Analysis Of Drug Resistance Of Streptococcus Suis And Bacteriocin In Large-scale Pig Farm In Jilin City

Streptococcus suis(S.suis)is one of the important pathogenic bacteria of pig respiratory diseases,it can infect the host through damaged skin mucosa and respiratory tract and other ways,causing livestock meningitis,myocarditis,arthritis and sepsis and other diseases,and S.suis can infect humans,and has a certain mortality rate.Due to the unreasonable application of antibiotics in intensive pig farms,the resistance level of S.suis is constantly improving,so it is urgent to find a new antibacterial drug to replace antibiotics for the treatment of S.suis Bacteriocins are a kind of small molecule proteins produced in the process of bacterial growth and metabolism,which have an inhibitory effect on some bacteria.Many studies show that bacteriocins have a relatively good inhibitory effect on S.suis.In this study,a total of 200 nasal swabs and diseased lung tissue of pigs were collected from a large-scale pig farm in Jilin City,and 39 strains of S.suis.were isolated by bacterial isolation,with a isolation rate of 19.5%.After the drug susceptibility test of isolated S.suis,the results showed that 39 S.suis strains were sensitive to ceftriaxone and amoxicillin,but the resistance rate to azithromycin and erythromycin was as high as 92.31%,and the resistance rate to co-trimoxazole,gentamicin,lincomycin,erythromycin,sulfadiazine sodium,streptomycin and clindamycin was over 50%.To screen for an antiseptic against S.suis,168 environmental samples from pig farms were collected in this study,and the bacteria in the samples were isolated and purified.A strain of Enterococcus faecalis was obtained through primary screening and rescreening,named ZFD-1.The results of Oxford Cup test showed that the bacteriocin secreted by ZFD-1 had an inhibitory effect on S.suis.The bacteriocin was purified by ammonium sulfate salting out method and ultrafiltration method.The results showed that the bacteriostatic effect of bacteriocin on Streptococcus suis was significantly enhanced after preliminary purification.The physicochemical properties of bacterin produced by this strain were analyzed.It was found that it had good acidbase tolerance and thermal stability,and was inactivated after treatment with papain and protease K.The antibacterial spectrum of bacteriocin was determined by Oxford Cup test,and it was found that it had certain inhibitory effects on Escherichia coli,Salmonella typhimurium,Klebsiella pneumoniae,Pasteurella multocida and Staphylococcus aureus.In order to mine the gene cluster of ZFD-1 encoding bacteriocin in Enterococcus faecalis,the whole genome was sequenced and found that ZFD-1 contained one chromosome and two plasmids,the full length of 2,955,518 bp,the GC content was37.36%,and the total base number was 890,867,950.The gene cluster encoding the bacteriocin was predicted by the BAGEL4 webserver,and the comparison results showed that the gene cluster encoding stbacterin and tobacillin existed.In addition,some genes may not be directly involved in the coding of antibacterial proteins,but are involved in the transport of thiobacteriocin in wool,which is speculated to play an important role in the regulation of bacteriocin synthesis.