Drug Resistance Analysis And Dissemination Of Methicillin-resistant Staphylococcus Aureus In Fresh Milk Production

Methicillin-resistant Staphylococcus aureus(MRSA)is one of the important pathogens causing food-borne infections in raw milk production.The bacterias are widely present in the dairy farming environment,and the cow’s milk is polluted by various means,which seriously endangers the health of humans and animals.In this study,the air,enclosure fence,cow nasal cavity,anus,nipples,feed,feces,milking machine,cow milk and the air samples in the surrounding residential areas of a dairy farming community in Shanxi Province were collected with the AGAR plate of 5% sheep blood as the sampling matrix.MRSA was screened by bacterial isolation,staining microscopic examination,selective purification culture,conserved sequence analysis of 16 S rRNA,MRSA phenotype identification and mecA gene amplification detection.Its sensitivity and drug resistance distribution to 14 kinds of antibiotic drugs were determined.mecA gene sequence alignment and ERIC-PCR fingerprint analysis technology were used to analyze the genetic similarity of MRSA in the production of fresh milk,and to explore the drug resistance and distribution characteristics of MRSA in various stages of fresh milk production,so as to provide a basis for the safe production of fresh milk.The results show:1.In the production process of fresh milk,721 samples were collected and 184 strains of staphylococcus aureus were isolated,with an average detection rate of 25.5%,including 42.9% fresh milk,22.4% milking workshop,18.5% farm environment and 31.8% air in surrounding residential areas.2.94 strains of MRSA phenotype resistant strain and 90 mecA gene positive strains were identified from 184 strains of Staphylococcus aureus.The detection rate of MRSA was 48.9%.The detection rate of cattle environment,utensils and cattle anus was 90.% ～ 52.6%,the detection rate of the environment,utensils and nipples in the milking room was 47.1%～62.5%,the detection rate of milk was 32.9%,and the air detection rate in the residential areas around the farm was 49.5%.3.MRSA showed different degrees of drug resistance and multi-drug resistance at each sampling point.Among them,penicillin G had the most serious drug resistance,and the drug resistance rate was 95.6%.Secondly,the resistance rates of rifampicin,clindamycin,nitrofurantoin and erythromycin were higher,and the drug resistance rates were respectively 95.6%,89%,86.8%,84.6%and80.2%.The multi-drugresistance rate was 98.9%(89/90),and the number of multi-drug resistant species was mainly concentrated between 6 and 8 resistance.4,mecA gene sequence alignment,according to the sampling points of MRSA mecA resistance gene homology was 95.22%,according to the homologous relationship is divided into five major branches,of which 2 seedlings respectively with cow nipple,cow milk to detect nasal mecA resistant gene sequence homology is above 99%,homologous relationship respectively corresponding to two branches,3 strains emulsion separation and air,milking machine,milking workshop homology is above 98%,and the homologous relationship is on the same branch.The MRSA in milk is derived from the cattle farm environment and the milking plant.5.ERIC-PCR homology analysis showed that the DNA fingerprinting similarity of 90 strains was between 52% and 100%,divided into 4 branches by 65%.Among them,the MRSA isolates in the milk have more than 90% homology with the cattle farm environment(15 strains),the milking workshop environment(3 strains),and the residential area(1 strain).The homology between the feed and the bovine body(4 strains),the cattle sports field air(1 strain),the milk and the milking environment(4 strains)is over 90;and the homology of the fence(6 strains)with the cattle is more than 90%;The milking room(6strains)has more than 90% homology with the bovine nasal cavity and anus,and the homology of the residential air(2 strains)with the bovine nipple is more than 85%;The genetic relationship of 1 MRSA from bovine nasal cavity resistance genes is far from other environments,but the homology with one feed isolate is more than 90%,and the homology with the two isolates is more than 85%;The genetic relationship is in the same branch;suggesting that MRSA in the environment inside and outside the cattle field can be spread by bovine body and air aerosol,polluting raw milk.