Study of the pathogenicity of Nocardia spp. by experimental infection in meagre, Argyrosomus regius (asso, 1801)
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2016
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A Nocardiose, causada por Nocardia spp. em peixes, foi primeiramente identificada por Rucker (1949) como Streptomyces salmonicida no salmão vermelho (Oncorhynchus nerka). Muitos casos desta doença têm sido descritos desde então, um pouco por todo o mundo, afetando um amplo leque de espécies. A Nocardiose é causada por uma bactéria Gram-positiva, álcool-ácido resistente, aeróbica e filamentosa. Sinais típicos de doença manifestam-se por anorexia, emaciação, inatividade, ascite, descoloração e úlceras da pele, brânquias e músculos, bem como granulomas no rim, baço, fígado, coração, olhos, cérebro, músculo e pele.
Neste trabalho, diferentes doses (101 to 108 CFU/mL) de Nocardia spp. foram inoculadas por via intraperitoneal em 160 corvinas, Argyrosomus regius (Asso, 1801) distribuídas por 8 tanques, cada um com diferente dose. Um nono tanque foi ainda adicionado como grupo controlo. A mortalidade cumulativa atingiu 6% sendo que todos os animais encontrados sem vida pertenciam aos tanques onde as doses inoculadas eram superiores. Os sinais clínicos observados traduziram-se em anorexia e emaciação e foram identificados apenas nos animais provenientes dos tanques com maior dose da bactéria inoculada (T1-T3).
Amostras de rim, baço e fígado foram retiradas e analisadas histológica e bacteriologicamente. Os estudos histológicos corados com Hematoxilina-Eosina revelaram lesões típicas granulomatosas no rim (23%), no fígado (11%) e baço (2%). Foi ainda observado que o número de granulomas identificados por órgão parece sofrer influência da dose inoculada, sendo que o maior número de granulomas por órgão foi encontrado em T1 e T2. O recurso a técnicas de coloração especiais como Gram e Ziehl-Neelsen não se revelou frutífero, tendo em conta que não permitiu a observação da bactéria em nenhuma das amostras. Nocardia spp. foi isolada nos mesmos órgãos acima descritos através de cultivo em meio Agar Sangue com 1.5% de Cloreto de Sódio, Brain Heart Infusion com 1.5% de Cloreto de Sódio e Yeast Extract-Malt Extract. No entanto, a percentagem revelou-se oposta à observada em histologia, fígado (10%), baço (5%) e rim (4%). O facto de a Nocardia ser uma bactéria difícil de isolar em meio de cultivo pode explicar a discrepância entre os resultados obtidos de histologia e bacteriologia. Foi também verificado que a incidência de granulomas parece ser afetada pelo tempo, enquanto o isolamento da bactéria está mais dependente da dose. Estes resultados
demonstram a evolução da Nocardiose numa infeção experimental de Nocardia spp. em corvina.
Nocardiosis caused by Nocardia spp. in fish was first identified by Rucker (1949) as Streptomyces salmonicida in sockeye salmon (Oncorhynchus nerka). Since then several cases of the disease have been reported all over the world in different species, caused by this Gram-positive, partially acid-fast, aerobic and filamentous bacteria. Typical signs of the disease include severe emaciation, inactivity, granulomas in gills, spleen, kidney and liver with skin discoloration, multiple ulcer and/or nodule formation, cachexia and in some cases ascites. The present work aimed at the characterization of nocardiosis in meagre. Nocardia spp. was inoculated via intraperitoneal injection in 160 meagres, Argyrosomus regius (Asso, 1801), distributed along 8 tanks with different inoculation doses (101 to 108 cfu/ml). The cumulative mortality was 6% and all dead fish belonged to tanks with higher doses (T1-T3). Anoreixa and emaciation were observed in animals from tanks inoculated with higher doses (T1-T3). Samples of liver, spleen and kidney were taken from all animals for microbiological and histological analysis. Histological studies showed typical granulomatous lesions in kidney (23%), liver (11%) and spleen (3%). However, special staining of lesions did not show the presence of the bacteria. A possible relation between the number of granulomas per organ and the dose inoculated was also perceived, with the most affected organs belonging to animals inoculated with higher doses of bacteria (T1 and T2). Nonetheless, Nocardia spp. was isolated from the same organs using Blood Agar with 1.5% of Sodium Chloride, Brain Heart Infusion with 1.5% Sodium Chloride and Yeast Extract-Malt Extract medium, although a different incidence was observed in liver (10%), spleen (5%) and kidney (4%). The fact that Nocardia is a difficult bacteria to isolate may explain to this discrepancy between histological and bacterial results. It was also observed that incidence of granulomas seems to be time related, while the isolation of the bacteria is dose related. Together, these results describe the pathological evolution of an experimental Nocardia infection in meagre.
Nocardiosis caused by Nocardia spp. in fish was first identified by Rucker (1949) as Streptomyces salmonicida in sockeye salmon (Oncorhynchus nerka). Since then several cases of the disease have been reported all over the world in different species, caused by this Gram-positive, partially acid-fast, aerobic and filamentous bacteria. Typical signs of the disease include severe emaciation, inactivity, granulomas in gills, spleen, kidney and liver with skin discoloration, multiple ulcer and/or nodule formation, cachexia and in some cases ascites. The present work aimed at the characterization of nocardiosis in meagre. Nocardia spp. was inoculated via intraperitoneal injection in 160 meagres, Argyrosomus regius (Asso, 1801), distributed along 8 tanks with different inoculation doses (101 to 108 cfu/ml). The cumulative mortality was 6% and all dead fish belonged to tanks with higher doses (T1-T3). Anoreixa and emaciation were observed in animals from tanks inoculated with higher doses (T1-T3). Samples of liver, spleen and kidney were taken from all animals for microbiological and histological analysis. Histological studies showed typical granulomatous lesions in kidney (23%), liver (11%) and spleen (3%). However, special staining of lesions did not show the presence of the bacteria. A possible relation between the number of granulomas per organ and the dose inoculated was also perceived, with the most affected organs belonging to animals inoculated with higher doses of bacteria (T1 and T2). Nonetheless, Nocardia spp. was isolated from the same organs using Blood Agar with 1.5% of Sodium Chloride, Brain Heart Infusion with 1.5% Sodium Chloride and Yeast Extract-Malt Extract medium, although a different incidence was observed in liver (10%), spleen (5%) and kidney (4%). The fact that Nocardia is a difficult bacteria to isolate may explain to this discrepancy between histological and bacterial results. It was also observed that incidence of granulomas seems to be time related, while the isolation of the bacteria is dose related. Together, these results describe the pathological evolution of an experimental Nocardia infection in meagre.
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Orientação : Pedro Faísca ; co-orientação : Maria José Caballero
Palavras-chave
MESTRADO INTEGRADO EM MEDICINA VETERINÁRIA, VETERINÁRIA, PEIXES, AQUICULTURA, PATOLOGIA, FISHES, AQUACULTURE, PATHOLOGY, MEDICINA VETERINÁRIA, VETERINARY MEDICINE