| Streptococcus suis is an important pathogen of pigs and also a zoonotic pathogen.It can cause meningitis and sepsis in pigs and huge economic losses to the pig industry worldwide.The pathogenic serotypes of this bacterium are numerous and complex,and there may be large differences in virulence between strains of the same serotype.Currently,more attention is paid to serotype 2,and there are relatively few studies on the population structure,pathogenicity and antimicrobial resistance of other pathogenic serotypes,such as serotype 7.The bacterium can colonize the tonsils of healthy pigs for a long time,and there may be multiple pathogenic serotypes in the same tonsil,which is a potential source of infection.In this study,S.suis strains were isolated and serotyped from tonsils from pigs in slaughterhouses in Jiangsu and Zhejiang provinces,and the epidemiological characteristics of S.suis in these two regions were analyzed and compared.In addition,22 S.suis serotype 7 strains isolated from healthy and diseased pigs were subjected to whole genome sequencing,antimicrobial sensitivity test,and zebrafish virulence test;the multilocus sequence typing(MLST)and minimum core genotyping(MCG)analyses were performed for these serotype 7 strains together with 51serotype 7 strains whose information was accessed from NCBI.The findings not only help to formulate prevention and control strategies for the disease caused by S.suis,but also contribute to the understanding of the population structure,pathogenicity and antimicrobial resistance of S.suis serotype 7.1.Epidemiological investigation of S.suis in slaughterhouses in Jiangsu and Zhejiang ProvincesIn 2020,64 tonsils from healthy pigs were collected from slaughterhouse in Jiangsu province,of which 35 were S.suis positive(54.68%).In total,36 strains were isolated,including serotypes 16,4,7,31,9,3,and 5.In 2020,70 tonsils from healthy pigs were collected from slaughterhouse in Zhejiang province,of which 46 were S.suis positive(65.71%).In total,42 strains were isolated including serotypes 16,3,31,8,2,and 9.The positive rate of S.suis in the slaughterhouses from Jiangsu and Zhejiang provinces exceeded 50%;S.suis serotype 2 has not been detected in Jiangsu province and the isolation rate of this serotype in Zhejiang is only 7.14%;serotype 16 had the highest isolation rate in both Jiangsu and Zhejiang provinces.Together with the samples isolated in 2017 and 2019 from slaughterhouses in Jiangsu province from our previous studies,518 samples were collected in total and 346 samples were S.suis positive(66.79%)in Jiangsu province.From 2017 to 2020,a total of 441 S.suis strains were isolated and further serotyped by PCR.There were 371(84.12%)traditional serotypes,21(4.76%)NCL strains,and 49 strains(11.11%)that were non-typeable.It was found that serotype31 was the highest,accounting for 13.6%(60/441).The remaining strains were serotype9(11.33%),serotype 16(10.88%),serotype 2(7.48%),serotype 4(7%),serotype 3(6.8%),and serotype 7(4.98%).Among NCL strains the highest isolation rate was NCL1and NCL4,each accounting for 28.57%(6/25).Two or more serotypes of S.suis were detected in 83 tonsil samples(16%),and one sample even contained five different serotypes strains.2.Pathogenicity and antimicrobial resistance of S.suis serotype 7S.suis serotype 7 is one of pathogenic serotypes,but the information of its population structure,pathogenicity,and antimicrobial resistance is very limited.22 strains of S.suis serotype 7 isolated from healthy and diseased pigs were subjected to whole genome sequencing,and a minimum core genome sequence typing(MCG)analysis was performed together with the 51 genome sequences of serotype 7 from NCBI database.We found that S.suis serotype 7 strains are mainly divided into 4 MCG groups,namely MCG1,MCG3,MCG4,and MCG7-2.Multilocus sequence typing(MLST)analysis revealed that S.suis serotype 7 strains are mainly divided into ST373,ST94,ST225,ST29,ST1611,and ST1612,and ST1611 and ST1612 are the new ST types.ST373strains belong to the MCG1 group,and ST29 and ST225 belong to the MCG4 group;serotype 7 strains from our laboratory were mainly located at ST373,ST225,and ST29.16 strains were resistant to three or more classes of antimicrobial agents,accounting for72.72%.72.7%(16/22)and 18.18%(4/22)of strains contained tet(O)and tet(M)respectively;the antimicrobial susceptibility testing results showed,except for strains WUSS413,WUSS415,and WUSS417,for the rest strains the phenotype of resistance to tetracycline corresponded to the genotype.The macrolides-lincosamides-streptogramin B resistance genes erm(B)(77.27%,17/22)is present and corresponded to phenotypes of resistance to macrolide antimicrobials tested,with the exception of strains WUSS366 and WUSS413.The aminoglycoside resistance genes ant(6)-Ia(22.72%,5/22)and aac(6’)-aph(2’’)(9.09%,2/22)are present alone or in combination and corresponded to phenotypes of resistance to aminoglycoside antimicrobials tested,with the exception of strain WUSS415.All serotype 7 strains from our lab were sensitive toβ-lactams,rifamycins,glycopeptides,oxazolidinones,quinolones,amide alcohols,and pleuromutilin antimicrobials tested.Virulence-associated genes analysis found that the hemolysin gene sly of ST373 strains contains nonsense mutation,and all ST29 strains are without sly.Six strains were selected for haemolytic activity testing.We found that:strains WUSS401(ST373,sly nonsense mutation)and WUSS013(ST255 sly~+)had hemolytic activity;strains WUSS417(ST1611 sly~+),WUSS415(ST1611 sly~+),WUSS413(ST29 sly~-),and 2018WUSS101(ST1612 sly~-)had no haemolytic activity.Strains WUSS417 and WUSS415 have sly gene but without hemolytic phenotype,and no expression or low expression of sly gene may be one explaination;strain WUSS401with sly nonsense mutation has hemolytic activity,which suggested that it may contain other hemolytic factors.The results of zebrafish infection experiment showed that the mortality rates in the groups infected with strains WUSS401,WUSS417,and WUSS013were 86.6-93.3%. |
PDF Full Text Request