Quorum-quenching activity of the AHL-lactonase from Bacillus licheniformis DAHB1 inhibits Vibrio biofilm formation in vitro and reduces shrimp intestinal colonisation and mortality

Antibiofilm agents: A new perspective for antimicrobial strategy

Biofilms are complex microbial architectures that attach to surfaces and encase microorganisms in a matrix composed of self-produced hydrated extracellular polymeric substances (EPSs). In biofilms, microorganisms become much more resistant to antimicrobial treatments, harsh environmental conditions, and host immunity. Biofilm formation by microbial pathogens greatly enhances survival in hosts and causes chronic infections that result in persistent inflammation and tissue damages. Currently, it is believed over 80% of chronic infectious diseases are mediated by biofilms, and it is known that conventional antibiotic medications are inadequate at eradicating these biofilm-mediated infections. This situation demands new strategies for biofilm-associated infections, and currently, researchers focus on the development of antibiofilm agents that are specific to biofilms, but are nontoxic, because it is believed that this prevents the development of drug resistance. Here, we review the most promising antibiofilm agents undergoing intensive research and development.

Secretome of Intestinal Bacilli: A Natural Guard against Pathologies

Current studies of human gut microbiome usually do not consider the special functional role of transient microbiota, although some of its members remain in the host for a long time and produce broad spectrum of biologically active substances. Getting into the gastrointestinal tract (GIT) with food, water and probiotic preparations, two representatives of Bacilli class, genera Bacillus and Lactobacillus, colonize epithelium blurring the boundaries between resident and transient microbiota. Despite their minor proportion in the microbiome composition, these bacteria can significantly affect both the intestinal microbiota and the entire body thanks to a wide range of secreted compounds. Recently, insufficiency and limitations of pure genome-based analysis of gut microbiota became known. Thus, the need for intense functional studies is evident. This review aims to characterize the Bacillus and Lactobacillus in GIT, as well as the functional roles of the components released by these members of microbial intestinal community. Complex of their secreted compounds is referred by us as the "bacillary secretome." The composition of the bacillary secretome, its biological effects in GIT and role in counteraction to infectious diseases and oncological pathologies in human organism is the subject of the review.

Detection of Diverse N-Acyl-Homoserine Lactones in Vibrio alginolyticus and Regulation of Biofilm Formation by N-(3-Oxodecanoyl) Homoserine Lactone In vitro

Quorum sensing (QS) is a cell-to-cell communication system based on the exchange of small intercellular signal molecules, such as N-Acyl homoserine lactones (AHLs), which act as cell-density mediators of QS gene expression, and are highly variable both in types and amounts in most Gram-negative Proteobacteria. Understanding the regulation of AHLs may contribute to the elucidation of cell density-dependent phenomena, such as biofilm formation. Vibrio alginolyticus is among the most frequently observed marine opportunistic Vibrio pathogens. However, AHL production of this species and its effects on biofilm formation remain to be understood. Here, our study reported the diverse AHL profiles of 47 marine-isolated V. alginolyticus strains and the effects of exogenous 3-oxo-C₁₀-HSL on biofilm formation under different temperature conditions (16°C and 28°C). A total of 11 detected AHLs were produced by the isolates, of which 3-OH-C₄-HSL, 3-oxo-C₁₀-HSL and 3-oxo-C₁₄-HSL comprised the largest proportions. We also observed that moderate levels of exogenous 3-oxo-C₁₀-HSL (10 and 20 μM) could induce or enhance biofilm formation and alter its structure, while high levels (40 and 100 μM) did not significantly improve and even inhibited biofilm formation in V. alginolyticus. Further, regulation by exogenous 3-oxo-C₁₀-HSL was both concentration- and temperature-dependent in V. alginolyticus.

Current applications, selection, and possible mechanisms of actions of synbiotics in improving the growth and health status in aquaculture: A review

Synbiotics, a conjunction between prebiotics and probiotics, have been used in aquaculture for over 10 years. However, the mechanisms of how synbiotics work as growth and immunity promoters are far from being unraveled. Here, we show that a prebiotic as part of a synbiotic is hydrolyzed to mono- or disaccharides as the sole carbon source with diverse mechanisms, thereby increasing biomass and colonization that is established by specific crosstalk between probiotic bacteria and the surface of intestinal epithelial cells of the host. Synbiotics may indirectly and directly promote the growth of aquatic animals through releasing extracellular bacterial enzymes and bioactive products from synbiotic metabolic processes. These compounds may activate precursors of digestive enzymes of the host and augment the nutritional absorptive ability that contributes to the efficacy of food utilization. In fish immune systems, synbiotics cause intestinal epithelial cells to secrete cytokines which modulate immune functional cells as of dendritic cells, T cells, and B cells, and induce the ability of lipopolysaccharides to trigger tumor necrosis factor-α and Toll-like receptor 2 gene transcription leading to increased respiratory burst activity, phagocytosis, and nitric oxide production. In shellfish, synbiotics stimulate the proliferation and degranulation of hemocytes of shrimp due to the presence of bacterial cell walls. Pathogen-associated molecular patterns are subsequently recognized and bound by specific pattern-recognition proteins, triggering melanization and phagocytosis processes.

Quorum Sensing and the Use of Quorum Quenchers as Natural Biocides to Inhibit Sulfate-Reducing Bacteria

Sulfate-reducing bacteria (SRB) are one of the main protagonist groups of biocorrosion in the seawater environment. Given their principal role in biocorrosion, it remains a crucial task to develop strategies to reduce the abundance of SRBs. Conventional approaches include the use of biocides and antibiotics, which can impose health, safety, and environmental concerns. This review examines an alternative approach to this problem. This is achieved by reviewing the role of quorum sensing (QS) in SRB populations and its impact on the biofilm formation process. Genome databases of SRBs are mined to look for putative QS systems and homologous protein sequences representative of autoinducer receptors or synthases. Subsequently, this review puts forward the potential use of quorum quenchers as natural biocides against SRBs and outlines the potential strategies for the implementation of this approach.

Biotechnological applications of quorum quenching enzymes

Numerous bacteria use quorum sensing (QS) to synchronize their behavior and monitor their population density. They use signaling molecules known as autoinducers (AI's) that are synthesized and secreted into their local environment to regulate QS-dependent gene expression. Among QS-regulated pathways, biofilm formation and virulence factor secretion are particularly problematic as they are involved in surface-attachment, antimicrobial agent resistance, toxicity, and pathogenicity. Targeting QS represents a promising strategy to inhibit undesirable bacterial traits. This strategy, referred to as quorum quenching (QQ), includes QS-inhibitors and QQ enzymes. These approaches are appealing because they do not directly challenge bacterial survival, and consequently selection pressure may be low, yielding a lower occurrence of resistance. QQ enzymes are particularly promising because they act extracellularly to degrade AI's and can be used in catalytic quantities. This review draws an overview of QQ enzyme related applications, covering several economically important fields such as agriculture, aquaculture, biofouling and health issues. Finally, the possibility of resistance mechanism occurrence to QQ strategies is discussed.

GFP tagged Vibrio parahaemolyticus Dahv2 infection and the protective effects of the probiotic Bacillus licheniformis Dahb1 on the growth, immune and antioxidant responses in Pangasius hypophthalmus

In this study, the pathogenicity of GFP tagged Vibrio parahaemolyticus Dahv2 and the protective effect of the probiotic strain, Bacillus licheniformis Dahb1 was studied on the Asian catfish, Pangasius hypophthalmus. The experiment was carried out for 24 days with three groups and one group served as the control (without treatment). In the first group, P. hypophthalmus was orally infected with 1 mL of GFP tagged V. parahaemolyticus Dahv2 at two different doses (10(5) and 10(7) cfu mL(-1)). In the second group, P. hypophthalmus was orally administrated with 1 ml of the probiotic B. licheniformis Dahb1 at two different doses (10(5) and 10(7) cfu mL(-1)). In the third group, P. hypophthalmus was orally infected first with 1 mL of GFP tagged V. parahaemolyticus Dahv2 followed by the administration of 1 mL of B. licheniformis Dahb1 (combined treatment) at two different doses (10(5) and 10(7) cfu mL(-1)). The growth, immune (myeloperoxidase, respiratory burst, natural complement haemolytic and lysozyme activity) and antioxidant (glutathione-S-transferase, reduced glutathione and total glutathione) responses of P. hypophthalmus were reduced after post infection of GFP tagged V. parahaemolyticus Dahv2 compared to control. However, after administration with the probiotic B. licheniformis Dahb1 at 10(5) cfu mL(-1), P. hypophthalmus showed significant increase in the growth, immune and antioxidant responses compared to 10(7) cfu mL(-1). On the otherhand, the growth, immune and antioxidant responses of P. hypophthalmus infected and administrated with combined GFP tagged Vibrio + Bacillus at 10(5) cfu mL(-1) were relatively higher than that of GFP tagged V. parahaemolyticus Dahv2 and control groups but lower than that of probiotic B. licheniformis Dahb1 groups. The results of the present study conclude that the probiotic B. licheniformis Dahb1 at 10(5) cfu mL(-1) has the potential to protect the P. hypophthalmus against V. parahaemolyticus Dahv2 infection by enhancing the growth, immune and antioxidant responses. The probiotic B. licheniformis Dahb1 would be effectively used in the treatment of aquatic diseases for improvement of aquaculture industry.