Acinetobacter baumannii : um novo mecanismo de difusão dos genes de resistência ao Carbapenem

 American Society for Microbiology

Horizontal Transfer of the OXA-24 Carbapenemase Gene via Outer Membrane Vesicles: A New Mechanism of Dissemination of the Carbapenem Resistance Genes in Acinetobacter baumannii Carlos Rumbo1, Esteban Fernández-Moreira1, María Merino1, Margarita Poza1, Jose Antonio Mendez1, Nelson C. Soares1, Alejandro Mosquera2, Fernando Chaves3, and Germán Bou1,*

1 Servicio de Microbiología, 2 Departamento Xenética, Complejo Hospitalario Universitario A Coruña-INIBIC; C/Xubias de Arriba s/n, 15006 La Coruña, 3 Servicio de Microbiología. Hospital 12 de Octubre, Madrid. Spain

ABSTRACT


The resistance of Acinetobacter baumannii to carbapenems is a worrying problem in hospital settings. The main mechanism of carbapenem resistance is expression of β-lactamases (metallo or class D enzymes). The mechanisms of dissemination of these genes among A. baumannii are not fully understood. In this study we used two carbapenem resistant clinical strains of A. baumannii (AbH12O-A2 and AbH12O-CU3) expressing the plasmid-encoded blaOXA-24 gene (plasmids pMMA2 and pMMCU3, respectively) to demonstrate that A. baumannii releases outer membrane vesicles (OMVs) during in vitro growth. Use of hybridization studies enabled us to show that these OMVs harboured the blaOXA-24 gene. Incubation of these OMVs with a carbapenem susceptible A. baumannii ATCC 17978 host strain yielded full resistance to carbapenems. The presence of the original plasmids harbouring the blaOXA-24 gene was detected in the ATCC 17978 strain after transformation of OMVs. New OMVs harbouring blaOXA-24 were released by A. baumannii ATCC 17978 after it being transformed with the original OMV-mediated plasmids, indicating the universality of the process. We present the first experimental evidence that clinical isolates of A. baumannii may release OMVs as a mechanism of gene horizontal transfer whereby carbapenem resistance genes are delivered to surrounding A. baumannii bacterial isolates

* Corresponding author: German Bou PhD, Servicio de Microbiología, Complejo Hospitalario Universitario La Coruña, C/Xubias de Arriba s/n, 15006 La Coruña. Spain, Phone: 34-981-176087, Fax: 34-981-176097, E-mail: German.Bou.Arevalo@sergas.es

 

AAC Accepts, published online ahead of print on 25 April 2011
Antimicrob. Agents Chemother. doi:10.1128/AAC.00929-10
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