Occurrence, Antimicrobial Susceptibility and Effect of Physico-chemical Factors on Potentially Pathogenic and Zoonotic Bacteria Isolated From Farmed and Wild Oreochromis Species in Taita-taveta County, Kenya

Abstract

Outbreaks of bacterial diseases in fish under intensive culture results in economic losses in aquaculture industry worldwide. In Kenya, fish diseases and antimicrobial resistance are among constraints for aquaculture sustainability. The objectives of this study were to determine physico-chemical factors, occurrence and antimicrobial susceptibility of potentially pathogenic and zoonotic bacteria in farmed and wild Oreochromis species in Taita-Taveta County, Kenya. One hundred and eleven apparently healthy fish consisting of 67 Oreochromis jipe, 34 Oreochromis niloticus and 10 hybrids; and 9 water samples were examined. Four organs from each fish were sampled, namely; skin and kidney swabs, gills and intestinal tissues. Conventional culture, biochemical and Matrix Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI-TOF) tests were done to identify bacterial isolates. The physico-chemical parameters of pond and lake-water were assessed “in situ” and further analyzed in the laboratory using the American Public Health Association's standard methods. Following Clinical Laboratory Standards Institute protocols, forty-five bacteria isolates were screened for resistance against six antibiotics using Kirby Bauer disc-diffusion method. This study found that external organs of the fish had the highest prevalence of the bacterial isolates with the gills having 29.7 % (177/596) while the kidneys had the lowest with 11.8% (p˂0.05). The source water had a lower prevalence of bacteria with 4.7%. Potential pathogenic and also zoonotic bacteria identified were Bacillus cereus (8%), Aeromonas veronii (8%), Aeromonas hydrophilla (5%), Acinetobacter Johnsonii (4%), and Acinetobacter solii (4%). All the bacteria were 100% (45/45) sensitive to Tetracycline and Gentamicin, 93.3%, 71.1% and 57.8% to Streptomycin, Co-trimoxazole and Ampicillin, respectively. A total of 42.2% of the xix bacteria showed multiple drug resistance against the antibiotics. The physico-chemical parameters of the ponds and lake water were either within normal, above or below the recommended range. Temperatures ranged between (20.68 -25.38OC) which is within the normal range of what is expected for tilapia farming. Wundanyi farm and lake Jipe were found to have the highest concentrations of dissolved oxygen, Wundanyi farms also had the highest concentration of Nitrates and Ammonia. The pH was alkaline (ranging between 8.2 and 10.9) and unsuitable for fish farming, with lowest value in Mwatate and highest in Wundanyi. Electrical conductivity was found to be highest in the lake compared to the farms. Mwatate farm had the highest concentration of phosphorous. Total suspended solids and turbidity levels were highest at Taveta farms. Sites with high Phosphorous, pH and NH3 had high number of pathogenic and zoonotic bacterial isolates {Aeromonas spp (A. hydrophila, A. veronii, A. hormaechei); Pseudomonas (P. fulva, P. putida, P. stutzeri); Bacillus cereus and Klebsiella pneumonia}. In conclusion, water, farmed and wild fish harbored potentially pathogenic and zoonotic bacteria which may cause diseases for fish and pose public health risks. In addition, some of the bacterial isolates showed high antimicrobial resistance to common antibiotics of human and animal health importance. Therefore, there is a need to educate fish farmers and other key value chain actors on proper control measures of fish bacterial infections, as well as water quality and antimicrobial resistance issues in Taita Taveta County