High frequency of integrons related to drug-resistance in clinical isolates of Acinetobacter baumannii

PURPOSE: As an opportunistic pathogen, Acinetobacter baumannii causes various nosocomial infections. In recent years, the increasing cumulative infection outbreaks involving A. baumannii have appeared worldwide. In addition, a perplexing trouble for clinical treatment is a severe drug-resistance problem with A. baumannii. In this study, we investigated the drug-resistance rates and integrons' distribution in A. baumannii clinical strains in East China. Furthermore, we explored the relationship between integrons and drug resistance. MATERIALS AND METHODS: Strains were identified using non-fermenting bacteria identification cards by Vitek-32 system. Disk-diffusion method (Kirby-Bauer) was used to judge antimicrobial sensitivity. Integrons and the gene cassettes of integrons were identified by PCR, restriction enzyme digestion and DNA sequencing. RESULTS: Except imipenem and cefoperazone/sulbactam, the drug-resistance rates of the A. baumannii clinical isolates to other 15 kinds of antibacterials, all surpassed 30%. Of 96 A. baumannii clinical isolates, 66 strains carried class 1 integrons (no class 2 or 3 integrons were found). Overall, the drug-resistance rates in integrons-positive A. baumannii to 14 kinds of antibacterials were higher than those in integrons-negative A. baumannii. Gene sequencing showed that 9 of 12 integrons contained seven different gene cassettes (aacA4, catB3, dfrA1, blam-1, orfX, aadA1, and sat2). The cassette arrays aacA4-catB3-dfrA1 was found in five detected integrons. CONCLUSIONS: High resistances in A. baumannii clinical strains to most common antimicrobial agents have appeared in East China, which was closely related with high frequencies class 1 integrons. A. baumannii integrons cassettes carried multi-drug-resistant gene codes. We believe that integrons cassettes gene could be taken as a marker of prognosticating A. baumannii antimicrobial resistance, but only reveal partial drug resistance profiles.