Pathogenicity of streptococcus agalactiae in oreochromis niloticus

Abstract

To extend our understanding of the pathogenesis of group B streptococcus (GBS), an infection model was established in the Nile tilapia, and the 50% lethal dose (LD50), the toxicity of the extracellular products, the histopathology, ultrapathology, and dynamic distribution of the bacterium were evaluated. After experimental intraperitoneal (i.p.) infection of the Nile tilapia, the LD50 of GBS resuspended in normal saline was 2.3 × 10 7 cfu/mL and that of GBS resuspended in bacterial culture medium was 7.7 × 10 6 cfu/mL. Enzymatic analysis of the extracellular products detected lipase and urease activities. The affected fish showed gross symptoms similar to those of naturally infected fish, including external signs (lethargy, abdominal distension, and abnormal swimming) and internal signs (hemorrhagic liver, enlarged and reddened spleen, hyperemic brain and kidney, empty stomach, and hemorrhagic enteritis). Histologically, hemorrhage, congestion, edema, and necrosis were apparent in the liver, kidney, spleen, heart, and brain. Bacterial colonization was first observed at 2 h postinfection (hpi) in the spleen, 4 hpi in the liver, and 12 hpi in the kidney, brain, and heart. Ultrastructurally, the cells showed nuclear shrinkage, hydropic mitochondrial damage, and increased secondary lysosomes. The bacteria were freely disseminated in the cytoplasm of phagocytes, brain microvascular endothelial cells, neurons, and blood vessels. These results indicate that GBS and their extracellular products are pathogenic to the Nile tilapia, damaging its splenic phagocytes, vascular and renal endothelial cells, liver hepatocytes, and brain neurocytes.

Standardization of Dose and Delivery of Oxytetracycline against Streptococcus agalactiae Infection in Genetically Improved Farmed Tilapia (GIFT)

“…Histopathological lesions such as severe tubulonephrosis, congested glomerulus and sharply decreased hemopoietic tissue observed in the kidney (Fig 4,5) of the infected fish and meningeal congestion and vacuolar degeneration of the neuron in the brain (Fig 6 , 7) were similar to the observation of He et al (2017).…”

Ergasilus extensusand bacterial co‐infection in flathead grey mullet,Mugil cephalus(Linnaeus, 1758), are associated with pathological changes and immunological gene expression alterations

“…have been isolated from both healthy and infected fish species, causing streptococcallike infections in Yellowtail (Seriola quinqueradiata) in Japan, tilapia (Oreochromis niloticus) in Egypt, catfish (Clarias batrachus) in Bangladesh and common carp (Cyprinus carpio) in Thailand (Elgohary et al, 2020;Nieto et al, 1995;Petersen & Dalsgaard, 2003;Plumb & Hanson, 2010;Rahman et al, 2017). (He et al, 2015;Kaewngernsong et al, 2019). Moreover, they have been isolated from infected humans, bovine and rabbits and are the leading cause of neonatal meningitis, mastitis and sepsis (Denga et al, 2019).…”