Dataset Information

A Novel, Integron-Regulated, Class C ?-Lactamase.

ABSTRACT: AmpC-type ?-lactamases severely impair treatment of many bacterial infections, due to their broad spectrum (they hydrolyze virtually all ?-lactams, except fourth-generation cephalosporins and carbapenems) and the increasing incidence of plasmid-mediated versions. The original chromosomal AmpCs are often tightly regulated, and their expression is induced in response to exposure to ?-lactams. Regulation of mobile ampC expression is in many cases less controlled, giving rise to constitutively resistant strains with increased potential for development or acquisition of additional resistances. We present here the identification of two integron-encoded ampC genes, blaIDC-1 and blaIDC-2 (integron-derived cephalosporinase), with less than 85% amino acid sequence identity to any previously annotated AmpC. While their resistance pattern identifies them as class C ?-lactamases, their low isoelectric point (pI) values make differentiation from other ?-lactamases by isoelectric focusing impossible. To the best of our knowledge, this is the first evidence of an ampC gene cassette within a class 1 integron, providing a mobile context with profound potential for transfer and spread into clinics. It also allows bacteria to adapt expression levels, and thus reduce fitness costs, e.g., by cassette-reshuffling. Analyses of public metagenomes, including sewage metagenomes, show that the discovered ampCs are primarily found in Asian countries.

SUBMITTER: Bohm ME

PROVIDER: S-EPMC7148499 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature

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A Novel, Integron-Regulated, Class C β-Lactamase.

Böhm Maria-Elisabeth ME Razavi Mohammad M Flach Carl-Fredrik CF Larsson D G Joakim DGJ

Antibiotics (Basel, Switzerland) 20200314 3

AmpC-type β-lactamases severely impair treatment of many bacterial infections, due to their broad spectrum (they hydrolyze virtually all β-lactams, except fourth-generation cephalosporins and carbapenems) and the increasing incidence of plasmid-mediated versions. The original chromosomal AmpCs are often tightly regulated, and their expression is induced in response to exposure to β-lactams. Regulation of mobile <i>ampC</i> expression is in many cases less controlled, giving rise to constitutivel ...[more]

PMID: 32183280

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Project description: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 beta-lactamase) was cloned, and its protein was expressed in Escherichia coli DH10B, where this pI-5. 8 beta-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 beta-lactamases (ESBLs). The highest percentage of amino acid identity was obtained with the carbenicillinase GN79 from Proteus mirabilis; with YENT, a chromosome-borne penicillinase from Yersinia 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, P(1) and P(2), for coordinated expression of the downstream antibiotic resistance genes and an attI1 recombination site; (ii) five antibiotic gene cassettes, bla(GES-1), aac(6')Ib' (gentamicin resistance and amikacin susceptibility), dfrXVb (trimethoprim resistance), a novel chloramphenicol resistance gene (cmlA4), and aadA2 (streptomycin-spectinomycin resistance); and (iii) a 3' conserved segment consisting of qacEDelta1 and sulI. The bla(GES-1) and aadA2 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.

Project description:A clinical isolate, Escherichia coli MG-1, isolated from a 4-month-old Vietnamese orphan child, produced a beta-lactamase conferring resistance to extended-spectrum cephalosporins and aztreonam. In a disk diffusion test, a typical synergistic effect between ceftazidime or aztreonam and clavulanic acid was observed along with an unusual synergy between cefoxitin and cefuroxime. The gene for VEB-1 (Vietnamese extended-spectrum beta-lactamase) was cloned and expressed in E. coli JM109. The recombinant plasmid pRLT1 produced a beta-lactamase with a pI of 5.35 and conferred high-level resistance to extended-spectrum (or oxyimino) cephalosporins and to aztreonam. Vmax values for extended-spectrum cephalosporins were uncommonly high, while the affinity of the enzyme for ceftazidime and aztreonam was relatively low. blaVEB-1 showed significant homology at the DNA level with only blaPER-1 and blaPER-2. Analysis of the deduced protein sequence showed that VEB-1 is a class A penicillinase having very low levels of homology with any other known beta-lactamases. The highest percentage of amino acid identity was 38% with PER-1 or PER-2, two uncommon class A extended-spectrum enzymes. Exploration of the genetic environment of blaVEB-1 revealed the presence of gene cassette features, i.e., (i) a 59-base element associated with blaVEB-1; (ii) a second 59-base element just upstream of blaVEB-1, likely belonging to the aacA1-orfG gene cassette; (iii) two core sites (GTTRRRY) on both sides of blaVEB-1; and (iv) a second antibiotic resistance gene 3' of blaVEB-1, aadB. blaVEB-1 may therefore be the first class A extended-spectrum beta-lactamase that is part of a gene cassette, which itself is likely to be located on a class 1 integron, as sulfamide resistance may indicate. Furthermore, blaVEB-1 is encoded on a large (> 100-kb) transferable plasmid found in a Klebsiella pneumoniae MG-2 isolated at the same time from the same patient, indicating a horizontal gene transfer.

Dataset Information

A Novel, Integron-Regulated, Class C ?-Lactamase.

Publications

A Novel, Integron-Regulated, Class C β-Lactamase.

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