Experimental Pseudomonas aeruginosa infection in adult and juvenile African catfish (Clarias gariepinus): Pathogenicity and pathology

Abstract

The pathology and pathogenesis of Pseudomonas aeruginosa, a Gram-negative bacterium often isolated from diseased Clarias gariepinus, remain unclear. This study seeks to elucidate its pathology and pathogenesis in this species through experimental infection. An overnight broth culture of Pseudomonas aeruginosa (1.7x109 CFU/ml) originally isolated from a Clarias gariepinus carcass during a previous outbreak was used. The culture was administered via intraperitoneal injection to 50 adult and 50 juveniles Clarias gariepinus, using doses of 1 ml and 0.2 ml, respectively, while a control group of 10 adults and 10 juveniles each received equivalent saline doses. Mortality was 70% in adults within 6 days and 16% in juveniles within 6 hours, with no subsequent deaths. Gross lesions, including enlarged pale yellow to brown enlarged livers, ascites and widespread haemorrhages were frequently observed in adults but absent in the juveniles. Histopathology revealed degenerative and inflammatory lesions mainly in the liver, gills and arborescent organs of infected adults. The haematology showed that infected adults developed anaemia (PCV 31.42±7.62% vs. control 39.60±5.62%), leukocytosis (WBC 18085.42±1810.75/μL vs. control 17060.00±936.84/μL), thrombocytosis (PLT 157083.33±32521.45/μL vs. control 103100.00±19941.30/μL) and hypoproteinaemia (TP 6.08±0.97g/dl vs. control 7.08±0.74g/dl) 48 hours post-infection. At day 35, there was also anaemia and thrombocytosis, however, there was a leukopaenia (WBC 15,795.33±1,050.09/μl vs. Control 17,060.00±936.84 /μl) and a hypoglobulinaemia (GLB 4.58±0.31g/dl vs. control 4.90±0.22). We conclude that the Pseudomonas aeruginosa isolate is highly pathogenic to Clarias gariepinus, causing acute fatal septicaemia with severe organ pathology. Adults were more susceptible, and survivors had suppressed immunity.