The disease outbreaks in aquaculture system of wetlands are the major cause of fish mortality. Among various bacterial septicaemic diseases, fish mortality caused by Acinetobacter spp. is recently reported in different fish species. Fish disease outbreak was investigated in a wetland of West Bengal, India to identify the aetiological factors involved. The moribund fish were examined and subjected to bacterial isolation. Two bacterial causative agents were identified as Acinetobacter junii and Acinetobacter pittii by biochemical characterization and 16S rRNA gene amplification. Both the isolates were oxidase-negative, nitrate-negative, catalase-positive and indole-negative. The molecular identification using 16S rRNA gene sequencing and phylogenetic tree analysis further confirmed the two Acinetobacter spp. with 97%-99% similarity. The antibiotic resistance patterns of these two bacteria revealed that both of them were resistant to β-lactam, cefalexin, cephalothin, amoxyclav, cefuroxime, cefadroxil, clindamycin, vancomycin and penicillin. In addition, A. pittii was also resistant to other antibiotics of cephams group such as ceftazidime and cefotaxime.In the challenge experiment, both A. junii and A. pittii were found to be pathogenic with LD 50 of 1.24 × 10 5 and 1.88 × 10 7 cfu/fish respectively. Histopathological examination of gill, liver and kidney revealed prominent changes supporting bacterial septicaemia. The investigation reports for the first time on concurrent infection by A. junii and multidrug-resistant (MDR)-A. pittii as emerging fish pathogens to cause severe mortality in Labeo catla and Hypophthalmichthys molitrix in a freshwater wetland.
Antifreeze proteins (AFPs) are known to polypeptide components formed by certain plants, animals, fungi and bacteria which support to survive in sub-zero temperature. Current study highlighted the seven different antifreeze proteins of fish Ocean pout (Zoarces americanus), in which protein (amino acids sequence) were collected from National Centre for Biotechnology Information and finely characterized using several in silico tools. Such biocomputational techniques applied to figure out the physicochemical, functional and conformational characteristics of targeted AFPs. Multiple physicochemical properties such as Isoelectric Point, Extinction Coefficient and Instability Index, Aliphatic Index, Grand Average Hydropathy were calculated and analysed by ExPASy-ProtParam prediction web server. EMBOSS: pepwheel online tool was used to represent the protein sequences in a helical form. The primary structure analysis shows that most of the AFPs are hydrophobic in nature due to the high content of non-polar residues. The secondary structure of these proteins was calculated using SOPMA tool. SOSUI server and CYS_REC program also run for ideal prediction of transmembrane helices and disulfide bridges of experimental proteins respectively. The modelling of 3D structures of seven desired AFPs were executed by the homology modelling programmes; SWISS MODEL and ProSA web server. UCSF Chimera, Antheprot 3D, PyMOL and RAMPAGE were used to visualize and analysis of the structural variation of the predicted protein model. MEGA7.0.9 software used to know the phylogenetic relationship among these AFPs. These models offered excellent and reliable baseline information for functional characterization of the experimentally derived protein domain composition by using the advanced tools and techniques of Computational Biology.
Aphanomyces invadans is an aquatic oomycete pathogen and the causative agent of epizootic ulcerative syndrome (EUS) in fresh and brackish water fish, which is responsible for severe mortalities and economic losses in aquaculture. Therefore, there is an urgent need to develop anti-infective strategies to control EUS. An Oomycetes, a fungus-like eukaryotic microorganism, and a susceptible species, i.e., Heteropneustes fossilis, are used to establish whether an Eclipta alba leaf extract is effective against the EUS-causing A. invadans. We found that treatment with methanolic leaf extract, at concentrations between 50–100 ppm (T4–T6), protects the H. fossilis fingerlings against A. invadans infection. These optimum concentrations induced anti-stress and antioxidative response in fish, marked by a significant decrease in cortisol and elevated levels of superoxide dismutase (SOD) and catalase (CAT) levels in treated animals, as compared with the controls. We further demonstrated that the A. invadans-protective effect of methanolic leaf extract was caused by its immunomodulatory effect and is linked to the enhanced survival of fingerlings. The analysis of non-specific and specific immune factors confirms that methanolic leaf extract-induced HSP70, HSP90 and IgM levels mediate the survival of H. fossilis fingerlings against A. invadans infection. Taken together, our study provides evidence that the generation of anti-stress and antioxidative responses, as well as humoral immunity, may play a role in protecting H. fossilis fingerlings against A. invadans infection. It is probable that E. alba methanolic leaf extract treatment might become part of a holistic strategy to control EUS in fish species.
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