Microbiological and histological studies of farmed-bullfrog (Rana catesbeiana) tissues displaying red-leg syndrome

Abstract

Rana catesbeiana is one of the delicacies of international gastronomy. Farming operations often lead to an increased risk of diseases and mortality. The present work addresses microbiological and histological studies in R. catesbeiana with red-leg syndrome (RLS), infection that causes significant economic losses in hatcheries. Partial phenotypical identification demonstrated that the microbial populations isolated from the skin of fattening phase animals and freshwater samples during the autumn (June) are grouped into the following taxa: Lactobacillus spp, Pediococcus spp, Micrococcus spp, Enterococcus faecalis, Ent. faecium and Enterobacteriaceae (Enterobacter spp and Proteus vulgaris). Microbial infection on target organs (liver/spleen) and blood showed the presence of Pr. vulgaris, Staphylococcus aureus and Enterococcus strains. Histological studies of skin ulcerations showed epithelial necrosis, diskeratosis, apoptosis and espongiosis. No sporangia associated with chitridiomycosis were observed. The dermis presented oedema, dilated vascular light, fibrin-leucocytic exudates and distortion of serous and granular glands. The liver showed centrolobullar necrosis and a decrease in melanin containing cells. The spleen presented wide areas of septic infarct. This paper reports the presence of lactic acid bacteria and other genera in the skin and freshwater from farmed R. catesbeiana during the autumn and a correlation between microbial infection and structural changes in tissues of bullfrogs with RLS. The severity of the structural changes is related to the level of microbial infection in the target organs and could be sustained by the isolation of Pr. vulgaris and other pathogens.