Plasmid-Mediated Class 1 and 2 Integron Carriage in Drug-Resistant Nosocomial Isolates of Acinetobacter baumannii

Acinetobacter baumannii is an opportunistic multidrug-resistant pathogen associated with nosocomial infections in critically ill patients. Antibiotic resistance genes are often encoded by class 1 and 2 integrons and located on plasmids that can facilitate their horizontal transfer among bacteria.
The aim of this research was to study the correlation between plasmid carriage and presence of class 1 and 2 integrons in nosocomial isolates of A. baumannii.
Fifty isolates collected between October 2014 and March 2015 from Imam Hussein hospital in Tehran were examined. Bacterial identification was carried out by biochemical identification as well as detection of the blaOXA-51 gene among the isolates. Susceptibility to 18 antibiotics was determined by disc diffusion method. Class 1 and 2 integrons were detected in total DNA extracts as well as in isolated plasmids using specific primers and PCR.
All isolates were extremely drug-resistant (XDR). Integron carriage was observed in 32 isolates (64%). Seventeen isolates (34%) carried plasmids with molecular sizes of > 20 kbp. Among them, six (35.4%) carried class 1, three (17.6%) harbored class 2, four (23.5%) had both integron classes, and four isolates (23.5%) carried no integrons. Of the plasmid negative isolates, 14 (42.4%) had no integron, 10 (30.3%) carried integron 2, five (15.2%) harbored integron 1 and interestingly, four (12.1%) carried both integron classes.
No correlation was found between antibiotic resistance profiles and integron carriage. Class 1 integron was significantly associated with plasmid carriage showing its role in the dissemination of drug resistance in A. baumannii. No association was observed between class 2 integrons and plasmid carriage suggesting their chromosomal location.