BIOCHEMICAL-PROPERTIES OF INDUCIBLE BETA-LACTAMASES PRODUCED FROM XANTHOMONAS-MALTOPHILIA

Four different beta-lactamases have been found in several strains of X anthomonas maltophilia isolated from blood cultures during 1984 to 199 1 at the Edinburgh Royal Infirmary. One was a metallo-beta-lactamase w ith predominantly penicillinase activity and an isoelectric point of 6 .8. Its molecular size as determined by gel filtration was 96 kDa but was only 26 kDa by sodium dodecyl sulfate-polyacrylamide gel electroph oresis (SDS-PAGE), suggesting a tetramer of four equal subunits. The e nzyme hydrolyzed all classes of beta-lactams except the monobactam azt reonam. This enzyme was not inhibited by potassium clavulanate or BRL 42715 but was inhibited by p-chloromercuribenzoate, mercuric chloride, and EDTA. The beta-lactamase was unstable in 50 mM sodium phosphate b uffer (pH 8.0) but stable in 50 mM Tris HCl (pH 8.0). The other beta-l actamases focused as a series of different isoelectric points, ranging from pI 5.2 to 6.6. Together, these enzymes exhibited a broad spectru m of activity, hydrolyzing most classes of beta-lactams bat not imipen em or aztreonam. Their molecular size was 48 kDa by Sephadex gel filtr ation and 24 kDa by SDS-PAGE, indicating that they were enzymes consis ting of two equal subunits. They were inhibited by p-chloromercuribenz oate, mercuric chloride, potassium clavulanate, and BRL 42715 but not EDTA. This study demonstrated that X. maltophilia produces more than j ust the L1 and L2 beta-lactamases.