Occurrence of extended-spectrum β-lactamases among isolates of Salmonella enterica subsp. enterica from food-producing animals and food products, in Portugal

A total of 1120 Salmonella spp. isolates, recovered from poultry, swine and food products of animal origin (bovine, swine and poultry) over the period of 2009–2011, were investigated in order to determine their serotype, susceptibility to a panel of eleven antimicrobials (A, ampicillin; Ct, cefotaxime; Cp, ciprofloxacin; Tm, trimethoprim; Su, sulfamethoxazole; C, chloramphenicol; S, streptomycin; G, gentamicin; T, tetracycline; NA, nalidixic acid; Fl, florfenicol), and the presence of resistance determinants of extended-spectrum cephalosporins. Overall, Salmonella Enteritidis was the most common serotype in all three animal species. In 618 isolates of poultry, 32.8% comprised S. Enteritidis, 18.3% Salmonella Havana and 16.5% Salmonella Mbandaka; in 101 isolates of pigs, 21.8% comprised Salmonella Rissen and Salmonella Typhimurium, 10.9% Salmonella Derby and Salmonella London. Salmonella I 4,[5],12:i:- was the most common serotype recovered from pork and beef food products comprising 32.6% and 30% of isolates respectively, followed by S. Rissen (26% and 24%) and S. Typhimurium (18.2% and 19%), respectively. In poultry products, S. Enteritidis was the most frequent serotype (62.7%), followed by S. Mbandaka (10.2%) and S. Derby (8.5%). Susceptibility profiles differed according to the origin of the isolates. Five multidrug resistant isolates (0.45%) were further characterized as extended-spectrum β-lactamase (ESBL) producers. Polymerase chain reaction and sequencing of the amplicons confirmed the presence of blaCTX-M-1 (n = 2), blaCTX-M-14 (n = 1), blaCTX-M-15 (n = 1) and blaCTX-M-32 (n = 1); blaSHV-12 and blaTEM-1 genes were also detected in two isolates of S. I 4,[5],12:i:-. Four isolates, two S. Havana and two S. I 4,[5],12:i:-, carried class 1 integrons and in three, two S. I 4,[5],12:i:- and one S. Havana, ISEcp1 was identified associated to blaCTX-M-1, blaCTX-M-32 and blaCTX-M-14 genes. Additionally, in one S. I 4,[5],12:i:- isolate, orf477 was identified linked to blaCTX-M-32. No plasmid mediated quinolone resistance-encoding genes were detected. Here, we report for the first time the presence of blaCTX-M genes in Salmonella enterica subsp enterica isolates recovered from poultry and food products of swine origin, in Portugal.