Identification of a new allelic variant of the Acinetobacter baumannii cephalosporinase, ADC-7 beta-lactamase: defining a unique family of class C enzymes.
Acinetobacter spp. are emerging as opportunistic hospital pathogens that demonstrate resistance to many classes of antibiotics. In a metropolitan hospital in Cleveland, a clinical isolate of Acinetobacter baumannii that tested resistant to cefepime and ceftazidime (MIC = 32 microg/ml) was identified. Herein, we sought to determine the molecular basis for the extended-spectrum-cephalosporin resistance. Using analytical isoelectric focusing, a beta-lactamase with a pI of > or = 9.2 was detected. PCR amplification with specific A. baumannii cephalosporinase primers yielded a 1,152-bp product which, when sequenced, identified a novel 383-amino-acid class C enzyme. Expressed in Escherichia coli DH10B, this beta-lactamase demonstrated greater resistance against ceftazidime and cefotaxime than cefepime (4.0 microg/ml versus 0.06 microg/ml). The kinetic characteristics of this beta-lactamase were similar to other cephalosporinases found in Acinetobacter spp. In addition, this cephalosporinase was inhibited by meropenem, imipenem, ertapenem, and sulopenem (K(i) < 40 microM). The amino acid compositions of this novel enzyme and other class C beta-lactamases thus far described for A. baumannii, Acinetobacter genomic species 3, and Oligella urethralis in Europe and South Africa suggest that this cephalosporinase defines a unique family of class C enzymes. We propose a uniform designation for this family of cephalosporinases (Acinetobacter-derived cephalosporinases [ADC]) found in Acinetobacter spp. and identify this enzyme as ADC-7 beta-lactamase. The coalescence of Acinetobacter ampC beta-lactamases into a single common ancestor and the substantial phylogenetic distance separating them from other ampC genes support the logical value of developing a system of nomenclature for these Acinetobacter cephalosporinase genes.
Research Service, Louis Stokes Cleveland Veterans Affairs Medical Center, Case School of Medicine, 10701 East Blvd., Cleveland, Ohio 44016, USA.
Kristine M
KM
Hujer
Nashaat S
NS
Hamza
Andrea M
AM
Hujer
Federico
F
Perez
Marion S
MS
Helfand
Christopher R
CR
Bethel
Jodi M
JM
Thomson
Vernon E
VE
Anderson
Miriam
M
Barlow
Louis B
LB
Rice
Fred C
FC
Tenover
Robert A
RA
Bonomo
D040981:Acinetobacter baumannii / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D000483:Alleles; D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000737:chemistry / Q000145:classification* / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D018550:Cephalosporin Resistance; D002510:Cephalosporinase / Q000737:chemistry / Q000145:classification / Q000235:genetics / Q000378:metabolism; D014644:Genetic Variation; D006801:Humans; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D001618:beta-Lactamases / Q000737:chemistry / Q000145:classification* / Q000235:genetics / Q000378:metabolism; D047090:beta-Lactams / Q000494:pharmacology
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D047090:beta-Lactams; D002510:Cephalosporinase; C048795:AmpC beta-lactamases; D001618:beta-Lactamases