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At least 217 records · Page 12Linked to original sources
PubMed2006

Characterization of antimicrobial resistance and class 1 integrons found in Escherichia coli isolates from human stools and drinking water sources in Jordan.

This study demonstrates that Escherichia coli isolates from human stools showed mostly higher minimum inhibitory concentrations (MICs) and significant rates of resistance (32%-67%, P<0.05) than Escherichia coli water isolates in Jordan, as follows: ampicillin (67% vs 28%), trimethoprim/sulfamethoxazole (67% vs 28%) nalidixic acid (63% vs 20%), cefuroxime (32% vs 4%), gentamicin (32% vs 17%), norfloxacin (32% vs 12%) and tetracycline (33% vs 16%). The prevalence of integron integrase genes (Intl1) in these isolates was also significantly higher in patients' stools (67%, P <0.05) than in water (36%), but the distribution of Sul 1/Sul 2 or both in association with postive Intl1 and resistance to ampicillin and sulfamethoxazole was not significantly higher (74% versus 62%, P <0.05) in isolates from stool and water. Plasmid profiles of representative multiresistant E. coli isolates from both sources indicated the presence of two common plasmids (49,25 kb) in 11/12 (91.6%), and all E. coli transconjugants were positive for class 1 integron markers (Intl 1, Sul 1 and Sul2) and mostly associated with three transferable drug-resistant determinants to ampicillin, sulfamethoxazole and tetracycline. These results indicate that class 1 integrons with conjugative R-plasmids are common and transferable among commensal antimicrobial multiresistant E. coli isolated from human feces and drinking water sources in Jordan.

Anti-Bacterial Agents↗
PubMed2006

Class 1 integrons in resistant Escherichia coli and Klebsiella spp., US hospitals.

We examined Escherichia coli and Klebsiella spp. from US hospitals for class 1 integrons. Of 320 isolates, 181 (57%) were positive; association of integrons with resistance varied by drug and organism. Thus, determining integron epidemiology will improve understanding of how antibacterial resistance determinants spread in the United States.

DNA, Bacterial↗
PubMed2005

Molecular characterization of InJR06, a class 1 integron located in a conjugative plasmid of Salmonella enterica ser. Typhimurium.

The presence of class 1, 2, and 3 integrons was investigated in four pediatric isolates of Salmonella enterica ser. Typhimurium (S. Typhimurium). A class 1 integron was detected in one S. Typhimurium strain, the only one that also showed resistance to various aminoglycoside antibiotics. This integron, called InJR06, and the aminoglycoside resistance determinants were located in pS06, a large (> or = 55 kb) conjugative plasmid. A single mobile cassette (encoding the aminoglycoside adenylyltransferase ANT(3'')-Ia) was detected in the variable region of InJR06, while the architecture of the attI1 and attC sites was conserved.

Anti-Bacterial Agents↗
PubMed1990

The structure of a partial duplication in the integron of plasmid pDGO100.

A family of novel potentially mobile DNA elements called integrons, has recently been described (H. W. Stokes and R. M. Hall, 1989, Mol. Microbiol. 3, 1669-1683). The integrons present in the plasmids pDGO100 and pSa are unusual in that they include a duplication of the sulI gene which is located in one of the two conserved segments that make up these elements. In order to define the nature of the duplication in pDGO100, we have sequenced the sulI gene region located between the aadB and the dhfr genes of pDGO100. This region includes the first 1355 bases of the 2026-base 3'-conserved segment present in the integrons of Tn21, R46 and R388, and the sequence identity in pDGO100 ceases 24 bases beyond the end of the sulI gene. This position corresponds to the center of a 59-base element, a remnant of which is located at the end of sulI. This finding suggests that the 59-base element may have been involved in the event which gave rise to the partial duplication.

Amino Acid Sequence↗
PubMed1991

Sequence analysis of the inducible chloramphenicol resistance determinant in the Tn1696 integron suggests regulation by translational attenuation.

The sequence of the Tn1696 determinant for inducible nonenzymatic chloramphenicol resistance has been determined. The cml region, the fourth insert of the Tn1696 integron, is 1547 bases and includes a 59-base element at the 3' end, as is typical of integron inserts. One gene, designated cmlA and predicting a polypeptide of 44.2 kDa, is encoded in the insert. However, the cmlA region shows one feature not previously found in an integron insert. A promoter is located within the cmlA insert, and translational attenuation signals related to those of the inducible cat and ermC genes found in gram-positive organisms are also present. The regulatory region includes a leader peptide of nine amino acids, a ribosome stall sequence related to those preceding cat genes, and two alternative pairs of stem-loop structures which either sequester or disclose the ribosome binding site and start codon preceding the cmlA gene.

Amino Acid Sequence↗
PubMed1992

The integron In1 in plasmid R46 includes two copies of the oxa2 gene cassette.

The sequence of the insert region of the integron In1 found in the IncN plasmid R46 was completed. The insert region is 2929 bases long and includes four gene cassettes, two of which are identical copies of the oxa2 gene cassette flanking an aadA1 cassette. The fourth cassette encodes an open reading frame orfD. From comparison of these data with published maps and sequences it is argued that the integrons found in the IncN plasmids pCU1 and R1767 and in the transposon Tn2410 are closely related to In1 from R46. Both site-specific gene insertion and recA-dependent recombination are likely to have contributed to the evolution of these integrons.

Amino Acid Sequence↗
PubMed1994

Diversity and relative strength of tandem promoters for the antibiotic-resistance genes of several integrons.

The integron is a new type of mobile element containing one or more antibiotic-resistance-encoding genes site-specifically integrated as cassettes. The integrated genes are expressed from a common promoter region located in an adjacent conserved segment. Sequence analysis has revealed the existence of four versions of the integron promoters. In this study, we have determined the relative strength of the different integron promoters and compared their activity with that of the tac promoter. Each version of the promoter was cloned upstream from a promoter-less chloramphenicol acetyltransferase-encoding gene (cat) in plasmid pKK232-8. CAT activity was used to measure transcriptional expression from the promoters of the antibiotic-resistance operon. The strongest promoter is the version (TTGACAN17TAAACT) found in plasmid R388 and in transposon Tn1696. This promoter is six times more efficient than the derepressed tac promoter.

Acetylation↗
PubMedDate not supplied

Super-integrons.

Integrons represent the primary mechanism for antibiotic resistance gene capture and dissemination among gram-negative bacteria. The recent finding of super-integron (SI) structures in the genomes of several bacterial species has expanded their role in genome evolution. The Vibrio cholerae superintegron is gathered in a single chromosomal super-structure harbouring hundreds of gene cassettes. The encoded functions, when identifiable, are linked to adaptations extending beyond antibiotic resistance and pathogenicity. Comparison of the cassette contents of super-integrons from remote Vibrio species suggests that most of their cassettes are species-specific. Many bacterial species belonging to several distinct genera of the gamma- and beta-proteobacteria undoubtedly carry or show strong evidence for the presence of chromosomal SIs. If each bacterial species harbouring a SI has its own cassette pool, the resource in terms of gene cassette availability may be immense.

Base Sequence↗
PubMed1997

Non-palindromic attl sites of integrons are capable of site-specific recombination with one another and with secondary targets.

Genes borne on cassettes are mobile owing to site-specific recombination systems called integrons, which have created various combinations of antibiotic resistance genes in R-plasmids. In these processes, the palindromic site, attC (59-base element), at cassette junctions has been proposed as being essential. Excised and circularized cassettes have been found to integrate with preference for an attl site at one end of the conserved sequence in integrons. In this work, we give evidence that recombination is possible in the absence of the highly organized attC sites between the more simply organized attl sites. Furthermore, at a very low frequency representing the background in our recombination assay, we observed cross-overs between attl and secondary sites. To characterize recombination excluding the attC sites, we have used naturally occurring attl variants and constructed mutants. The cross-over point was identified between a guanine and a thymine in attl using point mutations. Progressive deletions showed the extent of attl and identified two important regions in the conserved sequence 5' of the cross-over point. A region 27-36 bp 5' of attl influenced recombination with attC sites only, whereas a sequence 9-14 bp 5' of the cross-over point in attl was important for recombination with both attl and attC. Recombination between attl and secondary sites could allow fusion of the conserved sequence encoding the integron site-specific recombinase to new sequences.

Base Sequence↗
PubMed2002

An intrinsic control element for translational initiation in class 1 integrons.

Integrons are genetic elements able to capture anti-biotic resistance and other genes and to promote their transcription. Here, we have investigated integron-dependent translation of an aminoglycoside 6'-N-acetyltransferase gene (aac(6')-Ib7) inserted at the attI1 site. N-terminal sequencing revealed that translation of this gene was initiated at a GTG codon, which is not part of a plausible translation initiation region (TIR). A short open reading frame (called ORF-11) overlapping the attI1 site was probed by site-directed mutagenesis for its contribution to aac(6')-Ib7 translation. When ORF-11 and its TIR were deleted en bloc, translational efficiency dropped by over 80%, as determined with an acetyltransferase- luciferase fusion product. Invalidation of the ATG start codon of ORF-11 or its putative Shine-Dalgarno sequence resulted in a decrease of over 60%, whereas the decrease was much less pronounced when the amino acid sequence of the putative ORF-11-encoded peptide was altered or when the distance between ORF-11 and aac(6')-Ib7 was doubled. This demonstrates that aac(6')-Ib7 translation is dependent upon the translation of ORF-11, but almost certainly not upon the corresponding peptide. These results lead us to conclude that an intrinsic short ORF present in the 5'-conserved segment of many class 1 integrons may substantially enhance expression at the translational level of captured TIR-deficient anti-biotic resistance genes.

Amino Acid Sequence↗
PubMedDate not supplied

Importance of integrons in the diffusion of resistance.

Horizontal transfer of resistance genes is a successful mechanism for the transmission and dissemination of multiple drug resistance among bacterial pathogens. The impact of horizontally transmitted genetic determinants in the evolution of resistance is particularly evident when resistance genes are physically associated in clusters and transferred en bloc to the recipient cell. Recent advances in the molecular characterisation of antibiotic resistance mechanisms have highlighted the existence of genetic structures. called integrons, involved in the acquisition of resistance genes. These DNA elements have frequently been reported in multi-drug resistant strains isolated from animals and humans, and are located either on the bacterial chromosome or on broad-host-range plasmids. The role of integrons in the development of multiple resistance relies on their unique capacity to cluster and express drug resistance genes. Moreover, the spread of resistance genes among different replicons and their exchange between plasmid and bacterial chromosome are facilitated by the integration of integrons into transposable elements. The association of a highly efficient gene capture and expression system, together with the capacity for vertical and horizontal transmission of resistance genes represents a powerful weapon used by bacteria to combat the assault of antibiotics.

Animal Diseases↗
PubMed2001

Vibrio cholerae O1 outbreak isolates in Mozambique and South Africa in 1998 are multiple-drug resistant, contain the SXT element and the aadA2 gene located on class 1 integrons.

The characteristics of Vibrio cholerae O1 biotype El Tor, serotype Ogawa isolates from outbreaks of cholera in 1998 amongst migrant workers in the South African provinces of Gauteng and Mpumalanga, on the border of Mozambique, are reported. The isolates seem to have originated from the same clone since they are of two closely related BglI ribotypes. These ribotypes had a high similarity to ribotypes of V. cholerae O1 recently found in three South-east Asian countries. Isolates were resistant to furazolidone, streptomycin, sulfamethoxazole, trimethoprim and tetracycline. Only two isolates contained plasmids of 54 and 63 kb in size. PCR and DNA sequencing revealed that the chromosomally located resistance determinants present included an aadA2 gene cassette contained in a class 1 integron; the SXT element, which is a transposon-like element containing resistance genes; and the tetA gene. A co-transfer of chromosomal closely located genes encoding the SXT element and tetA was shown by mating experiments, PCR and pulsed-field gel electrophoresis analyses. Our study shows for the first time that multiple-resistant V. cholerae O1 isolates containing class 1 integrons and the SXT element were responsible for cholera outbreaks in Southern Africa. Studies are needed to determine the spread of this multiple-resistant O1 strain and further genetic details of the association of the SXT element, tetA and class 1 integrons, including their means of transfer.

Anti-Bacterial Agents↗
PubMed1994

Characterisation of specific and secondary recombination sites recognised by the integron DNA integrase.

Integrons determine a site-specific recombination system which is responsible for the acquisition of genes, particularly antibiotic resistance genes. The integrase encoded by integrons recognises two distinct classes of recombination sites. The first is the family of imperfect inverted repeats, known as 59-base elements, which are associated with the mobile gene cassettes. The second consists of a single site into which the cassettes are inserted. This site, here designated attI, is located adjacent to the int gene in the recipient integron structure. The attI site has none of the recognisable features of members of the 59-base element family except for a seven-base core site, GTTRRRY, at the recombination crossover point. Using a conduction assay to quantitate site activity, the sequence required for maximal attI site activity was confined to a region of > 39 and < or = 70 bases. Both integrative and excisive site-specific recombination events involving attI and a 59-base element site were demonstrated, but no evidence for events involving two attI sites was obtained. Integrase-mediated recombination between a 59-base element and several secondary sites in pACYC184 with the consensus GNT occurred at low frequency, and such events could potentially lead to insertion of gene cassettes at many non-specific sites.

Base Sequence↗
PubMed2001

Molecular heterogeneity of bla(VIM-2)-containing integrons from Pseudomonas aeruginosa plasmids encoding the VIM-2 metallo-beta-lactamase.

A bla(VIM-2) metallo-beta-lactamase determinant, identical to that previously identified in Pseudomonas aeruginosa COL-1 isolate from a French hospital, was detected on a 28-kb plasmid carried by a nosocomial isolate of P. aeruginosa from Verona, Italy. In this plasmid the bla(VIM-2) determinant was inserted into a class 1 integron of original structure, named In72, that contains a partially deleted intI1 integrase gene and two gene cassettes. The first cassette carries an aacA4 aminoglycoside acetyl transferase determinant. The second cassette carries a bla(VIM-2) determinant followed by a partially deleted attC site. The structure of In72 was notably different from that of In56, the bla(VIM-2)-containing integron found in the COL-1 isolate, revealing the existence of molecular heterogeneity among bla(VIM-2)-containing integrons in clinical isolates of P. aeruginosa from Europe.

Acetyltransferases↗
PubMed1999

Mobile gene cassettes and integrons in evolution.

Integrons and the site-specific recombination systems encoded by them provide a simple mechanism for the addition of new genes to bacterial chromosomes. Although there is substantial divergence among the four known integron-encoded integrases, they all recognize the recombination sites, known as 59-base elements, that are associated with genes that are packaged in gene cassettes. In contrast, the integron-associated recombination sites, attl sites, are preferentially recognized by the cognate integrase.

Base Sequence↗
PubMed1998

Molecular characterization of OXA-20, a novel class D beta-lactamase, and its integron from Pseudomonas aeruginosa.

The Pseudomonas aeruginosa Mus clinical isolate produces OXA-18, a pI 5.5 class D extended-spectrum beta-lactamase totally inhibited by clavulanic acid (L. N. Philippon, T. Naas, A.-T. Bouthors, V. Barakett, and P. Nordmann, Antimicrob. Agents Chemother. 41:2188-2195, 1997). A second beta-lactamase was cloned, and the recombinant Escherichia coli clone pPL10 expressed a pI 7.4 beta-lactamase which conferred high levels of amoxicillin and ticarcillin resistance and which was partially inhibited by clavulanic acid. The 2.5-kb insert from pPL10 was sequenced, and a 266-amino-acid protein (OXA-20) was deduced; this protein has low amino acid identity with most of the class D beta-lactamases except OXA-2, OXA-15, and OXA-3 (75% amino acid identity with each). OXA-20 is a restricted-spectrum oxacillinase and is unusually inhibited by clavulanic acid. OXA-20 is a peculiar beta-lactamase because its translation initiates with a TTG (leucine) codon, which is rarely used as a translational origin in bacteria. Exploration of the genetic environment of oxa20 revealed the presence of the following integron features: (i) a second antibiotic resistance gene, aacA4; (ii) an intI1 gene; and (iii) two 59-base elements, each associated with either oxa20 or aacA4. This integron is peculiar because it lacks the 3' conserved region, and therefore is not a sul1-associated integron like most of them, and because its 3' end is located within tnpR, a gene involved in the transposition of Tn5393, a gram-negative transposon. P. aeruginosa Mus produces two novel and unrelated oxacillinases, OXA-18 and OXA-20, both of which are inhibited by clavulanic acid.

Amino Acid Sequence↗
PubMed1999

Many class I integrons comprise distinct stable structures occurring in different species of Enterobacteriaceae isolated from widespread geographic regions in Europe.

Three sizes of inserted regions of DNA (800, 1,000, and 1,500 bp) were shown to be common among class I integrons in unrelated clinical isolates of Enterobacteriaceae from different European hospitals. Sequencing showed that 800-bp inserted regions comprised identical sequences including aacA4, that 1,000-bp inserted regions included aadA, and that 1,500-bp inserted regions included dfrI and aadA1, irrespective of host species and geographic origin. In addition promoter sequences were mostly identical for each size class. These data suggest that inserted gene cassettes and promoter regions of integrons are conserved and stable, with resistance genes transferred more often as part of the entire integron structure than as individual gene cassettes.

Base Sequence↗
PubMed1999

Structure of In31, a blaIMP-containing Pseudomonas aeruginosa integron phyletically related to In5, which carries an unusual array of gene cassettes.

The location and environment of the acquired blaIMP gene, which encodes the IMP-1 metallo-beta-lactamase, were investigated in a Japanese Pseudomonas aeruginosa clinical isolate (isolate 101/1477) that produced the enzyme. In this isolate, blaIMP was carried on a 36-kb plasmid, and similar to the identical alleles found in Serratia marcescens and Klebsiella pneumoniae clinical isolates, it was located on a mobile gene cassette inserted into an integron. The entire structure of this integron, named In31, was determined. In31 is a class 1 element belonging to the same group of defective transposon derivatives that originated from Tn402-like ancestors such as In0, In2, and In5. The general structure of In31 appeared to be most closely related to that of In5 from pSCH884, suggesting a recent common phylogeny for these two elements. In In31, the blaIMP cassette is the first of an array of five gene cassettes that also includes an aacA4 cassette and three original cassettes that have never been described in other integrons. The novel cassettes carry, respectively, (i) a new chloramphenicol acetyltransferase-encoding allele of the catB family, (ii) a qac allele encoding a new member of the small multidrug resistance family of proteins, and (iii) an open reading frame encoding a protein of unknown function. All the resistance genes carried on cassettes inserted in In31 were found to be functional in decreasing the in vitro susceptibilities of host strains to the corresponding antimicrobial agents.

Amino Acid Sequence↗