Occurrence of extended-spectrum β-lactamase-producing Salmonella enterica in northern Spain with evidence of CTX-M-9 clonal spread among animals and humans

Among the 1233 Salmonella enterica isolates obtained in two Spanish hospitals, five isolates (0.4%) (serovars: Virchow, four; Livingstone, one) had the phenotype of an extended-spectrum β-lactamase (ESBL) producer. The genetic characterization of the ESBL of S. enterica Livingstone revealed a blaSHV–2 gene. The blaCTX-M-10 gene in a phage-related genetic environment was found in one S. enterica Virchow isolate, and the ЫACTX-M-9 gene within the In60 integron was found in the three remaining Virchow isolates. These three isolates presented indistinguishable or closely related pulsed-field gel electrophoresis patterns among themselves and also as compared with the two other blaCTX-M-9-containing isolates previously obtained from animals. ESBL production is an emerging mechanism of resistance in S. enterica in the two studied hospitals.