Analysis of Integron-associated Gene Cassettes in Clinical Acinetobacter Calcoaceticus-Baumannii Complex Isolates from Central Taiwan

Abstract

Purpose: Acinetobacter calcoaceticus-baumannii complex (ABC) has become a major infectious pathogen in Taiwan, and mobile DNA such as integrons and transposons often contribute to its multiple antibiotic resistance characteristics. Methods: A clinical epidemiological study of the cassette contents of the class 1 integron of ABC isolates in two central Taiwan hospitals was performed. Results: It was found that 78% (39/50) of strains possessed the IntI1 integrase gene, while four major different sizes of class 1 integron cassette arrays were found: 3.0 kb (aacC1-ORF1-ORF2- ORF3-aadA1) (aacC1: aminoglycoside 3'-N-acetyltransferase; aadA1: aminoglycoside 3'-adenyltransferase), 2.5 kb (aacA4- catB8-aadA1) (aacA4: aminoglycoside 6'-N-acetyl-transferase), 2.0 kb (dhfrXII-ORF-aadA2) (dhfrXII: dihydrofolate reductase; aadA2: aminoacyl-adenyltransferase A) and 1.2 kb (dhfrAI-ORF) (dhfrAI: dihydrofolate reductase type AI). Six different combinations of cassette arrays were also noted. The co-relationships between antibiotic-resistant phenotypes and genotypic combinations of cassettes were analyzed. As the 2.5-kb cassette array was found to be the most common in this study, the flanking regions of the specific integron of ABC were also analyzed by inverse PCR. In addition to antibiotic resistance genes, such as aphA1 (kanamycin resistance gene) (AphA1: aminoglycosidephosphotransferase), the transposase gene (tnpIS15/tnpAIS26) was found in the 2.5-kb cassette array flanking regions. Furthermore, PCR-RFLP confirmed that these flanking regions were conserved in all of the examined isolates. Conclusion: The SXT and GM resistance phenotypes of ABC isolates could be used in clinical screening for the IntI1- associated genotype. ABC isolates that carry a 2.5-kb cassette array have become dominant in Central Taiwan, and dissemination of this specific type of integron may derive from the involvement of mobile DNA.