Mycobacteriosis has been recognized as an infectious disease caused by Mycobacterium fortuitum in aquaculture. In Indonesia, mycobacteriosis outbreak has been detected in West Java, Central Java, and East Java. However, no studies have yet described the pathogenesis of mycobacteriosis in gourami. Therefore, this study was designed to detect the portal of entry and tissue distribution of M. fortuitum in gourami through immersion challenge. The immersion route was selected for the infection method as it is capable of describing the occurrence of natural disease as an infection model. This study was conducted in two steps. First, the fish was immersed in M. fortuitum concentrations of 10⁴–10⁸ CFU mL⁻¹ to determine the lethal dose of 50 (LD50). Second, the fish was immersed in LD50 to examine the portal of entry and tissue distribution of M. fortuitum in gourami and to determine the nonspecific immune response of fish after infection. Results showed that the LD50 of M. fortuitum through immersion challenge in gourami was 10⁷ CFU mL⁻¹. The portal of entry of M. fortuitum was the skin and gills, after which it spread through blood circulation to internal organs such as the liver and kidney. Finally, it was observed that the bacteria were released through the intestine. These findings indicate the M. fortuitum infection outbreak in fish was chronic and systemic and distributed in tissues. The infected fish responded to the infection by increasing the total leukocyte count and phagocytic activity after challenge with M. fortuitum.

分枝杆菌病已被公认为水产养殖中由偶然分枝杆菌引起的传染病。在印度尼西亚，西爪哇、中爪哇和东爪哇已发现分枝杆菌病爆发。然而，尚无研究描述口蹄疫分枝杆菌病的发病机制。因此，本研究旨在通过浸入挑战来检测gourami中偶然发现的入口入口和组织分布。感染方法选择浸泡途径，因为它能够将自然疾病的发生描述为感染模型。本研究分两步进行。首先，将鱼浸入浓度为 10 ⁴ –10 ⁸ CFU mL 的M. fortuitum^-1确定致死剂量为 50 (LD50)。其次，将鱼浸泡在 LD50 中，以检查gourami中偶发分枝杆菌的入口入口和组织分布，并确定感染后鱼的非特异性免疫反应。结果表明，通过在 gourami 中浸泡挑战，偶然发现的 LD50为 10 ⁷ CFU mL ^-1。M. fortuitum的入口是皮肤和鳃，然后通过血液循环扩散到肝脏和肾脏等内脏器官。最后，观察到细菌通过肠道释放。这些发现表明M. fortuitum鱼类感染的爆发是慢性和全身性的，并分布在组织中。受感染的鱼在用M. fortuitum攻击后通过增加总白细胞计数和吞噬活性来对感染作出反应。