Study On Drug Resistance And Molecular Characteristics Of Animal-derived Staphylococcus Aureus

ObjectiveRoutine and non-therapeutic overuse of antibiotics in animal breeding can promote the reproduction of animal-related methicillin-resistant Staphylococcus aureus(MRSA).As one of the important pathogens of foodborne diseases,MRSA can spread to humans through the food chain or in close contact with animals,causing serious public health problems.This study aimed to examine the detection rate of Staphylococcus aureus(S.aureus)and MRSA in the nasal cavity of pigs,and to analyze the phenotypes and molecular characteristics of the isolates,so as to provide scientific basis for preventing and controlling the epidemics and spread of animal-related MRSA.MethodsAccording to cross-sectional study,nasal swabs were collected from 1,458 pigs in nine pig farms and three slaughterhouses.All S.aureus were tested for antimicrobial susceptibility,resistance genes and virulence genes were detected by PCR test,and molecular typing was performed by multilocus sequence typing(MLST).The correspondence analysis was conducted to explore the potential association between molecular typing and phenotypic-gene characteristics of S.aureus isolates.ResultsIn the 1,458 pigs,the detection rate is 9.5%(139/1458)for S.aureus and 3.3%(48/1458)for MRSA.Notably,97.1% S.aureus isolates were multidrug resistant,and the predominant resistance pattern was non-susceptible to clindamycin,tetracycline,erythromycin and trimethoprim-sulfamethoxazole.The main genotype of S.aureus and MRSA isolates was CC9(ST9).It is note that all S.aureus were negative for the scn gene and were resistant to tetracycline.Comparison of drug resistance phenotypes and molecular characteristics between S.aureus CC9 and non-CC9 isolateds,there were significant differences in prevalence of antibiotics resistance(clindamycin,tetracycline,erythromycin,trimethoprim-sulfamethoxazole,rifampicin and linezolid),resistance genes(erm(C),aacA-aphD,aadD,tet(K)and erm(A))and virulence genes(seg,sem,seo,sep and ebpS)between S.aureus CC9 and non-CC9 isolates.And there were significant differences in prevalence of resistance genes(tet(M)and tet(K))and virulence genes(sem,seo,sep and spa)between MRSA CC9 and non-CC9 isolates.The corresponding analysis showed that there was significant relationship between molecular type,antibiotic resistance patterns and virulence genes.CC398 was associated with PDR;CC9(ST9,ST2931 and ST2454)was associated with XDR;CC1(ST1),CC5(ST920),CC8,CC12 and CC97 isolates were associated with MDR.ST2931,ST920,ST2454,ST1,ST2359 and ST2269 were associated with the seh gene,ST9 was associated with multiple enterotoxin genes;ST2931 was associated with the hlb gene,ST2454 and ST2269 were associated with the hla gene,ST2358 and ST2359 were associated with two hemolysin genes(hla and hlb),ST1 and ST9 were associated with three hemolysin genes(hla,hlb and hld).Conclusions(1)The proportion of MDRSA was as high as 97.1%.The predominant resistance pattern of S.aureus was non-susceptible to clindamycin,tetracycline,erythromycin and trimethoprim-sulfamethoxazole,suggesting that it is necessary to dynamically monitor the trend of the prevalence of multidrug resistant isolates and its potential threat to the occupational animal contact population in the future.(2)Correspondence analysis revealed that there is a significant correlation between CC types(ST types)and phenotype-molecular characteristics of S.aureus,which provides some inspiration for the development of related vaccines and new ideas for monitoring new epidemic trends of S.aureus.(3)The results of this study indicated that scn gene negative may be a specific molecular marker of animal-related CC9 isolates,and tetracycline resistance may be a specific phenotypic marker of animal CC9 isolates.