| In recent years,nosocomial infections caused by Enterococcus have been increasing,most of which are caused by E.faecalis and E.faecium.In the clinical practice of human medicine,resistance rate against streptogramins antibiotics is increasing day by day but the mechanism of resistance is not very clear.Studies have revealed that the resistance of Quinupristin/Dalfopristin may be due to the use of virginiamycin as a feed additive in food animals thereby transmitting resistance factors to humans through the food chain.To verify that there is a risk of transmission of resistance,fecal samples were collected from different 59 pig farms from 18 provinces and cities of China.Isolation and identification of Enterococcus were carried out and susceptibility test for 13 different antibacterial drugs was performed.Isolated porcine E.faecium was confirmed by PCR,23 kinds of resistance genes related to streptogramins were subjected.Pulsed-field electrophoresis and analyzed for their genetic relationship.The detailed experimental results are as follows:1.836 samples were collected from 59 pig farms in 18 provinces and cities of China.225 Enterococcus isolates were obtained from samples including E.faecium(47.1%)and E.faecalis(24.9%)had the highest isolation rate;isolated E.hirae(15.1%),E.gallinarum(6.2%),E.casseliflavus(3.1%),E.durans(1.8%)and E.thailandicus(0.4%).2.No Enterococcus resistant to vancomycin and linezolid were detected,but the mediating rate of linezolid was 54.7%.There was spotted level of resistance against other antimicrobial agents.The resistance rate of 6 antimicrobial agents was up to 91.0%.The multidrug resistance of Enterococcus was mainly distributed in 6 resistant,7 resistant and 8 resistant accounting for 72.9%of the total number of Enterococcus(164/225).Different Enterococcus have different distributions of multidrug resistance.E.faecium and E.faecalis have mainly distributed in 7 and 8 resistant accounting for 53.8%and 76.8%of the total number of E.faecium and E.faecalis,respectively.E.hirae is mainly distributed in 6 resistant accounting for 61.8%of the total number of E.hirae.3.The drug susceptibility test of E.faecium to streptogramins antibacterial drugs showed that 28 strains of Quinupristin/Dalofopin(Q/D)resistant E.faecium,25 strains of virginiamycin-resistant E.faecium(MICs?4 ?g/mL).23 drug resistance genes related to the antibiotic resistance mechanism of streptogramins were detected in drug-resistant strains.The resistant strains only detected four genes ermB,LsaE,msrC,vatE and were coexistence.4.The PFGE results of E.faecium in China showed that there were 77 PFGE bands in 106 strains of E.faecium and 18 strains of E.faecium with homologs of?85%.28 strains of Quinupudin/Dafupudin E.faecium can be divided into 25 types of PFGE bands.25 strains of virginiamycin-resistant E.faecium(MICs?4 ?g/mL)can be divided into 23 types of PFGE bands.Conclusion:Isolation rate of Enterococcus in 18 provinces and cities of China is generally low but they comprise many types of predominantly E.faecium.The resistance of E.faecium is slightly more severe than other Enterococcus.The four-drug resistance genes detected could not directly explain the cause of resistance to streptogramins in E.faecium.It is speculated that the resistance mechanism of E.faecium to streptogramins is caused by a certain mutation of the detected gene or an unknown drug resistance gene.The strains with more than 85%homology were distributed in pig farms of different provinces and cities indicating that the dominant strains were widely prevalent.It suggests that concerned departments should conduct timely drug resistance and epidemiological investigations and surveys on Enterococcus in the future.Furthermore,traceability analysis should be carried out to reduce the risk of drug resistance caused by outbreaks of dominant strains. |
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