Current advances in Vibrio harveyi quorum sensing as drug discovery targets

Thiazolidin-4-Ones as a Promising Scaffold in the Development of Antibiofilm Agents-A Review

Thiazolidin-4-ones have a broad range of medical and clinical implementation, which is important for pharmaceutical and medicinal chemistry. This heterocyclic core has been reported to possess a diversity of bioactivities, including antimicrobial and antibiofilm-forming potential. The resistance of biofilms to antibiotics or disinfectants is a serious medical problem. Therefore, there is a natural need to discover new effective structures with properties that inhibit biofilm formation. This review aims to analyze the antibiofilm features of thiazolidin-4-ones described in the literature over the last two decades. The information gathered in this review could benefit the rational design of new effective antibiofilm small molecules with thiazolidin-4-one cores.

LPS-Induced Mortality in Zebrafish: Preliminary Characterisation of Common Fish Pathogens

Disease outbreaks are a common problem in aquaculture, with serious economic consequences to the sector. Some of the most important bacterial diseases affecting aquaculture are caused by Gram-negative bacteria including Vibrio spp. (vibriosis), Photobacterium damselae (photobacteriosis), Aeromonas spp. (furunculosis; haemorrhagic septicaemia) or Tenacibaculum maritimum (tenacibaculosis). Lipopolysaccharides (LPS) are important components of the outer membrane of Gram-negative bacteria and have been linked to strong immunogenic responses in terrestrial vertebrates, playing a role in disease development. To evaluate LPS effects in fish, we used a hot-phenol procedure to extract LPS from common fish pathogens. A. hydrophila, V. harveyi, T. maritimum and P. damselae purified LPS were tested at different concentrations (50, 100, 250 and 500 µg mL-1) at 3 days post-fertilisation (dpf) Danio rerio larvae, for 5 days. While P. damselae LPS did not cause any mortality under all concentrations tested, A. hydrophila LPS induced 15.5% and V. harveyi LPS induced 58.3% of zebrafish larvae mortality at 500 µg mL-1. LPS from T. maritimum was revealed to be the deadliest, with a zebrafish larvae mortality percentage of 80.6%. Analysis of LPS separated by gel electrophoresis revealed differences in the overall LPS structure between the bacterial species analysed that might be the basis for the different mortalities observed.

Identification and characterization of two novel antimicrobial peptides from Japanese sea bass (Lateolabrax japonicus) with antimicrobial activity and MO/MФ activation capability

Piscidins participate in the innate immune response of fish, which aims to eliminate recognized foreign microbes and restore the homeostasis of immune system. We characterized two piscidin-like antimicrobial peptides (LjPL-3 and LjPL-2) isolated from Japanese sea bass (Lateolabrax japonicus). LjPL-3 and LjPL-2 showed different expression patterns in tissues. After Vibrio harveyi infection, the mRNA expression of LjPL-3 and LjPL-2 was upregulated in the liver, spleen, head kidney, and trunk kidney. The synthetic mature peptides LjPL-3 and LjPL-2 exhibited different antimicrobial spectra. Furthermore, LjPL-3 and LjPL-2 treatments decreased inflammatory cytokine production while promoting chemotaxis and phagocytosis in monocytes/macrophages (MO/MФ). LjPL-2, but not LjPL-3, displayed bacterial killing capability in MO/MФ. LjPL-3 and LjPL-2 administration increased Japanese sea bass survival after V. harveyi challenge, which was accompanied by a decline in bacterial burden. These data suggested that LjPL-3 and LjPL-2 participate in immune response through direct bacterial killing and MO/MФ activation.

Anti-Vibrio potential of natural products from marine microorganisms

The emergence of drug-resistant Vibrio poses a serious threat to aquaculture and human health, thus there is an urgent need for the discovery of new related antibiotics. Given that marine microorganisms (MMs) are evidenced as important sources of antibacterial natural products (NPs), great attention has been gained to the exploration of potential anti-Vibrio agents from MMs. This review summarizes the occurrence, structural diversity, and biological activities of 214 anti-Vibrio NPs isolated from MMs (from 1999 to July 2022), including 108 new compounds. They were predominantly originated from marine fungi (63%) and bacteria (30%) with great structural diversity, including polyketides, nitrogenous compounds, terpenoids, and steroids, among which polyketides account for nearly half (51%) of them. This review will shed light on the development of MMs derived NPs as potential anti-Vibrio lead compounds with promising applications in agriculture and human health.

ACKR4a induces autophagy to block NF-κB signaling and apoptosis to facilitate Vibrio harveyi infection

Autophagy and apoptosis are two recognized mechanisms of resistance to bacterial invasion. However, bacteria have likewise evolved the ability to evade immunity. In this study, we identify ACKR4a, a member of an atypical chemokine receptor family, as a suppressor of the NF-κB pathway, which cooperates with Beclin-1 to induce autophagy to inhibit NF-κB signaling and block apoptosis, facilitating Vibrio harveyi infection. Mechanistically, V. harveyi-induced Ap-1 activates ACKR4a transcription and expression. ACKR4a forms a complex with Beclin-1 and MyD88, respectively, inducing autophagy and transporting MyD88 into the lysosome for degradation to suppress inflammatory cytokine production. Meanwhile, ACKR4a-induced autophagy blocks apoptosis by inhibiting caspase8. This study proves for the first time that V. harveyi uses both autophagy and apoptosis to evade innate immunity, suggesting that V. harveyi has evolved the ability to against fish immunity.

The implications of quorum sensing inhibition in bacterial antibiotic resistance- with a special focus on aquaculture

The aquaculture industry is an expanding and demanding industry and due to an increase in urbanization, with rise in income of developing countries population, it offers to provide a sustainable food supply. However, the industry is facing a number of challenges, out of which few needs to be tackled immediately to maximise the productivity. An upcoming problem is the emergence of antibiotic resistant pathogens due to the unchecked use of antibiotics in aquaculture and human clinical practices. A wide variety of aquatic pathogens such as Edwardsiella, Vibrio, and Aeromonas spp. use quorum sensing (QS) systems, a regulatory process involving cell communication via signalling molecules for the collective function of pathogens which regulates the genes expression including virulent genes. Quorum sensing results in bacterial biofilms formation, which leads to their reduced susceptibility towards antimicrobial agents. The usage of quorum sensing inhibitors (QSIs) has been proposed as an attractive strategy to tackle this problem. Due to the modulation of virulence genes expression, QSIs can be used as novel and viable approach to overcome antibiotic resistance in aquaculture. In this review, we direct our attention to the quorum sensing phenomenon and its viability as a target pathway for tackling the ever-growing problem of antimicrobial resistance in aquaculture. This review also provides a concise compilation of the currently available QSIs and investigates possible natural sources for quorum quenching.

A Small-Molecule Inhibitor of the Anthranilyl-CoA Synthetase PqsA for the Treatment of Multidrug-Resistant Pseudomonas aeruginosa

One of the challenges associated with the treatment of Pseudomonas aeruginosa infections is the high prevalence of multidrug resistance (MDR). Since conventional antibiotics are ineffective at treating such bacterial infections, innovative antibiotics acting upon novel targets or via mechanisms are urgently required. In this study, we identified a quorum sensing inhibitor (QSI), norharmane, that uniquely shows weak antibacterial activity but strongly inhibits pyocyanin production and biofilm formation of MDR P. aeruginosa. Biophysical experiments and molecular docking studies showed that norharmane competes with anthraniloyl-AMP for anthranilyl-CoA synthetase PqsA of P. aeruginosa at the ligand-binding pocket, which is not exploited by current inhibitors, thereby altering transcription regulatory activity. Moreover, norharmane exhibits synergy with polymyxin B. This synergism exhibits a high killing rate, low probability of resistance selection, and minimal cytotoxicity. Notably, norharmane can effectively boost polymyxin B activity against MDR P. aeruginosa-associated infections in animal models. Together, our findings provide novel insight critical to the design of improved PqsA inhibitors, and an effective combination strategy to overcome multiantibiotic bacterial resistance using conventional antibiotics and QSIs. IMPORTANCE Pseudomonas aeruginosa is a dominant hospital-acquired bacterial pathogen typically found in immunocompromised individuals. It is particularly dangerous for patients with chronic lung diseases and was identified as a serious threat for patients in the 2019 Antimicrobial Resistance Threats report (https://www.cdc.gov/drugresistance/biggest-threats.html). In this study, we used activity-based high-throughput screening to identify norharmane, a potent and selective inhibitor of P. aeruginosa PqsA, which is a well-conserved master quorum sensing (QS) regulator in multidrug resistant (MDR) P. aeruginosa. This compound competitively binds anthranilyl-CoA synthetase PqsA at the anthraniloyl-AMP binding domain, which has not been exploited by known inhibitors. Remarkably, norharmane can significantly block the production of the virulence factor, pyocyanin (87%), and biofilm formation (80%) in MDR P. aeruginosa. Furthermore, norharmane is capable of augmenting polymyxin B activity against MDR P. aeruginosa in cell cultures and animal models. Taken together, these results suggest that norharmane may be an effective adjuvant for combating multiantibiotic bacterial resistance.

Inhibitors of Bacterial Extracellular Vesicles

Both Gram-positive and Gram-negative bacteria can secrete extracellular vesicles (EVs), which contain numerous active substances. EVs mediate bacterial interactions with their hosts or other microbes. Bacterial EVs play a double-edged role in infections through various mechanisms, including the delivery of virulence factors, modulating immune responses, mediating antibiotic resistance, and inhibiting competitive microbes. The spread of antibiotic resistance continues to represent a difficult clinical challenge. Therefore, the investigation of novel therapeutics is a valuable research endeavor for targeting antibiotic-resistant bacterial infections. As a pathogenic substance of bacteria, bacterial EVs have gained increased attention. Thus, EV inhibitors are expected to function as novel antimicrobial agents. The inhibition of EV production, EV activity, and EV-stimulated inflammation are considered potential pathways. This review primarily introduces compounds that effectively inhibit bacterial EVs and evaluates the prospects of their application.