OXYTETRACYCLINE RESIDUES AND ANTIMICROBIAL DRUG RESISTANT ESCHERICHIA COLI IN RAW MILK FROM DAIRY FARMS IN KANO STATE, NIGERIA
The use of veterinary drugs in food animals may result in trace quantities of the drugs or their metabolites as residues in food. The aim of this study was to determine the occurrence and concurrence of oxytetracycline residues and antimicrobial drug resistant Escherichia coli in raw milk from some commercial dairy farms in Kano State. Eighteen (18%) percent of the total registered farms (54 farms) in the State were sampled using a purposive sampling technique. Twenty five percent (25%) occurrence of antimicrobial residues in milk was observed, of which 93.7% of them were tetracyclines. The distribution of antimicrobial residues in milk based on farm type indicated antimicrobial residue was highest in the conventional farms. There was a statistically significant (P<0.05) association in the premitest results between detection of antimicrobial residues and the type of farm. The conventional farms had 36.51% (46/126) antimicrobial residues in which 89.13% were tetracycline residues while the cooperatives had 17.65% (33/187) antimicrobial residues of which 100% were tetracycline residues. There was a statistically significant association (p<0.05) between detection of antimicrobial residue and the breeds of animal sampled. Occurrence of antimicrobial and tetracycline residues was highest further away from the metropolis with occurrence of 30.63% and 100%, respectively, compared to other locations. Out of 70 milk samples that were collected from within the metropolis, 19 (27.14%) had antimicrobial residues of which 14 (73.68%) were tetracycline residues. Eleven (13.25%) of the 83 samples collected from Local Governments Areas bordering Kano metropolis contained antimicrobial residues of which 100% of them are tetracycline residues. There was a statistically significant association (P< 0.05) in the distribution of residues between the different locations. Fifteen E. coli (4.8%) were isolated from the 313 milk samples collected and tested in which three (3) were from residue positive milk and twelve (12) were from residue negative milk. Out of the four moderately resistant E. coli that were tested, 3 (75%) of them were from residue positive milk while 1 (25%) was from residue negative milk. Ten (90.91%) of the Multi-Drug resistant E. coli were from residue negative milk samples. None of the E. coli isolates was resistant to any of the quinolones tested, (nalidixic acid and ciprofloxacin) 13.3% were resistant to chloramphenicol (a synthetic antibiotic) and cefixime (a cephalosporin) while 33.3% were resistant to amoxicillin+clavulanic acid (a synthetic penicillin) and co-trimoxazole (a sulfa drug). About 26.7% and 40% of the isolates were resistant to gentamicin and kanamycin (aminoglycosides), respectively, while resistance to tetracycline was 46.7%. However, all of the isolates were resistant to Ampicillin (a synthetic penicillin). Result from the PCR showed that one of the isolates was carrying tet M resistance gene while six (40%) others were carrying tet A resistance gene. This study revealed the occurrence of antimicrobial residues in milk samples from commercial dairy in Kano State, Nigeria. The study further revealed that the E. coli isolates carry tet resistant genes. It is recommended that farmers should avoid the indiscriminate use of antibiotics in production, and they should observe drug withdrawal periods before milking their cows.