Detection and characterization of extended-spectrum β-lactamases in Salmonella enterica strains of healthy food animals in Spain

Objectives: To carry out the characterization of the genes encoding extended-spectrum β-lactamases (ESBLs) and their genetic environments in four expanded-spectrum cephalosporin-resistant Salmonella enterica isolates (serovars: two Virchow, one Enteritidis, one Rissen) recovered during the monitoring programmes performed in Spain by the VAV Network from faecal samples of pigs, poultry and laying hens at the slaughterhouse level. Methods: The presence and characterization of ESBL genes as well as their genetic environments in the four S. enterica isolates were investigated by PCR and sequencing. The presence of other resistance genes was also analysed by PCR and sequencing. Results: Three avian S. enterica isolates (two Virchow and one Enteritidis) harboured the blaCTX-M-9 gene combined with blaTEM-1b. The blaCTX-M-9 gene was included in these three isolates in a class 1 integron with the following 5′→3′ structure: integron 1 variable region (dfrA16-aadA2 gene cassettes)-qacEΔ1-sul1-orf513-blaCTX-M-9-orf3-like-orf1005. The sul2 gene was also detected in these three blaCTX-M-9-containing isolates and tet(A) in one of them. The two serovar Virchow isolates showed an indistinguishable PFGE pattern, although they were recovered from different animal species (broiler and laying hen). A porcine ESBL-positive isolate (serovar Rissen) harboured the blaSHV-12 gene combined with blaTEM-1b. This blaSHV-12-containing isolate also harboured the tet(A), aadA and sul1 genes. Conclusions: The emergence of ESBL-producing S. enterica isolates among food animals is described for the first time in Spain, with those of the CTX-M group being the predominant ESBLs detected.