Antibiotic residues in edible tissues and antibiotic resistance of faecal Escherichia coli in pigs from Portugal.

The aims were to provide data on antibiotic residues in pig tissues and the trends in the occurrence of antibiotic resistance in Escherichia coli (a commensal bacteria that can colonize the intestinal tract of humans and animals) isolated from the animals studied. Muscle and kidney samples collected from freshly slaughtered pigs were tested for the presence of antibiotic residues using rapid screening tests. Ninety muscle and 90 kidney samples from the same animals, collected in the slaughterhouse of the central region of Portugal, were screened by microbial tests and only six samples did not fulfil the European Community regulations concerning maximum residue limits. When a more sensitive method was used for the detection of sulphamethazine, 36% of the animals contained residues of the antibiotic. This indication of a larger antibiotic occurrence than anticipated was confirmed by studying the susceptibility of their enteric E. coli. In all the animal faeces studied (n = 60), E. coli isolates resistant to amoxycillin, tetracyclines and sulphonamides were found. The majority of the faecal samples demonstrated a high degree of E. coli resistant to sulphonamides and tetracyclines, respectively 88% and 85%. These data raise important questions about the relevance of the detection of antibiotic residues as the only method to establish the quality and safety of animal products for human consumption.