Pseudomonas aeruginosa Biofilms

Overcoming Barriers to Preventing and Treating P. aeruginosa Infections Using AAV Vectored Immunoprophylaxis

Pseudomonas aeruginosa is a bacterial pathogen of global concern and is responsible for 10-15% of nosocomial infections worldwide. This opportunistic bacterial pathogen is known to cause serious complications in immunocompromised patients and is notably the leading cause of morbidity and mortality in patients suffering from cystic fibrosis. Currently, the only line of defense against P. aeruginosa infections is antibiotic treatment. Due to the acquired and adaptive resistance mechanisms of this pathogen, the prevalence of multidrug resistant P. aeruginosa strains has increased, presenting a major problem in healthcare settings. To date, there are no approved licensed vaccines to protect against P. aeruginosa infections, prompting the urgent need alternative treatment options. An alternative to traditional vaccines is vectored immunoprophylaxis (VIP), which utilizes a safe and effective adeno-associated virus (AAV) gene therapy vector to produce sustained levels of therapeutic monoclonal antibodies (mAbs) in vivo from a single intramuscular injection. In this review, we will provide an overview of P. aeruginosa biology and key mechanisms of pathogenesis, discuss current and emerging treatment strategies for P. aeruginosa infections and highlight AAV-VIP as a promising novel therapeutic platform.

Antimicrobial betalains

Betalains are nitrogen-containing plant pigments that can be red-violet (betacyanins) or yellow-orange (betaxanthins), currently employed as natural colourants in the food and cosmetic sectors. Betalains exhibit antimicrobial activity against a broad spectrum of microbes including multidrug-resistant bacteria, as well as single-species and dual-species biofilm-producing bacteria, which is highly significant given the current antimicrobial resistance issue reported by The World Health Organization. Research demonstrating antiviral activity against dengue virus, in silico studies including SARS-CoV-2, and anti-fungal effects of betalains highlight the diversity of their antimicrobial properties. Though limited in vivo studies have been conducted, antimalarial and anti-infective activities of betacyanin have been observed in living infection models. Cellular mechanisms of antimicrobial activity of betalains are yet unknown; however existing research has laid the framework for a potentially novel antimicrobial agent. This review covers an overview of betalains as antimicrobial agents and discussions to fully exploit their potential as therapeutic agents to treat infectious diseases.

Recombination Events in Putative Tail Fibre Gene in Litunavirus Phages Infecting Pseudomonas aeruginosa and Their Phylogenetic Consequences

Recombination is the main driver of bacteriophage evolution. It may serve as a tool for extending the phage host spectrum, which is significant not only for phages' ecology but also for their utilisation as therapeutic agents of bacterial infections. The aim of this study was to detect the recombination events in the genomes of Litunavirus phages infecting Pseudomonas aeruginosa, and present their impact on phylogenetic relations within this phage group. The phylogenetic analyses involved: the whole-genome, core-genome (Schitoviridae conserved genes), variable genome region, and the whole-genome minus variable region. Interestingly, the recombination events taking place in the putative host recognition region (tail fibre protein gene and the adjacent downstream gene) significantly influenced tree topology, suggesting a strong phylogenetic signal. Our results indicate the recombination between phages from two genera Litunavirus and Luzeptimavirus and demonstrate its influence on phage phylogeny.

Biofilms and Benign Colonic Diseases

The colon has a very large surface area that is covered by a dense mucus layer. The biomass in the colon includes 500-1000 bacterial species at concentrations of ~10¹² colony-forming units per gram of feces. The intestinal epithelial cells and the commensal bacteria in the colon have a symbiotic relationship that results in nutritional support for the epithelial cells by the bacteria and maintenance of the optimal commensal bacterial population by colonic host defenses. Bacteria can form biofilms in the colon, but the exact frequency is uncertain because routine methods to undertake colonoscopy (i.e., bowel preparation) may dislodge these biofilms. Bacteria in biofilms represent a complex community that includes living and dead bacteria and an extracellular matrix composed of polysaccharides, proteins, DNA, and exogenous debris in the colon. The formation of biofilms occurs in benign colonic diseases, such as inflammatory bowel disease and irritable bowel syndrome. The development of a biofilm might serve as a marker for ongoing colonic inflammation. Alternatively, the development of biofilms could contribute to the pathogenesis of these disorders by providing sanctuaries for pathogenic bacteria and reducing the commensal bacterial population. Therapeutic approaches to patients with benign colonic diseases could include the elimination of biofilms and restoration of normal commensal bacteria populations. However, these studies will be extremely difficult unless investigators can develop noninvasive methods for measuring and identifying biofilms. These methods that might include the measurement of quorum sensing molecules, measurement of bile acids, and identification of bacteria uniquely associated with biofilms in the colon.

Anti-Virulence Potential of a Chionodracine-Derived Peptide against Multidrug-Resistant Pseudomonas aeruginosa Clinical Isolates from Cystic Fibrosis Patients

Pseudomonas aeruginosa is an opportunistic pathogen causing several chronic infections resistant to currently available antibiotics. Its pathogenicity is related to the production of different virulence factors such as biofilm and protease secretion. Pseudomonas communities can persist in biofilms that protect bacterial cells from antibiotics. Hence, there is a need for innovative approaches that are able to counteract these virulence factors, which play a pivotal role, especially in chronic infections. In this context, antimicrobial peptides are emerging drugs showing a broad spectrum of antibacterial activity. Here, we tested the anti-virulence activity of a chionodracine-derived peptide (KHS-Cnd) on five P. aeruginosa clinical isolates from cystic fibrosis patients. We demonstrated that KHS-Cnd impaired biofilm development and caused biofilm disaggregation without affecting bacterial viability in nearly all of the tested strains. Ultrastructural morphological analysis showed that the effect of KHS-Cnd on biofilm could be related to a different compactness of the matrix. KHS-Cnd was also able to reduce adhesion to pulmonary cell lines and to impair the invasion of host cells by P. aeruginosa. A cytotoxic effect of KHS-Cnd was observed only at the highest tested concentration. This study highlights the potential of KHS-Cnd as an anti-biofilm and anti-virulence molecule against P. aeruginosa clinical strains.

Gut bacterial extracellular vesicles: important players in regulating intestinal microenvironment

Intestinal microenvironment dysbiosis is one of the major causes of diseases, such as obesity, diabetes, inflammatory bowel disease, and colon cancer. Microbiota-based strategies have excellent clinical potential in the treatment of repetitive and refractory diseases; however, the underlying regulatory mechanisms remain elusive. Identification of the internal regulatory mechanism of the gut microbiome and the interaction mechanisms involving bacteria-host is essential to achieve precise control of the gut microbiome and obtain effective clinical data. Gut bacteria-derived extracellular vesicles (GBEVs) are lipid bilayer nanoparticles secreted by the gut microbiota and are considered key players in bacteria-bacteria and bacteria-host communication. This review focusses on the role of GBEVs in gut microbiota interactions and bacteria-host communication, and the potential clinical applications of GBEVs.

Nutrient and organic pollutants removal in synthetic wastewater by Pseudomonas aeruginosa and Chryseobacterium sp./biofilter systems

Nutrient and organic pollution raise serious problems for aquatic ecosystems through the accumulation of organic carbon, the reduction of light penetration, and the loss of submerged aquatic vegetation. The over-enrichment of water with nitrogen and phosphorus leads to an imbalance in nutrient ratios, creating favorable conditions for toxic algal blooms, formation of oxygen-depleted water, etc. Thus, developing new technological solutions to reduce their amount is imperative. The present study investigates the capacity of Pseudomonas aeruginosa and Chryseobacterium sp. bacterial strains to form biofilm on solid support (biofilter), both individually and in tandem, using various analytical techniques. Also, the biofilm/biofilter systems' efficiency in removing nutrients such as nitrate, nitrite, ammonium, and phosphate ions from municipal wastewaters is assessed. The results showed a reduction of nutrient pollution of up to 91%, 98%, 55%, and 71% for nitrite, nitrate, ammonium, and phosphate ions. A reduction of about 78% of COD was also observed. The results were obtained in the absence of an additional aeration process, thus having a great potential for reducing total costs of wastewater treatment and developing ecological systems for wastewater management.

Pseudomonas aeruginosa reference strains PAO1 and PA14: A genomic, phenotypic, and therapeutic review

Pseudomonas aeruginosa is a ubiquitous, motile, gram-negative bacterium that has been recently identified as a multi-drug resistant pathogen in critical need of novel therapeutics. Of the approximately 5,000 strains, PAO1 and PA14 are common laboratory reference strains, modeling moderately and hyper-virulent phenotypes, respectively. PAO1 and PA14 have been instrumental in facilitating the discovery of novel drug targets, testing novel therapeutics, and supplying critical genomic information on the bacterium. While the two strains have contributed to a wide breadth of knowledge on the natural behaviors and therapeutic susceptibilities of P. aeruginosa, they have demonstrated significant deviations from observations in human infections. Many of these deviations are related to experimental inconsistencies in laboratory strain environment that complicate and, at times, terminate translation from laboratory results to clinical applications. This review aims to provide a comparative analysis of the two strains and potential methods to improve their clinical relevance.

Gallium Protoporphyrin Liquid Crystalline Lipid Nanoparticles: A Third-Generation Photosensitizer against Pseudomonas aeruginosa Biofilms

The looming antimicrobial resistance pandemic has encouraged the investigation of antimicrobial photodynamic therapy (aPDT) as a promising technology to combat recalcitrant bacterial infections caused by antibiotic resistant strains. Here, we report on the optimization and effective application of gallium protoporphyrin liquid crystalline lipid nanoparticles (GaPP-LCNP) as a photosensitizer for aPDT against the Gram-negative bacteria P. aeruginosa in both planktonic and biofilm modes of growth. LCNP significantly enhanced the performance of GaPP as photosensitizer by two-fold, which was correlated with higher antibacterial activity, reducing the viability of planktonic P. aeruginosa by 7 log₁₀ using 0.8 µM GaPP-LCNP and a light dose of 17 J.cm⁻². Importantly, GaPP-LCNP also reduced the viability of biofilms by 6 log₁₀ at relatively low light dose of 34.2 J.cm⁻² using only 3 µM GaPP-LCNP. The high antibiofilm activity of GaPP-LCNP at low GaPP-LCNP dose indicated the high efficiency and safety profile of GaPP-LCNP as a promising platform for photodynamic inactivation of recalcitrant infections.

A novel phenolic derivative inhibits AHL-dependent quorum sensing signaling in Pseudomonas aeruginosa

Increasing antibiotic resistance and the decline in the pharmaceutical industry’s investments have amplified the need for novel treatments for multidrug-resistant bacteria. Quorum sensing (QS) inhibitors reduce pathogens’ virulence without selective pressure on bacteria and provide an alternative to conventional antibiotic-based therapies. P. aeruginosa uses complex QS signaling to control virulence and biofilm formation. We aimed to identify inhibitors of P. aeruginosa QS acting on acyl-homoserine lactones (AHL)-mediated circuits. Bioluminescence and qRT-PCR assays were employed to screen a library of 81 small phenolic derivatives to reduce AHL-dependent signaling. We identified GM-50 as the most active compound inhibiting the expression of AHL-regulated genes but devoid of cytotoxic activity in human epithelial cells and biocidal effects on bacteria. GM-50 reduces virulence factors such as rhamnolipids, pyocyanin, elastase secretion, and swarming motility in P. aeruginosa PAO1 laboratory strain. By molecular docking, we provide evidence that GM-50 highly interacts with RhlR. GM-50 significantly improved aztreonam-mediated biofilm disruption. Moreover, GM-50 prevents adhesion of PAO1 and inflammatory damage in the human A549 cell line and protects Galleria mellonella from PAO1-mediated killing. GM-50 significantly reduces virulence factors in 20 P. aeruginosa clinical isolates from patients with respiratory tract infections. In conclusion, GM-50 inhibits AHL-signaling, reduces virulence factors, enhances the anti-biofilm activity of aztreonam, and protects G. mellonella larvae from damage induced by P. aeruginosa. Since GM-50 is active on clinical strains, it represents a starting point for identifying and developing new phenolic derivatives acting as QS-inhibitors in P. aeruginosa infections.

Neutrophil-mediated delivery of the combination of colistin and azithromycin for the treatment of bacterial infection

Novel treatment strategies are in urgent need to deal with the rapid development of antibiotic-resistant superbugs. Combination therapies and targeted drug delivery have been exploited to promote treatment efficacies. In this study, we loaded neutrophils with azithromycin and colistin to combine the advantages of antibiotic combinations, targeted delivery, and immunomodulatory effect of azithromycin to treat infections caused by Gram-negative pathogens. Delivery of colistin into neutrophils was mediated by fusogenic liposome, while azithromycin was directly taken up by neutrophils. Neutrophils loaded with the drugs maintained the abilitity to generate reactive oxygen species and migrate. In vitro assays demonstrated enhanced bactericidal activity against multidrug-resistant pathogens and reduced inflammatory cytokine production by the drug-loaded neutrophils. A single intravenous administration of the drug-loaded neutrophils effectively protected mice from Pseudomonas aeruginosa infection in an acute pneumonia model. This study provides a potential effective therapeutic approach for the treatment of bacterial infections.

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Neutrophils are loaded with colistin and azithromycin in vitro

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The loaded drugs enhance the bactericidal effect and reduce the inflammatory response

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Drug-loaded neutrophils conferred effective protection against bacterial infection

Antibacterial, Anticandidal, and Antibiofilm Potential of Fenchone: In Vitro, Molecular Docking and In Silico/ADMET Study

The aim of the present study is to investigate the effective antimicrobial and antibiofilm properties of fenchone, a biologically active bicyclic monoterpene, against infections caused by bacteria and Candida spp. The interactions between fenchone and three distinct proteins from Escherichia coli (β-ketoacyl acyl carrier protein synthase), Candida albicans (1, 3-β−D-glucan synthase), and Pseudomonas aeruginosa (Anthranilate-CoA ligase) were predicted using molecular docking and in silico/ADMET methods. Further, to validate the in-silico prediction, the antibacterial and antifungal potential of fenchone was evaluated against E. coli, P. aeruginosa, and C. albicans by determining minimum inhibitory concentration (MIC), minimum bacterial concentration (MBC), and minimum fungicidal concentration (MFC). The lowest MIC/MBC values of fenchone against E. coli and P. aeruginosa obtained was 8.3 ± 3.6/25 ± 0.0 and 266.6 ± 115.4/533.3 ± 230.9 mg/mL, respectively, whereas the MIC/MFC value for C. albicans was found to be 41.6 ± 14.4/83.3 ± 28.8 mg/mL. It was observed that fenchone has a significant effect on antimicrobial activity (p < 0.05). Our findings demonstrated that fenchone at 1 mg/mL significantly reduced the production of biofilm (p < 0.001) in E. coli, P. aeruginosa, and C. albicans by 70.03, 64.72, and 61.71%, respectively, in a dose-dependent manner when compared to control. Based on these results, it has been suggested that the essential oil from plants can be a great source of pharmaceutical ingredients for developing new antimicrobial drugs.

Bacteriophage as a potential therapy to control antibiotic-resistant Pseudomonas aeruginosa infection through topical application onto a full-thickness wound in a rat model

Background

Antibiotic-resistant Pseudomonas aeruginosa (P. aeruginosa) is one of the most critical pathogens in wound infections, causing high mortality and morbidity in severe cases. However, bacteriophage therapy is a potential alternative to antibiotics against P. aeruginosa. Therefore, this study aimed to isolate a novel phage targeting P. aeruginosa and examine its efficacy in vitro and in vivo.

Results

The morphometric and genomic analyses revealed that ZCPA1 belongs to the Siphoviridae family and could infect 58% of the tested antibiotic-resistant P. aeruginosa clinical isolates. The phage ZCPA1 exhibited thermal stability at 37 °C, and then, it decreased gradually at 50 °C and 60 °C. At the same time, it dropped significantly at 70 °C, and the phage was undetectable at 80 °C. Moreover, the phage ZCPA1 exhibited no significant titer reduction at a wide range of pH values (4–10) with maximum activity at pH 7. In addition, it was stable for 45 min under UV light with one log reduction after 1 h. Also, it displayed significant lytic activity and biofilm elimination against P. aeruginosa by inhibiting bacterial growth in vitro in a dose-dependent pattern with a complete reduction of the bacterial growth at a multiplicity of infection (MOI) of 100. In addition, P. aeruginosa-infected wounds treated with phages displayed 100% wound closure with a high quality of regenerated skin compared to the untreated and gentamicin-treated groups due to the complete elimination of bacterial infection.

Conclusion

The phage ZCPA1 exhibited high lytic activity against MDR P. aeruginosa planktonic and biofilms. In addition, phage ZCPA1 showed complete wound healing in the rat model. Hence, this research demonstrates the potential of phage therapy as a promising alternative in treating MDR P. aeruginosa.

In Vitro Synergistic Inhibitory Activity of Natural Alkaloid Berberine Combined with Azithromycin against Alginate Production by Pseudomonas aeruginosa PAO1

Background. Berberine (BER) is a natural isoquinoline alkaloid which extensively been applied to treat bacterial infection in TCM for a long time. Alginate is an important component of Pseudomonas aeruginosa biofilm. Herein, we investigated the effects of berberine and azithromycin (AZM) on alginate in the biofilm of P. aeruginosa PAO1. Methods. The MIC and synergistic activity of BER and AZM against PAO1 were determined using the micro broth dilution and checkerboard titration methods, respectively. The effect of BER on PAO1 growth was evaluated using a time-kill assay. Moreover, the effects of BER, AZM, and a combination of both on PAO1 biofilm formation, kinesis, and virulence factor expression were evaluated at subinhibitory concentrations. The alginate content in the biofilm was detected using ELISA, and the relative expression of alginate formation-related genes algD, algR, and algG was detected by qRT-PCR. Results. Simultaneous administration of berberine significantly reduced the MIC of azithromycin, and berberine at a certain concentration inhibited PAO1 growth. Moreover, combined berberine and azithromycin had synergistic effects against PAO1, significantly reducing biofilm formation, swarming, and twitching motility, and the production of virulence factors. The relative expression of alginate-related regulatory genes algG, algD, and algR of the combined treatment group was significantly lower than that of the control group. Conclusion. In summary, berberine and azithromycin in combination had a significant synergistic effect on the inhibition of alginate production by P. aeruginosa. Further molecular studies are in great need to reveal the mechanisms underlying the synergistic activity between berberine and azithromycin.

Effect of samarium oxide nanoparticles on virulence factors and motility of multi-drug resistant Pseudomonas aeruginosa

Biofilm formation and quorum sensing (QS) dependent virulence factors are considered the major causes of the emergence of drug resistance, therapeutic failure and development of Pseudomonas aeruginosa infections. This study aimed to investigate the effects of samarium oxide nanoparticles (Sm₂O₃NPs) on biofilm, virulence factors, and motility of multidrug-resistant P. aeruginosa. Sm₂O₃NPs were synthesized using curcumin and characterized by Transmission Electron Microscopy, X-ray diffractometer, Field Emission Scanning Electron Microscopy, and Energy-dispersive X-ray spectroscopy. Minimum inhibitory concentration (MIC) was determined using broth microdilution method. The antibiofilm potential of Sm₂O₃NPs was also evaluated by crystal violet staining and light microscopy examination. Then, the effect of sub-MICs concentrations of Sm₂O₃NPs on the proteolytic and hemolytic activities of P. aeruginosa was investigated. Finally, the effect of Sm₂O₃NPs on various types of motility including swarming, swimming, and twitching was studied. Our results showed that Sm₂O₃NPs significantly inhibited biofilm formation of P. aeruginosa by 49-61%. Additionally, sub-MICs concentrations of Sm₂O₃NPs effectively decreased virulence factors including pyocyanin (33-55%), protease (24-45%), and hemolytic activity (22-41%). Moreover, swarming, swimming, and twitching motility remarkably was reduced after exposure to the NPs. The findings of this work showed that Sm₂O₃NPs have a high potential in inhibiting QS-dependent virulence of P. aeruginosa, which could be considered for antibacterial chemotherapy after further characterization.

Effect of Biogenic Silver Nanoparticles on the Quorum-Sensing System of Pseudomonas aeruginosa PAO1 and PA14

The increase in multidrug-resistant microorganisms represents a global threat requiring the development novel strategies to fight bacterial infection. This study aimed to assess the effect of silver nanoparticles (bio-AgNPs) on bacterial growth, biofilm formation, production of virulence factors, and expression of genes related to the quorum-sensing (QS) system of P. aeruginosa PAO1 and PA14. Biofilm formation and virulence assays were performed with bio-AgNPs. RT-qPCR was carried out to determine the effect of bio-AgNPs on the QS regulatory genes lasI, lasR, rhlI, rhlR, pqsA, and mvfR. Bio-AgNPs had an MIC value of 62.50 μM, for both strains. Phenotypic and genotypic assays were carried out using sub-MIC values. Experimental results showed that treatment with sub-MICs of bio-AgNPs reduced (p < 0.05) the motility and rhamnolipids and elastase production in P. aeruginosa PAO1. In PA14, bio-AgNPs stimulated swarming and twitching motilities as well as biofilm formation and elastase and pyocyanin production. Bio-AgNP treatment increased (p < 0.05) the expression of QS genes in PAO1 and PA14. Despite the different phenotypic behaviors in both strains, both showed an increase in the expression of QS genes. Demonstrating that the bio-AgNPs acted in the induction of regulation. The possible mechanism underlying the action of bio-AgNPs involves the induction of the rhl and/or pqs system of PAO1 and of the las and/or pqs system of PA14. These results suggest that exposure to low concentrations of bio-AgNPs may promote the expression of QS regulatory genes in P. aeruginosa, consequently inducing the production of virulence factors such as elastase, pyocyanin, and biofilms.

In Vitro and In Silico Screening of Anti-Vibrio spp., Antibiofilm, Antioxidant and Anti-Quorum Sensing Activities of Cuminum cyminum L. Volatile Oil

Cuminum cyminum L. essential oil (cumin EO) was studied for its chemical composition, antioxidant and vibriocidal activities. Inhibition of biofilm formation and secretion of some virulence properties controlled by the quorum sensing system in Chromobacterium violaceum and Pseudomonas aeruginosa strains were also reported. The obtained results showed that cuminaldehyde (44.2%) was the dominant compound followed by β-pinene (15.1%), γ-terpinene (14.4%), and p-cymene (14.2%). Using the disc diffusion assay, cumin EO (10 mg/disc) was particularly active against all fifteen Vibrio species, and the highest diameter of growth inhibition zone was recorded against Vibrio fluvialis (41.33 ± 1.15 mm), Vibrio parahaemolyticus (39.67 ± 0.58 mm), and Vibrio natrigens (36.67 ± 0.58 mm). At low concentration (MICs value from 0.023–0.046 mg/mL), cumin EO inhibited the growth of all Vibrio strains, and concentrations as low as 1.5 mg/mL were necessary to kill them (MBCs values from 1.5–12 mg/mL). Using four antioxidant assays, cumin EO exhibited a good result as compared to standard molecules (DPPH = 8 ± 0.54 mg/mL; reducing power = 3.5 ± 0.38 mg/mL; β-carotene = 3.8 ± 0.34 mg/mL; chelating power = 8.4 ± 0.14 mg/mL). More interestingly, at 2x MIC value, cumin EO inhibited the formation of biofilm by Vibrio alginolyticus (9.96 ± 1%), V. parahaemolyticus (15.45 ± 0.7%), Vibrio cholerae (14.9 ± 0.4%), and Vibrio vulnificus (18.14 ± 0.3%). In addition, cumin EO and cuminaldehyde inhibited the production of violacein on Lauria Bertani medium (19 mm and 35 mm, respectively). Meanwhile, 50% of violacein inhibition concentration (VIC50%) was about 2.746 mg/mL for cumin EO and 1.676 mg/mL for cuminaldehyde. Moreover, elastase and protease production and flagellar motility in P. aeruginosa were inhibited at low concentrations of cumin EO and cuminaldehyde. The adopted in-silico approach revealed good ADMET properties as well as a high binding score of the main compounds with target proteins (1JIJ, 2UV0, 1HD2, and 3QP1). Overall, the obtained results highlighted the effectiveness of cumin EO to prevent spoilage with Vibrio species and to interfere with the quorum sensing system in Gram-negative bacteria by inhibiting the flagellar motility, formation of biofilm, and the secretion of some virulence enzymes.

Treatment of Pseudomonas aeruginosa infectious biofilms: Challenges and strategies

Pseudomonas aeruginosa, a Gram-negative bacterium, is one of the major pathogens implicated in human opportunistic infection and a common cause of clinically persistent infections such as cystic fibrosis, urinary tract infections, and burn infections. The main reason for the persistence of P. aeruginosa infections is due to the ability of P. aeruginosa to secrete extracellular polymeric substances such as exopolysaccharides, matrix proteins, and extracellular DNA during invasion. These substances adhere to and wrap around bacterial cells to form a biofilm. Biofilm formation leads to multiple antibiotic resistance in P. aeruginosa, posing a significant challenge to conventional single antibiotic therapeutic approaches. It has therefore become particularly important to develop anti-biofilm drugs. In recent years, a number of new alternative drugs have been developed to treat P. aeruginosa infectious biofilms, including antimicrobial peptides, quorum-sensing inhibitors, bacteriophage therapy, and antimicrobial photodynamic therapy. This article briefly introduces the process and regulation of P. aeruginosa biofilm formation and reviews several developed anti-biofilm treatment technologies to provide new directions for the treatment of P. aeruginosa biofilm infection.

Biofilms in hoses utilized to divert colostrum and milk on dairy farms: A report exploring their potential role in herd health, milk quality, and public health

Biofilms in milking equipment on dairy farms have been associated with failures in cleaning and sanitizing protocols. These biofilms on milking equipment can be a source of contamination for bulk tank milk and a concern for animal and public health, as biofilms can become on-farm reservoirs for pathogenic bacteria that cause disease in cows and humans. This report describes a cross-sectional study on 3 dairy farms, where hoses used to divert waste milk, transition milk, and colostrum were analyzed by culture methods and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) to assess the presence of pathogenic bacteria such as Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella spp. In addition, the presence of biofilms was analyzed using scanning electron microscopy and confocal spectral microscopy. Biofilms composed of multispecies microbial communities were observed on the surfaces of all milk hoses. In two dairy farms, S. aureus, P. aeruginosa, Klebsiella pneumoniae, and Klebsiella oxytoca were isolated from the milk hose samples collected. Cleaning and sanitation protocols of all surfaces in contact with milk or colostrum are crucial. Hoses used to collect waste milk, colostrum, and transition milk can be a source of biofilms and hence pathogenic bacteria. Waste milk used to feed calves can constitute a biosecurity issue and a source of pathogens, therefore an increased exposure and threat for the whole herd health and, potentially, for human health.

Synergistic antibacterial and anti-biofilm activities of resveratrol and polymyxin B against multidrug-resistant Pseudomonas aeruginosa

Bacterial infection caused by multidrug-resistant Pseudomonas aeruginosa has become a challenge in clinical practice. Polymyxins are used as the last resort agent for otherwise untreatable Gram-negative bacteria, including multidrug-resistant P.aeruginosa. However, pharmacodynamic (PD) and pharmacokinetic (PK) data on polymyxins suggest that polymyxin monotherapy is unlikely to generate reliably efficacious plasma concentrations. Also, polymyxin resistance has been frequently reported, especially among multidrug-resistant P.aeruginosa, which further limits its clinical use. A strategy for improving the antibacterial activity of polymyxins and preventing the development of polymyxin resistance is to use polymyxins in combination with other agents. In this study, we have demonstrated that resveratrol, a well tolerated compound, has synergistic effects when tested in vitro with polymyxin B on antibacterial and anti-biofilm activities. However, its' systemic use is limited as the required high plasma levels of resveratrol are not achievable. This suggests that it could be a partner for the combination therapy of polymyxin B in the treatment of topical bacterial infection caused by MDR P.aeruginosa.

Detection of biofilm production and antimicrobial susceptibility in clinical isolates of Acinetobacter baumannii and Pseudomonas aeruginosa

Acinetobacter baumannii and Pseudomonas aeruginosa are commensal which commonly colonize humans. As a result of their ubiquitous nature, reservoirs in hospital environment and resistance to many antimicrobial agents they are responsible for hospital – acquired infections. Additionally treatment of these infections is difficult because of the ability for biofilm formation. Aim of the paper was to determine the association between biofilm formation on medical devices and antibiotic resistance profile, compared to respiratory samples in clinical isolates of Acinetobacter baumannii and Pseudomonas aeruginosa. Material and methods: The study comprised 50 clinical samples (36 from medical devices and 14 as а control group from respiratory secretions). Acinetobacter baumannii and Pseudomonas aeruginosa were identified by routine microbiological methods. Modification of the microtiter plate assay described by Stepanovic et al. was used to investigate the formation of biofilm. The antimicrobial susceptibility testing was performed according to EUCAST guidelines. Results:  Of the 50 analyzed strains, 16 (32%) were non-biofilm producers, and 34 (68%) were producing biofilms. Out of these, 29 (58%) were from medical devices, and 5 (10%) from the control group. Acinetobacter baumannii showed biofilm formation in 19 (67.9%), of which 17 (60.7%) from medical devices, and 2 (7.1%) from control group. Pseudomonas aeruginosa produced biofilm in 15 (68.1%), of which 12 (54.5%) from medical devices, and  3 (13.6%) from the control group. Multidrug resistance was detected in 40 (80%). All strains of Acinetobacter baumannii were multidrug resistant (MDR). For Pseudomonas aeruginosa, 11 (73.3%) biofilm forming isolates were MDR, and 1 (14.2%) non-biofilm forming isolate was MDR. Conclusion: Biofilm production was higher in strains from medical devices. Eighty percent of isolates were MDR. This is a serious challenge for treatment of these hospital-acquired infections.

Rapid Synergistic Biofilm Production of Pseudomonas and Candida on the Pulmonary Cell Surface and in Mice, a Possible Cause of Chronic Mixed Organismal Lung Lesions

Due to the possible co-presence of Pseudomonas aeruginosa and Candida albicans (the most common nosocomial pathogens) in lungs, rapid interkingdom biofilm production is possible. As such, PA+CA produced more dominant biofilms on the pulmonary epithelial surface (NCI-H292) (confocal fluorescent extracellular matrix staining) with dominant psl upregulation, as demonstrated by polymerase chain reaction (PCR), after 8 h of experiments than PA alone. With a proteomic analysis, rhamnosyltransferase RhlB protein (Psl-associated quorum-sensing protein) was found to be among the high-abundance proteins in PA+CA than in PA biofilms, supporting psl-mediated biofilms in PA+CA on the cell surface. Additionally, PA+CA increased supernatant cytokines (IL-8 and IL-13, but not TNF-α, IL-6, and IL-10) with a similar upregulation of TLR-4, TLR-5, and TLR-9 (by PCR) compared with PA-stimulated cells. The intratracheal administration of PA+CA induced a greater severity of sepsis (serum creatinine, alanine transaminase, serum cytokines, and histology score) and prominent biofilms (fluorescent staining) with psl upregulation (PCR). In comparison with PA+CA biofilms on glass slides, PA+CA biofilms on biotic surfaces were more prominent (fluorescent staining). In conclusion, PA+CA induced Psl-predominant biofilms on the pulmonary cell surface and in mice with acute pneumonia, and these biofilms were more prominent than those induced by PA alone, highlighting the impact of Candida on rapid interkingdom biofilm production.

Pathogenesis in Pseudomonas aeruginosa PAO1 Biofilm-Associated Is Dependent on the Pyoverdine and Pyocyanin Siderophores by Quorum Sensing Modulation

Pseudomonas aeruginosa is an opportunistic pathogenic bacterium for humans, animals, and plants, through producing different molecular factors such as biofilm, siderophores, and other virulence factors which favor bacterial establishment and infection in the host. In P. aeruginosa PAO1, the production of these factors is regulated by the bacterial quorum sensing (QS) mechanisms. From them, siderophores are involved in iron acquisition, transport, and homeostasis. They are also considered some of the main virulence factors in P. aeruginosa; however, detailed mechanisms to induce bacterial pathogenesis are poorly understood. In this work, through reverse genetics, we evaluated the function of bacterial pathogenesis in the pvd cluster genes, which are required for synthesizing the siderophore pyoverdine (PVD). Single pvdI, pvdJ, pvdL, and double mutant strains were analyzed, and contrary to expected, the pvdL and pvdI mutations increased the concentration of PVD and other phenazines, such as pyocyanin (PYO) and phenazine-1-carboxylic acid (PCA) and also an increased biofilm production and morphology depending on the autoinducer 2-alkyl-4-quinolone (PQS) and the QS molecules acyl-homoserine lactones. Consequently, in the in vivo pathogenicity model of Caenorhabditis elegans, the mutations in pvdI, pvdJ, and pvdL increased the survival of the worms exposed to supernatants or biofilms of the bacterial cultures. However, the double mutant pvdI/pvdJ increased its toxicity in agreeing with the biofilm production, PVD, PYO, and PCA. The findings indicate that the mutations in pvd genes encode non-ribosomal peptide synthetases impacted the biofilm's structure, but suppressively also of the phenazines, confirming that the siderophores contribute to the bacterial establishment and pathogenicity of P. aeruginosa PAO1.

Clinical Efficacy and In Vitro Drug Sensitivity Test Results of Azithromycin Combined With Other Antimicrobial Therapies in the Treatment of MDR P. aeruginosa Ventilator-Associated Pneumonia

Objective: The aim of the research was to study the effect of azithromycin (AZM) in the treatment of MDR P. aeruginosa VAP combined with other antimicrobial therapies.

Methods: The clinical outcomes were retrospectively collected and analyzed to elucidate the efficacy of different combinations involving azithromycin in the treatment of MDR-PA VAP. The minimal inhibitory concentration (MIC) of five drugs was measured by the agar dilution method against 27 isolates of MDR-PA, alone or in combination.

Results: The incidence of VAP has increased approximately to 10.4% (961/9245) in 5 years and 18.4% (177/961) caused by P. aeruginosa ranking fourth. A total of 151 cases of MDR P. aeruginosa were included in the clinical retrospective study. Clinical efficacy results are as follows: meropenem + azithromycin (MEM + AZM) was 69.2% (9/13), cefoperazone/sulbactam + azithromycin (SCF + AZM) was 60% (6/10), and the combination of three drugs containing AZM was 69.2% (9/13). The curative effect of meropenem + amikacin (MEM + AMK) was better than that of the meropenem + levofloxacin (MEM + LEV) group, p = 0.029 (p < 0.05). The curative effect of cefoperazone/sulbactam + amikacin (SCF + AMK) was better than that of the cefoperazone/sulbactam + levofloxacin (SCF + LEV) group, p = 0.025 (p < 0.05). There was no significant difference between combinations of two or three drugs containing AZM, p > 0.05 (p = 0.806). From the MIC results, the AMK single drug was already very sensitive to the selected strains. When MEM or SCF was combined with AZM, the sensitivity of them to strains can be significantly increased. When combined with MEM and AZM, the MIC₅₀ and MIC₉₀ of MEM decreased to 1 and 2 ug/mL from 8 to 32 ug/mL. When combined with SCF + AZM, the MIC₅₀ of SCF decreased to 16 ug/mL, and the curve shifted obviously. However, for the combination of SCF + LEV + AZM, MIC₅₀ and MIC₉₀ could not achieve substantive changes. From the FIC index results, the main actions of MEM + AZM were additive effects, accounting for 72%; for the combination of SCF + AZM, the additive effect was 40%. The combination of AMK or LEV with AZM mainly showed unrelated effects, and the combination of three drugs could not improve the positive correlation between LEV and AZM.

Conclusion: AZM may increase the effect of MEM or SCF against MDR P. aeruginosa VAP. Based on MEM or SCF combined with AMK or AZM, we can achieve a good effect in the treatment of MDR P. aeruginosa VAP.

Probiotics and live biotherapeutic products aiming at cancer mitigation and patient recover

Molecular biology techniques allowed access to non-culturable microorganisms, while studies using analytical chemistry, as Liquid Chromatography and Tandem Mass Spectrometry, showed the existence of a complex communication system among bacteria, signaled by quorum sensing molecules. These approaches also allowed the understanding of dysbiosis, in which imbalances in the microbiome diversity, caused by antibiotics, environmental toxins and processed foods, lead to the constitution of different diseases, as cancer. Colorectal cancer, for example, can originate by a dysbiosis configuration, which leads to biofilm formation, production of toxic metabolites, DNA damage in intestinal epithelial cells through the secretion of genotoxins, and epigenetic regulation of oncogenes. However, probiotic strains can also act in epigenetic processes, and so be use for recovering important intestinal functions and controlling dysbiosis and cancer mitigation through the metabolism of drugs used in chemotherapy, controlling the proliferation of cancer cells, improving the immune response of the host, regulation of cell differentiation and apoptosis, among others. There are still gaps in studies on the effectiveness of the use of probiotics, therefore omics and analytical chemistry are important approaches to understand the role of bacterial communication, formation of biofilms, and the effects of probiotics and microbiome on chemotherapy. The use of probiotics, prebiotics, synbiotics, and metabiotics should be considered as a complement to other more invasive and hazard therapies, such chemotherapy, surgery, and radiotherapy. The study of potential bacteria for cancer treatment, as the next-generation probiotics and Live Biotherapeutic Products, can have a controlling action in epigenetic processes, enabling the use of these bacteria for the mitigation of specific diseases through changes in the regulation of genes of microbiome and host. Thus, it is possible that a path of medicine in the times to come will be more patient-specific treatments, depending on the environmental, genetic, epigenetic and microbiome characteristics of the host.

Inhibition of Bacterial Adhesion and Biofilm Formation by Seed-Derived Ethanol Extracts from Persea americana Mill

The increase in antibiotic resistance demands innovative strategies to combat microorganisms. The current study evaluated the antibacterial and antivirulence effects of ethanol extracts from Persea americana seeds obtained by the Soxhlet (SE) and maceration (MaE) methods. The UHPLC-DAD-QTOF analysis showed mainly the presence of polyphenols and neolignan. Ethanol extracts were not cytotoxic to mammalian cells (CC50 > 500 µg/mL) and displayed a moderate antibacterial activity against Pseudomonas aeruginosa (IC50 = 87 and 187 µg/mL) and Staphylococcus aureus (IC50 = 144 and 159 µg/mL). Interestingly, no antibacterial activity was found against Escherichia coli. SE and MaE extracts were also able to significantly reduce the bacterial adhesion to A549 lung epithelial cells. Additionally, both extracts inhibited the biofilm growth at 24 h and facilitated the release of internal cell components in P. aeruginosa, which might be associated with cell membrane destabilization. Real-time PCR and agarose electrophoresis gel analysis indicated that avocado seed ethanol extracts (64 µg/mL) downregulated virulence-related factors such as mexT and lasA genes. Our results support the potential of bioproducts from P. americana seeds as anti-adhesive and anti-biofilm agents.

Generation of a recombinant antibody for sensitive detection of Pseudomonas aeruginosa

Pseudomonas aeruginosa (P. aeruginosa) is a major pathogen that causes nosocomial infections and often exhibits antibiotic resistance. Therefore, the development of an accurate method for detecting P. aeruginosa is required to control P. aeruginosa-related outbreaks. In this study, we established an enzyme-linked immunosorbent assay method for the sensitive detection of three P. aeruginosa strains, UCBPP PA14, ATCC 27853, and multidrug-resistant ATCC BAA-2108. We produced a recombinant antibody (rAb) against P. aeruginosa V‐antigen (PcrV), which is a needle tip protein of the type III secretion system of P. aeruginosa using mammalian cells with high yield and purity, and confirmed its P. aeruginosa binding efficiency. The rAb was paired with commercial anti-P. aeruginosa Ab for a sandwich ELISA, resulting in an antigen-concentration-dependent response with a limit of detection value of 230 CFU/mL. These results suggest that the rAb produced herein can be used for the sensitive detection of P. aeruginosa with a wide range of applications in clinical diagnosis and point-of-care testing.

The Structures and Binding Modes of Small-Molecule Inhibitors of Pseudomonas aeruginosa Elastase LasB

Elastase B (LasB) is a zinc metalloprotease and a crucial virulence factor of Pseudomonas aeruginosa. As the need for new strategies to fight antimicrobial resistance (AMR) constantly rises, this protein has become a key target in the development of novel antivirulence agents. The extensive knowledge of the structure of its active site, containing two subpockets and a zinc atom, led to various structure-based medicinal chemistry programs and the optimization of several chemical classes of inhibitors. This review provides a brief reminder of the structure of the active site and a summary of the disclosed P. aeruginosa LasB inhibitors. We specifically focused on the analysis of their binding modes with a detailed representation of them, hence giving an overview of the strategies aiming at targeting LasB by small molecules.

Self-locomotive, antimicrobial microrobot (SLAM) swarm for enhanced biofilm elimination

Biofilm is a major cause of infections and infrastructure deterioration, largely due to molecular diffusion restrictions that hamper the antimicrobial activity of traditional antibiotics and disinfectants. Here, we present a self-locomotive, antimicrobial microrobot (SLAM) swarm that can penetrate, fracture, and detach biofilm and, in turn, nullify bacterial resistance to antibiotics. The SLAM is assembled by loading a controlled mass of manganese oxide nanosheets on diatoms with the polydopamine binder. In hydrogen peroxide solution, SLAMs produce oxygen bubbles that generate thrust to penetrate the rigid and dense Pseudomonas aeruginosa biofilm and self-assemble into a swarm that repeatedly surrounds, expands, and bursts oxygen bubbles. The resulting cavities continue to deform and fracture extracellular polymeric substances from microgrooved silicone substrates and wounded skin explants while decreasing the number of viable bacterial cells. Additionally, SLAM allows irrigating water or antibiotics to access the residual biofilm better, thus enhancing the synergistic efficacy in killing up to 99.9% of bacterial cells.

Actinomycin D: a novel Pseudomonas aeruginosa quorum sensing inhibitor from the endophyte Streptomyces cyaneochromogenes RC1

The infections caused by Pseudomonas aeruginosa are difficult to treat due to its multidrug resistance. A promising strategy for controlling P. aeruginosa infection is targeting the quorum sensing (QS) system. Actinomycin D isolated from the metabolite of endophyte Streptomyces cyaneochromogenes RC1 exhibited good anti-QS activity against P. aeruginosa PAO1. Actinomycin D (50, 100, and 200 μg/mL) significantly inhibited the motility as well as reduced the production of multiple virulence factors including pyocyanin, protease, rhamnolipid, and siderophores. The images of confocal laser scanning microscopy and scanning electron microscopy revealed that the treatment of actinomycin D resulted in a looser and flatter biofilm structure. Real-time quantitative PCR analysis showed that the expression of QS-related genes lasI, rhlI, rhlR, pqsR, pslA, and pilA were downregulated dramatically. The production of QS signaling molecules N-(3-oxododecanoyl)-L-homoserine lactone and N-butanoyl-L-homoserine lactone were also decreased by actinomycin D. These findings suggest that actinomycin D, a potent in vitro anti-virulence agent, is a promising candidate to treat P. aeruginosa infection by interfering with the QS systems.

Antibiofilm property and multiple action of peptide PEW300 against Pseudomonas aeruginosa

Pseudomonas aeruginosa (P. aeruginosa), an opportunistic pathogen, is often associated with difficulties in treating hospital-acquired infections. Biofilms formed by P. aeruginosa significantly improve its resistance to antimicrobial agents, thereby, posing a great challenge to the combat of P. aeruginosa infection. Antimicrobial peptides (AMPs) have recently emerged as promising antibiofilm agents and increasingly attracting the attention of scientists worldwide. However, current knowledge of their antibiofilm behavior is limited and their underlying mechanism remains unclear. In this study, a novel AMP, named PEW300, with three-point mutations (E9H, D17K, and T33A) from Cecropin A was used to investigate its antibiofilm property and antibiofilm pathway against P. aeruginosa. PEW300 displayed strong antibacterial and antibiofilm activity against P. aeruginosa with no significant hemolysis or cytotoxicity to mouse erythrocyte and human embryonic kidney 293 cells. Besides, the antibiofilm pathway results showed that PEW300 preferentially dispersed the mature biofilm, leading to the biofilm-encapsulated bacteria exposure and death. Meanwhile, we also found that the extracellular DNA was a critical target of PEW300 against the mature biofilm of P. aeruginosa. In addition, multiple actions of PEW300 including destroying the cell membrane integrity, inducing high levels of intracellular reactive oxygen species, and interacting with genomic DNA were adopted to exert its antibacterial activity. Moreover, PEW300 could dramatically reduce the virulence of P. aeruginosa. Taken together, PEW300 might be served as a promising antibiofilm candidate to combat P. aeruginosa biofilms.

The function of small RNA in Pseudomonas aeruginosa

Pseudomonas aeruginosa, the main conditional pathogen causing nosocomial infection, is a gram-negative bacterium with the largest genome among the known bacteria. The main reasons why Pseudomonas aeruginosa is prone to drug-resistant strains in clinic are: the drug-resistant genes in its genome and the drug resistance easily induced by single antibiotic treatment. With the development of high-throughput sequencing technology and bioinformatics, the functions of various small RNAs (sRNA) in Pseudomonas aeruginosa are being revealed. Different sRNAs regulate gene expression by binding to protein or mRNA to play an important role in the complex regulatory network. In this article, first, the importance and biological functions of different sRNAs in Pseudomonas aeruginosa are explored, and then the evidence and possibilities that sRNAs served as drug therapeutic targets are discussed, which may introduce new directions to develop novel disease treatment strategies.

Pseudomonas aeruginosa: Recent Advances in Vaccine Development

Pseudomonas aeruginosa is an important opportunistic human pathogen. Using its arsenal of virulence factors and its intrinsic ability to adapt to new environments, P. aeruginosa causes a range of complicated acute and chronic infections in immunocompromised individuals. Of particular importance are burn wound infections, ventilator-associated pneumonia, and chronic infections in people with cystic fibrosis. Antibiotic resistance has rendered many of these infections challenging to treat and novel therapeutic strategies are limited. Multiple clinical studies using well-characterised virulence factors as vaccine antigens over the last 50 years have fallen short, resulting in no effective vaccination being available for clinical use. Nonetheless, progress has been made in preclinical research, namely, in the realms of antigen discovery, adjuvant use, and novel delivery systems. Herein, we briefly review the scope of P. aeruginosa clinical infections and its major important virulence factors.

What Is New in the Anti–Pseudomonas aeruginosa Clinical Development Pipeline Since the 2017 WHO Alert?

The spread of antibiotic-resistant bacteria poses a substantial threat to morbidity and mortality worldwide. Carbapenem-resistant Pseudomonas aeruginosa (CRPA) are considered “critical-priority” bacteria by the World Health Organization (WHO) since 2017 taking into account criteria such as patient mortality, global burden disease, and worldwide trend of multi-drug resistance (MDR). Indeed P. aeruginosa can be particularly difficult to eliminate from patients due to its combinatory antibiotic resistance, multifactorial virulence, and ability to over-adapt in a dynamic way. Research is active, but the course to a validated efficacy of a new treatment is still long and uncertain. What is new in the anti–P. aeruginosa clinical development pipeline since the 2017 WHO alert? This review focuses on new solutions for P. aeruginosa infections that are in active clinical development, i.e., currently being tested in humans and may be approved for patients in the coming years. Among 18 drugs of interest in December 2021 anti–P. aeruginosa development pipeline described here, only one new combination of β-lactam/β-lactamase inhibitor is in phase III trial. Derivatives of existing antibiotics considered as “traditional agents” are over-represented. Diverse “non-traditional agents” including bacteriophages, iron mimetic/chelator, and anti-virulence factors are significantly represented but unfortunately still in early clinical stages. Despite decade of efforts, there is no vaccine currently in clinical development to prevent P. aeruginosa infections. Studying pipeline anti–P. aeruginosa since 2017 up to now shows how to provide a new treatment for patients can be a difficult task. Given the process duration, the clinical pipeline remains unsatisfactory leading best case to the approval of new antibacterial drugs that treat CRPA in several years. Beyond investment needed to build a robust pipeline, the Community needs to reinvent medicine with new strategies of development to avoid the disaster. Among “non-traditional agents”, anti-virulence strategy may have the potential through novel and non-killing modes of action to reduce the selective pressure responsible of MDR.

Current State of Knowledge Regarding WHO Critical Priority Pathogens: Mechanisms of Resistance and Proposed Solutions through Candidates Such as Essential Oils

The rise of multidrug-resistant (MDR) pathogens has become a global health threat and an economic burden in providing adequate and effective treatment for many infections. This large-scale concern has emerged mainly due to mishandling of antibiotics (ABs) and has resulted in the rapid expansion of antimicrobial resistance (AMR). Nowadays, there is an urgent need for more potent, non-toxic and effective antimicrobial agents against MDR strains. In this regard, clinicians, pharmacists, microbiologists and the entire scientific community are encouraged to find alternative solutions in treating infectious diseases cause by these strains. In its "10 global issues to track in 2021", the World Health Organization (WHO) has made fighting drug resistance a priority. It has also issued a list of bacteria that are in urgent need for new ABs. Despite all available resources, researchers are unable to keep the pace of finding novel ABs in the face of emerging MDR strains. Traditional methods are increasingly becoming ineffective, so new approaches need to be considered. In this regard, the general tendency of turning towards natural alternatives has reinforced the interest in essential oils (EOs) as potent antimicrobial agents. Our present article aims to first review the main pathogens classified by WHO as critical in terms of current AMR. The next objective is to summarize the most important and up-to-date aspects of resistance mechanisms to classical antibiotic therapy and to compare them with the latest findings regarding the efficacy of alternative essential oil therapy.

Virulence Factors of Pseudomonas Aeruginosa and Antivirulence Strategies to Combat Its Drug Resistance

Pseudomonas aeruginosa is an opportunistic pathogen causing nosocomial infections in severely ill and immunocompromised patients. Ubiquitously disseminated in the environment, especially in hospitals, it has become a major threat to human health due to the constant emergence of drug-resistant strains. Multiple resistance mechanisms are exploited by P. aeruginosa, which usually result in chronic infections difficult to eradicate. Diverse virulence factors responsible for bacterial adhesion and colonization, host immune suppression, and immune escape, play important roles in the pathogenic process of P. aeruginosa. As such, antivirulence treatment that aims at reducing virulence while sparing the bacterium for its eventual elimination by the immune system, or combination therapies, has significant advantages over traditional antibiotic therapy, as the former imposes minimal selective pressure on P. aeruginosa, thus less likely to induce drug resistance. In this review, we will discuss the virulence factors of P. aeruginosa, their pathogenic roles, and recent advances in antivirulence drug discovery for the treatment of P. aeruginosa infections.

Microencapsulation of carvacrol as an efficient tool to fight Pseudomonas aeruginosa and Enterococcus faecalis biofilms

Biofilms are involved in serious problems in medical and food sectors due to their contribution to numerous severe chronic infections and foodborne diseases. The high resistance of biofilms to antimicrobial agents makes their removal as a big challenge. In this study, spray-drying was used to develop microcapsules containing carvacrol, a natural antimicrobial agent, to enhance its activity against P. aeruginosa and E. faecalis biofilms. The physicochemical properties and microscopic morphology of the realized capsules and cells were characterized. The minimum inhibitory concentration of encapsulated carvacrol (E-CARV) (1.25 mg mL^-1) was 4-times lower than that of free carvacrol (F-CARV) (5 mg mL^-1) against P. aeruginosa, while it remained the same against E. faecalis (0.625 mg mL^-1). E-CARV was able to reduce biofilm below the detection limit for P. aeruginosa and by 5.5 log CFU ml^-1 for E. faecalis after 15 min of treatment. Results also showed that F-CARV and E-CARV destabilize the bacterial cell membrane leading to cell death. These results indicate that carvacrol exhibited a strong antimicrobial effect against both bacterial biofilms. In addition, spray-drying could be used as an effective tool to enhance the antibiofilm activity of carvacrol, while reducing the concentrations required for disinfection of abiotic surfaces.

Skeletal infections: microbial pathogenesis, immunity and clinical management

Osteomyelitis remains one of the greatest risks in orthopaedic surgery. Although many organisms are linked to skeletal infections, Staphylococcus aureus remains the most prevalent and devastating causative pathogen. Important discoveries have uncovered novel mechanisms of S. aureus pathogenesis and persistence within bone tissue, including implant-associated biofilms, abscesses and invasion of the osteocyte lacuno-canalicular network. However, little clinical progress has been made in the prevention and eradication of skeletal infection as treatment algorithms and outcomes have only incrementally changed over the past half century. In this Review, we discuss the mechanisms of persistence and immune evasion in S. aureus infection of the skeletal system as well as features of other osteomyelitis-causing pathogens in implant-associated and native bone infections. We also describe how the host fails to eradicate bacterial bone infections, and how this new information may lead to the development of novel interventions. Finally, we discuss the clinical management of skeletal infection, including osteomyelitis classification and strategies to treat skeletal infections with emerging technologies that could translate to the clinic in the future.

Antimicrobial Peptides against Multidrug-Resistant Pseudomonas aeruginosa Biofilm from Cystic Fibrosis Patients

Lung infection is the leading cause of morbidity and mortality in cystic fibrosis (CF) patients and is mainly dominated by Pseudomonas aeruginosa. Treatment of CF-associated lung infections is problematic because the drugs are vulnerable to multidrug-resistant pathogens, many of which are major biofilm producers like P. aeruginosa. Antimicrobial peptides (AMPs) are essential components in all life forms and exhibit antimicrobial activity. Here we investigated a series of AMPs (d,l-K₆L₉), each composed of six lysines and nine leucines but differing in their sequence composed of l- and d-amino acids. The d,l-K₆L₉ peptides showed antimicrobial and antibiofilm activities against P. aeruginosa from CF patients. Furthermore, the data revealed that the d,l-K₆L₉ peptides are stable and resistant to degradation by CF sputum proteases and maintain their activity in a CF sputum environment. Additionally, the d,l-K₆L₉ peptides do not induce bacterial resistance. Overall, these findings should assist in the future development of alternative treatments against resistant bacterial biofilms.

Hybrid N-Acylcysteines as Dual-Acting Matrix Disruptive and Anti-Quorum Sensing Agents Fighting Pseudomonas aeruginosa Biofilms: Design, Synthesis, Molecular Docking Studies, and In Vitro Assays

Biofilms facilitate the pathogenesis of life-threatening Pseudomonas aeruginosa infections by coating mucosal surfaces or invasive devices and offer protection from antimicrobial therapy and the host immune response, thus increasing mortality rates and financial burden. Herein, new hybrid N-acylcysteines (NAC) incorporating selected acyl groups from organic acids and their derivatives, which are capable of quenching pathogen quorum sensing (QS) systems, were designed and their antibiofilm activity and anti-QS were evaluated. N-acylcysteines (4a-h) were synthesized and characterized by ¹H NMR and ¹³C NMR, and their purity was confirmed by elemental analyses. N-(4-Hydroxy-3,5-dimethoxybenzoyl)-l-cysteine (4d) and N-(4-methoxybenzoyl)-l-cysteine (4h) showed a higher antibiofilm activity against PAO1 biofilms than the rest of the targets and the standard NAC. They showed 83 and 82% inhibition of biofilms at 5 mM and eradicated mature biofilms at 20 mM concentrations (NAC biofilm inhibition = 66% at 10 mM and minimum biofilm eradication concentration = 40 mM). This was confirmed via visualizing adherent biofilm cells on catheter pieces using scanning electron microscopy. In the same vein, both 4d and 4h showed the highest docking score with the QS signal receptor protein LasR (-7.8), which was much higher than that of NAC (-5) but less than the score of the natural agonist N-(3-oxododecanoyl)-l-homoserine (OdDHL) (-8.5). Target 4h (5 mM) decreased the expression of quorum sensing encoding genes in P. aeruginosa PAO1 strain by 53% for pslA, 47% for lasI and lasR, and 29% for filC, lowered PAO1 pyocyanin production by 76.43%, completely blocked the proteolytic activity of PAO1, and did not affect PAO1 cell viability. Targets 4d and 4h may find applications for the prevention and treatment of biofilm-mediated P. aeruginosa local infections of the skin, eye, and wounds. N-(4-Methoxybenzoyl)-l-cysteine 4h is a promising dual-acting matrix disruptive and anti-QS antibiofilm agent for further investigation and optimization.

Oil Absorbent Polypropylene Particles Stimulate Biodegradation of Crude Oil by Microbial Consortia

Oil absorbent particles made from surface-modified polypropylene can be used to facilitate the removal of oil from the environment. In this study, we investigated to what extent absorbed oil was biodegraded and how this compared to the biodegradation of oil in water. To do so, we incubated two bacterial communities originating from the Niger Delta, an area subject to frequent oil spills, in the presence and absence of polypropylene particles. One community evolved from untreated soil whereas the second evolved from soil pre-exposed to oil. We observed that the polypropylene particles stimulated the growth of biofilms and enriched species from genera Mycobacterium, Sphingomonas and Parvibaculum. Cultures with polypropylene particles degraded more crude oil than those where the oil was present in suspension regardless of whether they were pre-exposed or not. Moreover, the community pre-exposed to crude oil had a different community structure and degraded more oil than the one from untreated soil. We conclude that the biodegradation rate of crude oil was enhanced by the pre-exposure of the bacterial communities to crude oil and by the use of oil-absorbing polypropylene materials. The data show that bacterial communities in the biofilms growing on the particles have an enhanced degradation capacity for oil.

Architectural Features and Resistance to Food-Grade Disinfectants in Listeria monocytogenes-Pseudomonas spp. Dual-Species Biofilms

Listeria monocytogenes is considered a foodborne pathogen of serious concern capable of forming multispecies biofilms with other bacterial species, such as Pseudomonas spp., adhered onto stainless steel (SS) surfaces. In an attempt to link the biofilms' morphology and resistance to biocides, dual-species biofilms of L. monocytogenes, in co-culture with either Pseudomonas aeruginosa, Pseudomonas fluorescens, or Pseudomonas putida, were assayed to ascertain their morphological characteristics and resistance toward benzalkonium chloride (BAC) and neutral electrolyzed water (NEW). Epifluorescence microscopy analysis revealed that each dual-species biofilm was distributed differently over the SS surface and that these differences were attributable to the presence of Pseudomonas spp. Confocal laser scanning microscopy (CLSM) assays demonstrated that despite these differences in distribution, all biofilms had similar maximum thicknesses. Along with this, colocalization analyses showed a strong trend of L. monocytogenes to share location within the biofilm with all Pseudomonas assayed whilst the latter distributed throughout the surface independently of the presence of L. monocytogenes, a fact that was especially evident in those biofilms in which cell clusters were present. Finally, a modified Gompertz equation was used to fit biofilms' BAC and NEW dose-response data. Outcomes demonstrated that L. monocytogenes was less susceptible to BAC when co-cultured with P. aeruginosa or P. fluorescens, whereas susceptibility to NEW was reduced in all three dual-species biofilms, which can be attributable to both the mechanism of action of the biocide and the architectural features of each biofilm. Therefore, the results herein provided can be used to optimize already existing and develop novel target-specific sanitation treatments based on the mechanism of action of the biocide and the biofilms' species composition and structure.

Targeting Persistent Biofilm Infections: Reconsidering the Topography of the Infection Site during Model Selection

The physiology of an organism in the environment reflects its interactions with the diverse physical, chemical, and biological properties of the surface. These principles come into consideration during model selection to study biofilm–host interactions. Biofilms are communities formed by beneficial and pathogenic bacteria, where cells are held together by a structured extracellular matrix. When biofilms are associated with a host, chemical gradients and their origins become highly relevant. Conventional biofilm laboratory models such as multiwall biofilm models and agar plate models poorly mimic these gradients. In contrast, ex vivo models possess the partial capacity to mimic the conditions of tissue-associated biofilm and a biofilm associated with a mineralized surface enriched in inorganic components, such as the human dentin. This review will highlight the progress achieved using these settings for two models of persistent infections: the infection of the lung tissue by Pseudomonas aeruginosa and the infection of the root canal by Enterococcus faecalis. For both models, we conclude that the limitations of the conventional in vitro systems necessitate a complimentary experimentation with clinically relevant ex vivo models during therapeutics development.

The c-di-GMP Phosphodiesterase PipA (PA0285) Regulates Autoaggregation and Pf4 Bacteriophage Production in Pseudomonas aeruginosa PAO1

In Pseudomonas aeruginosa PAO1, 41 genes encode proteins predicted to be involved in the production or degradation of c-di-GMP, a ubiquitous secondary messenger that regulates a variety of physiological behaviors closely related to biofilm and aggregate formation. Despite extensive effort, the entire picture of this important signaling network is still unclear, with one-third of these proteins remaining uncharacterized. Here, we show that the deletion of pipA, which produces a protein containing two PAS domains upstream of a GGDEF-EAL tandem, significantly increased the intracellular c-di-GMP level and promoted the formation of aggregates both on surfaces and in planktonic cultures. However, this regulatory effect was not contributed by either of the two classic pathways modulating biofilm formation, exopolysaccharide (EPS) overproduction or motility inhibition. Transcriptome sequencing (RNA-Seq) data revealed that the expression levels of 361 genes were significantly altered in a ΔpipA mutant strain compared to the wild type (WT), indicating the critical role of PipA in PAO1. The most remarkably downregulated genes were located on the Pf4 bacteriophage gene cluster, which corresponded to a 2-log reduction in the Pf4 phage production in the ΔpipA mutant. The sizes of aggregates in ΔpipA cultures were affected by exogenously added Pf4 phage in a concentration-dependent manner, suggesting the quantity of phage plays a part in regulating the formation of aggregates. Further analysis demonstrated that PipA is highly conserved across 83 P. aeruginosa strains. Our work therefore for the first time showed that a c-di-GMP phosphodiesterase can regulate bacteriophage production and provided new insights into the relationship between bacteriophage and bacterial aggregation. IMPORTANCE The c-di-GMP signaling pathways in P. aeruginosa are highly organized and well coordinated, with different diguanylate cyclases and phosphodiesterases playing distinct roles in a complex network. Understanding the function of each enzyme and the underlying regulatory mechanisms not only is crucial for revealing how bacteria decide the transition between motile and sessile lifestyles, but also greatly facilitates the development of new antibiofilm strategies. This work identified bacteriophage production as a novel phenotypic output controlled transcriptionally by a phosphodiesterase, PipA. Further analysis suggested that the quantity of phage may be important in regulating autoaggregation, as either a lack of phage or overproduction was associated with higher levels of aggregation. Our study therefore extended the scope of c-di-GMP-controlled phenotypes and discovered a potential signaling circuit that can be target for biofilm treatment.

Antibiotic-producing Micrococcales govern the microbiome that inhabits the fur of two- and three-toed sloths

Sloths have a dense coat on which insects, algae, and fungi coexist in a symbiotic relationship. This complex ecosystem requires different levels of control, however, most of these mechanisms remain unknown. We investigated the bacterial communities inhabiting the hair of two- (Choloepus Hoffmani) and three-toed (Bradypus variegatus) sloths and evaluated their potential for producing antibiotic molecules capable of exerting control over the hair microbiota. The analysis of 16S rRNA amplicon sequence variants (ASVs) revealed that the communities in both host species are dominated by Actinobacteriota and Firmicutes. The most abundant genera were Brevibacterium, Kocuria/Rothia, Staphylococcus, Rubrobacter, Nesterenkonia, and Janibacter. Furthermore, we isolated nine strains of Brevibacterium and Rothia capable of producing substances that inhibited the growth of common mammalian pathogens. The analysis of the biosynthetic gene clusters (BCGs) of these nine isolates suggests that the pathogen-inhibitory activity could be mediated by the presence of siderophores, terpenes, beta-lactones, Type III polyketide synthases (T3PKS), ribosomally synthesized, and post-translationally modified peptides (RiPPs), non-alpha poly-amino acids (NAPAA) like e-Polylysin, ectoine or nonribosomal peptides (NRPs). Our data suggest that Micrococcales that inhabit sloth hair could have a role in controlling microbial populations in that habitat, improving our understanding of this highly complex ecosystem. This article is protected by copyright. All rights reserved.