Abstract
In CTX-M-9 extended-spectrum beta-lactamases (ESBLs), an S130G mutation induced a 40- to 650-fold increase in 50% inhibitory concentrations but decreased hydrolytic activity against cefotaxime. A D240K mutation did not modify enzymatic efficiency against ceftazidime. Residue K240 could interact with Q270 and therefore not with ceftazidime, in contrast with what was observed with certain TEM/SHV-type ESBLs.