Quorum sensing network in clinical strains of A. baumannii: AidA is a new quorum quenching enzyme

PLoS One. 2017 Mar 22;12(3):e0174454. doi: 10.1371/journal.pone.0174454. eCollection 2017.

Abstract

Acinetobacter baumannii is an important pathogen that causes nosocomial infections generally associated with high mortality and morbidity in Intensive Care Units (ICUs). Currently, little is known about the Quorum Sensing (QS)/Quorum Quenching (QQ) systems of this pathogen. We analyzed these mechanisms in seven clinical isolates of A. baumannii. Microarray analysis of one of these clinical isolates, Ab1 (A. baumannii ST-2_clon_2010), previously cultured in the presence of 3-oxo-C12-HSL (a QS signalling molecule) revealed a putative QQ enzyme (α/ß hydrolase gene, AidA). This QQ enzyme was present in all non-motile clinical isolates (67% of which were isolated from the respiratory tract) cultured in nutrient depleted LB medium. Interestingly, this gene was not located in the genome of the only motile clinical strain growing in this medium (A. baumannii strain Ab421_GEIH-2010 [Ab7], isolated from a blood sample). The AidA protein expressed in E. coli showed QQ activity. Finally, we observed downregulation of the AidA protein (QQ system attenuation) in the presence of H2O2 (ROS stress). In conclusion, most of the A. baumannii clinical strains were not surface motile (84%) and were of respiratory origin (67%). Only the pilT gene was involved in surface motility and related to the QS system. Finally, a new QQ enzyme (α/ß hydrolase gene, AidA protein) was detected in these strains.

MeSH terms

  • 4-Butyrolactone / analogs & derivatives
  • 4-Butyrolactone / genetics
  • Acinetobacter baumannii / genetics*
  • Bacterial Proteins / genetics*
  • Cross Infection / genetics
  • Cross Infection / microbiology
  • Down-Regulation / genetics
  • Escherichia coli / genetics
  • Genes, Bacterial / genetics
  • Homoserine / analogs & derivatives
  • Homoserine / genetics
  • Quorum Sensing / genetics*

Substances

  • Bacterial Proteins
  • N-(3-oxododecanoyl)homoserine lactone
  • Homoserine
  • 4-Butyrolactone

Grants and funding

This study was funded by grant PI13/02390 awarded to MT within the State Plan for R+D+I 2013-2016 (National Plan for Scientific Research, Technological Development and Innovation 2008-2011) and co-financed by the ISCIII-Deputy General Directorate of evaluation and Promotion of Research - European Regional Development Fund "A way of Making Europe" and Instituto de Salud Carlos III FEDER, Spanish Network for the Research in Infectious Diseases (REIPI RD12/0015). M. Tomás was financially supported by the Miguel Servet Research Programme (C.H.U.A Coruña and ISCIII). A. Muras was financially supported by a predoctoral fellowship from the Xunta de Galicia (Plan I2C). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.