Antibacterial Activity Of Two Pleuromutilin Derivatives Against MRSA And Their Pharmacokinetics In Mice

Methicillin resistant Staphylococcus aureus（MRSA）is a facultative anaerobic bacteria or aerobic bacteria,and its growing environmental requirements is not high and easy to survive because the strains can produce many toxic proteins,including enterotoxin the white blood cells-killing and exfoliative toxins,etc,which will cause acute blood poisoning and food poisoning.MRSA methicillin-resistant Staphylococcus aureus（MRSA）is widely found in the natural environment,and can also cause a variety of zoonotic diseases such as public health safety,necrotizing pneumonia and toxic shock syndrome.The Pharmacology Laboratory of South China Agricultural University,synthesized a series of new pleuromutilin derivatives,the new drug pleuromutilin derivatives,WL-18 and WL-20 have good antibacterial activity against MRSA,compared to the pleuromutilin drug Mycomycin has improved its chemical structure.This paper further analyzes the improved antibacterial effect and pharmacokinetics of WL-18 and WL-20,and discusses the drug potential of these two new synthetic antibacterial compounds.In this study,the minimum inhibitory concentration（MIC）of compound WL-18 and compound WL-20 against MRSA was measured by micro-broth method.The MICs of compound No.18 and compound WL-20 were 0.06μg/m L and 0.03μg/m L,respectively.The antibacterial effect of 1h,2h and the bactericidal curve of the two compounds can be designed and tested by using the MIC.The results showed that the 4 MIC of compound WL-18 applied to MRSA at 1 h and 2 h is 2.05 h and 3.47 h,respectively.The 4 MIC of compound 20 were 1.23h and 2.58h respectively.The bactericidal effect showed that the two new drugs synthesized were inhibited by the growth of MRSA over time,and the concentration of inhibition started was different.The cytotoxicity test of compound WL-18 and compound WL-20 and the acute toxicity test in mice were carried out to verify whether the newly synthesized drugs will accumulate toxicity in animals.The results showed that the IC₅₀is almost the same of WL-18 and WL-20,and tiamulin exist in the cell experiment.In vivo antibacterial efficacy of WL-18 and WL-20 on MRSA was studied in the mice thigh infection model and the mice peritonitis model.The results showed that the 30 mg/kg dose of WL-18,WL-20 and tiamulin in the thigh muscle of mice infected with bacteria achieved 50%,10%and 20%against immunosuppressive mice with intraperitoneal infection of MRSA.WL-18 and WL-20 at a dose of 30 mg/kg could significantly reduce the amount of bacteria in the thigh muscle of mice infected with MRSA,and the effect was better than that of tiamulin at the same dose.High performance liquid chromatography-tandem mass spectrometry（HPLC-MS/MS）was used to detect the pharmacokinetics of compound WL-18 and compound WL-20,and the detection method was also constructed.The pharmacokinetics was studied after intravenous administration and treatment of mouse serum.The main pharmacokinetic parameters of the compound WL-18 were T_1/2:0.06±0.004 h,AUC₀-_t:0.47±0.12μg·h/m L,MRT:0.09±0.01 h;the main pharmacokinetic parameters of the compound WL-20 were T_1/2:0.08±0.01 h,AUC_0-t:0.52±0.02μg·h/m L,MRT:0.09±0.02 h.