CHROMOSOMALLY ENCODED CEPHALOSPORIN-HYDROLYZING BETA-LACTAMASE OF PROTEUS-VULGARIS RO104 BELONGS TO AMBLERS CLASS-A

Proteus vulgaris RO104 strain produces a chromosomally encoded beta-la ctamase that confers resistance to various beta-lactam antibiotics inc luding methoxyimino third-generation cephalosporins. The beta-lactamas e hydrolyzes first- and second-generation cephalosporins efficiently a nd cefotaxime to a lesser extent. Catalytic activity is inhibited by l ow concentrations of clavulanic acid and sulbactam. By its broad-spect rum substrate profile, beta-lactamase of Proteus vulgaris RO104 belong s to the group 2e defined by Bush. The protein purified to homogeneity by a four-step procedure was characterized by a pI of 8.31 and a spec ific activity of 1200 U/mg. The beta-lactamase was digested by trypsin , endoproteinase Asp-N and chymotrypsin. Amino-acid sequence determina tions of the resulting peptides allowed the alignment of the 271 amino -acid residues of the protein which did not contain any cysteine resid ue. From amino-acid sequence comparisons, Proteus vulgaris RO104 beta- lactamase was found to share about 68% identity with the chromosomally mediated beta-lactamases of Klebsiella oxytoca D488 and E23004. There fore, the cephalosporin-hydrolyzing beta-lactamase of Proteus vulgaris RO104 belongs to Ambler's class A.