Efficacy and safety of boric acid as a preventive treatment against Saprolegnia infection in Nile tilapia (Oreochromis niloticus)

First report of Achlya bisexualis infection in captive-reared Endangered golden mahseer Tor putitora

Achlya bisexualis is a notorious oomycete pathogen with the potential to cause emerging disease in fish farms. In this study, we report the first isolation of A. bisexualis from captive-reared golden mahseer Tor putitora, an Endangered fish species. The infected fish showed a cotton-like growth of mycelia at the site of infection. The mycelium when cultured on potato dextrose agar produced radially growing white hyphae. The hyphae were non-septate, and some of them carried matured zoosporangium with dense granular cytoplasmic contents. Spherical gemmae with stout stalks were also observed. All the isolates had 100% identity in internal transcribed spacer (ITS)-rDNA sequence and showed highest similarity to that of A. bisexualis. In molecular phylogeny, all the isolates formed a monophyletic group with A. bisexualis which was supported by a bootstrap value of 99%. Based on the molecular and morphological findings, all the isolates were confirmed as A. bisexualis. Further, the anti-oomycete effect of boric acid, a known antifungal agent, against the isolate was evaluated. The minimum inhibitory concentration and minimum fungicidal concentration were found to be 1.25 and >2.5 g l-1, respectively. Isolation of A. bisexualis from a new fish species indicates its possible occurrence in other unreported hosts. Considering its wide infectivity and the potential to cause disease in farmed fishes, its probable prevalence in a new environment and host needs to be closely monitored to prevent the spread of infection, if any, by adopting suitable control measures.

S, Pande A, Pandey PK. Anti-oomycete Activity of Chlorhexidine Gluconate: Molecular Docking and in vitro Studies

Saprolegniosis is one of the most catastrophic oomycete diseases of freshwater fish caused by the members of the genus Saprolegnia. The disease is responsible for huge economic losses in the aquaculture industry worldwide. Until 2002, Saprolegnia infections were effectively controlled by using malachite green. However, the drug has been banned for use in aquaculture due to its harmful effect. Therefore, it has become important to find an alternate and safe anti-oomycete agent that is effective against Saprolegnia. In this study, we investigated the anti-oomycete activity of chlorhexidine gluconate (CHG) against Saprolegnia. Before in vitro evaluation, molecular docking was carried out to explore the binding of CHG with vital proteins of Saprolegnia, such as S. parasitica host-targeting protein 1 (SpHtp1), plasma membrane ATPase, and TKL protein kinase. In silico studies revealed that CHG binds with these proteins via hydrogen bonds and hydrophobic interactions. In an in vitro study, the minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of CHG against S. parasitica were found to be 50 mg/L. Further, it was tested against S. australis, another species of Saprolegnia, and the MIC and MFC were found to be 100 and 200 mg/L, respectively. At 500 mg/L of CHG, there was complete inhibition of the radial growth of Saprolegnia hyphae. In propidium iodide (PI) uptake assay, CHG treated hyphae had bright red fluorescence of PI indicating the disruption of the cell membrane. The results of the present study indicated that CHG could effectively inhibit Saprolegnia and hence can be used for controlling Saprolegniasis in cultured fish.

Efficacy of acriflavin chloride and Melaleuca alternifolia extract against Saprolegnia parasitica infection in Pterophyllum scalare

The article describes cases of saprolegniosis in Pterophyllum scalare in private aquaristics and assesses the therapeutic efficacy of acriflafin chloride against Saprolegnia parasitica infection. To establish the diagnosis, the clinical signs present in sick fish, the results of mycological and microscopic examinations are taken into account. Some chemical and mycological indices of aquarium water have been studied, and also mycological studies of fish feed have been carried out. It is established that the disease of fish develops against the background of adverse changes in physical, chemical composition and microbiocenosis of aquarium water. Low water temperature, high levels of phosphates and pH, a significant level of organic pollution, compared to the norm, provoke the accumulation of opportunistic microbiota, resulting in imbalance in the parasite-host system and the development of clinical manifestations of saprolegniosis in fish. It was found that 44.4% of the studied feed samples fed to fish were contaminated with epiphytic micromycetes. Micromycetes are represented by the genera Aspergillus, Penicilium, Fusarium, Mucor, Rhizopus. Among the studied feeds, the most affected by fungi were larvae of Chironomus plumosus and dry Daphnia pulex. According to the results of our studies during outbreaks of saprolegniosis, the pH of aquarium water was 8.1 ± 0.7, the content of phosphates – 5.6 ± 1.1 mg/L, micromycetes – 18.0 ± 1.2 CFU/100 cm3. Aspergillus flavus, A. niger and Penicillium canescens were detected in the studied water samples. With saprolegniosis, the angelfish have a reduced appetite, spots, ulcers, white thin threads, and a cotton-like plaque appear on certain areas of the skin, fins, eyes, and gills. It is established that effective means for the treatment of sick fish are external use in the form of a long bath of acriflavine chloride and extract of Melaleuca alternifolia. It is also effective to increase the water temperature to 25–27 °С, to ensure the normative fish-holding density in aquariums and to exclude from the diet fish feed contaminated with micromycetes. After using the drugs for two weeks every other day, water was replaced by 20% of the aquarium volume and aerated. As a result of the treatment, gradual healing of skin lesions and recovery of 65% of fish with signs of lesions of the outer coverings were registered. Thus, the article analyzes the causes of saprolegniosis in angelfish common in private aquariums, describes the clinical signs of the disease and assesses the therapeutic efficacy of acriflavine chloride and Melaleuca alternifolia extract against Saprolegnia parasitica infection. Prospects for further research lie in search of more effective and environmentally friendly means for the treatment of saprolegniosis in aquarium fish.

Anti-oomycetes and immunostimulatory activity of natural plant extract compounds against Saprolegnia spp.: Molecular docking and in-vitro studies

This study aimed to investigate the effectiveness of five natural plant extract compounds Curcumin (CUR); Eugenol (EUG), Cinnamaldehyde (CIN), Stigmasterol (ST) and Morin (MOR), on two species of Saprolegnia; Saprolegnia parasitica and S. australis. Selective compounds were screened for the minimum inhibitory concentration, first for anti-oomycetes activity and then mycelium growth inhibition, spore germination inhibition and colonisation test. Nitric oxide production and myeloperoxidase activity of the compounds were tested in head kidney leukocytes of rainbow trout, Oncorhynchus mykiss to assess the immunostimulatory potential. Molecular docking of effective compounds was carried out with effector proteins of S. parasitica to investigate the target binding sites. Among all, CUR could completely inhibit zoospore production and significantly (p ≤ .05) inhibit hyphal growth at 16 mg l^-1 against S. parasitica and S. australis. CIN at the concentration of 50 mg l^-1 completely inhibited hyphal growth of both Saprolegnia spp., although the zoospore production of S. parasitica and S. australis was reduced at 25 mg l^-1 and 10 mg l^-1. In the case of EUG, significant inhibition of the hyphal growth and germination of S. parasitica zoospores was observed at 50 mg l^-1. ST and MOR did not show antioomycetes activity. The molecular docking results were consistent with in vitro studies, possibly due to the binding with the vital proteins (Plasma membrane ATPase, V-type proton ATPase, TKL protein kinase, Host targeting protein 1) of S. parasitica and ultimately inhibiting their activity. CUR and CIN showed increased nitric oxide production at the highest concentration of 250 and 256 mg l^-1 but the value was not significant (p ≤ .05) with control. CUR showed significantly higher peroxidase activity (p ≤ .05) at a concentration of 256 mg l^-1 though values were significantly similar with concentration from 16 to 128 mg l^-1. The nitric oxide and total peroxidase activity of rainbow trout leukocytes in the case of CIN showed a significant difference only at 250 mg l^-1 against the control. The results conclude that CUR, CIN showed the better anti-Saprolegnia activity and could be used as phyto-additives in aquaculture. Among all, the inclusion of CUR as phyto-additives will provide additional immunostimulatory activity.

A facile wet-chemistry approach to engineer an Au-based SERS substrate and enhance sensitivity down to ppb-level detection

A two-dimensional flexible surface-enhanced Raman scattering (SERS) filter substrate provides an alternative strategy for the highly sensitive portable detection of various toxic molecules and biomaterials. Herein, we developed a solid-liquid interfacial reduction reaction to post-engineer a solid Au nanostructure surface on filter paper to improve the SERS effect. Among four reductants (ascorbic acid, l-dopamine, hydroquinone (HQ), and formaldehyde), HQ possessed a larger oxidation overpotential and facilitated homogeneous growth, forming small Au branch-structure nanoparticles from HAuCl4 solution. Due to the surface effect by exposing abundant -OH groups and intrinsic aromatic rings from TNA/HQ on nano-gold, the SERS effect on positively charged analytes near the plasmonic Au surface was enhanced, while forming a protective layer against severe water interruption. The resulting SERS substrate with branched nano-gold provided several SERS-enhanced sites, increased the enhancement by more than 6 times compared to original SERS sensing, and displayed a 1.4-7.4 × 105 analytical enhancement factor, which leads to a limit of detection down to several ppb. Less than 6% of deviation in the SERS intensity at different sensing sites was observed. We successfully improved the primary SERS substrate using a high overpotential reductant. Owing to its soft and flexible properties, the paper-based SERS substrate can be used conveniently in different sizes, pasting on curved materials, detecting additives in fish, and preventing the coffee-ring effect, showing high practicality and potential commercial value in the future.