Identification of plasmid-encoded extended spectrum beta-lactamases produced by a clinical strain of Proteus mirabilis.

Emergence and dissemination of multiresistant strain of Proteus mirabilis have made infections treatment more difficult that this bacterium is responsible. The aim of this study is to determine the implication of the enzymatic mechanism and to describe the properties of ESBLs (extended spectrum beta-lactamases). A clinical strain of Proteus mirabilis SM514 isolated in the intensive care unit at the Military hospital in Tunisia during the period 2004 was found to be highly resistant to cephalosporins and penicilins. Cells sonicate of the isolate hydrolysed cefotaxime more efficiently than ceftriaxone and ceftazidime and had three beta-lactamases bands of approximate of isoelectric points (pI) of 5.4; 5.6 and superior to 7.6. The specific activities (AS) vary from 5.26 to 7.77U/mg of protein respectively for cefotaxime and the benzylpenicillin. These activities are inhibited by the clavulanic acid and the sulbactam. The values of the IC(50) are respectively 3.7 and 11.7muM. Only the beta-lactamases of pI 5.4 and superior to 7.6 hydrolyze the cefotaxime. Transformant produces the ESBLs of pI 5.4; 7.45 and greater than 7.6. The genes coding for this enzymes are carried by a transferable plasmids.