Uji Patogenisitas Bakteri Asal Udang Vaname Litopenaeus vannamei yang Mengalami Kematian dengan Gejala Nekrosis

Abstract

Udang vaname (Litopenaeus vannamei) merupakan komoditas unggulan budi daya perikanan Indonesia dan komoditas ekspor utama yang masih rentan terhadap serangan penyakit akibat patogen. Kasus kematian udang dengan gejala nekrosis otot ditemukan di tambak Jawa Barat dan negatif IMNV berdasarkan PCR, sehingga diduga disebabkan oleh infeksi bakteri. Penelitian ini bertujuan mengisolasi dan mengidentifikasi bakteri penyebab kematian udang vaname dengan gejala nekrosis serta menguji tingkat virulensinya melalui uji Postulat Koch. Delapan isolat bakteri (JO1–JO8) diisolasi dari otot udang pada media SWC dan TCBS agar. Uji patogenisitas dilakukan melalui injeksi intramuskular dengan dosis 108 CFU mL-1 selama 7 hari dengan pengamatan gejala klinis, mortalitas, dan rata-rata waktu kematian (RWK). Identifikasi bakteri dilakukan secara morfologi, biokimia (pewarnaan Gram, uji O/F, motilitas, katalase, dan oksidase), serta molekuler menggunakan amplifikasi gen 16S rRNA dan analisis BLAST, didukung oleh pemeriksaan histopatologi jaringan otot. Isolat JO3 (Rothia koreensis) menunjukkan mortalitas tertinggi (100%), sedangkan JO6 (Acinetobacter radioresistens) memiliki rata-rata waktu kematian tercepat (17,70 jam). Isolat JO8 diduga termasuk genus Photobacterium, sedangkan genus lain meliputi Vibrio, Planococcus, dan Staphylococcus. Histopatologi menunjukkan kerusakan otot progresif dari edema hingga nekrosis lanjut disertai infiltrasi hemosit. Hasil penelitian menunjukkan bahwa BMN pada udang vaname dapat disebabkan oleh berbagai genus bakteri.

Pacific White shrimp (Litopenaeus vannamei) is a leading commodity in Indonesian aquaculture and a major export product that remains highly vulnerable to pathogenic diseases. Cases of shrimp mortality showing muscle necrosis symptoms were discovered in West Java ponds, which tested negative for IMNV via PCR, suggesting a potential bacterial infection. This study aimed to isolate and identify the bacteria causing mortality in whiteleg shrimp with necrosis symptoms and to test their virulence level using Koch's Postulates. Eight bacterial isolates (JO1–JO8) were isolated from shrimp muscle tissue on SWC and TCBS agar media. Pathogenicity tests were conducted via intramuscular injection at a dose of 108 CFU mL-1 over 7 days, monitoring clinical symptoms, mortality rate, and mean time to death (MTD). Bacterial identification was performed through morphological, biochemical (Gram staining, O/F test, motility, catalase, and oxidase), and molecular analyses using 16S rRNA gene amplification and BLAST analysis, supported by histopathological examination of the muscle tissue. Isolate JO3 (Rothia koreensis) exhibited the highest mortality rate (100%), while JO6 (Acinetobacter radioresistens) showed the fastest mean time to death (17.70 hours). Isolate JO8 was putatively identified as belonging to the genus Photobacterium, while other identified genera included Vibrio, Planococcus, and Staphylococcus. Histopathology revealed progressive muscle damage ranging from edema to advanced necrosis, accompanied by hemocyte infiltration. The results demonstrate that bacterial muscle necrosis (BMN) in whiteleg shrimp can be caused by various bacterial genera.