Co-infections of Aeromonas veronii and Nocardia seriolae in largemouth bass (Micropterus salmoides). (December 2022)

• Record Type: Journal Article
• Authors: Xu, Hongsen; Xu, Ruiping; Wang, Xiaoni; Liang, Qianrong; Zhang, Lin; Liu, Jun; Wei, Jin; Lu, Yulan; Yu, Denghang
• Is Part Of: Microbial pathogenesis. Volume 173(2022)Part A
• Publication Date: 2022-12
• Subjects: Micropterus salmoides -- Co-infection -- Nocardia seriolae -- Aeromonas veronii -- Pathological study -- Virulence factors; 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.2022.105815
• Languages: English
• ISSNs: 0882-4010

Abstract

Abstract: Largemouth bass ( Micropterus salmoides ) is an important commercial fish species that is widely cultured throughout China. With the application of high-density culture, M. salmoides is usually infected by different pathogens in water. Particularly, co-infection with multiple pathogens was common, which has considerably outweighed the impact caused by single infections. In this research, two bacteria strains were isolated from diseased fish by incubating on brain heart infusion agar. According to the results of 16S rRNA and gyrB sequence, as well as the analysis of morphological, physiological and biochemical features, the isolated bacterial strains were finally identified as Aeromonas veronii and Nocardia seriolae, respectively. In addition, eight virulence genes related to pathogenicity including enterotoxin, lipase, elastase, quorum sensing, hemolysin and adhesion were identified in A. veronii isolate and eight virulence genes encoding mammalian cell entry family proteins, glyceraldehyde-3-phosphate dehydrogenase, mycolyltransferase, nitrate reductase subunits, and putative cytotoxin/hemolysin were detected in N. seriolae isolate. Drug sensitivity testing indicated that both A. veronii and N. seriolae isolates were susceptible to kanamycin, streptomycin, gentamycin, neomycin, doxycycline, tetracycline, ciprofloxacin and levofloxacin, and resistant to amikacin, cefpimizole, ampicillin, piperacillin, carbenicillin, oxacillin, rifampicin, trimethoprim, vancomycin, meropenem, imipenem and sulfisoxazole. Moreover, serious histopathological changes, such as typical granulomas with necrotic center, cell degeneration and necrosis, hemorrhage and inflammatory cell infiltration, were found in the naturally diseased fish. The LD50 of A. veronii and N. seriolae isolates were 7.94 × 10 5 CFU/g and 3.16 × 10 6 CFU/g fish weight, respectively. In addition, the coinfection of A. veronii and N. seriolae induce quick and higher mortality in comparison with those challenged by single bacteria. These results revealed that both A. veronii and N. seriolae participated in the disease outbreaks of the M. salmoides, and concurrent of those two bacteria synergistically exacerbate the disease severity. Highlights: Co-existence of A. veronii and N. seriolae cause largemouth bass disease. Both A. veronii and N. seriolae harbor virulence-related genes. Pathological changes occur in gill, skin, spleen, kidney, liver and intestine. A. veronii and N. seriolae LD50 are 7.94 × 10 5 CFU/g and 3.16 × 10 6 CFU/g fish. Co-infection increase disease severity through synergistic interactions.