| With the abuse of various antibiotics,the superbacteria continually emerged.As a superbacteria,methicillin-resistant Staphylococcus aureus(methicillin-resistant Staphylococcus aureus,MRSA)has become one of the common pathogens of zoonosis.In this study,Chrysanthemum essential oil(CHEO)was used as an antibacterial agent to explore its antibacterial mechanism against MRSA and its application in raw meat.It provided new ideas for the development of natural antibacterial preservatives.The main research results were as follows:(1)The four main components in CHEO were borneol(19.55%),?-saurene(16.25%),dipthrone(13.48%)and levodolactonide(8.22%).The MIC and MBC of 10 kinds of pathogenic bacteria were determined by the multiple dilution method,results showed that CHEO had broad-spectrum antibacterial properties,the MIC and MBC for MRSA were 2.5 mg/ml and 5 mg/ml,respectively.According to the DPPH·free radical experiment,the free radical scavenging rate of CHEO can reach to 52.42%.At the same time,CHEO can cause bacteria to coagulate and die by increasing hydrophobicity of the surface of cells and reducing the surface charge of cells.After CHEO(1 / 2 MIC,MIC and 2MIC)treatment,the OD260 value of the bacterial liquid increased by 0.121,0.190 and 0.335,respectively;the conductivity increased by 97.53%,98.03% and 98.36% after 1 hour of treatment.The protein band content was significantly reduced.(2)The results of the resazurin experiment showed that the percentage of MRSA with metabolic activity decreased with the increase of essential oil concentration.Iodoacetic acid,malonic acid and sodium phosphate were three typical inhibitors of EMP pathway,TCA pathway and HMP pathway,respectively.The superposition rates of three inhibitors on CHEO are 20.45%,38.64% and 36.36%,respectively,with the smallest superposition rate of iodoacetic acid.The above result indicated that CHEO inhibit bacterial respiratory metabolism through the EMP pathway,and this conclusion was verified by measuring three key enzyme activities in the EMP pathway.When the ATP content was significantly inhibited by CHEO inhibition,the corresponding ATPase showed a significant downward trend.Within 4 hours,the expression activities of AKP and ?-galactosidase decreased with time due to inhibition of MRSA growth.(3)By measuring intracellular DNA content and intracellular nucleic acid fluorescence intensity,it was found that DNA synthesis in MRSA was inhibited by CHEO,and its content was significantly decreased(P<0.05).The preliminary study showed that CHEO could not affect the supercoiled density of DNA in bacteria by inhibiting the activity of topoisomerase.CHEO had a significant effect on the expression level of pvl gene(P<0.05)and showed a concentration dependence of CHEO.The relative expression levels of pvl gene of the groups(MIC,1/2 MIC,1/4 MIC,and 1/8 MIC)were 12.31%,35.24%,63.64%,and 80.18%,respectively,which indicated that CHEO can reduce the production of PVL invasive hormone thus inhibited the harmfulness of MRSA by inhibiting the expression of pvl gene.(4)Chicken,pork and beef were used as the representative meat products infected by MRSA to study the antibacterial and fresh-keeping effect of CHEO on the storage and preservation of meat products.The number of residual bacteria and the total number of colonies proved that CHEO can inhibit the proliferation of MRSA and other microorganisms in meat.The three physical and chemical indicators including MetMb%,pH value and SEA content indicated that CHEO can slow down the rate of lipid oxidation and reduce the content of harmful substances,thereby maintaining the quality of the meat for a certain period of time.Chroma evaluation and texture analysis showed that the CHEO did not have a negative impact on meat products,and can effectively maintain the appearance color of meat,which exhibited a great potential in meat storage applications. |
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