Abstract:

To identify the mortality cause of Macrobrachium rosenbergii, the strain with growth advantage was isolated from the dying M. rosenbergii, and its morphological characteristics, gram staining, physiology and biochemistry experiments were studied. The results showed that the isolated strain was a gram-negative, while oxidase, lysine decarboxylase, citrate, indole, d-mannose, sucrose, maltose, v-p, and cellobiose dihydrolase were positive. The 16S rRNA gene of this isolate was sequenced and phylogenetic tree was constructed. The isolated strain was clustered with Aeromonas veronii and had a close genetic relationship. The isolated strain was confirmed as Aeromonas veronii (Accession number MN733186) based on the biochemical characters and 16S rRNA sequence analysis. The artificial infection experiment with the immersion method confirmed that the isolated strain was highly pathogenetic to M. rosenbergii. The results of drug susceptibility tests revealed that the strain was highly sensitive to ceftriaxone, chloramphenicol, florfenicol, doxycycline, and rifampicin; it was moderately sensitivity to novobiocin and compound sulfamethoxazole and resistant to ciprofloxacin, norfloxacin, erythromycin, azithromycin, streptomycin, kanamycin, tetracycline. The current study could provide a reference and theoretical basis for the pathogen identification, drug diagnosis and treatment of Aeromonas cavia in M. rosenbergii.

Key words: Macrobrachium rosenbergii, Aeromonas veronii, isolation and identification, gram staining, biochemical identification, drug sensitivity test