β-Lactamases among extended-spectrum β-lactamase (ESBL)-resistant Salmonella from poultry, poultry products and human patients in The Netherlands

Objectives: The purpose of this work was to study the genetic determinants responsible for extended-spectrum β-lactamase (ESBL) resistance of Salmonella isolated from Dutch poultry, poultry meat and hospitalized humans. Methods: Thirty-four ESBL-resistant Salmonella isolates from The Netherlands were tested towards 21 antimicrobial agents. PCR and sequencing were used to determine the underlying genetic determinants responsible for the ESBL phenotypes. The transferability of the ESBL phenotypes was tested by conjugation to a susceptible Salmonella enterica serovar Dublin and plasmid purification, restriction fragment length polymorphism (RFLP) and pulsed-field gel electrophoresis (PFGE) were employed to further characterize a subset of the isolates. Results: A great genetic diversity was seen among the isolates. The blaTEM-52 gene was most predominant and was found among Salmonella enterica serovars Blockley, Thomson, London, Enteritidis phage type 14b, Paratyphi B, Virchow and Typhimurium phage types 11 and 507. We also found the blaTEM-20 gene in S. Paratyphi B var. Java and the blaTEM-63 gene in S. Isangi. Furthermore, we detected the blaCTX-M-28 gene in S. Isangi and the blaCTX-M-3 gene in S. Typhimurium phage type 507. The blaCTX-M-2 gene was identified in S. Virchow, which also contained a copy of the blaSHV-2 gene and a copy of the blaTEM-1 gene. The blaSHV-12 gene was found alone in S. Concord and together with the blaTEM-52 gene in S. Typhimurium. Finally, the blaACC-1 gene was cloned from a S. Bareilly isolate and was found to be present on indistinguishable plasmids in all S. Bareilly isolates examined as well as in a S. Braenderup isolate and a S. Infantis isolate. Conclusions: Our data underscore the diversity of ESBL genes in Salmonella enterica isolated from animals, food products and human patients.