Detection and Molecular Characterization of Some Bacteria Causing Skin Ulceration in Cultured Nile Tilapia (Oreochromis niloticus) in Kafr El-Sheikh Governorate

Background and Objective: Cultured Nile tilapia [Orechromis niloticus (O.niloticus)] is so far the most widespread species in earthen ponds in Egypt.These cultured fish suffers from yearly bacterial mass mortalities with a characteristic external hemorrhages and ulcer formation.This study aimed to investigate some of these bacterial pathogens with emphasis on their specific anti-biogram profile. Materials and Methods:A number of 150 naturally infected O. niloticus were collected from different fish farms at Kafr El-Sheikh Governorate, Egypt where the skin ulcers were the most common clinical sign.The fish were bacteriologically examined and all bacterial isolates were identified phenotypically, serologically and by using VITEK 2 Compact System and finally by polymerase chain reaction.Results: The results revealed that, the isolated bacteria; were Aeromonas sp.(25.9%) [A.hydrophila (23.3%) and A. caviae [2.6%)] and Pseudomonas sp.(23.3%) [P.fluorescens (9.3%), P. putida (2%) and P. aeruginosa (12%)] in addition to S. aureus (7.3%) while mixed infections were (36.6%).Antimicrobial sensitivity test of Aeromonas spp.revealed their sensitivity to ciprofloxacin, while the sensitivity of Pseudomonas spp.were to chloramphenicol, ciprofloxacin, tetracycline and streptomycin, respectively.Finally S. aureus was sensitive to ciprofloxacin, ampicillin, gentamicin and amoxicillin.Conclusion: The results concluded that antimicrobials (if applicable) could be used as effective candidate for fish treatment, after performing sensitivity testing and maintaining good water quality in fish ponds fish could be recovered from such infections.