LIVE/DEAD BacLight : application of a new rapid staining method for direct enumeration of viable and total bacteria in drinking water

Starvation induces shrinkage of the bacterial cytoplasm

Environmental fluctuations are a common challenge for single-celled organisms; enteric bacteria such as Escherichia coli experience dramatic changes in nutrient availability, pH, and temperature during their journey into and out of the host. While the effects of altered nutrient availability on gene expression and protein synthesis are well known, their impacts on cytoplasmic dynamics and cell morphology have been largely overlooked. Here, we discover that depletion of utilizable nutrients results in shrinkage of E. coli's inner membrane from the cell wall. Shrinkage was accompanied by an ∼17% reduction in cytoplasmic volume and a concurrent increase in periplasmic volume. Inner membrane retraction after sudden starvation occurred almost exclusively at the new cell pole. This phenomenon was distinct from turgor-mediated plasmolysis and independent of new transcription, translation, or canonical starvation-sensing pathways. Cytoplasmic dry-mass density increased during shrinkage, suggesting that it is driven primarily by loss of water. Shrinkage was reversible: upon a shift to nutrient-rich medium, expansion started almost immediately at a rate dependent on carbon source quality. A robust entry into and recovery from shrinkage required the Tol-Pal system, highlighting the importance of envelope coupling during shrinkage and recovery. Klebsiella pneumoniae also exhibited shrinkage when shifted to carbon-free conditions, suggesting a conserved phenomenon. These findings demonstrate that even when Gram-negative bacterial growth is arrested, cell morphology and physiology are still dynamic.

Rapid Determination of Antibiotic Resistance in Klebsiella pneumoniae by a Novel Antibiotic Susceptibility Testing Method Using SYBR Green I and Propidium Iodide Double Staining

Due to the broad-spectrum antibiotic usage and empirical treatments, the pathogenic bacterium, Klebsiella pneumoniae, has shown extremely high detection rates at hospitals with an increasing antibiotic resistance. Therefore, rapid detection of the antibiotic resistance is urgently required and essential for effective treatments. In this study, we evaluated the performance of a newly developed method for ultra-rapid detection of antibiotic resistance in 30–60 min in K. pneumoniae by using the SYBR Green I and propidium iodide (PI) staining. A total of 100 clinical isolates were tested for antibiotic resistance using four different antibiotics (ceftriaxone, cefepime, meropenem, and ciprofloxacin). The results showed that the SYBR Green I/PI rapid antibiotic susceptibility test (AST) could reliably detect antibiotic resistance to the four drugs in 60 min, and the results were highly concordant with the conventional AST (i.e., Kirby-Bauer method and broth microdilution method) for detection of ceftriaxone, cefepime, meropenem, and ciprofloxacin resistance with a high accuracy of 99, 96, 96, and 93%, respectively. Therefore, the rapid AST established in our study helps to enable targeted therapy to save lives and reduce the empirical use of antibiotics and ultimately the health and economic burdens of antibiotic resistance.

A biocompatible dual-AIEgen system without spectral overlap for quantitation of microbial viability and monitoring of biofilm formation

The lack of rapid and reliable microbial detection and sensing platforms and insufficient understanding of microbial behavior may delay precautions that could be made, which is a great threat to human life and increases the heavy financial burden on society. In this contribution, a dual-aggregation-induced emission luminogen (AIEgen) system is successfully developed for microbial imaging and metabolic status sensing. This system consists of two AIEgens (DCQA and TPE-2BA) that bear positively charged groups or boronic acid groups, providing universal microbial staining ability and specific affinity for dead microbes, respectively. Based on the distinctive fluorescence response produced by the diverse interaction of AIEgens with live or dead microbes, this dual-AIEgen system can detect all the microbes and identify their viabilities. Furthermore, the morphology and metabolic status of a sessile biofilm can also be imaged and monitored. The system exhibits rapid labelling properties that suitable for various microbes, and good biocompatibilities.

Enhanced efficacy of a Cu2+ complex of curcumin against Gram-positive and Gram-negative bacteria: Attributes of complex formation

Curcumin is a tantalizing molecule with multifaceted therapeutic potentials. However, its therapeutic applications are severely hampered because of poor bioavailability, attributed to its instability and aqueous insolubility. In an attempt to overcome this inherent limitation and develop curcumin-based antibacterials, we had earlier synthesized and characterized a metal complex of Cu(II) with curcumin, having the formula [Cu(Curcumin)(OCOCH₃)(H₂O)], hereafter referred to as Cu(Cur). In this study, the complex, i.e., Cu(Cur), was investigated for its stability and antibacterial activity along with its possible mechanism of action in comparison to the parent molecule, curcumin. Complex formation resulted in improved stability as Cu(Cur) was found to be highly stable under different physiological conditions. Such improved stability was verified with the help of UV-Vis spectroscopy and HPLC. With improved stability, Cu(Cur) exhibited potent and significantly enhanced activity over curcumin against both E. coli and S. aureus. Calcein leakage assay revealed that the complex triggered immediate membrane permeabilization in S. aureus. This membrane disruptive mode of action was further corroborated by microscopic visualization. The excellent potency of the complex was augmented by its safe toxicological profile as it was non-hemolytic and non-cytotoxic towards mammalian cells, making it a suitable candidate for in vivo investigations. Altogether, this investigation is a critical appraisal that advocates the antibacterial potential of this stable, membrane-targeting and non-toxic complex, thereby presenting new perspectives for its therapeutic application against bacterial infections.

Identification and characterization of andalusicin: N-terminally dimethylated class III lantibiotic from Bacillus thuringiensis sv. andalousiensis

Lanthipeptides, ribosomally synthesized and post-translationally modified peptides (RiPPs), can be divided into five classes based on their structures and biosynthetic pathways. Class I and II lanthipeptides have been well characterized, whereas less is known about members of the other three classes. Here, we describe a new family of class III lanthipeptides from Firmicutes. Members of the family are distinguished by the presence of a single carboxy-terminal labionin. We identified and characterized andalusicin, a representative of this family. Andalusicin bears two methyl groups at the α-amino terminus, a post-translational modification that has not previously been identified in class III lanthipeptides. Mature andalusicin A shows bioactivity against various Gram-positive bacteria, an activity that is highly dependent on the α-N dimethylation.

Highly Active, Entirely Biobased Antimicrobial Pickering Emulsions

We present the development of surfactant-free, silica-free and fully biobased oil-in-water antimicrobial Pickering emulsions, based on the self-assembly of β-cyclodextrin and phytoantimicrobial oils (terpinen-4-ol or carvacrol). Undecylenic acid (UA), derived from castor oil, can be used as bio-based drug to treat fungal infection, but is less effective than petroleum-based drugs as azole derivatives. To maximize its antifungal potential, we have incorporated UA in fully biobased Pickering emulsions. These emulsions are effective against fungi, Gram-positive and Gram-negative bacteria. The carvacrol emulsion charged with UA is +390 % and +165 % more potent against methicillin-resistant S. aureus (MRSA), compared to UA and azole-based commercial formulations. Moreover, this emulsion is up to +480 % more efficient that UA ointment against C. albicans. Finally, remarkable eradication of E. coli and MRSA biofilms was obtained with this environmental-friendly emulsion.

Viable but nonculturable bacteria and their resuscitation: implications for cultivating uncultured marine microorganisms

Culturing has been the cornerstone of microbiology since Robert Koch first successfully cultured bacteria in the late nineteenth century. However, even today, the majority of microorganisms in the marine environment remain uncultivated. There are various explanations for the inability to culture bacteria in the laboratory, including lack of essential nutrients, osmotic support or incubation conditions, low growth rate, development of micro-colonies, and the presence of senescent or viable but nonculturable (VBNC) cells. In the marine environment, many bacteria have been associated with dormancy, as typified by the VBNC state. VBNC refers to a state where bacteria are metabolically active, but are no longer culturable on routine growth media. It is apparently a unique survival strategy that has been adopted by many microorganisms in response to harsh environmental conditions and the bacterial cells in the VBNC state may regain culturability under favorable conditions. The resuscitation of VBNC cells may well be an important way to cultivate the otherwise uncultured microorganisms in marine environments. Many resuscitation stimuli that promote the restoration of culturability have so far been identified; these include sodium pyruvate, quorum sensing autoinducers, resuscitation-promoting factors Rpfs and YeaZ, and catalase. In this review, we focus on the issues associated with bacterial culturability, the diversity of bacteria entering the VBNC state, mechanisms of induction into the VBNC state, resuscitation factors of VBNC cells and implications of VBNC resuscitation stimuli for cultivating these otherwise uncultured microorganisms. Bringing important microorganisms into culture is still important in the era of high-throughput sequencing as their ecological functions in the marine environment can often only be known through isolation and cultivation.

Membrane Interactions of Virus-like Mesoporous Silica Nanoparticles

In the present study, we investigated lipid membrane interactions of silica nanoparticles as carriers for the antimicrobial peptide LL-37 (LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES). In doing so, smooth mesoporous nanoparticles were compared to virus-like mesoporous nanoparticles, characterized by a "spiky" external surface, as well as to nonporous silica nanoparticles. For this, we employed a combination of neutron reflectometry, ellipsometry, dynamic light scattering, and ζ-potential measurements for studies of bacteria-mimicking bilayers formed by palmitoyloleoylphosphatidylcholine/palmitoyloleoylphosphatidylglycerol. The results show that nanoparticle topography strongly influences membrane binding and destabilization. We found that virus-like particles are able to destabilize such lipid membranes, whereas the corresponding smooth silica nanoparticles are not. This effect of particle spikes becomes further accentuated after loading of such particles with LL-37. Thus, peptide-loaded virus-like nanoparticles displayed more pronounced membrane disruption than either peptide-loaded smooth nanoparticles or free LL-37. The structural basis of this was clarified by neutron reflectometry, demonstrating that the virus-like nanoparticles induce trans-membrane defects and promote incorporation of LL-37 throughout both bilayer leaflets. The relevance of such effects of particle spikes for bacterial membrane rupture was further demonstrated by confocal microscopy and live/dead assays on Escherichia coli bacteria. Taken together, these findings demonstrate that topography influences the interaction of nanoparticles with bacteria-mimicking lipid bilayers, both in the absence and presence of antimicrobial peptides, as well as with bacteria. The results also identify virus-like mesoporous nanoparticles as being of interest in the design of nanoparticles as delivery systems for antimicrobial peptides.

Anandamide alters the membrane properties, halts the cell division and prevents drug efflux in multidrug resistant Staphylococcus aureus

Antibiotic resistance is a serious public health problem throughout the world. Overcoming methicillin and multidrug-resistant Staphylococcus aureus (MRSA/MDRSA) infections has become a challenge and there is an urgent need for new therapeutic approaches. We have previously demonstrated that the endocannabinoid Anandamide (AEA) can sensitize MRSA to antibiotics. Here we have studied the mechanism of action using a MDRSA clinical isolate that are sensitized by AEA to methicillin and norfloxacin. We found that AEA treatment halts the growth of both antibiotic-sensitive and antibiotic-resistant S. aureus. The AEA-treated bacteria become elongated and the membranes become ruffled with many protrusions. AEA treatment also leads to an increase in the percentage of bacteria having a complete septum, suggesting that the cell division is halted at this stage. The latter is supported by cell cycle analysis that shows an accumulation of bacteria in the G2/M phase after AEA treatment. We further observed that AEA causes a dose-dependent membrane depolarization that is partly relieved upon time. Nile red staining of the bacterial membranes indicates that AEA alters the membrane structures. Importantly, 4'-6-diamidino-2-phenylindole (DAPI) accumulation assay and ethidium bromide efflux (EtBr) assay unveiled that AEA leads to a dose-dependent drug accumulation by inhibiting drug efflux. In conclusion, our study demonstrates that AEA interferes with cell division, alters the membrane properties of MDRSA, and leads to increased intracellular drug retention, which can contribute to the sensitization of MDRSA to antibiotics.

Broad-Spectrum Solvent-free Layered Black Phosphorus as a Rapid Action Antimicrobial

Antimicrobial resistance has rendered many conventional therapeutic measures, such as antibiotics, ineffective. This makes the treatment of infections from pathogenic micro-organisms a major growing health, social, and economic challenge. Recently, nanomaterials, including two-dimensional (2D) materials, have attracted scientific interest as potential antimicrobial agents. Many of these studies, however, rely on the input of activation energy and lack real-world utility. In this work, we present the broad-spectrum antimicrobial activity of few-layered black phosphorus (BP) at nanogram concentrations. This property arises from the unique ability of layered BP to produce reactive oxygen species, which we harness to create this unique functionality. BP is shown to be highly antimicrobial toward susceptible and resistant bacteria and fungal species. To establish cytotoxicity with mammalian cells, we showed that both L929 mouse and BJ-5TA human fibroblasts were metabolically unaffected by the presence of BP. Finally, we demonstrate the practical utility of this approach, whereby medically relevant surfaces are imparted with antimicrobial properties via functionalization with few-layer BP. Given the self-degrading properties of BP, this study demonstrates a viable and practical pathway for the deployment of novel low-dimensional materials as antimicrobial agents without compromising the composition or nature of the coated substrate.

PAMAM dendrimers with dual-conjugated vancomycin and Ag-nanoparticles do not induce bacterial resistance and kill vancomycin-resistant Staphylococci

The effective life-time of new antimicrobials until the appearance of the first resistant strains is steadily decreasing, which discourages incentives for commercialization required for clinical translation and application. Therefore, development of new antimicrobials should not only focus on better and better killing of antimicrobial-resistant strains, but as a paradigm shift on developing antimicrobials that prevent induction of resistance. Heterofunctionalized, poly-(amido-amine) (PAMAM) dendrimers with amide-conjugated vancomycin (Van) and incorporated Ag nanoparticles (AgNP) showed a 6-7 log reduction in colony-forming-units of a vancomycin-resistant Staphylococcus aureus strain in vitro, while not inducing resistance in a vancomycin-susceptible strain. Healing of a superficial wound in mice infected with the vancomycin-resistant S. aureus was significantly faster and more effective by irrigation with low-dose, dual-conjugated Van-PAMAM-AgNP dendrimer suspension than by irrigation with vancomycin in solution or a PAMAM-AgNP dendrimer suspension. Herewith, dual-conjugation of vancomycin together with AgNPs in heterofunctionalized PAMAM dendrimers fulfills the need for new, prolonged life-time antimicrobials killing resistant pathogens without inducing resistance in susceptible strains. Important for clinical translation, this better use of antibiotics can be achieved with currently approved and clinically applied antibiotics, provided suitable for amide-conjugation.

Increased particle size of goethite enhances the antibacterial effect on human pathogen Escherichia coli O157:H7: A Raman spectroscopic study

The persistence of Escherichia coli O157:H7 in soil is one of the most common causes of the food-borne outbreaks. Nano-sized iron oxide minerals in soil, especially goethite, have been found to reduce bacterial viability, which helps to control the spread of human pathogens. However, little is known about the antibacterial effects of iron oxides with different particle sizes. Our result revealed that the micro-sized goethite exhibited a more effective antibacterial activity against E. coli O157:H7 than the nano-sized goethite. The underlying antibacterial mechanisms were further investigated via single-cell Raman microspectroscopy. The exposure to nano-sized goethite increased the levels of ribonucleoside-related substances, phenylalanine and adenosine 5'-triphosphate, while decreased those of glycogen, protein and lipopolysaccharide & outer membrane porins (LPS & OMPs). Meanwhile, micro-sized goethite triggered less variation in ribonucleoside-related substances and induced more reduction in LPS & OMPs. Therefore, the antibacterial effects of nano-sized goethite were mediated by both ROS-dependent RNA damage and cell membrane destruction, whereas micro-sized goethite induced severer membrane damage and less ROS-dependent oxidative stress. This work demonstrates the role of particle sizes in antibacterial effects of iron oxides and provides implications for the pathogen control in soil.

Insight into probiotic properties of lactic acid bacterial endosymbionts of Apis mellifera L. derived from the Polish apiary

Taking into account that fructophilic lactic acid bacteria (FLAB) can play an important role in the health of honey bees and can be used as probiotics, phenotypic properties of probiotic interest of Lactobacillus kunkeei (12 strains) and Fructobacillus fructossus bacteria (2 strains), isolated from Apis mellifera gastrointestinal tract, have been studied. We have evaluated survival of tested FLAB in honey bee gut, their susceptibility to antibiotics (ampicillin, erythromycin, tylosin), cell surface hydrophobicity, auto-aggregation ability, co-aggregation with model pathogenic bacteria, biofilm formation capacity, and effect of studied FLAB, added to sucrose syrup bee diet, on longevity of honey bees. The tested FLAB exhibited good gastrointestinal tract tolerance and high antibiotic susceptibility, which are important criteria in the screening of probiotic candidates. It was also found that all FLAB studied have high cell surface hydrophobicity and fulfil next selection criterion for their use as probiotics. Symbionts of A. mellifera showed also auto- and co-aggregation capacities regarded as valuable features for biofilm formation and inhibition of pathogens adhesion to the bee gut cells. Biofilm-development ability is a desired characteristic of probiotic lactic acid bacteria. As indicated by quantitative crystal violet-stained microplate assay and confocal laser scanning microscopy imaging, all studied A. mellifera gut isolates exhibit a biofilm positive phenotype. Moreover, it was also documented, on honey bees kept in cages, that supplementation of A. mellifera sucrose diet with FLAB decreases mortality and improves significantly longevity of honey bees. Presented research showed that A. mellifera FLAB symbionts are good candidates for application as probiotics.

pH-Responsive copolymer micelles to enhance itraconazole efficacy against Candida albicans biofilms

Candida albicans (C. albicans) is a common fungal pathogen causing both localised and systemic infections. The majority of these infections are promoted by biofilm formation, providing a protective matrix for the embedded fungi thereby evading the host immune defence and promoting resistance against anti-mycotic agents. In this study, pH-responsive micellar systems based on poly-(ethylene glycol) ethyl ether methacrylate (PEGMA) and poly 2-(diethylamino) ethyl methacrylate (DEAEMA) block-copolymers of P(PEGMA-b-DEAEMA) were specifically developed and loaded with the antifungal itraconazole (ICZ) to defeat C. albicans biofilms. The P(PEGMA-b-DEAEMA) di-block polymer micelles demonstrated a particle size of 55 ± 6 nm and high ICZ loads (12.0 ± 0.5% w/w). Within the biofilm's acidic microenvironment, tertiary amines of the pH-sensitive DEAEMA block are protonated, altering their conformation and enhancing the release of the micellar contents. Encapsulation of ICZ within micelles significantly enhanced the activity against C. albicans biofilms, with a significant reduction in the biofilm biomass (>50%) and in the number of viable cells (2.4 Log reduction) achieved, compared with the non-encapsulated ICZ. Confocal microscopy revealed a high affinity and accumulation of the micelles in C. albicans biofilms as a result of their size and specific electrostatic interaction, hence their improved activity. P(PEGMA-b-DEAEMA) based pH-responsive micelles offer significant potential as antifungal carriers for controlling Candida infections.

Bioelectrochemical Fixation of Nitrogen to Extracellular Ammonium by Pseudomonas stutzeri

Diazotrophs can produce bioavailable nitrogen from inert N₂ gas by bioelectrochemical nitrogen fixation (e-BNF), which is emerging as an energy-saving and highly selective strategy for agriculture and industry. However, current e-BNF technology is impeded by requirements for NH₄⁺ assimilation inhibitors to facilitate intracellular ammonia secretion and precious metal catalysts to generate H₂ as the energy-carrying intermediate. Here, we initially demonstrate inhibitor- and catalystless extracellular NH₄⁺ production by the diazotroph Pseudomonas stutzeri A1501 using an electrode as the sole electron donor. Multiple lines of evidence revealed that P. stutzeri produced 2.32 ± 0.25 mg/liter extracellular NH₄⁺ at a poised potential of -0.3 V (versus standard hydrogen electrode [SHE]) without the addition of inhibitors or expensive catalysts. The electron uptake mechanism was attributed to the endogenous electron shuttle phenazine-1-carboxylic acid, which was excreted by P. stutzeri and mediated electron transfer from electrodes into cells to directly drive N₂ fixation. The faradaic efficiency was 20% ± 3%, which was 2 to 4 times that of previous e-BNF attempts using the H₂-mediated pathway. This study reports a diazotroph capable of producing secretable NH₄⁺ via extracellular electron uptake, which has important implications for optimizing the performance of e-BNF systems and exploring the novel nitrogen-fixing mode of syntrophic microbial communities in the natural environment. IMPORTANCE Ammonia greatly affects global ecology, agriculture, and the food industry. Diazotrophs with an enhanced capacity of extracellular NH₄⁺ excretion have been proven to be more beneficial to the growth of microalgae and plants, whereas most previously reported diazotrophs produce intracellular organic nitrogen in the absence of chemical suppression and genetic manipulation. Here, we demonstrate that Pseudomonas stutzeri A1501 is capable of extracellular NH₄⁺ production without chemical suppression or genetic manipulation when the extracellular electrode is used as the sole electron donor. We also reveal the electron uptake pathway from the extracellular electron-donating partner to P. stutzeri A1501 via redox electron shuttle phenazines. Since both P. stutzeri A1501 and potential electron-donating partners (such as electroactive microbes and natural semiconductor minerals) are abundant in diverse soils and sediments, P. stutzeri A1501 has broader implications on the improvement of nitrogen fertilization in the natural environment.

Cryptosporidium spp. and Giardia spp. (oo)cysts as target-organisms in sanitation and environmental monitoring: A review in microscopy-based viability assays

Cysts and (oo)cysts are the infective forms of parasitic protozoa, as Giardia and Cryptosporidium, which are widespread and associated to worldwide waterborne diseases outbreaks. These microorganisms pose a challenge to public health, as they are resistant to conventional disinfection methods, which make them important parameters when evaluating inactivation efficiency. However, when (oo)cysts are targets, it is challenging to infer inactivation efficacy, as it may require infectivity tests that are not often an option for laboratory routine analysis. In this scene, (oo)cyst viability based on induced excystation, membrane integrity and enzyme activity evaluated by dye inclusion and/or exclusion, as well as fluorescence reduction consist on microscopy-based techniques that may be options to estimate inactivation in the environmental context. This scoping review presents applications, advantages and limitations of these methodologies for viability assessment, in order to shed light on the (oo)cyst viability topic and provide insight strategies for choosing protocols in the environmental and sanitation field, in laboratory applications and novel research.

Free-floating extracellular DNA: Systematic profiling of mobile genetic elements and antibiotic resistance from wastewater

The free-floating extracellular DNA (exDNA) fraction of microbial ecosystems harbors antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs). Natural transformation of these xenogenetic elements can generate microbial cells resistant to one or more antibiotics. Isolating and obtaining a high yield of exDNA is challenging due to its low concentration in wastewater environments. Profiling exDNA is crucial to unravel the ecology of free-floating ARGs and MGEs and their contribution to horizontal genetransfer. We developed a method using chromatography to isolate and enrich exDNA without causing cell lysis from complex wastewater matrices like influent (9 µg exDNA out of 1 L), activated sludge (5.6 µg out of 1 L), and treated effluent (4.3 µg out of 1 L). ARGs and MGEs were metagenomically profiled for both the exDNA and intracellular DNA (iDNA) of activated sludge, and quantified by qPCR in effluent water. qPCR revealed that ARGs and MGEs are more abundant in the iDNA fraction while still significant on exDNA (100-1000 gene copies mL^-1) in effluent water. The metagenome highlighted that exDNA is mainly composed of MGEs (65%). According to their relatively low abundance in the resistome of exDNA, ARGs uptake by natural transformation is likely not the main transfer mechanism. Although ARGs are not highly abundant in exDNA, the prevalence of MGEs in the exDNA fraction can indirectly promote antibiotic resistance development. The combination of this method with functional metagenomics can help to elucidate the transfer and development of resistances in microbial communities. A systematic profiling of the different DNA fractions will foster microbial risk assessments across water systems, supporting water authorities to delineate measures to safeguard environmental and public health.

Polydimethylsiloxane-graphene oxide nanocomposite coatings with improved anti-corrosion and anti-biofouling properties

We demonstrate enhanced anti-corrosion and anti-biofouling properties of graphene oxide-silica-polydimethylsiloxane (GSP) coating on carbon steel (CS). Electrochemical analyses of GSP-coated carbon steel exposed to Gram-positive Bacillus sp., Gram-negative Pseudomonas sp., and freshwater bacterial cultures for 72 h showed a 3-5 orders of magnitude reduction in i_corr values and high impedance values (10⁷ Ω) as compared with polished specimens. The corrosion protection efficiency of GSP-coated specimens was 99.9% against Bacillus sp. and freshwater culture and it was 89.6% against Pseudomonas sp. Evaluation of anti-biofouling property of GSP coating using microbiological and epifluorescence microscopic techniques showed three order reductions in total viable cells on GSP-coated specimens exposed to bacterial cultures. Confocal laser scanning microscopic analysis of biofilm architecture confirmed a significant reduction of biomass and biofilm thickness on GSP-coated CS demonstrating an excellent anti-biofouling activity of GSP.

How to Evaluate Non-Growing Cells-Current Strategies for Determining Antimicrobial Resistance of VBNC Bacteria

Thanks to the achievements in sanitation, hygiene practices, and antibiotics, we have considerably improved in our ongoing battle against pathogenic bacteria. However, with our increasing knowledge about the complex bacterial lifestyles and cycles and their plethora of defense mechanisms, it is clear that the fight is far from over. One of these resistance mechanisms that has received increasing attention is the ability to enter a dormancy state termed viable but non-culturable (VBNC). Bacteria that enter the VBNC state, either through unfavorable environmental conditions or through potentially lethal stress, lose their ability to grow on standard enrichment media, but show a drastically increased tolerance against antimicrobials including antibiotics. The inability to utilize traditional culture-based methods represents a considerable experimental hurdle to investigate their increased antimicrobial resistance and impedes the development and evaluation of effective treatments or interventions against bacteria in the VBNC state. Although experimental approaches were developed to detect and quantify VBNCs, only a few have been utilized for antimicrobial resistance screening and this review aims to provide an overview of possible methodological approaches.

Detection and Potential Virulence of Viable but Non-Culturable (VBNC) Listeria monocytogenes: A Review

The detection, enumeration, and virulence potential of viable but non-culturable (VBNC) pathogens continues to be a topic of discussion. While there is a lack of definitive evidence that VBNC Listeria monocytogenes (Lm) pose a public health risk, recent studies suggest that Lm in its VBNC state remains virulent. VBNC bacteria cannot be enumerated by traditional plating methods, so the results from routine Lm testing may not demonstrate a sample's true hazard to public health. We suggest that supplementing routine Lm testing methods with methods designed to enumerate VBNC cells may more accurately represent the true level of risk. This review summarizes five methods for enumerating VNBC Lm: Live/Dead BacLight^TM staining, ethidium monoazide and propidium monoazide-stained real-time polymerase chain reaction (EMA- and PMA-PCR), direct viable count (DVC), 5-cyano-2,3-ditolyl tetrazolium chloride-4',6-diamidino-2-phenylindole (CTC-DAPI) double staining, and carboxy-fluorescein diacetate (CDFA) staining. Of these five supplementary methods, the Live/Dead BacLight^TM staining and CFDA-DVC staining currently appear to be the most accurate for VBNC Lm enumeration. In addition, the impact of the VBNC state on the virulence of Lm is reviewed. Widespread use of these supplemental methods would provide supporting data to identify the conditions under which Lm can revert from its VBNC state into an actively multiplying state and help identify the environmental triggers that can cause Lm to become virulent. Highlights: Rationale for testing for all viable Listeria (Lm) is presented. Routine environmental sampling and plating methods may miss viable Lm cells. An overview and comparison of available VBNC testing methods is given. There is a need for resuscitation techniques to recover Lm from VBNC. A review of testing results for post VBNC virulence is compared.

In situ synthesis of silver or selenium nanoparticles on cationized cellulose fabrics for antimicrobial application

In this study, we developed a method to prepare inorganic nanoparticles in situ on the surface of cationized cellulose using a rapid microwave-assisted synthesis. Selenium nanoparticles (SeNPs) were employed as a novel type of antimicrobial agent and, using the same method, silver nanoparticles (AgNPs) were also prepared. The results demonstrated that both SeNPs and AgNPs of about 100 nm in size were generated on the cationized cellulose fabrics. The antibacterial tests revealed that the presence of SeNPs clearly improved the antibacterial performance of cationized cellulose in a similar way as AgNPs. The functionalised fabrics demonstrated strong antibacterial activity when assessed using the challenge test method, even after repeated washing. Microscopic investigations revealed that the bacterial cells were visually damaged through contact with the functionalised fabrics. Furthermore, the functionalised fabrics showed low cytotoxicity towards human cells when tested in vitro using an indirect contact method. In conclusion, this study provides a new approach to prepare cationic cellulose fabrics functionalised with Se or Ag nanoparticles, which exhibit excellent antimicrobial performance, low cytotoxicity and good laundry durability. We have demonstrated that SeNPs can be a good alternative to AgNPs and the functionalised fabrics have great potential to serve as an anti-infective material.

Investigation of the effects of various stress factors on biofilms and planktonic bacteria in cooling tower model system

Biofilm is a microbial population which live in a self-produced extracellular polymeric matrix by attaching to surfaces. Biofilms consist of different different types of organisms such as bacteria, fungi, protozoa, etc. Many biofilms that develop in nature consist of more than one type of organism. Biofilms protect bacteria from adverse conditions such as temperature fluctuation and disinfectants. The aim of this study was to determine the effective elimination strategies for combating biofilm and planktonic bacteria in cooling tower model system using different decontamination / disinfection techniques. In this study, 14 week-old biofilms were treated with temperatures of 4 °C, 65 °C; pH of 3, 11; 2 and 10 mg/l chlorine, 2 and 10 mg/l monochloramine; hypotonic salt (0.01% NaCl) and hypertonic salt (3% NaCl) solution. For enumeration, number of aerobic heterotrophic bacteria was determined by conventional culture method, number of live bacteria was determined by LIVE/DEAD viability kit, CTC-DAPI and Alamar blue staining methods. Temperature of 65 °C, pH of 3, 10 mg/l monochloramine and hypertonic salt solution were the most effective parameters for decontamination of biofilm and planktonic bacteria. Biofilm bacteria in the circulating water system were significantly more resistant than planktonic bacteria against stress factors. When the numbers of epifluorescence microscopy and conventional culture technique were compared, significantly higher number of live bacteria were detected using epifluorescence microscopy. Bacteria enter the viable but non-culturable phase by loosing their culturability under stress conditions. For this reason, the conventional culture method should be supported by different techniques to get more realistic numbers.

Faecal microbiota transplantation for Clostridioides difficile: mechanisms and pharmacology

Faecal microbiota transplantation (FMT) has emerged as a remarkably successful treatment for recurrent Clostridioides difficile infection that cannot be cured with antibiotics alone. Understanding the complex biology and pathogenesis of C. difficile infection, which we discuss in this Perspective, is essential for understanding the potential mechanisms by which FMT cures this disease. Although FMT has already entered clinical practice, different microbiota-based products are currently in clinical trials and are vying for regulatory approval. However, all these therapeutics belong to an entirely new class of agents that require the development of a new branch of pharmacology. Characterization of microbiota therapeutics uses novel and rapidly evolving technologies and requires incorporation of microbial ecology concepts. Here, we consider FMT within a pharmacological framework, including its essential elements: formulation, pharmacokinetics and pharmacodynamics. From this viewpoint, multiple gaps in knowledge become apparent, identifying areas that require systematic research. This knowledge is needed to help clinical providers use microbiota therapeutics appropriately and to facilitate development of next-generation microbiota products with improved safety and efficacy. The discussion here is limited to FMT as a representative of microbiota therapeutics and recurrent C. difficile as the indication; however, consideration of the intrinsic basic principles is relevant to this entire class of microbiota-based therapeutics.

Reducing the Impacts of Biofouling in RO Membrane Systems through In Situ Low Fluence Irradiation Employing UVC-LEDs

Biofouling is a major concern for numerous reverse osmosis membrane systems. UV pretreatment of the feed stream showed promising results but is still not an established technology as it does not maintain a residual effect. By conducting accelerated biofouling experiments in this study, it was investigated whether low fluence UV in situ treatment of the feed using UVC light-emitting diodes (UVC-LEDs) has a lasting effect on the biofilm. The application of UVC-LEDs for biofouling control is a novel hybrid technology that has not been investigated, yet. It could be shown that a low fluence of 2 mJ∙cm^-2 delays biofilm formation by more than 15% in lab-scale experiments. In addition, biofilms at the same feed channel pressure drop exhibited a more than 40% reduced hydraulic resistance. The delay is probably linked to the inactivation of cells in the feed stream, modified adsorption properties or an induced cell cycle arrest. The altered hydraulic resistance might be caused by a change in the microbial community, as well as reduced adenosine triphosphate levels per cells, possibly impacting quorum sensing and extracellular polymeric substances production. Due to the observed biofilm attributes, low fluence UV-LED in situ treatment of the feed stream seems to be a promising technology for biofouling control.

Integrative characterization of the near-minimal bacterium Mesoplasma florum

The near-minimal bacterium Mesoplasma florum is an interesting model for synthetic genomics and systems biology due to its small genome (~ 800 kb), fast growth rate, and lack of pathogenic potential. However, fundamental aspects of its biology remain largely unexplored. Here, we report a broad yet remarkably detailed characterization of M. florum by combining a wide variety of experimental approaches. We investigated several physical and physiological parameters of this bacterium, including cell size, growth kinetics, and biomass composition of the cell. We also performed the first genome-wide analysis of its transcriptome and proteome, notably revealing a conserved promoter motif, the organization of transcription units, and the transcription and protein expression levels of all protein-coding sequences. We converted gene transcription and expression levels into absolute molecular abundances using biomass quantification results, generating an unprecedented view of the M. florum cellular composition and functions. These characterization efforts provide a strong experimental foundation for the development of a genome-scale model for M. florum and will guide future genome engineering endeavors in this simple organism.

Impact of green reduced graphene oxide on sewage sludge bioleaching with Acidithiobacillus ferrooxidanse

Worldwide graphene use is rapidly increasing in a variety of industrial applications to such an extent that efflux into the environment seems inevitable where the likely final reservoirs of graphene wastes is likely to be wastewater treatment plants are. Despite this an understanding of how graphene products impact the bioleaching of metals from sludge is still limited. In this study, the effect of reduced graphene oxide synthesized from eucalyptus leaf extracts (EL-rGO) on Zn²⁺ and Cu²⁺ bioleaching from sludge was investigated. The major new findings were that EL-rGO had a negative effect on Acidithiobacillus ferrooxidans (A. ferrooxidans) growth; since optical density decreased by 0.059 as EL-rGO dose increased from 1 to 50 mg/L, and the bioleaching of Cu²⁺ and Zn²⁺ decreased by 27.7 and 20.2%, respectively. While at a EL-rGO dose of 1 mg/L A. ferrooxidans grew better, scanning electron microscopy (SEM) confirmed that exposure to EL-rGO caused cell membrane disruption at 50 mg/L. Cytotoxicity tests showed that this was related to an increase in lactate dehydrogenase (LDH) release rate and a decrease in superoxide dismutase (SOD) activity. These new findings provide evidence that green synthesized rGO is toxic to microorganisms and that toxicity increased with rGO dose.

Thermo-resistance of ESKAPE-panel pathogens, eradication and growth prevention of an infectious biofilm by photothermal, polydopamine-nanoparticles in vitro

Nanotechnology offers many novel infection-control strategies that may help prevent and treat antimicrobial-resistant bacterial infections. Here, we synthesized polydopamine, photothermal-nanoparticles (PDA-NPs) without further surface-functionalization to evaluate their potential with respect to biofilm-control. Most ESKAPE-panel pathogens in suspension with photothermal-nanoparticles showed three- to four-log-unit reductions upon Near-Infra-Red (NIR)-irradiation, but for enterococci only less than two-log unit reduction was observed. Exposure of existing Staphylococcus aureus biofilms to photothermal-nanoparticles followed by NIR-irradiation did not significantly kill biofilm-inhabitants. This indicates that the biofilm mode of growth poses a barrier to penetration of photothermal-nanoparticles, yielding dissipation of heat to the biofilm-surrounding rather than in its interior. Staphylococcal biofilm-growth in the presence of photothermal-nanoparticles could be significantly prevented after NIR-irradiation because PDA-NPs were incorporated in the biofilm and heat dissipated inside it. Thus, unmodified photothermal nanoparticles have potential for prophylactic infection-control, but data also constitute a warning for possible development of thermo-resistance in infectious pathogens.

Broad-spectrum treatment of bacterial biofilms using magneto-responsive liquid metal particles

The formation and proliferation of bacterial biofilms on surfaces, particularly those on biomedical devices, is a significant issue that results in substantial economic losses, presenting severe health risks to patients. Furthermore, heterogeneous biofilms consisting of different bacterial species can induce the increase in pathogenicity, and the resistance to antimicrobial agents due to the synergistic interactions between the different species. Heterogeneous bacterial biofilms are notoriously difficult to treat due to the presence of extracellular polymeric substances (EPS) and, in conjunction with the rapid rise of multi-drug resistant pathogens, this means that new solutions for anti-biofilm treatment are required. In this study, we investigate the application of magneto-responsive gallium-based liquid metal (GLM-Fe) nanomaterials against a broad range of Gram-positive and Gram-negative bacterial mono-species and multi-species biofilms. The GLM-Fe particles exhibit a magneto-responsive characteristic, causing spherical particles to undergo a shape transformation to high-aspect-ratio nanoparticles with sharp asperities in the presence of a rotating magnetic field. These shape-transformed particles are capable of physically removing bacterial biofilms and rupturing individual cells. Following treatment, both mono-species and multi-species biofilms demonstrated significant reductions in their biomass and overall cell viability, demonstrating the broad-spectrum application of this antibacterial technology. Furthermore, the loss of integrity of the bacterial cell wall and membranes was visualized using a range of microscopy techniques, and the leakage of intracellular components (such as nucleic acids and protein) was observed. Insights gained from this study will impact the design of future liquid metal-based biofilm treatments, particularly those that rely on magneto-responsive properties.

Study of the effects of mineral salts on the biofilm formation on polypropylene fibers using three quantification methods

The microbial biofilms are ubiquitous in nature and represent important biological entities that affect various aspects of human life. As such, they attracted considerable attention during last decades, with the factors affecting the biofilm development being among the frequently studied topics. In our work, the biofilm was cultivated on the surface of polypropylene fibers in a nutrient medium inoculated by the suspension of two unsterile soils. The effects of ionic strength and valence of salt on the amount of the produced biofilm and on composition of biofilm microbial communities were investigated. The effect of valence was significant in some OTUs: Arthrobacter/Pseudarthrobacter/Paenarthrobacter and Bacillus with positive response to monovalent salt (KCl) and Streptomyces, Lysinibacillus, Pseudomonas, and Ensifer with positive response to divalent salt (MgSO₄). The significant preference for a certain concentration of salts was observed in the case of OTUs Agrobacterium, Bacillus (both 100 mM), and Brevundimonas (30 mM). A new quantification method based on measuring of oxidizable organic carbon in biofilm biomass, based on dichromate oxidation, was used. We compared the results obtained using this method with results of crystal violet destaining and measuring of extracted DNA concentration as proxies of the biofilm biomass. The dichromate oxidation is simple, inexpensive, and fast, and our results show that it may be more sensitive than crystal violet destaining. The highest biomass values tended to associate with high concentrations of the divalent salt. This trend was not observed in treatments where the monovalent salt was added. Our data confirm the importance of inorganic ions for biofilm composition and biomass accumulation.

Supramolecular antibiotics: a strategy for conversion of broad-spectrum to narrow-spectrum antibiotics for Staphylococcus aureus

The propensity of broad-spectrum antibiotics to indiscriminately kill both pathogenic and beneficial bacteria has a profound impact on the spread of resistance across multiple bacterial species. Alternative approaches that narrow antibacterial specificity towards desired pathogenic bacterial population are of great interest. Here, we report an enzyme-responsive antibiotic-loaded nanoassembly strategy for narrow delivery of otherwise broad-spectrum antibiotics. We specifically target Staphylococcus aureus (S. aureus), an important blood pathogen that secretes PC1 β-lactamases. Our nanoassemblies selectively eradicate S. aureus grown in vitro with other bacteria, highlighting its potential capability in targeting the desired pathogenic bacterial population.

An efficient way to achieve stable and high-rate ferrous ion-dependent nitrate removal (FeNiR): Batch sludge replacement

Ferrous ion can be used as electron donor for denitrification in the ferrous ion-dependent nitrate removal (FeNiR). To prevent the FeNiR performance decrease caused by iron encrustation, a modified FeNiR process with batch sludge replacement was developed. Based on the decay kinetics of sludge mass and sludge activity, the sludge retention time (SRT) was determined as 40 days in the modified FeNiR process. To keep the FeNiR rate at 0.70 kg-N/(m³·d), the sludge replacement amount was 25% of total sludge every 10 days. The FeNiR efficiency stabilized around 70%. The batch sludge replacement could be an effective method to offset the active sludge decay caused by iron encrustation, and therefore led to the good FeNiR performance. The wasted FeNiR sludge was found to adsorb phosphate at a rate of 0.9 mg-P/(g VS min). The modified FeNiR process was proposed to be coupled with phosphate removal, achieving the co-removal of nitrate and phosphate. The coupled technology is promising due to the less consumption of resources and energy, as well as the less production of excessive sludge.

Red fluorescence threshold for assessing the lesion activity of early caries

PURPOSE

The aim of this study was to determine a red fluorescence threshold for differentiating active from inactive non-cavitated carious lesions.

METHODS

Using the Nyvad criteria, 30 human teeth with non-cavitated carious lesions were divided into active lesions (15 teeth) and inactive lesions (15 teeth). Using the blue light of a quantitative light-induced fluorescence-digital camera, the red fluorescence of the lesions was measured as the ΔR value. By live/dead bacterial staining, bacterial viability was calculated as the Ratio_G/G+R. The ΔR and Ratio_G/G+R of active and inactive lesions were compared. The relationship between ΔR and Ratio_G/G+R was also analyzed. The ΔR threshold was determined for the classification of lesion activity, and its validity was tested.

RESULTS

The mean ΔR of active lesions was 1.85 fold higher than that of inactive lesions (p < 0.001), and the Ratio_G/G+R of active lesions was 1.97 fold higher than that of inactive lesions (p < 0.001). There was a significant positive correlation between the ΔR and the Ratio_G/G+R in non-cavitated carious lesions (p < 0.05). The ΔR threshold for the differentiating non-cavitated carious lesions by activity status was 37.55, and the sensitivity and specificity were both 83.33 %.

CONCLUSIONS

A red fluorescence threshold for categorizing non-cavitated carious lesion activity based on microbial metabolic activity was determined. Accurate evaluation of the activity status of non-cavitated carious lesions will assist in diagnosis and treatment planning for patients with dental caries.

Sensitive Detection of Broad-Spectrum Bacteria with Small-Molecule Fluorescent Excimer Chemosensors

Antibiotic resistance is a major problem for world health, triggered by the unnecessary usage of broad-spectrum antibiotics on purportedly infected patients. Current clinical standards require lengthy protocols for the detection of bacterial species in sterile physiological fluids. In this work, a class of small-molecule fluorescent chemosensors termed ProxyPhos was shown to be capable of rapid, sensitive, and facile detection of broad-spectrum bacteria. The sensors act via a turn-on fluorescent excimer mechanism, where close-proximity binding of multiple sensor units amplifies a red shift emission signal. ProxyPhos sensors were able to detect down to 10 CFUs of model strains by flow cytometry assays and showed selectivity over mammalian cells in a bacterial coculture through fluorescence microscopy. The studies reveal that the zinc(II)-chelates cyclen and cyclam are novel and effective binding units for the detection of both Gram-negative and Gram-positive bacterial strains. Mode of action studies revealed that the chemosensors detect Gram-negative and Gram-positive strains with two distinct mechanisms. Preliminary studies applying ProxyPhos sensors to sterile physiological fluids (cerebrospinal fluid) in flow cytometry assays were successful. The results suggest that ProxyPhos sensors can be developed as a rapid, inexpensive, and robust tool for the "yes-no" detection of broad-spectrum bacteria in sterile fluids.

Research on the effect of TiO2 nanotubes coated by gallium nitrate on Staphylococcus aureus-Escherichia coli biofilm formation

Background

In clinical practice, the cases with bacterial infection caused by titanium implants and bacterial biofilm formation on the surface of titanium materials implanted into human body can often be observed. Thus, this study aimed to demonstrate whether the mixed biofilm of Staphylococcus aureus/Escherichia coli can be formed on the surface of titanium material through in vitro experiments and its formation rules.

Methods

The titanium plates were put into the well containing S aureus or/and E coli. Bacterial adhesion and biofilm formation were analyzed by crystal violet, XTT method, confocal laser scanning microscopy, and scanning electron microscopy.

Results

The results of bacterial adhesion in each group at 6‐72 hours showed that the number of bacterial adhesion in each group was increased with the extension of time and reached to the highest level at 72 hours. Moreover, the biofilm structure in the S aureus‐E coli group was significantly more complex than that of the simple S aureus group or E coli group, and the number of bacteria was also significantly increased in the S aureus‐E coli group.

Conclusion

Those data provide a laboratory basis for the prevention and treatment of mixed infection of subsequent biological materials.

Characterization and in vitro Analysis of Probiotic-Derived Peptides Against Multi Drug Resistance Bacterial Infections

An inexorable switch from antibiotics has become a major desideratum to overcome antibiotic resistance. Bacteriocin from Lactobacillus casei, a cardinal probiotic was used to design novel antibacterial peptides named as Probiotic Bacteriocin Derived and Modified (PBDM) peptides (PBDM1: YKWFAHLIKGLC and PBDM2: YKWFRHLIKKLC). The loop-shaped 3D structure of peptides was characterized in silico via molecular dynamics simulation as well as biophysically via spectroscopic methods. Thereafter, in vitro results against multidrug resistant bacterial strains and hospital samples demonstrated the strong antimicrobial activity of PBDM peptides. Further, in vivo studies with PBDM peptides showed downright recovery of balb/c mice from Vancomycin Resistant Staphylococcus aureus (VRSA) infection to its healthy condition. Thereafter, in vitro study with human epithelial cells showed no significant cytotoxic effects with high biocompatibility and good hemocompatibility. In conclusion, PBDM peptides displayed significant antibacterial activity against certain drug resistant bacteria which cause infections in human beings. Future analysis are required to unveil its mechanism of action in order to execute it as an alternative to antibiotics.

A novel image cytometry-based Lactobacillus bacterial enumeration method for the production of kettle sour beer

The demands for a variety of craft beer flavors have been increasing in the United States. To meet this rising demand, breweries have been experimenting with kettle sour beer that utilizes lactic acid-producing bacteria for fermentation. The current standard bacterial quantification method is insufficient for rigorous quality control, thus there is a need for a better method to monitor lactobacilli concentration in a kettle sour environment. In this work, an automated Lactobacillus counting method was developed using fluorescence-based image cytometry. Three commonly used species were cultured, the concentrations were measured using image cytometry and evaluated against the standard spread-plating method. This procedure was undertaken in vitro at different dilutions and the method was repeated with two species in a kettle sour environment at different time points. Both the in vitro and fermentation experiments were repeated three times. Results demonstrated that the new method was not significantly different when compared to the standard plating method in either controlled settings or within the kettle sour fermentation. The proposed method provides a rapid tool to monitor and control lactobacilli growth in kettle sour beer production, and allows for standardization of the products due to the availability of near instantaneous information for quality control.

Microampere Electric Current Causes Bacterial Membrane Damage and Two-Way Leakage in a Short Period of Time

Physical agents, such as low electric voltage and current, have recently gained attention for antimicrobial treatment due to their bactericidal capability. Although microampere electric current was shown to suppress the growth of bacteria, it remains unclear to what extent the microampere current damaged the bacterial membrane. Here, we investigated the membrane damage and two-way leakage caused by microampere electric current (≤100 μA) with a short exposure time (30 min). Based on MitoTracker staining, propidium iodide staining, filtration assays, and quantitative single-molecule localization microscopy, we observed significant membrane damage, which allowed two-way leakage of ions, small molecules, and proteins. This study paves the way to new development of antimicrobial applications for ultralow electric voltage and current.IMPORTANCE Although electric voltage and current have been studied for a long time in terms of their ability to suppress the growth of bacteria and to kill bacteria, increasing interest has been aroused more recently due to the prevalence of antibiotic resistance of microbes in past decades. Toward understanding the antimicrobial mechanism of low electric voltage and current, previous studies showed that treating bacteria with milliampere electric currents (≥5 mA) for ≥72 h led to significant damage of the bacterial membrane, which likely resulted in leakage of cellular contents and influx of toxic substances through the damaged membrane. However, it remains unclear to what extent membrane damage and two-way (i.e., inward and outward) leakage are caused by lower (i.e., microampere) electric current in a shorter time frame. In this work, we set out to answer this question. We observed that the membrane damage was caused by microampere electric current in half an hour, which allowed two-way leakage of ions, small molecules, and proteins.

Hybrid Hydrogels for Synergistic Periodontal Antibacterial Treatment with Sustained Drug Release and NIR-Responsive Photothermal Effect

BACKGROUND

Periodontal pathogenic bacteria promote the destruction of periodontal tissues and cause loosening and loss of teeth in adults. However, complete removal of periodontal pathogenic bacteria, at both the bottom of the periodontal pocket and the root bifurcation area, remains challenging. In this work, we explored a synergistic antibiotic and photothermal treatment, which is considered an alternative strategy for highly efficient periodontal antibacterial therapy.

METHODS

Mesoporous silica (MSNs) on the surface of Au nanobipyramids (Au NBPs) were designed to achieve the sustained release of the drug and photothermal antibacterials. The mesoporous silica-coated Au NBPs (Au NBPs@SiO2) were mixed with gelatin methacrylate (GelMA-Au NBPs@SiO2). Au NBPs@SiO2 and GelMA-Au NBPs@SiO2 hybrid hydrogels were characterized, and the drug content and photothermal properties in terms of the release profile, bacterial inhibition, and cell growth were investigated.

RESULTS

The GelMA-Au NBPs@SiO2 hybrid hydrogels showed controllable minocycline delivery, and the drug release rates increased under 808 nm near-infrared (NIR) light irradiation. The hydrogels also exhibited excellent antibacterial properties, and the antibacterial efficacy of the antibiotic and photothermal treatment was as high as 90% and 66.7% against Porphyromonas gingivalis (P. gingivalis), respectively. Moreover, regardless of NIR irradiation, cell viability was over 80% and the concentration of Au NBPs@SiO2 in the hybrid hydrogels was as high as 100 µg/mL.

CONCLUSION

We designed a new near-infrared light (NIR)-activated hybrid hydrogel that offers both sustained release of antibacterial drugs and photothermal treatment. Such sustained release pattern yields the potential to rapidly eliminate periodontal pathogens in the periodontal pocket, and the photothermal treatment maintains low bacterial retention after the drug treatment.

Conformationally tuned antibacterial oligomers target the peptidoglycan of Gram-positive bacteria

The recent rise of antibiotic resistance amongst Staphylococcus aureus (S. aureus) populations has made treating Staph-based infections a global medical challenge. Therapies that specifically target the peptidoglycan layer of S. aureus have emerged as new treatment avenues, towards which bacteria are less likely to develop resistance. While the majority of antibacterial polymers/oligomers have the ability to disrupt bacterial membranes, the design parameters for the enhanced disruption of peptidoglycan outer layer of Gram-positive bacteria remain unclear. Here, the design of oligomeric structures with favorable conformational characteristics for improved disruption of the peptidoglycan outer layer of Gram-positive bacteria is reported. Molecular dynamics simulations were employed to inform the structure design and composition of cationic oligomers displaying collapsed and expanded conformations. The most promising diblock and triblock cationic oligomers were synthesized by photo-induced atom transfer radical polymerization (photo ATRP). Following synthesis, the diblock and triblock oligomers displayed average antibacterial activity of ~99% and ~98% for S. aureus and methicillin-resistant S. aureus (MRSA), respectively, at the highest concentrations tested. Importantly, triblock oligomers with extended conformations showed significantly higher disruption of the peptidoglycan outer layer of S. aureus compared to diblock oligomers with more collapsed conformation, as evidenced by a number of characterization techniques including scanning electron, confocal and atomic force microscopy. This work provides new insight into the structure/property relationship of antibacterial materials and advances the design of functional materials for combating the rise of drug-resistant bacteria.

Antimicrobial Susceptibility Testing of Antimicrobial Peptides to Better Predict Efficacy

During the development of antimicrobial peptides (AMP) as potential therapeutics, antimicrobial susceptibility testing (AST) stands as an essential part of the process in identification and optimisation of candidate AMP. Standard methods for AST, developed almost 60 years ago for testing conventional antibiotics, are not necessarily fit for purpose when it comes to determining the susceptibility of microorganisms to AMP. Without careful consideration of the parameters comprising AST there is a risk of failing to identify novel antimicrobials at a time when antimicrobial resistance (AMR) is leading the planet toward a post-antibiotic era. More physiologically/clinically relevant AST will allow better determination of the preclinical activity of drug candidates and allow the identification of lead compounds. An important consideration is the efficacy of AMP in biological matrices replicating sites of infection, e.g., blood/plasma/serum, lung bronchiolar lavage fluid/sputum, urine, biofilms, etc., as this will likely be more predictive of clinical efficacy. Additionally, specific AST for different target microorganisms may help to better predict efficacy of AMP in specific infections. In this manuscript, we describe what we believe are the key considerations for AST of AMP and hope that this information can better guide the preclinical development of AMP toward becoming a new generation of urgently needed antimicrobials.

Evaluating nitrite oxidizing organism survival under different nitrite concentrations

The objective of this study is to explore the optimal pre-treatment procedures and statistics methods for live/dead bacterial staining using nitrite oxidizing organism (NOO) as the research aim. This staining method was developed and widely utilized to evaluate activated bacterial survival situation, because it is direct and convenience to count live and dead bacteria amount by colour distinguishes (green/red) from pictures taken by microscope. The living cell (green colour) percentage and initial bacterial chemical oxygen demand (COD) could be used for accurate reaction rate calculation at the beginning of tests. While according to the physiological principles, the detection target was limited as the organism has a complete cell shape, that was applicable for the initial phase for decay stage (live cell → particulate dead cell), but it is impossible to evaluate the decayed soluble COD from particulate dead cell during whole reaction. To model the decay stage scientifically, a two-step decay model was developed to cater to the live/dead bacterial staining analysis of biological nitrite oxidizer under inhibition condition of high nitrite concentrations at 35 °C. As results of optimal pre-treatment, a three level ultrasonic wave with 45 seconds was explored, as a reasonable observed picture number, 30 sets with 95% confident interval for datasets statistics was summarized. A set of nitrite oxidizer inhibition test (total COD and oxygen uptake rates) under high nitrite concentrations was simulated using the above model and obtained experimental schemes. Additionally, the disintegration enhancement from particulate dead cell to soluble COD by nitrite was inspected and modelled on the basis of experimental datasets.

Eukaryotic phosphatase inhibitors enhance colistin efficacy in gram-negative bacteria

The mounting threat of multi-drug-resistant (MDR) bacteria places a tremendous strain on the antimicrobial clinical arsenal, forcing physicians to revert to near-obsolete antibiotics to treat otherwise intractable infections. Antibiotic adjuvant therapy has emerged as a viable alternative to the development of novel antimicrobial agents. This method uses combinations of an existing antibiotic and a non-antimicrobial small molecule, where the combination either breaks drug resistance or further potentiates antibiotic activity. Through a high-content screen of eukaryotic kinase inhibitors, our group previously identified two highly potent adjuvants that synergize with colistin, a cyclic, polycationic antimicrobial peptide that serves as a drug of last resort for the treatment of MDR Gram-negative bacterial infections. Cell signaling proteins implicated in colistin resistance mechanisms display both kinase and phosphatase activities. Herein, we explore the potential for eukaryotic phosphatase inhibitors to be repurposed as colistin adjuvants. From a panel of 48 unique structures, we discovered that the natural product kuwanon G breaks colistin resistance, while the non-antimicrobial macrolide ascomycin potentiates colistin in polymyxin-susceptible bacteria.

Efficacy of imidazolium and piperidinium based ionic liquids on inhibiting biofilm formation on titanium and carbon steel surfaces

In the present study, the efficacies of three different cationic and anionic ionic liquids (ILs) on biofilm formation on materials used in cooling water systems were evaluated. Two imidazolium based ILs; 1-Ethyl 3-Methylimidazolium tetrafluoroborate - (IL-E) and 1-Butyl-3-methylimidazolium chloride - (IL-I) with anionic fluoride and chloride groups and one piperidinium based IL, N-methyl-N-propylpiperidinium bis(trifluoromethylsulfonyl)imide - (IL-M) with fluoromethyl group as anion were used. The efficacy of these ILs were evaluated on planktonic and sessile cells of major biofilm formers in cooling water systems using Gram negative bacterium Pseudomonas sp. and Gram positive bacterium Bacillus sp. Further their effect on inhibiting biofilm formation on titanium and carbon steel surfaces were also evaluated. Results showed that planktonic cells of Pseudomonas sp. and Bacillus sp. were effectively inhibited by 25 ppm of IL-M and IL-E, respectively. For both bacteria, 50 ppm of IL-I was enough to inhibit and eradicate the sessile cell formation. Among the three ILs, IL-E was the best in inhibiting the adhesion of bacterial cells on Ti and CS surfaces. These results suggest that Imidazolium based ILs are effective in controlling sessile cell formation and eradicating mature biofilm as compared to piperidinium based IL. Further, Imidazolium based IL with fluoride anion (IL-E) was the best in inhibiting adhesion of these bacterial cells and thereby biofilm formation on material surfaces. This study establishes the feasibility of using ILs in cooling water system for bacterial biofilm control along with other conventional biofouling control methods.

The multi-faceted mechano-bactericidal mechanism of nanostructured surfaces

The mechano-bactericidal activity of nanostructured surfaces has become the focus of intensive research toward the development of a new generation of antibacterial surfaces, particularly in the current era of emerging antibiotic resistance. This work demonstrates the effects of an incremental increase of nanopillar height on nanostructure-induced bacterial cell death. We propose that the mechanical lysis of bacterial cells can be influenced by the degree of elasticity and clustering of highly ordered silicon nanopillar arrays. Herein, silicon nanopillar arrays with diameter 35 nm, periodicity 90 nm and increasing heights of 220, 360, and 420 nm were fabricated using deep UV immersion lithography. Nanoarrays of 360-nm-height pillars exhibited the highest degree of bactericidal activity toward both Gram stain-negative Pseudomonas aeruginosa and Gram stain-positive Staphylococcus aureus bacteria, inducing 95 ± 5% and 83 ± 12% cell death, respectively. At heights of 360 nm, increased nanopillar elasticity contributes to the onset of pillar deformation in response to bacterial adhesion to the surface. Theoretical analyses of pillar elasticity confirm that deflection, deformation force, and mechanical energies are more significant for the substrata possessing more flexible pillars. Increased storage and release of mechanical energy may explain the enhanced bactericidal action of these nanopillar arrays toward bacterial cells contacting the surface; however, with further increase of nanopillar height (420 nm), the forces (and tensions) can be partially compensated by irreversible interpillar adhesion that reduces their bactericidal effect. These findings can be used to inform the design of next-generation mechano-responsive surfaces with tuneable bactericidal characteristics for antimicrobial surface technologies.