Baicalin inhibits Escherichia coli isolates in bovine mastitic milk and reduces antimicrobial resistance

摘要

ABSTRACTIn this study, we aimed to evaluate the inhibitory effect of baicalin onEscherichia coliin vitro and the effects of baicalin treatment on antimicrobial resistance of theE. coliisolates. Through isolation, purification, and identification, a total of 56E. colistrains were isolated from 341 mastitic milk samples. The study of inhibition effect of baicalin on theE. colistrains in vitro was focused on permeability and morphology of the isolates using an alkaline phosphatase kit and scanning electron microscopy. Furthermore, the resistance spectrum of the isolates to the common antimicrobial agents was tested at sub-minimum inhibitory concentrations of baicalin by the agar dilution method. Extended-spectrum β-lactamase and plasmid-mediated quinolone resistance genes were amplified by PCR before and after incubation with baicalin. The results revealed that baicalin has certain inhibitory effects on the isolates in vitro. The alkaline phosphatase enzyme activity was significantly increased from 1.246 to 2.377 U/100 mL, and the surface ofE. coliwas concave and shriveled. Analysis of the resistance spectrum and PCR amplification showed that, after administration with baicalin, the sensitivity of most strains to the selected antimicrobial agents was enhanced. Strikingly, the drug-resistant genes from 71.43% (40/56) of these isolates were found to have drug-resistant genes to different extents. Altogether, the current study confirmed both the inhibitory effect onEscherichia coliin vitro and the reduction of antimicrobial resistance by baicalin. This is the first comprehensive study to report on baicalin, a traditional Chinese medicine that acts onE. coliisolated from the mastitic milk samples.