Table 1.

Nucleotide changes, corresponding deduced amino acid changes, number of isolates selected under continuous or fluctuating challenge conditions, and MICs of ceftazidime and amoxicillin forE. coli K-12 strain RYC1000 harboring plasmid pBGS19 containing bla TEM genes (wild-type and mutant derivatives)

TEM-1 mutationCodon changeNo. of isolates selected by:MIC (μg/ml)a
Continuous selectionFluctuating selectionCeftazidimeAmoxicillin
None0.25>1,024
L169RCTG→CGG2048
D179YGAC→TAC10432
D179GGAC→GGC10864
R164SCGT→AGT658>1,024
R164HCGT→CAT148>1,024
  • a All variants that contained the same mutation expressed the same level of resistance.