Veterinary Directorate, Kafrelsheikh, Egypt.
Fish Diseases Lab., National Institute of Oceanography and Fisheries, Qaitbay, P.O. Box: 22758, Alexandria, Egypt.
Int Microbiol. 2019 Dec;22(4):479-490. doi: 10.1007/s10123-019-00075-3. Epub 2019 Apr 15.
Bacterial diseases are the main cause of high economic loss in aquaculture, particularly gram-negative bacteria. This study was conducted for the isolation and identification of Aeromonas and Pseudomonas spp. from diseased fish. Twenty-two Aeromonas and sixteen Pseudomonas isolates were recovered from diseased Nile tilapia (Oreochromis niloticus) raised in eight earthen ponds in Elhox, Metoubes, Kafrelsheikh, Egypt. The recovered isolates were further identified using PCR as 22 Aeromonas hydrophila, 11 Pseudomonas aeruginosa, and 5 Pseudomonas fluorescens isolates. The 22 A. hydrophila isolates were screened for the presence of four virulence genes. Sixteen of the isolates (72.72%) were positive for the aerolysin gene (aer); 4 (18.18%) harbored the cytotoxic enterotoxin gene (act); and 2 (9.09%) carried the hemolysin A gene (hylA) while the cytotonic heat-stable enterotoxin gene (ast) was absent from all the tested isolates. The pathogenicity test indicated the direct relationship between the mortality percentage and the genotype of the tested A. hydrophila isolates as the mortality rates were 63.3 and 73.3% for isolates with two virulence genes (aer & act, and aer and hylA, respectively), followed by 40, 53.3, and 56.6% for isolates with only one virulence gene (hylA, act, and aer, respectively) and 20% for isolates lacking virulence genes. Based on the sensitivity test, the multi-antibiotic resistance profiles were as follows: 90.9% of the A. hydrophila isolates were sensitive to florfenicol and doxycycline; then 68.18% were susceptible to oxytetracycline, norfloxacin, and ciprofloxacin; and 63.63% were susceptible to sulfamethoxazole-trimethoprim, while only 27.27 and 4.5% were sensitive to erythromycin and cephradine, respectively, and all the isolates were resistant to amoxicillin and ampicillin.
细菌疾病是水产养殖中经济损失的主要原因，特别是革兰氏阴性菌。本研究旨在从患病的尼罗罗非鱼（Oreochromis niloticus）中分离和鉴定气单胞菌和假单胞菌。从埃及 Elhox、Metoubes、Kafrelsheikh 的 8 个土池中患病的尼罗罗非鱼中回收了 22 株气单胞菌和 16 株假单胞菌。回收的分离株进一步通过 PCR 鉴定为 22 株嗜水气单胞菌、11 株铜绿假单胞菌和 5 株荧光假单胞菌。对 22 株嗜水气单胞菌分离株进行了 4 种毒力基因的检测。16 株（72.72%）分离株携带溶细胞素基因（aer）；4 株（18.18%）携带细胞毒性肠毒素基因（act）；2 株（9.09%）携带溶血素 A 基因（hylA），而所有测试的分离株均未携带细胞毒性热稳定肠毒素基因（ast）。致病性试验表明，死亡率与测试的嗜水气单胞菌分离株的基因型之间存在直接关系，带有两种毒力基因（aer 和 act，以及 aer 和 hylA）的分离株的死亡率分别为 63.3%和 73.3%，其次是带有一种毒力基因（hylA、act 和 aer）的分离株的死亡率分别为 40%、53.3%和 56.6%，而缺乏毒力基因的分离株的死亡率为 20%。基于药敏试验，多抗生素耐药谱如下：90.9%的嗜水气单胞菌分离株对氟苯尼考和强力霉素敏感；其次 68.18%对氧氟沙星、诺氟沙星和环丙沙星敏感；63.63%对磺胺甲恶唑-甲氧苄啶敏感，而只有 27.27%和 4.5%对红霉素和头孢拉定敏感，所有分离株均对阿莫西林和氨苄西林耐药。
