A plasmid-mediated cephalosporinase from Achromobacter species.

An unusual cephalosporinase in Achromobacter species was characterized biochemically; the enzyme had a pI of 8.1 and a molecular mass of 36,200 daltons, and it was not inhibited by p-chloromercuribenzoate or cloxacillin. Specific antiserum neutralized enzymatic activity. Agarose gel electrophoresis of the DNA of two strains (MULB 906 and MULB 912) revealed at least three plasmid bands; cured strains demonstrated a simultaneous loss of beta-lactamase and plasmid DNA. Resistance to beta-lactam antibiotics was transferred by transformation of Escherichia coli strain HB101 with plasmid DNA. This plasmid-mediated beta-lactamase differed from the two types of chromosomal cephalosporinases (pI 7.4 and 9.3, respectively) found in a survey of clinical isolates of Achromobacter species. This enzyme also differed in its biochemical properties from all of the other known plasmid-mediated beta-lactamases.