Isolation, identification and characterization of Aeromonas allosaccharophila from infected farmed leech (Whitmania pigra) in Jiangsu, China

Abstract

Aeromonas allosaccharophila is a gram-negative, rod-shaped, non-spore-forming bacterium that causes disease and death in humans and aquaculture species, but studies on A. allosaccharophila in aquaculture have been more limited than those on other Aeromonas species. Here, we examined a pathogenic strain of A. allosaccharophila that causes “erysipelas” in leeches and mass mortality of farmed leech in Jiangsu, China. The main clinical signs of diseased leeches included severe rot of the head and tail, body cavity effusion, and redness or swelling of the clitellum. Histopathological observation of diseased leeches showed that the muscle tissue cells were scattered, randomly arranged with a large intercellular space and swollen. Eight strains were isolated from the rotten issue of a diseased leech, and WP204 was confirmed as having the strongest pathogenicity by Koch's postulates. This strain was identified as A. allosaccharophila WP204 by physiological and biochemical identification and phylogenetic analysis of the whole genome sequence. The optimal growth conditions were 18–38 °C, pH 5–9, and 0–3% salinity. The isolate was susceptible to 14 drugs, including chloramphenicol, ciprofloxacin and ofloxacin, and resistant to rifampicin and clindamycin. For leeches, the LD50 of WP204 was 3.65 × 105 CFU/mL, and the LT50 decreased with increasing WP204 concentration. The present study is the first report of a leech-pathogenic strain of A. allosaccharophila in China, providing a reference for the prevention and control of bacterial diseases in the standardized breeding of leeches.