Abstract
Objective To investigate the distribution of integrons in clinical isolates of carbapenem-resistant Acinetobacter baumannii and their relationships to bacterial resistance to antimicrobial agents. Methods A total of 115 carbapenem-resistant Acinetobacter baumannii strains were isolated from clinical samples of patients from January to October, 2017. Phoenix 100 automatic microbiological analyzer was used for antimicrobial sensitivity analysis. Classes 1 and 2 integrase genes and carbapenemase-encoding genes, blaIMP, blaVIM, blaKPC, blaNDM and blaOXA-23, were screened by PCR. The variable regions of integrons were amplified by long fragment PCR. The types of promoters and gene cassette arrays of variable regions were determined by sequencing and overlap PCR. Relationships between integrons and antimicrobial resistance were analyzed. Results The 115 isolates of carbapenem-resistant Acinetobacter baumannii were resistant to most commonly used antimicrobial agents, but sensitive to polymyxin E. All of the isolates carried blaOXA-23 gene and none of them were positive for blaIMP, blaVIM, blaKPC or blaNDM gene. Class 1 integrase gene intI1 was detected in 40 isolates (34.8%), while class 2 integrase gene intI2 was not detected. Two gene cassette arrays of variable regions, aacA4-catB8-aadA1 (39 isolates) and aacC1-gacP-gacQ-aadA1a (23 isolates), were detected in intI1-positive isolates. Twenty-two isolates carried both aacA4-catB8-aadA1 and aacC1-gacP-gacQ-aadA1a. The upstream promoters of the variable regions were relatively strong promoters, PcH2 and PcS. The gene cassettes of the variable regions endowed bacteria with resistance to chloramphenicol and aminoglycoside antibiotics. The resistance rate of class 1 integron-positive isolates to compound sulfamethoxazole was higher than that of negative strains. However, their resistance rate to ampicillin/sulbactam was lower than that of negative strains. Conclusions Antimicrobial resistance in carbapenem-resistant Acinetobacter baumannii was serious. Carbapenem resistance was associated with blaOXA-23 gene. The types of promoters of variable regions in class 1 integrons were all relatively strong promoters. Class 1 integrons were closely related to sulfonamides resistance. Key words: Acinetobacter baumannii; Carbapenem; Antimicrobial resistance; Integron; Promoter
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