Phenotypic, Molecular Detection and Antibiogram Analysis of Aeromonas Hydrophila from Oreochromis niloticus (Nile Tilapia) And Ready-To- Eat Fish Products in Selected Rift Valley Lakes of Ethiopia

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Addis Ababa University


Aeromonas hydrophila is a zoonotic bacterial pathogen that frequently causes disease and mass mortalities among cultured and feral fishes worldwide. In Ethiopia, A. hydrophila outbreak was reported in Sebeta fish ponds and in lake Tana fishery. However, there is no to little information on the molecular, and phenotypical characteristics of A. hydrophila in Ethiopian fisheries. Therefore, a cross-sectional study was conducted from November 2020 to May 2021 in selected Ethiopian Rift valley lakes namely Koka, Ziway, Langano and Hawassa Lakes with aim of isolation and determination of phenotypic and genotypic features of A. hydrophila infecting tilapia and fish products in respective towns. A total of 140 samples were collected aseptically from fish (Muscle, Gill, Intestine, Spleen and Kidney) from fish landing sites, market and restaurants from respective towns with purposive sampling methods. Aeromonas selective media (AMB), morphological and biochemical tests were used to isolate and identify A. hydrophila. Accordingly, the pathogen was isolated from 81 (60.45%) of samples. Among the isolates 92.59% expressed virulence trait through β hemolysis on blood agar media with 5% sheep blood. Moreover, 54 strains (66.67%) were further confirmed with Real-Time PCR (qPCR) using ahaI gene specific primers and optimized protocol. The highest (68.51%) were detected from live fish, (24.07%) were from market fish and the lowest (7.4%%) were from RTE. Antibiogram analysis was conducted on ten representative isolates. Accordingly, A. hydrophila isolates were susceptible to ciprofloxacin (100%), chloramphenicol (100%) and ceftriaxone (100%). However, all ten isolates were resistant to Amoxicillin and Penicillin. The present study revealed virulent, Amoxicillin and Penicillin resistant A. hydrophila stains in fish and fish products. Interestingly adhesive (ahaI) gene was detected in majority of the isolates. Moreover, we optimized the first Real time PCR protocol that would be useful for molecular epidemiological studies of A. hydrophila. In conclusion, A. hydrophila strains carrying virulence ahaI gene that were ß-hemolytic and resistant to antibiotics commonly used in human and veterinary medicine are circulating in the fishery. The detection of the pathogen in 140 of the sampled fish population is alarming for potential outbreaks and zoonosis. Therefore, further molecular epidemiology of the disease should be studied to establish potential inter host transmission and antibiotic resistance traits. Therefore, raising the public awareness on risk associated with consuming undercooked or raw fish meat is pertinent. Designing prevention and control strategies against A. hydrophila to safeguard the fishery sector is highly recommended.



A. hydrophila, Ethiopia, Nile tilapia, qPCR, Rift valley lake