一株中美貘源大肠埃希菌O157分离鉴定及致病性研究

Study of isolation, identification and pathogenicity of a strain of Escherichia coli O157 from Tapirus bairdii

2018年3月,某动物园1只中美貘突然精神沉郁,卧地不起,高热,呕吐,食欲废绝,第2天出现神经症状,死亡。剖检可见肺苍白,边缘有散在的出血点;气管有大量白色泡沫,轻度气肿;心肌和心耳有大面积出血;胃肠黏膜出血、坏死。无菌采集肝脏和脾脏,使用麦康凯和LB琼脂平板进行细菌培养、分离,麦康凯琼脂平板上可见粉红色光滑菌落,疑似大肠埃希菌。纯化细菌,经PCR鉴定为O157型大肠埃希菌,推断中美貘可能因O157型大肠埃希菌感染致死,进一步药敏试验表明,该菌仅对阿米卡星、氨苄西林和复方新诺明敏感,多重耐药率达87.5%。PCR方法检测了8种主要的毒力基因,结果表明该菌株携带ompA和fimC 2种毒力基因。小鼠致病性试验结果显示,该菌株的半数致死量(LD50)为1.0×108.5 cfu。

On March, 2018, a Tapirus bairdii from a zoo was sick with clinical symptoms of depressed spirit, lying on the ground, high fever, vomiting and abolished appetite. It was died with neurological symptoms in the next day. After autopsy, the lung was pale with scattered bleeding spots on the edges, the trachea was mild emphysema filled with white foam, the myocardium and auricle of heart were covered with numerous bleeding spots, and the gastrointestinal mucosa showed hemorrhage and necrosis. The liver and spleen were aseptically collected to isolate bacteria on MacConkey and LB agar plates. A suspected Escherichia coli strain was purified and identified as E.coli O157 by PCR. The drug sensitivity test indicated that the isolate was only sensitive to amikacin, ampicillin and cotrimoxazole. The multi-drug resistance rate of the isolate was 87.5%. Eight important virulence genes were detected by PCR, the identification results showed that the strain carried two virulence genes, ompA and fimC. The pathogenicity of the isolate showed that the LD50 of E.coli O157 was 1.0×108.5 cfu in mice.