JAC Advance Access originally published online on September 13, 2007
Journal of Antimicrobial Chemotherapy 2007 60(5):1137-1141; doi:10.1093/jac/dkm316
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Characterization of CTX-M and SHV extended-spectrum ß-lactamases and associated resistance genes in Escherichia coli strains of food samples in Tunisia
1 Laboratoire MBA, Département de Biologie, Faculté de Sciences de Tunis, Campus Universitaire, 2092 Tunis, Tunisia 2 Area de Bioquímica y Biología Molecular, Universidad de La Rioja, 26006 Logroño, Spain 3 Veterinary Research Institute, Tunis, Tunisia
Received 4 May 2007; returned 26 June 2007; revised 25 July 2007; accepted 31 July 2007
* Corresponding author. Tel: +34-941299750; Fax: +34-941299721; E-mail: carmen.torres{at}unirioja.es
Objectives: To assess the occurrence of extended-spectrum ß-lactamases (ESBLs) in Escherichia coli isolates of faecal samples of animals (n = 40) and food samples (n = 38) obtained in Tunisia in 2006, and to characterize the type of ESBLs, their genetic environments and the associated resistance genes.
Methods: Samples were inoculated in supplemented media (2 mg/L cefotaxime) for isolation of broad-spectrum cephalosporin-resistant E. coli isolates (one isolate/sample). ESBLs and their genetic environments as well as integrons and their gene cassette composition were characterized by PCR and sequencing.
Results: ESBL-producing E. coli isolates were detected in 10 of the 38 food samples analysed (26%) and in none of the tested animal faecal samples. Genes found were as follows (number of isolates): blaCTX-M-1 (5), blaCTX-M-1 + blaTEM-1b (1), blaCTX-M-14 + blaTEM-1b (2), blaCTX-M-8 (1) and blaSHV-5 (1). All ESBL-positive isolates showed unrelated PFGE patterns. ISEcp1 and IS903 were detected surrounding blaCTX-M-14, and ISEcp1/IS26 and orf477 surrounding some of the blaCTX-M-1 genes. Four of the ESBL-positive strains harboured class 1 integrons including different gene cassette combinations.
Conclusions: ESBLs, mainly of the CTX-M class, are detected in E. coli of food origin in Tunisia, being the first time that this mechanism has been detected in food E. coli strains in Africa.
Keywords: CTX-M-1 , CTX-M-8 , CTX-M-14 , SHV-5 , E. coli , animals
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