四川资阳地区猪链球菌2型检测及其特性比较研究

Identification and characterization of Streptococcus suis serotype 2 isolated from diseased pigs in Ziyang area of Sichuan province

目的对从四川省资阳及附近猪链球菌2型感染疫区采集的病料进行病原菌分离和特性比较研究。方法首先利用病原菌分离技术、多重定性PCR检测和荧光定量PCR检测技术进行病原菌的分离和鉴定;然后选取5株主要疫点代表菌株与1株国外参考菌株进行细菌药敏试验和实验动物腹腔接种感染试验;此外还对猪链球菌2型分离株基因组中的溶原性噬菌体进行了初步研究。结果(1)从采集的病料中分离到11株猪链球菌2型菌,都具有胞外因子(EF)和溶菌酶释放蛋白(MRP)两个特征性毒力因子;(2)6株试验菌株对氨苄青霉素、先锋必素、头胞克肟、乙酰螺旋霉素、万古霉素、复方新诺明和利福平等7种抗生素高度敏感。与国外参考菌株相比,资阳分离株具有链霉素抗性;(3)试验菌株对BALB/c鼠均具有一定的毒力,但毒力程度上有差异。资阳分离株449-1和国外参考株6#对鼠具有相同的强致死性(3/3死亡),资阳458分离株致死性较弱(0/3死亡),其它菌株具有中等强度的致死性。利用449-1、458和6#分离株进行家兔感染实验,各菌株均可引起家兔感染发病,死亡率分别是1/2、2/2和2/2;(4)国内首次获得了猪链球菌2型流行菌株匿藏着溶原性噬菌体的证据,该噬菌体与细菌毒力和适应性的关系有待深入研究。结论通过对资阳及附近地区猪链球菌2型分离株与国外分离株特性的比较研究,明确了流行菌株间在毒力和药物敏感性上存在着差异,细菌毒力差异表现为对动物种属的嗜性,并筛选出了猪链球菌病防治的可选择性药物。为进一步研究猪链球菌2型菌株的致病机理以及猪链球菌病的防治奠定了基础。

In summer of 2005 ,an outbreak of Streptococcus suis type 2 infections in animals and humans with deaths of hundreds of pigs and 38 human deaths was observed in Ziyang and adjacent area of Sichuan province. From the clinical samples of pigs died in this outbreak, 11 strains of Streptococcus suis type 2 were isolated, and these isolated strains were underwent identification by multiplex PCR and real-time PCR. It was found that all these 11 strains possessed 2 main virulence factors, i.e. muramidase released protein （MRP） gene and extracellular factor （EF） protein gene. Five of the 11 strains isolated from Sichuan and another strain isolated from Spain were compared for the susceptibility to antibiotics, in which all these 6 strains from Sichuan and Spain was found to be highly sensitive to amipicillin, cefoperazone, cefixime, acetylspiramycin, vancomycin, sinomin compositea and rifampicin, but in comparison with the Spanish isolate, the 5 strains of Sichuan were resistant to streptomycin. Meanwhile, all the tested strains showed different degree of pathogenicity to mice, in which both the strain 440-1 isolated from Sichuan and the isolate from Spain had high pathogenicity to mice （3/3 death）, but the strain 458 isolated from Sichuan showed low pathogenicity to mice. （ 0/3 death）. The death rates of rabbits inoculated with strain 449-1, 458 and 6 were 1/2, 2/2 and 2/2 respectively. In addition, we had obtained evidence of harboring the lysogenic phages in Stroptococcus suis type 2, but the relationship of this phage with the bacterial virulence and adaptation was uncertain.