摘要
[Objectives] This study aimed to determine the infection pathway and target organs of Streptococcus agalactiae in GIFT strain of Nile tilapia, thus providing theoretical basis for the breeding of disease-resistant tilapia and development of S. agalactiae vaccines.[Methods] GIFT strain of Nile tilapia was inoculated by S. agalactiae through intraperitoneal injection, oral gavage and in vitro immersion. The gill, spleen, liver and small intestine tissues of infected tilapia were collected for pathomorphological observation. Immunohistochemical localization was conducted using rabbit anti- S. agalactiae serum to identify the distribution pattern of S. agalactiae in various tissues of tilapia and its target organs via different infection pathways.[Results] GIFT strain of Nile tilapia could be infected by S. agalactiae via three artificial inoculation modes. Specifically, pathological changes occurred at 2 h post-inoculation in intraperitoneal injection and oral gavage groups, whereas tilapia in in vitro immersion group showed pathological changes at 5 h post-inoculation, and the lesion intensity in in vitro immersion group was slighter than that in intraperitoneal injection and oral gavage groups. Immunohistochemical localization indicated that the appearance time of positive signals in intraperitoneal injection group demonstrated an order of spleen→liver and gill→small intestine; positive signals in oral gavage group appeared in the order of small intestine→gill and spleen→liver; the appearance time of positive signals in in vitro immersion group showed an order of gill→spleen→liver and small intestine.[Conclusions] GIFT strain of Nile tilapia could be infected by S. agalactiae via intraperitoneal injection, oral gavage and in vitro immersion. The corresponding positive signals for pathogen infection were preferentially present in the spleen, intestine and gill tissues. Thus, preventing S. agalactiae contamination in aquaculture water and food sources is an effective measure to control the outbreak of S. agalactiae infections in tilapia under natural aquaculture conditions.
[Objectives] This study aimed to determine the infection pathway and target organs of Streptococcus agalactiae in GIFT strain of Nile tilapia, thus providing theoretical basis for the breeding of disease-resistant tilapia and development of S. agalactiae vaccines.[Methods] GIFT strain of Nile tilapia was inoculated by S. agalactiae through intraperitoneal injection, oral gavage and in vitro immersion. The gill, spleen, liver and small intestine tissues of infected tilapia were collected for pathomorphological observation. Immunohistochemical localization was conducted using rabbit anti- S. agalactiae serum to identify the distribution pattern of S. agalactiae in various tissues of tilapia and its target organs via different infection pathways.[Results] GIFT strain of Nile tilapia could be infected by S. agalactiae via three artificial inoculation modes. Specifically, pathological changes occurred at 2 h post-inoculation in intraperitoneal injection and oral gavage groups, whereas tilapia in in vitro immersion group showed pathological changes at 5 h post-inoculation, and the lesion intensity in in vitro immersion group was slighter than that in intraperitoneal injection and oral gavage groups. Immunohistochemical localization indicated that the appearance time of positive signals in intraperitoneal injection group demonstrated an order of spleen→liver and gill→small intestine; positive signals in oral gavage group appeared in the order of small intestine→gill and spleen→liver; the appearance time of positive signals in in vitro immersion group showed an order of gill→spleen→liver and small intestine.[Conclusions] GIFT strain of Nile tilapia could be infected by S. agalactiae via intraperitoneal injection, oral gavage and in vitro immersion. The corresponding positive signals for pathogen infection were preferentially present in the spleen, intestine and gill tissues. Thus, preventing S. agalactiae contamination in aquaculture water and food sources is an effective measure to control the outbreak of S. agalactiae infections in tilapia under natural aquaculture conditions.
基金
Supported by Science and Technology Major Project of Guangxi(GK AA17204080-2)
Guangxi Key Research and Development Program(GK AB16380077)
Freshwater Fishery Industry Technology System of China(CARS-46)
Aquathe Disease Resistance Breeding Project of Natinal Blue Granary plan(2019-2023)
