Antibiotic discovery: combatting bacterial resistance in cells and in biofilm communities

Orientia tsutsugamushi: An Unusual Intracellular Bacteria-Adaptation Strategies, Available Antibiotics, and Alternatives for Treatment

During evolution Orientia tsutsugamushi became a smarter obligate bacterium to establish as intracellular pathogens. O. tsutsugamushi is a human pathogenic bacterium responsible for 1 billion infections of scrub typhus. Several novel mechanisms make this bacterium unique (cell wall, genetic constitutions, secretion system, etc.). In 2007, O. tsutsugamushi Boryong was pioneer strain for whole-genome sequencing. But the fundamental biology of this bacterial cell is a mystery till date. The unusual biology makes this organism as model for host cell interaction. Only a few antibiotics are effective against this intracellular pathogen but emergence of less susceptibility toward antibiotics make the situation alarming. The review was captivated to highlight the unusual aspects of adaptation, antibiotics, and drugs beyond antibiotics.

Phenotypic and genotypic characteristics of mecA - positive oxacillin-sensitive Staphylococcus aureus isolated from patients with bloodstream infection in a tertiary hospital in Southern Brazil

Staphylococcus aureus are extremely important microorganisms, either from an epidemiological point of view or as a pathogen, responsible for causing a series of infectious processes, whether simple, restricted to the skin, or invasive infections such as bacteremia. The emergence of Oxacillin Sensitive-Methicillin Resistant S.aureus (OS-MRSA) isolates has imposed difficulties in the treatment of patients with staphylococcal infection, as such isolates can be mistakenly classified as sensitive and lead to failure of the therapy used. Thus, the objective of this study is to evaluate the prevalence, and genotypic and phenotypic characteristics, of OS-MRSA isolates, from bloodstream infections, collected from patients admitted to a hospital in southern Brazil, as well as to evaluate the treatment used. For this, 801 unique isolates of S. aureus, collected from blood cultures, between January 2011 and December 2020 were evaluated. Of these, 96 isolates were classified as sensitive to oxacillin. The isolates were identified and had their sensitivity profile performed by manual and automated methods. The minimum inhibitory concentration for vancomycin, daptomycin, oxacillin, linezolid and teicoplanine was performed by e-test. The mecA, vanA genes, typing of the SCCmec elements, as well as the search for the icaA, tst-1 and pvl virulence genes were performed by PCR. Biofilm formation was performed using the crystal violet technique. The Sequence Type (ST), as well as the Clonal Complex (CC) of the isolates was evaluated by the RTq -PCR. The clinical characteristics of the patients were evaluated through an active search in medical records. After investigating the mecA gene, 27.1% (26/96) of the isolates were considered OS-MRSA, with SCCmec type I being the most prevalent, 46.1% (12/26). Among the evaluated isolates, 41% (9/22) were included in CC5 and ST9. As for virulence, all isolates were positive for the icaA gene and characterized as strong biofilm formers. The pvl gene was found in 92.3% (24/26) of the isolates and the toxic shock syndrome toxin was present in 61.5% of the isolates (16/26). All isolates were negative for the presence of the van A gene. As for the clinical outcome, 73% (19/26) of the patients were discharged from the hospital and 27% (7/26) died. It was possible to observe a high frequency of OS-MRSA isolates causing bloodstream infections. Furthermore, such isolates contain several virulence genes, which may contribute to a worse clinical outcome.

Metabolic Modulation-Mediated Antibiotic and Immune Activation for Treatment of Chronic Lung Infections

The Pseudomonas aeruginosa biofilm in recalcitrant chronic lung infections not only develops high antimicrobial tolerance but also induces an aberrant host inflammatory response. The metabolic condition plays a vital role in both the antimicrobial susceptibility of bacteria and the inflammatory response of immune cells, thereby offering a potential therapeutic target. Herein, we described a metabolic modulation strategy by using ultrasound-responsive liposomal nanoparticles containing a sonosensitizer and a hypoxia-activated prodrug against biofilm-associated chronic lung infections. Under ultrasound stimulation, the sonosensitizer generates antibacterial reactive oxygen species by oxygen consumption. Subsequently, the oxygen consumption-mediated hypoxia not only induces the anaerobic metabolism of bacteria for antibiotic activation but also triggers the glycolysis pathway of immune cells for inflammatory activation. Such metabolic modulation strategy demonstrated efficient therapeutic efficacy for P. aeruginosa biofilm-induced chronic lung infections in mice models and provides a promising way for combating biofilm-associated chronic infections.

Quinolone scaffolds as potential drug candidates against infectious microbes: a review

Prevalence of microbial infections and new rising pathogens are signified as causative agent for variety of serious and lethal health crisis in past years. Despite medical advances, bacterial and fungal infections continue to be a rising problem in the health care system. As more bacteria develop resistance to antibiotics used in therapy, and as more invasive microbial species develop resistance to conventional antimicrobial drugs. Relevant published publications from the last two decades, up to 2024, were systematically retrieved from the MEDLINE/PubMed, SCOPUS, EMBASE, and WOS databases using keywords such as quinolones, anti-infective, antibacterial, antimicrobial resistance and patents on quinolone derivatives. With an approach of considerable interest towards novel heterocyclic derivatives as novel anti-infective agents, researchers have explored these as essential tools in vistas of drug design and development. Among heterocycles, quinolones have been regarded extremely essential for the development of novel derivatives, even able to tackle the associated resistance issues. The quinolone scaffold with its bicyclic structure and specific functional groups such as the carbonyl and acidic groups, is indeed considered a valuable functionalities for further lead generation and optimization in drug discovery. Besides, the substitution at N-1, C-3 and C-7 positions also subjected to be having a significant role in anti-infective potential. In this article, we intend to highlight recent quinolone derivatives based on the SAR approach and anti-infective potential such as antibacterial, antifungal, antimalarial, antitubercular, antitrypanosomal and antiviral activities. Moreover, some recent patents granted on quinolone-containing derivatives as anti-infective agents have also been highlighted in tabular form. Due consideration of this, future research in this scaffold is expected to be useful for aspiring scientists to get pharmacologically significant leads.

Exploring ex vivo biofilm dynamics: consequences of low ampicillin concentrations on the human oral microbiome

Prolonged exposure to antibiotics at low concentration can promote processes associated with bacterial biofilm formation, virulence and antibiotic resistance. This can be of high relevance in microbial communities like the oral microbiome, where commensals and pathogens share a common habitat and where the total abundance of antibiotic resistance genes surpasses the abundance in the gut. Here, we used an ex vivo model of human oral biofilms to investigate the impact of ampicillin on biofilm viability. The ecological impact on the microbiome and resistome was investigated using shotgun metagenomics. The results showed that low concentrations promoted significant shifts in microbial taxonomic profile and could enhance biofilm viability by up to 1 to 2-log. For the resistome, low concentrations had no significant impact on antibiotic resistance gene (ARG) diversity, while ARG abundance decreased by up to 84%. A positive correlation was observed between reduced microbial diversity and reduced ARG abundance. The WHO priority pathogens Streptococcus pneumoniae and Staphylococcus aureus were identified in some of the samples, but their abundance was not significantly altered by ampicillin. Most of the antibiotic resistance genes that increased in abundance in the ampicillin group were associated with streptococci, including Streptococcus mitis, a well-known potential donor of ARGs to S. pneumoniae. Overall, the results highlight the potential of using the model to further our understanding of ecological and evolutionary forces driving antimicrobial resistance in oral microbiomes.

Characterization of a Straboviridae phage vB_AbaM-SHI and its inhibition effect on biofilms of Acinetobacter baumannii

Acinetobacter baumannii (A. baumannii) is a popular clinical pathogen worldwide. Biofilm-associated antibiotic-resistant A. baumannii infection poses a great threat to human health. Bacteria in biofilms are highly resistant to antibiotics and disinfectants. Furthermore, inhibition or eradication of biofilms in husbandry, the food industry and clinics are almost impossible. Phages can move across the biofilm matrix and promote antibiotic penetration. In the present study, a lytic A. baumannii phage vB_AbaM-SHI, belonging to family Straboviridae, was isolated from sauce chop factory drain outlet in Wuxi, China. The DNA genome consists of 44,180 bp which contain 93 open reading frames, and genes encoding products morphogenesis are located at the end of the genome. The amino acid sequence of vB_AbaM-SHI endolysin is different from those of previously reported A. baumannii phages in NCBI. Phage vB_AbaM-SHI endolysin has two additional β strands due to the replacement of a lysine (K) (in KU510289.1, NC_041857.1, JX976549.1 and MH853786.1) with an arginine (R) (SHI) at position 21 of A. baumannii phage endolysin. Spot test showed that phage vB_AbaM-SHI is able to lyse some antibiotic-resistant bacteria, such as A. baumannii (SL, SL1, and SG strains) and E. coli BL21 strain. Additionally, phage vB_AbaM-SHI independently killed bacteria and inhibited bacterial biofilm formation, and synergistically exerted strong antibacterial effects with antibiotics. This study provided a new perspective into the potential application value of phage vB_AbaM-SHI as an antimicrobial agent.

Antibacterial Sesquiterpene Lactones from Kaunia lasiophthalma

Phytochemical study of the species Kaunia lasiophthalma enabled the isolation of three undescribed and three known guaianolide-type sesquiterpene lactones, and one new benzofuran. The bioguided fractionation methodology was successful in detecting antimicrobial metabolites against Staphylococcus aureus strains and permitted the description of undescribed guaianolide-type sesquiterpene lactones with substitution patterns matching all those described in the Oxylobinae subtribe.

Ultrasound-Stimulated "Exocytosis" by Cell-Like Microbubbles Enhances Antibacterial Species Penetration and Immune Activation Against Implant Infection

Host immune systems serving as crucial defense lines are vital resisting mechanisms against biofilm-associated implant infections. Nevertheless, biofilms hinder the penetration of anti-bacterial species, inhibit phagocytosis of immune cells, and frustrate host inflammatory responses, ultimately resulting in the weakness of the host immune system for biofilm elimination. Herein, a cell-like construct is developed through encapsulation of erythrocyte membrane fragments on the surface of Fe3 O4 nanoparticle-fabricated microbubbles and then loaded with hydroxyurea (EMB-Hu). Under ultrasound (US) stimulation, EMB-Hu undergoes a stable oscillation manner to act in an "exocytosis" mechanism for disrupting biofilm, releasing agents, and enhancing penetration of catalytically generated anti-bacterial species within biofilms. Additionally, the US-stimulated "exocytosis" by EMB-Hu can activate pro-inflammatory macrophage polarization and enhance macrophage phagocytosis for clearance of disrupted biofilms. Collectively, this work has exhibited cell-like microbubbles with US-stimulated "exocytosis" mechanisms to overcome the biofilm barrier and signal macrophages for inflammatory activation, finally achieving favorable therapeutic effects against implant infections caused by methicillin-resistant Staphylococcus aureus (MRSA) biofilms.

Enhanced Biofilm Formation by Tetracycline in a Staphylococcus aureus Naturally Lacking ica Operon and atl

Staphylococcus aureus is a major, widespread pathogen, and its biofilm-forming characteristics make it even more difficult to eliminate by biocides. Tetracycline (TCY) is a major broad-spectrum antibiotic, the residues of which can cause deleterious health impacts, and subinhibitory concentrations of TCY have the potential to increase biofilm formation in S. aureus. In this study, we showed how the biofilm formation of S. aureus 123786 is enhanced in the presence of TCY at specific subinhibitory concentrations. S. aureus 123786 used in this study was identified as Staphylococcal Cassette Chromosome mec III, sequence type239 and naturally lacking ica operon and atl gene. Two assays were performed to quantify the formation of S. aureus biofilm. In the crystal violet (CV) assay, the absorbance values of biofilm stained with CV at optical density (OD)540 nm increased after 8 and 16 hr of incubation when the concentration of TCY was 1/2 minimum inhibitory concentration (MIC), whereas at the concentration of 1/16 MIC, the absorbance values increased after 16 and 24 hr of incubation. In tetrazolium salt reduction assay, the absorbance value at OD490 nm of S. aureus 123786 biofilms mixed with 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium solution increased after 8 hr when the concentration of TCY was 1/4 MIC, which may be correlated with the higher proliferation and maturation of biofilm. In conclusion, the biofilm formation of S. aureus 123786 could be enhanced in the presence of TCY at specific subinhibitory concentrations.

Shifting from Ammonium to Phosphonium Salts: A Promising Strategy to Develop Next-Generation Weapons against Biofilms

Since they are difficult and sometimes impossible to treat, infections sustained by multidrug-resistant (MDR) pathogens, emerging especially in nosocomial environments, are an increasing global public health concern, translating into high mortality and healthcare costs. In addition to having acquired intrinsic abilities to resist available antibiotic treatments, MDR bacteria can transmit genetic material encoding for resistance to non-mutated bacteria, thus strongly decreasing the number of available effective antibiotics. Moreover, several pathogens develop resistance by forming biofilms (BFs), a safe and antibiotic-resistant home for microorganisms. BFs are made of well-organized bacterial communities, encased and protected in a self-produced extracellular polymeric matrix, which impedes antibiotics' ability to reach bacteria, thus causing them to lose efficacy. By adhering to living or abiotic surfaces in healthcare settings, especially in intensive care units where immunocompromised older patients with several comorbidities are hospitalized BFs cause the onset of difficult-to-eradicate infections. In this context, recent studies have demonstrated that quaternary ammonium compounds (QACs), acting as membrane disruptors and initially with a low tendency to develop resistance, have demonstrated anti-BF potentialities. However, a paucity of innovation in this space has driven the emergence of QAC resistance. More recently, quaternary phosphonium salts (QPSs), including tri-phenyl alkyl phosphonium derivatives, achievable by easy one-step reactions and well known as intermediates of the Wittig reaction, have shown promising anti-BF effects in vitro. Here, after an overview of pathogen resistance, BFs, and QACs, we have reviewed the QPSs developed and assayed to this end, so far. Finally, the synthetic strategies used to prepare QPSs have also been provided and discussed to spur the synthesis of novel compounds of this class. We think that the extension of the knowledge about these materials by this review could be a successful approach to finding effective weapons for treating chronic infections and device-associated diseases sustained by BF-producing MDR bacteria.

Three dimensional printed biofilms: Fabrication, design and future biomedical and environmental applications

Three dimensional printing has emerged as a widely acceptable strategy for the fabrication of mammalian cell laden constructs with complex microenvironments for tissue engineering and regenerative medicine. More recently 3D printed living materials containing microorganisms have been developed and matured into living biofilms. The potential for engineered 3D biofilms as in vitro models for biomedical applications, such as antimicrobial susceptibility testing, and environmental applications, such as bioleaching, bioremediation, and wastewater purification, is extensive but the need for an in-depth understanding of the structure-function relationship between the complex construct and the microorganism response still exists. This review discusses 3D printing fabrication methods for engineered biofilms with specific structural features. Next, it highlights the importance of bioink compositions and 3D bioarchitecture design. Finally, a brief overview of current and potential applications of 3D printed biofilms in environmental and biomedical fields is discussed.

A graphene microelectrode array based microfluidic device for in situ continuous monitoring of biofilms

In situ continuous monitoring of bacterial biofilms has been a challenging job so far, but it is fundamental to the screening of novel anti-biofilm reagents. In this work, a microfluidic system utilizing a graphene-modified microelectrode array sensor was proposed to realize the dynamic state of bacterial biofilm monitoring by electrochemical impedance. The results illustrated that the observation window period of the biofilm state is significantly prolonged due to the increment of bacterial cell load on the sensing interface, thereby greatly improving the sensing signal quality. Simulation of anti-biofilm drug screening demonstrated that the performance of this method manifestly exceeded that of its endpoint counterparts.

Octenidine with hyaluronan dressing versus a silver dressing in hard-to-heal wounds: a post-marketing study

OBJECTIVE

This study was conducted to provide comparative data on the clinical efficacy and safety of a novel hard-to-heal wound dressing (Sorelex; Contipro a.s., Czech Republic) that combines octenidine and hyaluronan, compared with a silver-based dressing.

METHOD

This multicentre, open-label, randomised, post-market, clinical follow-up study provides a comparison of a octenidine and hyaluronan combination with a standard-of-care (SoC) silver-containing dressing. The investigators evaluated the management of infection in the hard-to-heal wounds based on recorded changes in the appearance of the wound bed tissue and the presence of clinical signs of infection after three weeks of treatment. Other relevant assessed parameters of wound healing were: wound size; exudation level; wound pain level; and surrounding skin appearance.

RESULTS

The study cohort included 48 patients in the Sorelex arm and 39 patients in the SoC arm. Both products evinced numerous parameters of wound infection management: reductions in the wound bed slough; marked decreases in wound size; the formation of re-epithelialisation and granulation tissue; and improved pain management. Sorelex significantly improved the condition of surrounding skin after three weeks of treatment, unlike SoC. Sorelex reduced wound area significantly more than SoC (p=0.04). No statistically significant differences were detected in other assessed parameters between the two study arms. All the participating investigators expressed their satisfaction with both products. No adverse reactions to Sorelex were recorded over the mean treatment period of 53 days.

CONCLUSION

The octenidine and hyaluronan combination provides a new alternative choice of dressing for the treatment of infected hard-to-heal wounds when compared with a silver-based product.

3-Hydroxy coumarin demonstrates anti-biofilm and anti-hyphal efficacy against Candida albicans via inhibition of cell-adhesion, morphogenesis, and virulent genes regulation

Candida albicans, a common fungus of human flora, can become an opportunistic pathogen and causes invasive candidiasis in immunocompromised individuals. Biofilm formation is the prime cause of antibiotic resistance during C. albicans infections and treating biofilm-forming cells is challenging due to their intractable and persistent nature. The study intends to explore the therapeutic potential of naturally produced compounds by competitive marine bacteria residing in marine biofilms against C. albicans biofilm. To this end, 3-hydroxy coumarin (3HC), a compound identified from the cell-free culture supernatant of the marine bacterium Brevundimonas abyssalis, was found to exhibit anti-biofilm and anti-hyphal activity against both reference and clinical isolates of C. albicans. The compound demonstrated significant inhibitory effects on biofilms and impaired the yeast-to-hyphal transition, wrinkle, and filament morphology at the minimal biofilm inhibitory concentration (MBIC) of 250 µg mL^-1. Intriguingly, quantitative PCR analysis of 3HC-treated C. albicans biofilm revealed significant downregulation of virulence genes (hst7, ume6, efg1, cph1, ras1, als1) associated with adhesion and morphogenesis. Moreover, 3HC displayed non-fungicidal and non-toxic characteristics against human erythrocytes and buccal cells. In conclusion, this study showed that marine biofilms are a hidden source of diverse therapeutic drugs, and 3HC could be a potent drug to treat C. albicans infections.

QbD-Engineered Development and Validation of a RP-HPLC Method for Simultaneous Estimation of Rutin and Ciprofloxacin HCl in Bilosomal Nanoformulation

In the given study, a new reverse-phase high-performance liquid chromatography (RP-HPLC) method has been reported for the simultaneous estimation of ciprofloxacin hydrochloride (CPX) and rutin (RUT) using quality by design (QbD) approach. The analysis was carried out by applying the Box-Behnken design having fewer design points and less experimental runs. It relates between factors and responses and gives statistically significant values, along with enhancing the quality of the analysis. CPX and RUT were separated on the Kromasil C₁₈ column (4.6 × 150 mm, 5 μm) using an isocratic mobile phase combination of phosphoric acid buffer (pH 3.0) and acetonitrile with the ratio of 87:13% v/v at a flow rate of 1.0 mL/min. CPX and RUT were detected at their respective wavelengths of 278 and 368 nm using a photodiode array detector. The developed method was validated according to guideline ICH Q2 R (1). The validation parameters taken were linearity, system suitability, accuracy, precision, robustness, sensitivity, and solution stability which were in the acceptable range. The findings suggest that the developed RP-HPLC method can be successfully applied to analyze novel CPX-RUT-loaded bilosomal nanoformulation prepared by thin-film hydration technique.

Cell-free supernatant of probiotic bacteria exerted antibiofilm and antibacterial activities against Pseudomonas aeruginosa: A novel biotic therapy

Aim: This study aims to verify the antibacterial and antibiofilm action of cell-free spent medium (CFSM) from four lactic acid bacteria with potential probiotic characteristics (Lactiplantibacillus plantarum, Lactobacillus acidophilus, Lactobacillus johnsonii, and Lactobacillus delbrueckii) against two Pseudomonas aeruginosa strains. Main methods: The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the CFSM, antibacterial activity by analysing the formation of inhibition zones, and inhibition of planktonic cultures were determined. Whether an increase in the concentration of CFSM influenced the growth of pathogenic strains and the anti-adhesive activity of the CFSM in biofilm formation (crystal violet and MTT assays) were determined, which were all corroborated by using scanning electron microscopy. Key findings: The relationship between the MIC and MBC values showed a bactericidal or bacteriostatic effect for all the cell-free spent media (CFSMs) tested for P. aeruginosa 9027™ and 27853™ strains. The CFSM supplemental doses of 18 or 22%, 20 or 22%, 46 or 48%, and 50 or 54% of L. acidophilus, L. delbrueckii, L. plantarum, and L. johnsonii, respectively, could completely inhibit the growth of both pathogen strains. The antibiofilm activity of the CFSM in three biofilm conditions (pre-coated, co-incubated, and preformed) demonstrated values ranging between 40% and 80% for biofilm inhibition, and similar results were observed for cell viability. Significance: This work provides strong evidence that the postbiotic derived from different Lactobacilli could be practical as an adjuvant therapy for reducing the use of antibiotics, being a good candidate to overcome the growing challenge of hospital infections due to this pathogen.

Biofilm formation and correlations with drug resistance in Mycoplasma synoviae

Infectious synovitis in chickens caused by Mycoplasma synoviae infections are characterized by exudative synovial joint membranes and tenosynovitis. We isolated M. synoviae from chickens on farms in Guangdong, China and identifed 29 K-type and 3 A-type strains using vlhA genotyping and all displayed decreased susceptibilities to enrofloxacin, doxycycline, tiamulin and tylosin compared with the type strain WVU1853 (ATCC 25204). M. synoviae biofilms were present after staining as block or continuous dot shape morphologies and these appeared as tower-like and mushroom-like structures in scanning electron micrographs. The optimal temperature for biofilm formation was 33 °C and these biofilms enhanced the resistance of M. synoviae to all 4 antibiotics we tested and minimum biofilm inhibitory concentration for enrofloxacin and biofilm biomass were significantly negatively correlated (r < 0, 0.3 ≤|r|<0.5, P < 0.05). This work is the first study of the biofilm formation ability of M. synoviae and provides the foundation for further investigations.

Synthesis, Antimicrobial, and Antibiofilm Activities of Some Novel 7-Methoxyquinoline Derivatives Bearing Sulfonamide Moiety against Urinary Tract Infection-Causing Pathogenic Microbes

A new series of 4-((7-methoxyquinolin-4-yl) amino)-N-(substituted) benzenesulfonamide 3(a-s) was synthesized via the reaction of 4-chloro-7-methoxyquinoline 1 with various sulfa drugs. The structural elucidation was verified based on spectroscopic data analysis. All the target compounds were screened for their antimicrobial activity against Gram-positive bacteria, Gram-negative bacteria, and unicellular fungi. The results revealed that compound 3l has the highest effect on most tested bacterial and unicellular fungal strains. The highest effect of compound 3l was observed against E. coli and C. albicans with MIC = 7.812 and 31.125 µg/mL, respectively. Compounds 3c and 3d showed broad-spectrum antimicrobial activity, but the activity was lower than that of 3l. The antibiofilm activity of compound 3l was measured against different pathogenic microbes isolated from the urinary tract. Compound 3l could achieve biofilm extension at its adhesion strength. After adding 10.0 µg/mL of compound 3l, the highest percentage was 94.60% for E. coli, 91.74% for P. aeruginosa, and 98.03% for C. neoformans. Moreover, in the protein leakage assay, the quantity of cellular protein discharged from E. coli was 180.25 µg/mL after treatment with 1.0 mg/mL of compound 3l, which explains the creation of holes in the cell membrane of E. coli and proves compound 3l's antibacterial and antibiofilm properties. Additionally, in silico ADME prediction analyses of compounds 3c, 3d, and 3l revealed promising results, indicating the presence of drug-like properties.

Identification of Potential Antimicrobial Targets of Pseudomonas aeruginosa Biofilms through a Novel Screening Approach

Pseudomonas aeruginosa is an opportunistic pathogen of considerable medical importance, owing to its pronounced antibiotic tolerance and association with cystic fibrosis and other life-threatening diseases. The aim of this study was to highlight the genes responsible for P. aeruginosa biofilm tolerance to antibiotics and thereby identify potential new targets for the development of drugs against biofilm-related infections. By developing a novel screening approach and utilizing a public P. aeruginosa transposon insertion library, several biofilm-relevant genes were identified. The Pf phage gene (PA0720) and flagellin gene (fliC) conferred biofilm-specific tolerance to gentamicin. Compared with the reference biofilms, the biofilms formed by PA0720 and fliC mutants were completely eliminated with a 4-fold-lower gentamicin concentration. Furthermore, the mreC, pprB, coxC, and PA3785 genes were demonstrated to play major roles in enhancing biofilm tolerance to gentamicin. The analysis of biofilm-relevant genes performed in this study provides important novel insights into the understanding of P. aeruginosa antibiotic tolerance, which will facilitate the detection of antibiotic resistance and the development of antibiofilm strategies against P. aeruginosa. IMPORTANCE Pseudomonas aeruginosa is an opportunistic pathogen of high medical importance and is one of the main pathogens responsible for the mortality of patients with cystic fibrosis. In addition to inherited antibiotic resistance, P. aeruginosa can form biofilms, defined as communities of microorganisms embedded in a self-produced matrix of extracellular polymeric substances adhering to each other and/or to a surface. Biofilms protect bacteria from antibiotic treatments and represent a major reason for antibiotic failure in the treatment of chronic infections caused by cystic fibrosis. Therefore, it is crucial to develop new therapeutic strategies aimed at specifically eradicating biofilms. The aim of this study was to generalize a novel screening method for biofilm research and to identify the possible genes involved in P. aeruginosa biofilm tolerance to antibiotics, both of which could improve the understanding of biofilm-related infections and allow for the identification of relevant therapeutic targets for drug development.

Ultrasound-responsive catalytic microbubbles enhance biofilm elimination and immune activation to treat chronic lung infections

Efficient treatment of chronic lung infections caused by Pseudomonas aeruginosa biofilms is a great challenge because of drug tolerance and immune evasion issues. Here, we develop ultrasound-responsive catalytic microbubbles with biofilm elimination and immune activation properties to combat chronic lung infection induced by P. aeruginosa biofilms. In these microbubbles, piperacillin and Fe₃O₄ nanoparticles form a drug-loaded shell surrounding the air core. Under ultrasound stimulation, the microbubbles can physically disrupt the structure of biofilms and enhance the penetration of both Fe₃O₄ nanoparticles and piperacillin into the biofilm. Then, Fe₃O₄ nanoparticles chemically degrade the biofilm matrix and kill the bacteria with the assistance of piperacillin. Fe₃O₄ nanoparticles can activate the immune response for biofilm elimination by polarizing macrophages into a pro-inflammatory phenotype. These ultrasound-responsive catalytic microbubbles efficiently treat chronic lung infections in a mouse model by combining physical/chemical/antibiotic biofilm elimination and immune activation, thus providing a promising strategy for combating bacterial biofilm infections.

Cationic Liposomes with Different Lipid Ratios: Antibacterial Activity, Antibacterial Mechanism, and Cytotoxicity Evaluations

Due to their strong bacterial binding and bacterial toxicity, cationic liposomes have been utilized as effective antibacterial materials in many studies. However, few researchers have systematically compared their antibacterial activity with their mammalian cell cytotoxicity or have deeply explored their antibacterial and cytotoxicity mechanisms. Here, we prepared a series of cationic liposomes (termed CLs) using dimethyldioctadecylammonium chloride (DODAC) and lecithin at different molar ratios. CLs have the ability to effectively bind with Gram-positive and Gram-negative bacteria through electrostatic and hydrophobic interactions. Further, the CLs with high molar ratios of DODAC (30 and 40 mol%) can disrupt the bacterial wall/membrane, efficiently inducing the production of reactive oxygen species (ROS). More importantly, we carefully compared the antibacterial activity and the mammalian cell cytotoxicity of various CLs differing in DODAC contents and liposomal concentrations and revealed that, whether they are bacterial or mammalian cells, an increasing DODAC content in CLs can lead to an elevated cytotoxicity level. Further, there exists a critical DODAC contents (>20 mol%) in CLs to endow them with effective antibacterial ability. However, the variation in the DODAC content and liposomal concentration of CLs has different degrees of influence on the antibacterial activity or cytotoxicity. For example, CLs at high DODAC content (i.e., CL0.3 and CL0.4) could effectively kill both types of bacterial cells but only cause negligible toxicity to mammalian cells. We believe that a systematic comparison between the antibacterial activity and the cytotoxicity of CLs with different DODAC contents will provide an important reference for the potential clinical applications of cationic liposomes.

Purification and Characterization of Novel Anti-MRSA Peptides Produced by Brevibacillus sp. SPR-20

Methicillin-resistant Staphylococcus aureus (MRSA) is listed as a high-priority pathogen because its infection is associated with a high mortality rate. It is urgent to search for new agents to treat such an infection. Our previous study isolated a soil bacterium (Brevibacillus sp. SPR-20), showing the highest antimicrobial activity against S. aureus TISTR 517 and MRSA strains. The present study aimed to purify and characterize anti-MRSA substances produced by SPR-20. The result showed that five active substances (P1-P5) were found, and they were identified by LC-MS/MS that provided the peptide sequences of 14-15 residues. Circular dichroism showed that all peptides contained β-strand and disordered conformations as the major secondary structures. Only P1-P4 adopted more α-helix conformations when incubated with 50 mM SDS. These anti-MRSA peptides could inhibit S. aureus and MRSA in concentrations of 2-32 μg/mL. P1 (NH₂-VVVNVLVKVLPPPVV-COOH) had the highest activity and was identified as a novel antimicrobial peptide (AMP). The stability study revealed that P1 was stable in response to temperature, proteolytic enzymes, surfactant, and pH. The electron micrograph showed that P1 induced bacterial membrane damage when treated at 1× MIC in the first hour of incubation. The killing kinetics of P1 was dependent on concentration and time. Mechanisms of P1 on tested pathogens involved membrane permeability, leakage of genetic material, and cell lysis. The P1 peptide at a concentration up to 32 μg/mL showed hemolysis of less than 10%, supporting its safety for human erythrocytes. This study provides promising anti-MRSA peptides that might be developed for effective antibiotics in the post-antibiotic era.

Phase 1 safety trial of a natural product cocktail with antibacterial activity in human volunteers

New antibiotics are urgently needed to reduce the health burden of antibiotic-resistant bacterial infection. Natural products (NPs) derived from plants and animals are a current focus of research seeking to discover new antibacterial molecules with clinical potential. A cocktail of NPs based on a medieval remedy for eye infection eliminated biofilms of several highly antibiotic-resistant bacterial species in laboratory studies, and had a promising safety profile in vitro and in a mouse model. A necessary prelude to refining this remedy into a defined, synthetic mixture suitable for testing with wound infections is to firstly establish safety when applied to healthy human skin. We aimed to assess skin-related outcomes of the preparation in a sample of healthy volunteers. This prospective, single arm, non-randomised Phase I clinical trial consisted of a single patch test intervention with 48-h follow-up. Volunteers were staff, students and members of the public recruited from the University of Warwick and surrounding locality. Adults aged 18-79 years, with no history of severe immunity-related disease, diabetes, recent infection, or known pregnancy were eligible. A 100 µl application of a filter-sterilised NP mixture, comprising ground garlic, onion, white wine and bovine bile, was applied to skin on the upper arm and covered with a dressing. The primary outcome was skin-related adverse events over 48 h. Digital photographs were captured where bothersome, salve-related events were reported. 109 volunteers, aged 18-77 years, were recruited between June and July 2021. Sample mean age was 37.6 (SD 16.1) years, and 63 (58%) participants were female. Outcome data were obtained for 106/109 (97%); two participants were lost to follow-up and one removed the skin patch after nine hours due to a bothersome garlic odour. Twenty-one (19.8%) participants reported any patch-test related sign or symptom; of these 14 (13.2%) participants reported minor events related to the salve, including itchiness, redness, or garlic odour. No serious events were reported. We found no evidence of serious skin-related adverse events related to the NP preparation.Trial registration: International Standard Randomised Controlled Trial Number (ISRCTN10773579). Date registered: 08/01/2021.

Antibacterial, Antibiofilm, and Anti-Quorum Sensing Potential of Novel Synthetic Compounds Against Pathogenic Bacteria Isolated From Chronic Sinusitis Patients

Quorum sensing (QS) is a major controller of virulence and biofilm formation in pathogenic bacteria. The aim of the research was to screen novel synthetic compounds (18) from 2 series (Pyrazole and Diene dione) for quorum sensing and biofilm inhibitory potential against resistant pathogens isolated from patients with chronic sinusitis. Most of the compounds have documented zone of inhibition against Gram positive strains Staphylococcus aureus, Enterococcus faecalis and moderate activity against Gram negative Klebseilla pneumoniae and Proteus mirabilis in comparison with standard antibiotic. Compounds Q1 and Q7 have given the maximum zone of inhibition 18 and 20 mm with MICs 0.312 mg/mL and .156 mg/mL against S aureus and E faecalis, respectively. Some compounds were equally potent at inhibiting the formation of biofilm which later established by phase contrast microscopy. Regarding quorum sensing inhibition, the tested concentration of synthetic compound UA3 0.313 mg/mL inhibited violacein production without decreasing Chromobacterium pseudoviolaceum count which was significantly lower than determined MIC’s. It was depicted from the results that selected compounds exhibited low level of cytotoxicity toward human red blood cells. Hence, these findings revealed that most novel compounds were effective antibacterial, whereas compound UA3 has shared significant anti-quorum sensing potential against Chromobacterium pseudoviolaceum.

Acinetobacter baumannii Biofilm Formation: Association with Antimicrobial Resistance and Prolonged Survival under Desiccation

Biofilm-forming multidrug-resistant Acinetobacter baumannii has emerged as a global pathogen. This study investigated the impact of biofilm formation by A. baumannii on antimicrobial resistance and prolonged survival under desiccation, which is essential for effective infection control of A. baumannii in hospital settings. Seventy-eight clinical isolates of A. baumannii were identified, and antibiotic susceptibility profiles were assessed. All the isolates were investigated for their biofilm-forming abilities at 24 and 48 h. The biofilm inhibitory concentrations of antibiotics were evaluated for selected biofilm-forming isolates to determine the influence of biofilm on antibiotic tolerance. The impact of biofilm formation on desiccation tolerance was also evaluated for up to 48 days. The results revealed that out of 78 A. baumannii clinical isolates, 83% were MDR and 17% non-MDR. Overall, 79% of isolates formed high biofilm after 24 h. The extent of biofilm formation gets significantly increased after 48 h, and 87% of isolates formed high biofilm. It was observed that eradicating mature biofilm requires up to a thousandfold higher concentration of antibiotics than MICs, and biofilm-forming isolates can survive for a prolonged period under desiccation. In conclusion, our findings revealed that both MDR and non-MDR isolates of A. baumannii could form biofilms on abiotic surfaces. A. baumannii biofilms contribute to endurance in the presence of antimicrobials and desiccation conditions, which are significant trouble for hospital patient care management. The present findings may offer insights for developing preventive measures to tackle biofilm-associated A. baumannii infection.

Biofilm characteristics and transcriptomic profiling of Acinetobacter johnsonii defines signatures for planktonic and biofilm cells

Most bacteria in the natural environment have a biofilm mode of life, which is intrinsically tolerant to antibiotics. While until now, the knowledge of biofilm formation by Acinetobacter johnsonii is not well understood. In this study, the characteristics and the effect of a sub-inhibitory concentration of antibiotic on A. johnsonii biofilm and planktonic cells were determined. We discovered a positive relationship between biofilm formation and tetracycline resistance, and biofilms rapidly evolve resistance to tetracycline they are treated with. Persister cells commonly exist in both planktonic and biofilm cells, with a higher frequency in the latter. Further transcriptomic analysis speculates that the overexpression of multidrug resistance genes and stress genes were mainly answered to sub lethal concentration of tetracycline in planktonic cells, and the lower metabolic levels after biofilm formation result in high resistance level of biofilm cells to tetracycline. Altogether, these data suggest that A. johnsonii can adjust its phenotype when grown as biofilm and change its metabolism under antibiotic stress, and provide implications for subsequent biofilm control.

Development and Evaluation of Duplex MIRA-qPCR Assay for Simultaneous Detection of Staphylococcus aureus and non-aureus Staphylococci

Staphylococcus spp., especially Staphylococcus aureus (S. aureus), is an important pathogen in hospital-acquired infection and food poisoning. Here, we developed a multienzyme isothermal rapid amplification combined with duplex quantitative PCR (duplex MIRA-qPCR) method, which can simultaneously detect the S. aureus species-specific conserved gene FMN-bgsfp and the Staphylococcus genus-specific conserved gene tuf. This assay enabled the amplification of DNA within 20 min at a constant temperature of 39 °C. Specificity analysis indicated that all nine common Staphylococcus species were positive and non-Staphylococcus spp. were negative for tuf gene, whereas S. aureus was positive, non-aureus Staphylococci species and non-Staphylococcus spp. were negative for FMN-bgsfp gene, suggesting that duplex MIRA-qPCR exhibited high specificity. Meanwhile, the sensitivity was tested and the limit of detection (LoD) was 3 × 102 CFU/mL. The coefficient variation values ranged from 0.13% to 2.09%, indicating that the assay had good repeatability. Furthermore, all the nine common Staphylococcus species (including S. aureus) could be detected from four kinds of simulated samples and the LoD of S. aureus was 8.56 × 103 CFU/mL. In conclusion, the duplex MIRA-qPCR has advantages of stronger specificity, lower detection threshold, shorter detection time, and simpler operation, which is an effective tool to detect S. aureus and non-aureus Staphylococci spp. infections rapidly.

Antibacterial and Antibiofilm Activities of Novel Cyclic Peptides against Methicillin-Resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) has led to serious infections, especially in hospitals and clinics, where treatment and prevention have become more difficult due to the formation of biofilms. Owing to biofilm-derived antibiotic tolerance, the currently available traditional antibiotics have failed to treat MRSA infections. Hence, there is a urgent need to develop novel antibiotics for treating life-threatening MRSA infections. Lugdunin (cyclic peptide-1), a nonribosomal cyclic peptide produced by Staphylococcus lugdunensis, exhibits potent antimicrobial activity against MRSA. Amazingly, cyclic peptide-1 and its analogues cyclic peptide-11 and cyclic peptide-14 have the ability to disperse mature MRSA biofilms and show anti-clinical MRSA activity, including MRSA persister cells. In addition, these three cyclic peptide compounds have non-toxicity, lower hemolytic activity and lack of resistance development. Our results indicate that cyclic peptide-1, cyclic peptide-11, and cyclic peptide-14 have great potential as new antimicrobial drug candidates for the treatment of clinical MRSA infections.

Lyophilized Human Bone Allograft as an Antibiotic Carrier: An In Vitro and In Vivo Study

Background: Antibiotics delivered from implanted bone substitute materials (BSM) can potentially be used to prevent acute infections and biofilm formation, providing high concentrations of antibiotics at the surgical site without systemic toxicity. In addition, BSM should allow osteoconductivity supporting bone healing without further surgery. Promising results have been achieved using lyophilized bone allografts mixed with antibiotics. Methods: In this study specially prepared human bone allografts were evaluated as an antibiotic carrier in vitro and in vivo. The efficacy of different antibiotic-impregnated bone allografts was measured by drug release tests in vitro and in vivo and bacterial susceptibility tests using four bacterial species usually responsible for implant-associated infections. Results: The loading procedures of allograft bone substitutes with antibiotics were successful. Some of the antibiotic concentrations exceeded the MIC90 for up to 7 days in vitro and for up to 72 h in vivo. The susceptibility tests showed that S. epidermidis ATCC 12228 was the most susceptible bacterial species in comparison to the other strains tested for all antibiotic substances. Vancomycin and rifampicin showed the best results against standard and patient-isolated strains in vitro. In vivo, new bone formation was comparable in all study groups including the control group without antibiotic loading. Conclusions: Human bone allografts showed the capacity to act as customized loaded antibiotic carriers to prevent acute infections and should be considered in the management of bone infections in combination with systemic antimicrobial therapy.

Potentiating hypoxic microenvironment for antibiotic activation by photodynamic therapy to combat bacterial biofilm infections

Traditional antibiotic treatment has limited efficacy for the drug-tolerant bacteria present in biofilms because of their unique metabolic conditions in the biofilm infection microenvironment. Modulating the biofilm infection microenvironment may influence the metabolic state of the bacteria and provide alternative therapeutic routes. In this study, photodynamic therapy is used not only to eradicate methicillin-resistant Staphylococcus aureus biofilms in the normoxic condition, but also to potentiate the hypoxic microenvironment, which induces the anaerobic metabolism of methicillin-resistant Staphylococcus aureus and activates the antibacterial activity of metronidazole. Moreover, the photodynamic therapy-activated chemotherapy can polarize the macrophages to a M2-like phenotype and promote the repair of the biofilm infected wounds in mice. This biofilm infection microenvironment modulation strategy, whereby the hypoxic microenvironment is potentiated to synergize photodynamic therapy with chemotherapy, provides an alternative pathway for efficient treatment of biofilm-associated infections.

Bacteria in biofilms present unique metabolic conditions that limit the traditional antibiotic treatment. Here, the authors show a photodynamic therapy-activated chemotherapy potentiating the hypoxia of biofilms of methicillin-resistant Staphylococcus aureus, by developing hyaluronic acid nanoparticles functionalized with chlorin e6 and metronidazole.

GANAB and N-Glycans Substrates Are Relevant in Human Physiology, Polycystic Pathology and Multiple Sclerosis: A Review

Glycans are one of the four fundamental macromolecular components of living matter, and they are highly regulated in the cell. Their functions are metabolic, structural and modulatory. In particular, ER resident N-glycans participate with the Glc3Man9GlcNAc2 highly conserved sequence, in protein folding process, where the physiological balance between glycosylation/deglycosylation on the innermost glucose residue takes place, according GANAB/UGGT concentration ratio. However, under abnormal conditions, the cell adapts to the glucose availability by adopting an aerobic or anaerobic regimen of glycolysis, or to external stimuli through internal or external recognition patterns, so it responds to pathogenic noxa with unfolded protein response (UPR). UPR can affect Multiple Sclerosis (MS) and several neurological and metabolic diseases via the BiP stress sensor, resulting in ATF6, PERK and IRE1 activation. Furthermore, the abnormal GANAB expression has been observed in MS, systemic lupus erythematous, male germinal epithelium and predisposed highly replicating cells of the kidney tubules and bile ducts. The latter is the case of Polycystic Liver Disease (PCLD) and Polycystic Kidney Disease (PCKD), where genetically induced GANAB loss affects polycystin-1 (PC1) and polycystin-2 (PC2), resulting in altered protein quality control and cyst formation phenomenon. Our topics resume the role of glycans in cell physiology, highlighting the N-glycans one, as a substrate of GANAB, which is an emerging key molecule in MS and other human pathologies.

Artificial Lipids and Macrophage Membranes Coassembled Biomimetic Nanovesicles for Antibacterial Treatment

Tissue bacterial infections are a major pathological factor in many diseases. Effects on this aspect are in focus for the development of coordinated therapeutic strategies for bacterial killing and anti-inflammation. Here, inspired by the biodetoxification capacity of immune cells, multifunctional biomimetic nanovesicles (MϕM-LPs) that are co-assembled by macrophage membranes and artificial lipids to deliver antibiotics for treating bacterial infections, are presented. The macrophage membrane endows the MϕM-LPs with the capacity of lipopolysaccharide and inflammatory cytokine neutralization, while the artificial lipid membrane can be further engineered to increase the fluidity and anchor to bacteria. In addition, the MϕM-LPs can deliver sufficient ciprofloxacin with controllable release to accomplish an excellent antibacterial activity and biodetoxification capacity in vitro. Based on these advantages, it is demonstrated in a mouse model of Staphylococcus aureus (S. aureus) focal infection, that a single injection of the biomimetic nanovesicles can effectively anchor to and eliminate S. aureus in the infected tissue and reduce inflammatory cytokine levels. Thus, the tissue regeneration and collagen deposition can be accelerated. These results indicate the potential values of integrating natural and artificial membrane materials as a multifunctional biomimetic drug delivery system to treat bacterial infections.

Nanotechnologies for control of pathogenic microbial biofilms

Biofilms are formed at interfaces by microorganisms, which congregate in microstructured communities embedded in a self-produced extracellular polymeric substance (EPS). Biofilm-related infections are problematic due to the high resistance towards most clinically used antimicrobials, which is associated with high mortality and morbidity, combined with increased hospital stays and overall treatment costs. Several new nanotechnology-based approaches have recently been proposed for targeting resistant bacteria and microbial biofilms. Here we discuss the impacts of biofilms on healthcare, food processing and packaging, and water filtration and distribution systems, and summarize the emerging nanotechnological strategies that are being developed for biofilm prevention, control and eradication. Combination of novel nanomaterials with conventional antimicrobial therapies has shown great potential in producing more effective platforms for controlling biofilms. Recent developments include antimicrobial nanocarriers with enzyme surface functionality that allow passive infection site targeting, degradation of the EPS and delivery of high concentrations of antimicrobials to the residing cells. Several stimuli-responsive antimicrobial formulation strategies have taken advantage of the biofilm microenvironment to enhance interaction and passive delivery into the biofilm sites. Nanoparticles of ultralow size have also been recently employed in formulations to improve the EPS penetration, enhance the carrier efficiency, and improve the cell wall permeability to antimicrobials. We also discuss antimicrobial metal and metal oxide nanoparticle formulations which provide additional mechanical factors through externally induced actuation and generate reactive oxygen species (ROS) within the biofilms. The review helps to bridge microbiology with materials science and nanotechnology, enabling a more comprehensive interdisciplinary approach towards the development of novel antimicrobial treatments and biofilm control strategies.

Green Biosynthesis of Selenium Nanoparticles Using Orange Peel Waste: Characterization, Antibacterial and Antibiofilm Activities against Multidrug-Resistant Bacteria

There is an increase of pathogenic multidrug-resistant bacteria globally due to the misuse of antibiotics. Recently, more scientists used metal nanoparticles to counteract antibacterial resistance. In this study, orange peel waste (OPW) was used for selenium nanoparticles’ (Se-NPs) biosynthesis through the green and ecofriendly method, and their applications as antibacterial and antibiofilm agents. Green biosynthesized Se-NPs were characterized using FTIR, XRD, SEM, EDAX, and TEM. Characterization results revealed that biosynthesized Se-NPs were highly crystalline, spherical, and polydisperse, and had sizes in the range of 16–95 nm. The biosynthesized Se-NPs were evaluated as antibacterial and antibiofilm activities against multidrug-resistant bacteria. Results illustrated that Se-NPs exhibited potential antibacterial activity against Gram-positive bacteria (S. aureus ATCC 29213 and biofilm-producing clinical isolates of S. aureus) and Gram-negative bacteria (Pseudomonas aeruginosa PAO1, MDR, biofilm, and quorum-sensing and producing clinical isolates of MDR P. aeruginosa, MDR E. coli, and K. pneumonia). Moreover, results illustrated that S. aureus ATCC 29213 was the most sensitive bacteria to Se-NPs at 1000 µg/mL, where the inhibition zone was 35 mm and MIC was 25 µg/mL. Furthermore, Se-NPs at 0.25 and 0.5 MIC decreased the biofilm significantly. The largest inhibition of biofilm was noticed in MDR K. pneumonia, which was 62% and 92% at 0.25 and 0.5 MIC, respectively. In conclusion, Se-NPs were successfully biosynthesized using OPW through the green method and had promising antibacterial and antibiofilm activity against multidrug-resistant bacteria, which can be used later in fighting resistant bacteria.

Cytocompatible Amphipathic Carbon Quantum Dots as Potent Membrane-Active Antibacterial Agents with Low Drug Resistance and Effective Inhibition of Biofilm Formation

It is very challenging to design nanomaterials with both excellent antibacterial activity and cytocompatibility when facing bacterial infection. Here, inspired by antimicrobial peptides (AMPs), we fabricate carbon quantum dots (CQDs) derived from hydrophobic tryptophan and hydrophilic lysine or arginine (Lys/Trp-CQDs and Arg/Trp-CQDs), which possess amphipathic properties. These CQDs could effectively destroy bacterial membranes without developing resistance, inhibit biofilms formed by Staphylococcus aureus, and exhibit good in vitro biocompatibility. The antibacterial activities are caused by not only surface cationic structures and excess intracellular reactive oxygen species (ROS) generated by the CQDs but also the effects of the surface hydrophobic groups. These combined mechanisms of actions lead to bacterial membrane disruption, which raises the hope for combating bacterial infection without concern about drug resistance. What's more, the effect of amphiphilicity on balancing sterilization with biocompatibility expands the research ideas for developing available antibacterial nanomaterials.

Probing the growth and mechanical properties of Bacillus subtilis biofilms through genetic mutation strategies

Bacterial communities form biofilms on various surfaces by synthesizing a cohesive and protective extracellular matrix, and these biofilms protect microorganisms against harsh environmental conditions. Bacillus subtilis is a widely used experimental species, and its biofilms are used as representative models of beneficial biofilms. Specifically, B. subtilis biofilms are known to be rich in extracellular polymeric substances (EPS) and other biopolymers such as DNA and proteins like the amyloid protein TasA and the hydrophobic protein BslA. These materials, which form an interconnected, cohesive, three-dimensional polymer network, provide the mechanical stability of biofilms and mediate their adherence to surfaces among other functional contributions. Here, we explored how genetically-encoded components specifically contribute to regulate the growth status, mechanical properties, and antibiotic resistance of B. subtilis biofilms, thereby establishing a solid empirical basis for understanding how various genetic engineering efforts are likely to affect the structure and function of biofilms. We noted discrete contributions to biofilm morphology, mechanical properties, and survival from major biofilm components such as EPS, TasA and BslA. For example, EPS plays an important role in maintaining the stability of the mechanical properties and the antibiotic resistance of biofilms, whereas BslA has a significant impact on the resolution that can be obtained for printing applications. This work provides a deeper understanding of the internal interactions of biofilm components through systematic genetic manipulations. It thus not only broadens the application prospects of beneficial biofilms, but also serves as the basis of future strategies for targeting and effectively removing harmful biofilms.

Antibiofilm properties of Clitoria ternatea flower anthocyanin-rich fraction towards Pseudomonas aeruginosa

In Asia, Clitoria ternatea flowers are commonly used as a traditional medicinal herb and as a food colourant. Their bioactive compounds have anti-inflammatory, anti-microbial and anti-biofilm activities. Pseudomonas aeruginosa is one of the major pathogens that cause biofilm-associated infections resulting in an increase in antimicrobial resistance. Hence, the aim of this study was to investigate if the anti-biofilm properties of the anthocyanin-rich fraction of C. ternatea flowers were effective against P. aeruginosa . The effect of the anthocyanin-rich fraction of C. ternatea flowers on P. aeruginosa biofilms formed on a polystyrene surface was determined using the crystal violet assay and scanning electron microscopy (SEM). The anthocyanin-rich fraction reduced biofilm formation by four P. aeruginosa strains with a minimum biofilm inhibitory concentration value ranging between 0.625 and 5.0 mg ml−1. We further show that the biofilm-inhibiting activity of C. ternatea flowers is not due to the flavonols but is instead attributed to the anthocyanins, which had significant biofilm inhibitory activity (64.0±1.1 %) at 24 h in a time–response study. The anthocyanin-rich fraction also significantly reduced bacterial attachment on the polystyrene by 1.1 log c.f.u. cm−2 surface based on SEM analysis. Hence, anthocyanins from C. ternatea flowers have potential as an agent to decrease the risk of biofilm-associated infections.

Effective Therapy of Drug-Resistant Bacterial Infection by Killing Planktonic Bacteria and Destructing Biofilms with Cationic Photosensitizer Based on Phosphindole Oxide

Developing effective therapies to fight against biofilm-associated infection is extremely urgent. The complex environment of biofilm forces the bacteria to evade the elimination of antibiotics, resulting in recalcitrant chronic infections. To address this issue, a cationic antibacterial agent based on phosphindole oxide (β-PM-PIO) is designed and prepared. The unique molecular structure endows β-PM-PIO with aggregation-induced emission feature and efficient singlet oxygen generation ability. β-PM-PIO shows excellent visual diagnostic function to planktonic bacteria and biofilm. In addition, owing to the synergistic effect of phototoxicity and dark toxicity, β-PM-PIO can achieve superb antibacterial and antibiofilm performance against Gram-positive bacteria with less potential of developing drug resistance. Notably, β-PM-PIO also holds excellent anti-infection capacity against drug-resistant bacteria in vivo with negligible side effects. This work offers a promising platform to develop advanced antibacterial agents against multidrug-resistant bacterial infection.

Antimicrobial Resistance of Tannin Extract against E. coli Isolates from Sheep

Plants have been long valuable sources of natural materials that have served to preserve human and animal health; as a result, pharmacological purposes have arisen from the use of plant compounds in most countries, according to a World Health Organization report. The present study aimed to assess the antimicrobial resistance of tannin extract against Escherichia coli (E. coli) isolates in sheep. A total of 100 samples from sheep were used to isolate E. coli and treated with tannin extract (90% purity) to investigate the in vitro effect, as compared to some antibiotics (Clindamycin, Cephalexin, Kanamycin, Tetracycline, and Vancomycin). The bacterial samples were cultured in a selective and differential medium, and Gram staining was used to examine them. The biochemical assays were performed to purify and expose these cultures; moreover, the API 20E system and Rapid^TM ONE kits were utilized to confirm the bacterial strain. Based on the findings, 50% of the samples showed a positive result for the presence of E. coli. The well diffusion technique was used to investigate the antibacterial activity to confirm the antibacterial action of tannin extract (from pomegranate peel) in different concentrations against E. coli. The highest zone of inhibition for the bacteria ranged from 12±0.5 to 30.3±0.2 at 50% concentrations, proving that tannins extract was significantly effective against E. coli. The presence of E. coli was detected in 50 % of the samples. The well-diffusion technique was used to evaluate the antimicrobial property of tannin extract through various concentrations with the highest zone of inhibition for the bacteria ranging from 12.5 to 30.30.2 at 50%, demonstrating that tannin extract was significantly effective on E. coli.

Strategies to improve the potency of oxazolidinones towards bacterial biofilms

Biofilms are part of the natural lifecycle of bacteria and are known to cause chronic infections that are difficult to treat. Most antibiotics are developed and tested against bacteria in the planktonic state and are ineffective against bacterial biofilms. The oxazolidinones, including the last resort drug linezolid, are one of the main classes of synthetic antibiotics progressed to clinical use in the last 50 years. They have a unique mechanism of action and only develop low levels of resistance in the clinical setting. With the aim of providing insight into strategies to design more potent antibiotic compounds with activity against bacterial biofilms, we review the biofilm activity of clinically approved oxazolidinones and report on structural modifications to oxazolidinones and their delivery systems which lead to enhanced anti‐biofilm activity.

Synthesis of Metal-Loaded Carboxylated Biopolymers with Antibacterial Activity through Metal Subnanoparticle Incorporation

Carboxymethyl starch (CMS) and carboxymethyl cellulose (CMC) loaded by highly dispersed metal subnanoparticles (MSNPs) showed antibacterial activity against E. coli and B. subtilis strains. Copper and silver were found to act in both cationic and zero-valence forms. The antibacterial activity depends on the metal species content but only up to a certain level. Silver cation (Ag⁺) showed higher antibacterial activity as compared to Ag⁰, which was, however, more effective than Cu⁰, due to weaker retention. The number of carboxyl groups of the biopolymers was found to govern the material dispersion in aqueous media, the metal retention strength and dispersion in the host-matrices. Cation and metal retention in both biopolymers was found to involve interactions with the oxygen atoms of both hydroxyl and carboxyl groups. There exists a ternary interdependence between the Zeta potential (ZP), pH induced by the biocidal agent and its particle size (PS). This interdependence is a key factor in the exchange processes with the surrounding species, including bacteria. Clay mineral incorporation was found to mitigate material dispersion, due to detrimental competitive clay:polymer interaction. This knowledge advancement opens promising prospects for manufacturing metal-loaded materials for biomedical applications.

Bioprospecting the Antibiofilm and Antimicrobial Activity of Soil and Insect Gut Bacteria

Antimicrobial resistance is a growing concern in public health and current research shows an important role for bacterial biofilms in recurrent or chronic infections. New strategies, therefore, are necessary to overcome antimicrobial resistance, through the development of new therapies that could alter or inhibit biofilm formation. In this sense, antibiofilm natural products are very promising. In this work, a bioprospection of antimicrobial and antibiofilm extracts from Uruguayan soil bacteria and insect gut bacteria was carried out. Extracts from extracellular broths were tested for their ability to inhibit planktonic cell growth and biofilm formation. Genomic analysis of Bacillus cereus ILBB55 was carried out. All extracts were able to inhibit the growth of, at least, one microorganism and several extracts showed MICs lower than 500 µg mL⁻¹ against microorganisms of clinical relevance (Staphylococcus aureus, Pseudomonas aeruginosa, and Enterobacter cloacae). Among the extracts evaluated for biofilm inhibition only ILBB55, from B. cereus, was able to inhibit, S. aureus (99%) and P. aeruginosa (62%) biofilms. Genomic analysis of this strain showed gene clusters similar to other clusters that code for known antimicrobial compounds. Our study revealed that extracts from soil bacteria and insect gut bacteria, especially from B. cereus ILBB55, could be potential candidates for drug discovery to treat infectious diseases and inhibit S. aureus and P. aeruginosa biofilms.

Imaging and characterization of transitions in biofilm morphology via anomalous diffusion following environmental perturbation

Microorganisms form macroscopic structures for the purpose of environmental adaptation. Sudden environmental perturbations induce dynamics that cause bacterial biofilm morphology to transit to another equilibrium state, thought to be related to anomalous diffusion processes. Here, detecting the super-diffusion characteristics would offer a long-sought goal for a rapid detection method of biofilm phenotypes based on their dynamics, such as growth or dispersal. In this paper, phase-sensitive Doppler optical coherence tomography (OCT) and dynamic light scattering (DLS) are combined to demonstrate wide field-of-view and label-free internal dynamic imaging of biofilms. The probability density functions (PDFs) of phase displacement of the backscattered light and the dynamic characteristics of the PDFs are estimated by a simplified mixed Cauchy and Gaussian model. This model can quantify the super-diffusion state and estimate the dynamic characteristics and macroscopic responses in biofilms that may further describe dispersion and growth in biofilm models.

Electrospinning of antibacterial and anti-inflammatory Ag@hesperidin core-shell nanoparticles into nanofibers used for promoting infected wound healing

Bacterial infection and excessive inflammation are still the main obstacles to wound repair. Thus, antibacterial and anti-inflammation nanomaterials are always attracting for infected wound healing. In this work, ultra-uniform (∼20 nm) and colloidally stable Ag nanoparticles (Ag-Hes NPs) with core-shell structure were prepared by using hesperidin as reducing and caping agent. The obtained Ag-Hes NPs present effective antibacterial properties on both S. aureus and E. coli. Ag-Hes NPs also got high DPPH (1,1-Diphenyl-1-picrylhydrazyl) scavenging capability of 69%. Under the package of polyvinyl alcohol and sodium alginate, Ag-Hes NPs were encapsulated into electro spun nanofibers to form hydrogel (Ag-Hes@H). This strategy provides a moisture environment which could enrich and release Ag-Hes NPs gradually. Cell experiments and animal wound healing investigation proved that Ag-Hes@H could promote the proliferation and migration of HUVECS cells and accelerate infected wound healing. Meanwhile, Ag-Hes@H significantly reduced the expression of inflammatory cytokines, including IL-6, MMP9, and TNF-α. Immunohistochemistry data further suggested that Ag-Hes@H accelerated wound closure by promoting collagen deposition and skin cell proliferation. The designed antibacterial and anti-inflammatory Ag-Hes@H has great potential for promoting infected wound healing.

Manganese oxide nanomaterials for bacterial infection detection and therapy

Bacterial infection has received substantial attention and poses a serious threat to human health. Although antibiotics can effectively fight against bacterial infection, the occurrence of antibiotic resistance has become increasingly serious in recent years, which tremendously hinders its clinical application. Consequently, it is urgent to explore novel strategies to achieve efficacious treatment of bacterial diagnosis and detection. Manganese dioxide (MnO₂) nanomaterial has been extensively reported in tumor therapy. Nevertheless, there are few antibacterial reviews of MnO₂. Herein, we will discuss the applications of MnO₂ in the detection and treatment of bacterial infection, including photodynamic therapy, immunotherapy, improvement of hypoxia, dual-modal combination therapy, reactive oxygen species scavenging, magnetic resonance imaging, optical application of acoustic imaging, and so forth. This review is expected to provide meaningful guidance on further research of MnO₂ nanomaterial for antibacterial applications.

Drug Resistance Reversal Potential of Nanoparticles/Nanocomposites via Antibiotic's Potentiation in Multi Drug Resistant P. aeruginosa

Bacteria employ numerous resistance mechanisms against structurally distinct drugs by the process of multidrug resistance. A study was planned to discover the antibacterial potential of a graphene oxide nanosheet (GO), a graphene oxide-zinc oxide nanocomposite (GO/ZnO), a graphene oxide-chitosan nanocomposite (GO-CS), a zinc oxide decorated graphene oxide-chitosan nanocomposite (GO-CS/ZnO), and zinc oxide nanoparticles (ZnO) alone and in a blend with antibiotics against a PS-2 isolate of Pseudomonas aeruginosa. These nanocomposites reduced the MIC of tetracycline (TET) from 16 folds to 64 folds against a multidrug-resistant clinical isolate. Efflux pumps were interfered, as evident by an ethidium bromide synergy study with nanocomposites, as well as inhibiting biofilm synthesis. These nanoparticles/nanocomposites also decreased the mutant prevention concentration (MPC) of TET. To the best of our knowledge, this is the first report on nanomaterials as a synergistic agent via inhibition of efflux and biofilm synthesis.