罗氏沼虾源产气肠杆菌分离鉴定及耐药性分析

Identification and antibiotic sensitivity detection of pathogenic Enterobacter aerogenes isolated from Macrobrachium rosenbergii

2017至2018年春季罗氏沼虾育苗期间,江苏省高邮市多家育苗场幼体和仔虾持续发生死亡。从发病幼体和仔虾分离到大量优势生长的细菌,人工感染试验证明其对罗氏沼虾幼体和仔虾有较强的致病性。对分离菌进行了形态特征、理化特性、胞外酶及溶血素活性等表型生物学性状检验,测定了代表菌株的16S rRNA和gyrB基因序列,分析了16S rRNA和gyr B基因序列的同源性。结果显示:引起罗氏沼虾幼体大量死亡的病原之一为产气肠杆菌(Enterobacter aerogenes),代表菌株XL2-1对罗氏沼虾仔虾和蚤状幼体的半数致死量(LD50)分别为2. 0×106和7. 0×105CFU/m L,胞外酶活性及溶血活性检测表明分离菌不溶血,不产生蛋白酶、卵磷脂酶、淀粉酶、尿酶及DNA酶;分离菌的耐药谱测定结果发现,分离菌对头孢噻肟等7种药物敏感,对青霉素G等9种药物耐药,对头孢曲松等19种药物存在株间差异。

During the breeding seasons of spring in 2017 and 2018,the outbreak of mass mortality of Macrobrachium rosenbergii larva occurred in many hatcheries in Gaoyou County,Jiangsu Province. Clinical signs of the diseased prawns included weakness,poor appetite,slow growth,empty stomach,red body and aggregation at the bottom of the ponds. Of the isolates obtained from the diseased M. rosenbergii larva,the representative strain XL2-1 was pathogenic to the zoea and postlarva of M. rosenbergii in the virulence test,with an LD50 value 2. 0×10^6CFU/m L and 7. 0×10^5CFU/m L,respectively. The phenotypic characteristics and pathogenicity of the strain were examined,and the 16 S rRNA and gyr B were amplified by PCR and were compared with sequences in NCBI. The results showed that the E. aerogenes was the main pathogenic bacteria in M. rosenbergii larva. Extracellular enzyme analysis revealed that the isolate could not produce β-hemolysis on rabbit blood agar gelatinase,proteinase,lecithinase,diastase,urease and dnases. According to the antibiotic resistant assay,15 strains were sensitive to 7 drugs such as cefotaxime,and were tolerant to 9 drugs such as penicillin G,but they were in varied responses to the other 19 drugs such as ceftriaxone.