Avilamycin

Avilamycin, an excellent growth-promoting feed additive, produced by Streptomyces viridochromogenes, was widely used to promote the growth of poultry by inhibiting Gram-positive bacteria. In this work, the methods of combinational mutagenesis of UV (Ultraviolet) and ARTP (Atmospheric and room temperature plasma), and rational screening by high concentrations of CaCl2 were utilized to promote the production of avilamycin. The avilamycin high-yielding mutant strains of Z-6 (29.31 mg/L), A-9 (36.84 mg/L) and F-23 (45.73 mg/L) were screened out, with yields of avilamycin improved by 57.92%, 98.49% and 146.39%, respectively, compared with the wild strain (WT). The performance comparison showed that Z-6, A-9 and F-23 mutant strains had stronger abilities of substrate consumption, cell growth and antibiotic synthesis than WT. Furthermore, the composition of fermentation medium, inoculation parameters, supplementation strategies of oxygen vectors, glucose and precursors (L-valine, D-xylose and sodium acetate) had been optimized and the avilamycin yield of the mutant strain F-23 was significantly enhanced by 41.87% by fermentation optimization. In summary, the strategy of increasing the production of avilamycin in S. viridochromogenes in this work might provide an alternative method to enhance the synthesis of secondary metabolites in other Streptomyces.

The mechanisms by which antibiotic growth promoters (AGP) enhance growth rates, feed efficiencies, and disease resistance in poultry need to be understood for designing safer and alternative strategies to replace AGP. Avilamycin has been widely used as an AGP in poultry, but its impact on the structure and function of the gut microbiome of broiler chickens has not been fully elucidated. In this study, we investigated the bacterial communities of the ileum and cecum in broiler chickens fed with an avilamycin-supplemented diet, by high-throughput sequencing of bacterial 16S rRNA genes. Alpha diversity metrics indicated that the ileal bacterial diversity was higher in avilamycin-fed chickens than in the control group, whereas the opposite was true for the cecum. Multivariate analyses revealed that the ileal microbiota of the avilamycin-fed group were clearly distinguished from those of the control group, whereas the cecal bacterial communities were apparently not influenced by feeding diets containing avilamycin. In the ilea, 2 operational taxonomic units (OTU) that matched Lactobacillus reuteri and Clostridium were enriched (P = 0.016 and P = 0.007, respectively) in the avilamycin-fed group, and an OTU belonging to Lactobacillus crispatus was decreased (P = 0.016). In the cecal microbiota showing much higher diversity with 1,286 non-singleton OTU, 12 OTU were decreased, and 3 were increased in response to avilamycin treatment (P = 0.005-0.047). Functional profiling of bacterial communities based on PICRUSt analysis revealed that 10 functional categories were enriched by avilamycin treatments, and 4 functional categories were decreased. In conclusion, our results demonstrated that the influence of avilamycin supplementation on the diversity, taxonomic composition, and functional profiles of the microbiota was evidently different in the ileum and cecum. These results further our understanding of the impact of AGP on the composition and activity of commensal bacteria in the chicken gastrointestinal tract to develop novel feeding strategies for improving animal health and performance.

Clostridium perfringens causes significant morbidity and mortality in swine worldwide. Avilamycin showed no cross resistance and good activity for treatment of C. perfringens. The aim of this study was to formulate optimal regimens of avilamycin treatment for C. perfringens infection based on the clinical breakpoint (CBP). The wild-type cutoff value (COWT) was defined as 0.25 μg/ml, which was developed based on the minimum inhibitory concentration (MIC) distributions of 120 C. perfringens isolates and calculated using ECOFFinder. Pharmacokinetics-pharmacodynamics (PK-PD) of avilamycin in ileal content were analyzed based on the high-performance liquid chromatography method and WinNonlin software to set up the target of PK/PD index (AUC0-24h/MIC)ex based on sigmoid Emax modeling. The PK parameters of AUC0-24h, Cmax, and Tmax in the intestinal tract were 428.62 ± 14.23 h μg/mL, 146.30 ± 13.41 μg/ml,, and 4 h, respectively. The target of (AUC0-24h/MIC)ex for bactericidal activity in intestinal content was 36.15 h. The PK-PD cutoff value (COPD) was defined as 8 μg/ml and calculated by Monte Carlo simulation. The dose regimen designed from the PK-PD study was 5.2 mg/kg mixed feeding and administrated for the treatment of C. perfringens infection. Five respective strains with different MICs were selected as the infection pathogens, and the clinical cutoff value was defined as 0.125 μg/ml based on the relationship between MIC and the possibility of cure (POC) following nonlinear regression analysis, CART, and "Window" approach. The CBP was set to be 0.25 μg/ml and selected by the integrated decision tree recommended by the Clinical Laboratory of Standard Institute. The formulation of the optimal regimens and CBP is good for clinical treatment and to control drug resistance.