Prunus persica leaves aqueous extract mediated biosynthesis of Ag nanoparticles and assessment of its anti-quorum sensing potential against Hafnia species.

Hafnia sp. was one of the specific spoilage bacteria in aquatic products, and the aim of the study was to investigate the inhibition ability of the silver nanoparticles (AgNPs) biosynthesis by an aqueous extract of Prunus persica leaves toward the spoilage-related virulence factors of Hafnia sp. The synthesized P-AgNPs were spherical, with a mean particle size of 36.3 nm and zeta potential of 21.8 ± 1.33 mV. In addition, the inhibition effects of P-AgNPs on the growth of two Hafnia sp. strains and their quorum sensing regulated virulence factors, such as the formation of biofilm, secretion of N-acetyl-homoserine lactone (AHLs), proteases, and exopolysaccharides, as well as their swarming and swimming motilities were evaluated. P-AgNPs had a minimum inhibitory concentration (MIC) of 64 µg ml-1 against the two Hafnia sp. strains. When the concentration of P-AgNPs was below MIC, it could inhibit the formation of biofilms by Hafnia sp at 8-32 µg ml-1, but it promoted the formation of biofilms by Hafnia sp at 0.5-4 µg ml-1. P-AgNPs exhibited diverse inhibiting effects on AHLs and protease production, swimming, and swarming motilities at various concentrations.

Assessment of the growth inhibition and anti-biofilm activity of aptamer (PmA2G02) against Proteus mirabilis 1429T.

Proteus mirabilis is known to cause Catheter-associated urinary tract infections (CAUTIs), which exhibit virulence factors linked to forming biofilms. Aptamers have recently been explored as potential anti-biofilm agents. This study demonstrates the anti-biofilm activity of aptamer (PmA2G02) targeting P. mirabilis 1429T, a pathogenic bacteria known to cause Catheter-associated urinary tract infections (CAUTIs). The studied aptamer inhibited biofilm formation, swarming motility, and cell viability at a concentration of 3 µM. The study also showed that the PmA2G02 had a binding affinity towards fimbrial outer membrane usher protein (PMI1466), flagellin protein (PMI1619), and regulator of swarming behavior (rsbA), which are responsible for adhesion, motility, and quorum sensing, respectively. Crystal violet assay, SEM, and confocal imaging confirmed the effectiveness of the PmA2G02 as an anti-biofilm agent. Moreover, as verified by qPCR, the expression levels of fimD, fliC2, and rsbA were significantly reduced compared to the untreated group. This study suggests that aptamer may be a potential alternative to traditional antibiotics for the treatment of CAUTIs caused by P. mirabilis. These findings shed light on the mechanisms by which the aptamer inhibits biofilm formation.

In vitro and in silico assessment of anti-quorum sensing activity of Naproxen against Pseudomonas aeruginosa.

Serious infections caused by Pseudomonas aeruginosa are usually related to quorum sensing (QS)-dependent virulence factors. Hence, QS inhibition is a promising approach to overcoming P. aeruginosa infections. This study aimed to investigate the effect of naproxen on biofilm formation and QS-related virulence traits of P. aeruginosa. Furthermore, the anti-QS potential of naproxen was evaluated using real-time PCR and molecular docking analysis. Our findings supported the anti-QS activity of naproxen, as evidenced by down-regulation of the lasI and rhlI genes expression as well as the attenuation of bacterial protease, hemolysin, pyocyanin, biofilm, and motility. Additionally, the high binding affinity of naproxen with QS regulatory proteins was determined in the molecular docking simulation. Altogether, these findings suggest that naproxen has a promising potential in inhibiting QS-associated traits of P. aeruginosa.

Novel Benzothiazole Derivatives as Potential Anti-Quorum Sensing Agents for Managing Plant Bacterial Diseases: Synthesis, Antibacterial Activity Assessment, and SAR Study.

As quorum sensing (QS) regulates bacterial pathogenicity, antiquorum sensing agents have powerful application potential for controlling bacterial infections and overcoming pesticide/drug resistance. Identifying anti-QS agents thus represents a promising approach in agrochemical development. In this study, the anti-QS potency of 53 newly prepared benzothiazole derivatives containing an isopropanolamine moiety was analyzed, and structure-activity relationships were examined. Compound D3 exhibited the strongest antibacterial activity, with an in vitro EC50 of 1.54 µg mL-1 against Xanthomonas oryzae pv oryzae (Xoo). Compound D3 suppressed QS-regulated virulence factors (e.g., biofilm, extracellular polysaccharides, extracellular enzymes, and flagella) to inhibit bacterial infection. In vivo anti-Xoo assays indicated good control efficiency (curative activity, 47.8%; protective activity, 48.7%) at 200 µg mL-1. Greater control efficiency was achieved with addition of 0.1% organic silicone or orange peel essential oil. The remarkable anti-QS potency of these benzothiazole derivatives could facilitate further novel bactericidal compound development.

Critical Assessment of the Prospects of Quorum-Quenching Therapy for Staphylococcus aureus Infection.

Staphylococcus aureus is an important pathogen that causes a high number of infections and is one of the leading causes of death in hospitalized patients. Widespread antibiotic resistance such as in methicillin-resistant S. aureus (MRSA) has prompted research into potential anti-virulence-targeted approaches. Targeting the S. aureus accessory gene regulator (Agr) quorum-sensing system, a master regulator of virulence, is the most frequently proposed anti-virulence strategy for S. aureus. While much effort has been put into the discovery and screening for Agr inhibitory compounds, in vivo analysis of their efficacy in animal infection models is still rare and reveals various shortcomings and problems. These include (i) an almost exclusive focus on topical skin infection models, (ii) technical problems that leave doubt as to whether observed in vivo effects are due to quorum-quenching, and (iii) the discovery of counterproductive biofilm-increasing effects. Furthermore, potentially because of the latter, invasive S. aureus infection is associated with Agr dysfunctionality. Altogether, the potential of Agr inhibitory drugs is nowadays seen with low enthusiasm given the failure to provide sufficient in vivo evidence for their potential after more than two decades since the initiation of such efforts. However, current Agr inhibition-based probiotic approaches may lead to a new application of Agr inhibition strategies in preventing S. aureus infections by targeting colonization or for otherwise difficult-to-treat skin infections such as atopic dermatitis.

Enhanced quorum sensing capacity via regulating microenvironment to facilitate stress resistance of probiotic in alginate-based microcapsules.

Alginate-based microcapsule has becoming a promising carrier for probiotic encapsulation due to the improved stress resistant ability. Besides the physical protection of microcapsules, bacterial quorum sensing (QS) is another prominent factor affecting microbial stress resistance in microcapsules. In the present study, Vibrio harveyi cells were entrapped and proliferated into cell aggregates in alginate-based microcapsules. The microenvironment composed of cells and biomacromolecules was regulated by the diameter, alginate concentration and core state of microcapsule. Then the effect of microenvironment on bacterial QS capacity was investigated, including bioluminescence, autoinducers (AIs) production and QS related genes expression. The highest diameter of 1200 µm and highest alginate concentration of 2.0 % w/v under the investigation range presented strongest QS capacity, and the maintenance of hydrogel core could enhance bacterial QS. Moreover, the mechanism analysis revealed that the formed biofilm on the surface of cell aggregates hampered the outward transfer of AIs, and the local AIs inside the cell aggregates induced stronger bacteria QS by close-range interaction. As a whole, these findings are helpful to guide the technological development and optimization of microencapsulated probiotics with stronger stress resistance, and the potential application in food, dairy, wastewater treatment and biosensor.

Fast start-up of ANAMMOX biofilm processes at low temperatures by economical quorum sensing regulation: The importance of endogenous N-acyl-homoserine lactones from enhanced inoculated sludge.

The start-up of anaerobic ammonia oxidation (ANAMMOX) processes at low temperatures is quite difficult. In this study, the fast start-up (43 days) of ANAMMOX biofilm processes at 18 ± 3 °C was achieved by adding enhanced ANAMMOX granules (LT-granules) into the inoculated denitrification sludge. The results showed that the addition of LT-granules significantly reduced the duration of the three start-up phases (cell lysis phase, activity lag phase, and activity elevation phase) of reactor R2 compared with the control group R1 without LT-granules. It was demonstrated that LT-granules released high contents of N-hexanoyl-DL-homoserine lactone (C6-HSL), N-octanoyl-DL-homoserine lactone (C8-HSL), and N-3-oxohexanoyl-L-homoserine lactone (3OC6-HSL). The C6-HSL and C8-HSL from LT-granules were strongly positively correlated with the concentrations of polysaccharides (TB-PS) and proteins (TB-PN) in tightly bound extracellular polymeric substances (TB-EPS) in R2 biofilms, respectively. Thus, LT-granules promoted the release of TB-PS and TB-PN from the biofilm in R2 during activity lag and activity elevation phases, improving the biofilm adhesion performance. Furthermore, it was proved that the C6-HSL, C8-HSL, and 3OC6-HSL from LT-granules significantly stimulated the relative abundance of Candidatus Brocadia genus and the expression of functional genes hzo and hzsA in R2 biofilms during activity lag and activity elevation phases. These are the main reasons why adding LT-granules promoted the start-up of reactor R2 at 18 ± 3 °C effectively. This study is the first work to accelerate the start-up of the ANAMMOX biofilm system at the low temperature by the economical quorum sensing (QS) regulation based on endogenous N-acyl-homoserine lactone signals (AHLs) and supply a new way for the rapid start-up of ANAMMOX processes in the low-temperature environment.

An Immunochemical Approach to Detect the Quorum Sensing-Regulated Virulence Factor 2-Heptyl-4-Quinoline N-Oxide (HQNO) Produced by Pseudomonas aeruginosa Clinical Isolates.

Understanding quorum sensing (QS) and its role in the development of pathogenesis may provide new avenues for diagnosing, surveillance, and treatment of infectious diseases. For this purpose, the availability of reliable and efficient analytical diagnostic tools suitable to specifically detect and quantify these essential QS small molecules and QS regulated virulence factors is crucial. Here, we reported the development and evaluation of antibodies and an enzyme-linked immunosorbent assay (ELISA) for HQNO (2-heptyl-4-quinoline N-oxide), a QS product of the PqsR system, which has been found to act as a major virulence factor that interferes with the growth of other microorganisms. Despite the nonimmunogenic character of HQNO, the antibodies produced showed high avidity and the microplate-based ELISA developed could detect HQNO in the low nM range. Hence, a limit of detection (LOD) of 0.60 ± 0.13 nM had been reached in Müeller Hinton (MH) broth, which was below previously reported levels using sophisticated equipment based on liquid chromatography coupled to mass spectrometry. The HQNO profile of release of different Pseudomonas aeruginosa clinical isolates analyzed using this ELISA showed significant differences depending on whether the clinical isolates belonged to patients with acute or chronic infections. These data point to the possibility of using HQNO as a specific biomarker to diagnose P. aeruginosa infections and for patient surveillance. Considering the role of HQNO in inhibiting the growth of coinfecting bacteria, the present ELISA will allow the investigation of these complex bacterial interactions underlying infections. IMPORTANCE Bacteria use quorum sensing (QS) as a communication mechanism that releases small signaling molecules which allow synchronizing a series of activities involved in the pathogenesis, such as the biosynthesis of virulence factors or the regulation of growth of other bacterial species. HQNO is a metabolite of the Pseudomonas aeruginosa-specific QS signaling molecule PQS (Pseudomonas quinolone signal). In this work, the development of highly specific antibodies and an immunochemical diagnostic technology (ELISA) for the detection and quantification of HQNO was reported. The ELISA allowed profiling of the release of HQNO by clinical bacterial isolates, showing its potential value for diagnosing and surveillance of P. aeruginosa infections. Moreover, the antibodies and the ELISA reported here may contribute to the knowledge of other underlying conditions related to the pathology, such as the role of the interactions with other bacteria of a particular microbiota environment.

Biocomputational Assessment of Natural Compounds as a Potent Inhibitor to Quorum Sensors in Ralstonia solanacearum.

Ralstonia solanacearum is among the most damaging bacterial phytopathogens with a wide number of hosts and a broad geographic distribution worldwide. The pathway of phenotype conversion (Phc) is operated by quorum-sensing signals and modulated through the (R)-methyl 3-hydroxypalmitate (3-OH PAME) in R. solanacearum. However, the molecular structures of the Phc pathway components are not yet established, and the structural consequences of 3-OH PAME on quorum sensing are not well studied. In this study, 3D structures of quorum-sensing proteins of the Phc pathway (PhcA and PhcR) were computationally modeled, followed by the virtual screening of the natural compounds library against the predicted active site residues of PhcA and PhcR proteins that could be employed in limiting signaling through 3-OH PAME. Two of the best scoring common ligands ZINC000014762512 and ZINC000011865192 for PhcA and PhcR were further analyzed utilizing orbital energies such as HOMO and LUMO, followed by molecular dynamics simulations of the complexes for 100 ns to determine the ligands binding stability. The findings indicate that ZINC000014762512 and ZINC000011865192 may be capable of inhibiting both PhcA and PhcR. We believe that, after further validation, these compounds may have the potential to disrupt bacterial quorum sensing and thus control this devastating phytopathogenic bacterial pathogen.

Design and assessment of novel synthetic peptides to inhibit quorum sensing-dependent biofilm formation in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is one of the most common biofilm-producing bacteria, often leading to long-term and chronic infections. The LasR regulator protein acts as the central regulator of the quorum sensing (QS) system and coordinates the expression of some virulence and biofilm genes. In this study, novel peptides (WSF, FASK, YDVD) were designed for binding to the domain of the transcriptional activator of the LasR protein and interfere with LasR in the QS system of P. aeruginosa. The effects of these peptides on biofilm production, expression of biofilm-related genes (AlgC, PslA, PelA), and growth of planktonic P. aeruginosa were investigated. All three peptides inhibited the growth of P. aeruginosa planktonic cells at 1600 µg ml-1 and exhibited anti-biofilm effects at sub-inhibitory concentrations (800 µg ml-1). Measurements of the mRNA levels of biofilm-related genes at sub-inhibitory concentrations of the designed peptides showed a significant decrease.

Histological assessment, anti-quorum sensing, and anti-biofilm activities of Dioon spinulosum extract: in vitro and in vivo approach.

Pseudomonas aeruginosa is an opportunistic bacterium causing several health problems and having many virulence factors like biofilm formation on different surfaces. There is a significant need to develop new antimicrobials due to the spreading resistance to the commonly used antibiotics, partly attributed to biofilm formation. Consequently, this study aimed to investigate the anti-biofilm and anti-quorum sensing activities of Dioon spinulosum, Dyer Ex Eichler extract (DSE), against Pseudomonas aeruginosa clinical isolates. DSE exhibited a reduction in the biofilm formation by P. aeruginosa isolates both in vitro and in vivo rat models. It also resulted in a decrease in cell surface hydrophobicity and exopolysaccharide quantity of P. aeruginosa isolates. Both bright field and scanning electron microscopes provided evidence for the inhibiting ability of DSE on biofilm formation. Moreover, it reduced violacein production by Chromobacterium violaceum (ATCC 12,472). It decreased the relative expression of 4 quorum sensing genes (lasI, lasR, rhlI, rhlR) and the biofilm gene (ndvB) using qRT-PCR. Furthermore, DSE presented a cytotoxic activity with IC50 of 4.36 ± 0.52 µg/ml against human skin fibroblast cell lines. For the first time, this study reports that DSE is a promising resource of anti-biofilm and anti-quorum sensing agents.

The Epidemiology and Pathogenesis and Treatment of Pseudomonas aeruginosa Infections: An Update.

Pseudomonas aeruginosa is a Gram-negative bacterial pathogen that is a common cause of nosocomial infections, particularly pneumonia, infection in immunocompromised hosts, and in those with structural lung disease such as cystic fibrosis. Epidemiological studies have identified increasing trends of antimicrobial resistance, including multi-drug resistant (MDR) isolates in recent years. P. aeruginosa has several virulence mechanisms that increase its ability to cause severe infections, such as secreted toxins, quorum sensing and biofilm formation. Management of P. aeruginosa infections focuses on prevention when possible, obtaining cultures, and prompt initiation of antimicrobial therapy, occasionally with combination therapy depending on the clinical scenario to ensure activity against P. aeruginosa. Newer anti-pseudomonal antibiotics are available and are increasingly being used in the management of MDR P. aeruginosa.

Molecular Simulations and Markov State Modeling Reveal Inactive Form of Quorum Sensing Regulator SdiA of Escherichia Coli.

Enteropathogenic Escherichia coli remains one of the most important pathogens infecting children and it is one of the main causes of persistent diarrhea worldwide. Enteropathogenic Escherichia coli is capable of forming biofilms. Several E. coli mechanisms are regulated by quorum sensing, including virulence factors and biofilm formation. Quorum sensing is the communication system of bacteria with the ability to respond to chemical molecules known as autoinducers. Suppressor of division inhibitor (SdiA) is a quorum sensing receptor present in enteropathogenic E. coli in humans that detect acyl-homoserine lactone type autoinducers. SdiA receptor can also respond to autoinducers produced by other bacterial species that control cell division and virulence. SdiA is regulated by 1-octanoyl-rac-glycerol, which serves as an energy source, signaling molecule, and substrate for membrane biogenesis. SdiA is a potential target, which can be used as an anti-infectious technique. Current crystallographic structures for virtual screening may not be sufficient for molecular docking. So they are not very predictive, because the structures are in the active form. It has been shown that SdiA protein is not activated without a ligand. Generally, ligands bind to the ligand binding domain of SdiA. We employ Markov modeling and molecular dynamics simulations to understand the behaviour of SdiA protein and find the possible inactive form. We find an unknown conformation after 24 molecular dynamics simulation runs with random initial velocities and Markov state modeling. In summary, using molecular simulations and Markov state modeling, we have obtained an unknown conformation, which is not available in the crystallographic structures of SdiA. This unknown conformation could be the structure of the inactive form without a ligand. The obtained ensemble structures could be used for virtual screening.

Bacterial biofilm-derived antigens: a new strategy for vaccine development against infectious diseases.

INTRODUCTION: Microorganisms can develop into a social organization known as biofilms and these communities can be found in virtually all types of environment on earth. In biofilms, cells grow as multicellular communities held together by a self-produced extracellular matrix. Living within a biofilm allows for the emergence of specific properties for these cells that their planktonic counterparts do not have. Furthermore, biofilms are the cause of several infectious diseases and are frequently inhabited by multi-species. These interactions between microbial species are often critical for the biofilm process. Despite the importance of biofilms in disease, vaccine antigens are typically prepared from bacteria grown as planktonic cells under laboratory conditions. Vaccines based on planktonic bacteria may not provide optimal protection against biofilm-driven infections. AREAS COVERED: In this review, we will present an overview of biofilm formation, what controls this mode of growth, and recent vaccine development targeting biofilms. EXPERT OPINION: Previous and ongoing research provides evidence that vaccine formulation with antigens derived from biofilms is a promising approach to prevent infectious diseases and can enhance the protective efficacy of existing vaccines. Therefore, research focusing on the identification of biofilm-derived antigens merits further investigations.

Cooperative metabolic resource allocation in spatially-structured systems.

Natural selection has shaped the evolution of cells and multi-cellular organisms such that social cooperation can often be preferred over an individualistic approach to metabolic regulation. This paper extends a framework for dynamic metabolic resource allocation based on the maximum entropy principle to spatiotemporal models of metabolism with cooperation. Much like the maximum entropy principle encapsulates 'bet-hedging' behaviour displayed by organisms dealing with future uncertainty in a fluctuating environment, its cooperative extension describes how individuals adapt their metabolic resource allocation strategy to further accommodate limited knowledge about the welfare of others within a community. The resulting theory explains why local regulation of metabolic cross-feeding can fulfil a community-wide metabolic objective if individuals take into consideration an ensemble measure of total population performance as the only form of global information. The latter is likely supplied by quorum sensing in microbial systems or signalling molecules such as hormones in multi-cellular eukaryotic organisms.

Growth effects in oregano plants (Origanum vulgare L.) assessment through inoculation of bacteria isolated from crop fields located on desert soils.

Bacteria can establish beneficial interactions with plants by acting as growth promoters and enhancing stress tolerance during plant interactions. Likewise, bacteria can develop multispecies communities where multiple interactions are possible. In this work, we assessed the physiological effects of three bacteria isolated from an arid environment (Bacillus niacini, Bacillus megaterium, and Moraxella osloensis) applied as single species or as a consortium on oregano (Origanum vulgare L.) plants. Moreover, we assessed the quorum-sensing (QS) signaling activity to determine the molecular communication between plant-growth-promoting bacteria. The plant inoculation with B. megaterium showed a positive effect on morphometric and physiologic parameters. However, no synergistic effects were observed when a bacterial consortium was inoculated. Likewise, activation of QS signaling in biofilm assays was observed only for interspecies interaction within the Bacillus genus, not for either interaction with M. osloensis. These results suggest a neutral or antagonistic interaction for interspecific bacterial biofilm establishment, as well as for the interaction with oregano plants when bacteria were inoculated in a consortium. In conclusion, we were able to determine that the bacterial interactions are not always positive or synergistic, but they also might be neutral or antagonistic.

Assessment of quorum sensing effects of tyrosol on fermentative performance by chief ethnic fermentative yeasts from northeast India.

AIM: Tyrosol, a quorum sensing molecule in yeasts, was reported to reduce lag phase and induces hyphae formation during cell proliferation. However, evidence of any enhancing effect of tyrosol in cellular proliferation within fermentative environment is unclear. In this investigation, selected yeast cells were assessed for their ability to synthesize tyrosol followed by examining the role of the molecule during fermentation. METHODS AND RESULTS: Tyrosols were characterized in four fermentative yeasts viz., Saccharomyces cerevisiae, Wickerhamomyces anomalus, Candida glabrata and Candida tropicalis isolated from traditional fermentative cakes of northeast India. All the isolates synthesized tyrosol while C. tropicalis exhibited filamentous growth in response to tyrosols retrieved from other isolates. Purified tyrosols showed protective behaviour in C. tropicalis and S. cerevisiae under ethanol mediated oxidative stress. During fermentation, tyrosol significantly enhanced growth of W. anomalus in starch medium while C. tropicalis exhibited growth enhancement in starch and glucose sources. The chief fermentative yeast S. cerevisiae showed notable enhancement in fermentative capacity in starch medium under the influence of tyrosol con-commitment of ethanol production. CONCLUSION: The study concludes that tyrosol exerts unusual effect in cellular growth and fermentative ability of both Saccharomyces and non-Saccharomyces yeasts. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report of expression of tyrosol by non-conventional yeasts, where the molecule was found to exert enhancing effect during fermentation, thereby augmenting the process of metabolite production during traditional fermentation.

Green synthesis of silver nanoparticles using Carum copticum: Assessment of its quorum sensing and biofilm inhibitory potential against gram negative bacterial pathogens.

Antimicrobial resistance among pathogenic bacteria has become a global threat to human health. Due to poor progress in development of new antimicrobial drugs, there is a need for the development of novel alternative strategies to combat the problem of multidrug resistance. Moreover, there is focus on ecofriendly approach for the synthesis nanoparticles having efficient medicinal properties including antivirulence properties to tackle the emergence of multi-drug resistance. Targeting quorum sensing controlled virulence factors and biofilms has come out to be a novel anti-infective drug target. The silver nanoparticles (Ag@CC-NPs) were synthesized from aqueous extract of Carum copticum and characterized using UV-vis absorption spectroscopy, fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Ag@CC-NPs were checked for its ability to inhibit quorum sensing-mediated virulence factors and biofilms against three test pathogens at sub-MIC values. There was ~75% inhibition of violacein production by Ag@CC-NPs against C. violaceum. The P. aeruginosa virulence factors such as pyocyanin production, pyoverdin production, exoprotease activity, elastase activity, swimming motility and rhamnolipid production were inhibited by 76.9, 49.0, 71.1, 53.3, 89.5, and 60.0% at sub-MIC. Moreover, virulence factors of S. marcescens viz. prodigiosin production, exoprotease activity, and swarming motility was reduced by 78.4, 67.8, and 90.7%. Ag@CC-NPs also exhibited broad-spectrum antibiofilm activity with 77.6, 86.3, and 75.1% inhibition of biofilms of P. aeruginosa, S. marcescens, and C. violaceum respectively. The biofilm formation on glass coverslip was reduced remarkably as evident from SEM and CLSM analysis. The findings revealed the in vitro efficacy of Ag@CC-NPs against bacterial pathogens and can be exploited in the development of alternative therapeutic agent in management of bacterial infections for topical application, mainly wound infection, or coating of surfaces to prevent bacterial adherence on medical devices.

The cost and benefit of quorum sensing-controlled bacteriocin production in Lactobacillus plantarum.

Bacteria eliminate competitors via 'chemical warfare' with bacteriocins. Some species appear to adjust bacteriocin production conditionally in response to the social environment. We tested whether variation in the cost and benefit of producing bacteriocins could explain such conditional behaviour, in the bacteria Lactobacillus plantarum. We found that: (a) bacterial bacteriocin production could be upregulated by either the addition of a synthetic autoinducer peptide (PLNC8IF; signalling molecule), or by a plasmid which constitutively encodes for the production of this peptide; (b) bacteriocin production is costly, leading to reduced growth when grown in poor and, to a lesser extent, in rich media; (c) bacteriocin production provides a fitness advantage, when grown in competition with sensitive strains; and (d) the fitness benefits provided by bacteriocin production are greater at higher cell densities. These results show how the costs and benefits of upregulating bacteriocin production can depend upon abiotic and biotic conditions.

A Screen for Antibiotic Resistance Determinants Reveals a Fitness Cost of the Flagellum in Pseudomonas aeruginosa.

The intrinsic resistance of Pseudomonas aeruginosa to many antibiotics limits treatment options for pseudomonal infections. P. aeruginosa's outer membrane is highly impermeable and decreases antibiotic entry into the cell. We used an unbiased high-throughput approach to examine mechanisms underlying outer membrane-mediated antibiotic exclusion. Insertion sequencing (INSeq) identified genes that altered fitness in the presence of linezolid, rifampin, and vancomycin, antibiotics to which P. aeruginosa is intrinsically resistant. We reasoned that resistance to at least one of these antibiotics would depend on outer membrane barrier function, as previously demonstrated in Escherichia coli and Vibrio cholerae This approach demonstrated a critical role of the outer membrane barrier in vancomycin fitness, while efflux pumps were primary contributors to fitness in the presence of linezolid and rifampin. Disruption of flagellar assembly or function was sufficient to confer a fitness advantage to bacteria exposed to vancomycin. These findings clearly show that loss of flagellar function alone can confer a fitness advantage in the presence of an antibiotic.IMPORTANCE The cell envelopes of Gram-negative bacteria render them intrinsically resistant to many classes of antibiotics. We used insertion sequencing to identify genes whose disruption altered the fitness of a highly antibiotic-resistant pathogen, Pseudomonas aeruginosa, in the presence of antibiotics usually excluded by the cell envelope. This screen identified gene products involved in outer membrane biogenesis and homeostasis, respiration, and efflux as important contributors to fitness. An unanticipated fitness cost of flagellar assembly and function in the presence of the glycopeptide antibiotic vancomycin was further characterized. These findings have clinical relevance for individuals with cystic fibrosis who are infected with P. aeruginosa and undergo treatment with vancomycin for a concurrent Staphylococcus aureus infection.