The Antibacterial Activity Of Phenyllactic Acid Combined With Feed Antibiotics And The Influence Of Intestinal Flora In Mice

D-(+)-3-Phenyllactic acid(PLA)is novel natural substances found in recent years.It has broad-spectrum antibacterial properties,not only can inhibit gram positive and gram negative bacteria,but also can effectively inhibit a variety of funguses.In this paper,the antibacterial activity of PLA combined with common feed antibiotics was studied,in order to reduce the cost and the dosage of PLA.At the same time,the combined use can decrease the doses of some feed antibiotics,provide a more secure method for the control of pathogens.The Staphylococcus aureus(S.aureus)ATCC 25923 and Bacillus cereus were used as indicator bacteria.The minimal inhibitory concentrations(MIC)were determined by broth micro-dilution method and the interaction of PLA with fifteen kinds of feed antibiotics was determined using the checkerboard test,furthermore,the optimal ratio in the synergistic combination was further investigated by Time-kill curve.The results showed that only chlortetracycline hydrochloride could synergy with PLA against S.aureus.Time-kill curve showed that the combination of 1/4MIC PLA+1/2MIC chlortetracycline hydrochloride combined with S.aureus ATCC 25923 had the best antibacterial effect.Two kinds of organic acids,Chlortetracycline hydrochloride and Ampicillin,which could produce synergistic effect with PLA against Bacillus cereus were screened.Time-kill curve showed that the combination of 1/8MIC PLA+1/4MIC chlortetracycline hydrochloride and the combination of 1/2MIC PLA+1/4 MIC Ampicillin combined with Bacillus cereus had the best antibacterial effect.The intestinal microflora of mice was analyzed by 16 S rDNA high-throughput sequencing.The results showed that PLA and chlortetracycline hydrochloride all affect the intestinal microflora structure of mice,The chlortetracycline hydrochloride group reduced the diversity of intestinal flora in mice,and the other groups increased the intestinal flora diversity.1/2MIC PLA+1/4MIC chlortetracycline dose group and 1/4MIC PLA+1/4MIC chlortetracycline dose group increased S24-7 and other dominant bacteria and promoted the growth of mice.Through the determination of blood physiological and biochemical indexes of each treatment group,the results showed that chlortetracycline hydrochloride dose group reduced the immune cells of mice and TP,ALB and ALT were lower than the control group and BUN was higher than the control group.PLA dose group increased the number of immune cells in mice.1/2MIC PLA+1/4MIC chlortetracycline dose group and1/4MIC PLA +1/4MIC chlortetracycline dose group increased the number of white blood cells,lymphocytes,red blood cells,hemoglobin.ALB was significantly higher than the control group.BUN and ALT levels were lower than the control group.Each treatment group mice immune factor was lower than the control group,but the difference was not significant.