Cell adhesion and twitching motility influence strong biofilm formation in Pseudomonas aeruginosa

Proteomic approach to identify host cell attachment proteins provides protective Pseudomonas aeruginosa vaccine antigen FtsZ

Pseudomonas aeruginosa is an opportunistic Gram-negative pathogen that causes severe nosocomial infections in susceptible individuals due to the emergence of multidrug-resistant strains. There are no approved vaccines against P. aeruginosa infections nor candidates in active clinical development, highlighting the need for novel candidates and strategies. Using a cell-blot proteomic approach, we reproducibly identified 49 proteins involved in interactions with human lung epithelial cells across four P. aeruginosa strains. Among these were cell division protein FtsZ and outer membrane protein OpmH. Escherichia coli BL21 cells overexpressing recombinant FtsZ or rOpmH showed a 66- and 15-fold increased ability to attach to 16HBE14o- cells, further supporting their involvement in host cell attachment. Both antigens led to proliferation of NK and CD8+ cytotoxic T cells, significant increases in the production of IFN-γ, IL-17A, TNF and IL-4 in immunised mice and elicited strong antigen-specific serological IgG1 and IgG2c responses. Immunisation with FtsZ significantly reduced bacterial burden in the lungs by 1.9-log CFU and dissemination to spleen by 1.8-log CFU. The protective antigen candidate, FtsZ, would not have been identified by traditional approaches relying on either virulence mechanisms or sequence-based predictions, opening new avenues in the development of an anti-P. aeruginosa vaccine.

Evaluation of Antimicrobial Resistance Patterns of Pseudomonas aeruginosa Strains Isolated among COVID-19 Patients in Brazil Typed by Fourier-Transform Infrared Spectroscopy

This study aimed to characterize Pseudomonas aeruginosa strains isolated from hospitalized patients during the COVID-19 pandemic. This was achieved using phenotypic and molecular techniques, including their antimicrobial resistance profile and biofilm formation. Eighteen strains were isolated from a hospital in Rio de Janeiro, Brazil, and identified by VITEK®2, MALDI-TOF/MS (VITEK MS® and MALDI Biotyper®), and 16S rRNA sequencing. Fourier-transform infrared (FTIR) spectroscopy, antimicrobial susceptibility testing, and biofilm formation and disinfectant tolerance tests were applied to evaluate the virulence characteristics of the strains. VITEK®2 (≥99%), VITEK MS® (≥82.7%), and MALDI Biotyper® (score ≥ 2.01) accurately identified the P. aeruginosa strains, but 16S rRNA sequencing did not differentiate the species P. aeruginosa from P. paraeruginosa. FTIR typing identified three different clusters, but no correlation between the phenotypical or antimicrobial susceptibility testing patterns was found. Most strains exhibited resistance to various antimicrobials. The exceptions were sensitivity to amikacin and norfloxacin, and consequently, these could be considered potential treatment options. Most strains (n = 15, 83.3%) produced biofilms on polystyrene. Sodium hypochlorite treatment (0.5%/15 min) was shown to be the most effective disinfectant for biofilm elimination. P. aeruginosa biofilm formation and tolerance to disinfectants demonstrate the need for effective cleaning protocols to eliminate contamination by this organism in the hospital environment and medical equipment.

FTY720 Reduces the Biomass of Biofilms in Pseudomonas aeruginosa in a Dose-Dependent Manner

Pseudomonas aeruginosa, a nosocomial pathogen, has strong biofilm capabilities, representing the main source of infection in the human body. Repurposing existing drugs has been explored as an alternative strategy to combat emerging antibiotic-resistant pathogens. Fingolimod hydrochloride (FTY720), an immunomodulatory drug for multiple sclerosis, has shown promising antimicrobial effects against some ESKAPE pathogens. Therefore, the effects of FTY720 on the biofilm capabilities of Pseudomonas aeruginosa were investigated in this study. It was determined that FTY720 inhibited the growth of P. aeruginosa PAO1 at 100 µM. The significant reduction in PAO1 cell viability was observed to be dose-dependent. Additional cytotoxicity analysis on human cell lines showed that FTY720 significantly reduced viabilities at sub-inhibitory concentrations of 25-50 µM. Microtiter assays and confocal analysis confirmed reductions in biofilm mass and thickness and the cell survivability ratio in the presence of FTY720. Similarly, virulence production and biofilm-related gene expression (rhlA, rhlB, pilA, pilI, fliC, fliD and algR) were determined. The results demonstrate that pigment production was affected and quantitative real-time PCR analysis showed a variable degree of reduced gene expression in response to FTY720 at 12.5-50 µM. These findings suggest that FTY720 could be repurposed as an alternative antibiofilm agent against Pseudomonas aeruginosa.

Effect of ferric ions on Cronobacter sakazakii growth, biofilm formation, and swarming motility

Cronobacter sakazakii (C. sakazakii) is a common food-borne pathogen that induces meningitis, sepsis, and necrotizing enterocolitis, primarily in newborns and infants. Iron plays a pivotal role in the growth of cells and biofilm formation. However, the effects of hemin (ferric ion donor) on C. sakazakii cells are scarcely known. Here, we explored the effect of ferric ions on the growth of planktonic C. sakazakii, biofilm formation, and swarming motility by crystal violet staining (CVS), scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), and swarming assay. Our study demonstrated that ferric ions facilitated the growth of planktonic C. sakazakii, while hemin at concentrations ranging from 50 to 800 μmol/L promoted biofilm formation and at concentrations between 50 and 200 μmol/L enhanced the swarming motility of C. sakazakii. Furthermore, high hemin concentrations (400-800 μmol/L) were found to reduce flagellar length, as confirmed by transmission electron microscopy (TEM). These findings indicated that ferric ions mediated the swarming motility of C. sakazakii by regulating flagellar assembly. Finally, transcriptomic analysis of C. sakazakii was performed at hemin concentrations of 0, 50, and 200 μmol/L, which revealed that several genes associated with iron transport and metabolism, and flagellar assembly were essential for the survival of C. sakazakii under hemin treatment. Our findings revealed the molecular basis of ferric ions on C. sakazakii growth and biofilm formation, thus providing a novel perspective for its prevention and control.

Biofilm formation: mechanistic insights and therapeutic targets

Biofilms are complex multicellular communities formed by bacteria, and their extracellular polymeric substances are observed as surface-attached or non-surface-attached aggregates. Many types of bacterial species found in living hosts or environments can form biofilms. These include pathogenic bacteria such as Pseudomonas, which can act as persistent infectious hosts and are responsible for a wide range of chronic diseases as well as the emergence of antibiotic resistance, thereby making them difficult to eliminate. Pseudomonas aeruginosa has emerged as a model organism for studying biofilm formation. In addition, other Pseudomonas utilize biofilm formation in plant colonization and environmental persistence. Biofilms are effective in aiding bacterial colonization, enhancing bacterial resistance to antimicrobial substances and host immune responses, and facilitating cell‒cell signalling exchanges between community bacteria. The lack of antibiotics targeting biofilms in the drug discovery process indicates the need to design new biofilm inhibitors as antimicrobial drugs using various strategies and targeting different stages of biofilm formation. Growing strategies that have been developed to combat biofilm formation include targeting bacterial enzymes, as well as those involved in the quorum sensing and adhesion pathways. In this review, with Pseudomonas as the primary subject of study, we review and discuss the mechanisms of bacterial biofilm formation and current therapeutic approaches, emphasizing the clinical issues associated with biofilm infections and focusing on current and emerging antibiotic biofilm strategies.

Transcriptomic analysis reveals novel desiccation tolerance mechanism of Cronobacter based on type VI secretion system inhibition

Cronobacter malonaticus (C. malonaticus) is a food-borne pathogen inducing severe infections both in infants and adults, and it could survive in dry powdered infant formula (PIF) for a long time, implying its strong tolerance to desiccation. However, the thorough molecular mechanism of resistance to desiccation remains elusive. When C. malonaticus was exposed to desiccation conditions (7, 15, and 30 d), transcriptomic analysis provided a universal adaptation strategy to withstand desiccation with the increased compatible solutes accumulation, activated stress resistance-related regulators, suppressed protein export and bacterial secretion system, and reduced other unessential survival functions including adhesion, invasion, virulence, and flagellar motility. Importantly, type VI secretion system (T6SS) genes exhibited significantly downregulated expressions, as well as markedly increased survival and viability of their mutants after desiccation treatment, revealing the negative regulation of T6SS in desiccation tolerance. Meanwhile, the decreased expressions of T6SS structure genes in other six species further confirmed the vital role of T6SS in desiccation tolerance of Cronobacter spp. Thus, our studies present a novel hypothesis of desiccation resistance in Cronobacter based on type VI secretion system inhibition, causing the reduction of macromolecule secretion such as effectors and hyperosmolality development within the cytomembrane, which allow Cronobacter to survive in desiccation.

Characterization and bioactivities of exopolysaccharide produced from Azotobacter salinestris EPS-AZ-6

This study involved the extraction of an exopolysaccharide (EPS) from Azotobacter salinestris AZ-6, which was isolated from soil cultivated with leguminous plants. In a medium devoid of nitrogen, the AZ-6 strain displayed a maximum EPS yield of 1.1 g/l and the highest relative viscosity value of 3.4. The homogeneity of the polymer was demonstrated by the average molecular weight of 1.61 × 106 Da and a retention time of 17.211 min for levan. The presence of characteristic functional groups and structural units of carbohydrate polymers has been confirmed through spectroscopic analyses utilizing Fourier-transform infrared (FT-IR) and nuclear magnetic resonance (NMR) techniques. Thermogravimetric analysis (TGA) revealed a noteworthy decrease in weight (74 %) in the temperature range spanning from 260 to 350 °C. X-ray diffraction (XRD) was utilized to verify the crystalline and amorphous characteristics of EPS-AZ-6. The EPS-AZ-6 exhibited significant cytotoxicity against the MCF-7 tumor cell line, as evidenced by an IC50 value of 6.39 ± 0.05 μg/ml. It also demonstrated a moderate degree of cytotoxicity towards HepG-2 cell line, as indicated by an IC50 value of 29.79 ± 0.41 μg/ml. EPS-AZ-6 exhibited potent antioxidant and in vitro antibacterial properties. These characteristics suggest the potential application value of EPS-AZ-6 in the food industry and pharmaceutical applications.

Zingerone inhibits biofilm formation and enhances antibiotic efficacy against Salmonella biofilm

Salmonella enterica serovar Typhi is a significant cause of typhoid fever and a major public health problem. The ability of S. Typhi to form biofilms on living and non-living surfaces results in antibiotic resistance and poses a major challenge in health care. In this study, we assessed the ability of zingerone alone and in combination with antibiotics against the motility phenotypes and biofilm-forming ability of S. Typhi. Results showed that zingerone effectively reduced the swimming, swarming, and twitching phenotypes and exhibited biofilm inhibition potential. Moreover, zingerone enhanced the antibiofilm activity of ciprofloxacin and kanamycin. Microscopic analysis revealed a thinner biofilm in the presence of zingerone, which may have enhanced the antibiofilm efficacy of the antibiotics. The microscopic analysis showed that the presence of zingerone resulted in a reduction in the thickness of the biofilm, potentially increasing the antibiofilm efficacy of the antibiotics. In silico molecular docking and simulation studies further indicated that zingerone may bind to the fimbriae subunits (FimA, FimC, FimH, and FimY) of S. Typhi and form stable interactions. These findings provide important insights into the potential of zingerone to target biofilm-associated Salmonella infections. Further research is considered a promising option for designing innovative approaches to prevent infections associated with biofilms. Schematic representation of the role of zingerone in biofilm, motility inhibition and molecular interactions with biofilm associated proteins.

Antimicrobial Resistance, Genetic Lineages, and Biofilm Formation in Pseudomonas aeruginosa Isolated from Human Infections: An Emerging One Health Concern

Pseudomonas aeruginosa (PA) is a leading nosocomial pathogen and has great versatility due to a complex interplay between antimicrobial resistance and virulence factors. PA has also turned into one the most relevant model organisms for the study of biofilm-associated infections. The objective of the study focused on analyzing the antimicrobial susceptibility, resistance genes, virulence factors, and biofilm formation ability of thirty-two isolates of PA. PA isolates were characterized by the following analyses: susceptibility to 12 antimicrobial agents, the presence of resistance genes and virulence factors in PCR assays, and the quantification of biofilm production as evaluated by two distinct assays. Selected PA isolates were analyzed through multilocus sequence typing (MLST). Thirty PA isolates have a multi-resistant phenotype, and most of the isolates showed high levels of resistance to the tested antibiotics. Carbapenems showed the highest prevalence of resistance. Various virulence factors were detected and, for the quantification of biofilm production, the effectiveness of different methods was assessed. The microtiter plate method showed the highest accuracy and reproducibility for detecting biofilm-producing bacteria. MLST revealed four distinct sequence types (STs) in clinical PA, with three of them considered high-risk clones of PA, namely ST175, ST235, and ST244. These clones are associated with multidrug resistance and are prevalent in hospitals worldwide. Overall, the study highlights the high prevalence of antibiotic resistance, the presence of carbapenemase genes, the diversity of virulence factors, and the importance of biofilm formation in PA clinical isolates. Understanding these factors is crucial for effective infection control measures and the development of targeted treatment strategies.

Purification of exopolysaccharides from Lactobacillus rhamnosus and changes in their characteristics by regulating quorum sensing genes via polyphenols

To explore the effect of Lonicera caerulea fruit polyphenols (LCP) on caries-causing bacteria, strain RYX-01 with high production of biofilm and exopolysaccharides (EPS) was isolated from the oral cavity of caries patients and was identified as Lactobacillus rhamnosus by 16S rDNA analysis and morphology. The characteristics of EPS produced by RYX-01 (EPS-CK) and those produced by adding L. caerulea fruit polyphenols (EPS-LCP) were compared to reveal whether LCP reduced the cariogenicity of RYX-01 by influencing the structure and composition of EPS. The results showed that LCP could increase the content of galactose in EPS and destroy the original aggregation state of EPS-CK but had no significant effect on the molecular weight and functional group composition of EPS (p > 0.05). At the same time, LCP could inhibit the growth of RYX-01, reduce EPS and biofilm formation and inhibit the expression of quorum sensing (QS, luxS)- and biofilm formation (wzb)-related genes. Therefore, LCP could change the surface morphology, content and composition of RYX-01 EPS and reduce the cariogenic effect of EPS and biofilm. In conclusion, LCP can be used as a potential plaque biofilm inhibitor and QS inhibitor in drugs and functional foods.

Pseudomonas aeruginosa persister cell formation upon antibiotic exposure in planktonic and biofilm state

Persister cell (PC) is dormant, tolerant to antibiotics, and a transient reversible phenotype. These phenotypes are observed in P. aeruginosa and cause bacterial chronic infection as well as recurrence of biofilm-mediated infection. PC formation requires stringent response and toxin-antitoxin (TA) modules. This study shows the P. aeruginosa PC formation in planktonic and biofilm stages on ceftazidime, gentamicin, and ciprofloxacin treatments. The PC formation was studied using persister assay, flow cytometry using Redox Sensor Green, fluorescence as well as Confocal Laser Scanning Microscopy, and gene expression of stringent response and TA genes. In the planktonic stage, ceftazidime showed a high survival fraction, high redox activity, and elongation of cells was observed followed by ciprofloxacin and gentamicin treatment having redox activity and rod-shaped cells. The gene expression of stringent response and TA genes were upregulated on gentamicin followed by ceftazidime treatment and varied among the isolates. In the biofilm stage, gentamicin and ciprofloxacin showed the biphasic killing pattern, redox activity, gene expression level of stringent response and TA varied across the isolates. Ceftazidime treatment showed higher persister cells in planktonic growth while all three antibiotics were able to induce persister cell formation in the biofilm stage.

Virulence and Biofilm Inhibition of 3-Methoxycinnamic Acid against Agrobacterium tumefaciens

AIMS

In the current study the anti-virulence and anti-biofilm activities of the cinnamic acid derivative, 3-methoxycinnamic acid, was investigated against Agrobacterium tumefaciens.

METHODS AND RESULTS

Based on the disc diffusion test and β-galactosidase activity assay, 3-methoxycinnamic acid was shown to interfere with the quorum sensing (QS) system of A. tumefaciens. Crystal violet staining assay, phenol-sulfuric acid method, Bradford protein assay and confocal laser scanning microscopy (CLSM) revealed that the biofilm formation of A. tumefaciens was inhibited after the treatment of 3-methoxycinnamic acid. Employing high performance liquid chromatography (HPLC) analysis of culture supernatant revealed that the production of 3-oxo-octanoylhomoserine lactone (3-oxo-C8-HSL) decreased concentration-dependently after treatment with 3-methoxycinnamic acid. Swimming and chemotaxis assays also indicated that 3-methoxycinnamic acid had a good effect on reducing the motility and chemotaxis of A. tumefaciens. In addition, the RT-qPCR, molecular docking and simulations further demonstrated that 3-methoxycinnamic acid could competitively inhibit the binding of 3-oxo-C8-HSL to TraR and down-regulate virulence-related genes.

CONCLUSIONS

3-Methoxycinnamic acid is proved to have good anti-virulence and anti-biofilm activities against A. tumefaciens.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study that investigates the anti-virulence and anti-biofilm activities of 3-methoxycinnamic acid against A. tumefaciens. With its potential QS-related virulence and biofilm inhibitory activities, 3-methoxycinnamic acid is expected to be developed as a potent pesticide or adjuvant for the prevention and treatment of crown gall caused by A. tumefaciens.