Study On Antibiotic Resistance And Related Resistance Genes Of Enterococcus Isolates From Natural Fermented Food

As common lactic acid bacteria,Enterococci are gastrointestinal commensal bacteria in human and other animals.Meanwhile,Enterococci are also common in fermented dairy products,meat products and sausages and play an important role in fields of food fermentation.However,as some strains of Enterococci are opportunistic pathogen,the safety has not been generally accepted.Research on antibiotic resistance of Enterococci mainly focused on intestinal and pathogenic strains,but rare studies on natural fermented food isolates.In this study,the antibiotic resistance of 81 Enterococci(65 E.faecium and 16 E.faecalis)was detected with 15 common antibiotics by micro broth dilution method.Then the genome-wide association study(GWAS)was applied to find the potential antibiotic resistance genes of Enterococci by PhenoLink and Scoary.The results were showed as below:(1)The 65 strains of E.faecium were 100% sensitivity to ampicillin and linezolid,but 86.7% resistance to clindamycin.In addition,the different degrees of antibiotic resistance to other antibiotics were showed in E.faecium.(2)The 16 strains of E.faecalis were 100% sensitivity to kanamycin,vancomycin,linezolid and erythromycin,but 100% resistance to clindamycin.In addition,the different degrees of antibiotic resistance to other antibiotics were showed in E.faecalis.(3)The genome-wide association study using PhenoLink found nine potential antibiotic resistance genes,which were significantly correlated with the antibiotic resistance of five antibiotics(chloramphenicol,trimethoprim,streptomycin,tetracycline and ciprofloxacin).(4)The genome-wide association study using Scoaryfound 123 potential antibiotic resistance genes,which were significantly correlated with the antibiotic resistance of nine antibiotics(chloramphenicol,trimethoprim,streptomycin,tetracycline,ciprofloxacin,ampicillin,neomycin,quinupristin-dalfopristin and rifamycin),the former five antibiotics of which were same with the results of Phenolink.(5)A total of nine potential antibiotic resistance genes were found in this study.Genes FAM000296 and FAM005768 were related to the resistance of chloramphenicol,trimethoprim and ciprofloxacin.FAM000296 with chloramphenicol have positive related and with trimethoprim and ciprofloxacin have negative related.FAM005768 with chloramphenicol have negative related and with trimethoprim and ciprofloxacin have positive related.Interestingly,both the FAM000296 and FAM005768 encode secG.Compared to FAM000296,FAM005768 lost 21 bases at the 5' end of the DNA sequence.This deletion mutation are likely to be the cause of opposite effect on the same antibiotic drug resistance in strains.In addition,the gene FAM002893 encode EF-G,it is closely related to the resistance of tetracycline.In summary,these results showed Enterococci isolated from natural fermented food were resistant to many antibiotics.MIC of E.faecium was wider than that of E.faecalis.In addition,E.faecalis carries potentially antibiotic resistant genes in its genome.Therefore,safety assessment of Enterococcus was strongly recommended before use in food products.