Clinical Risk Factors Analysis And Resistance Mechanism Study Of Linezolid-nonsusceptible Enterococcus

Background:Linezolid is an oxazolidinone antimicrobial agent,has been used for treatment of complicated Gram-positive infection.In 2000,linezolid was approved by the American Food and Drug Administration(FDA)and in 2007,it was allowed to be used in Chnia.Linezolid is considered to be effective for treating infection of VRE?MRSA and penicillin-resistant Pneumococcus.In recent years,reserchers have found linezolid-nonsusceptible Staphylococcus and Enterococcus in several counties.It brings challenges to clinical therapy.Methods:In this study,we collected 75 cases,including 15 cases of LNSE infection and 60 cases of LSE infection from Peking union medical college hospital from 2015 to 2017,we isolated 16 strains of LNSE(including 14 strains of Enterococcus faecalis,1 strain of Enterococcus faecium and 1 strain of Enterococcus casselifavus)and 56 strains of LSEfs from 2012 to 2017,using the chi-square test and T-test to analysis the difference of clinical data.On the basis of the accurate identification of these strains,drug sensitivity test,clustering and homology analysis were done.In terms of resistance mechanism,amplification and sequencing analysis were also performanced for genes of drug resistance and virulence factor.Four Enterococcus faecalis strains of clinical isolates were cultured in different concentration of linezolid medium to induced resistance mutation.Conjugation experiments was done in 14 strains of linezolid-resistant Enterococcus faecalis to analysis the transferability of optrA among strains.Results:There were no difference in age,hospitalization days,invasive operation,patients' basic situation and the use of lineolid between the two groups of LNSE and LSE,In the LNSE,50%strains were from gynecology(25%,4/16)and surgery(25%,4/16),the specimen types were mainly urine(25%,4/16)and drainage fluid(25%,4/16).Tetracycline and chloramphenicol had high resistance rate,100%and 94.8%,respectively.The sensitivity rates of teicoplanin and daptomycin were both 100%;and vancomycin,teicoplanin and nitrofurantoin were all 93.8%.optrA,fexA and ermA gene were positive in LREfs,and positive rate were 100%,100%and 35.7%,respectively.The PFGE clustering analysis has higher resolution,and it has good consistency with MLST on the basis of 80%similarity.We only detected the G2237A mutation in two clinical isolated Enterococcus strains,optrA genes were all positive,with five different types OptrAE349,KD,RDK,EDM,and D.Induced tests in vitro suggested that strains without optrA gene might have G2576T and C260IT mutation in a long period of time of inducing,but strains with optrA gene had G2237A and G2504A mutations,but had no G2576T mutations.One strain with optrA gene found no mutations after the inducing,it suggests that there may be other resistance mechanisms.optrA gene location on plasmids,the rate of conjugation was 50%(7/14).Conclusion:This study found no significant differences in the factor of linezolid using.Virulence factors also showed no significant differences between the two groups.The main resistant mechanism is the carring of optrA gene and the gene can be transmitted between different strains.Mutation can also lead to resisitant of linezolid.