High Genetic Stability of Integrons in Clinical Isolates of Shigella spp. of Worldwide Origin

Abstract

Over a 12-year period, 68 Shigella strains (31 S. sonnei, 30 S. flexneri, 4 S. dysenteriae, and 3 S. boydii strains) were collected in a French University Hospital from the stools of patients who generally had a recent history of travel to various parts of the world (91%), particularly Africa (67%). These strains were often resistant (streptomycin, spectinomycin, trimethoprim, tetracycline, and sulfonamides, 66 to 84%; ampicillin and chloramphenicol, 34 to 38%; nalidixic acid, 4%) and even multiresistant (87%), and they generally carried integrons (81%) of class 1 (21%), class 2 (47%), or both (13%). Class 1 integrons were associated with ampicillin resistance due to the production of an OXA-30 ␤-lactamase in S. flexneri and S. dysenteriae. Class 2 integrons were associated with trimethoprim resistance in S. sonnei. Class 1 and class 2 integrons were inserted within transposons Tn21 and Tn7, respectively, themselves located on the bacterial chromosome, except in one strain. Class 1 integrons showed an atypical organization consisting of the insertion sequence IS1 at the 3 end instead of the typical 3 conserved segment and two bla OXA-30 and aadA1 gene cassettes, despite the absence of epidemiological relationships between the strains, and an apparently functional integrase. Class 2 integrons showed the same albeit classical organization with the three dfrA1, sat, and aadA1 gene cassettes. Occasionally, the 3 end was deleted and the aadA1 gene cassette was unexpressed. Thus, integrons contributed only in part to the multidrug resistance of the Shigella strains. The highly conserved organization of integrons might be related to their location within mobile genetic superstructures.

High prevalence of trimethoprim-resistance cassettes in class 1 and 2 integrons in Senegalese Shigella spp isolates

“…Here we found that 87.5% of 32 Shigella strains isolated in Senegal contained at least one integron. This marked dissemination of integrons among Shigella spp is partly linked to the propensity of this genus to acquire plasmids, as multidrug resistance integrons are usually plasmidborne [18]. In this study, class 1 integrons were the most prevalent, in keeping with the results of other studies of African Shigella isolates [18].…”

“…Dubois et al described Shigella strains containing a class 1 integron in which these two cassettes were followed by the insertion sequence IS1. Successful amplification with primers AadA3 and is1b (5'-GTGAACGCACTATGGCGACGC TG-3'), located within IS1 [17], confirmed that the genetic environment was the same as that described by Dubois et al [18].…”

“…This marked dissemination of integrons among Shigella spp is partly linked to the propensity of this genus to acquire plasmids, as multidrug resistance integrons are usually plasmidborne [18]. In this study, class 1 integrons were the most prevalent, in keeping with the results of other studies of African Shigella isolates [18]. In contrast, integron prevalence is very low in other parts of the world [20,21,22].…”

Antimicrobial resistance and PCR-ribotyping of Shigella responsible for foodborne outbreaks occurred in southern Brazil

“…Multi-resistance was verified in 87 % of the isolates, and a total of 13 antibiotic resistance patterns were identified (13). …”

Inadequately Treated Wastewater as a Source of Human Enteric Viruses in the Environment

“…About 10 % of bacterial genomes that have been partially or completely sequenced harbor this genetic element (Boucher et al 2007). The spread of antimicrobial-resistance genes by integrons was extensively investigated primarily in clinical settings (Grape et al 2003;Pan et al 2006;Dubois et al 2007). Nowadays, increased interest in their environmental role is observed (Elsaied et al 2007;Gillings et al 2009;Elsaied et al 2011) and also reviewed by Stalder et al (2012).…”