Antibiotic resistance integrons and extended-spectrum {beta}-lactamases among Enterobacteriaceae isolates recovered from chickens and swine in Portugal

J Antimicrob Chemother. 2008 Aug;62(2):296-302. doi: 10.1093/jac/dkn179. Epub 2008 May 2.


Objectives: To investigate the diversity of integrons and extended-spectrum beta-lactamases (ESBLs) among Enterobacteriaceae from chickens and swine in Portugal and analyse the clonal relationships between Portuguese ESBL-producing isolates of animal and human origin.

Methods: We analysed samples from faeces of healthy swine (HSF, n = 35), from uncooked chicken carcasses (CM, n = 20) and from faeces of healthy chickens (HCF, n = 20). Samples were plated on MacConkey agar with and without ceftazidime (1 mg/L) or cefotaxime (1 mg/L). ESBLs were characterized by PCR and DNA sequencing. Bacterial identification, antibiotic susceptibility and conjugation assays were performed by standard procedures. Isolate clonal relatedness was established by PFGE and by RAPD for PFGE non-typeable isolates. Escherichia coli phylogenetic groups were identified by a multiplex PCR. Integron analysis was accomplished by PCR-RFLP and sequencing.

Results: ESBL-producing Enterobacteriaceae were identified in 60% of CM, 10% of HCF and 5.7% of HSF samples, respectively, mostly corresponding to E. coli (phylogroups A, D and B1). TEM-52, SHV-2 and CTX-M-1 were detected from chicken and SHV-12 from swine samples. High clonal diversity was observed and most bla(ESBL) genes were transferable (67%). Class 1 and/or class 2 integrons were identified in 80% of CM, 10% of HCF and 63% of HSF samples, with class 1 integrons more common than class 2 integrons (36% versus 12% of the isolates recovered, respectively). Ten class 1 integron types are described, aadA1 and dfrA1-aadA1 being the most frequently found. Two class 1 integron types (aadA13-estX and dfrA14-aadA1-catB2) and one class 2 integron (aadA1) are first reported here.

Conclusions: This study is the first report of ESBLs and integrons from chickens and swine in Portugal and highlights the antibiotic-resistant bacteria and/or resistance genes that might be acquired by humans through the food chain.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Chickens / microbiology*
  • Cluster Analysis
  • Conjugation, Genetic
  • DNA Fingerprinting
  • DNA, Bacterial / chemistry
  • DNA, Bacterial / genetics
  • Drug Resistance, Microbial*
  • Electrophoresis, Gel, Pulsed-Field
  • Enterobacteriaceae / classification
  • Enterobacteriaceae / drug effects*
  • Enterobacteriaceae / genetics*
  • Enterobacteriaceae / isolation & purification
  • Feces / microbiology
  • Genetic Variation
  • Integrons*
  • Microbial Sensitivity Tests
  • Molecular Epidemiology
  • Phylogeny
  • Polymerase Chain Reaction
  • Portugal
  • Random Amplified Polymorphic DNA Technique
  • Sequence Analysis, DNA
  • Swine / microbiology*
  • beta-Lactamases / genetics*


  • DNA, Bacterial
  • beta-Lactamases