Site specific bacterial load, enterobacterial occurrence and antibiotic susceptibility patterns in Nile Tilapia (Oreochromis niloticus), water and sediment from earthen aquaculture ponds

Abstract

Introduction: aquaculture is the most rapidly growing food production sector. The intensive nature of freshwater fish aquaculture is associated with practices which predispose aquaculture produce to bacterial contamination. To prevent losses due to bacterial diseases, there has been an increase in the uncontrolled use of antibiotics, a good prerequisite to the development of antibiotic resistance - a major global problem. Hence, we aimed at investigating the enterobacterial diversity and occurrence of antimicrobial resistance in Nile Tilapia and its earth pond environment. Methods: fish samples, pond water and sediments were collected from four earthen ponds located at Yato, Cameroon, in three different collection trips for Total Heterotrophic Aerobic Plate Count (THAPC) and enterobacterial isolation. Bacterial characterisation and antibiotic sensitivity were assessed using the API 20E kit and the standard Kirby-Bauer disc diffusion method, respectively. Results: THAPC ranged from 1.0 x 102to 3.0x109CFU/mL across samples and within each pond, bacterial loads were highest in fish parts and lowest in the surrounding environment. Sixteen enteric genera and 24 species were identified, with Escherichia coli(16.49%) and Enterobacter cloacae(12.37%) being most abundant, especially in the gills and intestines. The highest degree of resistance was observed with Amoxicillin and Ampicillin, with more than 60% of tested isolates being resistant. Multiple drug resistance was also observed in all sample types, ponds and collection time points, and highest in fish parts. Conclusion: this study re-emphasizes the potential of freshwater fish aquaculture as carrier of human pathogenic and multiple drug resistant bacteria.