Integrons

Abstract

Integrons are genetic elements able to acquire and rearrange open reading frames (ORFs) embedded in gene cassette units and convert them to functional genes by ensuring their correct expression. They were originally identified as a mechanism used by Gram-negative bacteria to collect antibiotic resistance genes and express multiple resistance phenotypes in synergy with transposons. More recently, their role has been broadened with the discovery of chromosomal integron (CI) structures in the genomes of hundreds of bacterial species. This review focuses on the resources carried in these elements, on their unique recombination mechanisms, and on the different mechanisms controlling the cassette dynamics. We discuss the role of the toxin/antitoxin (TA) cassettes for the stabilization of the large cassette arrays carried in the larger CIs, known as superintegrons. Finally, we explore the central role played by single-stranded DNA in the integron cassette dynamics in light of the recent discovery that the integron integrase expression is controlled by the SOS response.

Quantitative and qualitative impact of hospital effluent on dissemination of the integron pool

“…Integrons may be located on the bacterial chromosome, in which case they may contain hundreds of cassettes, mostly encoding unknown functions; or on transposons or plasmids, in which case they contain few gene cassettes, usually encoding determinants of antibiotic resistance. Integrons are major determinants of antibiotic resistance in Gram-negative bacteria (Cambray et al, 2010). More than 130 different gene cassettes conferring resistance to most available antibiotics have been identified so far (Partridge et al, 2009).…”

“…Class 1 integrons are the most prevalent (Cambray et al, 2010), especially in multidrug-resistant Gram-negative clinical isolates. Class 2 integrons are less frequent, and few class 3 integrons have been described (Barraud et al, 2013).…”

Novel Class 1 Integrons in Multi-drug Resistant Isolates from Eastern China

“…The spread of resistance genes through mobile genetic elements is now an increasing global concern, as it can lead to the rapid emergence of multi-drug resistant (MDR) bacteria [1,2]. Integron is such a genetic element characterized by its ability to capture, express and excise resistance genes and its location often linked to plasmids and/or transposons, thus contributing to bacterial resistance [3].…”

“…Integron is such a genetic element characterized by its ability to capture, express and excise resistance genes and its location often linked to plasmids and/or transposons, thus contributing to bacterial resistance [3]. Based on the encoded sequence of integrase, three classes of integron have so far been found associated with the mobilization of resistance genes [2]. Class 1 integrons are the most important and clinically relevant, with a wide distribution among bacteria species [4], whereas class 2 integrons are less common, and class 3 integrons few reported in clinical isolates [5].…”

“…Over the past decades, much work has been done on the epidemiology of integrons and their important roles in bacterial resistance in both clinical and natural environments [2,4,[8][9][10][11]. Surveillance of integrons therefore is essential for the investigation of MDR bacteria evolution.…”