| Streptococcus suis(S.suis)is the main pathogen of swine streptococci,which can cause meningitis,pneumonia,sepsis,polyarthritis and skin purulent infections in pigs,causing serious losses in the pig industry worldwide.It is also an important zoonotic pathogen,representing a serious threat to the public health and safety of people and livestock,therefore,the prevention and control of the disease has attracted more and more attention.In this study,the distribution of serotype and antibiotic resistance,genotypes,and biofilm formation of 53 S.suis strains isolated from the apparently healthy pigs in the slaughterhouses in Anhui Province from 2017 to 2018 were detected and analyzed.This research could provide a theoretical basis for the molecular epidemiology,prevention and treatment of swine streptococcus pathogens of in Anhui Province.Between 2017 and 2018,lung tissues of clinically healthy pigs in slaughterhouses of different scale in Anhui Province were collected,and the suspected S.suis samples were identified by bacterial isolation and specific PCR methods based on gdh gene.And a total of 53 strains of S.suis were identified.The serotypes of 53 strains of S.suis were identified by a specific PCR method based on the cps gene.The percentage of S.suis serotype 3,2,8 1,9 and 29 are 20.7%,18.9%,11.3%,9.4%,5.7%and 5.7%,respectively.In addition,there were 1 strains of S.suis type 5,7,12 and 31,accounting for 1.9%each,and unknown serotype accounted for 20.7%.The results showed the serotypes of Streptococcus suis carried by apparently healthy pigs in slaughterhouses in parts of Anhui Province are complex and diverse,including S.suis type 3 as the most common serotype.The drug resistance of S.suis isolates to 18 antibiotics was analyzed in vitro by microdilution.The results showed that the resistance rate of Streptococcus suis to florfenicol,gentamicin,tetracycline,lincomycin,erythromycin,tiamulin,tilmicosin,streptomycin,doxycycline and trimethoprim/Sulfamethoxazole was relatively high,among which the resistance rate to erythromycin,gentamicin,streptomycin,tiamulin and trimethoprim/sulfamethoxazole is the highest,reaching 100%.The susceptibility rates of amoxicillin,cefotaxime,ceftiofur,enrofloxacin and penicillin were higher,reaching 85.71%,78.57%,76.19%and 83.33%,respectively.In addition,the comparison of drug resistance of different serotype isolates showed that the resistance rate of S.suis serotype 2 to tetracycline(up to 100%)was significantly higher than other serotypes,the resistance rate of S.suis serotype 3,8,9 and 29 to lincomycin(up to 100%)was significantly higher than that of other serotypes.The results showed S.suis is resistant to clinically used drugs to a certain extent,and enrofloxacin,cefotaxime and ceftiofur and penicillin remain the main therapeutic drugs for clinical use.Moreover,there is a certain correlation between the serotype and the drug resistance of S.suis,and it also reflects the difference in the ability of different serotypes to obtain resistance.The biofilm formation was carried out by the 96-well microplate method and the biofilm formation amount was measured by the crystal violet staining method.The results showed that these isolates exhibited different biofilm formation ability,and a total of 32 strains of S.suis were able to form biofilms.The positive strain showed 16 strong biofilm formation strains and weak biofilm formation strains,and the remaining 21 strains of S.suis(including 11 untyped strains)could not form biofilm.In addition,there are 13 isolates of S.suis that can form biofilms,and ss032 has the strongest film forming ability.In addition,S.suis serotype 2 was mainly composed of weak biofilm formation ability,and S.suis serotypes 3 and 8 were mainly composed of strong biofilm formation ability.In addition,all biofilm-forming strains and non-biofilm-forming strains showed resistance to amoxicillin,ceftiofur,cefquinome,enrofloxacin,florfenicol,gentamicin,lincomycin,penicillin and tilmicosin,and the biofilm formation strain was more resistant to antibiotics than the non-biofilm formation strain.However,biofilm producers have a lower resistance rate to trimethoprim/sulfamethoxazole compared to non-biofilm producers.This indicates a positive correlation between the presence of S.suis biofilm and antibiotic resistance,especially with ?-lactam antibiotics.Moreover,the ability of S.suis biofilm formation has a certain relationship with the serotype of bacteria.The genome diversity of 42 strains of S.suis was characterized by ERIC-PCR.These strains showed 14 distinct patterns consisting of 1 to 9 bands ranging from approximately 90?1200 bp.The majority of the strains belonged to two closely related ERIC-PCR types(A and D),while the other types contained only a few isolates each.The ERIC-PCR pattern was correlated with serotype for most isolates.Serotypes 2,3 and 2,3,8 corresponded to ERIC-PCR types A and D,respectively.This indicates that the strains have a genetic relationship in different regions and a high genetic heterogeneity,and the genotype has a certain correlation with serotype.Moreover,ERIC-PCR may be a suitable technique for the molecular identification of S.suis serotypes. |
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