A novel Vibrio parahaemolyticus strain JM20210818 causing glass post-larvae disease in Litopenaeus vannamei: Histopathology, antimicrobial resistance, genomic and transcriptomic insights.

A new disease commonly referred to as "glass post-larvae disease" (GPD) has emerged in many shrimp hatcheries in China since 2020. This highly infectious and lethal disease primarily affects 6 to 12-day-old post-larvae of Litopenaeus vannamei (L. vannamei). In hatchery environments, GPD spreads rapidly, often leading to a large-scale outbreak within 2-3 days from infection and can cause mortality rates as high as 90-100 %. The clinical signs of diseased post-larvae shrimp include low vitality, feeding cessation, empty digestive tract, white or colorless hepatopancreas and a translucent appearance. To identify the main pathogen responsible for GPD, pathogen isolation, pathogenicity tests and histopathological analysis were conducted on diseased post-larvae. A dominant strain, designated JM20210818, was isolated from diseased shrimp and identified as Vibrio parahaemolyticus by physiological and biochemical tests, as well as 16S rRNA and gyrB gene sequencing. JM20210818 did not carry the typical virulence genes pirAvp, pirBvp, tdh and trh. However, immersion challenge tests demonstrated that this strain could cause 100 % mortality in shrimp within 24 h at a concentration of 5.1 × 107 colony-forming units per milliliter (CFU/mL). Infected shrimp exhibited clinical signs consistent with GPD. Furthermore, gyrB sequence analysis confirmed that the dominant strain isolated from challenged shrimp was identical to JM20210818. Histopathological results revealed severe damage to the intestinal and hepatopancreatic tissues of shrimp infected with JM20210818. Antimicrobial-susceptibility results indicated that JM20210818 was resistant to several antibiotics, including ampicillin, cephalothin, tetracycline, amoxicillin, trimethoprim, amikacin and gentamicin. Whole-genome sequencing of JM20210818 (Illumina NovaSeq, ∼100 × coverage) assembled two circular chromosomes (5.903 Mb, 45.0 % GC) and three plasmids (p0818A-C), encoding 5396 CDS, 132 tRNAs and 37 rRNAs. A full complement of environmental-adaptation genes (σ/anti-σ factors, two-component systems, antioxidants) and complete Sec, Tat and T1-T4/VI secretion systems underscored its resilience and virulence potential. Bioinformatic screening identified 704 virulence genes and a broad array of antibiotic-resistance determinants-confirming its high pathogenicity and multidrug resistance. Transcriptomic results indicated that JM20210818 infection may induce shrimp pathology by affecting metabolic functions and regulating ferroptosis and PPAR signaling pathways. Together, these findings demonstrated that JM20210818 was not only a highly pathogenic Vibrio parahaemolyticus but also exhibited multi-drug resistance. It may further promote disease progression by disrupting shrimp metabolism and modulating ferroptosis and PPAR signaling pathways.