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The occurrence of Listeria spp. and Listeria monocytogenes in 63 samples of Portuguese poultry carcasses obtained from two local butcher shops and one canteen in the city of Porto, Portugal, and the susceptibility of these bacteria to antimicrobial agents allowed for use in human or animal therapeutics were evaluated. All poultry samples were contaminated with Listeria spp., and L. monocytogenes was isolated from 41% (26 of 63) of the samples. Other Listeria species, including L. innocua, L. welshimeri, and L. seeligeri, were also isolated from poultry samples. A multiplex polymerase chain reaction method was used for the identification of all of the Listeria isolates; this method showed total conformity with the conventional method of biochemical identification and proved to be more reliable, faster, and less arduous. In addition, high percentages of Listeria spp. (84%) and L. monocytogenes (73%) isolates were found to be resistant to one or more antimicrobial agents of different groups, and 12 different resistance profiles were recorded. The frequency of the resistance of L. monocytogenes isolates to enrofloxacin and clindamycin is notable. The results of this study suggest a high incidence of L. monocytogenes on Portuguese poultry products available for consumers and indicate that poultry could be a potential vehicle of foodborne infections due to strains of L. monocytogenes that are resistant to antimicrobial agents.

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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.