32 Alexandria Journal of Veterinary Sciences www.alexjvs.com AJVS. Vol. 57 (1): 32- 39 April 2018 DOI:10.5455/ajvs.293293 Biochemical and Molecular Characterization of Aeromonas Species Isolated from Fish Islam M. Wassif Animal health department, Desert Research Center, Cairo, Egypt ABSTRACT Key words: Aeromonas veronii biovar sobria, Oreochromis niloticus, Ictalurus punctatus, 16s rRNA, PCR In this study, a total of 150 Oreochromis niloticus (Nile tilapia) (90) and Ictalurus punctatus (Channel cat fish) (60) fish were collected randomly during an outbreak of disease mass mortalities from different fish farms in El Sharkia and El Ismailia governorate. Clinical signs and postmortem were recorded. Aeromonas veronii were isolated and presumptively identified using API20E system with recovery rate of 36.66% from total number of fish. The identification was confirmed for Aeromonas veronii biovar sobria by PCR and sequence analysis of 16s rRNA gene. The experimental infection was carried out by Aeromonas veronii biovar sobria isolate with 60 % of mortality rate. By antibiotic sensitivity test, Aeromonas veronii biovar sobria isolate was sensitive to Trimethoprim + Sulphamethoxazole and Erythromycin but it was resistant to Oxytetracyclin. *Correspondence to: Islam_wassif@hotmail.c om 1. INTRODUCTION Aeromonas species are gram-negative rods, non-spore forming, oxidase positive, ferment glucose and facultative anaerobic bacteria, widely distributed in freshwater, estuarine, and marine environments (Holmes et al., 1996 and Martin-Carnahanand Joseph, 2005). The organisms grow at a wide range of temperatures. Aeromonas species cause a wide spectrum of disease syndromes among warm- and cold-blooded animals, including fish, reptiles, amphibians, mammals, and humans (Roberts, 1993; Gosling, 1996 and Janda and Abbott, 2010). It is common in warm water aquaculture in Egypt and cause most serious infectious disease known as Motile Aeromonas Septicemia (MAS), associated with high mortality rates without symptoms in per acute phase but in acute phase, skin and fin ulcers appear on the external surface of fish with ascites in the abdomen and exophthalmia (Bondad et al., 2005 and Austin and Austin, 2012). The disease can produce significant losses in aquaculture industry because of reduced growth in survived cases (Pachanawan et al., 2008). Aeromonas sobria was responsible for outbreak of septicemia and red mouth disease with mass mortality in private fish farm at Sahl El-Housinia, Sharkia Governorate (El-Bouhy et al., 2015). Also, Aeromonas veronii biovar sobria was isolated and molecular identified from outbreak of disease mass mortalities in different fish farms at the areas of Bahr El-Baqar (Eissa et al., 2015). Nucleotide sequence analysis only for identification of Aeromonas veronii biovar sobria provides a rapid and reliable diagnostic techniques (Hassan et al., 2017). 2. MATERIALS AND METHODS 2.1. Fish samples: Ninety in addition to sixty of naturally infected Oreochromis niloticus and Ictalurus punctatus respectively with variable size were freshly collected aseptically and examined from private aquaculture fish farms at El Sharkia and El Ismailia Governorate, Egypt in September, 2015. Then immediately transported in a cleaning bag in ice box with cooled ice bags to the laboratory and processed within 3hrs. 2.2. Bacteriological examination: Swabs were collected from the surfaces of ulcers, erosion, tail, fin, gills, muscles, liver, spleen, kidney, eye and ascetic fluids which were firstly sterilized with heated spatula; sterile swab was inserted through the sterilized area and then inoculated into trypticase soya broth. The inoculated tubes were