Resistance integrons: class 1, 2 and 3 integrons

Abstract

As recently indiscriminate abuse of existing antibiotics in both clinical and veterinary treatment leads to proliferation of antibiotic resistance in microbes and poses a dilemma for the future treatment of such bacterial infection, antimicrobial resistance has been considered to be one of the currently leading concerns in global public health, and reported to widely spread and extended to a large variety of microorganisms. In China, as one of the currently worst areas for antibiotics abuse, the annual prescription of antibiotics, including both clinical and veterinary treatment, has approaching 140 gram per person and been roughly estimated to be 10 times higher than that in the United Kingdom, which is considered to be a potential area for the emergence of "Super Bugs". Based on the integrons surveillance in Guangzhou, China in the past decade, this review thus aimed at summarizing the role of integrons in the perspective of both clinical setting and environment, with the focus on the occurrence and prevalence of class 1, 2 and 3 integrons.

Fig. 1

Schematic representation of a class 1 integron. P1 promoter for transcription of gene cassettes, P2 second promoter that is usually inactive, int integrase gene, attI1 integration site, qacE partially deleted gene that encodes quaternary ammonium compound resistance, sulI sulphonamide resistance, orf5 unknown function, P promoters of the qacE△ and sulI genes, attC sequence on the gene cassette recognized by the integrase

Fig. 2

Structure of the attI1 site. The essential part of the attI1 site is formed by the simple site, the strong binding site and the intervening sequence. For details see Hall et al. [7]

Fig. 3

Integration and excision of gene cassettes by site-specific recombination. Intl encoded by the intl gene in the integron catalyses recombination between the attl1 site of the integron and/or the attC site(s) of gene cassette(s) resulting in insertion or excision of a cassette. One or more noncassette resistance genes may be inserted at the position of the 3′-CS. Horizontal arrows indicate the opposite orientations of intI and cassette-borne genes