Biofilms: Survival and defense strategy for pathogens

Influence of nanoscale-modified apatite-type calcium phosphates on the biofilm formation by pathogenic microorganisms

Nanoparticles (25–50 nm) of chemically modified calcium phosphates Ca10−x−y M ii x Na y (PO4)6−z (CO3) z (OH)2 (M ii  – Cu2+, Zn2+) were synthesized via a wet precipitation method at room temperature. The Fourier-transform infrared spectroscopy data confirmed the partial substitution of PO 4 3 − {\text{PO}}_{4}^{3-} → CO 3 2 − {\text{CO}}_{3}^{2-} (B-type) in apatite-type structure. The influence of prepared phosphates on biofilm formation by pathogenic microorganisms was investigated. It was found that the samples Na+, CO 3 2 − {\text{CO}}_{3}^{2-} -hydroxyapatite (HAP) and Na+, Zn2+, CO 3 2 − {\text{CO}}_{3}^{2-} -HAP (5–20 mM) had the highest inhibitory effect on biofilm formation by Staphylococcus aureus strains. The sample Na+, CO 3 2 − {\text{CO}}_{3}^{2-} -HAP had the slight influence on the formation of the biofilm by Pseudomonas aeruginosa, while for the samples Na+, Cu2+, CO 3 2 − {\text{CO}}_{3}^{2-} -HAP and Na+, Zn2+, CO 3 2 − {\text{CO}}_{3}^{2-} -HAP such an effect was not detected. According to transmission electron microscopy data, a correlation between the activity of synthesized apatite-related modified calcium phosphates in the processes of biofilm formation and their ability to adhere to the surface of bacterial cells was established. The prepared samples can be used for the design of effective materials with antibacterial activity for medicine.

Hydrodynamics and surface properties influence biofilm proliferation

A biofilm is an interface-associated colloidal dispersion of bacterial cells and excreted polymers in which microorganisms find protection from their environment. Successful colonization of a surface by a bacterial community is typically a detriment to human health and property. Insight into the biofilm life-cycle provides clues on how their proliferation can be suppressed. In this review, we follow a cell through the cycle of attachment, growth, and departure from a colony. Among the abundance of factors that guide the three phases, we focus on hydrodynamics and stratum properties due to the synergistic effect such properties have on bacteria rejection and removal. Cell motion, whether facilitated by the environment via medium flow or self-actuated by use of an appendage, drastically improves the survivability of a bacterium. Once in the vicinity of a stratum, a single cell is exposed to near-surface interactions, such as van der Waals, electrostatic and specific interactions, similarly to any other colloidal particle. The success of the attachment and the potential for detachment is heavily influenced by surface properties such as material type and topography. The growth of the colony is similarly guided by mainstream flow and the convective transport throughout the biofilm. Beyond the growth phase, hydrodynamic traction forces on a biofilm can elicit strongly non-linear viscoelastic responses from the biofilm soft matter. As the colony exhausts the means of survival at a particular location, a set of trigger signals activates mechanisms of bacterial release, a life-cycle phase also facilitated by fluid flow. A review of biofilm-relevant hydrodynamics and startum properties provides insight into future research avenues.

Distinct fungal plastisphere across different river functional zones: A watershed scale study

Fungi not only play important roles in biogeochemical processes but also can form biofilm on plastic debris. However, knowledge of structure composition and spatiotemporal pattern of fungal plastisphere on different kinds of plastic debris in river with specific usages, known as river functional zones, is still missing. In this study, we investigated the spatial distribution of the fungal plastisphere across a complete urban river with different functional zones (drinking, farm irrigation, aquaculture, and tail lake). Our research was performed based on both field residual plastic debris collection and a 30-day field in situ incubation experiments. Our study revealed that plastic debris enriched distinct fungal communities (including pathogenic fungi) significantly different from the surrounding water. Tracking the source of the fungi colonized on plastic debris suggested that the fungal taxa colonized on the different kinds of plastic debris were not from the surrounding water. Human activities had considerable effects on the fungal community structure on plastic debris, and the plastisphere fungal community structure strikingly varied across different river functional zones. Plastisphere may be used as an indicator for fungi biogeography and pathogenic fungi pollution in river with different functional zones. These findings are essential for ecological risk assessment and management decisions for pollution control of plastic debris and maintaining ecological health.

Singularities of Pyogenic Streptococcal Biofilms - From Formation to Health Implication

Biofilms are generally defined as communities of cells involved in a self-produced extracellular matrix adhered to a surface. In biofilms, the bacteria are less sensitive to host defense mechanisms and antimicrobial agents, due to multiple strategies, that involve modulation of gene expression, controlled metabolic rate, intercellular communication, composition, and 3D architecture of the extracellular matrix. These factors play a key role in streptococci pathogenesis, contributing to therapy failure and promoting persistent infections. The species of the pyogenic group together with Streptococcus pneumoniae are the major pathogens belonging the genus Streptococcus, and its biofilm growth has been investigated, but insights in the genetic origin of biofilm formation are limited. This review summarizes pyogenic streptococci biofilms with details on constitution, formation, and virulence factors associated with formation.

Conjugated polymer nanostructures displaying highly photoactivated antimicrobial and antibiofilm functionalities

This work reports the use of conjugated polymer nanostructures (CPNs) as photoactivated antimicrobial compounds against Gram-positive and Gram-negative microorganisms. Two representative CPNs of polythiophene (PEDOT) and polyaniline (PANI) were prepared as nanofibres with an average diameter of 40 nm and length in the micrometer range. Both CPNs exhibited strong antimicrobial activity under UVA irradiation with the same fluence rate as the UVA component of the solar spectrum. The effect was tested using the Gram-positive bacteria Staphylococcus aureus and the Gram-negative bacteria Escherichia coli. The reduction of colony forming units (CFUs) reached >6 log for PEDOT concentrations as low as 33 ng mL-1. For PEDOT nanofibers, a complete inhibition of S. aureus and E. coli growth was reached at 883 ng mL-1 and 333 ng mL-1 respectively. The photoactivation effect of PANI nanofibres on S. aureus and E. coli was also high, with a CFU reduction of about 7 log and 4 log respectively for an exposure concentration of 33 ng mL-1. The antimicrobial activity was only high under light irradiation and was almost negligible for bulk PEDOT and PANI. The effect of polymeric nanofibers could be attributed to the photoinduced generation of reactive oxygen species, which may induce cell membrane damage, eventually leading to bacterial impairment and inhibition of their biofilm forming capacity. CPN PEDOT and PANI coatings were able to keep surfaces free of bacterial attachment and growth even after 20 h of previous contact with exponentially growing cultures in the dark. PEDOT and PANI CPNs demonstrated good cytocompatibility with human fibroblasts and the absence of hemolytic activity. The materials demonstrated advantages in terms of broad antibacterial spectrum, biofilm inhibition, and the absence of acute toxicity for biomedical applications.

New developments in anti-biofilm intervention towards effective management of orthopedic device related infections (ODRI's)

Orthopedic device related infections (ODRI's) represent a difficult to treat situation owing to their biofilm based nature. Biofilm infections once established are difficult to eradicate even with an aggressive treatment regimen due to their recalcitrance towards antibiotics and immune attack. The involvement of antibiotic resistant pathogens as the etiological agent further worsens the overall clinical picture, pressing on the need to look into alternative treatment strategies. The present review highlightes the microbiological challenges associated with treatment of ODRI's due to biofilm formation on the implant surface. Further, it details the newer anti-infective modalities that work either by preventing biofilm formation and/or through effective disruption of the mature biofilms formed on the medical implant. The study, therefore aims to provide a comprehensive insight into the newer anti-biofilm interventions (non-antibiotic approaches) and a better understanding of their mechanism of action essential for improved management of orthopedic implant infections.

Photoactive antimicrobial coating based on a PEDOT-fullerene C60 polymeric dyad

A photostable and photodynamic antimicrobial surface was successfully obtained and applied to photoinactivate microorganisms. This approach was based on the synthesis of a fullerene C₆₀ derivative (EDOT-C₆₀) where fullerene C₆₀ is covalently linked to 3,4-ethylenedioxythiophene (EDOT) through a 1,3-dipolar cycloaddition reaction. This dual-functional monomer bears an EDOT center connected via an alkyl chain to a fullerene C₆₀ moiety. In this structure, EDOT acts as an electropolymerizable unit that allows the film formation over conducting substrates, while fullerene C₆₀ performs the photodynamic antimicrobial activity. Electrochemical polymerization of EDOT was used to obtain stable and photodynamic polymeric films (PEDOT-C₆₀) in a controllable procedure. Cyclic voltammetry and UV-visible spectroscopy studies showed that the fullerene C₆₀ units were not altered during the electropolymerization process, obtaining surfaces with high fullerene content. Photobleaching measurements demonstrated that the electropolymerized films were highly photostable. Moreover, photodynamic properties of PEDOT-C₆₀ were compared with fullerene C₆₀ and showed that electrodeposited films were able to generate reactive oxygen species (ROS) through the two photomechanisms, producing singlet molecular oxygen (type II) and superoxide radical anion (type I). All studies demonstrated that fullerene C₆₀ moieties covalently attached to the polymeric matrix mainly conserve the photodynamic characteristics. Hence, photodynamic action sensitized by PEDOT-C₆₀ was assessed in vitro against Staphylococcus aureus. The photosensitized inactivation by the electropolymerized films on bacteria suspensions produced >99.9% reduction in S. aureus survival. Fluorescence microscopy experiments with S. aureus adhered to the PEDOT-C₆₀ surface showed a complete microbe annihilation. Also, the eradication of biofilms formed on PEDOT-C₆₀ surfaces resulted in a photokilling >99.9% after visible light irradiation. Our results demonstrated that these antimicrobial photodynamic polymeric films are a promising and versatile platform to photoinactivate microorganisms and to obtain photostable self-sterilizing surfaces.

A photostable and photodynamic antimicrobial surface was developed. The antimicrobial activity of the material reached outstanding levels of inactivation under different conditions: planktonic suspensions, adhered cells to the surface, and biofilms.

Graphene Oxide Coatings as Tools to Prevent Microbial Biofilm Formation on Medical Device

The clinical challenge on surface engineering of medical devices to prevent microorganisms adhesion and biofilm formation, has become an essential aspect for medical implants. Antibacterial properties of Graphene Oxide (GO) have been demonstrated across a broad spectrum of bacteria, and the different mechanisms of action with which this nanomaterial interacts with the microbial surface have been elucidated in detail. Innovative protective coatings based on graphene film and hydrogel could represent an innovative solution for the prevention of nosocomial pathogens colonization on implantable device. This brief review mainly focuses on the applications of graphene in nanomedicine with a particular deepening on the antibacterial properties of GO and GO-based nanomaterials. In order to evaluate the possible future applications of GO as an anti-biofilm coating material for medical devices, studies on the ability of graphene coated surface to prevent microbial adhesion are also discussed. A concise review on in vitro toxicity and in vivo safety is also presented.

Antibiofilm Activity of Heather and Manuka Honeys and Antivirulence Potential of Some of Their Constituents on the DsbA1 Enzyme of Pseudomonas aeruginosa

Heather honey was tested for its effect on the formation of biofilms by Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, Enterococcus faecalis, Salmonella Enteriditis and Acinetobacter baumanii in comparison with Manuka honey. At 0.25 mg/mL, Heather honey inhibited biofilm formation in S. aureus, A. baumanii, E. coli, S. Enteriditis and P. aeruginosa, but promoted the growth of E. faecalis and K. pneumoniae biofilms. Manuka honey inhibited biofilm formation in K. pneumoniae, E. faecalis, and S. Enteriditis, A. baumanii, E. coli and P. aeruginosa, but promoted S. aureus biofilm formation. Molecular docking with Autodock Vina was performed to calculate the predictive binding affinities and ligand efficiencies of Manuka and Heather honey constituents for PaDsbA1, the main enzyme controlling the correct folding of virulence proteins in Pseudomonas aeruginosa. A number of constituents, including benzoic acid and methylglyoxal, present in Heather and/or Manuka honey, revealed high ligand efficiencies for the target enzyme. This helps support, to some extent, the decrease in P. aeruginosa biofilm formation observed for such honeys.

Targeted Stimuli-Responsive Mesoporous Silica Nanoparticles for Bacterial Infection Treatment

The rise of antibiotic resistance and the growing number of biofilm-related infections make bacterial infections a serious threat for global human health. Nanomedicine has entered into this scenario by bringing new alternatives to design and develop effective antimicrobial nanoweapons to fight against bacterial infection. Among them, mesoporous silica nanoparticles (MSNs) exhibit unique characteristics that make them ideal nanocarriers to load, protect and transport antimicrobial cargoes to the target bacteria and/or biofilm, and release them in response to certain stimuli. The combination of infection-targeting and stimuli-responsive drug delivery capabilities aims to increase the specificity and efficacy of antimicrobial treatment and prevent undesirable side effects, becoming a ground-breaking alternative to conventional antibiotic treatments. This review focuses on the scientific advances developed to date in MSNs for infection-targeted stimuli-responsive antimicrobials delivery. The targeting strategies for specific recognition of bacteria are detailed. Moreover, the possibility of incorporating anti-biofilm agents with MSNs aimed at promoting biofilm penetrability is overviewed. Finally, a comprehensive description of the different scientific approaches for the design and development of smart MSNs able to release the antimicrobial payloads at the infection site in response to internal or external stimuli is provided.

Unraveling Pseudomonas aeruginosa and Candida albicans Communication in Coinfection Scenarios: Insights Through Network Analysis

Modern medicine is currently facing huge setbacks concerning infection therapeutics as microorganisms are consistently knocking down every antimicrobial wall set before them. The situation becomes more worrying when taking into account that, in both environmental and disease scenarios, microorganisms present themselves as biofilm communities that are often polymicrobial. This comprises a competitive advantage, with interactions between different species altering host responses, antimicrobial effectiveness, microbial pathogenesis and virulence, usually augmenting the severity of the infection and contributing for the recalcitrance towards conventional therapy. Pseudomonas aeruginosa and Candida albicans are two opportunistic pathogens often co-isolated from infections, mainly from mucosal tissues like the lung. Despite the billions of years of co-existence, this pair of microorganisms is a great example on how little is known about cross-kingdom interactions, particularly within the context of coinfections. Given the described scenario, this study aimed to collect, curate, and analyze all published experimental information on the molecular basis of P. aeruginosa and C. albicans interactions in biofilms, in order to shed light into key mechanisms that may affect infection prognosis, increasing this area of knowledge. Publications were optimally retrieved from PubMed and Web of Science and classified as to their relevance. Data was then systematically and manually curated, analyzed, and further reconstructed as networks. A total of 641 interactions between the two pathogens were annotated, outputting knowledge on important molecular players affecting key virulence mechanisms, such as hyphal growth, and related genes and proteins, constituting potential therapeutic targets for infections related to these bacterial-fungal consortia. Contrasting interactions were also analyzed, and quorum-sensing inhibition approaches were highlighted. All annotated data was made publicly available at www.ceb.uminho.pt/ISCTD, a database already containing similar data for P. aeruginosa and Staphylococcus aureus communication. This will allow researchers to cut on time and effort when studying this particular subject, facilitating the understanding of the basis of the inter-species and inter-kingdom interactions and how it can be modulated to help design alternative and more effective tailored therapies. Finally, data deposition will serve as base for future dataset integration, whose analysis will hopefully give insights into communications in more complex and varied biofilm communities.

Combined Effect of Naturally-Derived Biofilm Inhibitors and Differentiated HL-60 Cells in the Prevention of Staphylococcus aureus Biofilm Formation

Nosocomial diseases represent a huge health and economic burden. A significant portion is associated with the use of medical devices, with 80% of these infections being caused by a bacterial biofilm. The insertion of a foreign material usually elicits inflammation, which can result in hampered antimicrobial capacity of the host immunity due to the effort of immune cells being directed to degrade the material. The ineffective clearance by immune cells is a perfect opportunity for bacteria to attach and form a biofilm. In this study, we analyzed the antibiofilm capacity of three naturally derived biofilm inhibitors when combined with immune cells in order to assess their applicability in implantable titanium devices and low-density polyethylene (LDPE) endotracheal tubes. To this end, we used a system based on the coculture of HL-60 cells differentiated into polymorphonuclear leukocytes (PMNs) and Staphylococcus aureus (laboratory and clinical strains) on titanium, as well as LDPE surfaces. Out of the three inhibitors, the one coded DHA1 showed the highest potential to be incorporated into implantable devices, as it displayed a combined activity with the immune cells, preventing bacterial attachment on the titanium and LDPE. The other two inhibitors seemed to also be good candidates for incorporation into LDPE endotracheal tubes.

Cochlospermum regium (Schrank) pilger leaf extract inhibit methicillin-resistant Staphylococcus aureus biofilm formation

ETHNOPHARMACOLOGICAL RELEVANCE

Cochlospermum regium, known as "algodãozinho", is an important plant belonging to Brazilian biodiversity used in traditional medicine to treat infections, wounds and skin conditions.

AIM OF THE STUDY

To assess the effects of aqueous and ethanolic extracts from C. regium leaves on methicillin-resistant Staphylococcus aureus planktonic cells and biofilm formation.

MATERIAL AND METHODS

The phytochemical characterization of the extracts was carried out by quantification of flavonoids, phenols and tannins and HPLC-DAD. Minimum inhibitory concentrations, cell viability, and enzyme activity inhibition were determined in planktonic cells exposed to C. regium extracts. The effect of the extracts on biofilms was assessed by quantifying colony-forming units (CFUs) and the extracellular matrix, and by visualizing the biofilm structure using scanning electron microscopy.

RESULTS

Leaf extract contents showed high concentration of phenols and the gallic and ellagic acids were identified. The extracts showed potent antimicrobial activities at concentrations ranging from 62.5-250 μg/mL, and decreased coagulase activity. In addition, the extracts prevented biofilm formation, and the aqueous extract completely inhibited its formation.

CONCLUSIONS

C. regium extracts stand out as promising alternative treatments for the prevention and treatment of methicillin-resistant Staphylococcus aureus infections.

Clarithromycin Exerts an Antibiofilm Effect against Salmonella enterica Serovar Typhimurium rdar Biofilm Formation and Transforms the Physiology towards an Apparent Oxygen-Depleted Energy and Carbon Metabolism

Upon biofilm formation, production of extracellular matrix components and alteration in physiology and metabolism allows bacteria to build up multicellular communities which can facilitate nutrient acquisition during unfavorable conditions and provide protection toward various forms of environmental stresses to individual cells. Thus, bacterial cells within biofilms become tolerant against antimicrobials and the immune system. In the present study, we evaluated the antibiofilm activity of the macrolides clarithromycin and azithromycin. Clarithromycin showed antibiofilm activity against rdar (red, dry, and rough) biofilm formation of the gastrointestinal pathogen Salmonella enterica serovar Typhimurium ATCC 14028 (Nal^r) at a 1.56 μM subinhibitory concentration in standing culture and dissolved cell aggregates at 15 μM in a microaerophilic environment, suggesting that the oxygen level affects the activity of the drug. Treatment with clarithromycin significantly decreased transcription and production of the rdar biofilm activator CsgD, with biofilm genes such as csgB and adrA to be concomitantly downregulated. Although fliA and other flagellar regulon genes were upregulated, apparent motility was downregulated. RNA sequencing showed a holistic cell response upon clarithromycin exposure, whereby not only genes involved in the biofilm-related regulatory pathways but also genes that likely contribute to intrinsic antimicrobial resistance, and the heat shock stress response were differentially regulated. Most significantly, clarithromycin exposure shifted the cells toward an apparent oxygen- and energy-depleted status, whereby the metabolism that channels into oxidative phosphorylation was downregulated, and energy gain by degradation of propane 1,2-diol, ethanolamine and l-arginine catabolism, potentially also to prevent cytosolic acidification, was upregulated. This analysis will allow the subsequent identification of novel intrinsic antimicrobial resistance determinants.

Antimicrobial and Antibiofilm Properties of Graphene Oxide on Enterococcus faecalis

The aim of this study was to evaluate the antibacterial properties of graphene oxide (GO) against Enterococcus faecalis in vitro conditions and when used to coat dentin surface to prevent E. faecalis adhesion. The ATCC strain of E. faecalis 29212 has been used to perform a viability test. The pellet was suspended in ultrapure water, NaCl, PBS buffer, CaCl2 and MgCl2, Luria-Bertani broth solutions. The viability was evaluated by the colony forming unit counting method. Atomic force microscopy images and the measure of surface zeta potential variation were analyzed. Dentin discs were covered with a film of GO (n = 15) or were not treated (n = 15). Bacterial suspension was added to each sample of dentine discs and microbial counts were calculated. Statistically significant differences between two groups were assessed by a two-tailed unpaired t-test. Bacteria cell morphology was investigated with scanning electron microscopy. The highest growth inhibition was obtained in ddH2O and CaCl2 solution while, in PBS and NaCl, GO had poor antibacterial efficacy with a growth enhancing effect in the latter. GO on dentin discs demonstrated high antibacterial activity. GO film has demonstrated acceptable adhesion properties to root dentin and a role in the inhibition of bacterial film proliferation and biofilm formation.

Tackling Multidrug Resistance in Streptococci - From Novel Biotherapeutic Strategies to Nanomedicines

The pyogenic streptococci group includes pathogenic species for humans and other animals and has been associated with enduring morbidity and high mortality. The main reason for the treatment failure of streptococcal infections is the increased resistance to antibiotics. In recent years, infectious diseases caused by pyogenic streptococci resistant to multiple antibiotics have been raising with a significant impact to public health and veterinary industry. The rise of antibiotic-resistant streptococci has been associated to diverse mechanisms, such as efflux pumps and modifications of the antimicrobial target. Among streptococci, antibiotic resistance emerges from previously sensitive populations as result of horizontal gene transfer or chromosomal point mutations due to excessive use of antimicrobials. Streptococci strains are also recognized as biofilm producers. The increased resistance of biofilms to antibiotics among streptococci promote persistent infection, which comprise circa 80% of microbial infections in humans. Therefore, to overcome drug resistance, new strategies, including new antibacterial and antibiofilm agents, have been studied. Interestingly, the use of systems based on nanoparticles have been applied to tackle infection and reduce the emergence of drug resistance. Herein, we present a synopsis of mechanisms associated to drug resistance in (pyogenic) streptococci and discuss some innovative strategies as alternative to conventional antibiotics, such as bacteriocins, bacteriophage, and phage lysins, and metal nanoparticles. We shall provide focused discussion on the advantages and limitations of agents considering application, efficacy and safety in the context of impact to the host and evolution of bacterial resistance.

Anti-biofilm activity of chlorhexidine digluconate against Candida albicans vaginal isolates

OBJECTIVES

Recurrent vulvovaginal candidiasis (RVVC) causes significant morbidity. Candida albicans is the main pathogen associated with both sporadic and recurrent candidiasis. Due to unsatisfactory treatment effect, the impact of chlorhexidine digluconate and fluconazole alone or in combination on C. albicans and biofilm was investigated.

METHODS

Vaginal C. albicans isolates from 18 patients with recurrent candidiasis and commensals from 19 asymptomatic women were isolated by culture. Crystal violet, XTT and colony forming unit assay were used to analyze the effect of chlorhexidine digluconate and fluconazole on growth of C. albicans, formation of new and already established, mature, biofilm.

RESULTS

Fluconazole reduced the growth of planktonic C. albicans. However, in established biofilm, fluconazole had no effect on the candida cells and was not able to disperse and reduce the biofilm. By contrast, chlorhexidine digluconate had a direct killing effect on C. albicans grown both planktonically and in biofilm. Chlorhexidine digluconate also dispersed mature biofilm and inhibited formation of new biofilm. No major differences were observed between commensal isolates and candida causing recurrent vulvovaginitis with respect to biofilm or growth after chlorhexidine digluconate treatment.

CONCLUSION

Biofilm is a problem in patients with recurrent vulvovaginal candidiasis reducing the effect of antifungal treatment. Development of new treatment strategies are urgently needed to decrease the recurrences. In already established biofilm, chlorhexidine digluconate dispersed the biofilm and was more effective in eradicating candida compared to fluconazole. Future treatment strategy may thus be a combination of chlorhexidine digluconate and fluconazole and prophylactic use of chlorhexidine digluconate to prevent biofilm formation and restrict infections.

Real-Time Single-Cell Imaging Reveals Accelerating Lipid Peroxyl Radical Formation in Escherichia coli Triggered by a Fluoroquinolone Antibiotic

The formation of reactive oxygen species (ROS) induced by bactericidal antibiotics has been associated with a common, nonspecific mechanism of cellular death. Herein, we report real-time single-cell fluorescence studies on Escherichia coli stained with a fluorogenic probe for lipid peroxyl radicals showing the generation of this form of ROS when exposed to the minimum inhibitory concentration (MIC) and 10× MIC of the fluoroquinolone antibiotic ciprofloxacin (3 and 30 μM, respectively). Single-cell intensity-time trajectories show an induction period followed by an accelerating phase for cells treated with antibiotic, where initial and maximum intensity achieved following 3.5 h of incubation with antibiotic showed dose-dependent average values. A large fraction of bacteria remains viable after the studies, indicating ROS formation is occurring a priori of cell death. Punctate structures are observed, consistent with membrane blebbing. The addition of a membrane embedding lipid peroxyl radical scavenger, an α-tocopherol analogue, to the media increased the MIC of ciprofloxacin. Lipid peroxyl radical formation precedes E. coli cell death and may be invoked in a cascade event including membrane disruption and consequent cell wall permeabilization. Altogether, our work illustrates that lipid peroxidation is caused by ciprofloxacin in E. coli and suppressed by α-tocopherol analogues. Lipid peroxidation may be invoked in a cascade event including membrane disruption and consequent cell wall permeabilization. Our work provides a methodology to assess antibiotic-induced membrane peroxidation at the single-cell level; this methodology provides opportunities to explore the scope and nature of lipid peroxidation in antibiotic-induced cell lethality.

Staphylococcus aureus ATP Synthase Promotes Biofilm Persistence by Influencing Innate Immunity

Staphylococcus aureus is a major cause of prosthetic joint infection (PJI), which is characterized by biofilm formation. S. aureus biofilm skews the host immune response toward an anti-inflammatory profile by the increased recruitment of myeloid-derived suppressor cells (MDSCs) that attenuate macrophage proinflammatory activity, leading to chronic infection. A screen of the Nebraska Transposon Mutant Library identified several hits in the ATP synthase operon that elicited a heightened inflammatory response in macrophages and MDSCs, including atpA, which encodes the alpha subunit of ATP synthase. An atpA transposon mutant (ΔatpA) had altered growth kinetics under both planktonic and biofilm conditions, along with a diffuse biofilm architecture that was permissive for leukocyte infiltration, as observed by confocal laser scanning microscopy. Coculture of MDSCs and macrophages with ΔatpA biofilm elicited significant increases in the proinflammatory cytokines interleukin 12p70 (IL-12p70), tumor necrosis factor alpha (TNF-α), and IL-6. This was attributed to increased leukocyte survival resulting from less toxin and protease production by ΔatpA biofilm as determined by liquid chromatography with tandem mass spectrometry (LC-MS/MS). The enhanced inflammatory response elicited by ΔatpA biofilm was cell lysis-dependent since it was negated by polyanethole sodium sulfanate treatment or deletion of the major autolysin, Atl. In a mouse model of PJI, ΔatpA-infected mice had decreased MDSCs concomitant with increased monocyte/macrophage infiltrates and proinflammatory cytokine production, which resulted in biofilm clearance. These studies identify S. aureus ATP synthase as an important factor in influencing the immune response during biofilm-associated infection and bacterial persistence.IMPORTANCE Medical device-associated biofilm infections are a therapeutic challenge based on their antibiotic tolerance and ability to evade immune-mediated clearance. The virulence determinants responsible for bacterial biofilm to induce a maladaptive immune response remain largely unknown. This study identified a critical role for S. aureus ATP synthase in influencing the host immune response to biofilm infection. An S. aureus ATP synthase alpha subunit mutant (ΔatpA) elicited heightened proinflammatory cytokine production by leukocytes in vitro and in vivo, which coincided with improved biofilm clearance in a mouse model of prosthetic joint infection. The ability of S. aureus ΔatpA to augment host proinflammatory responses was cell lysis-dependent, as inhibition of bacterial lysis by polyanethole sodium sulfanate or a ΔatpAΔatl biofilm did not elicit heightened cytokine production. These studies reveal a critical role for AtpA in shaping the host immune response to S. aureus biofilm.

Novel Nanotherapeutics as Next-generation Anti-infective Agents: Current Trends and Future Prospectives

With the ever-increasing population and improvement in the healthcare system in the 21st century, the incidence of chronic microbial infections and associated health disorders has also increased at a striking pace. The ability of pathogenic microorganisms to form biofilm matrix aggravates the situation due to antibiotic resistance phenomenon resulting in resistance against conventional antibiotic therapy which has become a public health concern. The canonical Quorum Sensing (QS) signaling system hierarchically regulates the expression of an array of virulence phenotypes and controls the development of biofilm dynamics. It is imperative to develop an alternative, yet effective and non-conventional therapeutic approach, popularly known as "anti-infective therapy" which seems to be interesting. In this regard, targeting microbial QS associated virulence and biofilm development proves to be a quite astonishing approach in counteracting the paucity of traditional antibiotics. A number of synthetic and natural compounds are exploited for their efficacy in combating QS associated microbial infections but the bioavailability and biocompatibility limit their widespread applications. In this context, the nanotechnological intervention offers a new paradigm for widespread biomedical applications starting from targeted drug delivery to diagnostics for the diagnosis and treatment of infectious diseases, particularly to fight against microbial infections and antibiotics resistance in biofilms. A wide range of nanomaterials ranging from metallic nanoparticles to polymeric nanoparticles and recent advances in the development of carbon-based nanomaterials such as Carbon Nanotubes (CNTs), Graphene Oxide (GO) also immensely exhibited intrinsic antiinfective properties when targeted towards microbial infections and associated MDR phenomenon. In addition, the use of nano-based platforms as carriers emphatically increases the efficacy of targeted and sitespecific delivery of potential drug candidates for preventing microbial infections.

Pharmacotherapeutic management of bronchial infections in adults: non-cystic fibrosis bronchiectasis and chronic obstructive pulmonary disease

INTRODUCTION

Effective management of both acute and chronic bronchial infections is mandatory due to their high frequency rate, the relevant morbidity and mortality and the significant burden to health care systems, especially with the aging of population. Bacteria are the main causative pathogens, followed by viruses, and less commonly by fungi. The clinical evaluation of new therapeutic associations is mandatory to cope with the increases in resistance, in association with better infection control and antimicrobial policies.

AREAS COVERED

The authors searched Medline for any article published in English language up until March 1, 2020 that concerns the treatment of acute exacerbations and chronic infections in chronic obstructive respiratory disease and bronchiectasis.

EXPERT OPINION

As acute exacerbations are a main common and detrimental event in patients with COPD and bronchiectasis, effective antimicrobial therapies and regimens should be optimized. The development of new molecules or combination regimens is vital to patients with severe and/or difficult-to-treat infections. Moreover, chronic infection control is mandatory in these patients to their improve quality of life, respiratory function and prognosis as well as for reducing health care costs.

Biological Safe Gold Nanoparticle-Modified Dental Aligner Prevents the Porphyromonas gingivalis Biofilm Formation

Oral microbiology could directly influence overall health. Porphyromonas gingivalis (P. gingivalis) is a highly pathogenic bacterium that causes periodontitis and other related systematic diseases, including Alzheimer's disease. Orthodontic devices (e.g., invisalign aligner) is commonly used in populations with periodontitis who are also at a high risk of systematic diseases. In this study, newly explored antibacterial 4,6-diamino-2-pyrimidinethiol-modified gold nanoparticles (AuDAPT) were coated onto aligners. The coated aligners showed favorable antibacterial activity against P. gingivalis. In the presence of the coated aligner, the number of planktonic cells was decreased, and biofilm formation was prevented. This material also showed favorable biocompatibility in vivo and in vitro. This study reveals a new method for treating oral P. gingivalis by coating aligners with AuDAPT, which has typical advantages compared to other treatments for both periodontitis and related systematic diseases.

3D-Printed Drug Delivery Systems: The Effects of Drug Incorporation Methods on Their Release and Antibacterial Efficiency

Additive manufacturing technologies have been widely used in the medical field. More specifically, fused filament fabrication (FFF) 3D-printing technology has been thoroughly investigated to produce drug delivery systems. Recently, few researchers have explored the possibility of directly 3D printing such systems without the need for producing a filament which is usually the feedstock material for the printer. This was possible via direct feeding of a mixture consisting of the carrier polymer and the required drug. However, as this direct feeding approach shows limited homogenizing abilities, it is vital to investigate the effect of the pre-mixing step on the quality of the 3D printed products. Our study investigates the two commonly used mixing approaches-solvent casting and powder mixing. For this purpose, polycaprolactone (PCL) was used as the main polymer under investigation and gentamicin sulfate (GS) was selected as a reference. The produced systems' efficacy was investigated for bacterial and biofilm prevention. Our data show that the solvent casting approach offers improved drug distribution within the polymeric matrix, as was observed from micro-computed topography and scanning electron microscopy visualization. Moreover, this approach shows a higher drug release rate and thus improved antibacterial efficacy. However, there were no differences among the tested approaches in terms of thermal and mechanical properties.

Promising Therapeutic Strategies Against Microbial Biofilm Challenges

Biofilms are communities of microorganisms that are attached to a biological or abiotic surface and are surrounded by a self-produced extracellular matrix. Cells within a biofilm have intrinsic characteristics that are different from those of planktonic cells. Biofilm resistance to antimicrobial agents has drawn increasing attention. It is well-known that medical device- and tissue-associated biofilms may be the leading cause for the failure of antibiotic treatments and can cause many chronic infections. The eradication of biofilms is very challenging. Many researchers are working to address biofilm-related infections, and some novel strategies have been developed and identified as being effective and promising. Nevertheless, more preclinical studies and well-designed multicenter clinical trials are critically needed to evaluate the prospects of these strategies. Here, we review information about the mechanisms underlying the drug resistance of biofilms and discuss recent progress in alternative therapies and promising strategies against microbial biofilms. We also summarize the strengths and weaknesses of these strategies in detail.

Persistence in Livestock Mycoplasmas—a Key Role in Infection and Pathogenesis

Purpose of Review

Mycoplasma, economically important pathogens in livestock, often establishes immunologically complex persistent infections that drive their pathogenesis and complicate prophylaxis and therapy of the caused diseases. In this review, we summarize some of the recent findings concerning cellular and molecular persistence mechanisms related to the pathogenesis of mycoplasma infections in livestock.

Recent Findings

Data from recent studies prove several mechanisms including intracellular lifestyle, immune dysregulation, and autoimmunity as well as microcolony and biofilm formation and apoptosis of different host cell types as important persistence mechanisms in several clinically significant Mycoplasma species, i.e., M. bovis, M. gallisepticum, M. hyopneumoniae, and M. suis.

Summary

Evasion of the immune system and the establishment of persistent infections are key features in the pathogenesis of livestock mycoplasmas. In-depth knowledge of the underlying mechanisms will provide the basis for the development of therapy and prophylaxis strategies against mycoplasma infections.

Nosocomial pathogen biofilms on biomaterials: Different growth medium conditions and components of biofilms produced in vitro

BACKGROUND/PURPOSE (S)

Nosocomial pathogens can develop biofilms on hospital surfaces and medical devices; however, few studies have focused on the evaluation of mono-and dual-species biofilms developed by nosocomial pathogens under different growth conditions.

METHODS

This study investigated biofilm development by nosocomial pathogens (Acinetobacter baumannii, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa) on biomaterials in different culture media and their components of the extracellular matrix biofilm.

RESULTS

The mono-species biofilms showed cell densities from 7.50 to 9.27 Log₁₀ CFU/cm² on natural rubber latex type I (NLTI) and from 7.58 to 8.79 Log₁₀ CFU/cm² on stainless steel (SS). Dual-species biofilms consisted of S. aureus + P. aeruginosa (7.87-8.27 Log₁₀ CFU/cm² in TSBP and TSBME onto SS; p < 0.05), E. coli + P. aeruginosa (8.32-8.86 Log₁₀ CFU/cm² in TSBME onto SS and TSBP onto NLTI; p < 0.05), and S. aureus + E. coli (7.82 Log₁₀ CFU/cm² in TSBME onto SS; p < 0.05). Furthermore, biofilm detachment after proteinase K treatment was 5.54-32.81% compared to 7.95-24.15% after DNase I treatment in the mono-dual species biofilm matrix. Epifluorescence microscopy and scanning electron microscopy (SEM) enabled visualizing the bacteria and extracellular polymeric substances of biofilms on SS and NLTI.

CONCLUSION

Nosocomial pathogens can develop biofilms on biomaterials. Mono-species biofilms of Gram-negative bacteria showed lower densities than dual-species biofilms in TSBME and TSBP. Additionally, dual-species biofilms showed a higher concentration of proteins and eDNA in the extracellular matrix.

Intrinsic disorder in proteins: Relevance to protein assemblies, drug design and host-pathogen interactions

Intrinsic disorder in proteins resulting in considerable variation in structure can lead to multiple functions including multi-specificity and diverse pathologies. Protein interfaces can involve disordered regions that assemble through a concerted-fold-and-bind mechanism. The binding involves both enthalpic and entropic gains by exploiting 'hot spots' on the partner and displacing water molecules placed in thermodynamically unfavorable situations. The examples of Rad51-BRCA2 and Artemis-DNA-PKCs/LigIV complexes illustrate this in the context of drug design. This overview tracks the seamless involvement of protein disorder in multi-specificity of biocatalysts, protein assembly formations and host-pathogen interactions, where intrinsic disorder can in Mycobacteria, compensate for genome reduction by carrying out multiple functions and in some RNA viruses facilitate adaption to the host. These present challenging opportunities for designing new drugs and interventions.

Cationic amphiphiles against Gardnerella vaginalis resistant strains and bacterial vaginosis-associated pathogens

Antibiotic resistance and infection recurrence are critical issues in treating bacterial vaginosis, the most common vaginal disorder in women of reproductive age. Novel alternatives to traditional antibiotics, such as peptidomimetics, have the potential to address this challenge. Previously, two series of cationic amphiphiles (CAms) were developed with both hydrophilic head groups and non-polar domains, giving them the ability to self-assemble into supramolecular nanostructures with membrane-lytic properties. Those CAms were shown to be effective against biofilms of Gardnerella vaginalis while preserving the commensal microbiota. Two new series of CAms were designed with varying levels of flexibility between the hydrophilic head groups and the hydrophobic domains. Activities against the vaginal pathogen G. vaginalis ranged from 1.3 to 18.5 µM, while the tested vaginal lactobacilli were significantly more tolerant of CAms, with minimal inhibitory concentration values as high as 208 µM. Minimal biofilm bactericidal concentrations of the tested CAms ranged from 21.47 to <388.3 µM, and were lowest against resistant forms of G. vaginalis, while Lactobacillus biofilms were tolerant of concentrations ≥687 µM. Safety aspects of the CAms were also investigated, and they were found to be safe for use against vaginal ectocervical tissue.

Nanomaterials for the Photothermal Killing of Bacteria

An upsurge in the multidrug-resistant (MDR) bacterial pestilence is a global cause for concern in terms of human health. Lately, nanomaterials with photothermal effects have assisted in the efficient killing of MDR bacteria, attributable to their uncommon plasmonic, photocatalytic, and structural properties. Examinations of substantial amounts of photothermally enabled nanomaterials have shown bactericidal effects in an optimized time under near-infrared (NIR) light irradiation. In this review, we have compiled recent advances in photothermally enabled nanomaterials for antibacterial activities and their mechanisms. Photothermally enabled nanomaterials are classified into three groups, including metal-, carbon-, and polymer-based nanomaterials. Based on substantial accomplishments with photothermally enabled nanomaterials, we have inferred current trends and their prospective clinical applications.

Selenium and tellurium-based nanoparticles as interfering factors in quorum sensing-regulated processes: violacein production and bacterial biofilm formation

A cell-to-cell communication system called quorum sensing (QS) promotes the transcription of certain target genes in bacterial cells leading to the activation of different cellular processes, some of them related to bacterial biofilm formation. The formation of bacterial biofilms favours antibiotic resistance, which is nowadays a significant public-health problem. In this study, the effect of selenium (SeNPs) and tellurium (TeNPs) nanoparticles was examined in two bacterial processes mediated by QS: violacein production by Chromobacterium violaceum and biofilm formation by Pseudomonas aeruginosa. For this purpose, quantification of the pigment production in the presence of these nanoparticles was monitored using the C. violaceum strain. Additionally, a combination of different microscopical imaging techniques was applied to examine the changes in the 3D biofilm structure of P. aeruginosa, which were quantified through performing architectural metric calculations (substratum area, cell area coverage and biovolume). SeNPs produce an 80% inhibition in the violacein production by C. violaceum and a significant effect on the P. aeruginosa biofilm architecture (a reduction of 80% in the biovolume of the bacterial biofilm was obtained). TeNPs similarly affect violacein production and the P. aeruginosa biofilm structure but at lower concentration levels. The results obtained suggest an important disruption of the QS signalling system by SeNPs and TeNPs, supporting nanotechnology as a promising tool to fight against the emerging problem of bacterial resistance related to bacterial biofilm formation.

Improved Activity of Rifampicin Against Biofilms of Staphylococcus aureus by Multicomponent Complexation

The aim of this study was to evaluate a multicomponent complex (MC) between rifampicin (RIF), β-cyclodextrin (β-CD), and selected amino acids to enhance the solubility and antibiofilm activity of RIF. After performing phase-solubility studies that demonstrated a considerable increase in the solubility of RIF for the MC, the corresponding solid system was prepared by a freeze-drying method. Characterization of the MC was performed by Fourier transform-infrared spectroscopy, thermal analysis, powder X-ray diffraction, and scanning electron microscopy. Structural analyses evidenced molecular interactions between the components, resulting in a MC with amorphous solid features. Structural studies involving both experimental (i.e., ¹H NMR) and theoretical (i.e., molecular modeling) methodologies demonstrated the inclusion of the RIF piperazine ring in the β-CD cavity. The bioactivity of the MC measured against biofilms of Staphylococcus aureus showed a significant reduction in the metabolic activity of the bacterium. Overall, the studied MC exhibited promising properties for the development of pharmaceutical formulations to treat bacterial infections.

Fate and effect of in-house synthesized tellurium based nanoparticles on bacterial biofilm biomass and architecture. Challenges for nanoparticles characterization in living systems

The unexpected impact of nanoparticles on environment and human health remains as a matter of concern. In this sense, understanding the interaction between nanoparticles and biological indicators such as microorganism may help to understand their fate and effect in environmental systems. However, the adverse effect of nanoparticles greatly depends on their properties and, therefore, a precise evaluation of nanoparticles physicochemical characteristics is mandatory as the first step in accurately elucidating their behaviour in different ecosystems. Here in this work, in house-synthesized tellurium-based nanoparticles have been fully characterized for first time by means of a multi-method approach. Once characterized, the effect of these nanoparticles on Staphylococcus aureus and Escherichia coli biofilm biomass and structure was explored and quantified for first time. Moreover, the morphological transformations of tellurium based nanoparticles within the confines of a biofilm are also highlighted. Architectural metric calculations evidenced that nanoparticles were able to reduce the biovolume of the biofilm produced for both bacteria. Interestingly, the interaction between nanoparticles and bacterial communities led to the transformation of tellurium nanoparticles from sphere to rod-shaped nanoparticles. These findings open new insights into the behaviour of a type of uncommon nanoparticles such as tellurium-based nanoparticles on microbial communities.

Antimicrobial resistance three ways: healthcare crisis, major concepts and the relevance of biofilms

Worldwide, infections are resuming their role as highly effective killing diseases, as current treatments are failing to respond to the growing problem of antimicrobial resistance (AMR). The social and economic burden of AMR seems ever rising, with health- and research-related organizations rushing to collaborate on a worldwide scale to find effective solutions. Resistant bacteria are spreading even in first-world nations, being found not only in healthcare-related settings, but also in food and in the environment. In this minireview, the impact of AMR in healthcare systems and the major bacteria behind it are highlighted. Ecological aspects of AMR evolution and the complexity of its molecular mechanisms are explained. Major concepts, such as intrinsic, acquired and adaptive resistance, as well as tolerance and heteroresistance, are also clarified. More importantly, the problematic of biofilms and their role in AMR, namely their main resistance and tolerance mechanisms, are elucidated. Finally, some of the most promising anti-biofilm strategies being investigated are reviewed. Much is still to be done regarding the study of AMR and the discovery of new anti-biofilm strategies. Gladly, considerable research on this topic is generated every day and increasingly concerted actions are being engaged globally to try and tackle this problem.

Potential probiotic of Lactobacillus strains isolated from the intestinal tracts of pigs and feces of dogs with antibacterial activity against multidrug-resistant pathogenic bacteria

The occurrence of multidrug-resistant pathogenic bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), multidrug-resistant Acinetobacter baumannii (MDRAB), extended-spectrum β-lactamase (ESBL) Escherichia coli, and Pseudomonas aeruginosa, has become a serious problem in animals and public. The objective of this study was to identify and isolate lactic acid bacterial (LAB) strains from the intestinal tracts of pigs and feces of dogs and then characterize them as potential probiotics with antimicrobial activity against multidrug-resistant pathogenic bacteria. In a preliminary isolation screening, 45 of 1167 isolated LAB strains were found to have anti-S. aureus ATCC 27,735 activity. Using 16S rDNA and 16S-23S rDNA intergenic spacer region (ISR) sequences, five of these isolates were further identified as Lactobacillus animalis 30a-2, Lactobacillus reuteri 4-12E, Weissella cibaria C34, Lactococcus lactis 5-12H, and Lactococcus lactis 6-3H. Antimicrobial substance assays suggest that the L. lactis 5-12H, L. lactis 6-3H, L. animalis 30a-2, L. reuteri 4-12E, and W. cibaria C34 strains might produce bacteriocins and hydrogen peroxide (H₂O₂) as antimicrobial substances. The L. animalis 30a-2 and W. cibaria C34 strains were further characterized for probiotic properties and shown to have high acid and bile salt tolerance. Additionally, they have broad antimicrobial spectra, and can significantly repress the growth of all of the tested strains of MRSA isolates, some MDRAB, ESBL E. coli, and P. aeruginosa isolates, along with food-borne pathogenic bacteria such as Bacillus cereus ATCC 11778, Listeria monocytogens ATCC 19111, Salmonella spp., Shigella spp., and Yersinia enterocolitica BCRC 12986. This is the first report of H₂O₂-producing L. animalis 30a-2 and W. cibaria C34 isolated from the intestinal tracts of pigs and feces of dogs that have good antimicrobial activity against multidrug-resistant and food-borne pathogenic bacteria and have excellent probiotic properties.

Ultrasound-mediated therapies for the treatment of biofilms in chronic wounds: a review of present knowledge

Bacterial biofilms are an ever-growing concern for public health, featuring both inherited genetic resistance and a conferred innate tolerance to traditional antibiotic therapies. Consequently, there is a growing interest in novel methods of drug delivery, in order to increase the efficacy of antimicrobial agents. One such method is the use of acoustically activated microbubbles, which undergo volumetric oscillations and collapse upon exposure to an ultrasound field. This facilitates physical perturbation of the biofilm and provides the means to control drug delivery both temporally and spatially. In line with current literature in this area, this review offers a rounded argument for why ultrasound-responsive agents could be an integral part of advancing wound care. To achieve this, we will outline the development and clinical significance of biofilms in the context of chronic infections. We will then discuss current practices used in combating biofilms in chronic wounds and then critically evaluate the use of acoustically activated gas microbubbles as an emerging treatment modality. Moreover, we will introduce the novel concept of microbubbles carrying biologically active gases that may facilitate biofilm dispersal.

Assessment of microbiota present on a Portuguese historical stone convent using high-throughput sequencing approaches

The study performed on the stone materials from the Convent of Christ revealed the presence of a complex microbial ecosystem, emphasizing the determinant role of microorganisms on the biodecay of this built cultural heritage. In this case study, the presence of Rubrobacter sp., Arthrobacter sp., Roseomonas sp., and Marinobacter sp. seems to be responsible for colored stains and biofilm formation while Ulocladium sp., Cladosporium sp., and Dirina sp. may be related to structural damages. The implementation of high-throughput sequencing approaches on the Convent of Christ's biodecay assessment allowed us to explore, compare, and characterize the microbial communities, overcoming the limitations of culture-dependent techniques, which only identify the cultivable population. The application of these different tools and insights gave us a panoramic view of the microbiota thriving on the Convent of Christ and signalize the main biodeteriogenic agents acting on the biodecay of stone materials. This finding highlighted the importance of performing metagenomic studies due to the improvements and the reduced amount of sample DNA needed, promoting a deeper and more detailed knowledge of the microbiota present on these dynamic repositories that support microbial life. This will further enable us to perform prospective studies in quarry and applied stone context, monitoring biogenic and nonbiogenic agents, and also to define long-term mitigation strategies to prevent biodegradation/biodeterioration processes.

Antimicrobial activity of a silver-microfibrillated cellulose biocomposite against susceptible and resistant bacteria

Antibiotic Microbial Resistance (AMR) is a major global challenge as it constitutes a severe threat to global public health if not addressed. To fight against AMR bacteria, new antimicrobial agents are continually needed, and their efficacy must be tested. Historically, many transition metals have been employed, but their cytotoxicity is an issue and hence must be reduced, typically by combination with organic polymers. Cellulose of natural origin, especially those derived from unavoidable residues in the food supply chain, appears to be a good capping agent for the green synthesis of silver nanoparticles. Herein, we describe a green synthesis method to produce a novel biocomposite, using ascorbic acid as reducing agent and microfibrillated cellulose as a capping agent and demonstrate this material to be an efficient antimicrobial agent. Silver nanoparticles were obtained in the cellulose matrix with an average size of 140 nm and with antimicrobial activity against both sensitive and resistant Gram positive (using 1500 ppm) as well as sensitive and resistant Gram negative (using 125 ppm) bacteria. Also, an inverted disk-diffusion methodology was applied to overcome the low-solubility of cellulose compounds. This novel silver nanoparticle-cellulose biocomposite synthesized by a green methodology shows the potential to be applied in the future development of biomedical instruments and therapeutics.

The M Protein of Streptococcus pyogenes Strain AP53 Retains Cell Surface Functional Plasminogen Binding after Inactivation of the Sortase A Gene

Streptococcus pyogenes (Lancefield group A Streptococcus [GAS]) is a β-hemolytic human-selective pathogen that is responsible for a large number of morbid and mortal infections in humans. For efficient infection, GAS requires different types of surface proteins that provide various mechanisms for evading human innate immune responses, thus enhancing pathogenicity of the bacteria. Many such virulence-promoting proteins, including the major surface signature M protein, are translocated after biosynthesis through the cytoplasmic membrane and temporarily tethered to this membrane via a type 1 transmembrane domain (TMD) positioned near the COOH terminus. In these proteins, a sorting signal, LPXTG, is positioned immediately upstream of the TMD, which is cleaved by the membrane-associated transpeptidase, sortase A (SrtA), leading to the covalent anchoring of these proteins to newly emerging l-Ala-l-Ala cross-bridges of the growing peptidoglycan cell wall. Herein, we show that inactivation of the srtA gene in a skin-tropic pattern D GAS strain (AP53) results in retention of the M protein in the cell membrane. However, while the isogenic AP53 ΔsrtA strain is attenuated in overall pathogenic properties due to effects on the integrity of the cell membrane, our data show that the M protein nonetheless can extend from the cytoplasmic membrane through the cell wall and then to the surface of the bacteria and thereby retain its important properties of productively binding and activating fluid-phase host plasminogen (hPg). The studies presented herein demonstrate an underappreciated additional mechanism of cell surface display of bacterial virulence proteins via their retention in the cell membrane and extension to the GAS surface.IMPORTANCE Group A Streptococcus pyogenes (GAS) is a human-specific pathogen that produces many surface factors, including its signature M protein, that contribute to its pathogenicity. M proteins undergo specific membrane localization and anchoring to the cell wall via the transpeptidase sortase A. Herein, we explored the role of sortase A function on M protein localization, architecture, and function, employing, a skin-tropic GAS isolate, AP53, which expresses a human plasminogen (hPg)-binding M (PAM) Protein. We showed that PAM anchored in the cell membrane, due to the targeted inactivation of sortase A, was nonetheless exposed on the cell surface and functionally interacted with host hPg. We demonstrate that M proteins, and possibly other sortase A-processed proteins that are retained in the cell membrane, can still function to initiate pathogenic processes by this underappreciated mechanism.

Accelerated Corrosion of 316L Stainless Steel Caused by Shewanella algae Biofilms

In the marine environment, microbiologically influenced corrosion (MIC) is a major problematic issue, which leads to severe damage to metals and alloys. The prerequisite to mitigate this worldwide problem is to investigate the mechanisms of marine-corroding microbes. Therefore, the corrosion behavior of 316L stainless steel in the presence of marine Shewanella algae was investigated by means of electrochemical measurements and surface analysis. The results revealed that S. algae is capable of forming a dense and thick biofilm on the surfaces of 316L SS coupons after 7 days of incubation, which reached about a thickness of 40.4 μm. According to electrochemical results, the S. algae biofilm also induced the corrosion of 316L SS coupons. The accelerated corrosion of 316L SS coupons was in the form of pits, which was formed underneath the biofilms. The largest pit depth after 14 days of incubation time reached 9.8 μm, which was 6.7 times higher than the one immersed in abiotic medium (1.45 μm). This is the first study demonstrating the MIC of 316L SS due to the S. algae biofilm.

Eradication of Candida albicans persister cell biofilm by the membranotropic peptide gH625

Biofilm formation poses an important clinical trouble due to resistance to antimicrobial agents; therefore, there is an urgent demand for new antibiofilm strategies that focus on the use of alternative compounds also in combination with conventional drugs. Drug-tolerant persisters are present in Candida albicans biofilms and are detected following treatment with high doses of amphotericin B. In this study, persisters were found in biofilms treated with amphotericin B of two clinical isolate strains, and were capable to form a new biofilm in situ. We investigated the possibility of eradicating persister-derived biofilms from these two Candida albicans strains, using the peptide gH625 analogue (gH625-M). Confocal microscopy studies allowed us to characterize the persister-derived biofilm and understand the mechanism of interaction of gH625-M with the biofilm. These findings confirm that persisters may be responsible for Candida biofilm survival, and prove that gH625-M was very effective in eradicating persister-derived biofilms both alone and in combination with conventional antifungals, mainly strengthening the antibiofilm activity of fluconazole and 5-flucytosine. Our strategy advances our insights into the development of effective antibiofilm therapeutic approaches.

Investigation of biofilm production and its association with genetic and phenotypic characteristics of OM (osteomyelitis) and non-OM orthopedic Staphylococcus aureus

Background

Staphylococcus aureus is a primary pathogen of orthopedic infections. By mediating antimicrobial resistance, S. aureus biofilm plays an important role in the recalcitrance of orthopedic infections, especially for the intractable osteomyelitis (OM). This study investigated the relationship between biofilm production and various genetic or phenotypic characteristics among orthopedic S. aureus strains.

Methods

A total of 137 orthopedic S. aureus isolates were enrolled and divided into OM and non-OM groups. Biofilm production was evaluated using the crystal violet assay. Genetic and phenotypic characteristics including MRSA identification, MLST and spa typing, carriage of virulence genes, drug resistance, and patients’ inflammatory responses indicators were characterized. The relationship between biofilm production and above-mentioned features was respectively analyzed among all isolates and compared between OM and non-OM isolates.

Results

Biofilm production presented no significant difference between OM (including 9 MRSA isolates) and non-OM (including 21 MRSA isolates) strains. We found that ST88, t377 and ST630-MSSA-t377 strains produced very strong biofilms, while MLST types of ST15, ST25, ST398, ST5, ST59 and spa types of t002, t2325, t437 tended to produce weaker biofilms. Strains with the following profiles produced stronger biofilms: fib(+)-hlgv(+)-lukED(+)-sei(-)-sem(-)-seo(-) for all isolates, sei(-)-sem(-)-seo(-) for OM isolates, and cna (+)-fib (+)-hlgv (+)-lukED (+)-seb(-)-sed(-) for non-OM isolates. In addition, not any single drug resistance was found to be related to biofilm production. We also observed that, among OM patients, strains with stronger biofilms caused weaker inflammatory responses.

Conclusion

Some genetic or phenotypic characteristics of orthopedic strains were associated with biofilm production, and this association could be different among OM and non-OM strains. The results are of great significance for better understanding, evaluating and managing different kinds of biofilm-associated orthopedic infections, and provide potential targets for biofilm clearance.

Ecological niche differentiation among anammox bacteria

Anaerobic ammonium oxidizing (anammox) bacteria can directly convert ammonium and nitrite to nitrogen gas anaerobically and were responsible for a substantial part of the fixed nitrogen loss and re-oxidation of nitrite to nitrate in freshwater and marine ecosystems. Although a wide variety of studies have been undertaken to investigate the abundance and biodiversity of anammox bacteria so far, ecological niche differentiation of anammox bacteria is still not fully understood. To assess their growth behavior and consequent population dynamics at a given environment, the Monod model is often used. Here, we summarize the Monod kinetic parameters such as the maximum specific growth rate (μ_max) and the half-saturation constant for nitrite (K_NO2-) and ammonium (K_NH4+) of five known candidatus genera of anammox bacteria. We also discuss potential pivotal environmental factors and metabolic flexibility that influence the community compositions of anammox bacteria. Particularly biodiversity of the genus "Scalindua" might have been largely underestimated. Several anammox bacteria have been successfully enriched from various source of biomass. We reevaluate their enrichment methods and culture medium compositions to gain a clue of niche differentiation of anammox bacteria. Furthermore, we formulate the current issues that must be addressed. Overall this review re-emphasizes the importance of enrichment cultures (preferably pure cultures), physiological characterization and direct microbial competition studies using enrichment cultures in laboratories.

Clustering of bacteria with heterogeneous motility

We study the clustering of a model cyanobacterium Synechocystis into microcolonies. The bacteria are allowed to diffuse onto surfaces of different hardness and interact with the others by aggregation and detachment. We find that soft surfaces give rise to more microcolonies than hard ones. This effect is related to the amount of heterogeneity of bacteria's dynamics as given by the proportion of motile cells. A kinetic model that emphasizes specific interactions between cells, complemented by extensive numerical simulations considering various amounts of motility, describes the experimental results adequately. The high proportion of motile cells enhances dispersion rather than aggregation.

The properties, biotechnologies, and applications of antifreeze proteins

By natural selection, organisms evolve different solutions to cope with extremely cold weather. The emergence of an antifreeze protein gene is one of the most momentous solutions. Antifreeze proteins possess an importantly functional ability for organisms to survive in cold environments and are widely found in various cold-tolerant species. In this review, we summarize the origin of antifreeze proteins, describe the diversity of their species-specific properties and functions, and highlight the related biotechnology on the basis of both laboratory tests and bioinformatics analysis. The most recent advances in the applications of antifreeze proteins are also discussed. We expect that this systematic review will contribute to the comprehensive knowledge of antifreeze proteins to readers.

Antibacterial, anti-biofilm activity and mechanism of action of pancreatin doped zinc oxide nanoparticles against methicillin resistant Staphylococcus aureus

Staphylococcus aureus are known to cause diseases from normal skin wound to life intimidating infections. Among the drug resistant strain, management of methicillin resistant Staphylococcus aureus (MRSA) is very difficult by using conventional antibiotic treatment. Both Zinc oxide nanoparticles (ZnONPs) and pancreatin (PK) are known to have antibacterial activity. Our main objective is to dope PK on ZnONPs to reduced zinc-oxide toxicity but increased anti-bacterial and anti-biofilms activity. In present study, we showed that, functions of zinc oxide nanoparticles with pancreatin enzyme (ZnONPs-PK) have anti-bacterial, anti-biofilms, anti-motility and anti-virulence properties against MRSA. Moreover, ZnONPs-PK were more potent to eradicate MRSA than only ZnONPs and PK. Application of the produced nano-composites as treatment on infected swine dermis predominantly reflects the potential treatment property of it. The vancomycin sensitivity of MRSA was significantly increased on application with ZnONPs-PK. Further study revealed cell membrane was the target of the ZnONPs-PK and that leads to oxidative damage of the cells. The produced nanoparticles were found completely non-toxic to human's keratinocytes and lung epithelial cell lines at its bactericidal concentration. Overall, this study emphasizes the potential mechanisms underlying the selective bactericidal properties of ZnONPs-PK against MRSA. This novel nanoparticle strategy may provide the ideal solution for comprehensive management of MRSA and its associated diseases with minimising the use of antibiotics.

Strategies to Prevent Biofilm Infections on Biomaterials: Effect of Novel Naturally-Derived Biofilm Inhibitors on a Competitive Colonization Model of Titanium by Staphylococcus aureus and SaOS-2 Cells

Biofilm-mediated infection is a major cause of bone prosthesis failure. The lack of molecules able to act in biofilms has driven research aimed at identifying new anti-biofilm agents via chemical screens. However, to be able to accommodate a large number of compounds, the testing conditions of these screenings end up being typically far from the clinical scenario. In this study, we assess the potential applicability of three previously discovered anti-biofilm compounds to be part of implanted medical devices by testing them on in vitro systems that more closely resemble the clinical scenario. To that end, we used a competition model based on the co-culture of SaOS-2 mammalian cells and Staphylococcus aureus (collection and clinical strains) on a titanium surface, as well as titanium pre-conditioned with high serum protein concentration. Additionally, we studied whether these compounds enhance the previously proven protective effect of pre-incubating titanium with SaOS-2 cells. Out of the three, DHA1 was the one with the highest potential, showing a preventive effect on bacterial adherence in all tested conditions, making it the most promising agent for incorporation into bone implants. This study emphasizes and demonstrates the importance of using meaningful experimental models, where potential antimicrobials ought to be tested for the protection of biomaterials in translational applications.