Tolerance and Resistance of Pseudomonas aeruginosa Biofilms to Antimicrobial Agents-How P. aeruginosa Can Escape Antibiotics

Exogenous Nitric Oxide Improves Antibiotic Susceptibility in Resistant Bacteria

Antibiotic resistance in bacteria is a major global threat and a leading cause for healthcare-related morbidity and mortality. Resistant biofilm infections are particularly difficult to treat owing to the protective biofilm matrix, which decreases both antibiotic efficacy and clearance by the host. Novel antimicrobial agents that are capable of eradicating resistant infections are greatly needed to combat the rise of antibiotic-resistant bacteria, particularly in patients with cystic fibrosis who are frequently colonized by multidrug-resistant species. Our research group has developed nitric oxide-releasing biopolymers as alternatives to conventional antibiotics. Here, we show that nitric oxide acts as a broad-spectrum antibacterial agent while also improving the efficacy of conventional antibiotics when delivered sequentially. Alone, nitric oxide kills a broad range of bacteria in planktonic and biofilm form without engendering resistance. In combination with conventional antibiotics, nitric oxide increases bacterial susceptibility to multiple classes of antibiotics and slows the development of antibiotic resistance. We anticipate that the use of nitric oxide in combination with antibiotics may improve the outcome of patients with refractory infections, particularly those that are multidrug-resistant.

It's Not Easy Being Green: A Narrative Review on the Microbiology, Virulence and Therapeutic Prospects of Multidrug-Resistant Pseudomonas aeruginosa

Pseudomonas aeruginosa is the most frequent cause of infection among non-fermenting Gram-negative bacteria, predominantly affecting immunocompromised patients, but its pathogenic role should not be disregarded in immunocompetent patients. These pathogens present a concerning therapeutic challenge to clinicians, both in community and in hospital settings, due to their increasing prevalence of resistance, and this may lead to prolonged therapy, sequelae, and excess mortality in the affected patient population. The resistance mechanisms of P. aeruginosa may be classified into intrinsic and acquired resistance mechanisms. These mechanisms lead to occurrence of resistant strains against important antibiotics-relevant in the treatment of P. aeruginosa infections-such as β-lactams, quinolones, aminoglycosides, and colistin. The occurrence of a specific resistotype of P. aeruginosa, namely the emergence of carbapenem-resistant but cephalosporin-susceptible (Car-R/Ceph-S) strains, has received substantial attention from clinical microbiologists and infection control specialists; nevertheless, the available literature on this topic is still scarce. The aim of this present review paper is to provide a concise summary on the adaptability, virulence, and antibiotic resistance of P. aeruginosa to a readership of basic scientists and clinicians.

Novel phenolic antimicrobials enhanced activity of iminodiacetate prodrugs against biofilm and planktonic bacteria

Prodrugs are pharmacologically attenuated derivatives of drugs that undergo bioconversion into the active compound once reaching the targeted site, thereby maximizing their efficiency. This strategy has been implemented in pharmaceuticals to overcome obstacles related to absorption, distribution, and metabolism, as well as with intracellular dyes to ensure concentration within cells. In this study, we provide the first examples of a prodrug strategy that can be applied to simple phenolic antimicrobials to increase their potency against mature biofilms. The addition of (acetoxy)methyl iminodiacetate groups increases the otherwise modest potency of simple phenols. Biofilm-forming bacteria exhibit a heightened tolerance toward antimicrobial agents, thereby accentuating the need for new antibiotics as well as those, which incorporate novel delivery strategies to enhance activity toward biofilms.

Antifungal strains and gene mapping of secondary metabolites in mangrove sediments from Semarang city and Karimunjawa islands, Indonesia

Infection caused by pathogenic fungal species is one of the most challenging disease to be tackled today. The antifungal bacteria candidate can be found in terrestrial as well as aquatic ecosystems, with mangrove forests being one of them. The purpose of this study is to obtain candidate isolates of antifungal strains with a detection approach and gene mapping simulation of bioactive compounds producers and screening to determine qualitative antifungal activity. The research will be carried out by collecting sediment samples from the mangrove ecosystems of Karimunjawa and Mangkang sub-district of Semarang city, isolating and purifying bacteria with Humic Acid Vitamin Agar (HVA), International Streptomyces Project 1 (ISP 1) and Zobell (Marine Agar). added with antibiotics, qualitative antifungal ability screening of each isolate obtained, detection of the presence of PKS gene and NRPS using special primers using the Polymerase Chain Reaction (PCR) method, and molecular identification of each isolate by 16s rRNA sequencing method. Of the total 59 isolates produced from the sample isolation process, 31 isolates from Karimunjawa sediments and 8 isolates from Semarang sediments showed activity against test pathogenic bacteria, namely Candida albicans, Trichoderma sp., and Aspergillus niger. Detection of Biosynthethic Gene Cluster (BGC) showed that the genes encoding secondary metabolites (NRPS, PKS 1 and PKS 2) were detected in KI 2-2 isolates from Karimunjawa. NRPS were detected only in isolates SP 3-9, SH 3-4, KI 1-6, KI 2-2, KI 2-4. The secondary metabolite-encoding gene, PKS1, was detected in isolates SP 3-5, SP 3-8, KI 2-2. PKS II genes were detected only on isolates SP 2-4, SH 3-8, KI 1-6, KI 2-2, and KI 2-4. Isolate SP 3-5 was revealed as Pseudomonas aeruginosa (93.14%), isolate SP 2-4 was Zhouia amylolytica strain HN-181 (100%) and isolate SP 3-8 was P. aeruginosa strain QK -2 (100%).

Quantitative confocal microscopy and calibration for measuring differences in cyclic-di-GMP signalling by bacteria on biomedical hydrogels

The growth of bacterial biofilms on implanted medical devices causes harmful infections and device failure. Biofilm development initiates when bacteria attach to and sense a surface. For the common nosocomial pathogen Pseudomonas aeruginosa and many others, the transition to the biofilm phenotype is controlled by the intracellular signal and second messenger cyclic-di-GMP (c-di-GMP). It is not known how biomedical materials might be adjusted to impede c-di-GMP signalling, and there are few extant methods for conducting such studies. Here, we develop such a method. We allowed P. aeruginosa to attach to the surfaces of poly(ethylene glycol) diacrylate (PEGDA) hydrogels. These bacteria contained a plasmid for a green fluorescent protein (GFP) reporter for c-di-GMP. We used laser-scanning confocal microscopy to measure the dynamics of the GFP reporter for 3 h, beginning 1 h after introducing bacteria to the hydrogel. We controlled for the effects of changes in bacterial metabolism using a promoterless plasmid for GFP, and for the effects of light passing through different hydrogels being differently attenuated by using fluorescent plastic beads as 'standard candles' for calibration. We demonstrate that this method can measure statistically significant differences in c-di-GMP signalling associated with different PEGDA gel types and with the surface-exposed protein PilY1.

[The problem of global development of antibiotic resistant nosocomial pathogens]

The problem of global expansion of multidrug-resistant nosocomial infections pathogens is under special attention at the moment. Antibiotic resistance increasing give us the limited treatment options. This problem is particularly acute for transplant clinics, because of patients need lifelong immunosuppressive therapy. From the one hand this ensures stable allograft functioning, but from the other increases the risk of severe infectious complications in the postoperative period. The purpose of this article is analysis carbapenem resistance dynamics of Klebsiella spp., Acinetobacter spp., Pseudomonas spp. and Staphylococcus spp. isolated from the blood of recipients of donor organs from 2009 to 2019 in the Shumakov National Medical Research Center of Transplantology and Artificial Organs. A significant annual decrease of carbapenem-sensitive strains of Klebsiella spp. and Acinetobacter spp. are shown. The study of a distinctive pathogen resistance profile specific to each institution can help one in selecting an adequate antimicrobial strategy and is an effective predictive tool for controlling the growth of multidrug-resistant microorganisms.

Airway immunometabolites fuel Pseudomonas aeruginosa infection

Pulmonary infections are associated with a brisk inflammatory reaction to bacterial surface components. Lipopolysaccharides (LPS) trigger macrophage activation and release of mitochondrial metabolites that control the intensity of the immune response. Whereas succinate induces oxidative stress (ROS), HIF1α stabilization, glycolysis and IL-1β release, itaconate suppresses inflammation by inhibiting succinate oxidation, glycolytic flux and promoting anti-oxidant Nrf2-HO-1 functions. P. aeruginosa is a major pathogen associated with acute and chronic lung infection. Although both secreted toxins, LPS and proteases are key factors to establish acute P. aeruginosa pneumonia, lack of these components in chronic P. aeruginosa isolates suggest these organisms exploit other mechanisms to adapt and persist in the lung. Upon inhalation, P. aeruginosa strains trigger airway macrophage reprograming and bacterial variants obtained from acutely and chronically infected subjects exhibit metabolic adaptation consistent with succinate and itaconate assimilation; namely, high expression of extracellular polysaccharides (EPS), reduced lptD-LPS function, increased glyoxylate shunt (GS) activity and substantial biofilm production. In this review we discuss recent findings illustrating how P. aeruginosa induces and adapts to macrophage metabolites in the human lung, and that catabolism of succinate and itaconate contribute to their formidable abilities to tolerate oxidative stress, phagocytosis and immune clearance.

Antimicrobial Susceptibility Testing in Pseudomonas aeruginosa Biofilms: One Step Closer to a Standardized Method

The ability of Pseudomonas aeruginosa to form biofilm during a long-term infection makes it difficult to treat patients correctly. The current clinical antimicrobial susceptibility testing methods are based on the study of planktonic strains. A standardized protocol to analyze the antimicrobial susceptibility in biofilms is necessary for routine laboratories. The aims of this study were to develop a simple biofilm model and to study the antimicrobial susceptibility of P. aeruginosa strains in biofilm growth. Different artificial sputum media, and aerobiosis and microaerobiosis conditions were analyzed using a microtiter plate method and P. aeruginosa PAO1 as reference strain. Planktonic and biofilm antimicrobial susceptibility to cefepime, imipenem, azithromycin, gentamicin, tobramycin, and ciprofloxacin were determined in clinical and non-clinical P. aeruginosa strains. The Synthetic Cystic Fibrosis Medium was proposed as a good medium. The biofilm greatly increased the resistance to tested antimicrobials, except for azithromycin. Cefepime and imipenem showed poor anti-biofilm effect while tobramycin, gentamicin, and ciprofloxacin showed good activity in some strains. Azithromycin showed a better activity in biofilm than in planktonic state when aerobic conditions were used. This study establishes useful information to test antimicrobial susceptibility in P. aeruginosa biofilms, and includes possible antimicrobial options to treat long-term infected patients.

Tackling Pseudomonas aeruginosa Virulence by Mulinane-Like Diterpenoids from Azorella atacamensis

Pseudomonas aeruginosa is an important multidrug-resistant human pathogen by dint of its high intrinsic, acquired, and adaptive resistance mechanisms, causing great concern for immune-compromised individuals and public health. Additionally, P. aeruginosa resilience lies in the production of a myriad of virulence factors, which are known to be tightly regulated by the quorum sensing (QS) system. Anti-virulence therapy has been adopted as an innovative alternative approach to circumvent bacterial antibiotic resistance. Since plants are known repositories of natural phytochemicals, herein, we explored the anti-virulence potential of Azorella atacamensis, a medicinal plant from the Taira Atacama community (Calama, Chile), against P. aeruginosa. Interestingly, A. atacamensis extract (AaE) conferred a significant protection for human lung cells and Caenorhabditis elegans nematodes towards P. aeruginosa pathogenicity. The production of key virulence factors was decreased upon AaE exposure without affecting P. aeruginosa growth. In addition, AaE was able to decrease QS-molecules production. Furthermore, metabolite profiling of AaE and its derived fractions achieved by combination of a molecular network and in silico annotation allowed the putative identification of fourteen diterpenoids bearing a mulinane-like skeleton. Remarkably, this unique interesting group of diterpenoids seems to be responsible for the interference with virulence factors as well as on the perturbation of membrane homeostasis of P. aeruginosa. Hence, there was a significant increase in membrane stiffness, which appears to be modulated by the cell wall stress response ECFσ SigX, an extracytoplasmic function sigma factor involved in membrane homeostasis as well as P. aeruginosa virulence.

Genetic requirements and transcriptomics of Helicobacter pylori biofilm formation on abiotic and biotic surfaces

Biofilm growth is a widespread mechanism that protects bacteria against harsh environments, antimicrobials, and immune responses. These types of conditions challenge chronic colonizers such as Helicobacter pylori but it is not fully understood how H. pylori biofilm growth is defined and its impact on H. pylori survival. To provide insights into H. pylori biofilm growth properties, we characterized biofilm formation on abiotic and biotic surfaces, identified genes required for biofilm formation, and defined the biofilm-associated gene expression of the laboratory model H. pylori strain G27. We report that H. pylori G27 forms biofilms with a high biomass and complex flagella-filled 3D structures on both plastic and gastric epithelial cells. Using a screen for biofilm-defective mutants and transcriptomics, we discovered that biofilm cells demonstrated lower transcripts for TCA cycle enzymes but higher ones for flagellar formation, two type four secretion systems, hydrogenase, and acetone metabolism. We confirmed that biofilm formation requires flagella, hydrogenase, and acetone metabolism on both abiotic and biotic surfaces. Altogether, these data suggest that H. pylori is capable of adjusting its phenotype when grown as biofilm, changing its metabolism, and re-shaping flagella, typically locomotion organelles, into adhesive structures.

Attachment and antibiotic response of early-stage biofilms studied using resonant hyperspectral imaging

Many bacterial species readily develop biofilms that act as a protective matrix against external challenge, e.g., from antimicrobial treatment. Therefore, biofilms are often responsible for persistent and recurring infections. Established methods for studying biofilms are either destructive or focus on the biofilm's surface. A non-destructive method that is sensitive to the underside of the biofilm is highly desirable, as it allows studying the penetration of antibiotics through the film. Here, we demonstrate that the high surface sensitivity of resonant hyperspectral imaging provides this capability. The method allows us to monitor the early stages of Escherichia coli biofilm formation, cell attachment and microcolony formation, in-situ and in real-time. We study the response of the biofilm to a number of different antibiotics and verify our observations using confocal microscopy. Based on this ability to closely monitor the surface-bound cells, resonant hyperspectral imaging gives new insights into the antimicrobial resistance of biofilms.

Multicellular and unicellular responses of microbial biofilms to stress

Biofilms are a ubiquitous mode of microbial life and display an increased tolerance to different stresses. Inside biofilms, cells may experience both externally applied stresses and internal stresses that emerge as a result of growth in spatially structured communities. In this review, we discuss the spatial scales of different stresses in the context of biofilms, and if cells in biofilms respond to these stresses as a collection of individual cells, or if there are multicellular properties associated with the response. Understanding the organizational level of stress responses in microbial communities can help to clarify multicellular functions of biofilms.

A glycoconjugate-based gold nanoparticle approach for the targeted treatment of Pseudomonas aeruginosa biofilms

In this study, "core-shell" gold nanoparticles (AuNPs) have been functionalised using a simple one-pot approach to form fucose-based glycoconjugate AuNPs (Fuc-AuNPs) and galactose-based glycoconjugate AuNPs (Gal-AuNPs), respectively. Owing to the selective carbohydrate-based recognition of the key virulence factors of P. aeruginosa, LecB (fucose-specific lectin)/LecA (galactose-specific lectin), Fuc-AuNPs and Gal-AuNPs-based imaging and therapeutic strategies were evaluated towards P. aeruginosa. Both Fuc-AuNPs and Gal-AuNPs were non-covalently loaded with the fluorophore dicyanomethylene 4H-pyran (DCM) to afford two highly selective fluorescence imaging agents for the visualisation of P. aeruginosa. The loading of Fuc-AuNPs and Gal-AuNPs with the known antibiotic Ceftazidime (CAZ) exhibited an enhanced therapeutic effect, illustrating the significance of this targeted drug delivery strategy. Exploiting the phototherapeutic properties of AuNPs, photoirradiation (600 nm) of Fuc-AuNP@CAZ/Gal-AuNP@CAZ provided both photothermal and photodynamic therapeutic (PTT/PDT) effects, which facilitated the release of CAZ. Fuc-AuNP@CAZ and Gal-AuNP@CAZ were shown to be effective photo/chemotherapeutics resulting in almost complete eradication of P. aeruginosa biofilms formed on clinically relevant surfaces (glass slides and steel surface).

Factors influencing the acquisition and eradication of early Pseudomonas aeruginosa infection in cystic fibrosis

In recent years considerable improvements have been made in increasing the life expectancy of patients with cystic fibrosis. New highly effective modulator therapies targeting the underlying defect in the cystic fibrosis transmembrane conductance regulator protein are expected to enhance lifespan even further. However, chronic Pseudomonas aeruginosa pulmonary infections continue to threaten CF patient lung health and mortality rates. Early and aggressive antibiotic eradication therapies targeting P. aeruginosa are standard practice, but these eradication therapies fail in 10-40% of patients. The reasons for P. aeruginosa eradication failure remain unclear. Thus, this review summarizes the evidence to date for pseudomonal acquisition and eradication failure in the cystic fibrosis lung. A complex combination of host and bacterial factors are responsible for initial establishment of P. aeruginosa pulmonary infections. Moreover, host and pseudomonal factors, polymicrobial interactions, and antimicrobial limitations in relation to P. aeruginosa eradication therapy failure are summarized.

Comparative genomics of the sequential Pseudomonas aeruginosa isolates obtained from the continuous imipenem stress evolution

Pseudomonas aeruginosa is a major opportunistic human pathogen that causes nosocomial infections, and the proportion of carbapenem resistance has recently dramatically increased in P. aeruginosa due to the overuse of them. In this study, strains G10 and G20, with minimum inhibitory concentration (MIC) of imipenem of 16 μg/ml and more than 32 μg/ml, were isolated during continuous subculture of cells exposed to stepwise increasing concentrations of imipenem, respectively. The genomes of G10 and G20 were sequenced and compared with parental strain (P. aeruginosa ATCC 27853, G0). There were 59, 59, and 58 genes involved in antibiotic resistance which were predicted in G0, G10, and G20, respectively, while 374, 366, and 363 genes involved in virulence factors were identified among these three strains. Due to the significantly different MICs of imipenem and highly similar profiles of antibiotic resistance and virulence factors related genes among three strains, the specific genetic variations that occurred were identified and compared, including single nucleotide polymorphisms (SNPs), insertions and deletions (InDels), and structural variations (SVs). The increase in the MIC of imipenem was proposed to be linked to mutations involved in polyamine biosynthesis, biofilm formation, OprD, and efflux pump functions. This study aims to clarify the underlying mechanism of imipenem resistance and provide alternative strategies for reducing resistance in P. aeruginosa. KEY POINTS: • Strains with different imipenem MIC were obtained via laboratory selection evolution. • Whole genomes of two strains with different MIC of imipenem were sequenced. • Underlying mechanism of imipenem resistance was clarified via comparative genomics.

Potential synergistic activity of quercetin with antibiotics against multidrug-resistant clinical strains of Pseudomonas aeruginosa

Development of drug resistance in opportunistic pathogens is one of the major healthcare challenges associated with infection management. Combination therapy has many advantages due to the simultaneous action of two drugs on two separate cellular targets. However, selection of the drugs should offer safety and synergistic interaction against most of the strains. Here, the efficacy of antibiotics in combination with quercetin, a natural flavonoid capable of targeting quorum sensing was tested against biofilm-forming Pseudomonas aeruginosa strains previously isolated from catheter associated urinary tract infection. Based on the antibiotic susceptibility pattern, synergistic effect of quercetin with selected antibiotics (levofloxacin, ceftriaxone, gentamycin, tobramycin and amikacin) was tested at the fractional concentrations of MIC by the checkerboard method and the fractional inhibitory concentration index (FIC_i) was calculated to estimate the synergistic effect. Effect of the synergistic combinations were further tested using time-kill assay, and against biofilm formation and biofilm cell viability. Cytotoxicity assays were performed using Human Embryonic Kidney 293T cells (HEK-293T) using the effective drug combinations with respective controls. The biofilm formation and biofilm cell viability were drastically affected with quercetin and selected antibiotics combinations with ≥80% inhibition. In vitro infection studies showed that all the strains could exert significant cell killing (68 to 85%) and the drug combinations decreased the infection rate significantly by reducing the cell killing effect of P. aeruginosa (p<0.05). The synergistic effect of quercetin is attributed to its quorum sensing inhibitory properties. These findings indicate that quercetin along with existing antibiotics can potentiate the treatment against P. aeruginosa infection and may reduce the selection pressure due to antibiotic overuse.

Natural Anti-biofilm Agents: Strategies to Control Biofilm-Forming Pathogens

Pathogenic microorganisms and their chronic pathogenicity are significant concerns in biomedical research. Biofilm-linked persistent infections are not easy to treat due to resident multidrug-resistant microbes. Low efficiency of various treatments and in vivo toxicity of available antibiotics drive the researchers toward the discovery of many effective natural anti-biofilm agents. Natural extracts and natural product-based anti-biofilm agents are more efficient than the chemically synthesized counterparts with lesser side effects. The present review primarily focuses on various natural anti-biofilm agents, i.e., phytochemicals, biosurfactants, antimicrobial peptides, and microbial enzymes along with their sources, mechanism of action via interfering in the quorum-sensing pathways, disruption of extracellular polymeric substance, adhesion mechanism, and their inhibitory concentrations existing in literature so far. This study provides a better understanding that a particular natural anti-biofilm molecule exhibits a different mode of actions and biofilm inhibitory activity against more than one pathogenic species. This information can be exploited further to improve the therapeutic strategy by a combination of more than one natural anti-biofilm compounds from diverse sources.

Phenotypic and genotypic analysis of biofilm production by Pseudomonas aeruginosa isolates from infection and colonization samples

INTRODUCTION

Pseudomonas aeruginosa is an opportunistic pathogen associated with healthcare-related infections, affecting mainly patients with underlying diseases and immunosuppression. This microorganism has several virulence mechanisms that favour its pathogenesis, including the production of biofilm. This study aimed to analyze the phenotypic production of biofilms, the occurrence of quorum sensing (QS) genes, and the clonal profile of clinical isolates of P. aeruginosa from colonized/infected patients in a tertiary hospital in Recife-PE.

METHODS

We obtained 21 isolates that were classified as infection isolates (II), and 10 colonization isolates (CI). The phenotypic analysis for biofilm production was performed quantitatively. The QS genes were detected by specific PCRs, and the clonal profile was assessed using ERIC-PCR.

RESULTS

Of the 31 isolates, 58.1 % (18/31) were biofilm producers, of which 70 % (7/10) were CI and classified as weakly adherent; 52.4 % (11/21) of the II produced biofilms, and were classified as weak (38.1 %, (8/21)), moderate (9.5 %, (2/21)), and strongly adherent (4.8 %, (1/21)). All isolates harbored the QS genes analyzed. In the clonal analysis, 26 distinct genetic profiles were identified, highlighting the presence of a clone in four samples, i.e., one infection isolate, and 3 colonization isolates.

CONCLUSIONS

The detection of biofilm formation is important in P. aeruginosa in addition to the identification of colonization and infection isolates, especially from complex environments such as ICUs. Further, we define a strategy for monitoring and analyzing P. aeruginosa strains that can potentially cause infections in hospitalized patients.

The Antibacterial and Anti-biofilm Activity of Metal Complexes Incorporating 3,6,9-Trioxaundecanedioate and 1,10-Phenanthroline Ligands in Clinical Isolates of Pseudomonas Aeruginosa from Irish Cystic Fibrosis Patients

Chronic infections of Pseudomonas aeruginosa in the lungs of cystic fibrosis (CF) patients are problematic in Ireland where inherited CF is prevalent. The bacteria’s capacity to form a biofilm in its pathogenesis is highly virulent and leads to decreased susceptibility to most antibiotic treatments. Herein, we present the activity profiles of the Cu(II), Mn(II) and Ag(I) tdda-phen chelate complexes {[Cu(3,6,9-tdda)(phen)₂]·3H₂O·EtOH}_n (Cu-tdda-phen), {[Mn(3,6,9-tdda)(phen)₂]·3H₂O·EtOH}_n (Mn-tdda-phen) and [Ag₂(3,6,9-tdda)(phen)₄]·EtOH (Ag-tdda-phen) (tddaH₂ = 3,6,9-trioxaundecanedioic acid; phen = 1,10-phenanthroline) towards clinical isolates of P. aeruginosa derived from Irish CF patients in comparison to two reference laboratory strains (ATCC 27853 and PAO1). The effects of the metal-tdda-phen complexes and gentamicin on planktonic growth, biofilm formation (pre-treatment) and mature biofilm (post-treatment) alone and in combination were investigated. The effects of the metal-tdda-phen complexes on the individual biofilm components; exopolysaccharide, extracellular DNA (eDNA), pyocyanin and pyoverdine are also presented. All three metal-tdda-phen complexes showed comparable and often superior activity to gentamicin in the CF strains, compared to their activities in the laboratory strains, with respect to both biofilm formation and established biofilms. Combination studies presented synergistic activity between all three complexes and gentamicin, particularly for the post-treatment of established mature biofilms, and was supported by the reduction of the individual biofilm components examined.

Mild magnetic nanoparticle hyperthermia enhances the susceptibility of Staphylococcus aureus biofilm to antibiotics

Objective:

A critical challenge in the treatment of biofilm infection is the capacity of biofilm-grown bacteria to develop resistance to traditional antimicrobial therapies. The objective of this study was to validate the therapeutic potential of magnetic nanoparticle/alternating magnetic field (MNP/AMF) hyperthermia in combination with conventional antibiotics against biofilm infection.

Materials and methods:

The impact of MNP/AMF hyperthermia on the viability of S. aureus biofilm in the absence and presence of antibiotics as well as on the bactericidal activity of macrophages were evaluated at varying conditions of MNPs concentration and AMF intensity using in vitro cell culture models.

Results:

The application of MNP/AMF alone at a CEM43 thermal dose below the threshold for skin tissue exhibited a modest efficacy in the eradication of Staphylococcus aureus (S. aureus) biofilm (<1-log reduction). The treatment of antibiotics (ciprofloxacin, vancomycin) alone at a bactericidal concentration for planktonic S. aureus had no significant effect on the eradication of biofilm phase of S. aureus. However, when the biofilm was pre-exposed to mild MNP/AMF hyperthermia, the treatment of antibiotics could exhibit bactericidal effects against S. aureus biofilm, which was associated with increased uptake of antibiotics to the bacterial cells. Importantly, the application of MNP/AMF could promote the bactericidal activity of macrophages against intracellular bacteria via MNP-dependent generation of reactive oxygen species (ROS).

Conclusion:

Our results validate that the application of mild MNP/AMF hyperthermia within a safe thermal dose threshold is synergistic with conventional antibiotics as well as aids host innate immune response of macrophages for the clearance of intracellular bacteria.

Magnetite enhances anaerobic digestion of high salinity organic wastewater

Biological treatment of high salinity organic wastewater is a significant challenge because many microorganisms involved in the anaerobic digestion process cannot survive high osmotic pressures. In order to alleviate some of the stresses associated with the treatment of high salinity wastewater, two lab-scale up-flow anaerobic sludge bed reactors with or without magnetite (100 g/L) were used to treat high salinity organic wastewater. This study showed that the bioreactor amended with magnetite had higher chemical oxygen demand removal efficiencies (90.2% ± 0.54% vs 73.1% ± 1.9%) and methane production rates (4082 ± 334 ml (standard temperature and atmospheric pressure, STP)/d vs 2640 ± 120 ml (STP)/d) than the non-amended control reactor. In addition, the consumption of volatile fatty acids (20.9 ± 3.4 mM vs 61.7 ± 2.0 mM) was accelerated. Microbial community analysis revealed that the addition of magnetite caused the enrichment of many bacterial genera known to form robust biofilms (i.e. Pseudomonas) that are also capable of extracellular electron transfer and methanogens from the genus Methanosarcina which have been shown to participate in direct interspecies electron transfer. These results show that magnetite addition could enhance the performance of anaerobic digesters treating high salinity wastewater.

Magnetotactic T-Budbots to Kill-n-Clean Biofilms

Treatment of persistent biofilm infections has turned out to be a formidable challenge even with broad-spectrum antibiotic therapies. In this direction, intelligent micromachines may serve as active mechanical means to dislodge such deleterious bacterial communities. Herein, we have designed biocompatible micromotors from tea buds, namely, T-Budbots, which shows the capacity to be magnetically driven on a biofilm matrix and remove or fragment biofilms with precision, as a part of the proposed non-invasive "Kill-n-Clean" strategy. In a way, we present a bactericidal robotic platform decorated with magnetite nanoparticles aimed at clearing in vitro biofilms present on the surfaces. We have also shown that the smart porous T-Budbots can integrate antibiotic ciprofloxacin due to electrostatic interaction on their surface to increase their antibacterial efficacy against dreadful pathogenic bacterial communities of Pseudomonas aeruginosa and Staphylococcus aureus. It is noteworthy that the release of this drug can be controlled by tuning the surrounding pH of the T-Budbots. For example, while the acidic environment of the biofilm facilitates the release of antibiotics from the porous T-Budbots, the drug release was rather minimal at higher pH. The work represents a first step in the involvement of a plant-based microbot exhibiting magneto-robotic therapeutic properties, providing a non-invasive and safe approach to dismantle harmful biofilm infections.

Evaluation of Viable Cells in Pseudomonas aeruginosa Biofilmsby Colony Count and Live/Dead Staining

Pseudomonas aeruginosa is a human pathogen capable to form robust biofilms. P. aeruginosa biofilms represent a serious problem because of the adverse effects on human health and industry, from sanitary and economic points of view. Typical strategies to break down biofilms have been long used, such as the use of disinfectants or antibiotics, but also, according to their high resistance to standard antimicrobial approaches, alternative strategies employing photocatalysis or control of biofilm formation by modifying surfaces, have been proposed. Colony forming units (cfu) counting and live/dead staining, two classic techniques used for biofilm quantification, are detailed in this work. Both methods assess cell viability, a key factor to analyze the microbial susceptibility to given treatment, then, they represent a good approach for evaluation of an antibiofilm strategy.

The Great ESKAPE: Exploring the Crossroads of Bile and Antibiotic Resistance in Bacterial Pathogens

Throughout the course of infection, many pathogens encounter bactericidal conditions that threaten the viability of the bacteria and impede the establishment of infection. Bile is one of the most innately bactericidal compounds present in humans, functioning to reduce the bacterial burden in the gastrointestinal tract while also aiding in digestion. It is becoming increasingly apparent that pathogens successfully resist the bactericidal conditions of bile, including bacteria that do not normally cause gastrointestinal infections. This review highlights the ability of Enterococcus, Staphylococcus, Klebsiella, Acinetobacter, Pseudomonas, Enterobacter (ESKAPE), and other enteric pathogens to resist bile and how these interactions can impact the sensitivity of bacteria to various antimicrobial agents. Given that pathogen exposure to bile is an essential component to gastrointestinal transit that cannot be avoided, understanding how bile resistance mechanisms align with antimicrobial resistance is vital to our ability to develop new, successful therapeutics in an age of widespread and increasing antimicrobial resistance.

Characterization of the Bacterial Biofilm Communities Present in Reverse-Osmosis Water Systems for Haemodialysis

Biofilm in reverse osmosis (RO) membranes is a common problem in water treatment at haemodialysis facilities. Bacteria adhere and proliferate on RO membranes, forming biofilms, obstructing and damaging the membranes and allowing the transfer of bacteria and/or cellular components potentially harmful to the health of haemodialysis patients. Our aim was to characterize the bacterial community associated to biofilm of RO membranes and to identify potentially pathogenic bacteria present in the haemodialysis systems of two dialysis centres in Chile. The diversity of the bacterial communities present on RO membranes and potable and osmosed water samples was evaluated using Illumina sequencing. Additionally, bacteria from potable water, osmosed water and RO membrane samples were isolated, characterized and identified by Sanger’s sequencing. The molecular analyses of metagenomics showed that the phyla having a greater relative abundance in both dialysis centres were Proteobacteria and Planctomycetes. Pseudomonas, Stenotrophomonas, Agrobacterium, Pigmentiphaga, Ralstonia, Arthrobacter, Bacteroides and Staphylococcus were bacterial genera isolated from the different samples obtained at both haemodialysis centres. Pseudomonas spp. was a bacterial genus with greater frequency in all samples. Pseudomonas and Staphylococcus showed higher levels of resistance to the antibiotics tested. Results demonstrated the presence of potentially pathogenic bacteria, showing resistance to antimicrobials on RO membranes and in osmosed water in both dialysis centres studied.

Bidirectional alterations in antibiotics susceptibility in Staphylococcus aureus-Pseudomonas aeruginosa dual-species biofilm

In mixed infections, the bacterial susceptibility differs significantly compared to monocultures of bacteria, and generally the concentrations of antibiotics required for the treatment increases drastically. For S. aureus and P. aeruginosa dual species biofilms, it has been numerously reported that P. aeruginosa decreases S. aureus susceptibility to a broad range of antibiotics, including beta-lactams, glycopeptides, aminoglycosides, macrolides, while sensitizes to quinolones via secretion of various metabolites. Here we show that S. aureus also modulates the susceptibility of P. aeruginosa to antibiotics in mixed cultures. Thus, S. aureus-P. aeruginosa consortium was characterized by tenfold increase in susceptibility to ciprofloxacin and aminoglycosides compared to monocultures. The same effect could be also achieved by the addition of cell-free culture of S. aureus to P. aeruginosa biofilm. Moreover, similar increase in antibiotics efficacy could be observed following addition of S. aureus suspension to the P. aeruginosa mature biofilm, compared to P. aeruginosa monoculture, and vice versa. These findings open promising perspectives to increase the antimicrobial treatment efficacy of the wounds infected with nosocomial pathogens by the transplantation of the skin residential microflora.

Antibiofilm activity of lactoferrin-derived synthetic peptides against Pseudomonas aeruginosa PAO1

Many pathogenic bacteria can protect themselves from the effects of antibiotics and the host immune response system by forming biofilms. Biofilms are polymer-entrapped bacterial cells, which adhere to each other and are often attached to a surface. Eradication of bacterial biofilms typically requires much higher concentrations of antibiotics than are normally needed to kill cultured planktonic cells, raising serious clinical concerns. In an attempt to prevent the formation of biofilms or to break up existing biofilms of pathogenic bacteria, herein we have used the standard crystal violet assay as well as the Calgary biofilm device to test several lactoferrin- and lactoferricin-derived antimicrobial peptides for their antibiofilm activity against Pseudomonas aeruginosa PAO1. Our results revealed that the short bovine lactoferricin-derived RRWQWR-NH₂ (20-25) hexapeptide has no activity against P. aeruginosa PAO1. Moreover, the longer human lactoferricin-derived peptide GRRRRSVQWCA (1-11) and the bovine lactoferrampin (268-284) peptide were also almost devoid of activity. However, several different "mix-and-match" dimeric versions of the two lactoferricin-derived peptides proved quite effective in preventing the formation of biofilms at low concentrations, and in some cases, could even eradicate an existing biofilm. Moreover, the full-length bovine lactoferricinB (17-41) peptide also displayed considerable antimicrobial activity. Some of the longer lactoferricin-derived dimeric peptides acted through a bactericidal mechanism, whereas others seemed to interfere in cell-signalling processes. Taken together, our results indicate that synthetic dimeric peptides comprising short naturally occurring human and bovine lactoferricin constructs could be further developed as antibiofilm agents.

The effect of Cyclic-di-GMP on biofilm formation by Pseudomonas aeruginosa in a novel empyema model

Background

Pseudomonas aeruginosa (P. aeruginosa) is a common pathogenic bacterium which causes pleural empyema, and infection of P. aeruginosa is often associated with biofilm. The aim of this study was to establish a model of rabbit empyema infected by P. aeruginosa to determine whether it causes the formation of biofilm in the pleural cavity. Furthermore, we investigated the effect of cyclic diguanosine monophosphate (c-di-GMP) on biofilm formation in this P. aeruginosa empyema model.

Methods

Twenty rabbits were used and randomly divided into five groups: PAO1, PAO1ΔwspF, and PAO1/p_lac-yhjH infection groups, and Luria-Bertani (LB) broth and turpentine control groups. A drainage catheter was implanted into the pleural cavity through thoracentesis. The three infection groups were respectively infected with PAO1, PAO1ΔwspF, and PAO1/p_lac-yhjH strains, which caused empyema. The two control groups were injected with LB or turpentine. After 4 days of infection, we sacrificed the rabbits. We evaluated the pathology of pleura through hematoxylin-eosin staining. Colony count and crystal violet assay were used to analyze the biofilm formation on the surface of catheters. Scanning electron was used to observe the biofilm on the surface of the pleura. Peptide nucleic acids-fluorescence in situ hybridization (PNA-FISH) was used to observe the biofilm in the fibrinous deposition.

Results

By the PNA-FISH assay, biofilms were observed in the fibrinous deposition of the three infection groups. The red fluorescence area of the PAO1ΔwspF infection group was larger than that of the PAO1 and PAO1/p_lac-yhjH infection groups. Through electron microscopy, we observed that PAO1 strains were embedded in an electron-dense extracellular matrix on the surface of pleural tissue, and appeared to be biofilm-like structures. For the crystal violet assay, the optical density values of different groups were significantly different: PAO1ΔwspF > PAO1 > PAO1/p_lac-yhjH > control groups (P<0.05).

Conclusions

To the best knowledge of the authors, this is the first study to report P. aeruginosa forming biofilm in a novel animal model of pleural empyema. In addition, c-di-GMP signaling molecules played an important role in biofilm formation in the pleural cavity.

Optimization of nitric oxide donors for investigating biofilm dispersal response in Pseudomonas aeruginosa clinical isolates

Pseudomonas aeruginosa biofilms contribute heavily to chronic lung infection in cystic fibrosis patients, leading to morbidity and mortality. Nitric oxide (NO) has been shown to disperse P. aeruginosa biofilms in vitro, ex vivo and in clinical trials as a promising anti-biofilm agent. Traditional NO donors such as sodium nitroprusside (SNP) have been extensively employed in different studies. However, the dosage of SNP in different studies was not consistent, ranging from 500 nM to 500 μM. SNP is light sensitive and produces cyanide, which may lead to data misinterpretation and inaccurate predictions of dispersal responses in clinical settings. New NO donors and NO delivery methods have therefore been explored. Here we assessed 7 NO donors using P. aeruginosa PAO1 and determined that SNP and Spermine NONOate (S150) successfully reduced > 60% biomass within 24 and 2 h, respectively. While neither dosage posed toxicity towards bacterial cells, chemiluminescence assays showed that SNP only released NO upon light exposure in M9 media and S150 delivered much higher performance spontaneously. S150 was then tested on 13 different cystic fibrosis P. aeruginosa (CF-PA) isolates; most CF-PA biofilms were significantly dispersed by 250 μM S150. Our work therefore discovered a commercially available NO donor S150, which disperses CF-PA biofilms efficiently within a short period of time and without releasing cyanide, as an alternative of SNP in clinical trials in the future. KEY POINTS: • S150 performs the best in dispersing P. aeruginosa biofilms among 7 NO donors. • SNP only releases NO in the presence of light, while S150 releases NO spontaneously. • S150 successfully disperses biofilms formed by P. aeruginosa cystic fibrosis clinical isolates.

Tolerance and Persistence of Pseudomonas aeruginosa in Biofilms Exposed to Antibiotics: Molecular Mechanisms, Antibiotic Strategies and Therapeutic Perspectives

Pseudomonas aeruginosa biofilm-related infections are difficult to treat with antibiotics. Along the different layers of the biofilm, the P. aeruginosa population is heterogeneous, exhibiting an extreme ability to adapt his metabolic activity to the local microenvironment. At the deepest layers of the biofilm is a subset of dormant cells, called persister cells. Though antimicrobial failure might be multifactorial, it is now demonstrated that these persister cells, genetically identical to a fully susceptible strain, but phenotypically divergent, are highly tolerant to antibiotics, and contribute to antimicrobial failure. By eradicating susceptible, metabolically active cells, antibiotics bring out pre-existing persister cells. The biofilm mode of growth creates microenvironment conditions that activate stringent response mechanisms, SOS response and toxin-antitoxin systems that render the bacterial population highly tolerant to antibiotics. Using diverse, not standardized, models of biofilm infection, a large panel of antibiotic regimen has been evaluated. They demonstrated that biofilm growth had an unequal impact of antibiotic activity, colistin and meropenem being the less impacted antibiotics. Different combination and sequential antimicrobial therapies were also evaluated, and could be partially efficient, but none succeeded in eradicating persister cells, so that non-antibiotic alternative strategies are currently under development. This article reviews the molecular mechanisms involved in antibiotic tolerance and persistence in P. aeruginosa biofilm infections. A review of the antimicrobial regimen evaluated for the treatment of P. aeruginosa biofilm infection is also presented. While tremendous progress has been made in the understanding of biofilm-related infections, alternative non-antibiotic strategies are now urgently needed.

The Role of Bacterial Biofilm in Antibiotic Resistance and Food Contamination

Biofilm is a microbial association or community attached to different biotic or abiotic surfaces or environments. These surface-attached microbial communities can be found in food, medical, industrial, and natural environments. Biofilm is a critical problem in the medical sector since it is formed on medical implants within human tissue and involved in a multitude of serious chronic infections. Food and food processing surface become an ideal environment for biofilm formation where there are sufficient nutrients for microbial growth and attachment. Therefore, biofilm formation on these surfaces, especially on food processing surface becomes a challenge in food safety and human health. Microorganisms within a biofilm are encased within a matrix of extracellular polymeric substances that can act as a barrier and recalcitrant for different hostile conditions such as sanitizers, antibiotics, and other hygienic conditions. Generally, they persist and exist in food processing environments where they become a source of cross-contamination and foodborne diseases. The other critical issue with biofilm formation is their antibiotic resistance which makes medication difficult, and they use different physical, physiological, and gene-related factors to develop their resistance mechanisms. In order to mitigate their production and develop controlling methods, it is better to understand growth requirements and mechanisms. Therefore, the aim of this review article is to provide an overview of the role of bacterial biofilms in antibiotic resistance and food contamination and emphasizes ways for controlling its production.

Ex Vivo Murine Skin Model for B. burgdorferi Biofilm

Borrelia burgdorferi, the causative agent of Lyme disease, has been recently shown to form biofilm structures in vitro and in vivo. Biofilms are tightly clustered microbes characterized as resistant aggregations that allow bacteria to withstand harsh environmental conditions, including the administration of antibiotics. Novel antibiotic combinations have recently been identified for B. burgdorferi in vitro, however, due to prohibiting costs, those agents have not been tested in an environment that can mimic the host tissue. Therefore, researchers cannot evaluate their true effectiveness against B. burgdorferi, especially its biofilm form. A skin ex vivo model system could be ideal for these types of experiments due to its cost effectiveness, reproducibility, and ability to investigate host-microbial interactions. Therefore, the main goal of this study was the establishment of a novel ex vivo murine skin biopsy model for B. burgdorferi biofilm research. Murine skin biopsies were inoculated with B. burgdorferi at various concentrations and cultured in different culture media. Two weeks post-infection, murine skin biopsies were analyzed utilizing immunohistochemical (IHC), reverse transcription PCR (RT-PCR), and various microscopy methods to determine B. burgdorferi presence and forms adopted as well as whether it remained live in the skin tissue explants. Our results showed that murine skin biopsies inoculated with 1 × 107 cells of B. burgdorferi and cultured in BSK-H + 6% rabbit serum media for two weeks yielded not just significant amounts of live B. burgdorferi spirochetes but biofilm forms as well. IHC combined with confocal and atomic force microscopy techniques identified specific biofilm markers and spatial distribution of B. burgdorferi aggregates in the infected skin tissues, confirming that they are indeed biofilms. In the future, this ex vivo skin model can be used to study development and antibiotic susceptibility of B. burgdorferi biofilms in efforts to treat Lyme disease effectively.

Characterization of Putative Virulence Factors of Pseudomonas aeruginosa Strain RBS Isolated from a Saltern, Tunisia: Effect of Metal Ion Cofactors on the Structure and the Activity of LasB

Pseudomonas aeruginosa is a ubiquitous Gram-negative bacterium able to survive in diverse environments such as soil, plants, freshwater, and seawater. P. aeruginosa can be an opportunistic pathogen to humans when their immune system is deficient. Its pathogenicity may be linked to the production of virulence factors. We isolated P. aeruginosa strain RBS from the saltern of Sfax in Tunisia. In this study, we characterized the halotolerance, antibiotic susceptibility, and some virulence factors of strain RBS. High NaCl concentrations inhibited growth and motility. However, biofilm formation was enhanced to protect bacteria against salt stress. Among the 18 antibiotics tested, quinolones and tetracycline showed a significant inhibitory effect on growth, motility, and biofilm formation of strain RBS. β-Lactams, however, did not have any inhibitory effect on neither bacterial growth nor motility. In some cases, resistance was due, in part, to biofilm formation. We also showed that RBS produces two proteases, LasB and AprA, which have been shown to be implicated in host infection. LasB was further characterized to study the role of metal ions in enzyme stability. It possesses two distinct metal ion-binding sites coordinating a calcium and a zinc ion. The effect of metal ion chelation was evaluated as well as substitutions of residues involved in metal ion binding. Impairing metal ion binding of LasB led to a loss of activity and a sharp decrease of stability. Our findings suggest that the binding of both metal ions is interdependent as the two metal ions' binding sites are linked via a hydrogen bond network.

Use of non-thermal plasma pre-treatment to enhance antibiotic action against mature Pseudomonas aeruginosa biofilms

Non-thermal plasma (NTP), generated at atmospheric pressure by DC cometary discharge with a metallic grid, and antibiotics (gentamicin-GTM, ceftazidime-CFZ and polymyxin B-PMB), either alone or in combination, were used to eradicate the mature biofilm of Pseudomonas aeruginosa formed on Ti-6Al-4V alloy. Our aim was to find the conditions for NTP pre-treatment capable of enhancing the action of the antibiotics and thus reducing their effective concentrations. The NTP treatment increased the efficacy of relatively low concentrations of antibiotics. Generally, the highest effect was achieved with GTM, which was able to suppress the metabolic activity of pre-formed P. aeruginosa biofilms in the concentration range of 4-9 mg/L by up to 99%. In addition, an apparent decrease of biofilm-covered area was confirmed after combined NTP treatment and GTM action by SYTO®13 staining using fluorescence microscopy. Scanning electron microscopy confirmed a complete eradication of P. aeruginosa ATCC 15442 mature biofilm from Ti-6Al-4V alloy when using 0.25 h NTP treatment and subsequent treatment by 8.5 mg/L GTM. Therefore, NTP may be used as a suitable antibiofilm agent in combination with antibiotics for the treatment of biofilm-associated infections caused by this pathogen.

Cystic Fibrosis: Overview of the Current Development Trends and Innovative Therapeutic Strategies

Cystic Fibrosis (CF), an autosomal recessive genetic disease, is caused by a mutation in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR). This mutation reduces the release of chloride ions (Cl-) in epithelial tissues, and hyperactivates the epithelial sodium channels (ENaC) which aid in the absorption of sodium ions (Na+). Consequently, the mucus becomes dehydrated and thickened, making it a suitable medium for microbial growth. CF causes several chronic lung complications like thickened mucus, bacterial infection and inflammation, progressive loss of lung function, and ultimately, death. Until recently, the standard of clinical care in CF treatment had focused on preventing and treating the disease complications. In this review, we have summarized the current knowledge on CF pathogenesis and provided an outlook on the current therapeutic approaches relevant to CF (i.e., CFTR modulators and ENaC inhibitors). The enormous potential in targeting bacterial biofilms using antibiofilm peptides, and the innovative therapeutic strategies in using the CRISPR/Cas approach as a gene-editing tool to repair the CFTR mutation have been reviewed. Finally, we have discussed the wide range of drug delivery systems available, particularly non-viral vectors, and the optimal properties of nanocarriers which are essential for successful drug delivery to the lungs.

Multidrug Resistance (MDR) and Collateral Sensitivity in Bacteria, with Special Attention to Genetic and Evolutionary Aspects and to the Perspectives of Antimicrobial Peptides-A Review

Antibiotic poly-resistance (multidrug-, extreme-, and pan-drug resistance) is controlled by adaptive evolution. Darwinian and Lamarckian interpretations of resistance evolution are discussed. Arguments for, and against, pessimistic forecasts on a fatal “post-antibiotic era” are evaluated. In commensal niches, the appearance of a new antibiotic resistance often reduces fitness, but compensatory mutations may counteract this tendency. The appearance of new antibiotic resistance is frequently accompanied by a collateral sensitivity to other resistances. Organisms with an expanding open pan-genome, such as Acinetobacter baumannii, Pseudomonas aeruginosa, and Klebsiella pneumoniae, can withstand an increased number of resistances by exploiting their evolutionary plasticity and disseminating clonally or poly-clonally. Multidrug-resistant pathogen clones can become predominant under antibiotic stress conditions but, under the influence of negative frequency-dependent selection, are prevented from rising to dominance in a population in a commensal niche. Antimicrobial peptides have a great potential to combat multidrug resistance, since antibiotic-resistant bacteria have shown a high frequency of collateral sensitivity to antimicrobial peptides. In addition, the mobility patterns of antibiotic resistance, and antimicrobial peptide resistance, genes are completely different. The integron trade in commensal niches is fortunately limited by the species-specificity of resistance genes. Hence, we theorize that the suggested post-antibiotic era has not yet come, and indeed might never come.

Recent Advances in Surface Nanoengineering for Biofilm Prevention and Control. Part I: Molecular Basis of Biofilm Recalcitrance. Passive Anti-Biofouling Nanocoatings

Medical device-associated infections are becoming a leading cause of morbidity and mortality worldwide, prompting researchers to find new, more effective ways to control the bacterial colonisation of surfaces and biofilm development. Bacteria in biofilms exhibit a set of "emergent properties", meaning those properties that are not predictable from the study of free-living bacterial cells. The social coordinated behaviour in the biofilm lifestyle involves intricate signaling pathways and molecular mechanisms underlying the gain in resistance and tolerance (recalcitrance) towards antimicrobial agents as compared to free-floating bacteria. Nanotechnology provides powerful tools to disrupt the processes responsible for recalcitrance development in all stages of the biofilm life cycle. The present paper is a state-of-the-art review of the surface nanoengineering strategies currently used to design antibiofilm coatings. The review is structurally organised in two parts according to the targeted biofilm life cycle stages and molecular mechanisms intervening in recalcitrance development. Therefore, in the present first part, we begin with a presentation of the current knowledge of the molecular mechanisms responsible for increased recalcitrance that have to be disrupted. Further, we deal with passive surface nanoengineering strategies that aim to prevent bacterial cells from settling onto a biotic or abiotic surface. Both "fouling-resistant" and "fouling release" strategies are addressed as well as their synergic combination in a single unique nanoplatform.

Helicobacter pylori Biofilm Confers Antibiotic Tolerance in Part via A Protein-Dependent Mechanism

Helicobacter pylori, a WHO class I carcinogen, is one of the most successful human pathogens colonizing the stomach of over 4.4 billion of the world's population. Antibiotic therapy represents the best solution but poor response rates have hampered the elimination of H. pylori. A growing body of evidence suggests that H. pylori forms biofilms, but the role of this growth mode in infection remains elusive. Here, we demonstrate that H. pylori cells within a biofilm are tolerant to multiple antibiotics in a manner that depends partially on extracellular proteins. Biofilm-forming cells were tolerant to multiple antibiotics that target distinct pathways, including amoxicillin, clarithromycin, and tetracycline. Furthermore, this tolerance was significantly dampened following proteinase K treatment. These data suggest that H. pylori adapts its phenotype during biofilm growth resulting in decreased antibiotic susceptibility but this tolerance can be partially ameliorated by extracellular protease treatment.

Clinically Relevant Epithelial Lining Fluid Concentrations of Meropenem with Ciprofloxacin Provide Synergistic Killing and Resistance Suppression of Hypermutable Pseudomonas aeruginosa in a Dynamic Biofilm Model

Treatment of exacerbations of chronic Pseudomonas aeruginosa infections in patients with cystic fibrosis (CF) is highly challenging due to hypermutability, biofilm formation, and an increased risk of resistance emergence. We evaluated the impact of ciprofloxacin and meropenem as monotherapy and in combination in the dynamic in vitro CDC biofilm reactor (CBR). Two hypermutable P. aeruginosa strains, PAOΔmutS (MIC of ciprofloxacin [MIC_{ciprofloxacin}], 0.25 mg/liter; MIC_meropenem, 2 mg/liter) and CW44 (MIC_{ciprofloxacin}, 0.5 mg/liter; MIC_meropenem, 4 mg/liter), were investigated for 120 h. Concentration-time profiles achievable in epithelial lining fluid (ELF) following FDA-approved doses were simulated in the CBR. Treatments were ciprofloxacin at 0.4 g every 8 h as 1-h infusions (80% ELF penetration), meropenem at 6 g/day as a continuous infusion (CI) (30% and 60% ELF penetration), and their combinations. Counts of total and less-susceptible planktonic and biofilm bacteria and MICs were determined. Antibiotic concentrations were quantified by an ultrahigh-performance liquid chromatography photodiode array (UHPLC-PDA) assay. For both strains, all monotherapies failed, with substantial regrowth and resistance of planktonic (≥8 log₁₀ CFU/ml) and biofilm (>8 log₁₀ CFU/cm²) bacteria at 120 h (MIC_{ciprofloxacin}, up to 8 mg/liter; MIC_meropenem, up to 64 mg/liter). Both combination treatments demonstrated synergistic bacterial killing of planktonic and biofilm bacteria of both strains from ∼48 h onwards and suppressed regrowth to ≤4 log₁₀ CFU/ml and ≤6 log₁₀ CFU/cm² at 120 h. Overall, both combination treatments suppressed the amplification of resistance of planktonic bacteria for both strains and of biofilm bacteria for CW44. The combination with meropenem at 60% ELF penetration also suppressed the amplification of resistance of biofilm bacteria for PAOΔmutS Thus, combination treatment demonstrated synergistic bacterial killing and resistance suppression against difficult-to-treat hypermutable P. aeruginosa strains.

Profiling and Role of Bioactive Molecules from Puntius sophore (Freshwater/Brackish Fish) Skin Mucus with Its Potent Antibacterial, Antiadhesion, and Antibiofilm Activities

Epidermal fish mucus comprises of diverse bioactive metabolites which plays an immense role in defense mechanisms and other important cellular activities. Primarily, this study aims to screen the unexplored mucus extract of Puntius sophore(P. sophore) for its antagonistic potential against common pathogens, which are commonly implicated in foodborne and healthcare associated infections, with effects on their adhesion and biofilm formation. Profiling of the skin mucus was carried out by High Resolution-Liquid Chromatography Mass Spectrometry (HR-LCMS), followed by antibacterial activity and assessment of antibiofilm potency and efficacy on the development, formation, and texture of biofilms. Furthermore, bacterial cell damage, viability within the biofilm, checkerboard test, and cytotoxicity were also evaluated. As a result, P. sophore mucus extract was found to be effective against all tested strains. It also impedes the architecture of biofilm matrix by affecting the viability and integrity of bacterial cells within biofilms and reducing the total exopolysaccharide content. A synergy was observed between P. sophore mucus extract and gentamicin for Escherichia coli(E. coli), Pseudomonas aeruginosa(P. aeruginosa), and Bacillus subtilis(B. subtilis), whereas, an additive effect for Staphylococcus aureus(S. aureus). Thus, our findings represent the potent bioactivities of P. sophore mucus extract for the first time, which could be explored further as an alternative to antibiotics or chemically synthesized antibiofilm agents.

Release mechanisms and molecular interactions of Pseudomonas aeruginosa extracellular DNA

Pseudomonas aeruginosa infection is a significant threat for clinicians. Increasing incidents of resistant biofilm infection result in high mortality rates worldwide. There is a considerable current interest in the field of extracellular DNA (eDNA)-mediated P. aeruginosa biofilm formation. eDNA acts as a glue to make biofilm more stable. This review focuses on the diverse mechanisms and factors, which enhance the eDNA release into the extracellular milieu. Furthermore, eDNA-mediated molecular interactions within the biofilm are emphasized. In addition, drug resistance mechanisms due to the versatility of eDNA are discussed. Spatial physiological diversity is expected due to different metabolic activity of bacterial subpopulation present in P. aeruginosa biofilm layers. In P. aeruginosa, eDNA release is accomplished by cell lysis and OMVs (outer membrane vesicles). eDNA release is a spontaneous and multifactorial process, which may be accomplished by PQS, pyocyanin, and lambda prophage induction. Hydrogen peroxide and pyocin trigger cell death, which may facilitate eDNA release. Lung mucosa of cystic fibrosis patients is enriched with eDNA, which acidifies biofilm and develops P. aeruginosa resistance to aminoglycosides. Further studies on spatial and molecular characterization of bacterial subpopulation in biofilm will shed light on eDNA-biofilm interaction more precisely.Key Points• Extracellular DNA (eDNA) is a key component of Pseudomonas aeruginosa biofilm.• P. aeruginosa eDNA acts as a glue to make biofilm more stronger.• Bacterial cell death or lysis may be the potential way to release P. aeruginosa eDNA into extracellular milieu.• P. aeruginosa eDNA contributes to develop resistance to antimicrobials.

Size and Charge Adaptive Clustered Nanoparticles Targeting the Biofilm Microenvironment for Chronic Lung Infection Management

Chronic lung infection caused by bacterial biofilms is an extremely serious clinical problem, which can lead to the failure of antibiotic therapy. Although nanoparticles have shown great potential in the treatment of biofilms, the efficient penetration and retention of nanoparticles in biofilms is still a big challenge. To address this issue, we herein fabricate size and charge adaptive azithromycin (AZM)-conjugated clustered nanoparticles (denoted as AZM-DA NPs) as therapeutic agents for treating biofilms. The AZM-DA NPs are prepared by electrostatic complexation between AZM conjugated amino-ended poly(amidoamine) dendrimer (PAMAM) and 2,3-dimethyl maleic anhydride (DA) modified poly(ethylene glycol)-block-polylysine (PEG-b-PLys). It is noteworthy that the AZM-DA NPs can disassemble in an acidic biofilm microenvironment (pH 6.0), leading to the release of secondary AZM-conjugated PAMAM nanoparticles (PAMAM-AZM NPs). PAMAM-AZM NPs with small size and positive charge are beneficial for improved penetration and retention inside biofilms, enhanced permeabilization of the bacterial membrane, and increased internalization of AZM, thus exhibiting excellent antibiofilm activities. AZM-DA NPs are also favorable as long-term antibacterial agents due to the reduced occurrence of drug resistance. In vivo therapeutic performance is confirmed by the reduced bacterial burden and the alleviated inflammation in the chronic lung infection model. This research not only develops an innovative strategy for antibiotic delivery in vivo but also provides an effective way for the management of biofilm-associated infections, including chronic lung infection.

Beyond Risk: Bacterial Biofilms and Their Regulating Approaches

Bacterial biofilms are complex surface attached communities of bacteria held together by self-produced polymer matrixs mainly composed of polysaccharides, secreted proteins, and extracellular DNAs. Bacterial biofilm formation is a complex process and can be described in five main phases: (i) reversible attachment phase, where bacteria non-specifically attach to surfaces; (ii) irreversible attachment phase, which involves interaction between bacterial cells and a surface using bacterial adhesins such as fimbriae and lipopolysaccharide (LPS); (iii) production of extracellular polymeric substances (EPS) by the resident bacterial cells; (iv) biofilm maturation phase, in which bacterial cells synthesize and release signaling molecules to sense the presence of each other, conducing to the formation of microcolony and maturation of biofilms; and (v) dispersal/detachment phase, where the bacterial cells depart biofilms and comeback to independent planktonic lifestyle. Biofilm formation is detrimental in healthcare, drinking water distribution systems, food, and marine industries, etc. As a result, current studies have been focused toward control and prevention of biofilms. In an effort to get rid of harmful biofilms, various techniques and approaches have been employed that interfere with bacterial attachment, bacterial communication systems (quorum sensing, QS), and biofilm matrixs. Biofilms, however, also offer beneficial roles in a variety of fields including applications in plant protection, bioremediation, wastewater treatment, and corrosion inhibition amongst others. Development of beneficial biofilms can be promoted through manipulation of adhesion surfaces, QS and environmental conditions. This review describes the events involved in bacterial biofilm formation, lists the negative and positive aspects associated with bacterial biofilms, elaborates the main strategies currently used to regulate establishment of harmful bacterial biofilms as well as certain strategies employed to encourage formation of beneficial bacterial biofilms, and highlights the future perspectives of bacterial biofilms.

The Potential of Frog Skin Peptides for Anti-Infective Therapies: The Case of Esculentin-1a(1-21)NH2

Antimicrobial Peptides (AMPs) are the key effectors of the innate immunity and represent promising molecules for the development of new antibacterial drugs. However, to achieve this goal, some problems need to be overcome: (i) the cytotoxic effects at high concentrations; (ii) the poor biostability and (iii) the difficulty in reaching the target site. Frog skin is one of the richest natural storehouses of AMPs, and over the years, many peptides have been isolated from it, characterized and classified into several families encompassing temporins, brevinins, nigrocins and esculentins. In this review, we summarized how the isolation/characterization of peptides belonging to the esculentin-1 family drove us to the design of an analogue, i.e. esculentin-1a(1-21)NH2, with a powerful antimicrobial action and immunomodulatory properties. The peptide had a wide spectrum of activity, especially against the opportunistic Gram-negative bacterium Pseudomonas aeruginosa. We described the structural features and the in vitro/in vivo biological characterization of this peptide as well as the strategies used to improve its biological properties. Among them: (i) the design of a diastereomer carrying Damino acids in order to reduce the peptide's cytotoxicity and improve its half-life; (ii) the covalent conjugation of the peptide to gold nanoparticles or its encapsulation into poly(lactide- co-glycolide) nanoparticles; and (iii) the peptide immobilization to biomedical devices (such as silicon hydrogel contact lenses) to obtain an antibacterial surface able to reduce microbial growth and attachment. Summing up the best results obtained so far, this review traces all the steps that led these frog-skin AMPs to the direction of peptide-based drugs for clinical use.

Inhibition of biofilm and virulence properties of Pseudomonas aeruginosa by sub-inhibitory concentrations of aminoglycosides

Aminoglycosides are a commonly used class of antibiotics; however, their application has been discontinued due to the emergence of multi-drug resistance bacterial strains. In the present study, the subinhibitory concentrations (sub-MIC) of several aminoglycosides were determined and tested as an antibiofilm and for their anti-virulence properties against Pseudomonas aeruginosa PAO1, which is an opportunistic foodborne pathogen. P. aeruginosa PAO1 exhibits multiple mechanisms of resistance, including the formation of biofilm and production of several virulence factors, against aminoglycoside antibiotics. The sub-MIC of these antibiotics exhibited biofilm inhibition of P. aeruginosa in alkaline TSB (pH 7.9). Moreover, various concentrations of these aminoglycosides also eradicate the mature biofilm of P. aeruginosa. In the presence of sub-MIC of aminoglycosides, the morphological changes of P. aeruginosa were found to change from rod-shaped to the filamentous, elongated, and streptococcal forms. Similar growth conditions and sub-MIC of aminoglycosides were also found to attenuate several virulence properties of P. aeruginosa PAO1. Molecular docking studies demonstrate that these aminoglycosides possess strong binding properties with the LasR protein, which is a well-characterized quorum-sensing receptor of P. aeruginosa. The present study suggests a new approach to revitalize aminoglycosides as antibiofilm and antivirulence drugs to treat infections caused by pathogenic bacteria.

Nosocomial outbreak linked to a flexible gastrointestinal endoscope contaminated with an amikacin-resistant ST17 clone of Pseudomonas aeruginosa

Endoscope contamination is infrequent but can be the source of nosocomial infections and outbreaks. In August 2016, an unexpected increase in the incidence of amikacin-resistant P. aeruginosa isolates (AK-Pae) was observed at a tertiary care center in the south of Spain. An epidemiological and microbiological investigation (August-October 2016) was performed to explain this finding. Isolates from clinical and environmental samples (2 endoscopes used for retrograde cholangiopancreatography; ERCP) were identified by MALDI-TOF. Antimicrobial susceptibility testing was performed using the MicroScan system. Whole-Genome-Sequencing (Miseq, Illumina) was performed to determine the resistome and virulome. Clonal relatedness among isolates was assessed by SpeI-PFGE and MLST. A Caenorhabditis elegans killing assay was performed for virulence testing. Biofilm formation was performed using a colorimetric assay. Four of the 5 patients infected and/or colonized with AK-Pae in August 2016 had undergone ERCP ≤5 days before sample collection. Two endoscopes were contaminated with AK-Pae. Isolates from one endoscope showed an identical PFGE pattern to 9 isolates (cluster I) and differed (1-2 bands) to 5 isolates (cluster II). Isolates from these clusters belonged to the ST17 clone. This S17 clone was characterized by its low virulence in the C. elegans killing assay, and its biofilm-forming ability, slightly superior to that of high-risk clones of P. aeruginosa ST175 and ST235. This outbreak was caused by an endoscope used for ERCP contaminated with an invasive, moderately virulent, biofilm-forming AK-Pae ST17 clone, suggesting the possible emergence of a new high-risk lineage of this clone.