Amal Karim

Biochemical Sequence Analyses of GES-1, a Novel Class A Extended-Spectrum β-Lactamase, and the Class 1 Integron In52 from Klebsiella pneumoniae

ABSTRACT Klebsiella pneumoniae ORI-1 was isolated in 1998 in France from a rectal swab of a 1-month-old girl who was previously hospitalized in Cayenne Hospital, Cayenne, French Guiana. This strain harbored a ca. 140-kb nontransferable plasmid, pTK1, that conferred an extended-spectrum cephalosporin resistance profile antagonized by the addition of clavulanic acid, tazobactam, or imipenem. The gene for GES-1 (Guiana extended-spectrum β-lactamase) was cloned, and its protein was expressed in Escherichia coli DH10B, where this pI-5.8 β-lactamase of a ca. 31-kDa molecular mass conferred resistance to oxyimino cephalosporins (mostly to ceftazidime). GES-1 is weakly related to the other plasmid-located Ambler class A extended-spectrum β-lactamases (ESBLs). The highest percentage of amino acid identity was obtained with the carbenicillinase GN79 from Proteus mirabilis; with YENT, a chromosome-borne penicillinase fromYersinia enterocolitica; and with L-2, a chromosome-borne class A cephalosporinase from Stenotrophomonas maltophilia(36% amino acid identity each). However, a dendrogram analysis showed that GES-1 clustered within a class A ESBL subgroup together with ESBLs VEB-1 and PER-1. Sequencing of a 7,098-bp DNA fragment from plasmid pTK1 revealed that the GES-1 gene was located on a novel class 1 integron named In52 that was characterized by (i) a 5′ conserved segment containing an intI1 gene possessing two putative promoters, P1 and P2, for coordinated expression of the downstream antibiotic resistance genes and an attI1 recombination site; (ii) five antibiotic gene cassettes, blaGES-1,aac(6′)Ib′ (gentamicin resistance and amikacin susceptibility), dfrXVb (trimethoprim resistance), a novel chloramphenicol resistance gene (cmlA4), andaadA2 (streptomycin-spectinomycin resistance); and (iii) a 3′ conserved segment consisting of qacEΔ1 andsulI. The blaGES-1 andaadA2 gene cassettes were peculiar, since they lacked a typical 59-base element. This work identified the second class A ESBL gene of a non-TEM, non-SHV series which was located in the plasmid and integron, thus providing it additional means for its spread and its expression.

CTX-M-Type Extended-Spectrum β-Lactamase That Hydrolyzes Ceftazidime through a Single Amino Acid Substitution in the Omega Loop

ABSTRACT Escherichia coli ILT-1, Klebsiella pneumoniae ILT-2, and K. pneumoniaeILT-3 were isolated in May 1999 in Paris, France, from a rectal swab of a hospitalized 5-month-old girl. These isolates had a clavulanic acid-inhibited substrate profile that included expanded-spectrum cephalosporins. The MICs of cefotaxime were higher for E. coli ILT-1 and K. pneumoniae ILT-2 than for K. pneumoniae ILT-3, while the opposite was found for the MICs of ceftazidime. Genetic and biochemical analyses revealed that E. coli ILT-1 and K. pneumoniae ILT-2 produced the CTX-M-18 β-lactamase, while K. pneumoniae ILT-3 produced the CTX-M-19 β-lactamase. The amino acid sequence of the CTX-M-18 β-lactamase differed from that of the CTX-M-9 β-lactamase by an Ala-to-Val change at position 231, while CTX-M-19 possessed an additional Pro-to-Ser change at position 167 in the omega loop of Ambler class A enzymes. The latter amino acid substitution may explain the CTX-M-19-mediated hydrolysis of ceftazidime, which has not been reported for other CTX-M-type enzymes. TheblaCTX-M-18 andblaCTX-M-19 genes were located on transferable plasmids that varied in size (ca. 60 and 50 kb, respectively) but that showed similar restriction patterns.

Molecular Epidemiology of the Integron-Located VEB-1 Extended-Spectrum β-Lactamase in Nosocomial Enterobacterial Isolates in Bangkok, Thailand

ABSTRACT Over a 2½-month period in 1999, 37 ceftazidime-resistant nonrepetitive enterobacterial isolates were collected from 37 patients in a Bangkok hospital, Thailand. Eighty-one percent of these strains expressed a clavulanic acid-inhibited extended-cephalosporin resistance profile. An identical extended-spectrum β-lactamase (ESBL), VEB-1, was found in 16 unrelated enterobacterial isolates (Escherichia coli, n = 10; Enterobacter cloacae, n = 2;Enterobacter sakazakii, n= 1; and Klebsiella pneumoniae, n = 3) and in two clonally related E. cloacae isolates. TheblaVEB-1 gene was located on mostly self-conjugative plasmids (ca. 24 to 200 kb) that conferred additional non-β-lactam antibiotic resistance patterns. Additionally, theblaVEB-1 gene cassette was part of class 1 integrons varying in size and structure. TheblaVEB-1-containing integrons were mostly associated with blaOXA-10-like andarr-2-like gene cassettes, the latter conferring resistance to rifampin. These data indicated the spread ofblaVEB-1 in Bangkok due to frequent transfer of different plasmids and class 1 integrons and rarely to clonally related strains. Plasmid- and integron-mediated resistance to rifampin was also found in enterobacterial isolates.

Biochemical-Genetic Characterization and Regulation of Expression of an ACC-1-Like Chromosome-Borne Cephalosporinase from Hafnia alvei

ABSTRACT A naturally occurring AmpC β-lactamase (cephalosporinase) gene was cloned from the Hafnia alvei 1 clinical isolate and expressed in Escherichia coli. The deduced AmpC β-lactamase (ACC-2) had a pI of 8 and a relative molecular mass of 37 kDa and showed 50 and 47% amino acid identity with the chromosome-encoded AmpCs from Serratia marcescens andProvidentia stuartii, respectively. It had 94% amino acid identity with the recently described plasmid-borne cephalosporinase ACC-1 from Klebsiella pneumoniae, suggesting the chromosomal origin of ACC-1. The hydrolysis constants (kcat and Km) showed that ACC-2 was a peculiar cephalosporinase, since it significantly hydrolyzed cefpirome. Once its gene was cloned and expressed inE. coli (pDEL-1), ACC-2 conferred resistance to ceftazidime and cefotaxime but also an uncommon reduced susceptibility to cefpirome. A divergently transcribed ampR gene with an overlapping promoter compared with ampC(blaACC-2) was identified in H. alvei 1, encoding an AmpR protein that shared 64% amino acid identity with the closest AmpR protein from P. stuartii. β-Lactamase induction experiments showed that the ampCgene was repressed in the absence of ampR and was activated when cefoxitin or imipenem was added as an inducer. From H. alvei 1 cultures that expressed an inducible-cephalosporinase phenotype, several ceftazidime- and cefpirome-cross-resistant H. alvei 1 mutants were obtained upon selection on cefpirome- or ceftazidime-containing plates, and H. alvei 1 DER, a ceftazidime-resistant mutant, stably overproduced cephalosporinase. Transformation of H. alvei 1 DER or E. coliJRG582 (ampDE mutant) harboring ampC andampR from H. alvei 1 with a recombinant plasmid containing ampD from E. coli resulted in a decrease in the MIC of β-lactam and recovery of an inducible phenotype for H. alvei 1 DER. Thus, AmpR and AmpD proteins may regulate biosynthesis of the H. alvei cephalosporinase similarly to other enterobacterial cephalosporinases.

Heterogeneity of AmpC Cephalosporinases of Hafnia alvei Clinical Isolates Expressing Inducible or Constitutive Ceftazidime Resistance Phenotypes

ABSTRACT Ten unrelated Hafnia alvei clinical isolates were grouped according to either their low-level and inducible cephalosporinase production or their high-level and constitutive cephalosporinase production phenotype. Their AmpC sequences shared 85 to 100% amino acid identity. The immediate genetic environment ofampC genes was conserved in H. alvei isolates but was different from that found in other ampC-possessing enterobacterial species.

EBR-1, a Novel Ambler Subclass B1 β-Lactamase from Empedobacter brevis

ABSTRACT Empedobacter brevis (formerly designated Flavobacterium breve) is a gram-negative aerobe involved in nosocomial infections. The Ambler class B β-lactamase gene blaEBR-1 was cloned and expressed in Escherichia coli from E. brevis clinical strain ASS-1, which had reduced susceptibility to expanded-spectrum cephalosporins and carbapenems. Purified β-lactamase EBR-1 hydrolyzed penicillins, cephalosporins, and carbapenems efficiently but not aztreonam. Kinetic parameters of EBR-1 were similar to those of class B enzymes such as BlaB, IND-2, and GOB-1 identified from other Flavobacteriaceae species, except for meropenem, which was more hydrolyzed by β-lactamase GOB-1. EBR-1, with a pI of 8.0 and a relative molecular mass of ca. 25 kDa, was classified in functional subgroup 3a, which includes most of the class B β-lactamases. EBR-1, which belongs to molecular subclass B1 of metalloenzymes, shares 58, 57, and 42% amino acid identity with the most closely related β-lactamases, IND-1/IND-2 from Chryseobacterium indologenes, CGB-1 from Chryseobacterium gleum, and BlaB from Chryseobacterium meningosepticum, respectively.