Comparative study of the beta-lactamase activity found in Achromobacter

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Abstract
A survey of 21 clinical isolates of Achromobacter species demonstrated a high level of β-lactamase activity in all strains tested. The β-lactamases were characterized by isoelectric focusing, purification by affinity chromatography, determination of molecular weight, immunological identity, and genetic analysis. At least three distinct patterns of β-lactamases were found in 19 strains. The kinetic values Km and Vmax measured by a microacidimetric method showed that all three types of enzymes are cephalosporinases and did not hydrolyse oxacillin, cloxacillin, and methicillin. Two of the three types of cephalosporinases studied, namely MULB 901 (isoelectric point (pI) 7.4) and MULB 905 (pI 9.3) are enzymes mediated by genes of chromosomal origin. The MULB 906 (pI 8.1) enzyme, however, which has been previously shown to be mediated by an 8.2 MDal nonconjugative plasmid, showed hydrolysis of cefoxitime, cefotaxin, and moxalactam by the bioassay. In all cases, β-lactamase synthesis appeared constitutive. This study confirms that β-lactamase activity is commonly found in Achromobacter and that these enzymes are different and of clinical interest when compared with those observed in other Gram-negative bacteria.