| In recent years,the abuse of antibiotics has not only caused the residual pollution of antibiotics in the environment,but increased the pollution and spread of antibiotic-resistant bacteria(ARB)and antibiotics resistant genes(ARGs),which leaded more health risks and environmental risks.ARBs and ARGs are widely spread in freshwater environments that may harm the growth and reproduction of aquatic organisms.In this study,Shigella flexneri HL,a multi-drug resistant enteric pathogen,isolated from the breeding environment in the early stage of the research group was selected as the exposure factor,and the Xenopus tropicalis was selected as the model organism receptor.And experiments of short-term exposure of embryos and long-term exposure of tadpoles were carried out,which revealed the effects and related mechanisms of X.tropicalis under S.flexneri exposure.In this study,the growth characteristics,resistance types and subpathogenic concentrations of S.flexneri were determined by growth incubation,drug susceptibility experiments,PCR amplification and gradient exposure experiments.Secondly,according to the subpathogenic concentration of S.flexneri,a short-term exposure experiment was carried out with the embryos of X.tropicalis.By comparing the toxicity indicators,developmental gene expression,enzyme activity and immune response of different experimental groups,it was revealed that S.flexneri had an adverse effect on growth and developmental of X.tropicalis'embryos.Subsequently,an experiment was carried out in which tadpoles was exposed to subpathogenic concentrations of S.flexneri for long-tern.By comparing the changes of triglyceride and enzyme activities in the head,the expression of immune factors and Notch pathway genes in the gut,pathological sections and the abundance of resistance genes,it was revealed that the body health of X.tropicalis'tadpoles under S.flexneri exposure.Therefore,we reveal the health effects of multidrug-resistant pathogenic bacteria S.flexneri on the X.tropicalis'embryos and tadpoles at the individual,molecular and gene level,which will be helpful to provide a certain theoretical basis on the spread and treatment of drug-resistant pathogenic bacteria in aquatic organisms in the future.The study found that the exposure toxicity of S.flexneri to X.tropicalis'embryos was positively correlated with its concentration,and the gut and heart were the target organs at the embryonic stage.Compared with the control group,S.flexneri exposure resulted in down-regulated expression of embryonic development-related genes nkx2.5 and pax6,which caused embryonic malformation and even death.Among them,exposure to high concentrations of S.flexneri can even cause embryos deformation or death due to excessive oxidative stress;while the surviving embryos are exposed to moderate oxidative stress and the expression levels of cellular immune factors,such as IL-1?,IL-10,TNF-?and IFN-?,they are regulated to eliminate bacterial infection in vivo to protect embryos.In addition,long-term exposure to S.flexneri caused significant accumulation of triglycerides in the head of tadpoles,which disrupted lipid homeostasis and resulted in oxidative stress damage.Compared with the control group,long-term under S.flexneri exposure can lead to the down-regulation of the expression of Notch signaling pathway transduction factors and immune factors in the intestinal tract of tadpoles,damage the intestinal structure,even destroy the stability of the intestinal microecology.What's more,the long-term stress of S.flexneri will significantly increase the absolute abundance of 16S r RNA,tet B,tet X,sul2,bla TEM,and int I1 in the intestine,which aggravate the spread of ARGs and may also affect the intestinal flora to affect the health of X.tropicalis'tadpoles.Therefore,S.flexneri,a multidrug-resistant enteric pathogen,not only affects the growth and development of X.tropicalis,which has a negative impact on intestinal health,but also promotes the spread of ARGs,posing a potential threat to the aquatic ecosystem. |
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