Molecular characterization of chromosomal class C beta-lactamase and its regulatory gene in Ochrobactrum anthropi

Ochrobactrum anthropi, formerly known as CDC group Vd, is an oxidase-produc ing, gram-negative, obligately aerobic, non-lactose-fermenting bacillus of low virulence that occasionally causes human infections. It is highly resis tant to all beta -lactams except imipenem, A clinical isolate, SLO74, and s ix reference strains were tested. MICs of penicillins, aztreonam, and most cephalosporins tested, including cefotaxime and ceftazidime, were > 128 mug /ml and of cefepime were 64 to > 128 mug/ml. Clavulanic acid was ineffectiv e and tazobactam had a weak effect in association with piperacillin, Two ge nes, ampR and ampC, were cloned by inserting restriction fragments of genom ic DNA, from the clinical strain O. amthropi SLO74 into pBK-CMV to give the recombinant plasmid pBK-OA1. The pattern of resistance to beta -lactams of this clone was similar to that of the parental strain, except for its resi stance to cefepime (MIC, 0.5 mug/ml). The deduced amino acid sequence of th e AmpC beta -lactamase (pI, 8.9) was only 41 to 52% identical to the sequen ce of other chromosomally encoded and plasmid-encoded class C beta -lactama ses, The kinetic properties of this beta -lactamase were typical for this c lass of beta -lactamases. Upstream from the ampC gene, the ampR gene encode s a protein with a sequence that is 46 to 62% identical to those of other A mpR proteins and with an amino-terminal DNA-binding domain typical of trans criptional activators of the Lys-R family. The deduced amino acid sequences of the ampC genes of the six reference strains mere 96 to 99% identical to the sequence of the clinical strain. The beta -lactamase characterized fro m strain SLO74 nas named OCH-1 (gene, bla(OCH-I)).