The contribution of β-lactamases to β-lactam resistance in Bacteroides fragilis

Abstract

A simple and convenient method for obtaining high yields of β-lactamase from Bacteroides fragilis, using routine laboratory facilities was developed. The contribution of β-lactamases to β-lactam resistance was then investigated using eleven clinical isolates of Bact. fragilis. Isoelectric focusing revealed that the eleven isolates produced four distinct β-lactamase types. The four enzyme types were constitutive, gave similar substrate profiles with predominantly cephalosporinase activity and were sensitive to inhibition by cloxacillin, cefoxitin, clavulanic acid and p-chloromercuribenzoate. Resistance to β-lactam antibiotics was highly dependent upon level of β-lactamase activity but not associated with any particular enzyme type. Marked differences in the β-lactamase stability of β-lactam antibiotics to cell free extracts generally conferred little or no advantage in the minimum inhibitory concentration required against growing cultures.