Quorum Sensing as a Target for Controlling Surface Associated Motility and Biofilm Formation in Acinetobacter baumannii ATCC® 17978TM

Abstract

The important nosocomial pathogen Acinetobacter baumannii presents a quorum sensing (QS) system (abaI/abaR) mediated by acyl-homoserine-lactones (AHLs) and several quorum quenching (QQ) enzymes. However, the roles of this complex network in the control of the expression of important virulence-related phenotypes such as surface-associated motility and biofilm formation is not clear. Therefore, the effect of the mutation of the AHL synthase AbaI, and the exogenous addition of the QQ enzyme Aii20J on surface-associated motility and biofilm formation by A. baumannii ATCC R 17978 TM was studied in detail. The effect of the enzyme on biofilm formation by several multidrug-resistant A. baumannii clinical isolates differing in their motility pattern was also tested. We provide evidence that a functional QS system is required for surface-associated motility and robust biofilm formation in A. baumannii ATCC R 17978 TM. Important differences were found with the well-studied strain A. nosocomialis M2 regarding the relevance of the QS system depending on environmental conditions The in vitro biofilm-formation capacity of A. baumannii clinical strains was highly variable and was not related to the antibiotic resistance or surface-associated motility profiles. A high variability was also found in the sensitivity of the clinical strains to the action of the QQ enzyme, revealing important differences in virulence regulation between A. baumannii isolates and confirming that studies restricted to a single strain are not representative for the development of novel antimicrobial strategies. Extracellular DNA emerges as a key component of the extracellular matrix in A. baumannii biofilms since the combined action of the QQ enzyme Aii20J and DNase reduced biofilm formation in all tested strains. Results demonstrate that QQ strategies in combination with other enzymatic treatments such as DNase could represent an alternative approach for the prevention of A. baumannii colonization and survival on surfaces and the prevention and treatment of infections caused by this pathogen.

Quorum Sensing Inhibition or Quenching in Acinetobacter baumannii: The Novel Therapeutic Strategies for New Drug Development

“…It has been proved that MomL reduced biofilm formation and increased biofilm susceptibility to different antibiotics in A. baumannii ( Zhang et al, 2017 ). It is worth mentioning that, Mayer et al (2020) found that the combined action of QQ enzyme Aii20J and DNase could reduce the biofilm formation of A. baumannii ATCC® 17978™, indicating that QQ strategy combined with other enzyme treatment methods, such as DNase, could represent an alternative approach to prevent the colonization and survival of the pathogen on the surface and to treat of infections caused by this pathogen.…”

Use of Quorum Sensing Inhibition Strategies to Control Microfouling

“…Over the last years, interfering with QS bacterial communication systems has been proposed as a promising mechanism to prevent the development of different types of bacterial biofilms [ 11 , 12 , 13 , 14 , 15 ]. Commonly, the term “quorum quenching” (QQ) refers to the enzymatic inactivation of QS processes [ 16 ], while the more general term “quorum sensing inhibition” (QSI) is preferred to describe the chemical disruption of the cell-to-cell communication system caused by QS inhibitory compounds [ 17 ].…”

“…Species of the genus Pseudoalteromonas , Cobetia , or Shewanella have been used as models for marine biofilms [ 36 , 38 , 39 , 40 , 41 , 42 ], although little information is available on the role of QS in biofilm formation in these species. Moreover, it should be taken into account that the culture conditions can have a significant impact on QS-QQ systems, biofilm formation, and/or surface attachment [ 12 , 22 , 23 ]. Due to this complexity, new methods are needed to understand and characterize bacterial biofilms [ 43 ] and identify novel anti-biofilm compounds.…”

“…While the traditional biofilm quantification methods, such as the staining assays using crystal violet, the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) tetrazolium reduction assay, or the colony forming unit (CFU) estimation are end-point techniques, the xCELLigence ® system allows the continuous analysis of bacterial cell adhesion based on single-frequency impedance spectroscopy. However, the system is not suitable for measuring biofilms formed in the liquid/air interphase and has demonstrated low sensitivity for strictly aerobic human pathogens such as Acinetobacter baumannii compared to other biofilm measurement systems [ 12 ]. The xCELLigence ® system allows simple, high-throughput screening for novel anti-biofilm compounds, but it is necessary to assess whether it is suitable for accurate measurement of marine biofilms, since impedance could be affected by the high salinity required for marine bacteria cultivation.…”

“…In the present study, we compare the xCELLigence ® real-time measurement system with the attachment model [ 14 ], a modification of the Amsterdam Active Attachment biofilm model [ 47 , 48 ], in which glass coverslips (18 × 18 mm) are immersed vertically in the culture medium in 12-well cell-culture plates. The attachment model allows refreshment of the culture medium without disturbing the biofilm, provides a higher adhesion surface (up to 1.62 cm 2 ), and allows direct observation of structural changes in the biofilm, addressing some disadvantages of the use of 96-well microtiter plates [ 12 ].…”