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

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.

The Structural Determinants Accounting for the Broad Substrate Specificity of the Quorum Quenching Lactonase GcL

“…We have evaluated the ability of the lactonase GcL to inhibit biofilm formation of A. baumannii ; a human pathogen known to produce and utilize acyl homoserine lactone. QQ lactonases are known to disrupt AHL‐based signaling and inhibit bacterial behavior that depends on signaling, such as biofilm formation, and even disrupt existing biofilms . Herein, we show that GcL can inhibit the formation of biofilms of A. baumannii in a dose‐dependent manner.…”

“…Yet, these low K M values are similar to those observed for AidC and AaL . The K M values of lactonases are important to consider in light of the concentration thresholds for QS activation, which are reported to be in the range of about 5 n m. Additionally, we tested the ability of GcL to degrade the insecticide derivative Paraoxon, and determined that it was capable of degrading it, albeit with slow rates. This promiscuous activity of GcL is consistent with previous observations in other lactonases, such as AaL, and the PLL family, such as VmoLac and SsoPox, which exhibit higher phosphotriesterase activities.…”

Identification ofN‐acyl homoserine lactone‐degrading bacteria isolated from rainbow trout (Oncorhynchus mykiss)

“…; Lopez et al . ) and our current finding revealed that A . radioresistens shows AHL degradation capacity.…”

Mechanisms of Bacterial Tolerance and Persistence in the Gastrointestinal and Respiratory Environments

“…However, addition of an exogenous AHL obtained from Acinetobacter restored biofilm formation in the mutant (292). Moreover, the important role of a new QS enzyme, AidA, in bacterial defense against 3-oxo-C 12 -homoserine-lactone, an inhibitor of the quorum sensing system (293), was recently analyzed (294). Finally, in A. baumannii clinical strains from clone ST79/PFGE-HUI-1 (which lacks the AdeABC efflux pump) and a modified strain (named ATCC 17978 ΔadeB), the presence of bile salts (a stress condition) induced overexpression of genes involved in biofilm production, the T6SS, and surface motility, which are associated with QS (173).…”