Identification And Function Analysis Of ICES?2603 Family Transposons In Streptococcus Suis

In recent years,with the wide use of antibiotics in veterinary medicine,the problem of bacterial resistance is becoming increasingly serious,especially the horizonal transfer of resistance gene has brought great difficulties to clinical treatment.Streptococcus suis as an important zoonotic pathogen,has long been considered a variety of drug-resistance gene storage.So far,a variety of drug resistance genes have been found to be disseminated horizontally through S.suis.ICE as an important mobile genetic element,can carry drug-resistant genes and even virulence genes to transfer,which lead to the transfer of these gene between various bacteria.Therefore,the study of S.suis ICES?2603 family transposon mediated drug resistance gene transfer has important clinical significance.In this study,197 strains of S.suis were isolated and identified,and the ICES?2603 family transposon integrase gene int and ser were detected,and the whole genome sequencing of some int or ser positive stains,drug susceptibility test,MLST typing,the amplication of int-rep A and ser-rep A circular intermediates,and conjugative experiments were performed to explore the relationship between the horizontal transfer of the resistance gene in S.suis and ICES?2603 family transposon.In order to study the relationship between the transfer of lsa(E)gene and ICES?2603 family transposons,a series of experiments were conducted,including the detcetion of lsa(E)gene,drug susceptibility testing and conjugation experiments.The results showed that the int and ser of ICES?2603 family transposon integrase gene were detected in S.suis.Five ICES?2603 family transposons(ICESsu SC23?ICESsu SC53?ICESsu SC117?ICESsu SC31 and ICESsu SC37-1)and two ICES?2603 family-like transposons(ICESsu SC37-2 and ICESsu SC111)were obtained by the whole genome sequencing of int and ser gene positive strains.Except ICESsu SC37-2,the other six transposons carry the erm(B),erm(T),tet(O)and tet(O/W/32/O)genes.Drug susceptibility testing results showed that these strains have a higher resistance to tetracycline and erythromycin.The MLST typing showed that these positive strains belonged to the new ST types.The amplification of int-rep A and ser-rep A circular intermediates showed that SC31,SC53 and SC117 is positive for the int-rep A circular intermediates,while SC37 is positive for both int-rep A and ser-rep A circular intermediates.The conjugation experiment and the drug susceptibility testing showed that tet(O/W/32/O)-carrying ICESsu SC37-1 had transferred.The detection rate of lsa(E)gene was 12.6%,and these positive strains showed high resistance to lincomycin,but the seven randomly selected lsa(E)positive strains have not transferred by conjugation experiment.The relationship between the horizontal transfer of the the lsa(E)gene and ICES?2603 family transposons remains to be further studied.In summary,ICES?2603 family and ICES?2603 family-like transposons were identified in S.suis,which all carried tetracycline or erythromycin resistance genes.It is particularly worth mentioning that S.suis SC37 carring one ICES?2603 family transposon and one ICES?2603 family-like transposon was found,where the ICESsu SC37-1 carring tet(O/W/32/O)can transfer.The identification and functional analysis of ICES?2603 family transposons provide some theoretical explanation and basis for the rapid emergence of multidrug resistance of S.suis.