The Dissemination Mechanism Of The Lsa(E) Gene Among Swine Enterococci Strains

In recent years,with the widely use of antimicrobial agents in clinic,the antimicrobial resistance is becoming more and more serious.Enterococci,a clinically important pathogen of humans and animals,has long been considered the reservoir pool of the resistant genes.Now,enterococci has become one of the main pathogens that cause nosocomial infection.Therefore,research on the dissemination mechanism of the resistance genes among enterococci strains,has important public health significance.In this study,PCR detection of the lincosamide-pleuromutilin-streptogramin A efflux pump gene lsa(E),conjugation?Pulsed Field Gel Electrophoresis?southern hybridization,and whole genome sequencing were performed among 69 enterococci strains isolated from pigs,to explore the dissemination mechanism of the resistance gene lsa(E).The results showed that the detection rate of the lsa(E)gene among swine enterococci strains were 53.6%(37/69).Partial strains were selected to carry out conjugation testing.Conjugation experiments showed that the lsa(E)gene can transfer and the transfer efficiencies of 0.18-3.3×10-6 were performed.Location testing showed that the lsa(E)gene can be located either on the plasmid,or on the chromosome.Two different genetic environments of the lsa(E)were obtained by the whole genome sequencing:(1)The lsa(E)gene located on a 50 kb conjugative plasmid.A 14.8kb multi-drug resistance gene cluster on this conjugative plasmid was formed by the genes of lsa(E)?erm(B)?aac?aac A-aph D?aad E?apt?spw?lnu(B)and rec.(2)The lsa(E)gene located on the chromosome with the genes of erm(B)?aac?aac A-aph D?aad E?sat4?aph A3?apt?spw and lnu(B).These resistance genes formed a 19.1kb multi-drug resistance gene cluster,which was flanked by the IS element and the transposase gene.These data inferred that the conjugation or transpositon can play an important role in the horizontal transfer of the lsa(E)gene and its multi-drug resistance gene cluster.These multi-drug resistance gene clusters can confer the resistantance to macrolides?aminoglycosides?lincosamide?pleuromutilin?streptogramin,therefore accelerate the emergence of multidrug resistant enterococci in clinic.In summary,the lsa(E)gene can be located either on the plasmid,or on the chromosome in this study.Two novel genetic environments of the lsa(E)gene were obtained.The transposition or recombination can accelerate the formation of the lsa(E)multi-drug resistance gene clusters.The conjugation can lead to the horizontal transfer of the lsa(E)gene and its multi-drug resistance gene cluster,which provided the partial theoretical explanation for the rapid dissemination of the lsa(E)gene and its multi-drug resistance gene cluster in the veterinary clinic.