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Published on: April 21, 2015
Establishment of a model of Streptococcus iniae meningoencephalitis in Nile tilapia (Oreochromis niloticus)
C G Baums1, K Hermeyer, S Leimbach
1Institute for Microbiology, Centre for Infection Medicine, University of Veterinary Medicine, D-30173 Hannover, Germany. christoph.baums@gmx.de
Abstract:
Streptococcus iniae is an invasive pathogen causing meningitis and other lesions in various fish species. Furthermore, S. iniae is an emerging zoonotic agent that causes cellulitis in man. The aims of this study were to establish an intraperitoneal infection model for S. iniae in Nile tilapia (Oreochromis niloticus) and to develop a new histopathological scoring system to reflect the degree and extent of inflammation as well as the presence of necrosis in the brain and eye. Intraperitoneal administration of 10(6) colony-forming units (CFU) led to 80% mortality and numerous fish developing clinical signs of central nervous system dysfunction. Microscopical examination of four regions of the brain (olfactory bulb, cerebellum, cerebrum and optical lobe) and the eye revealed the presence of lymphohistiocytic leptomeningitis, meningoencephalitis and endophthalmitis. Lesions were dominated by macrophages that often contained intracellular bacteria. Necrosis was recorded in some cases. Bacteriological screening revealed that multiple organs, including brain and eye, were infected with S. iniae and S. iniae colonized the scales and gills in high number. S. iniae was detected in tank water during the first week post infection, suggesting that infected tilapia might shed up to 3 × 10(7) CFU of S. iniae within 24 h. A multiplex polymerase chain reaction allowed confirmation of the challenge strain by detection of the virulence factors simA, scpI, cpsD, pgi, pgm and sagA.
Insights
Streptococcus iniae causes severe disease in Nile tilapia, leading to high mortality and central nervous system lesions. This study developed a histopathological scoring system to assess inflammation and necrosis in fish brains and eyes.
Area of Science:
- Aquatic Animal Health
- Fish Pathology
- Bacteriology
Background:
- Streptococcus iniae is a significant pathogen in aquaculture, causing disease in various fish species.
- It is also an emerging zoonotic agent, posing a risk to human health.
Purpose of the Study:
- To establish an intraperitoneal infection model for S. iniae in Nile tilapia (Oreochromis niloticus).
- To develop a novel histopathological scoring system for evaluating brain and eye lesions.
Main Methods:
- Intraperitoneal inoculation of Nile tilapia with 10(6) colony-forming units (CFU) of S. iniae.
- Histopathological examination of brain regions (olfactory bulb, cerebellum, cerebrum, optical lobe) and eyes.
- Bacteriological screening of organs, scales, gills, and tank water.
- Multiplex polymerase chain reaction (PCR) to confirm the challenge strain and detect virulence factors.
Main Results:
- Intraperitoneal S. iniae challenge resulted in 80% mortality and clinical signs of central nervous system dysfunction.
- Histopathology revealed lymphohistiocytic leptomeningitis, meningoencephalitis, and endophthalmitis, characterized by macrophage infiltration and intracellular bacteria.
- S. iniae was detected in multiple organs, scales, gills, and shed into tank water, indicating potential for transmission.
- PCR confirmed the presence of key S. iniae virulence factors.
Conclusions:
- The established intraperitoneal infection model effectively reproduces S. iniae disease in Nile tilapia.
- The developed histopathological scoring system accurately reflects lesion severity and bacterial presence.
- Findings highlight the systemic nature of S. iniae infection in tilapia and its potential for environmental shedding.
