Evaluation of health and environmental risks for juvenile tilapia (Oreochromis niloticus) exposed to florfenicol

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 short-term florfenicol exposure on the gene expression pattern, midgut microbiota, and metabolome in the lepidopteran model silkworm (Bombyx mori)

Florfenicol (FF), an alternative veterinary antibiotic for chloramphenicol, has been widely utilized in livestock breeding to prevent and treat bacterial diseases. However, the toxicological effects of FF have yet to be fully disclosed. The domesticated silkworm (Bombyx mori), a lepidopteran model, was selected to assess the toxicological effects of FF dietary exposure with multi-omics. The findings showed that high-dose (250 μg/L) FF exposure increased the whole cocoon weight. High-dose FF exposure affected the species richness and community diversity of the microbiota in the silkworm midgut. Biochemical processes and innate immunity were impacted by FF exposure. The KEGG pathways impacted by the midgut microbiota and their metabolites were compared, and several pathways were found to be related to the two ecosystems. In addition, the innate immunity and lipid metabolism pathways were impacted, and some of the differentially expressed genes were enriched in these pathways. These related pathways may involve crosstalk between the midgut microbiota shift, midgut biological functions, and global gene expression. Therefore, our study also advances the application of the silkworm larval model in assessing antibiotic metabolic toxicity and provides novel insights into the potential risks of FF.

Dechlorination Helps Defluorination: Insights into the Defluorination Mechanism of Florfenicol by S-nZVI and DFT Calculations on the Reaction Pathways

Defluorination is essential to eliminate the antibiotic resistance and detrimental effects of florfenicol (C12H14Cl2FNO4S, FF), which is achievable by sulfidated nanoscale zerovalent iron (S-nZVI), yet a comprehensive understanding of the mechanism is lacking. Herein, we used experimental data and density functional theory calculations to demonstrate four dechlorination-promoted defluorination pathways of FF, depending on S-nZVI or not. FF was defluorinated in a rapid and then slow but continuous manner, accompanying a consecutive dechlorination to deschloro (dFF) and dideschloro FF (ddFF). Unexpectedly, the predominant defluorination occurs by spontaneous hydrolysis of ddFF to form the hydrolyzed byproduct (HO-ddFF), i.e., independent of S-nZVI, which is initiated by intramolecular attack from carbonyl O to alkyl F and is thus limited for FF and dFF owing to the diminished nucleophilicity by electron-withdrawing Cl. The removal of Cl also makes the reductive defluorination of ddFF by S-nZVI amenable. The other two minor but more rapid defluorination pathways occur in synergy with the dechlorination of FF and dFF, which are mediated by the reactive carbanion intermediates and generate HO-dFF and HO-ddFF, respectively. The reliability of these dechlorination-facilitated defluorination pathways was verified by the consistency of theoretical calculations with experimental data, providing valuable insights into the degradation of fluorinated contaminants.

Impacts of florfenicol on immunity, antioxidant activity, and histopathology of Oreochromis niloticus: a potential protective effect of dietary spirulina platensis

The misuse of antibiotics enhances the development of resistant microorganisms and decreases the efficacy of treatments. Florfenicol (FF) is one of the antibiotics approved for use in aquaculture in Egypt. Because of its extensive usage, potential negative impacts on aquatic creatures are a major concern. This motivates us to search for an appropriate neoadjuvant to work synergistically with FF and reduce adverse effects. Results from this study will contribute towards improving the understanding of the impacts of FF on Oreochromis niloticus and the possible amelioratory effects of Spirulina platensis algae (SP). O. niloticus (n = 240; 40 ± 2.5 g) were fed on two diets supplemented with or without SP for 4 weeks, then divided into four treatments each in three replicates (n = 60/treatment). G1; was fed a control diet, and the other groups were fed diets supplemented with FF (10 mg /kg of BW, G2), SP (2 g/kg of diet, G3), or FF + SP (G4) for 10 days. Among the four groups, the SP group (G3) had the best immunostimulatory effects as observed by a significant (p < 0.05) elevation in phagocytic activity, phagocytic index, IL6, and TNF-α. The treatment with FF had significantly impacted hepatic and renal tissues, as the values of liver enzymes and creatinine demonstrated tissue deterioration and also resulted in oxidative stress, which was expressed by an increase of GPx, CAT, and SOD in (G2). Additionally, the combined FF + SP improved the hematological parameters and decreased the oxidative damage induced by FF (G4). Thus, it was clear that FF has harmful effects on O. niloticus and that SP can modulate such impacts. These data recommend the use of SP as an effective immunostimulant and a probable adjuvant to FF in O. niloticus diets to attain maximum disease resistance.

Maternal transfer of florfenicol impacts development and disrupts metabolic pathways in F1 offspring zebrafish by destroying mitochondria

Maternal exposure to antibiotics existing in the environment is a predisposing factor for developmental malformation with metabolic disorders in offspring. In this study, female zebrafish (3 months) were exposed to 0.05 mg/L and 0.5 mg/L florfenicol (FF) for 28 days. After pairing and spawning with healthy male fish, F1 embryos were collected and developed to 5 d post-fertilization (dpf) in clear water. And the adverse effects on the F1 generation were examined thoroughly. The fecundity of F0 female fish and the hatchability, mortality, and body length of F1 larvae significantly decreased in the treatment group. Meanwhile, multi-malformation types were found in the exposure group, including delayed yolk sac absorption, lack of swim bladder, and spinal curvature. Metabolomic and transcriptomic results revealed alterations in metabolism with dysregulation in tricarboxylase acid cycle, amino acid metabolism, and disordered lipid metabolism with elevated levels of glycerophospholipid and sphingolipid. Accompanying these metabolic derangements, decreased levels of ATP and disordered oxidative-redox state were observed. These results were consistent with the damaged mitochondrial membrane potential and respiratory chain function, suggesting that the developmental toxicity and perturbed metabolic signaling in the F1 generation were related to the mitochondrial injury after exposing F0 female zebrafish to FF. Our findings highlighted the potential toxicity of FF to offspring generations even though they were not directly exposed to environmental contaminants.

Impact of emerging pollutant florfenicol on enhanced biological phosphorus removal process: Focus on reactor performance and related mechanisms

Florfenicol (FF), an emerging pollutant antibiotic that is difficult to biodegrade, inevitably enters sewage treatment facilities with high level. To date, however, the performance and related mechanism of FF on enhanced biological phosphorus removal (EBPR) have not been reported. In order to fill this gap, this work investigated the potential impacts of FF on EBPR and revealed the relevant mechanisms. The effect of FF on EBPR was dose-dependent, that was, low dose had no effect on EBPR, while high FF concentration inhibited EBPR. Mechanism investigation showed that FF had no effect on anaerobic phosphate release, but reduced oxic phosphorus uptake. Three-dimensional Excitation-emission Matrix fluorescence spectroscopy and X-ray photoelectron spectroscopy analysis showed that FF affected the structure and components of activated sludge extracellular polymers (EPS). High content of FF stimulated sludge to secrete more EPS. High level of FF reduced the relative abundance of microorganisms responsible for biological phosphorus removal. Microbiological community structure analysis indicated 2.0 mg FF/L increased the relative abundance of Candidatus_Competibacter and Terrimonas from 9.22 % and 12.49 % to 19.00 % and 16.28 %, respectively, but significantly reduced the relative abundance of Chinophagaceae from 11.32 % to 0.38 %, compared with the blank.

Impacts of Oral Florfenicol Medication and Residues on the Kidney and Liver of Nile Tilapia Oreochromis niloticus (L.)

Florfenicol (FFC), an approved aquaculture antibiotic, is administered in feed at doses of 10-15 mg kg biomass^-1 day^-1 for 10 successive days. In this study, healthy Oreochromis niloticus were fed with 0-10 times the therapeutic dose of 15 mg kg biomass^-1 day^-1 for 10 days and tracked for 43 days post dosing. Assessments of residue accrual and depletion, oxidative stress, serum biochemistry, histopathology and extent of kidney and liver damages were made. FFC dosing reduced the feed intake significantly. The therapeutic dose produced no mortalities on day 10. Dose-dependent alterations in serum biochemistry were noted upon dosing. Several histopathological alterations were observed in the kidney and liver, which vindicated the toxic potentials of FFC. The residual FFC and florfenicol amine (FFA) accrual, depletion and oxidative stress responses, such as increased malondialdehyde, total nitric oxide, ferric reducing antioxidant power and reduced glutathione S-transferase activity, were documented. The dietary FFC persuaded the physiological state of O. niloticus, the effects of which normalized sparsely with time upon cessation of dosing at the higher doses. The study provided a brief outlook on the physiological responses upon oral FFC administration, which should be kept in mind during its application for fish health safety purposes.

Proteome and transcriptome explore the mechanism of Salvia miltiorrhiza polysaccharides to relieve florfenicol-induced kidney injury in broilers

This experiment explored the mechanism of Salvia miltiorrhiza polysaccharides (SMPs) on florfenicol (FFC)-induced kidney injury in broilers. Ninety healthy 1-day-old Arbor Acres broilers were randomly divided into 3 groups with 6 replicates in each group and 5 chickens in each replicate. The three groups included control group, model group (0.15 g/L FFC), and SMPs group (0.15 g/L FFC + 5.00 g/L SMPs). After 5 days of experimental period, blood was collected, and kidney tissues were extracted. Renal injury was evaluated by serum biochemical indicators and pathological sections. Renal oxidative stress indexes were detected; transcriptomics and proteomics were used to comprehensively analyze the effects of SMPs on broiler kidney injury. The results showed that the model group inhibited average day gain (P < 0.01) and significantly adjusted blood urea nitrogen (BUN), uric acid (UA), and creatinine (Cr) (P < 0.01 or P < 0.05). The histological observation of the kidneys in the model group showed abnormal morphology, and the oxidative stress parameters showed that FFC induced oxidative stress in the kidneys. Comprehensive transcriptome proteomic analysis data showed phosphoribose pyrophosphate synthase 2 (PRPS2), cytochrome 2AC1 (CYP2AC1), cytochrome 2D6 (CYP2D6), glutathione transferase (GST), and sulfotransferase 1B (SULT1B) expression levels changed. It is worth noting that our data showed that supplementation of 5.00 g/L SMPs in drinking water reversed the changes in BUN, Cr, and daily weight gain (P < 0.05) and relieved the abnormal kidney morphology caused by FFC. After SMPs processing, it improved the detoxification process of drug-metabolizing enzymes and improved the oxidative stress state induced by FFC. Therefore, SMPs reduced the nephrotoxicity caused by FFC by promoting drug-metabolizing enzymes and alleviating oxidative stress in the kidneys.

The effects of extended feeding of florfenicol coated medicated diets on the safety, serum biomarkers and blood cells morphology of Nile tilapia Oreochromis niloticus (L.)

Tilapia is one of the most consumed farmed fish, which requires the use of antibiotics in certain phases of its production. This study assessed the safety of 30 days of oral florfenicol (FFC) dosing at 0-10 times the therapeutic dose (1 × : 10 mg/kg biomass/day) in Oreochromis niloticus juveniles. Behavioural changes, feed consumption, mortality and biomass were evaluated. Besides, the levels of serum glucose, calcium, chloride, creatinine, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase and blood cell morphology were determined at scheduled intervals. The 30 days of oral FFC dosing caused 3.33% (1 ×) to 18.33% (10 ×) mortalities, reduced feed intake and biomass in a dose-dependent manner. The fish fed the therapeutic dose recorded 1.25-fold increase in biomass, while the control group recorded 1.45-fold increase in 30 days. No significant erythrocyte morphological alterations were observed in the 1 × group compared to the control. However, marked morphological alterations like tear-shaped, spindle-shaped and degenerative erythrocytes in higher dosing groups indicated FFC cytotoxicity. All the serum biomarkers of O. niloticus increased significantly on day 10 and day 30 FFC dosing in a dose-dependent manner, except for calcium and chloride, which reduced significantly during the dosing period. Within 2 weeks of suspension of FFC dosing, the serum biomarker levels became normal except for alkaline phosphatase and creatinine. The recovery of biomass, feed intake, serum biomarker levels and erythrocyte morphological changes suggested that the FFC-induced changes are reversible. This study has, thus, proclaimed the safety of FFC at the therapeutic dose in O. niloticus.