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Updated: Dec 26, 2025
Screening Foodstuffs for Class 1 Integrons and Gene Cassettes
Published on: June 19, 2015
A Novel, Integron-Regulated, Class C β-Lactamase
Maria-Elisabeth Böhm1,2, Mohammad Razavi1,2, Carl-Fredrik Flach1,2
1Centre for Antibiotic Resistance Research (CARe), University of Gothenburg, Gothenburg, Sweden.
Abstract:
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 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 β-lactamases, their low isoelectric point (pI) values make differentiation from other β-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.
Insights
Two novel integron-encoded AmpC-type beta-lactamase genes, bla_IDC-1 and bla_IDC-2, were identified. These mobile genetic elements contribute to antibiotic resistance in bacteria, particularly in Asian countries.
Area of Science:
- Microbiology
- Genetics
- Biochemistry
Background:
- AmpC-type beta-lactamases confer resistance to a broad spectrum of beta-lactam antibiotics, posing a significant challenge in treating bacterial infections.
- Plasmid-mediated AmpC enzymes are increasingly prevalent, often exhibiting less regulated expression compared to chromosomal versions, leading to constitutive resistance.
Purpose of the Study:
- To identify and characterize novel AmpC-type beta-lactamase genes.
- To investigate the mobile genetic context and potential for dissemination of these newly identified genes.
Main Methods:
- Bioinformatic analysis of bacterial genomes and metagenomic datasets.
- Sequence identity comparison with known beta-lactamase databases.
- Analysis of gene location within mobile genetic elements like integrons.
Main Results:
- Identification of two novel integron-encoded AmpC genes, bla_IDC-1 and bla_IDC-2, with <85% amino acid identity to known AmpCs.
- These genes possess low isoelectric points, hindering differentiation by traditional methods.
- The first evidence of ampC gene cassettes within a class 1 integron was found, indicating a mobile context.
Conclusions:
- The discovery of integron-encoded bla_IDC-1 and bla_IDC-2 highlights a new mechanism for the spread of AmpC-mediated resistance.
- These mobile elements have the potential for widespread dissemination in clinical settings.
- Metagenomic analysis suggests a higher prevalence of these genes in Asian countries.
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