A novel metabolite of Streptomyces coeruleorubidus exhibits antibacterial activity against Streptococcus agalactiae through modulation of physiological performance, inflammatory cytokines, apoptosis, and oxidative stress-correlated gene expressions in Nile tilapia (Oreochromis niloticus).

Using the unique structures found in natural materials to produce new antibacterial drugs is crucial. Actinobacteria is well-known for its ability to produce naturally occurring chemicals with a variety of structural features that can be used as weapons against infectious bacteria. In the present study, the Streptomyces coeruleorubidus metabolites were characterized and their efficacy in suppressing Streptococcus agalactiae growth was carried out both in vitro and in vivo. The metabolites of S. coeruleorubidus were purified and identified as octasiloxane-hexadecamethyl (OHM). In vivo antibacterial activity of OHM revealed an inhibitory minimum concentration value of 0.5 µg/ml against S. agalactiae and induced ultrastructural cell changes revealed by scanning electron microscope. The safe concentration of OHM was determined as 0.8 mg/L for Nile tilapia. Four in vivo treatments were treated with 0 and 0.8 mg/L OHM and with or without challenge by S. agalactiae (1 × 107 CFU/mL) named control, OHM, S. agalactiae, and S. agalactiae + OHM groups. The OHM treatment improved the survival of Nile tilapia by 33.33% than S. agalactiae challenge group. Waterborne OHM treatment significantly mitigated the deleterious effects of S. agalactiae on hematological, hepato-renal functions, stress indicators, and antioxidant balance. OHM significantly alleviated nitric oxide levels, complement 3, IgM, and lysozyme activity, downregulation of liver antioxidant genes expression in S. agalactiae group. Furthermore, the addition of OHM to challenged fish with S. agalactiae-significantly reversed dramatic negative regulation of inflammatory, apoptosis, and immune related gene expression (caspase-3, bax, pcna, tnf-α, ifn-γ, il-8 il-1ß, il-10, tgf-ß, and bcl-2 in the Nile tilapia spleen. Additionally, the damaged hepatic and splenic structure induced by bacterial infection was restored with OHM treatment. Finally, S. coeruleorubidus metabolites (mainly OHM) revealed in vitro and in vivo antibacterial activity and showed alleviated effects on the physiological status of S. agalactiae infected tilapia.

Pseudomonas putida infection induces immune-antioxidant, hepato-renal, ethological, and histopathological/immunohistochemical disruptions in Oreochromis niloticus: the palliative role of titanium dioxide nanogel.

BACKGROUND: Pseudomonas putida is a pathogenic bacterium that induces great losses in fishes, including Nile tilapia (Oreochromis niloticus). Currently, the application of nanomaterials in aquaculture practices has gained more success as it endows promising results in therapies compared to traditional protocols. OBJECTIVE: Therefore, the current perspective is considered the first report to assess the anti-bacterial efficacy of titanium dioxide nanogel (TDNG) against Pseudomonas putida (P. putida) in Nile tilapia. METHODS: The fish (n = 200; average body weight: 47.50±1.32 g) were allocated into four random groups (control, TDNG, P. putida, and TDNG + P. putida), where 0.9 mg/L of TDNG was applied as bath treatment for ten days. RESULTS: Outcomes revealed that P. putida infection caused ethological alterations (surfacing, abnormal movement, and aggression) and depression of immune-antioxidant variables (complement 3, lysozyme activity, total antioxidant capacity, superoxide dismutase, and reduced glutathione content). Additionally, a substantial elevation in hepatorenal biomarkers (aspartate and alanine aminotransferases and creatinine) with clear histopathological changes and immuno-histochemical alterations (very weak BCL-2 and potent caspase-3 immuno-expressions) were seen. Surprisingly, treating P. putida-infected fish with TDNG improved these variables and obvious restoration of the tissue architectures. CONCLUSION: Overall, this report encompasses the key role of TDNG as an anti-bacterial agent for controlling P. putida infection and improving the health status of Nile tilapia.

Hematological, immuno-antioxidant disruptions, and genes down-regulation induced by Aeromonas veronii challenge in Clarias gariepinus: The ameliorative role of silica nanoparticles.

Aeromonas veronii is a pathogenic bacterium associated with various diseases in aquaculture. However, few studies address the antibacterial activity using nanoparticles (NPs). Hence, the current study is innovative to evaluate the antibacterial efficacy of silica nanoparticles (SiNPs) against A. veronii infection in-vitro with a trial for treatment in-vivo. Primarily, we assessed the in-vitro antibacterial activity against A. veronii. Further, we investigated the hematological profile, immune-antioxidant response, and gene expression of African catfish (Clarias gariepinus) in response to SiNPs exposure and the A. veronii challenge. Fish (N = 120; weight: 90 ± 6.19 g) were distributed into four groups (30 fish/group) for a ten-days-treatment trial. The first (control) and second (SiNPs) groups were treated with 0 mg/L and 20 mg/L SiNPs in water, respectively. The third (A. veronii) and fourth (SiNPs + A. veronii) groups were treated with 0 mg/L and 20 mg/L SiNPs in water, respectively, and infected with A. veronii (1.5 × 107 CFU/mL). Results demonstrated that SiNPs displayed an in-vitro antibacterial activity against A. veronii with a 21 mm inhibitory zone. A. veronii infection caused a high mortality rate (56.67%) and substantial reductions in hematological indices and immune indicators [nitric oxide (NO) and immunoglobulin M (IgM)]. Additionally, marked decline in the level of antioxidants [superoxide dismutase (SOD), catalase (CAT), and reduced glutathione content (GSH)] as well as down-regulation in the immune-related genes [interleukins (IL-1ß and IL-8) and tumor necrosis factor-alpha (TNF-α)] and antioxidant-related genes [SOD1, glutathione peroxidase (GPx), and glutathione-S-transferase (GST)] were the consequences of A. veronii infection. Surprisingly, treatment of A. veronii-infected fish with SiNPs lessened the mortality rate, enhanced the blood picture, modulated the immune-antioxidant parameters, and resulted in gene up-regulation. Overall, this study encompasses the significant role of SiNPs, a new versatile tool for combating hematological, immuno-antioxidant alterations, and gene down-regulation induced by A. veronii infection and sustainable aquaculture production.

Dietary Salvia officinalis leaves enhances antioxidant-immune-capacity, resistance to Aeromonas sobria challenge, and growth of Cyprinus carpio.

The current perspective is a pioneer to assess the efficacy of Salvia officinalis leave powder (SOLP) on growth, intestinal enzymes, physiological and antioxidant status, immunological response, and gene expression of Common carp (Cyprinus carpio). We also looked into fish resistance after being challenged with Aeromonas sobria, a pathogenic zoonotic bacteria. Fish (N = 120) were fed four different experimental diets in triplicate for 8 weeks. The control diet (SOLP0 - without SOLP); meanwhile, the other three diets included SOLP of 2, 4, and 8 g kg-1 concentrations (SOLP2, SOLP4, and SOLP8), respectively. Findings demonstrated that fish fed SOLP4 and SOLP8 diets had better growth performance and improved digestion by noticeable enhancing lipase and amylase enzymes activity than other groups. Additionally, the antioxidant (superoxide dismutase and glutathione peroxidase) and immune activities (immunoglobulin M, nitric oxide, and antiprotease) clarified a significant increase (p < 0.05) in SOLP4 and SOLP8 groups. Enriched diets with SOLP4 and SOLP8 exhibited better expression of splenic genes (IL-1ß, IL-6, IL-10, TLR-2, and SOD), intestinal genes (Slc26a6) and (PepT1 or Slc15a1), and muscular genes (IGF-1 and SOD), while MSTN was down-regulated. After 8 weeks of the experimental trial, C. carpio challenged by A. sobria exhibited the highest cumulative mortality (66.67%), while SOLP8-dietary intervention showed the best results in enhancing the fish resistance against A. sobria by lessening mortalities to 13.33% followed by SOLP4 diet (20%). The outcomes indicate that the expression of splenic, muscular, and intestinal genes confirm the efficacy of SOLP on enhancing growth, digestion, and immune-antioxidant status, and recommend the potential use of SOLP especially at 4 g kg-1 level as a valuable natural economic diet additive in C. carpio culture for sustaining aquaculture.

Emergence of extensively drug-resistant Aeromonas hydrophila complex isolated from wild Mugil cephalus (striped mullet) and Mediterranean seawater.

Background and Aim: Antibiotic resistance has been a progressively documented problem, resulting in treatment failure in humans and animals. This study aimed to investigate the antimicrobial susceptibility and virulence of extensively drug-resistant (XDR) Aeromonas spp. in wild Mugil cephalus and its surrounding seawater along the coastal road of Port Said, Egypt. Materials and Methods: Specimens were examined bacteriologically, confirmed biochemically, and tested for their sensitivity against 11 antimicrobial agents. Molecular confirmation of the obtained isolates by 16S rRNA was performed, followed by the detection of antimicrobial resistance and virulence genes. Results: Aeromonas spp. was recovered from fish (44%) and water samples (36%). A. hydrophila was the most prevalent identified strain, followed by Aeromonas sobria, Aeromonas caviae, and Aeromonas schubertii. Moreover, 90% of the tested isolates were multidrug-resistant (MDR), while 26.67% were XDR. Tested isolates were resistant to b-lactams and sulfonamides (100%), oxytetracycline (90%), and streptomycin (62.22%) but completely susceptible to cefotaxime. XDR isolates successfully amplified resistance genes (blaTEM , sul1, and tetA(A)) but not the (aadA1) gene, although there was phenotypic resistance to streptomycin on plates. All XDR isolates carry the cytotoxic enterotoxin gene (act), but alt gene was detected in only one isolate (12.5%). Conclusion: Data in this study provide a recent update and highlight the role of wild mullet and seawater as reservoirs for MDR and XDR Aeromonas spp. that may pose a risk to humans as food-borne infection or following direct contact.