Effects of Florfenicol on Intestinal Histology, Apoptosis and Gut Microbiota of Chinese Mitten Crab (Eriocheir sinensis)

Assessing the ecotoxicity of florfenicol exposure at environmental levels: A case study of histology, apoptosis and microbiota in hepatopancreas of Eriocheir sinensis

The intensification of production practices in the aquaculture industry has led to the indiscriminate use of antibiotics to combat diseases and reduce costs, which has resulted in environmental pollution, posing serious threats to aquaculture sustainability and food safety. However, the toxic effect of florfenicol (FF) exposure on the hepatopancreas of crustaceans remains unclear. Herein, by employing Chinese mitten crab (Eriocheir sinensis) as subjects to investigate the toxic effects on histopathology, oxidative stress, apoptosis and microbiota of hepatopancreas under environment-relevant (0.5 and 5 μg/L), and extreme concentrations (50 μg/L) of FF. Our results revealed that the damage of hepatopancreas tissue structure caused by FF exposure in a dose-and time-dependent manner. Combined with the increased expression of apoptosis-related genes (Caspase 3, Caspase 8, p53, Bax and Bcl-2) at mRNA and protein levels, activation of catalase (CAT) and superoxide dismutase (SOD), and malondialdehyde (MDA) accumulation, FF exposure also induced oxidative stress, and apoptosis in hepatopancreas. Interestingly, 7 days exposure triggered more pronounced toxic effect in crabs than 14 days under environment-relevant FF concentration. Integrated biomarker response version 2 (IBRv2) index indicated that 14 days FF exposure under extreme concentration has serious toxicity effect on crabs. Furthermore, 14 days exposure to FF changed the diversity and composition of hepatopancreas microbiota leading remarkable increase of pathogenic microorganism Spirochaetes following exposure to 50 μg/L of FF. Taken together, our study explained potential mechanism of FF toxicity on hepatopancreas of crustaceans, and provided a reference for the concentration of FF to be used in culture of Chinese mitten crab.

A review on the antibiotic florfenicol: Occurrence, environmental fate, effects, and health risks

Florfenicol, as a replacement for chloramphenicol, can tightly bind to the A site of the 23S rRNA in the 50S subunit of the 70S ribosome, thereby inhibiting protein synthesis and bacterial proliferation. Due to the widespread use in aquaculture and veterinary medicine, florfenicol has been detected in the aquatic environment worldwide. Concerns over the effects and health risks of florfenicol on target and non-target organisms have been raised in recent years. Although the ecotoxicity of florfenicol has been widely reported in different species, no attempt has been made to review the current research progress of florfenicol toxicity, hormesis, and its health risks posed to biota. In this study, a comprehensive literature review was conducted to summarize the effects of florfenicol on various organisms including bacteria, algae, invertebrates, fishes, birds, and mammals. The generation of antibiotic resistant bacteria and spread antibiotic resistant genes, closely associated with hormesis, are pressing environmental health issues stemming from overuse or misuse of antibiotics including florfenicol. Exposure to florfenicol at μg/L-mg/L induced hormetic effects in several algal species, and chromoplasts might serve as a target for florfenicol-induced effects; however, the underlying molecular mechanisms are completely lacking. Exposure to high levels (mg/L) of florfenicol modified the xenobiotic metabolism, antioxidant systems, and energy metabolism, resulting in hepatotoxicity, renal toxicity, immunotoxicity, developmental toxicity, reproductive toxicity, obesogenic effects, and hormesis in different animal species. Mitochondria and the associated energy metabolism are suggested to be the primary targets for florfenicol toxicity in animals, albeit further in-depth investigations are warranted for revealing the long-term effects (e.g., whole-life-cycle impacts, multigenerational effects) of florfenicol, especially at environmental levels, and the underlying mechanisms. This will facilitate the evaluation of potential hormetic effects and construction of adverse outcome pathways for environmental risk assessment and regulation of florfenicol.

Effects of Prometryn Exposure on Hepatopancreas Oxidative Stress and Intestinal Flora in Eriocheir sinensis (Crustacea: Decapoda)

There is growing evidence that long-term exposure to prometryn (a widely used herbicide) can induce toxicity in bony fish and shrimp. Our previous study demonstrated its 96 h acute toxicity on the crab Eriocheir sinensis. However, studies on whether longer exposure to prometryn with a lower dose induces toxicity in E. sinensis are scarce. Therefore, we conducted a 20 d exposure experiment to investigate its effects on the hepatopancreas and intestine of E. sinensi. Prometryn reduce the activities of antioxidant enzymes, increase the level of lipid peroxidation and cause oxidative stress. Moreover, long-term exposure resulted in immune and detoxification fatigue, while short-term exposure to prometryn could upregulate the expression of genes related to immunity, inflammation and detoxification. Prometryn altered the morphological structure of the hepatopancreas (swollen lumen) and intestine (shorter intestinal villi, thinner muscle layer and thicker peritrophic membrane). In addition, prometryn changed the species composition of the intestinal flora. In particular, Bacteroidota and Proteobacteria showed a dose-dependent decrease accompanied by a dose-dependent increase in Firmicutes at the phylum level. At the genus level, all exposure groups significantly increased the abundance of Zoogloea and a Firmicutes bacterium ZOR0006, but decreased Shewanella abundance. Interestingly, Pearson correlation analysis indicated a potential association between differential flora and hepatopancreatic disorder. Phenotypic abundance analysis indicated that changes in the gut flora decreased the intestinal organ's resistance to stress and increased the potential for opportunistic infection. In summary, our research provides new insights into the prevention and defense strategies in response to external adverse environments and contributes to the sustainable development of E. sinensis culture.