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.

中文翻译：

---

在尼罗罗非鱼中致死嗜水气单胞菌致病性的致病基因。

细菌性疾病是造成水产养殖业高经济损失的主要原因，特别是革兰氏阴性细菌。这项研究是为了分离和鉴定气单胞菌和假单胞菌属。来自病鱼。从埃及尼古拉河Elhox，Metoubes，Kafrelsheikh的八个土池中饲养的患病的尼罗罗非鱼（Oreochromis niloticus）中回收了22种气单胞菌和16种假单胞菌。使用PCR进一步鉴定出回收的分离株为22个嗜水气单胞菌，11个铜绿假单胞菌和5个荧光假单胞菌。22 A.亲水筛选分离株中是否存在四个毒力基因。其中有16株（72.72％）的aerolysin基因（aer）呈阳性; 4（18.18％）含有细胞毒性肠毒素基因（act）；有2个（9.09％）带有溶血素A基因（hylA），而所有测试的分离株中都没有胞质热稳定肠毒素基因（ast）。致病性测试所指示的死亡率百分比和测试的基因型之间的直接关系嗜水分离为死亡率分别为63.3和对于具有两个毒力基因（株73.3％AER ⁺＆行为⁺，和AER ⁺和hylA ⁺，分别为仅具有一个毒力基因的分离株（分别为hylA，act和aer），分别为40、53.3和56.6％，而缺乏毒力基因的分离株为20％。根据灵敏度测试中，多抗生素抗性曲线是如下：90.9％嗜水菌株对氟苯尼考和强力霉素敏感; 然后有68.18％的人对土霉素，诺氟沙星和环丙沙星敏感；分别对磺胺甲恶唑-甲氧苄啶敏感的占63.63％，对红霉素和头孢拉定敏感的分别只有27.27和4.5％，所有分离株均对阿莫西林和氨苄青霉素具有抗药性。