Potential evolution of hydrolysis spectrum for AmpC  -lactamase of Escherichia coli

Detection of an extended-spectrum b-lactamase (ESBL)positive E. coli from livestock in Norway was unexpected as there are no commercial preparations containing cephalosporins licensed for veterinary use.An interview with the farmer confirmed that there had been no use of cephalosporins for animals or humans at the farm.The strain, or plasmid, might have been part of bacterial flora of animals taken to Norway for breeding purposes.The bla TEM-20 plasmid conferring low-level resistance to cephalosporins may represent a challenge with regard to detection of ESBL-positive isolates.The plasmids might also have the potential to develop into variants conferring higher levels of resistance as only one mutation may contribute to a change in the phenotype.