Characterization of β-lactam resistant clinical isolates.

aCAZ, ceftazidime; PIP-TZ, piperacillin-tazobactam; IMP, imipenem; CEP, cefepime.
bStrains JSG1H9/JSG2A1 and OFC2H1/OFC2I4 additionally overexpressed the efflux pumps MexAB-OprM and MexEF-OprN, respectively [6].
cThe information on antibiotic treatments, β-lactamase activity, and ampD mutations was obtained from previous work [6].
dFold increase of beta-lactamase activity in the ceftazidime-resistant isolate compared to its preceding clonally related susceptible isolate.
eMutations detected in the ceftazidime-resistant isolates not present in the preceding isogenic susceptible isolates. None of the isolates contained mutations in ampR or ampC-ampR intergenic region.
fCeftazidime MIC (µg/ml) of: ceftazidime-susceptible isolates, subsequent ceftazidime-resistant clonally related isolates, ceftazidime-resistant isolates complemented with plasmid pUCPdB harbouring the wild-type dacB gene, and CreBC knockout mutants of the ceftazidime-resistant isolates.
gCreBC knockout mutants of this strain were not obtained after several attempts.
hp<0.05 for the comparison of creD expression in CAZ R – CAZ S pairs of sequential isolates.