title: Novel class A beta-lactamase Sed-1 from Citrobacter sedlakii: genetic diversity of beta-lactamases within the Citrobacter genus.
abstract: Citrobacter sedlakii 2596, a clinical strain resistant to aminopenicillins, carboxypenicillins, and early cephalosporins such as cephalothin, but remaining susceptible to acylureidopenicillins, carbapenems, and later cephalosporins such as cefotaxime, was isolated from the bile of a patient treated with beta-lactam and quinolone antibiotics. The isolate produced an inducible class A beta-lactamase of pI 8.6, named Sed-1, which was purified. Characterized by a molecular mass of 30 kDa, Sed-1 preferentially hydrolyzed benzylpenicillin, cephalothin, and cloxacillin. The corresponding gene, bla(Sed-1), was cloned and sequenced. Its deduced amino acid sequence shared more than 60% identity with the chromosome-encoded beta-lactamases from Citrobacter koseri (formerly C. diversus) (84%), Klebsiella oxytoca (74%), Serratia fonticola (67%), and Proteus vulgaris (63%) and 71% identity with the plasmid-mediated enzyme MEN-1. A gene coding for a LysR transcriptional regulator was found upstream from bla(Sed-1). This regulator, named SedR, displayed 90% identity with the AmpR sequence of the chromosomal beta-lactamase from C. koseri and 63 and 50% identity with the AmpR sequences of P. vulgaris and Enterobacter cloacae, respectively. By using DNA-DNA hybridization, a bla(Sed-1)-like gene was identified in two reference strains, C. sedlakii (CIP-105037) and Citrobacter rodentium (CIP-104675), but not in the 18 strains of C. koseri studied. Two DNA fragments were amplified and sequenced from the reference strains of C. sedlakii CIP-105037 and C. rodentium CIP-104675 using two primers specific for bla(Sed-1). They shared 98 and 80% identity with bla(Sed-1), respectively, confirming the diversity of the chromosomally encoded class A beta-lactamases found in Citrobacter.
authors.affiliation: Laboratoire de Recherche Moléculaire sur les Antibiotiques, Faculté de Médecine Pitié-Salpêtrière, Université Pierre et Marie Curie, Paris, France.
authors.forename: S
authors.initials: S
authors.lastname: Petrella
authors.forename: D
authors.initials: D
authors.lastname: Clermont
authors.forename: I
authors.initials: I
authors.lastname: Casin
authors.forename: V
authors.initials: V
authors.lastname: Jarlier
authors.forename: W
authors.initials: W
authors.lastname: Sougakoff
mesh_terms: D000595:Amino Acid Sequence; D000668:Ampicillin Resistance; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001483:Base Sequence; D002954:Citrobacter / Q000201:enzymology* / Q000235:genetics / Q000302:isolation & purification; D003001:Cloning, Molecular; D017931:DNA Primers / Q000737:chemistry; D004269:DNA, Bacterial / Q000032:analysis; D014644:Genetic Variation; D006801:Humans; D007526:Isoelectric Point; D008969:Molecular Sequence Data; D009693:Nucleic Acid Hybridization; D016133:Polymerase Chain Reaction; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D018440:beta-Lactam Resistance; D001618:beta-Lactamases / Q000235:genetics* / Q000378:metabolism; D047090:beta-Lactams
chemical_list: D000900:Anti-Bacterial Agents; D017931:DNA Primers; D004269:DNA, Bacterial; D047090:beta-Lactams; C436758:beta-lactamase Sed-1; D001618:beta-Lactamases