Journal of Antimicrobial Chemotherapy (1982) 9,29^45 The contribution of /Mactamases to/Mactam resistance in

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