Effects Of Florfenicol On Antioxidant,Immunity And Intestinal Flora Of Zebrafish(Danio Rerio)

Antibiotics play an important role in the treatment of animal and human diseases,but in recent years,the abuse of antibiotics and improper sewage treatment lead to a high probability of their occurrence in the natural water environment,which poses a threat to the health of aquatic organisms and human beings.At present,many studies focus on the toxicity of antibiotics to benthos and plankton.There are few reports on the effects of antibiotics,especially chloramphenicol antibiotics,on antioxidant,immunity and intestinal flora of fish.In this study,zebrafish(Danio rerio)was selected as the model organism and exposed to the water environment with different concentrations of florfenicol(FF).The effects of FF on the antioxidation,immunity and intestinal flora of zebrafish were studied,the residue of FF in muscle was detected,the minimum concentration of biological toxic effect of FF on zebrafish was evaluated,the minimum risk of healthy consumption of aquatic products was estimated,and the risk degree of biological toxic effect of FF on zebrafish was comprehensively evaluated.The experiment was divided into five florfenicol concentration groups: 0(c),5(T5),10(T10),20(T20)and 40 mg / L(T40),with 5 repetitions in each group and 20 zebrafish in each repetition.The experiment was exposed for 8 weeks with the following results:1.The results of antioxidant index showed that compared with the control group,the CAT activity in the liver and gill of T20 and T40 groups was significantly reduced,and the MDA level in liver of the T40 group was significantly increased.While,the GSH-Px activity in the gill of T40 group was significantly reduced.The expression levels of SOD and CAT gene in the liver and gill of T20 and T40 groups were significantly down-regulated,and the expression level of GSH-Px gene in the T40 group was significantly down-regulated.In general,the activity of antioxidant-related enzymes and the expression of antioxidant-related genes in the high concentration groups of florfenicol(T20 and T40)were inhibited to varying degrees.2.The immune-related gene expression results showed that the expression level of inflammatory factors IFN-??IL-8?TNF-? and IL-1? in the liver of T20 and T40 groups was significantly up-regulated,the IL-8 gene expression in the gill of T20 and T40 groups was significantly up-regulated,the expression of TNF-? and IL-1? in the gill of T40 group was significantly up-regulated.Overall,the expression of immune-related genes in the high concentration groups of florfenicol(T20 and T40)were up-regulated to different degrees.3.The results of intestinal flora analysis showed that FF exposure had two effects on intestinal flora.On the one hand,FF inhibited the relative abundance of conditional pathogenic bacteria in intestinal tract and provided survival space for potential beneficial bacteria.On the other hand,FF exposure promotes the transmission of antibiotic resistance genes(ARGs)among intestinal microorganisms,accelerates the generation of intestinal bacterial resistance,activates nutrient synthesis pathways and consumes host energy.In addition,exposure to FF at 5 mg/L concentration resulted in a significant decrease in intestinal flora diversity and evenness.4.The florfenicol residue in zebrafish muscle showed that the FF residue concentration in muscle of group T40 was 1,049 ?g/kg,exceeding the maximum residue limit(1,000 ?g/kg)in edible tissues in China.The FF concentration in water above 37.52mg/L may pose a potential health risk to aquatic products.In conclusion,when the FF exposure concentration exceeds 20 mg/L,it can produce biological toxicity to antioxidant and immune system of zebrafish,mainly oxidative stress toxicity.Exposure concentrations of more than 20 mg/L can cause oxidative damage to the liver and gills of fish,resulting in the accumulation of oxidative products in tissues,significant inhibition of antioxidant enzyme activities,oxidative modification of nucleic acids,and severe damage to antioxidant capacity.Moreover,ROS generated by intense oxidative stress activate TLR pathways of immune cells to stimulate immune cell activation,induce liver and gill inflammation and stimulate up-regulation of the expression levels of inflammatory factors,leading to immune system disorders.The effects of different concentrations of FF exposure on the gut microbiota of zebrafish were two-sided,with FF exposure at a concentration of 5 mg/L resulting in a significant decrease in both gut microbiota diversity and evenness.The average residue rate of FF in water bodies is 2.981%,and a FF concentration above 37.52 mg/L in water bodies can pose a potential risk to human health.The results of this experiment can provide data support for FF ecological risk threshold concentration assessment,and provide a scientific basis for watershed environmental decision-making and ecological risk assessment of fisheries production.