Phenotypic and molecular characterization of the causative agents of edwardsiellosis causing Nile tilapia (Oreochromis niloticus) summer mortalities. (August 2022)

• Record Type: Journal Article
• Authors: Elgendy, Mamdouh Y.; Sherif, Ahmed H.; Kenawy, Amany M.; Abdelsalam, Mohamed
• Is Part Of: Microbial pathogenesis. Volume 169(2022)
• Publication Date: 2022-08
• Subjects: Antibiotic resistance -- Edwardsiellosis -- Nile tilapia -- Mortalities -- sodB gene sequencing -- Virulence characteristics; Pathogenic microorganisms -- Periodicals; Pathology, Molecular -- Periodicals; Communicable Diseases -- microbiology -- Periodicals; Communicable Diseases -- parasitology -- Periodicals; Micro-organismes pathogènes -- Périodiques; Pathologie moléculaire -- Périodiques; Electronic journals; 616.9041
• DOI: 10.1016/j.micpath.2022.105620
• Languages: English
• ISSNs: 0882-4010

Abstract

Abstract: Edwardsiellosis is a serious bacterial disease affecting Nile tilapia ( Oreochromis niloticus ), causing septicemia and mortalities. Edwardsiella tarda and Edwardsiella anguillarum were isolated from Nile tilapia summer mortality events in Egypt. Diseased fish showed hemorrhagic septicemia, skin erosions, and eye opacity. A total of 24 Edwardsiella spp. isolates were retrieved from the investigated fish specimens. Phenotypic and biochemical characteristics grouped isolates into typical Ed. tarda (n = 14 strains) and atypical Ed. tarda (n = 10 strains). The BLAST analysis of sodB gene sequencing confirmed the conventional identification of typical Ed. tarda strains (n = 14) and reidentified all the atypical strains (n = 10) as Ed. anguillarum. Isolates showed a combination of virulence factors, including biofilm formation (66.6%), hemolysis (100%), chondroitinase (50%), and proteolytic activity (20.8%). The major part of isolates showed high resistance to ampicillin, amoxicillin, gentamycin antibiotics and harbored tet A, bla CTX-M, and aad A1 resistance genes. Pathogenicity testing of isolates in O. niloticus confirmed their virulence. Challenged fish exhibited septicemic signs similar to naturally diseased fish. Infections in naturally infected tilapia triggered acute and chronic histopathological alterations. Degenerative and necrotic changes were noticed in hematopoietic organs. Granulomas were noticed in between the hepatic parenchyma. The data extracted from the study confirm that accurate identification of the causative agents of edwardsiellosis should be reliant on genetic-based approaches. Analysis of the bacterium virulence properties offers insights into establishing novel therapeutics for edwardsiellosis control. The findings refer to the need for antimicrobial sensitivity testing to minimize antimicrobial resistance and increase therapy efficacy. Highlights: Edwardsiellosis is a serious disease in farmed Nile tilapia causing massive mortality. Conventional identification methods identified the causative agents of edwardsiellosis as typical and atypical Ed. tarda. The sodB gene sequencing differentiated Edwardsiella spp. as Ed. tarda and Ed. anguillarum. Edwardsiella spp. have combination of virulence factors and harbors numerous antibiotic resistance genes. Edwardsiella anguillarum was more virulent than Ed. tarda in the experimental infection trials.