Determination of antibiotic residues in fish sold in the supermarkets around Mafikeng, North West Province
Aquaculture production has grown in the past decade, leading to a concurrent substantial growth in the use of antibiotics by the industry. The primary aim of this study was to determine antimicrobial residue levels of tetracycline, chloramphenicol, sulphonamide (sulfadiazine), quinolone (ciprofloxacin), nitrofuran, doxycycline, and penicillin to identify bacterial species in fish samples and observe their sensitivity to different antibiotics. This investigation was performed by collecting fish samples from supermarkets in Mafikeng, North West Province (n=50). Five samples of each fish type were collected during the study. Determination and detection of antibiotic residues from fish samples were conducted by using the Enzyme Linked Immuno-Sorbent Assay (ELISA), Thin Layer Chromatography (TLC) and High-Pressure Liquid Chromatography (HPLC). The results obtained revealed the presence of antimicrobial residues to be within the following ranges: 84; 84; 96; 12 and 20% of samples with concentrations ranging between 0-2240 (398 μg/kg); 0-120 (22.19 μg/kg); 0.3-9.7 (40.44 μg/kg); 0-30 (3.92 μg/kg) and 0-4840 (259.96 μg/kg) respectively for tetracycline, chloramphenicol, sulphonamide, quinolone and nitrofuran. It was also observed that among the positive samples, 54%, 84%, 6%, 4% and 10% respectively for tetracycline, chloramphenicol, sulphonamide, quinolone and nitrofuran were found to be above the Codex Alimentarius/ Republic of South African Maximum residue limits (Codex/ RSA MRL) using ELISA. The The results for TLC showed a high prevalence rate of antimicrobials (88%, 76%, 74%, 74% and 64%) for sulphonamide, ciprofloxacin, tetracycline, doxycycline and chloramphenicol respectively. HPLC detected 28%, 74%, 14%, 21% and 0% with concentrations ranging between 0-0.69 (0.23 μg/kg), 0-279.8% (49.47 μg/kg), 0.68-8 (2.79 μg/kg), 0.68-7% (0.24 μg/kg) and 0% (0 μg/kg) respectively for tetracycline, chloramphenicol, sulphonamide and doxycycline. However, no penicillin residues were detected in samples analyzed using HPLC. Among the positive samples, chloramphenicol was found to be above the Codex/ South African MRL (72% of samples were detected with the same antibiotic). The presence of antimicrobial is regarded as a public health concern as they may cause allergic reactions, intestinal disruptions, soft tissue damage and nμ (P≥0.05) between the different methods used (ELISA, TLC and HPLC) were used to show the regularity, repeatability and quality in the methods used. The calibration curves of each antibiotic and process show the reliability of results obtained in this study. Although this study was limited in size, all samples were subjected to conventional methods as well as molecular techniques of 16rDNA species specific gene amplification by PCR. Furthermore, the bacterial isolates revealed the presence of Bacillus cereus (11.11%), Clostridium sordeli (5.56%), Enterococcus faecium (19.44%) and Enterococcus species (13.89%). Other micro-organisms had only 2.78% of the 20 samples. The isolates were evaluated for their antibiotic resistance pattern against some antibiotics using Kirby-Bauer antibiotic discs' diffusion method. In this study, most of the strains were susceptible to tetracycline (42%), followed by resistant strains (33%) and those that were intermediate (25%). In addition, the results obtained revealed that most of the strains (47%) had an intermediate resistance reaction to chloramphenicol, followed by strains that were susceptible (39%) and those that were resistant (25%). Majority of the strains (97%) were susceptible to ciprofloxacin, with only 3% were resistant while none was intermediate. Three quarters (75%) of the strains were susceptible to sulphonamide, followed by strains that were resistant (17%) and those that were intermediate (8%). Furthermore, 39% of strains were resistant to norfloxacin, followed by strains that were susceptible (36%), while only a quarter were intermediate (25%). Generally, ciprofloxacin is the best antibiotic among the five used in this study since more than 90% of the bacterial strains were susceptible to it. Nonetheless, the study revealed low levels of antimicrobial residues and MRL; their presence in fish might be of risk to consumers. There is, therefore, a need for proper monitoring of the quality of fish sold in the country as well as training on antibiotic monitoring. This would enable farmers to be able to adhere to withdrawal periods of antibiotics and maintain healthy standards.