection of soft tissue such as dermis, subcutaneous tissue, or muscle that linked with necrotizing changes. Curcumin is well known for its excellent antioxidant, anti-carcinogenic and anti-inflammatory activities. In this study, we aimed to synthesize curcumin quantum dots by using a combination of mechanical and ultrasonic milling techniques. Besides, the antimicrobial efficacy of the quantum dots was also tested on necrotizing fasciitis causing bacteria. Electron micrograph of curcumin quantum dots showed that the particles were irregular in shape, with an average size of 13.7 nm. Curcumin quantum dots possess a zeta potential of −13.3 mV based on zeta potential analysis. The antimicrobial activity was tested on 7 test bacteria. Curcumin quantum dots exhibited wide spectrum antibacterial activity, as the particles inhibit both Gram-positive and Gram-negative bacteria. The minimal inhibitory concentration (MIC) of curcumin quantum dots ranged from 7.8 to 62.5 µg/ml, which indicates different susceptibility of test bacteria to curcumin quantum dots. The lowest MIC was recorded on Streptococcus sp. and Klebsiella pneumoniae. The antibacterial activity of curcumin quantum dots was bacteriostatic as high minimal bactericidal concentrations (MBC) were reported. On growth profile analysis, curcumin quantum dots displayed concentration-dependent killing capacity on Streptococcus sp. and K. pneumoniae. At the concentration of MBC, 99.9% killing of bacterial cells was observed throughout the experimental period. A significantly lower bacterial growth was observed relative to control. The synthesized quantum dots exhibited broad-spectrum antibacterial activity, particularly on Streptococcus sp. and K. pneumoniae. The antibacterial activity was bacteriostatic. Further investigations should be conducted to evaluate the antibacterial efficiency of curcumin quantum dots by using in vivo animal models.

Cathelicidin-related Antimicrobial Peptide Contributes to Host Immune Responses Against Pulmonary Infection with Acinetobacter baumannii in Mice.

Acinetobacter baumannii is known for its multidrug antibiotic resistance. New approaches to treating drug-resistant bacterial infections are urgently required. Cathelicidin-related antimicrobial peptide (CRAMP) is a murine antimicrobial peptide that exerts diverse immune functions, including both direct bacterial cell killing and immunomodulatory effects. In this study, we sought to identify the role of CRAMP in the host immune response to multidrug-resistant Acinetobacter baumannii. Wild-type (WT) and CRAMP knockout mice were infected intranasally with the bacteria. CRAMP−/− mice exhibited increased bacterial colony-forming units (CFUs) in bronchoalveolar lavage (BAL) fluid after A. baumannii infection compared to WT mice. The loss of CRAMP expression resulted in a significant decrease in the recruitment of immune cells, primarily neutrophils. The levels of IL-6 and CXCL1 were lower, whereas the levels of IL-10 were significantly higher in the BAL fluid of CRAMP−/− mice compared to WT mice 1 day after infection. In an in vitro assay using thioglycollate-induced peritoneal neutrophils, the ability of bacterial phagocytosis and killing was impaired in CRAMP−/− neutrophils compared to the WT cells. CRAMP was also essential for the production of cytokines and chemokines in response to A. baumannii in neutrophils. In addition, the A. baumannii-induced inhibitor of κB-α degradation and phosphorylation of p38 MAPK were impaired in CRAMP−/− neutrophils, whereas ERK and JNK phosphorylation was upregulated. Our results indicate that CRAMP plays an important role in the host defense against pulmonary infection with A. baumannii by promoting the antibacterial activity of neutrophils and regulating the innate immune responses.

Understanding Ciprofloxacin Failure in Pseudomonas aeruginosa Biofilm: Persister Cells Survive Matrix Disruption.

Biofilms are commonly recalcitrant to antibiotics, through incompletely elucidated mechanisms such as tolerance and persistence. We aimed at investigating how a Pseudomonas aeruginosa biofilm escapes ciprofloxacin treatment. P. aeruginosa PA14 in vitro mature biofilms were challenged with supra-MIC ciprofloxacin concentrations. Cell viability was quantified by fluorescein diacetate assay. Population dynamics were determined by counts of surviving culturable cells. Biofilms were analyzed using confocal laser scanning microscopy (CLSM), and the expression of genes involved in stringent response, toxin-antitoxin HigB/HigA, and type 3 secretion system (T3SS) was quantified by RT-qPCR in untreated and treated biofilms. Ciprofloxacin exposure resulted in an initial reduction of bacterial counts following a biphasic time-kill curve. After 24 h of treatment, the overall cell activity and the density of culturable cells significantly decreased as compared to untreated biofilm. No resistant mutant was isolated among the <1% surviving cells. Phenotypic adaptation toward persistence appeared to start after only 1 h of antibiotic exposure, by an overexpression of the genes involved in stringent response and in the toxin-antitoxin system, whereas the expression of genes encoding for the T3SS remained unchanged. After 4 h of ciprofloxacin exposure, stringent response genes returned to their basal level of expression. After a prolonged ciprofloxacin exposure, a deep alteration in the matrix structure that became thinner and lost mushroom-like aggregates was observed, in relation with reduced biovolumes of exopolysaccharides and extracellular DNA. These results support that ciprofloxacin might first induce the bacterial killing of most bacterial cells, but simultaneously activate stringent response mechanisms contributing to the switch of a subpopulation toward a persister phenotype. Once the persister phenotype is expressed, and despite an unexpected alteration of the biofilm matrix, ciprofloxacin fails to eradicate biofilm.

How Oxygen Availability Affects the Antimicrobial Efficacy of Host Defense Peptides: Lessons Learned from Studying the Copper-Binding Peptides Piscidins 1 and 3.

The development of new therapeutic options against Clostridioides difficile (C. difficile) infection is a critical public health concern, as the causative bacterium is highly resistant to multiple classes of antibiotics. Antimicrobial host-defense peptides (HDPs) are highly effective at simultaneously modulating the immune system function and directly killing bacteria through membrane disruption and oxidative damage. The copper-binding HDPs piscidin 1 and piscidin 3 have previously shown potent antimicrobial activity against a number of Gram-negative and Gram-positive bacterial species but have never been investigated in an anaerobic environment. Synergy between piscidins and metal ions increases bacterial killing aerobically. Here, we performed growth inhibition and time-kill assays against C. difficile showing that both piscidins suppress proliferation of C. difficile by killing bacterial cells. Microscopy experiments show that the peptides accumulate at sites of membrane curvature. We find that both piscidins are effective against epidemic C. difficile strains that are highly resistant to other stresses. Notably, copper does not enhance piscidin activity against C. difficile. Thus, while antimicrobial activity of piscidin peptides is conserved in aerobic and anaerobic settings, the peptide–copper interaction depends on environmental oxygen to achieve its maximum potency. The development of pharmaceuticals from HDPs such as piscidin will necessitate consideration of oxygen levels in the targeted tissue.

Iodide modulates protein damage induced by the inflammation-associated heme enzyme myeloperoxidase

Iodide ions (I−) are an essential dietary mineral, and crucial for mental and physical development, fertility and thyroid function. I− is also a high affinity substrate for the heme enzyme myeloperoxidase (MPO), which is involved in bacterial cell killing during the immune response, and also host tissue damage during inflammation. In the presence of H2O2 and Cl−, MPO generates the powerful oxidant hypochlorous acid (HOCl), with excessive formation of this species linked to multiple inflammatory diseases. In this study, we have examined the hypothesis that elevated levels of I− would decrease HOCl formation and thereby protein damage induced by a MPO/Cl−/H2O2 system, by acting as a competitive substrate. The presence of increasing I− concentrations (0.1–10 μM; i.e. within the range readily achievable by oral supplementation in humans), decreased damage to both model proteins and extracellular matrix components as assessed by gross structural changes (SDS-PAGE), antibody recognition of parent and modified protein epitopes (ELISA), and quantification of both parent amino acid loss (UPLC) and formation of the HOCl-biomarker 3-chlorotyrosine (LC-MS) (reduced by ca. 50% at 10 μM I−). Elevated levels of I− ( > 1 μM) also protected against functional changes as assessed by a decreased loss of adhesion (eg. 40% vs. < 22% with >1 μM I−) of primary human coronary artery endothelial cells (HCAECs), to MPO-modified human plasma fibronectin. These data indicate that low micromolar concentrations of I−, which can be readily achieved in humans and are readily tolerated, may afford protection against cell and tissue damage induced by MPO.

Animal Models for Drug Development for MRSA.

One of the foremost challenges of drug discovery in any therapeutic area is that of solidifying the correlation between in vitro activity and clinical efficacy. Between these is the confirmation that affecting a particular target in vivo will lead to a therapeutic benefit. In antibacterial drug discovery, there is a key advantage from the start, since the targets are bacteria-therefore, it is simple to ascertain in vitro whether a drug has the desired effect, i.e., bacterial cell inhibition or killing, and to understand the mechanism by which that occurs. The downstream criteria, whether a compound reaches the infection site and achieves appropriately high levels to affect bacterial viability, can be evaluated in animal models of infection. In this way animal models of infection can be a highly valuable and predictive bridge between in vitro drug discovery and early clinical evaluation.The Gram-positive pathogen Staphylococcus aureus causes a wide variety of infections in humans (Archer, Clin Infect Dis 26:1179-1181, 1998), and has been said to be able to infect every tissue type. Fortunately, over the years a great deal of effort has been expended toward developing infection models in rodents using this organism, with good success. This chapter describes the advantages, setups, and outcome measurements of the rodent models most used in drug discovery for S. aureus. Mouse models will be the focus of this chapter, as they are the most economical and thus most commonly used, but a rat infection model is included as well.

Effects of alkali-treated sludge supplementation for enhanced biological phosphorus removal in a membrane bioreactor

Waste activated sludge treated with an alkaline solution was used as external carbon substrates to improve the performance of enhanced biological phosphorus removal (EBPR) in a pilot plant. Supplementation of the alkali-treated sludge significantly enhanced the phosphorus removal of the pilot plant from 81.6 to 98.7%. Microscopic observations revealed that alkali treatment was effective in killing bacterial cells in the sludge, and deconstructed its morphology into a reticular form. The change in cell viability and morphology facilitated organic matter release, mostly in the form of proteins. Furthermore, supplementation of the alkali-treated sludge changed the major phosphorus accumulating organisms (PAOs) from Accumulibacter to Tetrasphaera. Enrichment of PAOs within the Tetrasphaera was due to specific carbon substrates (i.e. proteins) released by the alkali-treated sludge. Taken together, this study strongly suggests that supplementation of alkali-treated sludge was an efficient method for improving EBPR performance by enrichment of Tetrasphaera PAOs.

PH-Selective Fluorescent Probe with Photothermal Ablation of Bacteria Based NIR Dye-Embedded Zwitterionic Carbon Dots

We developed a highly pH-sensitive fluorescent carbon dot probe containing IR825 photothermal dye for rapid detection of environmental bacteria, with subsequent killing activity via near-infrared (NIR) driven photothermal ablation. The IR825-loaded fluorescent carbon dot (I-CD) interacted strongly with the negative charge of bacterial surface, expressed via fluorescence ON/OFF behavior under a broad range of pH conditions, by modifying the zwitterionic conformation of the carbon dot. In acidic and basic conditions, I-CD is activated, losing its hydrophobicity in neutral condition and releasing IR825, inducing NIR-mediated photothermal activity. Release of IR825 from the I-CD core contributed to high thermal conversion, killing bacterial cells with 99% efficiency. This material shows potential to be used as a convenient, rapid, low-cost, high-sensitivity fluorescent bacterial biosensor, combined with effective bacterial killing activity via photothermal conversion with pH and NIR triggers.

Alarmone Ap4A is elevated by aminoglycoside antibiotics and enhances their bactericidal activity

Second messenger molecules play important roles in the responses to various stimuli that can determine a cell's fate under stress conditions. Here, we report that lethal concentrations of aminoglycoside antibiotics result in the production of a dinucleotide alarmone metabolite-diadenosine tetraphosphate (Ap4A), which promotes bacterial cell killing by this class of antibiotics. We show that the treatment of Escherichia coli with lethal concentrations of kanamycin (Kan) dramatically increases the production of Ap4A. This elevation of Ap4A is dependent on the production of a hydroxyl radical and involves the induction of the Ap4A synthetase lysyl-tRNA synthetase (LysU). Ectopic alteration of intracellular Ap4A concentration via the elimination of the Ap4A phosphatase diadenosine tetraphosphatase (ApaH) and the overexpression of LysU causes over a 5,000-fold increase in bacterial killing by aminoglycosides. This increased susceptibility to aminoglycosides correlates with bacterial membrane disruption. Our findings provide a role for the alarmone Ap4A and suggest that blocking Ap4A degradation or increasing its synthesis might constitute an approach to enhance aminoglycoside killing potency by broadening their therapeutic index and thereby allowing lower nontoxic dosages of these antibiotics to be used in the treatment of multidrug-resistant infections.

The Effects of Ultraviolet Light-Emitting Diodes with Different Wavelengths on Periodontopathic Bacteria In Vitro.

Objective: The aim of this study was to examine effects of recently developed ultraviolet light-emitting diodes (UV LEDs) wavelengths on in vitro growth and gene expression of cultural periodontopathic bacteria, and on viability of experimental gingival fibroblasts. Materials and methods: Porphyromonas gingivalis, Prevotella intermedia, Fusobacterium nucleatum, Aggregatibacter actinomycetemcomitans, and Streptococcus oralis were irradiated by UV LEDs (265, 285, 310, 365, and 448 nm) at 600 mJ/cm2 and grown anaerobically in vitro. The colony forming units were counted after 1 week. Cell morphology was observed using a scanning electron microscope (SEM). Quantitative real-time polymerase chain reaction was performed to investigate gene expression changes by 310 nm irradiation. Viability of the irradiated human gingival fibroblasts was evaluated using WST-8 assay. Results: Both 265 and 285 nm resulted in the complete death of bacteria and fibroblasts, whereas 310 nm caused partial killing and suppression of bacterial growth and much less damage to the fibroblasts in vitro. Both 365 and 448 nm resulted in no significant change. SEM showed that P. gingivalis cells gradually degraded from day 2 or 3 and were severely destructed on day 5 for 265, 285, and 310 nm. The 310 nm irradiation transiently suppressed the transcripts of SOS response- and cell division-relative genes. Conclusions: Both 265 and 285 nm may induce powerful bactericidal effects and severe fibroblast phototoxicity, and 310 nm may induce partial killing or growth suppression of bacterial cells with much less fibroblast phototoxicity. UV lights may have potential for bacterial suppression, with situations dependent on wavelength, in periodontal and peri-implant therapy.

Relationship between Dislocation Density and Antibacterial Activity of Cryo-Rolled and Cold-Rolled Copper.

In the present work, cold rolling and cryo-rolling were performed on 99% commercially pure copper substrates. Both cold and cryo-rolling processes caused severe plastic deformation that led to an increase in dislocation density by 14× and 28× respectively, as compared to the pristine material. Increases in average tensile strengths, by 75% (488 MPa) and 150% (698 MPa), were observed in the two rolled materials as the result of the enhancement in dislocation density. In addition to strength, enhanced antibacterial property of cryo-rolled copper was observed in comparison to cold rolled and pristine copper. Initial adhesion and subsequent proliferation of bio-film forming Gram-positive bacteria Staphylococcus aureus was reduced by 66% and 100% respectively for cryo-rolled copper. Approximately 55% protein leakage, as well as ethidium bromide (EtBr) uptake, were observed confirming rupture of cell membrane of S. aureus. Inductively coupled plasma-mass spectroscopy reveals higher leaching of elemental copper in nutrient broth media from the cryo-rolled copper. Detailed investigations showed that increased dislocation led to leaching of copper ions that caused damage to the bacterial cell wall and consequently killing of bacterial cells. Cryo-rolling enhanced both strength, as well as antibacterial activity, due to the presence of dislocations.

The Combination of Fosfomycin plus Meropenem Is Synergistic for Pseudomonas aeruginosa PAO1 in a Hollow-Fiber Infection Model.

Treating high-density bacterial infections is a challenging clinical problem. We have a paucity of new agents that can address this problem. Pseudomonas aeruginosa is a particularly difficult pathogen to treat effectively because of the plethora of resistance mechanisms it carries. Fosfomycin is an agent discovered circa 40 years ago. Recently, it has been resurrected in the United States and studied for intravenous therapy. We hypothesized that, to maximize its utility, it would require combination chemotherapy when used in a clinical circumstance in high-bacterial-burden infections. We chose to examine the combination of meropenem plus fosfomycin. These agents were studied in the hollow-fiber infection model. We utilized a fully factorial study design, looking at 2 doses of meropenem alone (1 and 2 g 8-hourly) and two doses of fosfomycin alone (6 and 8 g 8-hourly), as well as all possible combinations plus a no-treatment control. We used a high-dimensional model of 5 inhomogeneous differential equations with 5 system outputs to analyze all data simultaneously. Combination therapy outperformed all monotherapy regimens, with all combinations driving >6 log10 CFU/ml of bacterial killing. Combination therapy was able to counterselect resistance emergence (meropenem mutants being killed by the combination, as well as fosfomycin mutants being killed by the combination) in all regimens studied. The analysis demonstrated that the combination was significantly synergistic for bacterial cell killing and resistance suppression. Meropenem plus fosfomycin is a promising combination for therapy of high-burden Pseudomonas aeruginosa infections and requires further study.

Cell-Selective Pore Forming Antimicrobial Peptides of the Prodomain of Human Furin: A Conserved Aromatic/Cationic Sequence Mapping, Membrane Disruption, and Atomic-Resolution Structure and Dynamics.

Antimicrobial peptides are promising molecules in uprising consequences of drug-resistant bacteria. The prodomain of furin, a serine protease, expressed in all vertebrates including humans, is known to be important for physiological functions. Here, potent antimicrobial peptides were mapped by extensive analyses of overlapping peptide fragments of the prodomain of human furin. Two peptides, YR26 and YR23, were active against bacterial cells including MRSA-resistant Staphylococcus aureus and Staphylococcus epidermis 51625. Peptides were largely devoid of hemolytic and cytotoxic activity. Bacterial cell killing occurred as a result of the disruption of the permeability barrier of the lipopolysaccharide (LPS)-outer membrane and fragmentation of LPS into small micelles. Furthermore, antibacterial peptides specifically interacted with the negatively charged lipids causing membrane leakage and fusion. The YR26 peptide in sodium dodecyl sulfate micelles demonstrated a long-helix-turn-short-helix structure exhibiting restricted backbone motions. The cell-selective activity of the furin peptides and their unique mode of action on membranes have a significant potential for the development of therapeutics.