Mobilome and antibiotic resistance in Acinetobacter baumannii

Abstract

Acinetobacter baumannii is an important microorganism involved in hospital-acquired infections with a remarkable ability to develop resistance to multiple antibiotics (multidrug-resistance, MDR) which makes it a highly troublesome pathogen in many hospitals around the world. Third-generation cephalosporins (such as ceftazidime) and carbapenems (such as imipenem and meropenem) represent important treatment options for infections caused by this microorganism. Nevertheless, the number of strains resistant to these antibiotics has been increasing during the last decade. The ability to capture, mobilise and regulate the expression of resistance-genes of this microorganism is a cornerstone factor in the development of the MDR, where the Mobilome, defined as “all the mobile genetic elements in a cell”, is responsible for its genetic plasticity. The aim of this work was to analyse the role of insertion sequences (ISs), transposon-like structures, resistance-plasmids and ISCR1-like elements in the resistance to carbapenems and ceftazidime in A. baumannii. Fifteen carbapanem-resistant strains of Acinetobacter baumannii isolated from Chile and two ceftazidime-resistant strains from the United Arab Emirates were studied. Different ceftazidime- and carbapenem-resistance genes were analysed and their genetic environments were characterised. The Mobilome in the carbapenem-resistant strains was composed of insertion sequences (ISs), specifically by ISAba1 associated with blaOXA-51-like, ISAba3 associated to blaOXA-58, which in turn was detected in two different plasmids, and ISAba15 interrupting ISAba3. In the case of the ceftazidime-resistant strain, the presence of an ISCR1 element was harbouring the blaPER-7, which was detected in a megaplasmid. The Mobilome, in the strains analysed, was composed of a wide variety of genetic elements, such as plasmids, insertion sequences, ISCR-like elements, which reflects the ability of A. baumannii to use different genetic platforms to capture and use resistance genes, making the Mobilome an important contributor in the resistance and the dissemination of resistance genes among nosocomial pathogens around the world.