RESUMO
Resistance to third generation cephalosporins due to the acquisition and expression of extended spectrum beta-lactamases (ESBLs) enzymes among Gram negative bacteria continue to pose a challenge to infection management worldwide. The aim of this study was to determine the implication of the enzymatic mechanism and to describe the properties of ESBLs from a clinical strain of Proteus mirabilis NC4150 isolated in the intensive care unit at the Military Hospital in Tunisia during the period 2004. The isolate was identified, tested for antimicrobial susceptibility and analysed for presence of ESBL genes. Two beta - lactamases which confers a multirésistance on antibiotics including the oxyimino beta-lactams were identified. Isoelectric points of these two beta-lactamases are 5.4 and 5.7. The specific activities (AS) vary from 0.2 to 36.27 U/mg of protein respectively for ampicilline and the ceftazidime. These activities are inhibited by the clavulanic acid and the sulbactam. The values of the IC 50 are respectively 16 muM and 2.4 mu M. Only the beta - lactamase of pI 5.7 hydrolyze the ceftazidime. Transformant and transconjugant produces only the ESBL (extended spectrum beta-lactamases) of pI 5.7. The gene coding for this enzyme is carried by a transferable plasmid named pNC4150.
