家禽病例中马链球菌兽疫亚种的分离鉴定及致病性观察

Isolation,identification of Streptococcus equi subsp. zooepidemicus and the determination of minimum inhibition concentration

为研究马链球菌兽疫亚种对家禽的致病性,采集流行地区发病鸡和鸽的肺脏,分离了8株链球菌,并利用染色镜检、生化试验和PCR方法进行鉴定,结果为3株属马链球菌兽疫亚种,5株属粪肠球菌。在此基础上,选择1株马链球菌兽疫亚种内蒙分离株,经腹腔注射途径人工感染SPF(Specific pathogen free chicken)鸡和肉鸡,攻毒后死亡率分别为40%和80%。剖检观察到出血性肺炎、气囊炎和心包炎,尤其是肉鸡出现60%的支气管栓塞病变,这与临床病理学变化相似。此外,采用微量肉汤测定法测定8个临床分离菌株测定对15种药物的最小抑菌浓度(Minimum inhibition concentration,MIC),结果显示10株链球菌对于氟苯尼考、莫西沙星、甲磺酸加替沙星、乳酸环丙沙星及强力霉素高度敏感,MIC值均小于7.813μg/mL。分离株对于泰乐菌素、磷霉素钠、螺旋霉素和阿莫西林高度耐药,MIC值大于250μg/mL。试验提示马链球菌兽疫亚种可能是家禽气囊炎一个重要的病原之一,临床防治中应使用敏感性高的抗菌素。

The purpose of this experiment is to seek the probable pathogenicity of the Streptococcus equi subsp. zooepidemicus in poultry and to find the proper medical treatment for the disease caused by the pathogen. Eight isolates were isolated from the lungs of broilers and laying hens in Liaoning, Inner Mongolia, Hebei, Shandong and Beijing,which were suffered from the severe pneumonia. Three of the isolates were identified as S. equi subsp. zooepidemicus and five were identified as S. faecalis by using Gram-stain, biochemical test and PCR methods. Subsequently,specific pathogen free chicken （SPF） chicken and commercial broilers were administered intraperitoneally with S. equi subsp, zooepidemicus,which was isolated from Inner Mongolia,and the post mortality was40% and 80% for SPF chicken and commercial broilers, respectively. Typically bronchial obstruction was found except for hemorrhagic pneumonia,air sacculitis and pericarditis,which corresponded with the clinical observation. Based on the identification, minimum inhibition concentrations （MIC） of eight isolates and two reference strains were determined post incubation with the different antibiotics. Ten Streptococcus strains were more sensitive to florfenicol, moxifloxacin, gatifloxacin, ciprofloxacin and doxycycline,the MIC of them is less than 7. 813 μg/mL. Two isolates were found with higher antibiotic resistance to the specific medications, such as amoxicillin, tylosin, fosfomycin sodium and spiramycin, whose MIC is more than 500 g/mL. Taken together, Streptococcus equi subsp, zooepidemicus infection might be one of the main pathogens and contributes to severe avian pneumonia. Highly sensitive antibiotics should be implemented against S. equi subsp, zeoepidemicus infection.