Occurrence of Antibiotic Residues and Antibiotic-Resistant Bacteria in Nile Tilapia Sold in Some Markets in Accra, Ghana: Public Health Implication

In Ghana there are concerns that antibiotics may be used inappropriately to boost fish production, though no study has investigated this problem. To provide preliminary insights into public health aspects of the problem, we investigated the occurrence of antibiotic residues and antibiotic-resistant bacteria in Nile tilapia (Oreochromis niloticus), a fish commonly cultivated and consumed in Ghana. Two hundred Nile Tilapia fish were randomly sampled from four major markets in Accra, the capital city of Ghana. One hundred samples were screened for antibiotic residues using a microbial inhibition plate test that detects sixteen different antibiotics commonly used in animal husbandry and aquaculture. The other 100 samples were cultured for bacteria using direct culture methods, and the isolates were tested against seven antibiotics by the Kirby Bauer method. The overall prevalence of antibiotic residues in the fish samples was 7%. Bacteria that were isolated from the fish samples were Shigella sonnei (10%), Enterobacter cloacae (7%), Escherichia coli (6%), Salmonella Typhi (3%), Klebsiella pneumoniae (2%), and Proteus mirabilis (2%). All bacteria isolated were susceptible to gentamicin and ciprofloxacin but resistant to ampicillin. Multi-drug resistance (ie resistance to three or more different classes of antibiotics) occurred in 86.7% of the isolates. Nile Tilapia sold in Accra is a source of multi-drug resistant bacteria. Consumption of the fish can also lead to significant exposure to antibiotic residues.