Extended-spectrum β-lactamases and AmpC β-lactamases in ceftiofur-resistant Salmonella enterica isolates from food and livestock obtained in Germany during 2003–07

Abstract

Detection and characterization of extended-spectrum β-lactamases (ESBLs) and AmpC-encoding genes was conducted in German Salmonella isolated from different sources from 2003 to 2007. Non-duplicate German isolates from the National Salmonella Reference Laboratory Collection (2003–07) with ceftiofur MICs of ≥4 mg/L were tested for β-lactam/β-lactamase inhibitor susceptibility, presence of ESBLs or AmpC-encoding genes, class 1 and 2 integrons, other resistance genes, and IS26 and ISEcp1 sequences by PCR/sequencing. The isoelectric point of the β-lactamase was determined. Strains were analysed by PFGE and plasmid profiling. The bla genes were mapped by Southern-blot hybridization. Plasmids were characterized by rep-PCR typing. Sixteen isolates (10 Salmonella Typhimurium, 2 Salmonella Anatum, 2 Salmonella Paratyphi B dT + , 1 Salmonella Infantis and 1 Salmonella London) carried bla_CTX-M (15 bla_CTX-M-1 and one bla_CTX-M-15) genes located on self-transferable IncB/O, IncI1 and/or IncN plasmids. Seven of the Salmonella Typhimurium isolates carried the SGI1-M variant. Six isolates (five Salmonella Agona and one Salmonella Kentucky) carried the bla_CMY-2 gene on IncI1 conjugative plasmids. bla_TEM-20 genes were detected in two Salmonella Paratyphi B dT+ isolates, and bla_TEM-52 in one Salmonella Paratyphi B dT+ and one Salmonella Virchow, located on IncI1 plasmids. All Salmonella Paratyphi isolates harboured a 2300 bp/dfrA1-sat2-aadA1 class 2 integron. Among the 22 679 German Salmonella isolates investigated, the ESBL and AmpC β-lactamase prevalence was still low; however, it is slowly increasing. Various β-lactamase genes are linked to a variety of genetic elements capable of horizontal DNA transfer. Consequently, their dissemination is likely and demands adequate risk management strategies.