Molecular specificities of R factor-determined beta-lactamases: correlation with plasmid compatibility.

Beta (beta)-lactamases determined by 29 ampicillin resistance plasmids could be divided into two types. One, TEM-type, was very uniform with respect to substrate specificity but heterogeneous in absolute levels of beta-lactamase activity. The TEM-type beta-lactamase was determined by R factors of compatibility groups FII, Ialpha, Iepsilon, N, C, A, T, W, P, L, and X, and by prophage phi Amp. The other type, characterized by the ability to hydrolyze oxacillin, was less common, showed lower absolute levels of activity, and was heterogeneous as regards substrate specificities. Oxacillin-hydrolyzing beta-lactamases were determined by R factors of compatibility groups FI, Ialpha, N, C, and O.