Assessment of antibiotic residues by microbial inhibitor tests in fresh cow milk sold in Bamako (Mali)

In a first series of 220 fresh milk samples, originating from 18 selling points in Bamako, Mali, 6% were shown to contain antibiotic residues by the yoghurt test. These positive samples all came from 4 selling points in the Commune 1 district. A second confirmatory series of 72 samples from 2 selling points selected out of the 4 positive selling points showed a prevalence of 16% with both yoghurt and Delvo tests. Milk sampled during the rainy season (July to October) contained less frequently antibiotics than during the rest of the year (odds ratio = 5.1; 95% confidence limits 1.1-24.7). Milk adulteration did not affect the detection of the presence of antibiotics in the milk. According to a survey with 56 people involved in the milk supply chain (vendors, herders, livestock owners), oxytetracycline is widely used by local dairy farmers. The study indicated that the main reasons for the presence of such antibiotic residues are the uncontrolled use of drugs, the fact that farmers do not comply with recommended withdrawal times, and low productivity, which makes producers very reluctant to discard milk from treated cows.