Biofilm Bacteria Research Articles

Bacteria debridement efficacy of two sonic root canal irrigant activation systems

ObjectiveTo evaluate the bacteria debridement efficacy of two generations of sonic root canal irrigant activation systems: EndoActivator (Dentsply Sirona), the first generation, and SmartLite Pro EndoActivator, the second generation. MethodsInstrumented, autoclaved, single-rooted human premolars were inoculated with Enterococcus faecalis (ATCC-29212) for 21 days. The bacteria biofilm-containing teeth were randomly divided into 5 groups (N=8): Group 1: Syringe-side-vented needle (S-N) delivery of saline for 1 min; Group 2: S-N delivery of 2% NaOCl for 1 min; Group 3: S-N delivery of 2% NaOCl for 5 min; Group 4: EndoActivator activation of 2% NaOCl for 1 min; Group 5: SmartLite Pro EndoActivator activation of 2% NaOCl for 1 min. The teeth were evaluated for bacterial reduction using CFU counts, and the percentages of dead bacteria within the dentinal tubules using confocal laser scanning microscopy. ResultsActivation of NaOCl with EndoActivator or SmartLite Pro EndoActivator significantly reduced the overall intracanal bacterial load, compared with S-N irrigant delivery (P<0.05), with no significant difference between the two agitation devices (P>0.05). Nevertheless, S-N delivery of 2% NaOCl for 5 min produced better bacteria debridement than either sonic agitation system. Different degrees of bacteria kill were identified in the coronal-middle portions and apical portion of the canal space. ConclusionDelivery time of NaOCl affects the efficacy of bacteria disinfection. Activation for 1 min with the EndoActivator or SmartLite Pro EndoActivator demonstrated comparable canal wall biofilm and intracanal bacteria reduction efficacy when 2% NaOCl was used as irrigant for disinfecting E. faecalis in single-rooted teeth. Clinical significanceAlthough the sonic root canal irrigant activation devices investigated do not completely eliminate live bacteria biofilms from the canal space, they help reduce bacteria load during irrigant activation.

Theranostic gold-in-gold cage nanoparticles enable photothermal ablation and photoacoustic imaging in biofilm-associated infection models.

Biofilms are structured communities of microbial cells embedded in a self-produced matrix of extracellular polymeric substances. Biofilms are associated with many health issues in humans, including chronic wound infections and tooth decay. Current antimicrobials are often incapable of disrupting the polymeric biofilm matrix and reaching the bacteria within. Alternative approaches are needed. Here, we described a complex structure of a dextran-coated gold-in-gold cage nanoparticle that enabled photoacoustic and photothermal properties for biofilm detection and treatment. Activation of these nanoparticles with a near infrared laser could selectively detect and kill biofilm bacteria with precise spatial control and in a short timeframe. We observed a strong biocidal effect against both Streptococcus mutans and Staphylococcus aureus biofilms in mouse models of oral plaque and wound infections, respectively. These effects were over 100 times greater than those seen with chlorhexidine, a conventional antimicrobial agent. Moreover, this approach did not adversely affect surrounding tissues. We concluded that photothermal ablation using theranostic nanoparticles is a rapid, precise, and nontoxic method to detect and treat biofilm-associated infections.

Photodynamic antimicrobial chemotherapy activities of phthalocyanine-antibiotic conjugates against bacterial biofilms and interactions with extracellular polymeric substances

This study sheds light on how to rationally design efficient photodynamic antimicrobial chemotherapy (PACT) agents by covalently linking phthalocyanines (Pcs) as photosensitizers with an antibiotic: Ciprofloxacin (CIP). Pcs used are zinc (II) 3-(4-((3,17,23-tris(4-(Benzo(d)thiazol-2-yl] thiol) phthalocyanine-9-yl) oxy) phenyl) propanoic acid (1) and zinc (II) 3-(4-(3,17,23-tris(3-(4-(triphenylphosphine) butyl) benzo[d]thiazol-3-ium bromide phthalocyanine-9-yl) oxy) phenyl) propanoic acid (2). High singlet oxygen quantum yields are observed in the presence of CIP. Square wave voltammetry was used to analyse the Pc-CIP uptake by bacteria biofilms of Streptococcus pneumoniae (S. pneumonia) and Escherichia coli (E. coli). Electrochemical impedance spectroscopy and scanning electron spectroscopy were used to study the stability of the biofilms in the presence Pc-CIP complexes and when exposed to light. Raman and time of flight-secondary ion mass spectrometry (TOF-SIMS) are used to identify the breakdown of cellular components of the biofilm and penetration of the Pc-CIP into the biofilms, respectively.

Sprayable chitosan nanogel with nitric oxide to accelerate diabetic wound healing through bacteria inhibition, biofilm eradication and macrophage polarization

Bacterial infection and chronic inflammation are two major risks in diabetic wound healing, which increase patient mortality. In this study, a multifunctional sprayable nanogel (Ag-G@CS) based on chitosan has been developed to synergistically inhibit bacterial infection, eradicate biofilm, and relieve inflammation of diabetic wounds. The nanogel is successfully crafted by encapsulating with a nitric oxide (NO) donor and performing in-situ reduction of silver nanoparticles (Ag). The released NO enhances the antibacterial efficacy of Ag, nearly achieving complete eradication of biofilms in vitro. Upon application on both normal or diabetic chronic wounds, the combination effects of released NO and Ag offer a notable antibacterial effect. Furthermore, after bacteria inhibition and biofilm eradication, the NO released by the nanogel orchestrates a transformation of M1 macrophages into M2 macrophages, significantly reducing tumor necrosis factor α (TNF-α) release and relieving inflammation. Remarkably, the released NO also promotes M2a to M2c macrophages, thereby facilitating tissue remodeling in chronic wounds. More importantly, it upregulates the expression of vascular endothelial growth factor (VEGF), further accelerating the wound healing process. Collectively, the formed sprayable nanogel exhibits excellent inhibition of bacterial infections and biofilms, and promotes chronic wound healing via inflammation resolution, which has excellent potential for clinical use in the future.

Incidence of co-resistance to antibiotics and chlorine in bacterial biofilm of hospital water systems: Insights into the risk of nosocomial infections

The presence of biofilms in drinking water distribution systems (DWDS) in healthcare settings poses a considerable risk to the biological security of water, particularly when the biofilm bacteria demonstrate antimicrobial resistance characteristics. This study aimed to investigate the occurrence of antibiotic-resistant bacteria (ARB) in biofilms within DWDS of hospitals. The chlorine resistance of the isolated ARB was analyzed, and then chlorine-resistant bacteria (CRB) were identified using molecular methods. Additionally, the presence of several antibiotic resistance genes (ARGs) was monitored in the isolated ARB. Out of the 41 biofilm samples collected from hospitals, ARB were detected in 32 (78%) of the samples. A total of 109 colonies of ARB were isolated from DWDS of hospitals, with β-lactam resistant bacteria, including ceftazidime-resistant and ampicillin-resistant bacteria, being the most frequently isolated ARB. Analyzing of ARGs revealed the highest detection of aac6, followed by sul1 gene. However, the β-lactamase genes blaCTX-M and blaTEM were not identified in the ARB, suggesting the presence of other β-lactamase genes not included in the tested panel. Exposure of ARB to free chlorine at a concentration of 0.5 mg/l showed that 64% of the isolates were CRB. However, increasing the chlorine concentration to 4 mg/l decreased the high fraction of ARB (91%). The domi‌‌nant CRB identified were Sphingomonas, Brevundimonas, Stenotrophomonas, Bacillus and Staphylococcus with Bacillus exhibiting the highest frequency. The results highlight the potential risk of biofilm formation in the DWDS of hospitals, leading to the dissemination of ARB in hospital environments, which is a great concern for the health of hospitalized patients, especially vulnerable individuals. Surveillance of antimicrobial resistance in DWDS of hospitals can provide valuable insights for shaping antimicrobial use policies and practices that ensure their efficacy.

Antibacterial and antibiofilm activity of Abroma augusta stabilized silver (Ag) nanoparticles against drug-resistant clinical pathogens.

Infectious diseases remain among the most pressing concerns for human health. This issue has grown even more complex with the emergence of multidrug-resistant (MDR) bacteria. To address bacterial infections, nanoparticles have emerged as a promising avenue, offering the potential to target bacteria at multiple levels and effectively eliminate them. In this study, silver nanoparticles (AA-AgNPs) were synthesized using the leaf extract of a medicinal plant, Abroma augusta. The synthesis method is straightforward, safe, cost-effective, and environment friendly, utilizing the leaf extract of this Ayurvedic herb. The UV-vis absorbance peak at 424nm indicated the formation of AA-AgNPs, with the involvement of numerous functional groups in the synthesis and stabilization of the particles. AA-AgNPs exhibited robust antibacterial and antibiofilm activities against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococci (VRE). The MIC values of AA-AgNPs ranged from 8 to 32μg/mL. Electron microscopic examination of the interaction of AA-AgNPs with the test bacterial pathogens showed a deleterious impact on bacterial morphology, resulting from membrane rupture and leakage of intracellular components. AA-AgNPs also demonstrated a dose-dependent effect in curtailing biofilm formation below inhibitory doses. Overall, this study highlights the potential of AA-AgNPs in the successful inhibition of both the growth and biofilms of MRSA and VRE bacteria. Following studies on toxicity and dose optimization, such AgNPs could be developed into effective medical remedies against infections.

The Inhibitory Effects of Amylase and Streptokinase on Minimum Inhibitory Concentration of Antibiotics Used to Treat Gram Negative Bacteria Biofilm Infection on Indwelling Devices.

The study evaluated and compared the effect of adding streptokinase and amylase to antibiotics that are already used in clinical practice to treat Gram negative bacteria biofilm infection on indwelling devices on the antibiotics' minimum inhibitory concentration (MIC). 24h-old biofilms were developed on 96-well plate with eight clinical isolates. MIC of amikacin, cefepime, ceftazidime, colistin, meropenem, and piperacillin-tazobactam, on biofilms were measured before and after the addition of 25U/ml streptokinase and 25μg/ml amylase with microplate reader. The addition of streptokinase reduces the MICs of cefepime, ceftazidime, colistin, meropenem from (16, 16, 8, 4μg/ml) to (8, 1, 1, 0.5μg/ml) in Escherichia coli (isolate 1). While the addition of amylase reduces the MICs of only cefepime, ceftazidime from (16, 16μg/ml) to (2, 4μg/ml) in E. coli (isolate 1). In Pseudomonas aeruginosa (isolate 4), the MICs of amikacin, cefepime, ceftazidime, colistin and meropenem (64, 16, 32, 4, 32μg/ml) reduced to (2, 1, 0.5, 0.25, 0.5μg/ml) with streptokinase and (4, 4, 4, 2, 0.5μg/ml) with amylase respectively. Similar inhibitions were seen in Pseudomonas putida, Proteus mirabilis. We can conclude that the addition of streptokinase and amylase were effective in reducing the MICs of antibiotics that are commonly used to treat Gram negative bacteria biofilm infection on indwelling devices, thereby increasing susceptibility of bacteria to antibiotics. Streptokinase obviously had a greater effect than amylase, implying that it should be prioritized in future in vivo and clinical studies to obtain successful therapy with antibiotics on biofilm infections.

Biofilms as Battlefield Armor for Bacteria against Antibiotics: Challenges and Combating Strategies.

Bacterial biofilms are formed by communities, which are encased in a matrix of extracellular polymeric substances (EPS). Notably, bacteria in biofilms display a set of 'emergent properties' that vary considerably from free-living bacterial cells. Biofilms help bacteria to survive under multiple stressful conditions such as providing immunity against antibiotics. Apart from the provision of multi-layered defense for enabling poor antibiotic absorption and adaptive persistor cells, biofilms utilize their extracellular components, e.g., extracellular DNA (eDNA), chemical-like catalase, various genes and their regulators to combat antibiotics. The response of biofilms depends on the type of antibiotic that comes into contact with biofilms. For example, excessive production of eDNA exerts resistance against cell wall and DNA targeting antibiotics and the release of antagonist chemicals neutralizes cell membrane inhibitors, whereas the induction of protein and folic acid antibiotics inside cells is lowered by mutating genes and their regulators. Here, we review the current state of knowledge of biofilm-based resistance to various antibiotic classes in bacteria and genes responsible for biofilm development, and the key role of quorum sensing in developing biofilms and antibiotic resistance is also discussed. In this review, we also highlight new and modified techniques such as CRISPR/Cas, nanotechnology and bacteriophage therapy. These technologies might be useful to eliminate pathogens residing in biofilms by combating biofilm-induced antibiotic resistance and making this world free of antibiotic resistance.

Cystic fibrosis and pulmonary biofilms

Cystic fibrosis (CF) is an autosomal recessive disorder that involves the cystic fibrosis transmembrane conductance regulator. This protein is an anion channel that transfers chloride and bicarbonate from an intracellular location to an extracellular location. This transfer supports the formation of a normal periciliary fluid layer that is essential for ciliary function and the clearance of particulates from bronchi. Changes in mucociliary function can result in chronic bronchitis and recurrent infections. Studies using micro computed tomography of explanted lungs from CF patients have demonstrated that there is a significant reduction in the number of terminal bronchi and that approximately 50% of these bronchi are obstructed with secretions. These airways become colonized with bacteria, such as Pseudomonas aeruginosa, which can form biofilms, and this results in chronic inflammation and chronic airway damage. Biofilm formation can be predicted when mucoid colonies of pseudomonas grow out on routine bacterial cultures of sputum. Studies on the prognosis of patients with CF have demonstrated that there is lack of clear genotype-phenotype correlation, but one recent longitudinal study did report an association between more severe CFTR genotypes and clinical outcomes. In addition, the degree of pulmonary dysfunction and pseudomonas colonization, especially with drug resistant pseudomonas, predict poor outcomes. Bacteria in biofilms are more resistant to antibiotics, and the structure of biofilms limits host defense responses. Treatment approaches include the use of more than one antibiotic, the addition of inhaled antibiotics, the use of enzymes that degrade biofilms, and the use of small molecules that inhibit community metabolism in biofilms.&#x0D; &#x0D; Key words: cystic fibrosis transmembrane conductance regulator, extracellular secretions, periciliary fluid, Pseudomonas aeruginosa, biofilms

L-Arginase from P. aeruginosa Isolated from Sewage as Anti-Biofilm Formation by Pathogenic Bacteria

Background: The enzyme arginase plays a significant role in the growth of many organisms as important biological enzyme. Objective: The study was designed to isolate L-arginase from P. aeruginosa that isolated from sewages and to evaluate the influence of arginase on biofilm-generating bacteria. Materials and Methods: The current study includes 28(54.8%) isolates from soil with 24 (46.2%) from sewage water out of 52 isolated from soil and sewage for the purpose of obtaining Pseudomonas aeruginosa. Using standard laboratory methods to isolate Pseudomonas aeruginosa, 33 isolates were isolated, of which 15 (45.45%) were from soil and 18 (54.54%) from sewage. The study also included 177 different eyes (urinary fluid, excrement, blood, wounds, sputum, and cerebrospinal fluid) of patients suffering from various injuries. Results: The statistical analysis of the isolates indicated that there is a high significant (P≤0.01) for the growth of some types of bacteria, such as P. aeruginosa 30(16.89%), Klebsiella, Serratia 33(18.88%) and Acinetobacter 33(18.88%). While the results showed that Lactobacillus is the lowest number of isolates 7(3.9%). Optimum condition of arginase activity and stability comprising pH level of eight degrees, the temperature of 37℃ is the best conditions for the production of arginine, concentrations of L-arginine substrate (0.1-2.5)g/l on the activity of arginase enzyme for arginine production, The finding also shows that the arginase enzyme exhibited the highest activity after 96 hours of the incubation process L- arginase Purification Assay including Ammonium Sulphate precipitation in (60-80)%, Dialysis, Ion exchange chromatography, Gel filtration. Conclusions: This study concluded that the enzyme arginase had a significant effect on the strong biofilm of pathogenic bacteria.

Oregano Essential Oil versus Conventional Disinfectants against Salmonella Typhimurium and Escherichia coli O157:H7 Biofilms and Damage to Stainless-Steel Surfaces.

This study compared the effect of oregano essential oil versus sodium hypochlorite, hydrogen peroxide, and benzalkonium chloride against the viability of adhered Salmonella Typhimurium and Escherichia coli O157:H7 on 304 stainless steel. Oregano essential oil was effective in disrupting the biofilms of both bacteria at concentrations ranging from 0.15 to 0.52 mg mL-1. In addition, damage to stainless-steel surfaces following disinfection treatments was assessed by weight loss analysis and via visual inspection using light microscopy. Compared to the other treatments, oregano oil caused the least damage to stainless steel (~0.001% weight loss), whereas sodium hypochlorite caused the most severe damage (0.00817% weight loss) when applied at 0.5 mg mL-1. Moreover, oregano oil also had an apparent protective impact on the stainless steel as weight losses were less than for the control surfaces (distilled water only). On the other hand, sodium hypochlorite caused the most severe damage to stainless steel (0.00817% weight loss). In conclusion, oregano oil eliminated monoculture biofilms of two important foodborne pathogens on 304 stainless-steel surfaces, while at the same time minimizing damage to the surfaces compared with conventional disinfectant treatments.

Drug resistance and influencing factors of biofilm bacteria in upper urinary calculi patients with double J stent indwelling

ObjectiveTo analyze the distribution and drug resistance of biofilm bacteria infected with upper urinary calculi patients with double J stent indwelling, and to explore the influencing factors of Biofilm Bacteria Infections.MethodsA total of 400 patients with upper urinary calculi who adopted double J stent inserting in our hospital from January 2019 to January 2022 were included. Urine and double J stent samples were collected, pathogen cultures were performed, and then drug sensitivity test analysis was carried out for isolates. Univariate and multivariate logistic regression analyzes were used to analyze the influencing factors of patients with double J stent associated biofilm bacteria infections.ResultsA total of 13 strains (3.2%) of biofilm bacteria were detected in urine samples and 168 strains (42%) in double J stent samples (P < 0.05), 95 strains (23.7%) of pathogenic bacteria were separated from urine samples and 117 strains (29.2%) from double J-stent samples (P > 0.05). Escherichia coli were the most common bacteria. There was significantly higher drug resistance observed in biofilm bacteria versus urine-cultured pathogens (P < 0.05). Advanced age, long-term catheterization, inadequate water intake, hypoproteinemia, abnormal renal function, and diabetes mellitus were independent risk factors for biofilm bacteria infection associated with double J stent(P < 0.05).ConclusionAmong the upper urinary calculi patients with double J stent indwelling, the positive rate and drug resistance of biofilm bacteria obtained from double J stent were significantly higher than that from urine. More attention should be paid to the factors that influence biofilm bacteria infections.

Amino acids as in-situ electron donors drive medium chain fatty acids production from sludge acidogenic fermentation liquid by electro-fermentation enhancement

The production of medium chain fatty acids (MCFAs) from waste biomass by chain elongation often requires the supplementation of exogenous chemical electron donor (ED), to support the chain elongator. This study explored the feasibility of producing MCFAs using amino acids in acidogenic fermentation liquid from protein-rich sludge hydrolysate, and proposed a two-stage electro-fermentation process to realize MCFAs production without exogenous chemical ED. Stage I aimed to convert organic substrates into short chain fatty acids (SCFAs) through anodic alkaline acidogenic fermentation. Stage II utilized residual amino acids as in-situ ED in acidogenic fermentation liquid to generate MCFAs in cathodic chamber under open circuit (OC) and 0.9 V conditions. Results indicated that acetate (6.9 g/L) and butyrate (4.5 g/L) were accumulated as the main products in stage I, and 2.7 g/L of amino acids remained in acidogenic fermentation liquid. In stage II, the remained amino acids were consumed as in-situ ED to drive the conversion of acetate and butyrate into caproate, and 1.1 g/L and 3.01 g/L caproate were respectively determined at OC and 0.9 V conditions. Microbial community and function prediction mechanisms revealed the presence of abundant chain elongator (Clostridium_sensu_stricto_12) and electroactive bacteria (Desulfovibrio) in cathodic biofilm, as well as the organic degrader (Pseudomonas) in plankton, these microbes synergistically converted SCFAs and amino acids into MCFAs. This study for the first time explored the feasibility of using amino acids as alternative chemical ED to drive chain elongation, and provides a novel technical solution foralleviating dependence on exogenous chemical ED in the production of MCFAs from waste biomass.

Paradigm shift: Bacterial quorum sensing and possible control targets

QS Designates a cell-to-cell communication process that enables bacteria to collectively modify their behaviour in response to changes in the cell density and species composition of the surrounding microbial community. These processes involve the production, release and group-wide detection of extracellular signalling molecules, which are generically called Autoinducers (AIs). It controls various genes which are responsible for various phenotypes like bioluminescence, the secretion of virulence factors, and the formation of biofilms in bacteria. Quorum quenching inhibits QS and the substances that inhibit it are called quorum sensing inhibitors. Several chemical compounds and enzymes mediate inhibition of QS, such as, lactonases, acylases and oxidoreductases. Other than these, there are some non-enzymatic methods for quorum quenching and also some plant phytochemicals have been found to inhibit it. Blocking of QS by QS Inhibition (QSI) may play an important role to disrupt biofilm formation in a device associated infection and chronic drug resistant infection. More researches are required in this area related with QS and QSI. However, some chemicals have been found to be mimicking the quorum sensing AIs activities like serotonin and rosmaric acid.

Fabric Fiber as a Biofilm Carrier for Halomonas sp. H09 Mixed with Lactobacillus rhamnosus GG.

Biofilm bacteria have stronger resistance to the adverse external environment compared to planktonic bacteria, and biofilms of non-pathogenic bacteria have strong potential for applications in food. In this experiment, Halomonas sp. H09 and Lactobacillus rhamnosus GG, which have film-forming ability in monoculture and better film-forming ability in mixed culture than the two strains alone, were selected as the target strains for mixed culture. According to SEM observation and bacterial dry weight measurement, the target strain formed a dense biofilm on a 0.1g/L chitosan-modified cellulose III carrier. Furthermore, the presence of extracellular polymeric substances in biofilms was verified by EDS and FTIR. The results showed that 0.1g/L chitosan-modified cellulose III was an ideal carrier material for immobilization of Halomonas sp. H09 with Lactobacillus rhamnosus GG biofilm. This research provided a basis for the selection of non-pathogenic mixed-bacteria biofilm carriers.

Extracellular DNA enhances biofilm integrity and mechanical properties of mucoid Pseudomonas aeruginosa.

Pseudomonas aeruginosa is one of the most common biofilm-forming pathogens responsible for lung infections of individuals with cystic fibrosis (CF). P. aeruginosa becomes tolerant to antimicrobials in the biofilm state and is difficult to treat. Production of extracellular polymeric substances (EPS), such as alginate and extracellular DNA (eDNA), can allow adherence to abiotic and biotic surfaces, antimicrobial evasion, and resilience to environmental pressures. Alginate-producing mucoid variants of P. aeruginosa are frequently isolated from CF airway samples and are associated with worsening patient outcomes. While eDNA is a major structural component of nonmucoid P. aeruginosa biofilms, the potential role of eDNA in mucoid biofilms is unclear. Here, we investigate how eDNA contributes to clinical mucoid biofilm physiology and integrity. We predicted that eDNA plays a structural and mechanical role in mucoid biofilms. To test this, we quantified biofilm eDNA in mucoid biofilms and used microscopy and rheology to visualize eDNA and detect changes in biofilm structure and mechanics upon DNaseI treatment. We showed that biofilm eDNA abundance is diverse across clinical mucoid strains and observed a temporal increase in foci of eDNA within intact mucoid biofilms. Increased cell dispersal and reduced biomass were also observed following DNaseI treatment of mucoid biofilms. Degradation of eDNA also impacted the mechanical integrity of mucoid biofilms by increasing the stiffness and decreasing the cohesion of the biofilm. These findings advance our understanding of clinical mucoid P. aeruginosa biofilms and facilitate the development of new approaches to target biofilms by exploiting the functions of EPS components. IMPORTANCE Understanding the role of eDNA in mucoid Pseudomonas aeruginosa biofilms will lead to therapeutic strategies that combat the biophysical and structural function of EPS for the eradication of bacteria in mucoid biofilms during chronic infections. This knowledge can be used to further identify unknown matrix component interactions within pathogenic biofilm-forming clinical isolates.

Application of positively charged red mud-based carriers for anaerobic ammonium oxidizing bacteria biofilm formation

Enrichment of anaerobic ammonium oxidizing bacteria (AnAOB) in the anaerobic ammonium oxidation (anammox) process remains a challenge in engineering applications. In this study, for faster enrichment of AnAOB, red mud-based carriers were positively charged with FeCl3 and microbial promoters. The experimental results showed that the average nitrogen removal rates of the red mud-based carriers (RMGA), FeCl3-modified red mud-based carriers (RMGA-Fe), and microbial promoter-modified red mud-based carriers (RMGA-MA) increased by 24.4%–175% compared with the commercially available K3 carriers. Combining the results of SEM and laser confocal microscope, electrostatic attraction played a leading role on loading AnAOB. The increase in the surface roughness and specific area of the carriers after the attachment and the presence of Fe2+, Ca2+, and Mg2+ plasma were necessary for the subsequent growth of AnAOB, while the leaching of Cr(VI) promoted the nitrogen removal effect of AnAOB.

Quantitative Insights and Visualization of Antimicrobial Tolerance in Mixed-Species Biofilms.

Biofilms are a major problem in hard-to-heal wounds. Moreover, they are composed of different species and are often tolerant to antimicrobial agents. At the same time, interspecific synergy and/or competition occurs when some bacterial species clash. For this reason, the tolerance of two dual-species wound biofilm models of Pseudomonas aeruginosa and Staphylococcus aureus or Enterococcus faecium against antimicrobials and antimicrobial dressings were analyzed quantitatively and by confocal laser scanning microscopy (CLSM). The results were compared to findings with planktonic bacteria. Octenidine-dihydrochloride/phenoxyethanol and polyhexamethylene biguanide (PHMB) irrigation solutions showed a significant, albeit delayed reduction in biofilm bacteria, while the PHMB dressing was not able to induce this effect. However, the cadexomer-iodine dressing caused a sustained reduction in and killed almost all bacteria down to 102 cfu/mL within 6 days compared to the control (1010 cfu/mL). By means of CLSM in untreated human biofilm models, it became evident that P. aeruginosa dominates over E. faecium and S. aureus. Additionally, P. aeruginosa appeared as a vast layer at the bottom of the samples, while S. aureus formed grape-like clusters. In the second model, the distribution was even clearer. Only a few E. faecium were visible, in contrast to the vast layer of P. aeruginosa. It seems that the different species avoid each other and seek their respective niches. These mixed-species biofilm models showed that efficacy and tolerance to antimicrobial substances are nearly species-independent. Their frequent application appears to be important. The bacterial wound biofilm remains a challenge in treatment and requires new, combined therapy options.

A novel indolylbenzoquinone compound HL-J6 suppresses biofilm formation and α-toxin secretion in methicillin-resistant Staphylococcus aureus

Eradication of methicillin-resistant Staphylococcus aureus (MRSA) is challenging due to multi-drug resistance of strains and biofilm formation, the latter of which is an important barrier to the penetration of antibiotics and host defences. As such, there is an urgent need to discover and develop novel agents to fight MRSA-associated infection. In this study, HL-J6, a novel indolylbenzoquinone compound, was shown to inhibit S. aureus strains, with a minimum inhibitory concentration against MRSA252 of 2 µg/mL. Moreover, HL-J6 exhibited potent antibiofilm activity in vitro and was able to kill bacteria in biofilm. In the mouse models of wound infection, HL-J6 treatment reduced the MRSA load significantly and inhibited biofilm formation on the wounds. The potent targets of its antibiofilm activity were explored by real-time reverse transcriptase polymerase chain rection, which indicated that HL-J6 downregulated the transcription levels of sarA, atlAE and icaADBC. Moreover, Western blot results showed that HL-J6 reduced the secretion level of α-toxin, a major virulence factor. These findings indicate that HL-J6 is a promising lead compound for the development of novel drugs against MRSA biofilm infections.

Microplastics Enhance the Prevalence of Antibiotic Resistance Genes in Anaerobic Sludge Digestion by Enriching Antibiotic-Resistant Bacteria in Surface Biofilm and Facilitating the Vertical and Horizontal Gene Transfer.

Antibiotic resistance genes (ARGs) and microplastics (MPs) are recognized as emerging contaminants and threats to global human health. Despite both of them being significantly detected in their "hotspots", i.e., waste activated sludge (WAS), rare studies on how MPs affect ARGs and antibiotic-resistant bacteria (ARB) in anaerobic sludge digestion are available. Herein, the fate of ARGs and ARB after exposure to MPs of three dosages (10, 30, and 80 particles/g-TS), three polymer types (LDPE, PET, and PS), and three branching extents (LDPE, LLDPE, and HDPE) in anaerobic sludge digestion was investigated. Metagenomic results indicated that all variants of MPs resulted in an increase of the relative abundance of ARGs in the digester compared to the control. The abundance of ARGs demonstrated a dosage-dependent relationship within the range from 10 to 80 particles/g-TS, resulting in an increase from 4.5 to 27.9% compared to the control. Branching structure and polymer type influence ARG level in the sludge digester as well. Mechanism studies revealed that LDPE selectively enriched potential ARB and ARGs in the surface biofilm, possibly creating a favorable environment for ARB proliferation and ARG exchange. Furthermore, vertical transfer of ARGs was facilitated by LDPE through increasing bacterial cell proliferation accompanied by the enhancement of relevant functional genes. The elevated abundance of mobile genetic elements (MGEs) and ARGs-carrying plasmids also demonstrated that MGE-mediated horizontal transfer was promoted by LDPE at 80 particles/g-TS. This effect was compounded by increased oxidative stress, cell membrane permeability, and cell cohesion, collectively facilitating horizontal ARG transfer. Consequently, both vertical and horizontal transfer of ARGs could be concurrently promoted by LDPE an in anaerobic sludge digester.