Pathological and PCR detection of mycobacteriosis in pond-cultured Chinese soft shell turtles, Trionyx sinensis

Mycobacteriosis due to infection of Mycobacterium marinum is a common disease in pond-cultured Chinese soft shell turtles, especially in those surviving beyond their first year. The infected turtles independently showed either heterophilic or histiocytic granulomas in various organs such as the spleen, liver, lungs, intestine, kidneys, stomach and pancreas. The heterophilic granuloma contained many acid-fast unbranching bacilli intracellularly in macrophages and extracellularly in the necrotic center. The histiocytic granuloma had only a few bacteria, mainly in the cytoplasm of Langhan's giant cells. The organisms were rarely observed in the advanced lesions of both types. Based on PCR assays for partial hsp65 gene of Mycobacterium spp., all of our strains were identified as M. marinum which can be divided into two groups. The strains of the first group induced heterophilic granulomas and had very high nucleotide sequence identities (99.8%–100%) to the reference strains of M. marinum ( AF456471) and M. pseudoshottsii ( AY550226). Those strains of the second group caused histiocytic granulomas and also showed very high identities (99.8%–100%) to the reference strains of M. marinum ATCC 927 ( AF456470) and M. shottsii ( AY550225). However, when we compared the partial sequence of the hsp65 gene from group one and two strains the identities between the two groups range from 98.8% to 99.3%, therefore we can not assert that these two belong to the same species.