Molecular Characterisation of Trimethoprim Resistance in Escherichia coli and Klebsiella pneumoniae during a Two Year Intervention on Trimethoprim Use (original) (raw)

Genetic characterization of trimethoprim resistance in Haemophilus influenzae

Antimicrobial agents and chemotherapy, 1996

We previously demonstrated that trimethoprim (Tmp) resistance in Haemophilus influenzae is mediated by chromosomally encoded dihydrofolate reductase (DHFR) with a modified primary structure and distinct kinetic properties. To gain insight into the relationship of the DHFR structure and the level of Tmp resistance that it confers on the host bacterium, we cloned and characterized the folH genes of one Tmp-susceptible and two Tmp-resistant H. influenzae strains. Differences were observed between Tmp-susceptible and Tmp-resistant isolates both in the promoter region and in the coding sequences. The effect of differences between H. influenzae folH genes on Tmp susceptibility was investigated in Escherichia coli. Various folH gene hybrids were constructed, and their influence on Tmp susceptibility was determined. Resistance in E. coli mediated by folH from H. influenzae strain R1047 was associated with alterations in the promoter and the central part of folH. In contrast, the E. coli Tmp...

Trimethoprim-resistant dihydrofolate reductase genes in South African isolates of aerobic Gram-negative commensal faecal flora

1996

Resistance to antimicrobial agents is an increasing problem, especially in developing countries where resistant strains have undermined the effectiveness of antimicrobial agents such as trimethoprim. Since the commensal faecal flora are strongly implicated as a reservoir for resistant organisms. A survey was conducted in South Africa to determine the incidence of resistance in aerobic Gram-negative commensal faecal flora. Faecal specimens from 272 out of 361 (75%) healthy volunteers carried trimethoprimresistant bacteria; 357 trimethoprim-resistant strains were isolated. Trimethoprim resistance was transferable by conjugation in 55% of the isolates. The majority of the isolates were resistant to other antimicrobial agents including ampicillin 71.4% and tetracycline 88%. Most of these resistance phenotypes co-transferred with trimethoprim resistance. Analysis of 189 plasmids revealed 107 different restriction profiles which indicated that there is a large gene pool of trimethoprim-re...

Discovery of Highly Trimethoprim-Resistant DfrB Dihydrofolate Reductases in Diverse Environmental Settings Suggests an Evolutionary Advantage Unrelated to Antibiotic Resistance

Antibiotics

Type B dihydrofolate reductases (DfrB) are intrinsically highly resistant to the widely used antibiotic trimethoprim, posing a threat to global public health. The ten known DfrB family members have been strongly associated with genetic material related to the application of antibiotics. Several dfrB genes were associated with multidrug resistance contexts and mobile genetic elements, integrated both in chromosomes and plasmids. However, little is known regarding their presence in other environments. Here, we investigated the presence of dfrB beyond the traditional areas of enquiry by conducting metagenomic database searches from environmental settings where antibiotics are not prevalent. Thirty putative DfrB homologues that share 62 to 95% identity with characterized DfrB were identified. Expression of ten representative homologues verified trimethoprim resistance in all and dihydrofolate reductase activity in most. Contrary to samples associated with the use of antibiotics, the new...

Trimethoprim resistance in surface and wastewater is mediated by contrasting variants of the dfrB gene

The ISME Journal

Trimethoprim (TMP) is a low-cost, widely prescribed antibiotic. Its effectiveness is increasingly challenged by the spread of genes coding for TMP-resistant dihydrofolate reductases: dfrA, and the lesser-known, evolutionarily unrelated dfrB. Despite recent reports of novel variants conferring high level TMP resistance (dfrB10 to dfrB21), the prevalence of dfrB is still unknown due to underreporting, heterogeneity of the analyzed genetic material in terms of isolation sources, and limited bioinformatic processing. In this study, we explored a coherent set of shotgun metagenomic sequences to quantitatively estimate the abundance of dfrB gene variants in aquatic environments. Specifically, we scanned sequences originating from influents and effluents of municipal sewage treatment plants as well as river-borne microbiomes. Our analyses reveal an increased prevalence of dfrB1, dfrB2, dfrB3, dfrB4, dfrB5, and dfrB7 in wastewater microbiomes as compared to freshwater. These gene variants w...

An Integron Cassette Carryingdfr1with 90-bp Repeat Sequences Located on the Chromosome of Trimethoprim-Resistant Isolates ofCampylobacter jejuni

Microbial Drug Resistance, 2000

The frequent occurrence of high-level trimethoprim resistance in clinical isolates of Campylobacter jejuni was shown to be related to the acquisition of foreign resistance genes (dfr1 or dfr9 or both) coding for resistant variants of the enzyme dihydrofolate reductase, the target of trimethoprim. The dfr1 gene detected on the chromosome of 40 different clinical strains of C. jejuni was studied further regarding structure and genetic organization. Most of the dfr1 genes were found as integron cassettes inserted in the chromosome. In 36% of the examined isolated, the dfr1 gene showed identity to that previously characterized in trimethoprim-resistant Escherichia coli. In 40% of the cases, however, a variant of the dfr1 gene containing a 90-bp direct repeat was detected, and in 5% of the isolates, the repeat-containing dfr1 variant was found to occur in the form of two cassettes in tandem in an integron context. The existence of the 90-bp repeat within the coding sequence of the dfr1 gene was found to play a role in the adaptation of C. jejuni to ambient concentrations of trimethoprim.

The Bacterial Genomic Context of Highly Trimethoprim-Resistant DfrB Dihydrofolate Reductases Highlights an Emerging Threat to Public Health

Antibiotics

Type B dihydrofolate reductase (dfrb) genes were identified following the introduction of trimethoprim in the 1960s. Although they intrinsically confer resistance to trimethoprim (TMP) that is orders of magnitude greater than through other mechanisms, the distribution and prevalence of these short (237 bp) genes is unknown. Indeed, this knowledge has been hampered by systematic biases in search methodologies. Here, we investigate the genomic context of dfrbs to gain information on their current distribution in bacterial genomes. Upon searching publicly available databases, we identified 61 sequences containing dfrbs within an analyzable genomic context. The majority (70%) of those sequences also harbor virulence genes and 97% of the dfrbs are found near a mobile genetic element, representing a potential risk for antibiotic resistance genes. We further identified and confirmed the TMP-resistant phenotype of two new members of the family, dfrb10 and dfrb11. Dfrbs are found both in Bet...

High-Level Resistance to Trimethoprim in Clinical Isolates of Campylobacter jejuni by Acquisition of Foreign Genes ( dfr1 and dfr9 ) Expressing Drug-Insensitive Dihydrofolate Reductases

Antimicrobial Agents and Chemotherapy, 1998

The pathogenic bacterium Campylobacter jejuni has been regarded as endogenously resistant to trimethoprim. The genetic basis of this resistance was characterized in two collections of clinical isolates of C. jejuni obtained from two different parts of Sweden. The majority of these isolates were found to carry foreign dfr genes coding for resistant variants of the dihydrofolate reductase enzyme, the target of trimethoprim. The resistance genes, found on the chromosome, were dfr1 and dfr9 . In about 10% of the strains, the dfr1 and dfr9 genes occurred simultaneously. About 10% of the examined isolates were found to be negative for these dfr genes and showed a markedly lower trimethoprim resistance level than the other isolates. The dfr9 and dfr1 genes were located in the context of remnants of a transposon and an integron, respectively. Two different surroundings for the dfr9 gene were characterized. One was identical to the right-hand end of the transposon Tn 5393 , and in the other,...