Bacterial drug resistance is becoming an increasingly serious problem, and the development of antibacterial synergists is urgently needed. Combining existing antibiotics with promising nonantibiotic agents is one strategy that has been shown to be effective at overcoming the widespread emergence of antibiotic-resistant pathogens. In this study, we investigated the antibacterial activities and mechanism of naringenin (NG) combined with amikacin (AMK) against multidrug-resistant Escherichia coli (E. coli). We first measured the fractional inhibitory concentration (FIC) of NG combined with antibiotics via the checkerboard method. The results indicated that the combination of NG and AMK had a synergistic effect on E. coli ATCC 25922 and E. coli C7F3. In addition, this synergistic effect was verified by time-kill assays. Moreover, scanning electron microscopy (SEM) was used to observe cell morphology. The results showed that the cell wall of E. coli was destroyed. Furthermore, we assessed the leakage of alkaline phosphatase (AKP), K⁺, and protein. The extracellular AKP activity increased after the combinational group of 1/2MIC NG and 1/2MIC AMK, suggesting an impairment in cell wall permeability. An increase in the leakage of intracellular K⁺ and protein indicated an increase in cell inner membrane permeability. These results revealed that NG and AMK inhibited E. coli by damaging cell walls and membranes. In addition, PI uptake rapidly increased after treatment with NG and AMK. Confocal laser scanning microscopy (CLSM) revealed that NG caused cell wall and cell membrane damage in E. coli. In summary, our results provide a new strategy for responding to the development of E. coli drug resistance.

Antibiotic resistance genes (ARGs) have become recognized contaminants and pose a high public health risk. The animal gut microbiota is a reservoir of ARGs, but the knowledge of the origin and dissemination of ARGs remains unclear. In this study, we provide a comprehensive profile of ARGs and mobile genetic elements in the gut microbiota from 30 bovines to study the impact of modern antibiotics on resistance. A total of 42 ARG types were detected by annotating the metagenomic sequencing data from Comprehensive Antibiotic Resistance Database (CARD). We found that the diversity and abundance of ARGs in individual yaks were significantly lower than those in dairy and beef cattle ( p < 0.0001). The results of heat map and single nucleotide polymorphism clustering suggest that ARGs from dairy and beef cattle are more similar, whereas those from yaks cluster separately. The long-term use of antibiotics may contribute to this difference, suggesting that antibiotic consumption is the main cause of ARG prevalence. Furthermore, abundant insertions were also found in this study, signifying a strong potential for horizontal transfer of ARGs among microbes, especially pathogens.

This study aimed to investigate the effects of dietary riboflavin levels on the reproductive performance of pigeon breeders and the growth performance and carcass traits of offspring squabs to estimate the riboflavin requirement of pigeon breeders. The natural riboflavin content in the basic diet of corn–peas–soybean–wheat–sorghum–corn gluten is 1.20 mg/kg. Different doses of riboflavin (0, 2.5, 5, 10, and 15 mg/kg) were supplemented with the basal diet to produce five dietary treatments with total riboflavin levels of 1.20, 3.70, 6.20, 10.20, and 16.20 mg/kg. A total of 120 pairs of White King pigeons, aged 60 wks, were randomly allocated into five treatment groups, each consisting of 24 pairs. Each pair was individually raised for 8 wks. After the experiment, an assessment was conducted to evaluate the reproductive performance of the pigeon breeders, as well as the growth and carcass traits of offspring squabs at 28 days of age. The results showed that the dietary riboflavin levels had no significant effect on body weight, feed intake, egg weight, egg production, and egg fertility (p > 0.05). However, pigeons fed a diet without riboflavin had the lowest egg hatchability, egg yolk color, carcass trait, and riboflavin status, while exhibiting higher liver weight and liver index (p < 0.05). Moreover, the indices above showed increased or decreased linearly as the level of riboflavin was increased in the diet. Based on the broken-line regression model, pigeon breeders were determined to require a dietary riboflavin content of 11.4, 13.6, 13.4, 6.60, 4.28, 4.47, 4.67, 6.69, and 6.82 mg/kg to optimize hatchability, eviscerated weight, half-eviscerated weight, breast muscle weight, breast muscle percentage, liver weight, liver index, egg yolk riboflavin, and squab plasma riboflavin, respectively. In conclusion, the optimal supplemental dosage of riboflavin in the diets of pigeon breeders is 13.6 mg/kg.