Immunomodulatory effects of orally administrated florfenicol in rainbow trout (Oncorhynchus mykiss) following experimental challenge with streptococcosis/lactococcosis

Systemic immune response of rainbow trout exposed to Flavobacterium psychrophilum infection

Bacterial cold-water disease (BCWD) caused by Flavobacterium psychrophilum is one of the most serious bacterial diseases leading to significant economic loss for rainbow trout (Oncorhynchus mykiss) aquaculture. However, little is known about the systemic immune response of rainbow trout against F. psychrophilum infection. This study investigated the immune response of rainbow trout to F. psychrophilum infection using multiple experiments, including bacterial load detection, phagocyte activity assessment, enzyme activity evaluation, and gene expression profiling. Results showed that the spleen index and intestinal pathogen load reached a peak at 3 days post-infection, with strong pro-inflammatory gene expression observed in rainbow trout. Leukocytes RBA and PKA were significantly elevated in the spleen, blood and intestine at 7 days post-infection. Heat map analysis demonstrated that the spleen had a more substantial pro-inflammatory response compared to the intestine post-infection and exhibited higher expression levels of immune-related genes, including IgM, il1β, il6, cd4, cd8a, cd8b, c1q, chathelicidin, inos, and lysozyme. Both Th1 and Th2 polarized responses in the spleen were activated, with Th2 (il4/13a, gata3) (FC > 4) being more intense than Th1 (tnfα, t-bet) (FC > 2). Tight junction proteins exhibited down-regulation followed by up-regulation post-infection. Collectively, the results of this study expand our current understanding of the immune response of rainbow trout post F. psychrophilum infection but also provide new avenues for investigation in salmonid aquaculture.

Beyond the surface: Consequences of methyl tert-butyl ether (MTBE) exposure on oxidative stress, haematology, genotoxicity, and histopathology in rainbow trout

Concerns have been raised about the possible environmental effects of methyl tert-butyl ether (MTBE), which is widely used as a gasoline additive. This research aimed to look at the consequences of MTBE contamination on rainbow trout (Oncorhynchus mykiss), emphasizing oxidative stress, genotoxicity, and histopathological damage. After determining the LC50-96 h value, the effects of sub-lethal doses of MTBE (0 (control), 90, 180, and 450 ppm) on rainbow trout were investigated. In fish tissues, the levels of oxidative stress indicators such as malondialdehyde (MDA) and superoxide dismutase (SOD) were measured. The comet assay, which measures DNA damage in erythrocytes, was used to determine genotoxicity. Histopathological examinations were done on liver and gill tissues to examine potential structural anomalies. The results of this study show that MTBE exposure caused considerable alterations in rainbow trout. Increased oxidative stress was demonstrated by elevated MDA levels and decreased SOD activity, while the comet assay revealed dose-dependent DNA damage, implying genotoxic effects. Histopathological study revealed liver and gill tissue abnormalities, including cell degeneration, necrosis, and inflammation. Overall, this research highlights the possible sub-lethal effects of MTBE contamination on rainbow trout, stressing the need of resolving this issue. Future research should look at the impacts of chronic MTBE exposure and the possibility of bioaccumulation in fish populations.

Exploring the combined interplays: Effects of cypermethrin and microplastic exposure on the survival and antioxidant physiology of Astacus leptodactylus

Plastic waste and micro/nanoplastic particles pose a significant global environmental challenge, along with concerns surrounding certain pesticides' impact on aquatic organisms. This study investigated the effects of microplastic particles (MPPs) and cypermethrin (CYP) on crayfish, focusing on biochemical indices, lipid peroxidation, oxidative stress, hematological changes, and histopathological damage. After determining the LC50-96 h value (4.162 μg/L), crayfish were exposed to sub-lethal concentrations of CYP (1.00 ppb (20%) and 2.00 ppb (50%)) and fed a diet containing 100 mg/kg MPPs for 60 days. Hemolymph transfusion and histopathological examinations of the hepatopancreas were conducted. The results showed significant alterations in crayfish. Total protein levels decreased, indicating protein breakdown to counteract contaminants, while total cholesterol and triglyceride levels declined, suggesting impaired metabolism. Glucose levels increased in response to chemical stress. The decline in total antioxidant capacity highlighted the impact of prolonged xenobiotic exposure and oxidative stress, while increased CAT, SOD, and MDA activities helped mitigate oxidative stress and maintain cellular homeostasis. The elevated total hemocyte count, particularly in semi-granular cells, suggests their active involvement in the detoxification process. Further research is needed to fully understand the implications of these effects.

Effects of florfenicol on the antioxidant and immune systems of Chinese soft-shelled turtle (Pelodiscus sinensis)

Florfenicol is a commonly used antibiotic for the treatment of bacterial diseases of the Chinese soft-shelled turtle (Pelodiscus sinensis). The study investigated the effects of florfenicol on the antioxidant and immune system of P. sinensis. Results showed that the total antioxidant capacity (T-AOC), superoxide dismutase (SOD), and catalase (CAT) activities were significantly increased in the 10 mg/kg and 40 mg/kg florfenicol treatment groups compared with the control group. Besides, the malondialdehyde (MDA) content was significantly increased, and the glutathione peroxidase (GSH-Px) activity was significantly decreased with 40 mg/kg florfenicol treatment. In addition, florfenicol has effects on the immune system, 10 mg/kg of florfenicol significantly promoted the activities of acid phosphatase (ACP) and alkaline phosphatase (AKP), whereas 40 mg/kg of florfenicol significantly inhibited their activities. To elucidate the molecular mechanisms, a comparative transcriptome analysis was conducted. A total of 59 differentially expressed genes (DEGs) and 12 significantly enriched KEGG pathways were identified in the 10 mg/kg group; 150 DEGs and 10 significantly enriched KEGG pathways were identified in the 40 mg/kg group. Among them, the complement and coagulation cascade pathways were the most significant which may play an important regulatory role in the immune response. The MADCAM1, STAT3, and IL4I1 genes may be the key genes of florfenicol affecting the immune response. The APOA1, APOA4, SPLA2, FADS1, and FADS2 genes may play a key role in anti-inflammatory and antioxidant effects through redox-related pathways. The study lays the foundation for a deeper understanding of the mechanism of the florfenicol effect on P. sinensis.

Dietary Olive Leaf Extract Differentially Modulates Antioxidant Defense of Normal and Aeromonas hydrophila-Infected Common Carp (Cyprinus carpio) via Keap1/Nrf2 Pathway Signaling: A Phytochemical and Biological Link

Olive leaves are an immense source of antioxidant and antimicrobial bioactive constituents. This study investigated the effects of dietary incorporation of olive leaf extract (OLE) on the growth performance, hematobiochemical parameters, immune response, antioxidant defense, histopathological changes, and some growth- and immune-related genes in the common carp (Cyprinus carpio). A total of 180 fish were allocated into four groups with triplicate each. The control group received the basal diet without OLE, while the other three groups were fed a basal diet with the OLE at 0.1, 0.2, and 0.3%, respectively. The feeding study lasted for 8 weeks, then fish were challenged with Aeromonas hydrophila. The results revealed that the group supplied with the 0.1% OLE significantly exhibited a higher final body weight (FBW), weight gain (WG%), and specific growth rate (SGR) with a decreased feed conversion ratio (FCR) compared to the other groups (p < 0.05). An increase in immune response was also observed in the fish from this group, with higher lysosome activity, immunoglobulin (IgM), and respiratory burst than nonsupplemented fish, both before and after the A. hydrophila challenge (p < 0.05). Similarly, the supplementation of the 0.1% OLE also promoted the C. carpio's digestive capacity pre- and post-challenge, presenting the highest activity of protease and alkaline phosphatase (p < 0.05). In addition, this dose of the OLE enhanced fish antioxidant capacity through an increase in the activity of superoxide dismutase (SOD) and glutathione peroxidase (GPx) and decreased hepatic lipid peroxidation end products (malondialdehyde-MDA), when compared to the control group, both pre- and post-infection (p < 0.05). Concomitantly with the superior immune response and antioxidant capacity, the fish fed the 0.1% OLE revealed the highest survival rate after the challenge with A. hydrophila (p < 0.05). A significant remarkable upregulation of the hepatic sod, nrf2, and protein kinase C transcription levels was detected as a vital approach for the prevention of both oxidative stress and inflammation compared to the infected unsupplied control group (p < 0.05). Interestingly, HPLC and UPLC-ESI-MS/MS analyses recognized that oleuropein is the main constituent (20.4%) with other 45 compounds in addition to tentative identification of two new compounds, namely oleuroside-10-carboxylic acid (I) and demethyl oleuroside-10-carboxylic acid (II). These constituents may be responsible for the OLE exerted potential effects. To conclude, the OLE at a dose range of 0.66-0.83 g/kg w/w can be included in the C. carpio diet to improve the growth, antioxidant capacity, and immune response under normal health conditions along with regulating the infection-associated pro-inflammatory gene expressions, thus enhancing resistance against A. hydrophila.

Atlantic Salmon (Salmo salar) bacterial and viral innate immune responses are not impaired by florfenicol or tetracycline administration

Antibiotics are used to treat bacterial infections in fish aquaculture, and these drugs can interact with immune cells/the immune system and potentially leave fish vulnerable to viral, fungal, parasitic, or other bacterial infections. However, the effects of antibiotics on fish immunity have largely been overlooked by the aquaculture industry. We tested, at 12 and 20 °C, whether tetracycline and florfenicol (the most commonly used antibiotics in commercial aquaculture), affected the Atlantic salmon's capacity to respond to bacterial or viral stimulation. Atlantic salmon were acclimated to 12 or 20 °C and fed with tetracycline or florfenicol (100 and 10 mg kg of body weight^-1 day^-1, respectively) medicated feed for 15 or 10 days, respectively. Thereafter, we evaluated their immune function prior to, and after, an intraperitoneal injection of Forte Micro (containing inactivated cultures of Aeromonas salmonicida, Vibrio anguillarum, Vibrio ordalii and Vibrio salmonicida) or the viral mimic polyriboinosinic polyribocytidylic acid (pIC). We measured the transcript expression levels of 8 anti-bacterial and 8 anti-viral putative biomarker genes, and the innate (leukocyte respiratory burst, plasma lysozyme activity and hemolytic activity of the alternative complement pathway) and cellular (relative number of erythrocytes, lymphocytes and thrombocytes, and granulocytes such as monocytes and neutrophils) responses to these challenges. Overall, we only found a few minor effects of either tetracycline or florfenicol on immune gene expression or function at either temperature. Although several studies have reported that antibiotics may negatively affect fish immune responses, our results show that industry-relevant dietary tetracycline and florfenicol treatments do not substantially impact the salmon's innate immune responses. Currently, this is the most comprehensive study on the effects of antibiotics administrated according to industry protocols on immune function in Atlantic salmon.

Comparative Transcriptomic Analysis Reveals the Regulated Expression Profiles in Oreochromis niloticus in Response to Coinfection of Streptococcus agalactiae and Streptococcus iniae

Tilapia (Oreochromis sp.) is one of the important economical fishes in the world. Streptococcosis is commonly found in tilapia, causing severe and devastating effects in tilapia cultures. Streptococcus agalactiae and Streptococcus iniae are the predominant pathogens causing tilapia streptococcosis. To understand the molecular mechanisms underlying differential streptococcal infection patterns, Nile tilapias (Oreochromis niloticus) were infected by 1 × 107 CFU/mL S. agalactiae, 1 × 107 CFU/mL S. iniae, and 1 × 107 CFU/mL S. agalactiae and S. iniae (1:1), respectively, and transcriptome analysis was conducted to the intestine samples of Nile tilapia (Oreochromis niloticus) at 6, 12, 24 h, and 7 days post-infection. A total of 6,185 genes that differentially expressed among groups were identified. Eight differentially expressed genes (DEGs) including E3 ubiquitin-protein ligase TRIM39-like, C-X-C motif chemokine 10-like(CXCL 10), C-C motif chemokine 19-like, interleukin-1 beta-like, IgM heavy chain VH region, partial, IgG Fc-binding protein, proteasome subunit beta type-8 (PSMB8), and ATP synthase F(0) complex subunit B1, mitochondrial that involved in the immune system were selected, and their expression levels in the coinfection group were significantly higher than those in either of the single infection groups. These genes were associated with four different KEGG pathways. Additionally, the differential expression of eight DEGs was validated by using the RT-qPCR approach, and their immunological importance was discussed. The results provided insights into the responses of tilapia against S. agalactiae and S. iniae at the transcriptome level, promoting our better understanding of immune responses for aquatic animal against Streptococcus.

Cutaneous mucosal immune-parameters and intestinal immune-relevant genes expression in streptococcal-infected rainbow trout (Oncorhynchus mykiss): A comparative study with the administration of florfenicol and olive leaf extract

This study evaluated changes in cutaneous mucosal immunity (total protein (TP) and immunoglobulin (TIg), lysozyme, protease, esterase, and alkaline phosphatase (ALP)) and some immune-related genes expression (tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-8, hepcidin-like antimicrobial peptides (HAMP), and immunoglobulin M (IgM)) in the intestine of rainbow trout (Oncorhynchus mykiss) orally-administrated florfenicol (FFC) and/or olive leaf extract (OLE), experimentally infected with Streptococcus iniae. The juvenile fish (55 ± 7.6 g) were divided into different groups according to the use of added OLE (80 g kg^-1 food), the presence/absence of FFC (15 mg kg^-1 body weight for 10 consecutive days), and the streptococcal infectivity (2.87 × 10⁷ CFU mL^-1 as 30% of LD₅₀-96h). The extract's chemical composition was analyzed using the high-performance liquid chromatography (HPLC) system. The skin mucus and intestine of fish were sampled after a 10-day therapeutic period for all groups, and their noted indices were measured. Our results signified that the oleuropein, quercetin, and trans-ferulic acid were the most obvious active components of OLE which were found by HPLC analysis. The combined use of OLE and FFC could lowered some skin mucus immunological indices (e.g., TP, TIg, and ALP), and the gene expression of inflammatory cytokines (e.g., TNF-α and IL-1β) of rainbow trout. Moreover, lysozyme and protease activities respectively were invigorated by the FFC and OLE treatment. Also, the use of OLE as a potential medicine induced the gene expression of HAMP. As the prevention approach, it would be recommended to find the best dose of OLE alone or in combination with the drug through therapeutics period before the farm involved in the streptococcal infection.

Florfenicol alleviated lipopolysaccharide (LPS)-induced inflammatory responses in Ctenopharyngodon idella through inhibiting toll / NF-κB signaling pathways

The present study was conducted to evaluate the anti-inflammatory activity of florfenicol (FFC) against lipopolysaccharide (LPS)-induced inflammatory responses in Ctenopharyngodon idella in vivo and in vitro. Head-kidney (HK) macrophages were pre-treated with 10 μg/mL LPS and then exposed to different concentrations of FFC to determine its in vitro anti-inflammatory activity. Inhibitory effect of FFC on inflammatory mediators TNF-α, IL-6 and IL-1β, as well as LPS-induced nitric oxide (NO) and prostaglandin E 2 (PGE 2) production were assayed by ELISA. The expression level of nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) were investigated by RT-PCR. Expression level of TLR-related genes (TLR1, TLR2, TLR4, TLR7, TLR8) expression, tumor necrosis factor receptor-associated factor 6 (TRAF6), transforming growth factor-b-activated kinase 1 (TAK1), Myeloid differentiation factor 88 (MyD88), nucleus p65, NF-κBα (IκBα) were measured by RT-PCR after grass carp were treated with 50, 100 and 200 mg FFC/kg body weight for 3 days. Results from in vitro tests demonstrated that FFC dose-dependently inhibited LPS-induced inflammatory cytokines TNF-α, IL-6 and IL-1β, inflammatory factors NO and PGE 2 production in macrophages. In addition, iNOS and COX-2 expression levels decreased significantly as compared with LPS treated group. In vivo test demonstrated that treatment with FFC prevented the LPS-induced upregulation of TNF-α, IL-6, IL-1β, NO and PGE 2. The expression level of iNOS, and COX-2 in FFC-treated grass carp were also downregulated as compared with LPS treated fish. Besides, FFC blocked the expression of Toll-like receptor 2 (TLR2) and then suppressed the phosphorylation of nuclear transcription factor-kappa B (NF-κB) p65 and degradation inhibitor of IκBα. Furthermore, administration of FFC inhibited the up-regulation of IRAK4, TRAF6 and TAK1 induced by LPS. These results suggest that the anti-inflammatory properties of FFC might be the results from the inhibition of iNOS, COX-2, IL-6, IL-1β, and TNF-α expressions through the down-regulation of Toll/NF-κB signaling pathways.