Inhibition of P. aeruginosa c-di-GMP phosphodiesterase RocR and swarming motility by a benzoisothiazolinone derivative

The Anti-Microbial Peptide Citrocin Controls Pseudomonas aeruginosa Biofilms by Breaking Down Extracellular Polysaccharide

Citrocin is an anti-microbial peptide that holds great potential in animal feed. This study evaluates the anti-microbial and anti-biofilm properties of Citrocin and explores the mechanism of action of Citrocin on the biofilm of P. aeruginosa. The results showed that Citrocin had a significant inhibitory effect on the growth of P. aeruginosa with a minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 0.3 mg/mL. All five concentrations (1/4MIC, 1/2MIC, MIC, 2MIC, and 4MIC) of Citrocin inhibited P. aeruginosa biofilm formation. Citrocin at the MIC, 2MIC and 4MIC removed 42.7%, 76.0% and 83.2% of mature biofilms, respectively, and suppressed the swarming motility, biofilm metabolic activity and extracellular polysaccharide production of P. aeruginosa. Metabolomics analysis indicated that 0.3 mg/mL of Citrocin up- regulated 26 and down-regulated 83 metabolites, mainly comprising amino acids, fatty acids, organic acids and sugars. Glucose and amino acid metabolic pathways, including starch and sucrose metabolism as well as arginine and proline metabolism, were highly enriched by Citrocin. In summary, our research reveals the anti-biofilm mechanism of Citrocin at the metabolic level, which provides theoretical support for the development of novel anti-biofilm strategies for combatting P. aeruginosa.

Regulating bacterial biofilms in food and biomedicine: unraveling mechanisms and Innovating strategies

Bacterial biofilm has brought a lot of intractable problems in food and biomedicine areas. Conventional biofilm control mainly focuses on inactivation and removal of biofilm. However, with robust construction and enhanced resistance, the established biofilm is extremely difficult to eradicate. According to the mechanism of biofilm development, biofilm formation can be modulated by intervening in the key factors and regulatory systems. Therefore, regulation of biofilm formation has been proposed as an alternative way for effective biofilm control. This review aims to provide insights into the regulation of biofilm formation in food and biomedicine. The underlying mechanisms for early-stage biofilm establishment are summarized based on the key factors and correlated regulatory networks. Recent developments and applications of novel regulatory strategies such as anti/pro-biofilm agents, nanomaterials, functionalized surface materials and physical strategies are also discussed. The current review indicates that these innovative methods have contributed to effective biofilm control in a smart, safe and eco-friendly way. However, standard methodology for regulating biofilm formation in practical use is still missing. As biofilm formation in real-world systems could be far more complicated, further studies and interdisciplinary collaboration are still needed for simulation and experiments in the industry and other open systems.

pGpG-signaling regulates virulence and global transcriptomic targets in Erwinia amylovora

Cyclic-di-GMP (c-di-GMP) is a critical bacterial second messenger that enables the physiological phase transition in Erwinia amylovora, the phytopathogenic bacterium that causes fire blight disease. C-di-GMP generation is dependent on diguanylate cyclase enzymes while the degradation of c-di-GMP can occur through the action of phosphodiesterase (PDE) enzymes that contain an active EAL and/or a HD-GYP domain. The HD-GYP-type PDEs, which are absent in E. amylovora, can directly degrade c-di-GMP into two GMP molecules. PDEs that contain an active EAL domain, as found in all active PDEs in E. amylovora, degrade c-di-GMP into pGpG. The signaling function of pGpG is not fully understood in bacterial systems. A transcriptomic approach revealed that elevated levels of pGpG in E. amylovora impacted several genes involved in metabolic and regulatory functions including several type III secretion and extracellular appendage related genes. The heterologous overexpression of an EAL or HD-GYP-type PDE in different background E. amylovora strains with varying c-di-GMP levels revealed that in contrast to the generation of pGpG, the direct breakdown of c-di-GMP into GMP by the HD-GYP-type PDE led to an elevation in amylovoran production and biofilm formation despite a decrease in c-di-GMP levels. The breakdown of c-di-GMP into pGpG (as opposed to GTP) also led to a decrease in virulence in apple shoots. The expression of hrpS was significantly increased in response to the breakdown of c-di-GMP into pGpG. Further, our model suggests that a balance in the intracellular ratio of pGpG and c-di-GMP is essential for biofilm regulation in E. amylovora.

c-di-GMP signaling in Pseudomonas syringae complex

The Pseudomonas syringae Complex is one of the model phytopathogenic bacteria for exploring plant-microbe interactions, causing devastating plant diseases and economic losses worldwide. The ubiquitous second messenger bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) plays an important role in the 'lifestyle switch' from single motile cells to biofilm formation and modulates bacterial behavior, thus influencing virulence in Pseudomonas and other bacterial species. However, less is known about the role of c-di-GMP in the P. syringae complex, in which c-di-GMP levels are controlled by diguanylate cyclases (DGCs) and phosphodiesterases (PDEs), such as Chp8, BifA and WspR. Deletion the chemotaxis receptor PscA also influences c-di-GMP levels, suggesting a cross-talk between chemotaxis and c-di-GMP pathways. Another transcription factor, FleQ, plays a dual role (positive or negative) in regulating cellulose synthesis as a c-di-GMP effector, whereas the transcription factor AmrZ regulates local c-di-GMP levels by inhibiting the DGC enzyme AdcA and the PDE enzyme MorA. Our recent research demonstrated that an increase in the c-di-GMP concentration increased biofilm development, siderophore biosynthesis and oxidative stress tolerance, while it decreased the siderophore content, bacterial motility and type III secretion system activity in P. syringae complex. These findings show that c-di-GMP intricately controls virulence in P. syringae complex, indicating that adjusting c-di-GMP levels may be a valuable tactic for defending plants against pathogens. This review highlights recent research on metabolic enzymes, regulatory mechanisms and the phenotypic consequences of c-di-GMP signaling in the P. syringae.

Recent advances on the regulation of bacterial biofilm formation by herbal medicines

Biofilm formation is a fundamental part of life cycles of bacteria which affects various aspects of bacterial-host interactions including the development of drug resistance and chronic infections. In clinical settings, biofilm-related infections are becoming increasingly difficult to treat due to tolerance to antibiotics. Bacterial biofilm formation is regulated by different external and internal factors, among which quorum sensing (QS) signals and nucleotide-based second messengers play important roles. In recent years, different kinds of anti-biofilm agents have been discovered, among which are the Chinese herbal medicines (CHMs). CHMs or traditional Chinese medicines have long been utilized to combat various diseases around the world and many of them have the ability to inhibit, impair or decrease bacterial biofilm formation either through regulation of bacterial QS system or nucleotide-based second messengers. In this review, we describe the research progresses of different chemical classes of CHMs on the regulation of bacterial biofilm formation. Though the molecular mechanisms on the regulation of bacterial biofilm formation by CHMs have not been fully understood and there are still a lot of work that need to be performed, these studies contribute to the development of effective biofilm inhibitors and will provide a novel treatment strategy to control biofilm-related infections.

The Association between Biofilm Formation and Antimicrobial Resistance with Possible Ingenious Bio-Remedial Approaches

Biofilm has garnered a lot of interest due to concerns in various sectors such as public health, medicine, and the pharmaceutical industry. Biofilm-producing bacteria show a remarkable drug resistance capability, leading to an increase in morbidity and mortality. This results in enormous economic pressure on the healthcare sector. The development of biofilms is a complex phenomenon governed by multiple factors. Several attempts have been made to unravel the events of biofilm formation; and, such efforts have provided insights into the mechanisms to target for the therapy. Owing to the fact that the biofilm-state makes the bacterial pathogens significantly resistant to antibiotics, targeting pathogens within biofilm is indeed a lucrative prospect. The available drugs can be repurposed to eradicate the pathogen, and as a result, ease the antimicrobial treatment burden. Biofilm formers and their infections have also been found in plants, livestock, and humans. The advent of novel strategies such as bioinformatics tools in treating, as well as preventing, biofilm formation has gained a great deal of attention. Development of newfangled anti-biofilm agents, such as silver nanoparticles, may be accomplished through omics approaches such as transcriptomics, metabolomics, and proteomics. Nanoparticles’ anti-biofilm properties could help to reduce antimicrobial resistance (AMR). This approach may also be integrated for a better understanding of biofilm biology, guided by mechanistic understanding, virtual screening, and machine learning in silico techniques for discovering small molecules in order to inhibit key biofilm regulators. This stimulated research is a rapidly growing field for applicable control measures to prevent biofilm formation. Therefore, the current article discusses the current understanding of biofilm formation, antibiotic resistance mechanisms in bacterial biofilm, and the novel therapeutic strategies to combat biofilm-mediated infections.

Biofilm control by interfering with c-di-GMP metabolism and signaling

Biofilm formation and biofilm-induced biodeterioration of surfaces have deeply affected the life of our community. Cyclic dimeric guanosine monophosphate (c-di-GMP) is a small nucleic acid signal molecule in bacteria, which functions as a second messenger mediating a wide range of bacterial processes, such as cell motility, biofilm formation, virulence expression, and cell cycle progression. C-di-GMP regulated phenotypes are triggered by a variety of determinants, such as metabolic cues and stress factors that affect c-di-GMP synthesis, the transduction and conduction of signals by specific effectors, and their actions on terminal targets. Therefore, understanding of the regulatory mechanisms of c-di-GMP would greatly benefit the control of the relevant bacterial processes, particularly for the development of anti-biofilm technologies. Here, we discuss the regulatory determinants of c-di-GMP signaling, identify the corresponding chemical inhibitors as anti-biofilm agents, and shed light on further perspectives in the metabolic regulation of c-di-GMP through chemical and biological approaches. This Review will advance the development of anti-biofilm policies applied in the industries of medicine, environment and engineering.

Controlling Biofilm Development Through Cyclic di-GMP Signaling

The cyclic di-GMP (c-di-GMP) second messenger represents a signaling system that regulates many bacterial behaviors and is of key importance for driving the lifestyle switch between motile loner cells and biofilm formers. This review provides an up-to-date summary of c-di-GMP pathways connected to biofilm formation by the opportunistic pathogen P. aeruginosa. Emphasis will be on the timing of c-di-GMP production over the course of biofilm formation, to highlight non-uniform and hierarchical increases in c-di-GMP levels, as well as biofilm growth conditions that do not conform with our current model of c-di-GMP.

Identification of small molecules that interfere with c-di-GMP signaling and induce dispersal of Pseudomonas aeruginosa biofilms

Microbial biofilms are involved in a number of infections that cannot be cured, as microbes in biofilms resist host immune defenses and antibiotic therapies. With no strict biofilm-antibiotic in the current pipelines, there is an unmet need for drug candidates that enable the current antibiotics to eradicate bacteria in biofilms. We used high-throughput screening to identify chemical compounds that reduce the intracellular c-di-GMP content in Pseudomonas aeruginosa. This led to the identification of a small molecule that efficiently depletes P. aeruginosa for c-di-GMP, inhibits biofilm formation, and disperses established biofilm. A combination of our lead compound with standard of care antibiotics showed improved eradication of an implant-associated infection established in mice. Genetic analyses provided evidence that the anti-biofilm compound stimulates the activity of the c-di-GMP phosphodiesterase BifA in P. aeruginosa. Our work constitutes a proof of concept for c-di-GMP phosphodiesterase-activating drugs administered in combination with antibiotics as a viable treatment strategy for otherwise recalcitrant infections.

The oralome and its dysbiosis: New insights into oral microbiome-host interactions

The oralome is the summary of the dynamic interactions orchestrated between the ecological community of oral microorganisms (comprised of up to approximately 1000 species of bacteria, fungi, viruses, archaea and protozoa - the oral microbiome) that live in the oral cavity and the host. These microorganisms form a complex ecosystem that thrive in the dynamic oral environment in a symbiotic relationship with the human host. However, the microbial composition is significantly affected by interspecies and host-microbial interactions, which in turn, can impact the health and disease status of the host. In this review, we discuss the composition of the oralome and inter-species and host-microbial interactions that take place in the oral cavity and examine how these interactions change from healthy (eubiotic) to disease (dysbiotic) states. We further discuss the dysbiotic signatures associated with periodontitis and caries and their sequalae, (e.g., tooth/bone loss and pulpitis), and the systemic diseases associated with these oral diseases, such as infective endocarditis, atherosclerosis, diabetes, Alzheimer's disease and head and neck/oral cancer. We then discuss current computational techniques to assess dysbiotic oral microbiome changes. Lastly, we discuss current and novel techniques for modulation of the dysbiotic oral microbiome that may help in disease prevention and treatment, including standard hygiene methods, prebiotics, probiotics, use of nano-sized drug delivery systems (nano-DDS), extracellular polymeric matrix (EPM) disruption, and host response modulators.

Regulatory Networks of the T4SS Control: From Host Cell Sensing to the Biogenesis and the Activity during the Infection

Delivery of effectors, DNA or proteins, that hijack host cell processes to the benefit of bacteria is a mechanism widely used by bacterial pathogens. It is achieved by complex effector injection devices, the secretion systems, among which Type 4 Secretion Systems (T4SSs) play a key role in bacterial virulence of numerous animal and plant pathogens. Considerable progress has recently been made in the structure-function analyses of T4SSs. Nevertheless, the signals and processes that trigger machine assembly and activity during infection, as well as those involved in substrate recognition and transfer, are complex and still poorly understood. In this review, we aim at summarizing the last updates of the knowledge on signaling pathways that regulate the biogenesis and the activity of T4SSs in important bacterial pathogens.

Identification of a Mycobacterium tuberculosis Cyclic Dinucleotide Phosphodiesterase Inhibitor

Immune cells sense bacteria-derived c-di-GMP and c-di-AMP as well as host-derived cGAMP, which is synthesized by cGAS upon binding to the pathogen's DNA, to mount an immunological response (cytokine production) via the STING-TBK1 pathway. Successful pathogens, such as Mycobacterium tuberculosis and group B streptococcus, harbor phosphodiesterases (PDEs) that can cleave bacterial c-di-AMP as well as host-derived cGAMP to blunt the host's response to infection. Selective inhibitors of bacterial cyclic dinucleotide (CDN) PDEs are needed as tool compounds to study the role(s) of CDN PDEs during infection and they could also become bona fide antivirulence compounds, but there is a paucity of such compounds. Using a high-throughput assay, we identified six inhibitors of MTB CDN PDE (CdnP). The most potent inhibitor, C82 with an IC₅₀ of ∼18 μM, did not inhibit the enzymatic activities of three other bacterial CDN PDEs (Yybt, RocR, and GBS-CdnP), a viral CDN PDE (poxin) or mammalian ENPP1.

Adaptive behaviors of planktonic Pseudomonas aeruginosa in response to the surface-deposited dead siblings

In this study, the 3D motion behaviors and the underlying adaptation mechanism of planktonic Pseudomonas aeruginosa (PAO1) in response to the deposited dead siblings nearby were explored. Utilizing a real-time 3D tracking technique, digital holographic microscopy (DHM), we demonstrate that planktonic cells near the surface covered with dead siblings have a lower density and a reduced 3D velocity compared with those upon viable ones. As a sign of chemosensory responses, bacteria swimming near the dead siblings exhibit increase in frequency of the 'flick' motion. Transcriptomic analysis by RNA-seq reveals an upregulated expression of dgcM and dgcE inhibited the movement of PAO1, accompanied by increased transcriptional levels of the virulence factor-related genes hcp1, clpV1, and vgrG1. Moreover, the decrease in l-glutamate and the increase in succinic acid in the metabolites of the dead bacteria layer promote the dispersion of planktonic bacteria. As a result, the dead siblings on a surface inhibit the bacterial accumulation and activate the adaptive defensive responses of planktonic PAO1 in the vicinity.

Biofilm matrix disrupts nematode motility and predatory behavior

In nature, bacteria form biofilms by producing exopolymeric matrix that encases its entire community. While it is widely known that biofilm matrix can prevent bacterivore predation and contain virulence factors for killing predators, it is unclear if they can alter predator motility. Here, we report a novel "quagmire" phenotype, where Pseudomonas aeruginosa biofilms could retard the motility of bacterivorous nematode Caenorhabditis elegans via the production of a specific exopolysaccharide, Psl. Psl could reduce the roaming ability of C. elegans by impeding the slithering velocity of C. elegans. Furthermore, the presence of Psl in biofilms could entrap C. elegans within the matrix, with dire consequences to the nematode. After being trapped in biofilms, C. elegans could neither escape effectively from aversive stimuli (noxious blue light), nor leave easily to graze on susceptible biofilm areas. Hence, this reduced the ability of C. elegans to roam and predate on biofilms. Taken together, our work reveals a new function of motility interference by specific biofilm matrix components, and emphasizes its importance in predator-prey interactions.

Enzymatic Syntheses and Applications of Fluorescent Cyclic Dinucleotides

Bacterial cyclic dinucleotides (CDNs) play important roles in regulating biofilm formation, motility and virulence. In eukaryotic cells, theses bacterial CDNs are recognized as pathogen-associated molecular patterns (PAMPs) and trigger an innate immune response. We report the photophysical analyses of a novel group of enzymatically synthesized emissive CDN analogues comprised of two families of isomorphic ribonucleotides. The highly favorable photophysical features of the CDN analogues, when compared to their non-emissive natural counterparts, are used to monitor in real time the dinucleotide cyclase-mediated synthesis and phosphodiesterase (PDE)-mediated hydrolysis of homodimeric and mixed CDNs, providing effective means to probe the activities of two classes of bacterial enzymes and insight into their biomolecular recognition and catalytic features.

Multiple Roles of c-di-GMP Signaling in Bacterial Pathogenesis

The intracellular signaling molecule cyclic di-GMP (c-di-GMP) regulates the lifestyle of bacteria and controls many key functions and mechanisms. In the case of bacterial pathogens, a wide variety of virulence lifestyle factors have been shown to be regulated by c-di-GMP. Evidence of the importance of this molecule for bacterial pathogenesis has become so great that new antimicrobial agents are tested for their capacity of targeting c-di-GMP signaling. This review summarizes the current knowledge on this topic and reveals its application for the development of new antivirulence intervention strategies.

Inhibitors of Bacterial Swarming Behavior

Bacteria can migrate in groups of flagella-driven cells over semisolid surfaces. This coordinated form of motility is called swarming behavior. Swarming is associated with enhanced virulence and antibiotic resistance of various human pathogens and may be considered as favorable adaptation to the diverse challenges that microbes face in rapidly changing environments. Consequently, the differentiation of motile swarmer cells is tightly regulated and involves multi-layered signaling networks. Controlling swarming behavior is of major interest for the development of novel anti-infective strategies. In addition, compounds that block swarming represent important tools for more detailed insights into the molecular mechanisms of the coordination of bacterial population behavior. Over the past decades, there has been major progress in the discovery of small-molecule modulators and mechanisms that allow selective inhibition of swarming behavior. Herein, an overview of the achievements in the field and future directions and challenges will be presented.

Small Molecule Anti-biofilm Agents Developed on the Basis of Mechanistic Understanding of Biofilm Formation

Microbial biofilms are the cause of persistent infections associated with various medical implants and distinct body sites such as the urinary tract, lungs, and wounds. Compared with their free living counterparts, bacteria in biofilms display a highly increased resistance to immune system activities and antibiotic treatment. Therefore, biofilm infections are difficult or impossible to treat with our current armory of antibiotics. The challenges associated with biofilm infections have urged researchers to pursue a better understanding of the molecular mechanisms that are involved in the formation and dispersal of biofilms, and this has led to the identification of several steps that could be targeted in order to eradicate these challenging infections. Here we describe mechanisms that are involved in the regulation of biofilm development in Pseudomonas aeruginosa, Escherichia coli, and Acinetobacter baumannii, and provide examples of chemical compounds that have been developed to specifically inhibit these processes. These compounds include (i) pilicides and curlicides which inhibit the initial steps of biofilm formation by E. coli; (ii) compounds that interfere with c-di-GMP signaling in P. aeruginosa and E. coli; and (iii) compounds that inhibit quorum-sensing in P. aeruginosa and A. baumannii. In cases where compound series have a defined molecular target, we focus on elucidating structure activity relationship (SAR) trends within the particular compound series.

Context-Specific Requirement of Forty-Four Two-Component Loci in Pseudomonas aeruginosa Swarming

Swarming in Pseudomonas aeruginosa is a coordinated movement of bacteria over semisolid surfaces (0.5%-0.7% agar). On soft agar, P. aeruginosa exhibits a dendritic swarm pattern, with multiple levels of branching. However, the swarm patterns typically vary depending upon the experimental design. In the present study, we show that the pattern characteristics of P. aeruginosa swarm are highly environment dependent. We define several quantifiable, macroscale features of the swarm to study the plasticity of the swarm, observed across different nutrient formulations. Furthermore, through a targeted screen of 113 two-component system (TCS) loci of the P. aeruginosa strain PA14, we show that forty-four TCS genes regulate swarming in PA14 in a contextual fashion. However, only four TCS genes-fleR, fleS, gacS, and PA14_59770-were found essential for swarming. Notably, many swarming-defective TCS mutants were found highly efficient in biofilm formation, indicating opposing roles for many TCS loci.

The State of the Union Is Strong: a Review of ASM's 6th Conference on Cell-Cell Communication in Bacteria

The 6th American Society for Microbiology Conference on Cell-Cell Communication in Bacteria convened from 16 to 19 October 2017 in Athens, GA. In this minireview, we highlight some of the research presented at that meeting that addresses central questions emerging in the field, including the following questions. How are cell-cell communication circuits designed to generate responses? Where are bacteria communicating? Finally, why are bacteria engaging in such behaviors?

Disarming the virulence arsenal of Pseudomonas aeruginosa by blocking two-component system signaling

Pseudomonas aeruginosa infections have reached a “critical” threat status making novel therapeutic approaches required.

Pseudomonas aeruginosa infections have reached a “critical” threat status making novel therapeutic approaches required. Inhibiting key signaling enzymes known as the histidine kinases (HKs), which are heavily involved with its pathogenicity, has been postulated to be an effective new strategy for treatment. Herein, we demonstrate the potential of this approach with benzothiazole-based HK inhibitors that perturb multiple virulence pathways in the burn wound P. aeruginosa isolate, PA14. Specifically, our compounds significantly reduce the level of toxic metabolites generated by this organism that are involved in quorum-sensing and redox-balancing mechanisms. They also decrease the ability of this organism to swarm and attach to surfaces, likely by influencing their motility appendages. Quantitative transcription analysis of inhibitor-treated cultures showed substantial perturbations to multiple pathways including expression of response regulator GacA, the cognate partner of the “super regulator” of virulence, HK GacS, as well as flagella and pili formation. These promising results establish that blocking of bacterial signaling in P. aeruginosa has dramatic consequences on virulence behaviours, especially in the context of surface-associated infections.

Fluorescent 2-Aminopurine c-di-GMP and GpG Analogs as PDE Probes

c-di-GMP is widely recognized as an important ubiquitous signaling molecule in bacteria. c-di-GMP phosphodiesterases (PDEs) regulate the intracellular concentration of c-di-GMP and some could be potential drug targets. Here, we describe a class of dinucleotide probes suitable for monitoring the enzymatic activities of c-di-GMP PDEs in real time. Such probes contain fluorescent nucleobases and can be readily cleaved by PDEs, resulting in a change in fluorescence. Fluorescent cyclic and linear dinucleotide probes could be used in diverse applications, such as confirming the activity of an expressed PDE or oligoribonuclease (Orns) or identifying inhibitors of PDEs or Orns using high-throughput screening formats.

Targeting c-di-GMP Signaling, Biofilm Formation, and Bacterial Motility with Small Molecules

Bacteria possess several signaling molecules that regulate distinct phenotypes. Cyclic di-GMP (c-di-GMP) has emerged as a ubiquitous second messenger that regulates bacterial virulence, cell cycle, motility, and biofilm formation. The link between c-di-GMP signaling and biofilm formation affords novel strategies for treatment of biofilm-associated infections, which is a major public health problem. The complex c-di-GMP signaling pathway creates a hurdle in the development of small molecule modulators. Nonetheless, some progress has been made in this regard and inhibitors of c-di-GMP metabolizing enzymes that affect biofilm formation and motility have been documented. Herein we discuss the components of c-di-GMP signaling, their correlation with biofilm formation as well as motility and reported small molecule inhibitors of c-di-GMP signaling.

The consistent differential expression of genetic pathways following exposure of an industrial Pseudomonas aeruginosa strain to preservatives and a laundry detergent formulation

Pseudomonas aeruginosa is a common contaminant associated with product recalls in the home and personal care industry. Preservation systems are used to prevent spoilage and protect consumers, but greater knowledge is needed of preservative resistance mechanisms used by P. aeruginosa contaminants. We aimed to identify genetic pathways associated with preservative exposure by using an industrial P. aeruginosa strain and implementing RNA-Seq to understand gene expression changes in response to industry relevant conditions. The consistent differential expression of five genetic pathways during exposure to multiple industrial growth conditions associated with benzisothiazolone (BIT) and phenoxyethanol (POE) preservatives, and a laundry detergent (LD) formulation, was observed. A MexPQ-OpmE Resistance Nodulation Division efflux pump system was commonly upregulated in response to POE, a combination of BIT and POE, and LD together with BIT. In response to all industry conditions, a putative sialic acid transporter and isoprenoid biosynthesis gnyRDBHAL operon demonstrated consistent upregulation. Two operons phnBA and pqsEDCBA involved in Pseudomonas quinolone signaling production and quorum-sensing were also consistently downregulated during exposure to all the industry conditions. The ability to identify consistently differentially expressed genetic pathways in P. aeruginosa can inform the development of future targeted preservation systems that maintain product safety and minimise resistance development.

Bacterial Biofilm Control by Perturbation of Bacterial Signaling Processes

The development of effective strategies to combat biofilm infections by means of either mechanical or chemical approaches could dramatically change today’s treatment procedures for the benefit of thousands of patients. Remarkably, considering the increased focus on biofilms in general, there has still not been invented and/or developed any simple, efficient and reliable methods with which to “chemically” eradicate biofilm infections. This underlines the resilience of infective agents present as biofilms and it further emphasizes the insufficiency of today’s approaches used to combat chronic infections. A potential method for biofilm dismantling is chemical interception of regulatory processes that are specifically involved in the biofilm mode of life. In particular, bacterial cell to cell signaling called “Quorum Sensing” together with intracellular signaling by bis-(3′-5′)-cyclic-dimeric guanosine monophosphate (cyclic-di-GMP) have gained a lot of attention over the last two decades. More recently, regulatory processes governed by two component regulatory systems and small non-coding RNAs have been increasingly investigated. Here, we review novel findings and potentials of using small molecules to target and modulate these regulatory processes in the bacterium Pseudomonas aeruginosa to decrease its pathogenic potential.

Cyclic Dinucleotides in Oral Bacteria and in Oral Biofilms

Oral cavity acts as a reservoir of bacterial pathogens for systemic infections and several oral microorganisms have been linked to systemic diseases. Quorum sensing and cyclic dinucleotides, two "decision-making" signaling systems, communicate to regulate physiological process in bacteria. Discovery of cyclic dinucleotides has a long history, but the progress in our understanding of how cyclic dinucleotides regulate bacterial lifestyle is relatively new. Oral microorganisms form some of the most intricate biofilms, yet c-di-GMP, and c-di-AMP signaling have been rarely studied in oral biofilms. Recent studies demonstrated that, with the aid of bacterial messenger molecules and their analogs, it is possible to activate host innate and adaptive immune responses and epithelial integrity with a dose that is relevant to inhibit bacterial virulence mechanisms, such as fimbriae and exopolysaccharide production, biofilm formation, and host cell invasion. The aim of this perspective article is to present available information on cyclic dinucleotides in oral bacteria and in oral biofilms. Moreover, technologies that can be used to detect cyclic dinucleotides in oral biofilms are described. Finally, directions for future research are highlighted.

Hydroxybenzylidene-indolinones, c-di-AMP synthase inhibitors, have antibacterial and anti-biofilm activities and also re-sensitize resistant bacteria to methicillin and vancomycin

Hydroxybenzylidene-indolinones, newly identified inhibitors of c-di-AMP synthases, inhibit biofilm formation, Gram-positive bacterial growth and sensitize resistant bacteria to methicillin and vancomycin.

Fluorescent analogs of cyclic and linear dinucleotides as phosphodiesterase and oligoribonuclease activity probes

2-Aminopurine or etheno adenosine cyclic dinucleotide probes can report the activity of cyclic dinucleotide PDEs or oligoribonucleases.