Retrospective diagnosis of archived marine fish experienced unexplained mortality reveals dual infections of Nocardia seriolae and Streptococcus iniae
- 74 Downloads
Due to the limitation of accessible laboratory facilities for disease diagnosis at the time of the events, clinical samples of snubnose pompano (Trachinotus blochii) and orange-spotted grouper (Epinephelus coioides) were frozen preserved for retrospective investigation. This study employed a simple challenged test using crude homogenate prepared from the long-term frozen preserved tissues (~ 16 months) to infect Asian sea bass (Lates calcarifer) model. The experimental fish became sick and exhibited visceral white spots similar clinical signs previously observed in natural cases. Two morphologically different Gram-positive bacteria were concurrently recovered from the experimentally sick fish but not directly from the archived frozen tissue. Based on sequence homology of 16S rRNA, the bacterial strains were identified as Nocardia seriolae and Streptococcus iniae, respectively. Subsequent specific PCR assays confirmed co-infections of N. seriolae and S. iniae in the majority of naturally diseased fish preserved. Concurrent infection of N. seriolae and S. iniae is new to both pompano and grouper. This study also suggests that frozen preservation combined with challenged assay might be useful for retrospective diagnosis and recovery of infectious agents in under-equipped laboratories in Southeast Asia or elsewhere.
KeywordsConcurrent infection Nocardia seriolae Streptococcus iniae PCR Retrospect
The National Center for Genetic Engineering and Biotechnology (BIOTEC) under its human resource development program provided a research fellowship to VV Nguyen. The authors thank C. Techatanakitarnan for technical assistance.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable international, national, and institutional guidelines for the care and use of animals were followed by the authors.
- Bowater RO, Forbes-Faulkner J, Anderson IG, Condon K, Robinson B, Kong F, Gilbert GL, Reynolds A, Hyland S, McPherson G, Brien JO, Blyde D (2012) Natural outbreak of Streptococcus agalactiae (GBS) infection in wild giant Queensland grouper, Epinephelus lanceolatus (Bloch), and other wild fish in northern Queensland, Australia. J Fish Dis 35:173–186CrossRefGoogle Scholar
- FAO 2012 Regional overview of fisheries and aquaculture in Asia and the Pacific 2012. RAP Publication 2012/26, Available at [http://www.fao.org/docrep/017/i3185e/i3185e3100.htm]
- Giang N, Binh D, Hoa D (2012) Preliminary study of white spot disease in internal organs in snubnose pompano (Trachinotus blochii). J Fish Sci Technol 4:26–33 (In Vietnamese) Google Scholar
- Labrie L 2008 Nocardial infections in fish : an emerging problem in both freshwater and marine aquaculture systems in Asia. Diseases in Asian Aquaculture 297–312Google Scholar
- Luna LG (1968) Manual of histologic staining methods of the Armed Forces Institue of Pathology. McGraw-Hill, New YorkGoogle Scholar
- Oliver JD 2005 The viable but nonculturable state in bacteria. J Microbiol 43 Spec No, 93–100Google Scholar