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.
Highlights
Quorum Sensing (QS) is a general mechanism used by Gram-negative bacteria to regulate many biological processes, including virulence, competence, conjugation, resistance, motility and biofilm formation [1]
Seven clinical strains shown by multilocus sequence typing (MLST) to have different allelic profiles or sequence types (STs) and different susceptibility to several antimicrobials were used in this study (Table 1)
To confirm the role of AidA as a new Quorum Quenching (QQ) enzyme, we studied the presence of this protein in the clinical strains of A. baumannii that did not display surface motility on modified LB-LN
Summary
Quorum Sensing (QS) is a general mechanism used by Gram-negative bacteria to regulate many biological processes, including virulence, competence, conjugation, resistance, motility and biofilm formation [1]. The production and detection of bacterial cell-cell signalling molecules by various species have been linked to the enhanced development of single and multispecies biofilms [2]. A variety of structurally different bacterial cell-cell signalling molecules have been shown to mediate cell-cell communication, including acyl homoserine lactones. Quorum network in clinical strains of Acinetobacter baumannii. Network for the Research in Infectious Diseases (REIPI RD12/0015). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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