| Streptococcus suis is the main pathogen of porcine streptococcosis,which can cause a variety of diseases such as meningitis and septicemia in pigs,and can also infect humans and many other animals,and is an important zoonotic pathogen.The widespread spread of Streptococcus suis has not only caused serious economic losses to the pig industry,but also posed a serious risk to the world public health.In this study,the serotypes,virulence factors,drug resistance phenotypes and drug resistance genes of Streptococcus suis isolated from some large-scale pig farms in Jiangxi from2017 to 2022 were examined,and five typical isolates of Streptococcus suis from meningitidis were selected for MLST typing and combined drug analysis.The results of the study will provide a theoretical basis for the molecular epidemiological study of Streptococcus suis in Jiangxi and the prevention and control of Streptococcus suis infections in pigs.(1)Isolation and staining identification of Streptococcus suis from brain tissue and liver of dead pigs with suspected Streptococcus suis infection between 2017 and2022.The suspected strains were analyzed by amplification and sequencing of the16 S r RNA gene,and the gdh gene was detected by PCR.The strains identified as Streptococcus suis were tested for serotyping and virulence genes by PCR.A total of33 strains of Streptococcus suis were obtained after identification.The serotyping results showed that 12 strains of SS2 and SS9 each accounted for 36.4%,2 strains of SS18 accounted for 6.1%,1 strain of SS3 and SS7 each accounted for 3%,and 5strains of unknown serotypes were detected accounting for 15.2%.The results of virulence gene testing showed that the orf2 gene had the highest detection rate(33/100%),followed by the mrp gene(16/48.5%)and the sly gene(14/42.4%),and the lowest detection rate was the ef gene(11/33.3%).There were eight virulence genotypes in 33 isolates,with mrp-sly-ef-orf2+ being the dominant virulence genotype(14/42.4%),followed by mrp+sly+ef+orf2+(7/21.2%)and mrp+sly+ef-orf2+(5/15.2%).Twelve SS2 strains contained four virulence genotypes,with mrp+sly+ef+orf2+ being the dominant virulence genotype(7/58.3%),followed by two each of mrp+sly+ef-orf2+ and mrp+sly-ef-orf2+,and one strain of mrp-sly-ef+orf2+.Twelve SS9 strains with three virulence genotypes,There were 10strains(83.3%)of mrp-sly-ef-orf2+ type,followed by one strain each of mrp-sly+ef-orf2+ type and mrp-sly+ef+orf2+ type.(2)Twenty-two drug-sensitive papers were selected for drug-sensitivity testing of30 Streptococcus suis isolates.The results showed that the isolates were sensitive toβ-lactams,fluoroquinolones,amidol and polyphosphazenes.Resistance to tetracyclines,macrolides,aminoglycosides,and sulfonamides occurred to varying degrees,with clindamycin,cotrimoxazole,and gentamicin having the resistance rate of 100%,followed by clarithromycin,tetracycline,neomycin,erythromycin,and doxycycline.All isolates were resistant to more than 6 drugs and up to 10 drugs,with12 strains(40%)resistant to 9 drugs.The results of drug resistance gene testing showed that resistance genes were detected for tetracyclines,macrolides,aminoglycosides and sulfonamides.The detection rates were tet O(78.8%),tet M(15.2%),erm B(90.9%),mef A(40%),erm A(9%),str A(97%),str B(93.93%),Aph3’(72.7%),sul 1(100%),sul 2(21.2%).As a whole,the detection of drug resistance genes corresponded to the bacterial drug resistance phenotype.(3)Five strains of Streptococcus suis isolated from the brain tissue of dead pigs with typical meningitis symptoms were selected for MLST analysis.The results showed that JXS190401 of SS2 was ST7 and belonged to the ST1 clonal group;SS9types JXS171101,JXS171201,JXS2209 and JXS2212 of unknown serotype are ST243 belonging to separate ST clonal group.The isolates JXS171101,JXS171201,JXS190401 and JXS2209 were selected for the determination of minimum inhibitory concentrations of florfenicol,tilmicosin,m-sulfamethoxazole and doxycycline hydrochloride.The results were 2μg/m L,2048μg/m L,4096-8192μg/m L and4-8μg/m L,respectively.In vitro combination tests showed that the combination of tilmicosin + m-sulfamethoxypyrimidine,tilmicosin + doxycycline hydrochloride and m-sulfamethoxypyrimidine + doxycycline hydrochloride all showed synergistic or additive effects on the inhibition of experimental bacteria according to the FICI score. |
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