Beta-lactamase III of Bacillus cereus 569: membrane lipoprotein and secreted protein.

A third beta-lactamase in Bacillus cereus 569 has been identified and characterized. It corresponds to gamma-penicillinase reported by Pollock [Pollock, M. R. (1956) J. Gen. Microbiol. 15, 154-169] but whose existence has been questioned since then. It will be called beta-lactamase III. It resembles the class A beta-lactamases but is immunologically distinct from the major class A secreted beta-lactamase I of B. cereus. As with several other Gram-positive beta-lactamases it occurs in two forms, membrane bound as a glyceride-cysteine lipoprotein and as a hydrophilic secreted protein formed by cleavage on the carboxyl side of the modified cysteine that is the membrane attachment site. It is produced in all B. cereus 569 strains tested but is absent in B. cereus 5/b. Antibody to beta-lactamase III interacts to varying degrees with all the known class A beta-lactamases, most strongly with that of B. licheniformis 749/C.