Biofilm Formation Characteristics Research Articles

Distinct microbial community structures formed on the biofilms of PLA and PP, influenced by physicochemical factors of sediment and polymer types in a 60-day indoor study

Microplastics (MPs) are colonized by biofilm-forming microbes. Biodegradable plastics, popular replacements for traditional plastics, still have unknown biofilm formation characteristics. We conducted a 60-day indoor experiment, where sediment was exposed to traditional MPs (polypropylene, PP), biodegradable MPs (polylactic acid, PLA), and glass beads (GLASS). The microbial communities in the MPs-biofilm were analyzed using high-throughput sequencing. Results indicated that Proteobacteria was the dominant phylum on all substrates, followed by Actinobacteria, and Firmicutes. At the genus level, the majority of microorganisms colonizing PP possessed nitrification and denitrification capabilities, while the dominant bacteria on PLA were capable of degrading lignin, cellulose and carbon metabolism. The genus Sphingomonas, a promising bacteria capable of degrading biodegradable microplastics, was particularly discovered on the PLA biofilm, meanwhile, bacterial colonization of PLA indirectly increased the potential for human transmission of pathogens. Redundancy analysis revealed that the pH and moisture significantly affected the bacterial communities. Pearson correlation heatmap indicated that the abundance of the majority of dominant bacterial genera of two MPs biofilms is negatively correlated with the physicochemical parameters of sediment (pH, moisture, TN, TP), except for salinity. The microbial communities associated with PP and PLA exhibited distinct differences caused by the combined effects of changes in physicochemical properties of sediment and different material substrates. This study provides further evidence of the significant selective features exhibited by microbial colonization on these two MPs when exposed to the same source community, offering insights into the exploration of promising bacteria for MPs degradation.

Evaluation of In Vitro Biofilm Formation of Helicobacter pylori in Different Culture Media

Objective: Biofilms are surface-attached cell communities that play a role in the survival of bacteria. Helicobacter pylori, a gram-negative pathogen that colonizes the human gastric mucosa, forms biofilms, causing treatment failure and the risk of developing peptic ulcers, gastritis and gastric cancer in infected individuals. The aim of the study is to evaluate the biofilm formation abilities of H. pylori ATCC 26695 and three clinical strains in different culture media. Material and Method: Biofilm formation characteristics of H. pylori strains using different culture media were evaluated, and the crystal violet (CV) staining method (measured at OD 595 ) was used. Various media were used for incubating H. pylori strains: Brucella broth (BB), TSB with 10% FBS, BHI with 10% FBS, BB with 10% FBS, BB with 10% FBS + 0.25% glucose, and BB with 10% FBS + 1% glucose (incubated for 3 days). Additionally, BB with 1% FBS, BB with 10% FBS, and BB with 5% inactivated human serum were incubated for 2 and 4 days at 37°C under microaerophilic conditions. Results: It was observed that 5% inactived human serum was more effective in biofilm formation of H. pylori ATCC 26695 and three clinical strains. However, there was no biofilm production in the strains cultured with Brucella broth alone and that the strains cultured with TSB + 10% FBS could not form a strong biofilm compared to other media. Conclusion: Different culture media used for H. pylori ATCC 26695 and three clinical strains affect biofilm formation. It is thought that in vitro experiments to prevent biofilm formation may provide a solution to the prevention of H. pylori infection.

Pathogenicity of Multidrug-Resistant Salmonella typhimurium Isolated from Ducks.

Salmonella typhimurium (S. typhimurium) is one of the most common Salmonella serotypes in epidemiological surveys of poultry farms in recent years. It causes growth retardation, mortality, and significant economic losses. The extensive use of antibiotics has led to the emergence of multi-drug resistance (MDR) in Salmonella, which has become a significant global problem and long-term challenge. In this study, we investigated the prevalence and features of S. typhimurium strains in duck embryos and cloacal swabs from large-scale duck farms in Shandong, China, including drug resistance and virulence genes and the pathogenicity of an S. typhimurium strain by animal experiment. The results demonstrated that a total of 8 S. typhimurium strains were isolated from 13,621 samples. The drug resistance results showed that three of the eight S. typhimurium strains were MDR with the dominant resistance profile of CTX-DX-CTR-TE-AMX-AMP-CAZ. In particular, the virulence genes invA, hilA, pefA, rck, and sefA showed high positive rates. Based on the analysis of the biological characteristics of bacterial biofilm formation and mobility, a strain of S. typhimurium with the strongest biofilm formation ability, designated 22SD07, was selected for animal infection experiments with broiler ducklings. The results of animal experiments demonstrated that infection with 22SD07 reduced body weight and bursa index but increased heart and liver indexes compared to the control group. Histological examination revealed desquamation of the intestinal villous epithelium, the presence of large aggregates of lymphocytes, and a decrease in goblet cells following infection. Furthermore, the expression of IL-10 was significantly increased in the liver at 3 dpi, while TNF-α was significantly increased in the spleen at 7 dpi. The above results indicate that S. typhimurium may pose a potential threat to human health through the food chain. This helps us to understand the frequency and characteristics of S. typhimurium in duck farms and emphasizes the urgent need to strengthen and implement effective continuous monitoring to control its infection and transmission.

Potential risk of biofilm-forming Bacillus cereus group in fresh-cut lettuce production chain

Bacillus cereus and Bacillus thuringiensis, which belong to the B. cereus group, are widely distributed in nature and can cause food poisoning symptoms. In this study, we collected 131 isolates belonging to the B. cereus group, comprising 124B. cereus and seven B. thuringiensis isolates, from fresh-cut lettuce production chain and investigated their potential risk by analyzing genotypic (enterotoxin and emetic toxin gene profiles) and phenotypic (antibiotic susceptibility, sporulation, and biofilm formation) characteristics. Enterotoxin genes were present only in B. cereus, whereas the emetic toxin gene was not detected in any of the B. cereus isolates. All isolates were susceptible to vancomycin, which is a last resort for treating B. cereus group infection symptoms, but generally resistant to β-lactam antimicrobials, and had the ability to form spores (at an average sporulation rate of 24.6 %) and biofilms at 30 °C. Isolates that formed strong biofilms at 30 °C had a superior possibility of forming a dense biofilm by proliferating at 10 °C compared to other isolates. Additionally, confocal laser scanning microscopy (CLSM) images revealed a notable presence of spores within the submerged biofilm formed at 10 °C, and the strengthened attachment of biofilm inner cells to the substrate was further revealed through biofilm structure parameters analysis. Collectively, our study revealed the prevalence and contamination levels of B. cereus and B. thuringiensis at fresh-cut lettuce production chain and investigated their genotypic and phenotypic characteristics, aiming to provide valuable insights for the development of potential risk management strategies to ensure food safety, especially along the cold chain.

Exploring the efficiency of tide flow constructed wetlands for treating mariculture wastewater: A comprehensive study on antibiotic removal mechanism under salinity stress

Antibiotic residues in aquaculture environment pose persistent threats to ecology and human health, exacerbated by salt-alkali mariculture wastewater. Yet, little is known about antibiotic removal in tidal flow constructed wetlands (TFCWs) under salinity stress, especially considering TFCW constitution, configuration, and influent water characteristics. Here, the removal performance and mechanism of different TFCWs for sulfonamide antibiotics (SAs: sulfadiazine, sulfamethazine, sulfamonomethoxine, and sulfamethoxazole) and trimethoprim (TMP) from mariculture wastewater (with low, medium, and high salinity) were evaluated alongside comparisons of environmental factors and microbial responses. Results showed substantial reduction in alkalinity (from 8.25–8.26 to 7.65–8.18), salinity (from 3.67–11.30 ppt to 3.20–10.79 ppt), and SAs concentrations (from 7.79–15.46 mg/L to 0.25–10.00 mg/L) for mariculture wastewater using TFCWs. Zeolite and yellow flag configurations exhibited superior performance in SAs removal from mariculture wastewater. Furthermore, the salt-alkali neutralization and oxygen transport capabilities of zeolite, along with the salt-alkali tolerance and biofilm formation characteristics of yellow flag, promoted the development of a biofilm in the rhizosphere dominated by oxidative stress tolerance and facultative anaerobic traits, thereby improving the TFCW microenvironment. Consequently, aerobic (Sulfuritalea and Enterobacter) and salt-tolerant (Pseudomonas) functional bacteria involved in antibiotic degradation were selectively enriched in the zeolite- and yellow flag-TFCWs, contributing to the effective biodegradation of SAs (achieving removal efficiency of 92–97 %). Besides, the high salt-alkali levels of mariculture wastewater and the strong oxygen-enriched capacity of the TFCWs not only enhanced the aerobic oxidation reaction of SAs, but also bidirectionally inhibited the substrate adsorption and anaerobic reduction process of TMP. These findings address a critical gap by investigating the efficacy of TFCWs in removing antibiotics from mariculture wastewater under various salinity conditions, providing essential insights for optimizing wetland design and improving wastewater management in mariculture environments.

Characteristics of drug resistance and biofilm formation in carbapenem-resistant Acinetobacter baumannii in hospitalized children

To study the distribution, drug resistance, and biofilm characteristics of carbapenem-resistant Acinetobacter baumannii (CRAB) isolated from hospitalized children, providing a reference for the prevention and treatment of CRAB infections in hospitalized children. Forty-eight CRAB strains isolated from January 2019 to December 2022 were classified into epidemic and sporadic strains using repetitive extragenic palindromic sequence-based polymerase chain reaction. The drug resistance, biofilm phenotypes, and gene carriage of these two types of strains were compared. Both the 22 epidemic strains and the 26 sporadic strains were producers of Class D carbapenemases or extended-spectrum β-lactamases with downregulated outer membrane porins, harboring the VIM, OXA-23, and OXA-51 genes. The biofilm formation capability of the sporadic strains was stronger than that of the epidemic strains (P<0.05). Genes related to biofilm formation, including Bap, bfs, OmpA, CsuE, and intI1, were detected in both epidemic and sporadic strains, with a higher detection rate of the intI1 gene in epidemic strains (P<0.05). CRAB strains are colonized in the hospital, with sporadic strains having a stronger ability to form biofilms, suggesting the potential for forming new clonal transmissions in the hospital. Continuous monitoring of the epidemic trends of CRAB and early warning of the distribution of epidemic strains are necessary to reduce the risk of CRAB infections in hospitalized children.

Characteristics of Bacterial Biofilm Formation in Nasolacrimal Silicone Tubes Post-dacryocystorhinostomy.

To examine the biofilm formation characteristics of bacteria identified at the genus level in samples obtained from silicone tubes after dacryocystorhinostomy surgery. In the study involving consecutive patients who underwent dacryocystorhinostomy surgery at Ankara Bilkent City Hospital and whose silicone tubes were removed six months after surgery, between January 2023 and May 2023; the tubes were placed in glycerol-PBS (phosphate buffered saline) solution and cultured on descriptive selective media at the genus level. The biofilm-forming properties of the obtained isolates were examined in solid-air and liquid-air interphases. Salmonella Typhimurium ATCC SL1344 strain was used as the control bacterium. As a result of the analysis of the samples taken from the patients, Pseudomonas spp. was identified in three of the samples, Staphylococcus spp. in five of the samples, and Streptococcus spp. in one of the samples. Among these samples, except for the bacteria identified in samples one and five, the rest were found to be strong biofilm producers. In all strong biofilm producers, the maximum biofilm production time was determined as 72 h and the incubation temperature was 37°C. The presence of cellulose and amyloid proteins in biofilm matrix structures is identified. Swimming and swarming motilities were observed in all bacterial samples. Since biofilms are considered potential factors in the pathogenesis of infectious and inflammatory diseases, they are a subject that needs to be thoroughly investigated. In our study, although there were no clinical infections in any of the patients, biofilm formation was detected in the patient samples. The fact that the bacteria exhibited moderate to strong biofilm formation characteristics suggests that these microorganisms could be persistent infectious agents.

Culture dependent analysis of bacterial activity, biofilm-formation and oxidative stress of seawater with the contamination of microplastics under climate change consideration

Temperature changes due to climate change and microplastic contamination are worldwide concerns, creating various problems in the marine environment. Therefore, this study was carried out to discover the impact of different temperatures of seawater exposed to different types of plastic materials on culture dependent bacterial responses and oxidative characteristics. Seawater was exposed to microplastics obtained from various plastic materials at different temperature (−18, +4, +20, and +35 °C) for seven days. Then microplastics were removed from the suspension and microplastic-exposed seawater samples were analyzed for bacterial activity, biofilm formation and oxidative characteristics (antioxidant, catalase, glutathione, and superoxide dismutase) using Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus. The results showed that the activity and biofilm formation of Pseudomonas aeruginosa and Staphylococcus aureus were affected through oxidative stress by catalase, glutathione, and superoxide dismutase due to the microplastic deformation by temperature changes. This study confirms that temperature changes as a result of climate change might influence microplastic degradation and their contamination impact in seawater in terms of bacterial metabolic and oxidation reactions.

Airborne signals of Pseudomonas fluorescens modulate swimming motility and biofilm formation of Listeria monocytogenes in a contactless coculture system

Bacterial volatile compounds (BVCs) facilitate interspecies communication in socio-microbiology across physical barriers, thereby influencing interactions between diverse species. The impact of BVCs emitted from Pseudomonas on the biofilm formation characteristics of Listeria monocytogenes within the same ecological niche has been scarcely investigated under practical conditions of food processing. The objective of this study was to explore the motility and biofilm formation characteristics of L. monocytogenes under the impact of Pseudomonas BVCs. It was revealed that BVCs of P. fluorescens, P. lundensis, and P. fragi significantly promoted swimming motility of L. monocytogenes (P < 0.05). As evidenced by crystal violet staining, the L. monocytogenes biofilms reached a maximum OD570 value of approximately 3.78 at 4 d, which was 0.65 units markedly higher than that of the control group (P < 0.05). Despite a decrease in adherent cells of L. monocytogenes biofilms among the BVCs groups, there was a remarkable increase in the abundance of extracellular polysaccharides and proteins with 3.58 and 4.90 μg/cm2, respectively (P < 0.05), contributing to more compact matrix architectures, which suggested that the BVCs of P. fluorescens enhanced L. monocytogenes biofilm formation through promoting the secretion of extracellular polymers. Moreover, the prominent up-regulated expression of virulence genes further revealed the positive regulation of L. monocytogenes under the influence of BVCs. Additionally, the presence of BVCs significantly elevated the pH and TVB-N levels in both the swimming medium and biofilm broth, thereby exhibiting a strong positive correlation with increased motility and biofilm formation of L. monocytogenes. It highlighted the crucial signaling regulatory role of BVCs in bacterial interactions, while also emphasizing the potential food safety risk associated with the hitchhiking behavior of L. monocytogenes, thereby shedding light on advancements in control strategies for food processing.

Novel Antimicrobial Approaches to Combat Bacterial Biofilms Associated with Urinary Tract Infections.

Urinary tract infections (UTIs) are prevalent bacterial infections in both community and healthcare settings. They account for approximately 40% of all bacterial infections and require around 15% of all antibiotic prescriptions. Although antibiotics have traditionally been used to treat UTIs for several decades, the significant increase in antibiotic resistance in recent years has made many previously effective treatments ineffective. Biofilm on medical equipment in healthcare settings creates a reservoir of pathogens that can easily be transmitted to patients. Urinary catheter infections are frequently observed in hospitals and are caused by microbes that form a biofilm after a catheter is inserted into the bladder. Managing infections caused by biofilms is challenging due to the emergence of antibiotic resistance. Biofilms enable pathogens to evade the host's innate immune defences, resulting in long-term persistence. The incidence of sepsis caused by UTIs that have spread to the bloodstream is increasing, and drug-resistant infections may be even more prevalent. While the availability of upcoming tests to identify the bacterial cause of infection and its resistance spectrum is critical, it alone will not solve the problem; innovative treatment approaches are also needed. This review analyses the main characteristics of biofilm formation and drug resistance in recurrent uropathogen-induced UTIs. The importance of innovative and alternative therapies for combatting biofilm-caused UTI is emphasised.

Antifungal and antibiofilm activities of chromones against nine Candida species.

Candida species are the most common cause of fungal infections, and thus the emergence of antifungal-resistant species and biofilm formation by Candida further threatens the limited availability of antifungal agents. We investigated the antifungal and antibiofilm activities of 27 chromones against nine Candida species, including Candida albicans, Candida glabrata, Candida parapsilosis, and Candida auris. Four chromone-3-carbonitriles exhibited good antifungal activity with minimum inhibitory concentrations from 5 to 50 µg/mL and significantly inhibited biofilm formation by C. albicans. Furthermore, these four chromone-3-carbonitriles markedly inhibited cell aggregation and hypha formation, which are virulence factors and prerequisites for C. albicans biofilm formation. Transcriptomic analyses showed that the most active 6-bromochromone-3-carbonitrile downregulated the expressions of hypha-forming and biofilm-related genes (TEC1 and UME6) but upregulated the hyphal regulator UCF1. Toxicity assays conducted using plant and nematode models showed that the four chromone-3-carbonitriles were non-to-mildly toxic. This study suggests that chromones bearing the 3-carbonitrile motif should be considered potential antifungal agents against Candida species.IMPORTANCEThe persistence of Candida infections is due to its ability to form biofilms that enable it to resist antifungals and host immune systems. Hence, inhibitions of the biofilm formation and virulence characteristics of Candida sp. provide potential means of addressing these infections. Among various chromone derivatives tested, four chromone-3-carbonitriles showed antifungal, antibiofilm, and antivirulence activities against several Candida species. Their mode of action has been partially revealed, and their toxicity is reported here using nematode and plant models.

Phenotypic Investigation of Virulence Factors, Susceptibility to Ceragenins, and the Impact of Biofilm Formation on Drug Efficacy in Candida auris Isolates from Türkiye.

Candida auris has emerged as a significant fungal threat due to its rapid worldwide spread since its first appearance, along with its potential for antimicrobial resistance and virulence properties. This study was designed to examine virulence characteristics, the efficacy of ceragenins, and biofilm-derived drug resistance in seven C. auris strains isolated from Turkish intensive care patients. It was observed that none of the tested strains exhibited proteinase or hemolysis activity; however, they demonstrated weak phospholipase and esterase activity. In addition, all strains were identified as having moderate to strong biofilm formation characteristics. Upon determining the minimum inhibitory concentrations (MIC) of ceragenins, it was discovered that CSA-138 exhibited the highest effectiveness with a MIC range of 1-0.5 µg/mL, followed by CSA-131 with a MIC of 1 µg/mL. Also, antimicrobial agents destroyed mature biofilms at high concentrations (40-1280 µg/mL). The investigation revealed that the strains isolated from Türkiye displayed weak exoenzyme activities. Notably, the ceragenins exhibited effectiveness against these strains, suggesting their potential as a viable treatment option.

Effect of plasma-activated water on the biofilm-forming ability of Salmonella enterica serovar Enteritidis and expression of the related genes

In recent years, microbial decontamination with plasma-activated water (PAW) has attracted a lot of research attention in the field of food industry. Despite several studies showing that PAW effectively inactivates planktonic bacteria, few studies have been conducted on biofilms. The present study was, therefore, designed to evaluate the effect of PAW on the biofilm formation characteristics of Salmonella Enteritidis. Comparing the expression patterns of biofilm-related genes in PAW-treated and non-treated planktonic and biofilm cells provided insight into how PAW regulates this process. The results showed that a 30-minute exposure to PAW at room temperature significantly reduced S. enteritidis planktonic cells. This exposure resulted in a decreased expression of the genes involved in the early stages of biofilm formation (csgD, agfA, fimA, lpfE, and rpoS), and an increased expression of the csrA gene in S. enteritidis planktonic cells. These results indicated the inhibitory effect of PAW on the biofilm formation process in S. enteritidis. Results of the initial attachment assay confirmed these findings, where, after 6 h, the number of PAW-treated cells attached to the stainless steel surfaces were significantly lower than non-treated ones. Furthermore, biofilm development assay revealed that the number of PAW-treated biofilm cells were significantly lower than non-treated ones after 24 h incubation at 37 °C. These findings were confirmed by measurements of the major components of biofilm i.e., extracellular DNA (eDNA), protein and carbohydrate. The amount of these components in 24-hour biofilms produced by PAW-treated S. enteritidis cells was significantly lower than that of non-treated cells. PAW's treatment on preformed 24-hour biofilms for 30 min led to a decrease in the expression of genes involved in quorum sensing and cellulose synthesis (csgD, bapA, adrA, luxS and sdiA) and an increase in the expression of the csrA gene. This treatment also reduced the number and metabolic activity of biofilm cells compared to non-treated biofilm cells. In total, the present study demonstrated that PAW has an inhibitory effect on the process of biofilm formation in S. enteritidis and hence, the food industry should pay special attention to PAW as a promising treatment to eliminate bacterial biofilms.

An overview of various methods for in vitro biofilm formation: a review.

Biofilms are widely present in the natural environment and are difficult to remove as they are a survival strategy of microorganisms. Thus, the importance of studying biofilms is being increasingly recognized in food, medical, dental, and water quality-related industries. While research on biofilm detection methods is actively progressing, research on biofilm formation is not progressing rapidly. Moreover, there are few standardized methods because biofilm formation is affected by various factors. However, comprehensive knowledge of biofilm formation is essential to select a suitable method for research purposes. To better understand the various in vitro biofilm formation methods, the principles and characteristics of each method are explained in this review by dividing the methods into static and dynamic systems. In addition, the applications of biofilm research based on various assays are also discussed.

Biofilm formation, hyphae growth, and transcriptome characteristics of C. albicans surviving high-pressure processing

High-pressure processing (HPP) is considered effective for sterilizing minimally processed vegetable-based products. This study found that HPP could not completely inactivate the microorganisms in pickles. Candida albicans (C. albicans), an opportunistic pathogen in pickles, survived HPP exposure, while its death rate did not increase significantly with a further increase in holding time and pressure. It was striking that the biofilm formation and hyphae growth of C. albicans survived from 400 MPa HPP increased. Transcriptome analysis showed that 400 MPa affected more C. albicans genes than 300 MPa. The treatment at 300 MPa mainly facilitated transmembrane transport changes, while 400 MPa modified several metabolic processes. Furthermore, different pressure conditions caused various changes in important biofilm/hyphae-related genes, many of which were downregulated after 300 MPa treatment while upregulated after exposure to 400 MPa (NDT80, BRG1, GZF3, UME6, SET3, PES1, XOG1, RHR2, and SUN41). In addition, the GDH3, HGT9, and AAT21 genes may also play a vital role in the C. albicans tolerance of HPP. These findings emphasized the potential increased risk caused by the inability of HPP to inactive yeasts in food industry.

Comparative Analysis of MRSA Isolation, Biofilm Formation, and Molecular Characteristics: Hospital-Acquired Versus Community-Acquired Strains

The current study was to look into the molecular characterisation and biofilm development of MRSA in patients who visited the Khyber Teaching Hospital, Hayatabad Medical Complex, and Lady Reading Hospital in Peshawar. Antibiotic susceptibility tests identify Methicillin-resistant Staphylococcus aureus in confirmed isolates of S. aureus. PCR was used to identify a gene, which proved that the MRSA isolates were real. HA- and CA-MRSA were distinguished by SCC mec typing. The microtiter plate assay was employed to look for signs of biofilm formation. 133 (82.60%) of the 161 samples that were positive for S. aureus. Of them, 32 (19.87%) had MSSA isolates, 28 (17.39%) were culture-negative, and 101 (62.73%) were determined to carry MRSA. To confirm all positive isolates one more time, Mec A gene analysis was performed. Twenty-one (20.79%) of the eighty (79.20%) confirmed isolates were classified as undistinguishable MRSA isolates, twenty-six (32.5%) as HA-MRSA isolates, and fifty-five (67.5%) as CA-MRSA isolates.

Acceleration of Aerobic Granulation in Sidestream Treatment with Exogenous Autoinducer

Aerobic granular sludge (AGS) is a special type of biofilm formed by the self-aggregation of microorganisms and extracellular polymers and is considered a promising technology for wastewater treatment. However, new strategies are still being proposed as to how to improve the extracellular polymeric substances (EPS) production that influences the formation of AGS. Recently, the acceleration of aerobic granulation using autoinducers such as N-acyl-homoserine lactone (AHL)-mediated quorum sensing has been reported. However, it is not yet fully understood due to knowledge gaps on the correlations depending on the type of AHL used. In this study, to evaluate the effects of various AHL on the AGS formation of activated sludge, the secretion of extracellular polymeric substances, biofilm formation, and sludge characteristics were comprehensively investigated. Among the AHL types, tightly bound EPS (TB-EPS) and loosely bound EPS (LB-EPS) in the reactor with C8-HSL added were 18.49 and 74.07 mg/g VSS, respectively, which represented increases of 3.15% and 53.76% compared to the control group. Additionally, C8-HSL increased the relative hydrophobicity and biomass volume by 153% and 218%, respectively. As a result, AHL had a positive effect on biomass content, an increase in sludge size, and an improvement in sludge sedimentation in the early stage of granulation, and C8-HSL was found to be the most suitable for initial granulation among AHL types.

Sublethal chlorine stress promotes the biofilm-forming ability of Salmonella enterica serovars enteritidis and expression of the related genes

Chlorine treatment is the most common disinfection method in food-related environments. In addition to being simple and inexpensive, this method is very effective if used properly. However, insufficient chlorine concentrations only cause a sublethal oxidative stress in the bacterial population and may alter the growth behavior of stressed cells. In the present study, the effect of sublethal chlorine stress on the biofilm formation characteristics of Salmonella Enteritidis was evaluated. Our results demonstrated that, sublethal chlorine stress (350 ppm total chlorine) activates the biofilm (csgD, agfA, adrA and bapA) and quorum-sensing (sdiA and luxS) related genes in planktonic cells of S. Enteritidis. The higher expression of these genes illustrated that the chlorine stress induced the initiation of the biofilm formation process in S. Enteritidis. Results of the initial attachment assay confirmed this finding. In addition, the number of chlorine-stressed biofilm cells was significantly higher than non-stressed biofilm cells after 48 h incubation at 37 °C. In S. Enteritidis ATCC 13076 and S. Enteritidis KL19, the number of chlorine-stressed biofilm cells were 6.93 ± 0.48 and 7.49 ± 0.57 log CFU/cm2, while the number of non-stressed biofilm cells were 5.12 ± 0.39 and 5.63 ± 0.51 log CFU/cm2, respectively. These findings were confirmed by measurements of the major components of biofilm, i.e., eDNA, protein and carbohydrate. The amount of these components in 48-h biofilms was higher when the cells were initially subjected to sublethal chlorine stress. However, the up-regulation of the biofilm and quorum sensing genes was not observed in 48-h biofilm cells, indicating that the effect of chlorine stress had vanished in the subsequent generations of Salmonella. In total, these results revealed that sublethal chlorine concentrations can promote the biofilm-forming ability of S Enteritidis.

Stutzerimonas frequens strain TF18 with superior heterotrophic nitrification-aerobic denitrification ability for the treatment of aquaculture effluent

Currently, microbial techniques have been comprehensively exploited in aquaculture effluent treatment. However, strains for bioaugmentation face many issues, such as poor adaptability, long colonization time, and unsatisfactory treatment effect. Herein, an efficient heterotrophic nitrifying-aerobic denitrifying bacterium Stutzerimonas frequens strain TF18 was isolated from the Whiteleg shrimp (Penaeus vannamei) mariculture environment. Strain TF18 exhibited strong biofilm formation and auto-aggregation characteristics, which indicated its robust adaptability and short colonization time. Remarkably, the total ammonia nitrogen, NO2--N, and NO3--N removal efficiencies of the strain were 89.21 %, 99.76 %, and 96.16 %, respectively, in the presence of sodium acetate as carbon source and carbon-nitrogen ratio of 10. Most importantly, identification of genes related to nitrogen removal, including nirS, norB, nosZ, nasA, napA, narG, and nirB, and their relative expression further demonstrated the existence of nitrate transformation pathways in strain TF18. These results provided new guidance for practical application of S. frequens strain TF18 in aquaculture effluent treatment.

Synthesis of Bio-Based Polybenzoxazine and Its Antibiofilm and Anticorrosive Activities.

Candida albicans are highly widespread pathogenic fungi in humans. Moreover, its developed biofilm causes serious clinical problems, leading to drug failure caused by its inherent drug tolerance. Hence, the inhibition of biofilm formation and virulence characteristics provide other means of addressing infections. Polymer composites (PCs) derived from natural products have attracted increasing interest in the scientific community, including antimicrobial applications. PCs are a good alternative approach to solving this challenge because of their excellent penetration power inside biofilms. The main objectives of this study were to synthesize a novel curcumin-based polybenzoxazine polymer composite (poly(Cu-A) PC) using Mannich condensation reaction and evaluate their potency as an antibiofilm and anticorrosive candidate against C. albicans. In addition, their anticorrosive efficacy was also explored. PC exhibited significant antibiofilm efficacy versus C. albicans DAY185 by the morphologic changing of yeast to hyphae, and>90% anticorrosive efficacy was observed at a higher dose of PC. These prepared PC were safe in vivo against Caenorhabditis elegans and Raphanus raphanistrum. The study shows that a polybenzoxazine polymer composite has the potential for controlling biofilm-associated fungal infections and virulence by C. albicans, and opens a new avenue for designing PCs as antifungal, anticorrosive agents for biofilm-associated fungal infections and industrial remediation.