| Streptococcus suis (SS) is the causative agent which can cause septicemia, meningitis, endocarditis and arthritis in pigs. It is also a zoonostic pathogen with potential significance to public health. Therefore, the etiological investigation on swine streptococusis possesses remarkable theoretical and practical values. This study carried out a serotype survey of SS prevalent in different areas of Hebei Province, and analyzed the drug resistances and virulence genes of SS, and developed bivalent inactivated vaccine of swine streptococcosis using dominant pathogenic strains of SS prevalent in the areas of Hebei province in order to provide scientific basis for the prevention of swine streptococcosis.An enrichment culture, Gram’s staining and microscopy, and PCR was implemented from600samples of nosal swabs collected from clinical healthy pigs in Shijiazhuang, Xingtai, Zhangjiakou, Cangzhou, Tangshan and Qinghuangdao of Hebei province. The results showed that148strains (24.67%) of Streptococcus suis were isolated from the samples, and of them,27strains (18.24%) belonged to serotype7,24strains (16.22%) were serotype2,20strains (13.51%) were serotype9, and2strains belonged to serotype1, and the serotypes of remaining75strains (50.68%) were undetermined, suggesting that there are various complex serotypes of SS in clinical healthy pigs.Ninety-six isolates of SS from sick or dead pigs during2005to2012were identified by biological characteristics and serum grouping. Among these isolates,34.4%mainly belonged to Group D, and18.8%belonged to Group C. The species and genotypes of96isolates were further identified by PCR amplifying species-specific gdh gene and genes (cpsl I, cps2J, cps7H and cps9H) of capsular polysaccharide of SS. The results indicated that47of96isolates were SS in which65.96%(31/47) belonged to serotype2(SS2),2.13%(1/47) was SS7,4.25%(2/47) was SS9and27.66%(13/47) belonged to other serotypes.The drug resistance of96isolates to27antibiotics was analyzed in vitro by microdilution. The results revealed that most of isolates exhibited obvious drug resistance to14antimicrobial drugs and94.8%of isolates displayed multi-drug resistance in which resistance to sulfonamides, aminoglycosides, tetracyclines, lincosamides and macrolides were most frequent, and then to penicillins, cephalosporins, quinolones and amphenicols.87.5%,85.4%and83.3%of isolates were susceptible to ceftiofur, cefazolin and cephalothin, respectively, showing that SS isolated from clinical sick or dead pigs are resistant to common antimicrobial drugs to some degree.Six virulence genes(gdh, cps, mrp, ef, sly and orf2) for34isolates of SS were detected by PCR. It was indicated that31out of34SS had9genotypes in which32.3%(10/31) was positive in cps2+lgdh+lepf+/mrp+/sly+lorf2+and35.5%(11/31) in cps2+gdh+sly-ef+mrp+orf2+, showing that the dominant strains of SS in Hebei province are highly pathogenic strains with six virulence genes and those of sly gene deletion; out of34,1(SS7) was positive in cps7+/gdh+/sly+/ef-/mrp+/orf2+, and2(SS9) were positive to cps9+/gdh+/sly+/ef-/mrp+/orf2+and cps9+/gdh+/sly-/ef-/mrp+/orf2+, respectively. Furthermore, animal trials showed that the strains with genotypes of cps2+/gdh+/sly+/ef+/mrp+/orf2+and cps2+/gdh+/sly-/ef+/mrp+/orf2+had stronger pathogenicity and fatality (100%mortality) for pigs.Bivalent inactivated vaccine with aluminium hydroxide adjuvant of swine streptococcosis was developed with two highly virulent strains of LN-2and BBD-1belonging to serogroup C and D. Challenge trials for the vaccinated animals indicated that the vaccine was safe for weaning pigs and finishing pigs which could provide complete protection against LN-2and BBD-1. |
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