| The research of the safe,high efficient and innovative veterinary drugs is the essential measure to treat animal diseases and deal with the problem of drug resistance.Faced with the huge shortage of the special and effective antibacterial drugs for animal in clinic,we designed,synthesised and screened two hybrid compounds OBP-1 and OBP-2,which exhibited the exactly activity against bacteria,multi-drug resistant bacteria and the mechanism of action of mutitarget.In this paper,we researched the oral acute toxicity in mice,the antibacterial spectrum in vitro and the antibacterial mechanism of action of OBP-1and OBP-2 to further discuss the safety and antibacterial activity of OBP-1 and OBP-2.The oral acute toxicity test of OBP-1 and OBP-2 in mice were carried out by the simplify Karber’s Method.The result showed the LD500 of OBP-1 and OBP-2 were all high than 10 g/kg,the visibly adverse reaction and death of the mice were not found,According to the chemical toxicant classification,OBP-1 and OBP-2 were actually no toxic.The broth microdilution method was used to measure the minimal inhibitory concentration（MIC）of the new compounds.The result demonstrated that OBP-1 and OBP-2 possessed highly active against Gram-positive bacteria including Linezolid/quinolone/Vancomycin resistant strains（MIC≤0.5μg/ml）,and had no cross-resistance.OBP-1 and OBP-2 also exhibited some activity against certain Gram-negative species（1-4μg/ml）.Time-kill curve was performed to identify the interactions between the OBP-1/2 and bacteria,the result indicated that OBP-2 killed bacteria by the concentration dependent manner,however,the OBP-1 was by the non-concentration dependent manner.The effects of OBP-1 and OBP-2 on process of DNA replication（Gyrase,Topo IV）and protein synthesis were used to evaluate the mechanism of action of OBP-1 and OBP-2.DNA gyrase and topoisomerase IV（topo IV）inhibition assays indicated OBP-1 exhibited better activity against DNA gyrase(IC50,1-5μM)compared with topo IV(IC50,10-15μM),while OBP-2 had only the weak effect on DNA gyrase(IC50,20μM)and had no effect on topo IV.For protein synthesis,OBP-2 had a strong inhibitory activity with IC500 of 2μM,which was obviously strong than OBP-1 and linezolid,the IC500 of OBP-1 and linezolid were both 5μM.In conclusion,OBP-1 showed the activity against bacteria by the effect on gyrase,topo IV and protein synthesis,and OBP-2 exhibited the activity against gyrase and protein synthesis.In conclusion,two compounds OBP-1 and OBP-2 were actually no toxic.OBP-1 and OBP-2exhibited well activity against Gram-positive bacteria and multi-resistance Gram-positive bacteria,and the cross-resistance was not found.OBP-1 and OBP-2 killed bacteria by the non-concentration dependent manner and the concentration-dependent manner,respectively.Besides,OBP-2 showed the potent activity against protein synthesis,while OBP-1 preferred to select DNA gyrase and protein synthesis as the primary targets.This work may offer potential for OBP-1 and OBP-2 as the antibacterial candidate drugs. |
