Isolation, identification and antibiotic sensitivity of Aeromonas veronii from Litopenaeus vannamei

Abstract:

[Objective] Litopenaeus vannamei is one of the most important species of shrimp farming in the world, with high output and value and strong market demand. From May to June of 2017, Litopenaeus vannamei was found to have unexplained high morbidity and mortality in one shrimp farm in Shanghai. To determine and identify the cause of death for Litopenaeus vannamei and screen out sensitive drugs, a dominant bacterium strain AVZ01 was isolated from sick L. vannamei. The aim of this study was to provide reference for further prevention and treatment of Aeromonas veronii in China. [Methods] The pathogenic bacteria were isolated from the hepatopancreas and intestinal tract of dead L. vannamei. The LD50 assay was carried out by Bliss method. According to morphological, biochemical characteristics and 16S rRNA gene sequence analysis, the isolated strain was identified. Antibiotic susceptibility test was carried out by K-B methods. [Results] After the artificial infection test with strain AVZ01 from the diseased shrimp, the symptoms of shrimp were similar to those of natural disease, the LD50 was counted to 8.7×105 CFU/mL. According to the morphological characteristics, biochemical characteristics and 16S rRNA gene sequence analysis, the pathogen was identified as A. veronii. The results of antibiotic sensitivity test showed that the AVZ01 strain is highly sensitive to 16 antibiotics, such as metolycins, norfloxacin and gentamicin, etc, and resistant to 9 antibiotics, such as penicillin, oxacillin and cephalexin, etc. [Conclusion] The isolated strain AVZ01 has strong pathogenic to L. vannamei, and the gentamicin and neomycin could be used for the control and treatment in the future.