aac(6)-Ib | GeneID:1446564 | Escherichia coli

AAO49600   NP_863005  

1. [ ] Zienkiewicz M, et al. (2007) "Mosaic structure of p1658/97, a 125-kilobase plasmid harboring an active amplicon with the extended-spectrum beta-lactamase gene blaSHV-5." Antimicrob Agents Chemother. 51(4):1164-1171. PMID:17220406

Escherichia coli isolates recovered from patients during a clonal outbreak in a Warsaw, Poland, hospital in 1997 produced different levels of an extended-spectrum beta-lactamase (ESBL) of the SHV type. The beta-lactamase hyperproduction correlated with the multiplication of ESBL gene copies within a plasmid. Here, we present the complete nucleotide sequence of plasmid p1658/97 carried by the isolates recovered during the outbreak. The plasmid is 125,491 bp and shows a mosaic structure in which all modules constituting the plasmid core are homologous to those found in plasmids F and R100 and are separated by segments of homology to other known regions (plasmid R64, Providencia rettgeri genomic island R391, Vibrio cholerae STX transposon, Klebsiella pneumoniae or E. coli chromosomes). Plasmid p1658/97 bears two replication systems, IncFII and IncFIB; we demonstrated that both are active in E. coli. The presence of an active partition system (sopABC locus) and two postsegregational killing systems (pemIK and hok/sok) indicates that the plasmid should be stably maintained in E. coli populations. The conjugative transfer is ensured by the operons of the tra and trb genes. We also demonstrate that the plasmidic segment undergoing amplification contains the blaSHV-5 gene and is homologous to a 7.9-kb fragment of the K. pneumoniae chromosome. The amplicon displays the structure of a composite transposon of type I.

2. [ ] Eckert C, et al. (2006) "DNA sequence analysis of the genetic environment of various blaCTX-M genes." J Antimicrob Chemother. 57(1):14-23. PMID:16291869

OBJECTIVES: Over a 3 year period (2000-2003) 21 Escherichia coli, 5 Klebsiella pneumoniae, 1 Serratia marcescens and 1 Proteus mirabilis producing CTX-M-type beta-lactamase were collected from five different hospitals in Paris, France. This study was conducted to analyse the genetic environment of these 28 bla(CTX-M) genes. METHODS: Antimicrobial susceptibility testing was performed by the disc diffusion method and MICs of various beta-lactams were determined by an agar dilution method. PCR was used to detect and sequence alleles encoding CTX-M, TEM, SHV and CMY enzymes. The genetic environment was analysed by amplification and direct sequencing using various set of PCR primers or cloning in pBK-CMV. RESULTS: Sequence analysis revealed that these isolates contained seven different bla(CTX-M) genes: bla(CTX-M-1) (4 strains), bla(CTX-M-2) (2 strains), bla(CTX-M-3) (4 strains), bla(CTX-M-9) (1 strain), bla(CTX-M-14) (5 strains), bla(CTX-M-15) (11 strains), bla(CTX-M-24) (1 strain). TEM-1 was associated with CTX-M-type enzymes in 15 isolates. Two strains produced both CTX-M-15 and SHV-2 or CTX-M-14 and CMY-2. In 25 strains the insertion sequence ISEcp1 was located upstream of the 5' end of the bla(CTX-M) gene. Among these strains, in five isolates, ISEcp1 was disrupted by insertion sequences such as IS26 (in three of them) or IS1 or IS10. Insertion sequence IS903 was found downstream of bla(CTX-M-14) or bla(CTX-M-24). Examination of the other three bla(CTX-M) genes (two bla(CTX-M-2) and one bla(CTX-M-9)) by cloning, sequencing and PCR analysis revealed the presence of complex Class 1 integrons, In35, an integron similar to In60 and a novel integron. CONCLUSIONS: This work further confirmed the predominant role of ISEcp1 in the mobilization of bla(CTX-M) genes of the CTX-M-1 cluster and the presence of In35, of an integron similar to In60 and a novel complex Class 1 integron.

3. [ ] Jeong JY, et al. (2005) "Detection of qnr in clinical isolates of Escherichia coli from Korea." Antimicrob Agents Chemother. 49(6):2522-2524. PMID:15917562

qnr was detected in 2 of 260 Escherichia coli clinical isolates collected from a Korean hospital during the period 2001 to 2003. The two strains were not clonally related. qnr was located in In4 family class 1 integrons of original structure, downstream of orf513 and upstream from another resistance gene (dfrA3b) and a gene of unknown function (orf105). Transfer of the qnr determinant by conjugation could be detected from only one strain.

4. [ ] Tortola MT, et al. (2005) "First detection of a carbapenem-hydrolyzing metalloenzyme in two enterobacteriaceae isolates in Spain." Antimicrob Agents Chemother. 49(8):3492-3494. PMID:16048967

Two strains of Enterobacteriaceae, Escherichia coli and Klebsiella pneumoniae, producing VIM-1 were isolated for the first time in Spain. In both strains, bla(VIM-1) was found to be carried on a gene cassette inserted into a class 1 integron. The bla(VIM-1)-containing integron was located on a transferable plasmid.

5. [ ] Scoulica EV, et al. (2004) "Spread of bla(VIM-1)-producing E. coli in a university hospital in Greece. Genetic analysis of the integron carrying the bla(VIM-1) metallo-beta-lactamase gene." Diagn Microbiol Infect Dis. 48(3):167-172. PMID:15023424

Bla(VIM-1) gene was detected in four Escherichia coli clinical isolates with both reduced susceptibility to carbapenems and an ESBL phenotype. The VIM-1 determinant was located within the variable region of a Class I integron along with a 6'-N-aminoglycoside acetyltransferase gene (aac(6')-Ib) and it could be transferred by conjugation. In all four clinical isolates the VIM-1 gene cassette presented a characteristic duplication of the 3' end coding 153 nucleotides followed by the first 14 nucleotides of the 59 base element (59be) that however did not seem to affect either the integrity of the coding sequence or the 59be of the gene cassette. These clinical isolates not only harbored the same Class I integron, but they also shared the same discrete ribotype-pattern, indicative for their clonal origin. Spread of carbapenem resistance genes among Enterobacteriaceae in hospital is a matter of great concern.

6. [ ] Wang M, et al. (2003) "Plasmid-mediated quinolone resistance in clinical isolates of Escherichia coli from Shanghai, China." Antimicrob Agents Chemother. 47(7):2242-2248. PMID:12821475

Although quinolone resistance usually results from chromosomal mutations, recent studies indicate that quinolone resistance can also be plasmid mediated. The gene responsible, qnr, is distinct from the known quinolone resistance genes and in previous studies seemed to be restricted to Klebsiella pneumoniae and Escherichia coli isolates from the University of Alabama in Birmingham, where this resistance was discovered. In Shanghai, the frequency of ciprofloxacin resistance in E. coli has exceeded 50% since 1993. Seventy-eight unique ciprofloxacin-resistant clinical isolates of E. coli from Shanghai hospitals were screened for the qnr gene by colony blotting and Southern hybridization of plasmid DNA. Conjugation experiments were done with azide-resistant E. coli J53 as a recipient with selection for plasmid-encoded antimicrobial resistance (chloramphenicol, gentamicin, or tetracycline) and azide counterselection. qnr genes were sequenced, and the structure of the plasmid DNA adjacent to qnr was analyzed by primer walking with a sequential series of outward-facing sequencing primers with plasmid DNA templates purified from transconjugants. Six (7.7%) of 78 strains gave a reproducible hybridization signal with a qnr gene probe on colony blots and yielded strong signals on plasmid DNA preparations. Quinolone resistance was transferred from all six probe-positive strains. Transconjugants had 16- to 250-fold increases in the MICs of ciprofloxacin relative to that of the recipient. All six strains contained qnr with a nucleotide sequence identical to that originally reported, except for a single nucleotide change (CTA-->CTG at position 537) encoding the same amino acid. qnr was located in complex In4 family class 1 integrons. Two completely sequenced integrons were designated In36 and In37. Transferable plasmid-mediated quinolone resistance associated with qnr is thus prevalent in quinolone-resistant clinical strains of E. coli from Shanghai and may contribute to the rapid increase in bacterial resistance to quinolones in China.

7. [ ] Vourli S, et al. (2003) "Characterization of In111, a class 1 integron that carries the extended-spectrum beta-lactamase gene blaIBC-1." FEMS Microbiol Lett. 225(1):149-153. PMID:12900034

A class 1 integron, In111, carried by a self-transferable plasmid from an Escherichia coli clinical strain was characterized. The variable region of In111 constituted an array of gene cassettes encoding the extended-spectrum beta-lactamase IBC-1, the aminoglycoside-modifying enzymes AAC(6')-Ib and ANT(3")-Ia, dihydrofolate reductase I and a putative polypeptide (SMR-2) sharing similarity with the Qac transporters. Transcription of the gene cassettes was driven by a hybrid-type P1 promoter located in a typical 5' conserved segment (CS). The 3'CS included sulI, qacEDelta1, orf5 and orf6. In111 was bounded on the right by an inversely oriented IRt. The 5'CS was preceded by an intact IS26 element followed by an aphA1 gene.

8. [ ] Collis CM, et al. (1995) "Expression of antibiotic resistance genes in the integrated cassettes of integrons." Antimicrob Agents Chemother. 39(1):155-162. PMID:7695299

Plasmids containing cloned integron fragments which differ only with respect to either the sequence of the promoter(s) or the number and order of inserted cassettes were used to examine the expression of resistance genes encoded in integron-associated gene cassettes. All transcripts detected commenced at the common promoter P(ant), and alterations in the sequence of P(ant) affected the level of resistance expressed by cassette genes. When both P(ant) and the secondary promoter P2 were present, transcription from both promoters was detected. When more than one cassette was present, the position of the cassette in the array influenced the level of antibiotic resistance expressed by the cassette gene. In all cases, the resistance level was highest when the gene was in the first cassette, i.e., closest to P(ant), and was reduced to different extents by the presence of individual upstream cassettes. In Northern (RNA) blots, multiple discrete transcripts originating at P(ant) were detected, and only the longer transcripts contained the distal genes. Together, these data suggest that premature transcription termination occurs within the cassettes. The most abundant transcripts appeared to contain one or more complete cassettes, and is possible that the 59-base elements found at the end of the cassettes (3' to the coding region) not only function as recombination sites but may also function as transcription terminators.

9. [ ] Bito A, et al. (1994) "Revised analysis of aadA2 gene of plasmid pSa." Antimicrob Agents Chemother. 38(5):1172-1175. PMID:7915099

The nucleotide sequence of gene aadA2 of plasmid pSa, coding for aminoglycoside-3"-adenyltransferase, has been reexamined. We found differences with respect to the sequence previously determined by Tait et al. (R. C. Tait, H. Rempel, R. L. Rodriguez, and C. I. Kado, Gene 36:97-104, 1985). These deviations are located in the coding region and in the 3' noncoding region. By making deletions in the region for initiation of protein synthesis, we identified a GTG triplet as the most probable start codon for translation.