Quorum sensing and bacterial social interactions in biofilms. Sensors (Basel). 2012;12:2519-2538. [PMID: 22736963 PMCID: PMC3376616 DOI: 10.3390/s120302519]

Harnessing the Potential of Killers and Altruists within the Microbial Community: A Possible Alternative to Antibiotic Therapy?

In the context of a post-antibiotic era, the phenomenon of microbial allolysis, which is defined as the partial killing of bacterial population induced by other cells of the same species, may take on greater significance. This phenomenon was revealed in some bacterial species such as Streptococcus pneumoniae and Bacillus subtilis, and has been suspected to occur in some other species or genera, such as enterococci. The mechanisms of this phenomenon, as well as its role in the life of microbial populations still form part of ongoing research. Herein, we describe recent developments in allolysis in the context of its practical benefits as a form of cell death that may give rise to developing new strategies for manipulating the life and death of bacterial communities. We highlight how such findings may be viewed with importance and potential within the fields of medicine, biotechnology, and pharmacology.

Exploitation of plant extracts and phytochemicals against resistant Salmonella spp. in biofilms

Salmonella is one of the most frequent causes of foodborne outbreaks throughout the world. In the last years, the resistance of this and other pathogenic bacteria to antimicrobials has become a prime concern towards their successful control. In addition, the tolerance and virulence of pathogenic bacteria, such as Salmonella, are commonly related to their ability to form biofilms, which are sessile structures encountered on various surfaces and whose development is considered as a universal stress response mechanism. Indeed, the ability of Salmonella to form a biofilm seems to significantly contribute to its persistence in food production areas and clinical settings. Plant extracts and phytochemicals appear as promising sources of novel antimicrobials due to their cost-effectiveness, eco-friendliness, great structural diversity, and lower possibility of antimicrobial resistance development in comparison to synthetic chemicals. Research on these agents mainly attributes their antimicrobial activity to a diverse array of secondary metabolites. Bacterial cells are usually killed by the rupture of their cell envelope and in parallel the disruption of their energy metabolism when treated with such molecules, while their use at sub-inhibitory concentrations may also disrupt intracellular communication. The purpose of this article is to review the current available knowledge related to antimicrobial resistance of Salmonella in biofilms, together with the antibiofilm properties of plant extracts and phytochemicals against these detrimental bacteria towards their future application to control these in food production and clinical environments.

Antimicrobial, Antioxidant, and Immunomodulatory Properties of Essential Oils: A Systematic Review

Essential oils (EOs) are a mixture of natural, volatile, and aromatic compounds obtained from plants. In recent years, several studies have shown that some of their benefits can be attributed to their antimicrobial, antioxidant, anti-inflammatory, and also immunomodulatory properties. Therefore, EOs have been proposed as a natural alternative to antibiotics or for use in combination with antibiotics against multidrug-resistant bacteria in animal feed and food preservation. Most of the results come from in vitro and in vivo studies; however, very little is known about their use in clinical studies. A systematic and comprehensive literature search was conducted in PubMed, Embase®, and Scopus from December 2014 to April 2019 using different combinations of the following keywords: essential oils, volatile oils, antimicrobial, antioxidant, immunomodulation, and microbiota. Some EOs have demonstrated their efficacy against several foodborne pathogens in vitro and model food systems; namely, the inhibition of S. aureus, V. cholerae, and C. albicans has been observed. EOs have shown remarkable antioxidant activities when used at a dose range of 0.01 to 10 mg/mL in cell models, which can be attributed to their richness in phenolic compounds. Moreover, selected EOs exhibit immunomodulatory activities that have been mainly attributed to their ability to modify the secretion of cytokines.

Infected chronic ischemic wound topically treated with a multi-strain probiotic formulation: a novel tailored treatment strategy

Background

A wide debate is ongoing regarding the role of cutaneous dysbiosis in the pathogenesis and evolution of difficult-to-treat chronic wounds. Nowadays, probiotic treatment considered as an useful tool to counteract dysbiosis but the evidence in regard to their therapeutic use in the setting of difficult-to-treat cutaneous ulcers is still poor.

Aim: clinical report

An 83-year-old woman suffering a critical limb ischemia and an infected difficult-to-treat ulcerated cutaneous lesion of the right leg, was complementary treated with local application of a mixture of probiotic bacteria.

Methods

Microbiological and metabolomic analysis were conducted on wound swabs obtained before and after bacteriotherapy.

Results

During the treatment course, a progressive healing of the lesion was observed with microbiological resolution of the polymicrobial infection of the wound. Metabolomic analysis showed a significant difference in the local concentration of propionate, 2-hydroxyisovalerate, 2-oxoisocaproate, 2,3-butanediol, putrescine, thymine, and trimethylamine before and after bacteriotherapy.

Conclusion

The microbiological and metabolomic results seem to confirm the usefulness of complementary probiotic treatment in difficult-to-treat infected wounds. Further investigations are needed to confirm these preliminary findings.

Pyrosequencing of the subgingival microbiome in peri-implantitis after non-surgical mechanical debridement therapy

BACKGROUND AND OBJECTIVES

Peri-implantitis remains a challenge for dental implant therapy, and the prognosis of non-surgical therapy for peri-implantitis is unsatisfactory. In order to reveal the impact of non-surgical mechanical debridement therapy on microbial communities, we investigated the subgingival microbial communities of healthy implants and implants with peri-implantitis, both before and after the therapy.

MATERIAL AND METHODS

Subgingival plaques were collected from patients with healthy dental implants (HC; n = 10) and from patients with peri-implantitis (n = 13) before and after non-surgical mechanical debridement therapy. The treatment was conducted using curettes for submucosal debridement followed by irrigation with 0.2% (w/v) chlorhexidine, with re-examination 1 month later. 16S rRNA pyrosequencing was used to analyze the subgingival microbiome, and co-occurrence networks were adopted to explore the interactions between pathogens in the microbial communities.

RESULTS

A total of 506 955 high-quality reads were generated, and 2222 operational taxonomic units were finally detected using a 97% similarity cutoff, with a mean of 249 ± 69 per sample. The peri-implantitis sites harbored similar microbial communities before and after the treatment, as demonstrated by the microbial diversity, relative abundance, and prevalence of bacteria. Most importantly, the microbial community structures were stable before and after non-surgical therapy based on the microbial diversity and bacterial composition, as well as the interactions between key pathogens, including Enterobacteriaceae, Selenomonas sputigena, Parvimonas, Eubacterium infirmum, Campylobacter gracilis, Tannerella forsythia, and Fusobacterium, which were measured using a co-occurrence network analysis. Periodontal pathogens were also detected in subgingival plaque after the treatment. Distinct microbial communities were found between the healthy and peri-implantitis sites.

CONCLUSION

Our results demonstrate that non-surgical mechanical debridement therapy did not significantly affect the subgingival microbial communities in peri-implantitis, and the stable microbial networks created via interactions among pathogens may be responsible for the poor prognosis of peri-implantitis treatment.

Natural Microbial Communities Can Be Manipulated by Artificially Constructed Biofilms

Biofouling proceeds in successive steps where the primary colonizers affect the phylogenetic and functional structure of a future microbial consortium. Using microbiologically influenced corrosion (MIC) as a study case, a novel approach for material surface protection is described, which does not prevent biofouling, but rather shapes the process of natural biofilm development to exclude MIC-related microorganisms. This approach interferes with the early steps of natural biofilm formation affecting how the community is finally developed. It is based on a multilayer artificial biofilm, composed of electrostatically modified bacterial cells, producing antimicrobial compounds, extracellular antimicrobial polyelectrolyte matrix, and a water-proof rubber elastomer barrier. The artificial biofilm is constructed layer-by-layer (LBL) by manipulating the electrostatic interactions between microbial cells and material surfaces. Field testing on standard steel coupons exposed in the sea for more than 30 days followed by laboratory analyses using molecular-biology tools demonstrate that the preapplied artificial biofilm affects the phylogenetic structure of the developing natural biofilm, reducing phylogenetic diversity and excluding MIC-related bacteria. This sustainable solution for material protection showcases the usefulness of artificially guiding microbial evolutionary processes via the electrostatic modification and controlled delivery of bacterial cells and extracellular matrix to the exposed material surfaces.

Quorum sensing in food spoilage and natural-based strategies for its inhibition

Food can harbor a variety of microorganisms including spoilage and pathogenic bacteria. Many bacterial processes, including production of degrading enzymes, virulence factors, and biofilm formation are known to depend on cell density through a process called quorum sensing (QS), in which cells communicate by synthesizing, detecting and reacting to small diffusible signaling molecules - autoinducers (AI). The disruption of QS could decisively contribute to control the expression of many harmful bacterial phenotypes. Several quorum sensing inhibitors (QSI) have been extensively studied, being many of them of natural origin. This review provides an analysis on the role of QS in food spoilage and biofilm formation within the food industry. QSI from natural sources are also reviewed towards their putative future applications to prolong shelf life of food products and decrease foodborne pathogenicity.

Diketopiperazines Synthesis Gene in Shewanella baltica and Roles of Diketopiperazines and Resveratrol in Quorum Sensing

The synthesis pathways of quorum sensing (QS) signal molecules and the mechanism of action of quorum sensing inhibitors (QSIs) have gained considerable attention as research topics in the field of food preservation. Here, Shewanella baltica was detected as the specific spoilage organism in large yellow croaker during 4 °C storage, and it produced the QS signal molecules autoinducer-2 (AI-2) and diketopiperazines (DKPs). Then, a cyclodipeptide synthase (CDPS) homologous gene, sb1370, was screened, and knockout and rescue results revealed that this gene was involved in DKP synthesis but not in AI-2 synthesis, and it also played an important role in QS. Furthermore, fish fillets and mutant strains were treated with resveratrol, and the results suggested that resveratrol was an ideal QSI for inhibition of DKPs production via the sb1370 gene and reduced QS in S. baltica, thus delaying the process of fish spoilage during chilling storage.

Role of bacterial efflux pumps in biofilm formation

Efflux pumps are widely implicated in antibiotic resistance because they can extrude the majority of clinically relevant antibiotics from within cells to the extracellular environment. However, there is increasing evidence from many studies to suggest that the pumps also play a role in biofilm formation. These studies have involved investigating the effects of efflux pump gene mutagenesis and efflux pump inhibitors on biofilm formation, and measuring the levels of efflux pump gene expression in biofilms. In particular, several key pathogenic species associated with increasing multidrug resistance, such as Acinetobacter baumannii, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus, have been investigated, whilst other studies have focused on Salmonella enterica serovar Typhimurium as a model organism and problematic pathogen. Studies have shown that efflux pumps, including AcrAB-TolC of E. coli, MexAB-OprM of P. aeruginosa, AdeFGH of A. baumannii and AcrD of S. enterica, play important roles in biofilm formation. The substrates for such pumps, and whether changes in their efflux activity affect biofilm formation directly or indirectly, remain to be determined. By understanding the roles that efflux pumps play in biofilm formation, novel therapeutic strategies can be developed to inhibit their function, to help disrupt biofilms and improve the treatment of infections. This review will discuss and evaluate the evidence for the roles of efflux pumps in biofilm formation and the potential approaches to overcome the increasing problem of biofilm-based infections.

Novel Probiotic Mechanisms of the Oral Bacterium Streptococcus sp. A12 as Explored with Functional Genomics

Health-associated biofilms in the oral cavity are composed of a diverse group of microbial species that can foster an environment that is less favorable for the outgrowth of dental caries pathogens, like Streptococcus mutans A novel oral bacterium, designated Streptococcus A12, was previously isolated from supragingival dental plaque of a caries-free individual and was shown to interfere potently with the growth and virulence properties of S. mutans In this study, we applied functional genomics to begin to identify molecular mechanisms used by A12 to antagonize, and to resist the antagonistic factors of, S. mutans Using bioinformatics, genes that could encode factors that enhance the ability of A12 to compete with S. mutans were identified. Selected genes, designated potential competitive factors (pcf), were deleted. Certain mutant derivatives showed a reduced capacity to compete with S. mutans compared to that of the parental strain. The A12 pcfO mutant lost the ability to inhibit comX -inducing peptide (XIP) signaling by S. mutans, while mutants with changes in the pcfFEG locus were impaired in sensing of, and were more sensitive to, the lantibiotic nisin. Loss of PcfV, annotated as a colicin V biosynthetic protein, resulted in diminished antagonism of S. mutans Collectively, the data provide new insights into the complexities and variety of factors that affect biofilm ecology and virulence. Continued exploration of the genomic and physiological factors that distinguish commensals from truly beneficial members of the oral microbiota will lead to a better understanding of the microbiome and new approaches to promote oral health.IMPORTANCE Advances in defining the composition of health-associated biofilms have highlighted the important role of beneficial species in maintaining health. Comparatively little, however, has been done to address the genomic and physiological bases underlying the probiotic mechanisms of beneficial commensals. In this study, we explored the ability of a novel oral bacterial isolate, Streptococcus A12, to compete with the dental pathogen Streptococcus mutans using various gene products with diverse functions. A12 displayed enhanced competitiveness by (i) disrupting intercellular communication pathways of S. mutans, (ii) sensing and resisting antimicrobial peptides, and (iii) producing factors involved in the production of a putative antimicrobial compound. Research on the probiotic mechanisms employed by Streptococcus A12 is providing essential insights into how beneficial bacteria may help maintain oral health, which will aid in the development of biomarkers and therapeutics that can improve the practice of clinical dentistry.

Beyond nitrogen metabolism: nitric oxide, cyclic-di-GMP and bacterial biofilms

The nitrogen cycle pathways are responsible for the circulation of inorganic and organic N-containing molecules in nature. Among these pathways, those involving amino acids, N-oxides and in particular nitric oxide (NO) play strategic roles in the metabolism of microorganisms in natural environments and in host-pathogen interactions. Beyond their role in the N-cycle, amino acids and NO are also signalling molecules able to influence group behaviour in microorganisms and cell-cell communication in multicellular organisms, including humans. In this minireview, we summarise the role of these compounds in the homeostasis of the bacterial communities called biofilms, commonly found in environmental, industrial and medical settings. Biofilms are difficult to eradicate since they are highly resistant to antimicrobials and to the host immune system. We highlight the effect of amino acids such as glutamate, glutamine and arginine and of NO on the signalling pathways involved in the metabolism of 3',5'-cyclic diguanylic acid (c-di-GMP), a master regulator of motility, attachment and group behaviour in bacteria. The study of the metabolic routes involving these N-containing compounds represents an attractive topic to identify targets for biofilm control in both natural and medical settings.

Metaproteomics analysis of microbial diversity of human saliva and tongue dorsum in young healthy individuals

Background: The human oral microbiome influences initiation or progression of diseases like caries or periodontitis. Metaproteomics approaches enable the simultaneous investigation of microbial and host proteins and their interactions to improve understanding of oral diseases.

Objective: In this study, we provide a detailed metaproteomics perspective of the composition of salivary and tongue microbial communities of young healthy subjects.

Design: Stimulated saliva and tongue samples were collected from 24 healthy volunteers, subjected to shotgun nLC-MS/MS and analyzed by the Trans-Proteomic Pipeline and the Prophane tool.

Results: 3,969 bacterial and 1,857 human proteins could be identified from saliva and tongue, respectively. In total, 1,971 bacterial metaproteins and 1,154 human proteins were shared in both sample types. Twice the amount of bacterial metaproteins were uniquely identified for the tongue dorsum compared to saliva. Overall, 107 bacterial genera of seven phyla formed the microbiome. Comparative analysis identified significant functional differences between the microbial biofilm on the tongue and the microbiome of saliva.

Conclusion: Even if the microbial communities of saliva and tongue dorsum showed a strong similarity based on identified protein functions and deduced bacterial composition, certain specific characteristics were observed. Both microbiomes exhibit a great diversity with seven genera being most abundant.

Burst statistics in an early biofilm quorum sensing model: the role of spatial colony-growth heterogeneity

Quorum-sensing bacteria in a growing colony of cells send out signalling molecules (so-called “autoinducers”) and themselves sense the autoinducer concentration in their vicinity. Once—due to increased local cell density inside a “cluster” of the growing colony—the concentration of autoinducers exceeds a threshold value, cells in this clusters get “induced” into a communal, multi-cell biofilm-forming mode in a cluster-wide burst event. We analyse quantitatively the influence of spatial disorder, the local heterogeneity of the spatial distribution of cells in the colony, and additional physical parameters such as the autoinducer signal range on the induction dynamics of the cell colony. Spatial inhomogeneity with higher local cell concentrations in clusters leads to earlier but more localised induction events, while homogeneous distributions lead to comparatively delayed but more concerted induction of the cell colony, and, thus, a behaviour close to the mean-field dynamics. We quantify the induction dynamics with quantifiers such as the time series of induction events and burst sizes, the grouping into induction families, and the mean autoinducer concentration levels. Consequences for different scenarios of biofilm growth are discussed, providing possible cues for biofilm control in both health care and biotechnology.

Bioactive Brominated Oxindole Alkaloids from the Red Sea Sponge Callyspongia siphonella

In the present study, LC-HRESIMS-assisted dereplication along with bioactivity-guided isolation led to targeting two brominated oxindole alkaloids (compounds 1 and 2) which probably play a key role in the previously reported antibacterial, antibiofilm, and cytotoxicity of Callyspongia siphonella crude extracts. Both metabolites showed potent antibacterial activity against Gram-positive bacteria, Staphylococcus aureus (minimum inhibitory concentration (MIC) = 8 and 4 µg/mL) and Bacillus subtilis (MIC = 16 and 4 µg/mL), respectively. Furthermore, they displayed moderate biofilm inhibitory activity in Pseudomonasaeruginosa (49.32% and 41.76% inhibition, respectively), and moderate in vitro antitrypanosomal activity (13.47 and 10.27 µM, respectively). In addition, they revealed a strong cytotoxic effect toward different human cancer cell lines, supposedly through induction of necrosis. This study sheds light on the possible role of these metabolites (compounds 1 and 2) in keeping fouling organisms away from the sponge outer surface, and the possible applications of these defensive molecules in the development of new anti-infective agents.

Identification potential inhibitors against the Streptococcus quorum-sensing signal pathway

Streptococcal infections are common in human and antibiotics are frequently prescribed in clinical practice. However, infections caused by drug-resistant strains are particularly difficult to treat using common antibiotics. Hence, there is an urgent need for new antibiotics. Quorum sensing is a regulatory mechanism involving cell communication that is thought to play an important role in various bacterial infections, including those caused by Streptococcus. The ATP-binding cassette transporter ComA of Streptococcus is essential for quorum-sensing signal production. The inhibition of the ComA peptidase domain (ComA PEP) suppresses the quorum-sensing pathway and resulting changes in phenotype and/or behavior. Using virtual screening and molecular dynamics simulations, two promising candidate compounds, ZINC32918029 and ZINC6751571, were found. These compounds had similar binding modes and interactions to the experimentally determined reference inhibitor 6CH. However, a significantly stronger negative binding energy was achieved (-113.501 ± 15.312 KJ/mol and -103.153 ± 11.912 KJ/mol for ZINC32918029 and ZINC6751571, respectively). Molecular dynamics simulations also revealed that ZINC32918029 and ZINC6751571 had a strong affinity for ComA PEP. These results indicate that ZINC32918029 and ZINC6751571 are promising candidate inhibitors of the Streptococcus quorum-sensing pathway.Communicated by Ramaswamy H. Sarma.

Antibacterial Activities of Aliphatic Polyester Nanocomposites with Silver Nanoparticles and/or Graphene Oxide Sheets

Aliphatic polyesters such as poly(lactic acid) (PLA), polycaprolactone (PCL) and poly(lactic-co-glycolic) acid (PLGA) copolymers have been widely used as biomaterials for tissue engineering applications including: bone fixation devices, bone scaffolds, and wound dressings in orthopedics. However, biodegradable aliphatic polyesters are prone to bacterial infections due to the lack of antibacterial moieties in their macromolecular chains. In this respect, silver nanoparticles (AgNPs), graphene oxide (GO) sheets and AgNPs-GO hybrids can be used as reinforcing nanofillers for aliphatic polyesters in forming antimicrobial nanocomposites. However, polymeric matrix materials immobilize nanofillers to a large extent so that they cannot penetrate bacterial membrane into cytoplasm as in the case of colloidal nanoparticles or nanosheets. Accordingly, loaded GO sheets of aliphatic polyester nanocomposites have lost their antibacterial functions such as nanoknife cutting, blanket wrapping and membrane phospholipid extraction. In contrast, AgNPs fillers of polyester nanocomposites can release silver ions for destroying bacterial cells. Thus, AgNPs fillers are more effective than loaded GO sheets of polyester nanocomposiites in inhibiting bacterial infections. Aliphatic polyester nanocomposites with AgNPs and AgNPs-GO fillers are effective to kill multi-drug resistant bacteria that cause medical device-related infections.

Purification and study of anti-cancer effects of Serratia marcescens serralysin

BACKGROUND AND OBJECTIVES

Serralysin is an extracellular metalloprotease from Serratia marcescens which has been the subject of extensive biological investigations. The goal of this study was to extract and purify serralysin from S. marcescens and to investigate its cytotoxic activity on the colorectal cancer cell line.

MATERIALS AND METHODS

The presence of the serralysin gene was confirmed using PCR. The supernatant of bacterial culture was collected and precipitated using ammonium sulfate. The precipitated protein was dialyzed and subjected to ion exchange chromatography for further purification. Casein assay and skim milk assay was used to confirm the enzymatic activity. SDS-PAGE was used to visualize the presence of serralysin. Metalloprotease inhibition activity was performed using 50 mM EDTA. Cytotoxic activity of serralysin was assessed on MTT assay.

RESULTS

The PCR product corresponding to serralysin was estimated to be approximately 1500 bp. A transparent zone around the bacterial colonies on skim milk agar and casein digestion confirmed the proteolytic activity of serralysin. A 52 kDa band in SDS-PAGE corresponding to serralysin was observed before and after purification processes. MTT assay showed IC50 values 24.78 μg/ml and 19.16 μg/ml after 24 h and 48 h exposure of Caco-2 cells to serralysin, respectively.

CONCLUSION

Our results showed that native serralysin has anticancer potential and may be a candidate for further pharmaceutical research and development. Further in vivo and in vitro mechanistic studies are suggested to confirm the biological activities.

Medicinal Plant Compounds for Combating the Multi-drug Resistant Pathogenic Bacteria: A Review

BACKGROUND

Globally, people utilize plants as the main source of remedy to heal various ailments. Medicinal plants have been utilized to treat ailments since the invention of modern scientific systems of medicine. The common remedy of infectious diseases mainly depends on the inhibition capacity of compounds or killing potential. The issue may give a clue for the development of a novel antimicrobial agent.

METHODS

Currently, microorganisms which are resistant towards antibiotics are probably a matter of serious concern for the overall well-being of health. At the moment, new therapeutic targets aside from the microorganism wall-based activities are in progress. For instance, the autoinducer molecules produced by the quorum sensing system are used to control antibiotic resistance and biofilm formation.

RESULTS

This therapeutic target is well-studied worldwide, however, the scientific data are not updated and only current studies started to gain insight into its perspective as a target to struggle against infectious diseases. Microbial resistance against antimicrobial compounds is a topic of serious concern in recent time.

CONCLUSION

Hence, this paper aims to confer a current overview of the novel compounds, quorum sensing, quorum quenching, biofilm formation in the development of antibiotic resistance and an update on their importance as a potential target for natural substances.

Clostridioides difficile LuxS mediates inter-bacterial interactions within biofilms

The anaerobic gut pathogen, Clostridioides difficile, forms adherent biofilms that may play an important role in recurrent C. difficile infections. The mechanisms underlying C. difficile community formation and inter-bacterial interactions are nevertheless poorly understood. C. difficile produces AI-2, a quorum sensing molecule that modulates biofilm formation across many bacterial species. We found that a strain defective in LuxS, the enzyme that mediates AI-2 production, is defective in biofilm development in vitro. Transcriptomic analyses of biofilms formed by wild type (WT) and luxS mutant (luxS) strains revealed a downregulation of prophage loci in the luxS mutant biofilms compared to the WT. Detection of phages and eDNA within biofilms may suggest that DNA release by phage-mediated cell lysis contributes to C. difficile biofilm formation. In order to understand if LuxS mediates C. difficile crosstalk with other gut species, C. difficile interactions with a common gut bacterium, Bacteroides fragilis, were studied. We demonstrate that C. difficile growth is significantly reduced when co-cultured with B. fragilis in mixed biofilms. Interestingly, the absence of C. difficile LuxS alleviates the B. fragilis-mediated growth inhibition. Dual species RNA-sequencing analyses from single and mixed biofilms revealed differential modulation of distinct metabolic pathways for C. difficile WT, luxS and B. fragilis upon co-culture, indicating that AI-2 may be involved in induction of selective metabolic responses in B. fragilis. Overall, our data suggest that C. difficile LuxS/AI-2 utilises different mechanisms to mediate formation of single and mixed species communities.

The new buzz: Investigating the antimicrobial interactions between bioactive compounds found in South African propolis

ETHNOPHARMACOLOGICAL RELEVANCE

Propolis, a resinous substance produced by the Apis mellifera bee, contains a number of flavonoids sourced from plants found in the surrounding region. Whilst bees use this substance to seal off and protect the beehive, humans have used propolis therapeutically for centuries, making use of its antibacterial, antiseptic, antipyretic and wound healing properties, among others. South African propolis is rich in the flavonoids pinocembrin, galangin, and chrysin and very little previous research has been conducted on the antimicrobial effects of these compounds.

AIM OF THE STUDY

To obtain an understanding of the antimicrobial activity of the compounds pinocembrin, galangin, and chrysin, both independently and in combination.

MATERIALS AND METHODS

The compounds pinocembrin, galangin and chrysin were investigated for interactive antimicrobial activity by determining the minimum inhibitory concentrations (MIC), minimum bactericidal concentrations (MBC), anti-quorum sensing activity, biofilm studies, and toxicity studies (brine shrimp lethality assay).

RESULTS

Minimum inhibitory concentration results demonstrated that combinations of compounds showed better inhibitory activity than single compounds. When the flavonoids were tested in combination using the MIC assay, synergy was noted for 22% of the 1:1 ratio combinations and for 66% of the triple 1:1:1 ratio combinations. Similarly, MBC results showed bactericidal activity from selected combinations, while the compounds on their own demonstrated no cidal activity. Quorum sensing studies showed that compound combinations are more effective at inhibiting bacterial communication than the individual compounds. Biofilm assays showed that the highest percentage inhibition was observed for the triple combination against E. coli at 24 h. Finally, brine shrimp lethality studies revealed that combinations of the three compounds had reduced cytotoxicity when compared to the individual compounds.

CONCLUSION

The results obtained in this study demonstrate that the compounds found in South African propolis work synergistically to achieve an optimal antimicrobial effect, whilst simultaneously minimizing cytotoxicity.

Quorum-sensing system in Acinetobacter baumannii: a potential target for new drug development

Acinetobacter baumannii causes several nosocomial infections and poses major threat when it is multidrug resistant. Even pan drug-resistant strains have been reported in some countries. The intensive care unit (ICU) mortality rate ranged from 45.6% to 60.9% and it is as high as 84.3% when ventilator-associated pneumonia was caused by XDR (extensively drug resistant) A. baumannii. Acinetobacter baumannii constituted 9.4% of all Gram-negative organisms throughout the hospital and 22.6% in the ICUs according to a study carried out in an Indian hospital. One of the major factors contributing to drug resistance in A. baumannii infections is biofilm development. Quorum sensing (QS) facilitates biofilm formation and therefore the search for 'quorum quenchers' has increased recently. Such compounds are expected to inhibit biofilm formation and hence reduce/prevent development of drug resistance in the bacteria. Some of these compounds also target synthesis of some virulence factors (VF). Several candidate drugs have been identified and are at various stages of drug development. Since quorum quenching, inhibition of biofilm formation and inhibition of VF synthesis do not pose any threat to the DNA replication and cell division of the bacteria, chances of resistance development to such compounds is presumably rare. Thus, these compounds ideally qualify as adjunct therapeutics and could be administered along with an antibiotic to reduce chances of resistance development and also to increase the effectiveness of antimicrobial therapy. This review describes the state-of-art in QS process in Gram-negative bacteria in general and in A. baumannii in particular. This article elaborates the nature of QS mediators, their characteristics, and the methods for their detection and quantification. Various potential sites in the QS pathway have been highlighted as drug targets and the candidate quorum quenchers which inhibit the mediator's synthesis or function are enlisted.

Multivalent Affidendrons with High Affinity and Specificity toward Staphylococcus aureus as Versatile Tools for Modulating Multicellular Behaviors

Multivalency is a widely occurring natural phenomenon often exploited in nanotechnology to enhance biorecognition. We report the preparation and characterization of versatile, multivalent Affitin-dendrimer conjugates (Affidendrons) showcased by a set targeting Staphylococcus aureus ( S. aureus), an opportunistic pathogen causing numerous hospital- and community-acquired infections. Affitins are small affinity proteins characterized by higher stability and lower cost-effective production than antibodies. The strategy presented provides a platform for the rational design of multivalent nanodevices that, retaining the ability of Affitins to recognize their target with high specificity, achieve a largely enhanced affinity. Affidendrons with precisely designed size and valency have been exploited to modulate complex multicellular behaviors of S. aureus, such as agglutination and biofilm formation. Agglutination assays showed that Affidendrons rapidly cross-link S. aureus strains with high bacterial cell selectivity. Moreover, remarkably low concentrations of Affidendrons were able to effectively prevent biofilm formation. Overall, Affidendrons represent a promising platform for the rapid and selective pathogen identification, infection imaging, and theranostic applications.

A neural network model predicts community-level signaling states in a diverse microbial community

Signal crosstalk within biological communication networks is common, and such crosstalk can have unexpected consequences for decision making in heterogeneous communities of cells. Here we examined crosstalk within a bacterial community composed of five strains of Bacillus subtilis, with each strain producing a variant of the quorum sensing peptide ComX. In isolation, each strain produced one variant of the ComX signal to induce expression of genes associated with bacterial competence. When strains were combined, a mixture of ComX variants was produced resulting in variable levels of gene expression. To examine gene regulation in mixed communities, we implemented a neural network model. Experimental quantification of asymmetric crosstalk between pairs of strains parametrized the model, enabling the accurate prediction of activity within the full five-strain network. Unlike the single strain system in which quorum sensing activated upon exceeding a threshold concentration of the signal, crosstalk within the five-strain community resulted in multiple community-level quorum sensing states, each with a unique combination of quorum sensing activation among the five strains. Quorum sensing activity of the strains within the community was influenced by the combination and ratio of strains as well as community dynamics. The community-level signaling state was altered through an external signal perturbation, and the output state depended on the timing of the perturbation. Given the ubiquity of signal crosstalk in diverse microbial communities, the application of such neural network models will increase accuracy of predicting activity within microbial consortia and enable new strategies for control and design of bacterial signaling networks.

Many plant pathogenic Pseudomonas savastanoi pv glycinea isolates possess an inactive quorum sensing ahlR gene via a point mutation

Many plant bacterial pathogens monitor their group behaviour and their population density via production of N-acyl homoserine lactone signals which regulate the expression of several genes via the LuxI/R homologs. This regulatory network, termed quorum sensing (QS), is present in the soybean bacterial pathogen Pseudomonas savastanoi pv glycinea (Psg). The sequenced genomes of two strains of Psg, race 4 and B076, contain an N-acyl homoserine lactone (AHL) based LuxI/R QS system named AhlI/R. While studying the QS system of Psg strains race 4 and B076 isolated in USA, LMG5066 in New Zealand and IBSBF355 in Brazil, we found that B076, LMG5066 and IBSBF355 possess a point mutation in the ahlR gene that causes a frameshift resulting in a truncated AhlR protein. Psg race 4 does not possess the mutation in ahlR and the QS system is functional. The same mutation in the ahlR gene was found to be also present in 9 of 19 Psg strains isolated from diseased soybean in Illinois. Phenotypic analysis of strains showed that swarming motility is repressed whereas phosphate solubilisation was activated by QS in Psg. Analysing the secretome, we also found that four proteins were under QS regulation.

Spatial quorum sensing modelling using coloured hybrid Petri nets and simulative model checking

BACKGROUND

Quorum sensing drives biofilm formation in bacteria in order to ensure that biofilm formation only occurs when colonies are of a sufficient size and density. This spatial behaviour is achieved by the broadcast communication of an autoinducer in a diffusion scenario. This is of interest, for example, when considering the role of gut microbiota in gut health. This behaviour occurs within the context of the four phases of bacterial growth, specifically in the exponential stage (phase 2) for autoinducer production and the stationary stage (phase 3) for biofilm formation.

RESULTS

We have used coloured hybrid Petri nets to step-wise develop a flexible computational model for E.coli biofilm formation driven by Autoinducer 2 (AI-2) which is easy to configure for different notions of space. The model describes the essential components of gene transcription, signal transduction, extra and intra cellular transport, as well as the two-phase nature of the system. We build on a previously published non-spatial stochastic Petri net model of AI-2 production, keeping the assumptions of a limited nutritional environment, and our spatial hybrid Petri net model of biofilm formation, first presented at the NETTAB 2017 workshop. First we consider the two models separately without space, and then combined, and finally we add space. We describe in detail our step-wise model development and validation. Our simulation results support the expected behaviour that biofilm formation is increased in areas of higher bacterial colony size and density. Our analysis techniques include behaviour checking based on linear time temporal logic.

CONCLUSIONS

The advantages of our modelling and analysis approach are the description of quorum sensing and associated biofilm formation over two phases of bacterial growth, taking into account bacterial spatial distribution using a flexible and easy to maintain computational model. All computational results are reproducible.

Connect and Conquer: Collectivized Behavior of Mitochondria and Bacteria

The connectedness of signaling components in network structures is a universal feature of biologic information processing. Such organization enables the transduction of complex input stimuli into coherent outputs and is essential in modulating activities as diverse as the cooperation of bacteria within populations and the dynamic organization of mitochondria within cells. Here, we highlight some common principles that underpin collectivization in bacteria and mitochondrial populations and the advantages conferred by such behavior. We discuss the concept that bacteria and mitochondria act as signal transducers of their localized metabolic environments to bring about energy-dependent clustering to modulate higher-order function across multiple scales.

Differential expression profiling of ΔlitR and ΔrpoQ mutants reveals insight into QS regulation of motility, adhesion and biofilm formation in Aliivibrio salmonicida

BACKGROUND

The coordination of group behaviors in bacteria is achieved by a cell-cell signaling process called quorum sensing (QS). QS is an intercellular communication system, which synchronously controls expression of a vast range of genes in response to changes in cell density and is mediated by autoinducers that act as extracellular signals. Aliivibrio salmonicida, the causative agent of cold-water vibrosis in marine aquacultures, uses QS to regulate several activities such as motility, biofilm formation, adhesion and rugose colony morphology. However, little is known about either genes or detailed mechanisms involved in the regulation of these phenotypes.

RESULTS

Differential expression profiling allowed us to define the genes involved in controlling phenotypes related to QS in A. salmonicida LFI1238. RNA sequencing data revealed that the number of expressed genes in A. salmonicida, ΔlitR and ΔrpoQ mutants were significantly altered due to changes in cell density. These included genes that were distributed among the 21 functional groups, mainly presented in cell envelope, cell processes, extrachromosomal/foreign DNA and transport-binding proteins functional groups. The comparative transcriptome of A. salmonicida wild-type at high cell density relative to low cell density revealed 1013 genes to be either up- or downregulated. Thirty-six downregulated genes were gene clusters encoding biosynthesis of the flagellar and chemotaxis genes. Additionally we identified significant expression for genes involved in acyl homoserine lactone (AHL) synthesis, adhesion and early colonization. The transcriptome profile of ΔrpoQ compared to the wild-type revealed 384 differensially expressed genes (DEGs) that allowed us to assign genes involved in regulating motility, adhesion and colony rugosity. Indicating the importance of RpoQ in controlling several QS related activities. Furthermore, the comparison of the transcriptome profiles of ΔlitR and ΔrpoQ mutants, exposed numerous overlapping DEGs that were essential for motility, exopolysaccharide production via syp operon and genes associated with tad operon.

CONCLUSION

Our findings indicate previously unexplained functional roles for LitR and RpoQ in regulation of different phenotypes related to QS. Our transcriptome data provide a better understanding of the regulation cascade of motility, wrinkling colony morphology and biofilm formation and will offer a major source for further research and analysis on this important field.

Biofilms: Architecture, Resistance, Quorum Sensing and Control Mechanisms

Biofilm is a mode of living employed by many pathogenic and environmental microbes to proliferate as multicellular aggregates on inert inanimate or biological substrates. Several microbial diseases are associated with biofilms that pose challenges in treatment with antibiotics targeting individual cells. Bacteria in biofilms secrete exopolymeric substances that contribute to architectural stability and provide a secure niche to inhabiting cells. Quorum sensing (QS) plays essential roles in biofilm development. Pathogenic bacteria in biofilms utilize QS mechanisms to activate virulence and develop antibiotic resistance. This review is a brief overview of biofilm research and provides updates on recent understandings on biofilm development, antibiotic resistance and transmission, and importance of QS mechanisms. Strategies to combat biofilm associated diseases including anti-biofilm substances, quorum quenching molecules, bio-surfactants and competitive inhibitors are briefly discussed. The review concludes with updates on recent approaches utilized for biofilm inhibition and provides perspectives for further research in the field.

Costless metabolic secretions as drivers of interspecies interactions in microbial ecosystems

Metabolic exchange mediates interactions among microbes, helping explain diversity in microbial communities. As these interactions often involve a fitness cost, it is unclear how stable cooperation can emerge. Here we use genome-scale metabolic models to investigate whether the release of “costless” metabolites (i.e. those that cause no fitness cost to the producer), can be a prominent driver of intermicrobial interactions. By performing over 2 million pairwise growth simulations of 24 species in a combinatorial assortment of environments, we identify a large space of metabolites that can be secreted without cost, thus generating ample cross-feeding opportunities. In addition to providing an atlas of putative interactions, we show that anoxic conditions can promote mutualisms by providing more opportunities for exchange of costless metabolites, resulting in an overrepresentation of stable ecological network motifs. These results may help identify interaction patterns in natural communities and inform the design of synthetic microbial consortia.

In considering cross-feeding among microbes within communities, it is typically assumed that metabolic secretions are costly to produce. However, Pacheco et al. use metabolic models to show that ‘costless’ secretions could be common in some environments and important for structuring interactions among microbes.

The Diverse Impacts of Phage Morons on Bacterial Fitness and Virulence

The viruses that infect bacteria, known as phages, are the most abundant biological entity on earth. They play critical roles in controlling bacterial populations through phage-mediated killing, as well as through formation of bacterial lysogens. In this form, the survival of the phage depends on the survival of the bacterial host in which it resides. Thus, it is advantageous for phages to encode genes that contribute to bacterial fitness and expand the environmental niche. In many cases, these fitness factors also make the bacteria better able to survive in human infections and are thereby considered pathogenesis or virulence factors. The genes that encode these fitness factors, known as "morons," have been shown to increase bacterial fitness through a wide range of mechanisms and play important roles in bacterial diseases. This review outlines the benefits provided by phage morons in various aspects of bacterial life, including phage and antibiotic resistance, motility, adhesion and quorum sensing.

A New Method for Determination of Minimum Biofilm Eradication Concentration for Accurate Antimicrobial Therapy

Antimicrobial susceptibility testing (AST) is an important technique to find the susceptibility pattern of clinical isolates in order to administer the appropriate drug. One such technique is minimum inhibitory concentration (MIC), which not only identifies the right drug but also suggests the appropriate concentration necessary to neutralize the organisms in planktonic form. MIC can vary in case of adherent organisms since they form biofilms and activate survival mechanisms like quorum sensing. Here we have strategized a new method which used an inoculator plate, a resazurin dye, and a standard plate to identify minimum biofilm eradication concentration (MBEC) of adherent organisms.

Towards Understanding the Molecular Basis of Nitric Oxide-Regulated Group Behaviors in Pathogenic Bacteria

Pathogenic bacteria have many strategies for causing disease in humans. One such strategy is the ability to live both as single-celled motile organisms or as part of a community of bacteria called a biofilm. Biofilms are frequently adhered to biotic or abiotic surfaces and are extremely antibiotic resistant. Upon biofilm dispersal, bacteria become more antibiotic susceptible but are also able to readily infect another host. Various studies have shown that low, nontoxic levels of nitric oxide (NO) may induce biofilm dispersal in many bacterial species. While the molecular details of this phenotype remain largely unknown, in several species, NO has been implicated in biofilm-to-planktonic cell transitions via ligation to 1 of 2 characterized NO sensors, NosP or H-NOX. Based on the data available to date, it appears that NO binding to H-NOX or NosP triggers a downstream response based on changes in cellular cyclic di-GMP concentrations and/or the modulation of quorum sensing. In order to develop applications for control of biofilm infections, the identification and characterization of biofilm dispersal mechanisms is vital. This review focuses on the efforts made to understand NO-mediated control of H-NOX and NosP pathways in the 3 pathogenic bacteria Legionella pneumophila, Vibrio cholerae, and Pseudomonas aeruginosa.

Cytochalasans Act as Inhibitors of Biofilm Formation of Staphylococcus Aureus

During the course of our ongoing work to discover new inhibitors of biofilm formation of Staphylococcus aureus from fungal sources, we observed biofilm inhibition by cytochalasans isolated from cultures of the ascomycete Hypoxylon fragiforme for the first time. Two new compounds were purified by a bioassay-guided fractionation procedure; their structures were elucidated subsequently by nuclear magnetic resonance (NMR) spectroscopy and high-resolution mass spectrometry (HR-MS). This unexpected finding prompted us to test further cytochalasans from other fungi and from commercial sources for comparison. Out of 21 cytochalasans, 13 showed significant inhibition of Staphylococcus aureus biofilm formation at subtoxic levels. These findings indicate the potential of cytochalasans as biofilm inhibitors for the first time, also because the minimum inhibitory concentrations (MIC) are independent of the anti-biofilm activities. However, cytochalasans are known to be inhibitors of actin, making some of them very toxic for eukaryotic cells. Since the chemical structures of the tested compounds were rather diverse, the inclusion of additional derivatives, as well as the evaluation of their selectivity against mammalian cells vs. the bacterium, will be necessary as next step in order to develop structure-activity relationships and identify the optimal candidates for development of an anti-biofilm agent.

Microbial Degradation of Epoxy

Epoxy resins have a wide range of applications, including in corrosion protection of metals, electronics, structural adhesives, and composites. The consumption of epoxy resins is predicted to keep growing in the coming years. Unfortunately, thermoset resins cannot be recycled, and are typically not biodegradable. Hence, they pose environmental pollution risk. Here, we report degradation of epoxy resin by two bacteria that are capable of using epoxy resin as a sole carbon source. These bacteria were isolated from soil samples collected from areas around an epoxy and polyurethanes manufacturing plant. Using an array of molecular, biochemical, analytical, and microscopic techniques, they were identified as Rhodococcus rhodochrous and Ochrobactrum anthropi. As epoxy was the only carbon source available for these bacteria, their measured growth rate reflected their ability to degrade epoxy resin. Bacterial growth took place only when the two bacteria were grown together, indicating a synergistic effect. The surface morphology of the epoxy droplets changed significantly due to the biodegradation process. The metabolic pathway of epoxy by these two microbes was investigated by liquid chromatography mass spectrometry. Bisphenol A, 3,3′-((propane-2,2-diylbis(4,1-phenylene))bis(oxy))bis(propane-1,2-diol) and some other constituents were identified as being consumed by the bacteria.

Thinking Outside the Box-Novel Antibacterials To Tackle the Resistance Crisis

The public view on antibiotics as reliable medicines changed when reports about "resistant superbugs" appeared in the news. While reasons for this resistance development are easily spotted, solutions for re-establishing effective antibiotics are still in their infancy. This Review encompasses several aspects of the antibiotic development pipeline from very early strategies to mature drugs. An interdisciplinary overview is given of methods suitable for mining novel antibiotics and strategies discussed to unravel their modes of action. Select examples of antibiotics recently identified by using these platforms not only illustrate the efficiency of these measures, but also highlight promising clinical candidates with therapeutic potential. Furthermore, the concept of molecules that disarm pathogens by addressing gatekeepers of virulence will be covered. The Review concludes with an evaluation of antibacterials currently in clinical development. Overall, this Review aims to connect select innovative antimicrobial approaches to stimulate interdisciplinary partnerships between chemists from academia and industry.

Cyclic Peptides that Govern Signal Transduction Pathways: From Prokaryotes to Multi-Cellular Organisms

Cyclic peptide scaffolds are key components of signal transduction pathways in both prokaryotic and eukaryotic organisms since they act as chemical messengers that activate or inhibit specific cognate receptors. In prokaryotic organisms these peptides are utilized in non-essential pathways, such as quorum sensing, that are responsible for virulence and pathogenicity. In the more evolved eukaryotic systems, cyclic peptide hormones play a key role in the regulation of the overall function of multicellular organisms, mainly through the endocrine system. This review will highlight several prokaryote and eukaryote systems that use cyclic peptides as their primary signals and the potential associated with utilizing these scaffolds for the discovery of novel therapeutics for a wide range of diseases and illnesses.

Synthesis and biological screening of new thiazolo[4,5-d]pyrimidine and dithiazolo[3,2-a:5',4'-e]pyrimidinone derivatives as antimicrobial, antiquorum-sensing and antitumor agents

New thiazolopyrimidine and dithiazolopyrimidinone derivatives 2-11 were synthesized and estimated for antimicrobial activity against S. aureus, B. cereus, E. coli, C. albicans, A. fumigatus and A. terreus. The attained results proved that 4, 8a and 11g have significant effectiveness against S. aureus and B. cereus. On the other hand, 7, 10b, 10c and 11h exhibited prominent activity against B. cereus, whereas 8a, 10b and 11g were proved to be active against E. coli. From another point of view, 4 and 8a exhibited promising efficacy against A. fumigatus and A. terreus; moreover, 8a showed outstanding efficacy against C. albicans. Quorum-sensing inhibitory activity of the new compounds was esteemed against C. violaceum, where 7, 8a, 9b, 10a-c, 11d and 11g have acceptable efficacy. In vitro antitumor efficacy of the same compounds against HepG2, HCT-116 and MCF-7 cancer cell lines was also tested. Compounds 4 and 11h showed enhanced effectiveness against the three cell lines, whereas 10b displayed eminent activity against HCT-116 and MCF-7 cells. Moreover, 11a was found to have outstanding activity against MCF-7 cells, while 11i showed promising efficacy against HepG2 cells. The in vitro active antitumor compounds were evaluated for in vivo antitumor effectiveness against EAC in mice, as well as in vitro cytotoxicity against WI38 and WISH normal cells. Results manifested that 4 has the strongest in vivo activity, and that all investigated analogs are less cytotoxic than 5-FU against both normal cell lines. DNA-binding affinity of the active compounds was examined, where 4, 8a, 10c, 11d and 11g,h displayed strong affinity. In silico studies proved that majority of the analyzed compounds are in conformity with the optimum needs for good oral absorption.

The Effect of Quorum-Sensing and Efflux Pumps Interactions in Pseudomonas aeruginosa Against Photooxidative Stress

Resistant infections essentially cause mortality in a burn unit. Several bacteria contribute to burn infections; among these, Pseudomonas aeruginosa majorly contributes to these infections revealing significant drug resistance. Similar to other bacteria, P. aeruginosa reveals various mechanisms to attain highest pathogenicity and resistance; among these, efflux pumps and quorum sensing are crucial. Quorum sensing enables effective communication between bacteria and synchronizes their gene expression resulting in optimum effect of the secreted proteins; alternatively, efflux pumps increase the bacterial resistance by pumping out the antimicrobial factors as well as the QS signals and precursors. Of recent, increasing episodes of drug resistance led to new findings and approaches for killing pathogenic bacteria without inducing the drug-resistant species. Photodynamic therapy (PDT), considered as an adjuvant and innovative method for conventional antibiotic therapy, is a photochemical reaction that includes visible light, oxygen, and a photosensitizer (PS). In this therapy, after exposure to visible light, the PS generates reactive oxygen species (ROS) that are bacteriostatic or bactericidal. Furthermore, this oxidative stress can disrupt the coordination of gene expression and alter the bacterial behavior. Considering the fact that the adaption and several gene expression patterns of microorganisms within the biofilm make them notably resistant to the recent antimicrobial treatments, this study aimed to emphasize the relationship between the efflux pump and QS under oxidative stress and their role in P. aeruginosa's reaction to PDT.

The Role of Functional Amyloids in Bacterial Virulence

Amyloid fibrils are best known as a product of human and animal protein misfolding disorders, where amyloid formation is associated with cytotoxicity and disease. It is now evident that for some proteins, the amyloid state constitutes the native structure and serves a functional role. These functional amyloids are proving widespread in bacteria and fungi, fulfilling diverse functions as structural components in biofilms or spore coats, as toxins and surface-active fibers, as epigenetic material, peptide reservoirs or adhesins mediating binding to and internalization into host cells. In this review, we will focus on the role of functional amyloids in bacterial pathogenesis. The role of functional amyloids as virulence factor is diverse but mostly indirect. Nevertheless, functional amyloid pathways deserve consideration for the acute and long-term effects of the infectious disease process and may form valid antimicrobial targets.

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Functional amyloids are widespread in bacteria, pathogenic and non-pathogenic.

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Bacterial biofilms most commonly function as structural support in the extracellular matrix of biofilms or spore coats, and in cell–cell and cell-surface adherence.

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The amyloid state can be the sole structured and functional state, or can be facultative, as a secondary state to folded monomeric subunits.

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Bacterial amyloids can enhance virulence by increasing persistence, cell adherence and invasion, intracellular survival, and pathogen spread by increased environmental survival.

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Bacterial amyloids may indirectly inflict disease by triggering inflammation, contact phase activation and possibly induce or aggravate human pathological aggregation disorders.

Phenotypic Variation during Biofilm Formation: Implications for Anti-Biofilm Therapeutic Design

Various bacterial species cycle between growth phases and biofilm formation, of which the latter facilitates persistence in inhospitable environments. These phases can be generally characterized by one or more cellular phenotype(s), each with distinct virulence factor functionality. In addition, a variety of phenotypes can often be observed within the phases themselves, which can be dependent on host conditions or the presence of nutrient and oxygen gradients within the biofilm itself (i.e., microenvironments). Currently, most anti-biofilm strategies have targeted a single phenotype; this approach has driven effective, yet incomplete, protection due to the lack of consideration of gene expression dynamics throughout the bacteria’s pathogenesis. As such, this article provides an overview of the distinct phenotypes found within each biofilm development phase and demonstrates the unique anti-biofilm solutions each phase offers. However, we conclude that a combinatorial approach must be taken to provide complete protection against biofilm forming bacterial and their resulting diseases.