A Common System Controls the Induction of Very Different Genes. The Class-A beta-Lactamase of Proteus vulgaris and the Enterobacterial Class-C beta-Lactamase

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 ␤-lactam and quinolone antibiotics. The isolate produced an inducible class A ␤-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 ␤-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 ␤-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 ␤-lactamases found in Citrobacter.

Section: Discussionmentioning

confidence: 90%

“…Two numbering schemes are indicated: the one in boldface is for the Sed-1 amino acid sequence, and the other one is for the Sed-1 and SedR nucleotide sequences. (30), CUV from S. fonticola (44), CUM from P. vulgaris (22), and TEM from E. coli (54).…”

Section: Fig 1 Nucleotide Sequences Of Bla Sed-i and Bla Sedr From mentioning

confidence: 99%

Novel Class A β-Lactamase Sed-1 from Citrobacter sedlakii : Genetic Diversity of β-Lactamases within the Citrobacter Genus

Pétrella¹,

Clermont

Casin

et al. 2001

“…1). Indeed, some class A ␤-lactamases closely related to K. ascorbata enzymes are regulated by an ampR gene: cumR (Proteus vulgaris) (5), sedR (C. sedlakii), (19) and fonR (S. fonticola) (C. Humeniuk, unpublished data).…”

Section: Bacterial Strainsmentioning

confidence: 99%

β-Lactamases of Kluyvera ascorbata , Probable Progenitors of Some Plasmid-Encoded CTX-M Types

Humeniuk

Arlet

Gautier

et al. 2002

299

173

Kluyvera ascorbata produces a ␤-lactamase that results in an atypical susceptibility pattern, including lowlevel resistance to penicillins, cephalothin, and cefuroxime, but this resistance is reversed by clavulanate. Ten nucleotide sequences of the corresponding gene, bla KLUA , were obtained and were found to have minor variations (96 to 100%). Otherwise, bla KLUA was found to be similar (95 to 100%) to some plasmid-encoded CTX-M-type ␤-lactamases. Finally, mobilization of bla KLUA on a plasmid was found to be mediated probably by a genetic mobile element like ISEcp1.

“…No putative LysR-type regulator gene was identified upstream of the gene encoding HER-1, whereas such chromosome-encoded AmpR regulators were divergently transcribed upstream of the gene coding for the class A ␤-lactamase of C. sedlakii, C. diversus, and P. vulgaris (8,13,21).…”

mentioning

confidence: 99%

Molecular and Biochemical Characterization of a Novel Class A β-Lactamase (HER-1) from Escherichia hermannii

Beauchef-Havard

Arlet

Gautier³

et al. 2003

Escherichia hermannii showed a low level of resistance to amoxicillin and ticarcillin, reversed by clavulanate, and a moderate susceptibility to piperacillin but was susceptible to all cephalosporins. A bla gene was cloned and encoded a typical class A ␤-lactamase (HER-1, pI 7.5), which shares 45, 44, 41, and 40% amino acid identity with other ␤-lactamases, AER-1 from Aeromonas hydrophila, MAL-1/Cko-1 from Citrobacter koseri, and TEM-1 and LEN-1, respectively. No ampR gene was detected. Only penicillins were efficiently hydrolyzed, and no hydrolysis was observed for cefuroxime and broad-spectrum cephalosporins. Sequencing of the bla gene in 12 other strains showed 98 to 100% identity with bla HER-1 .