DETERMINATION AND ANTIBIOTIC RESISTANCE PROFILES OF BACTERIAL PATHOGENS OF Oreochromis niloticus AND Clarius gariepinus IN UGANDA
Bacterial diseases are a major constraint to fish production worldwide. Proper management of these diseases requires clear understanding of the prevalent etiological agents and available control options. In Uganda just like many other developing countries, there is limited reliable information about the prevalent species of fish bacterial pathogens. This study was carried out to establish the different species of bacteria infecting Oreochromis niloticus and Clarius gariepinus in Uganda and to determine their antibiotic susceptibility profiles.
A total of 288 fish samples from 40 fish farms and 8 wild sources were aseptically processed to isolate bacteria from internal organs (kidney, liver and spleen). Bacteriological swabs were also taken from the skin and any gross lesions observed. The samples were inoculated on Brain Heart Infusion agar (BHI) and/or Tripticase soy agar (TSA) together with selective agar plates for major tropical fish bacterial pathogens. The plates were incubated at 25- 300C for 24 to 48 hours. Isolates were identified by their phenotypic and biochemical properties using conventional means and Analytical Profile Index (API) test kits (API20E and API 20NE). The antibiotic resistance profiles of selected isolates against fourteen (14) selected antibiotics were determined by Kirby-Bauer disc diffusion method.
Well-known fish pathogens were identified at a farm prevalence of; Aeromonas hydrophila (44%), Aeromonas sobria (21%), Edwardsiella tarda (8%), Flavobacterium spp. (4%), Pseudomonas aeruginosa (4%), Pseudomonas fluorescens (10%), Citrobacter spp (4%), and Streptococcus spp. (6%). Other identified pathogens with varying and unclear significance in fish production include; Chryseobacterium indolgenes (13%), Pseudomonas stutzeri (2%), Burkholderia cepacia (2%), Plesiomonas shigelloides (25%), Comamonas testosterone (8%), Ralstonia picketti (2%), Serratia marcescens (4%), Vibrio spp. (10%), Klebsiella spp. (4%) and Proteus spp (6 %). There was a significant difference (P<0.05) in the occurrence of the bacteria according to production systems. Some bacteria species were highly associated with clinical disease in farmed fish. All bacteria evaluated for antibiotic sensitivity were sensitive to at-least ten (10) of the fourteen antibiotics tested. Some isolates expressed high levels of resistance to Penicillin, Oxacillin, Ampicillin, Clindamycin and Vancomycin, which is most probably intrinsic in nature, suggesting minimal or no acquired antibiotic resistance. To our knowledge, this is the first study to identify several of the different species of bacteria infecting fish and to determine antibiotic sensitivity profiles of fish bacteria in Uganda. This is vital information for fish disease management and provides baseline data for future reference. Characterization of the isolated bacteria is of great significance.