Marie-Cécile Ploy, Thierry Lambert, Jean-Pierre Couty, François Denis
Integrons: an Antibiotic Resistance Gene Capture and Expression System
Bacteria can transfer genetic information to provide themselves with protection against most antibiotics. The acquisition of resistance gene arrays involves genetic mobile elements like plasmids and transposons. Another class of genetic structures, termed integrons, have been described and contain one or more gene cassettes located at a specific site. Integrons are defined by an intI gene encoding an integrase, a recombination site attI and a strong promoter. At least six classes of integrons have been determined according to their intI gene. Classes 1, 2 and 3 are the most studied and are largely implicated in the dissemination of antibiotic resistance. A gene cassette includes an open reading frame and, at the 3?-end, a recombination site attC. Integration or excision of cassettes occur by a site-specific recombination mechanism catalyzed by the integrase. However, insertion can occur, albeit rarely, at non-specific sites leading to a stable situation for the cassette. Cassettes are transcribed from the common promoter located in the 5?-conserved segment and expression of distal genes is reduced by the presence of upstream cassettes. Most gene cassettes encode antibiotic resistant determinants but antiseptic resistant genes have also been described. Integrons seem to have a major role in the spread of multidrug resistance in Gram-negative bacteria but integrons in Gram-positive bacteria were described recently. Moreover, the finding of super-integrons with gene-cassettes coding for other determinants (biochemical functions, virulence factors) in Vibrio isolates dating from 1888 suggests the likely implication of this multi-component cassette-integron system in bacterial genome evolution before the antibiotic era and to a greater extent than initially believed.
Clinical Chemical Laboratory Medicine, Walter de Gruyter
Print ISSN: 1434-6621
Volume: 38, 06/2000
Pages: 483 - 487
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