Detection And Spread Mechanism Of Florfenicol Resistance In Streptococcus Suis

Streptococcus suis is a zoonotic pathogen.The widespread use of antibiotics and the resulting horizontal transfer of resistance genes are the causes of the resistance of Streptococcus suis,and florfenicol is the most widely used antibacterial drug in veterinary clinics,and it is urgent to solve the problems such as florfenicol.Drug resistance issues.The florfenicol resistance gene optrA is the second gene found to be able to mediate both oxazolidinone and amide alcohol antibiotic resistance,and can be transferred horizontally between bacteria.Therefore,using the drug resistance gene optrA as the entry point,the current status and diffusion mechanism of florfenicol resistance in Streptococcus suis were studied,which provided a theoretical basis for the diffusion and prevention of florfenicol resistance in medical and veterinary clinics.In this study,based on the isolation and identification of Streptococcus suis,the florfenic resistance gene optrA was detected.Some of the optrA positive strains were tested for susceptibility to florfenicol,and several positive strains were randomly selected for conjugation experiments,MLST typing,and drug susceptibility testing.Subsequently,three generations of whole-genome sequencing of optrA-positive strain SC317 were performed to analyze the genetic environment of optrA.The primers were designed to amplify the ICE cyclic intermediate and the optrA cyclic intermediate,respectively,to verify the presence of cyclic intermediates,and further analysis of florfenicol.The genetic environment and transmission mechanism of the drug resistance gene optrA.The optrA gene test of 237 strains of Streptococcus showed that the optrA positive strain was 28 strains with a positive rate of 11.8%(28/237).The drug susceptibility results showed that most of the strains were florfenicol,linezolid,tetracycline.And lincomycin has high resistance.Two randomly selected strains of Streptococcus suis SC262 and SC317 containing the optrA resistance gene were used as donor bacteria,and the binding experiments were carried out with the recipient strain S.suis BAA-853.Only the successful coupling of SC317,the susceptibility test results of the zygote showed that the zygote T-SC317 was resistant to florfenicol and linezolid,indicating that the optrA gene can function in the recipient bacteria.The results of the conjugation test indicated that the optrA gene carried by Streptococcus suis was horizontally transferred and the junction efficiency was 2.1×10-8.SC317 whole genome sequencing revealed that optrA is located on a putative transposon formed by IS1216 of the same repeat sequence,and the putative transposon is located in a tandem ICE in the ICESa2603 family,and this tandem ICE is named tandem.ICESsuSC317(103.324Kb).The results of amplification of the optrA circular intermediate and ICE cyclic intermediate showed that ICE cyclic intermediate and optrA cyclic intermediate were obtained in SC317.In this study,we first discovered that the florfenicol resistance gene optrA is located in a tandem ICE in the ICESa2603 family.In summary,this study detected the florfenicol resistance gene optrA in Streptococcus suis,which may be inserted into a tandem ICE of the ICE&2603 family by transposition,and the ICE can undergo horizontal transfer.This study provides a partial theoretical explanation for the diffusion of florfenicol in Streptococcus suis.