Role of integrons in antimicrobial susceptibility patterns of Acinetobacter baumannii

The relationship between the presence and types of integrons and the antimicrobial susceptibility patterns of Acinetobacter baumannii was investigated. A total of 134 non-duplicated A. baumannii isolates, 54.5% (n=73) of which were subsequently found to carry class 1 integrons, were collected from a regional hospital in Taiwan between March and September 2007. Only two types of gene cassette array, aacA4-catB8-aadA1 and aacC1-orfP-orfP-orfQ-aadA1, were identified. Susceptibility data showed that those strains carrying integrons were significantly more resistant to all antibiotics tested except ampicillin/sulbactam and imipenem. An epidemiological study revealed that the same integron could be found in different unrelated strains. These findings suggest that the presence of integrons in A. baumannii is responsible for both the horizontal transfer of antibiotic-resistance genes related to aminoglycosides and chloramphenicol and also represents a marker of multidrug resistance and epidemic potential.