Genetic structures associated with spread of the type la trimethoprimresistant dihydrofolate reductase gene amongst <i>Escherichia coli</i> strains isolated in the Nottingham area of the United Kingdom

Towner, K. J.; Brennan, Angela K.; Zhang, Y.; Holtham, Carol; Brough, Joanne L.; Carter, G. I.

doi:10.1093/jac/33.1.25

Cited by 19 publications

(17 citation statements)

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“…Particularly, dfrA1 has spread rapidly on the transposon Tn7 to become the most prevalent gene responsible for trimethoprim resistance in the UK [30], and the most prevalent in our study, followed by dfrA12 and dfrA17 . The dfrA9 was found only in one isolate in the present study.…”

Section: Discussionmentioning

confidence: 77%

Antimicrobial resistance in equine faecal Escherichia coli isolates from North West England

Ahmed

Clegg

Williams

et al. 2010

Ann Clin Microbiol Antimicrob

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BackgroundEscherichia coli isolates of equine faecal origin were investigated for antibiotic resistance, resistance genes and their ability to perform horizontal transfer.MethodsIn total, 264 faecal samples were collected from 138 horses in hospital and community livery premises in northwest England, yielding 296 resistant E. coli isolates. Isolates were tested for susceptibility to antimicrobial drugs by disc diffusion and agar dilution methods in order to determine minimum inhibitory concentrations (MIC). PCR amplification was used to detect genes conferring resistance to: ampicillin (TEM and SHV beta-lactamase), chloramphenicol (catI, catII, catIII and cml), tetracycline (tetA, tetB, tetC, tetD, tet E and tetG), and trimethoprim (dfrA1, dfrA9, dfrA12, dfrA13, dfr7, and dfr17).ResultsThe proportion of antibiotic resistant isolates, and multidrug resistant isolates (MDR) was significantly higher in hospital samples compared to livery samples (MDR: 48% of hospital isolates; 12% of livery isolates, p < 0.001). Resistance to ciprofloxacin and florfenicol were identified mostly within the MDR phenotypes. Resistance genes included dfr, TEM beta-lactamase, tet and cat, conferring resistance to trimethoprim, ampicillin, tetracycline and chloramphenicol, respectively. Within each antimicrobial resistance group, these genes occurred at frequencies of 93% (260/279), 91%, 86.8% and 73.5%, respectively; with 115/296 (38.8%) found to be MDR isolates. Conjugation experiments were performed on selected isolates and MDR phenotypes were readily transferred.ConclusionsOur findings demonstrate that E. coli of equine faecal origin are commonly resistant to antibiotics used in human and veterinary medicine. Furthermore, our results suggest that most antibiotic resistance observed in equine E. coli is encoded by well-known and well-characterized resistant genes common to E. coli from man and domestic animals. These data support the ongoing concern about antimicrobial resistance, MDR, antimicrobial use in veterinary medicine and the zoonotic risk that horses could potentially pose to public health.

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Section: Discussionmentioning

confidence: 77%

Antimicrobial resistance in equine faecal Escherichia coli isolates from North West England

Ahmed

Clegg

Williams

et al. 2010

Ann Clin Microbiol Antimicrob

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“…We identified specific cassettes by sequencing and restriction fragment length polymorphism analyses. Based on data from similar studies elsewhere in the world, we hypothesized that dfrA genes would be detected and that dfrA1 , the most commonly reported allele worldwide [5], [10], [16], [18], [43], [44] would feature predominantly. We did indeed identify only dfrA alleles, including several strains harboring dfrA1 .…”

Section: Resultsmentioning

confidence: 99%

“…There have since been many studies cataloguing the relative distribution of different dfr cassettes across the globe but, in spite of increasing interest in the forces underlying evolution to trimethoprim resistance [16], [17], [18], very little is known about the context in which more than a handful of the most promiscuous alleles are spread. Trimethoprim resistance rates among commensal and pathogenic enteric bacteria reported in the literature from Africa are very high, typically approaching or exceeding 60% [19], [20], [21], [22], [23], [24].…”

Section: Introductionmentioning

confidence: 99%

Regional Dissemination of a Trimethoprim-Resistance Gene Cassette via a Successful Transposable Element

et al. 2012

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BackgroundAntimicrobial resistance is a growing international problem. We observed a 50% increase in the prevalence of trimethoprim resistance among fecal Escherichia coli from healthy Nigerian students between 1998 and 2005, a trend to increase that continued in 2009.Methods and FindingsA PCR-based screen revealed that 131 (43.1%) of isolates obtained in Nigeria in 2005 and 2009 carried integron-borne dfrA cassettes. In the case of 67 (51.1%) of these isolates, the cassette was a class 1-integron-borne dfrA7 gene, which has been reported at high prevalence from E. coli isolates from other parts of Africa. Complete sequencing of a 27 Kb dfrA7-bearing plasmid from one isolate located the dfrA7 gene within a Tn21-type transposon. The transposon also contained an IS26-derived bla/sul/str element, encoding resistance to β-lactams, sulphonamides and streptomycin, and mercury resistance genes. Although the plasmid backbone was only found in 12 (5.8%) of trimethoprim-resistant isolates, dfrA7 and other transposon-borne genes were detected in 14 (16.3%) and 32 (26.3%) of trimethoprim resistant isolates collected in Nigeria in 2005 and 2009, respectively. Additionally, 37 (19.3%) of trimethoprim-resistant E. coli isolates collected between 2006 and 2008 from Ghana were positive for the dfrA7 and a transposon marker, but only 4 (2.1%) harbored the plasmid backbone.ConclusionsOur data point to transposition as a principal mechanism for disseminating dfrA7 among E. coli from Nigeria and Ghana. On-going intensive use of the affordable broad-spectrum antibacterials is likely to promote selective success of a highly prevalent transposable element in West Africa.

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“…It is difficult to predict how widely distributed dfr13 may be in other parts of the world. However, since this DHFR was extremely widespread in South Africa and was detected in all the rural and urban population groups, it is thought that this DHFR may be widely distributed in other parts of the world and may account for a proportion of the 10 to 68% of DHFR genes which were not identified in a number of studies (13,23,25,30,44,49). On the basis of the similarity between the sequence and inhibitor profile of the type 12 and 13 DHFRs, it is clear that these enzymes should be regarded as a monophyletic group (family 3) since they share similar degrees of homology to that found within the type I-like and type II-like DHFR enzyme families.…”

Section: Discussionmentioning

confidence: 99%

New Gene Cassettes for Trimethoprim Resistance, dfr13 , and Streptomycin-Spectinomycin Resistance, aadA4 , Inserted on a Class 1 Integron

Adrian

Thomson

Klugman

et al. 2000

Antimicrob Agents Chemother

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In a previous survey of 357 trimethoprim-resistant isolates of aerobic gram-negative bacteria from commensal fecal flora, hybridization experiments showed that 25% (90 of 357) of the isolates failed to hybridize to specific oligonucleotide probes for dihydrofolate reductase types 1, 2b, 3, 5, 6, 7, 8, 9, 10, and 12. Subsequent cloning and sequencing of a plasmid-borne trimethoprim resistance gene from one of these isolates revealed a new dihydrofolate reductase gene, dfr13, which occurred as a cassette integrated in a site-specific manner in a class 1 integron. The gene product shared 84% amino acid identity with dfr12 and exhibited a trimethoprim inhibition profile similar to that of dfr12. Gene probing experiments with an oligonucleotide probe specific for this gene showed that 12.3% (44 of 357) of the isolates which did not hybridize to probes for other dihydrofolate reductases hybridized to this probe. Immediately downstream of dfr13, a new cassette, an aminoglycoside resistance gene of the class AADA [ANT(3؆)(9)-I], which encodes streptomycin-spectinomycin resistance, was identified. This gene shares 57% identity with the consensus aadA1 (ant(3؆)-Ia) and has been called aadA4 (ant(3؆)-Id). The 3 end of the aadA4 cassette was truncated by IS26, which was contiguous with a truncated form of Tn3. On the same plasmid, pUK2381, a second copy of IS26 was associated with sul2, which suggests that both integrase and transposase activities have played major roles in the arrangement and dissemination of antibiotic resistance genes dfr13, aadA4, bla TEM-1 , and sul2.Class 1 integrons are DNA elements that encode a sitespecific recombinase (intI1) of the family of integrases and are capable of catalyzing the insertion and recombination of mobile DNA elements (gene cassettes) at specific sites (core ite) with a consensus sequence, GTTRRRY. The integron also provides a 5Ј conserved core site, attI1, into which gene cassettes are preferentially inserted, and the promoters responsible for expression of the cassette-encoded genes (10,19). Gene cassettes are identified by a 59-base element which occurs at the 3Ј end of the cassette and which consists of an inverted imperfect repeat of between 50 and 150 bp which has an inverse core site at the 5Ј end of the inverted repeat and a core site at the 3Ј end. The insertion of a gene cassette into the attI1 site results in the formation of a secondary site (attC) downstream of the cassette. The attI1 site differs from attC sites in that the inverse core site and secondary structure are missing 5Ј of the attI1 core site (21). The majority of published cassettes contain genes for resistance to various antimicrobial agents including trimethoprim and aminoglycosides (41). Trimethoprim selectively inhibits the bacterial dihydrofolate reductase (DHFR), thus preventing reduction of dihydrofolate to tetrahydrofolate (11). The most common mechanism of resistance to trimethoprim in enterobacteria is the production of an additional plasmid-mediated DHFR which, unlike the chromosomal enzyme, i...

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Genetic structures associated with spread of the type la trimethoprimresistant dihydrofolate reductase gene amongst Escherichia coli strains isolated in the Nottingham area of the United Kingdom

Cited by 19 publications

References 0 publications

Antimicrobial resistance in equine faecal Escherichia coli isolates from North West England

Antimicrobial resistance in equine faecal Escherichia coli isolates from North West England

Regional Dissemination of a Trimethoprim-Resistance Gene Cassette via a Successful Transposable Element

New Gene Cassettes for Trimethoprim Resistance, dfr13 , and Streptomycin-Spectinomycin Resistance, aadA4 , Inserted on a Class 1 Integron

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