The in vitro activities of fourth generation cephalosporins cefepime and β lactamase inhibitor sulbactam combined with
cefuroxime, cefotaxime and ceftazidime against 34 strains ceftazidime resistant, 6 strains ceftazidime intermediate, and 15 strains ceftazidime susceptible
Enterobacter cloacae selected from clinics; the stability of β lactam antibiotics to Amp C enzyme; the molecular weigh and isoelectric point of Amp C enzyme, and PCR amplification of amp C structure gene were studied. Results showed sulbactam could enhance the activity of ceftazidime against
Enterobacter cloacae . The MICs of 32.7% Enterobacter cloacae decreased 4 folds and were in the range of intermediate and susceptibility. 96.4%(53/55) Enterobacter cloacae was susceptible to cefepime. The study of stability to β lactamase indicated that cephalexin, cefazolin, cefaclor, cefoperazone, penicillin, ampicillin and piperacillin were not stable to Amp C enzyme. However, the hydrolysis rates of cefotaxime, ceftriaxone, ceftazidime, tazobactam, imipenem, meropenem and cefepime were low. The hrdrolysis rate of sulbactam by enzymes extracted from 10 strains Enterobacter cloacae was almost 100%. The measurement of molecular weigh showed the molecular weigh of β lactamase extracted from 4 standard strains and 6 clinical isolates were 39.6kD. The measurement of isoelectric point of 10 strains Enterobacter cloacae showed the PI value of 2 standard strains were 8.35 and the PI value of 4 clinical isolates were in the range of 8.35~ 9.30 . Results of PCR amplification revealed that of 55 Enterobacter cloacae strains, 51 strains had amp C structure gene.