Identification Of An Anti-MRSA Actinomycetes And Preliminary Analysis Of Antibacterial Metabolite

Methicillin-resistant Staphylococcus aureus(MRSA)is an important pathogen,it can cause hospital infections and its drug resistance is strong.Since its discovery,it spreads faster and faster,and seriously affecting human health because of the drug resistance of the MRSA.So the prevention and treatment of the MRSA has become the focus of attention of all countries in the world.Actinomycete is a kind of important microorganisms,it is closely related to human and it can produce a large number of antibiotics.This paper is to study the actinomycetes which have antagonistic activity to the MRSA and it is isolated from soil of Danzhou City of Hainan Province in order to find a new effective anti-MRSA substance.A total of 240 actinomycetes were isolated from the soil on Gause No.1 medium(GAU)containing 70 ?g/mL K2Cr2O7.Through primary screening,4 strains of actinomycetes with antagonistic activity to the MRSA were obtained.One strain,KM1,whose anti-MRSA activation was very strong and the diameter of inhibition zone reached 20 mm or more,which was choosed as target strain for the deeper research.Based on 16S rDNA and phylogenetic tree,the KM1 strain was the most similar of 99%to Streptomyces durhamensis,and then,we found that the KM1 strain has most of the same characteristics of Streptomyces durhamensis combined with the cultural characteristics,morphology,physiological and biochemical propertices.Therefore,the KM1 strain was proposed as Streptomyces durhamensis.Using different plant pathogens to test the antimicrobial spectrum of the KM 1,the result is that the KM1 has the effect on most of the Colletotrichum gloeosporioides,and has no effect on the Fusarium oxysporum f.sp.cubense.By choosing the different culture medium for fermentation of the KM1,we found the fermentation broth of liquid of Gau's has best activity on the MRSA,whose diameter of inhibition zone reached 24.8mm.By analyzing the stability of the fermentation broth of the KM1 was extracted with ethyl acetate and the crude extract of the active substance is obtained by reducing pressure concentration,the results show that the KM 1 active material crude extract has a good stability between 20 ? and 120?,it still has antibacterial activity to the MRSA after placing at 120? for 30 minutes,UV irradiation has little influence on it,pH has great influence on the crude extract of the active substance,there was no antibacterial activity under the condition of 2.0-3.0 pH and 7.0-12.0 pH,there was antibacterial activity under the condition of 4.0-6.0 pH and there was no obvious change in the inhibition zone compared with the blank control.The conclusion is that the stability of the crude extract of the active substance was good when it under the condition of 4.0-6.0 pH.