The Research On The Resistance And Dissemination Of Methicillin-resistant Staphylococcus Aureus In Mutton Production

Methicillin-resistant Staphylococcus aureus(MRSA)is a major pathogenic bacterium in the meat production,which largely exists in breeding environments and can infect humans through the food chain,causing serious public health problems.This study investigated a fattening sheep farm and a designated slaughtering room of this farm in Shanxi Province.5% sheep blood agar medium was used as sampling medium.The samples included the air inside and outside sheep houses,swabs from fences,appliance,nasal cavity,feces,sheep feeds,air in slaughtering room,slaughter appliance,sheep carcass,swabs from nasal cavity of slaughter and sewage of slaughtering room.MRSA was detected and screened through isolation and culture of MRSA,16 S r DNA identification,oxacillin and cefoxitin susceptibility disk test and mec A gene amplification,then determining its susceptibility to 14 antibiotics.The genetic similarity of MRSA was compared by ERIC-PCR fingerprint and mec A gene sequence.The aim of this study was to explore the resistance and distribution pattern of MRSA in each link of mutton production.The results showed that:(1)A total of 752 samples were collected from each link of breeding and slaughtering,and 160 strains of Staphylococcus aureus were isolated and identified,with isolation rate of 21.28%.The isolation rate of samples in sheep houses,slaughtering and swabs from sheep carcass was 29.69%,14.68%(48 positive strains)and 25% respectively.(2)According to K-B and PCR method,82 mec A-positive MRSAs were screened from 160 Staphylococcus aureus strains,the detection rate was 51.25%.The detection rate of MRSA in sheep houses,slaughter room and sheep carcass was 33.33%-64.29%(with the highest of the air inside sheep houses),22%-66.67%(with the highest of sewage and swabs from nasal cavity swabs)and 60.71% respectively.(3)The susceptibility of MRSA to 14 antibiotics was determined according to CLSI standard.The drug resistance of MRSA from different sampling sites was different.Among them,the resistance rate to penicillin was the highest,almost 98.78%.Other drugs: compound neotamine,rifampicin,clindamycin,tetracycline and streptomycin(52.44%-84.15%),gentamicin,cefotaxime and doxycycline(19.51%-43.90%.),ciprofloxacin was the lowest(7.32%).No vancomycin-resistant Staphylococcus aureus was found.In this study,the multiple drug resistance rate of MRSA was 92.68%.MRSA isolated from sheep house,slaughtering room and mutton showed similar trend in the proportion of drug-resistant strains to penicillin,cefotaxime,ciprofloxacin,streptomycin,compound neotamine and chloramphenicol.(4)The homology analysis of MRSA gene was performed after ERIC-PCR.There were 15 genotypes and the genetic similarity coefficient among the strains was higher than 75%,6 of which were identified as6 genotypes and the MRSA isolated from sheep houses was the main epidemic clone.Some strains were selected for mec A gene sequencing,and the similarity of resistance gene was more than 96%.The drug resistance gene of isolates at each link was highly similar,which suggests that MRSA is disseminated in a cross way during mutton production.