Amino acid changes and β-lactam MIC values associated with CTX-M-3 derivatives constructed in this study.

aAmino acid changes corresponding to non-synonymous substitutions introduced by site-directed mutagenesis in CTX-M-3 in order to obtain the corresponding CTX-M allele, “+” indicates presence.
bMIC values as determined by E-test to the following β-lactam antibiotics: CTX, cefotaxime; CAZ, ceftazidime; FEP, cefepime; CXM, cefuroxime; CEF: cephalotin; FXT: cefoxitine; AMC: amoxicillin-clavulanic acid (2∶1).
cThe binary code indicates the content of mutations in each CTX-M variant in this order: A77V, N114D, A140S, P167S, D240G and D288N.
dGenBank accession numbers of blaCTX-M alleles constructed by site-directed mutagenesis in this work and previously described.
eCTX-M-3 derivatives corresponding to natural variants are shown.
fVariants closely related to others described in nature (differing in only one mutation or presenting a different amino acid change).