Abstract
For several decades, many bacteria, among which A. baumannii, have shown their ability to colonize the upper surface of static liquids, forming a biofilm at the air-liquid interface named pellicle. Despite the ubiquity of these pellicles in both natural and artificial environments, few studies have investigated this biofilm type. The present data set provides the first description of the whole proteome of A. baumannii cells grown as pellicle, using a label-free mass spectrometry approach. Results are in accord with the general findings reporting that sessile bacteria are far more resistant to detrimental conditions than their planktonic counterparts, by the accumulation of stress proteins. The present investigation also confirmed previous studies suggesting a correlation between the pellicle forming ability and the bacterial virulence. Indeed, we showed the up-regulation of numerous virulence factors during the pellicle growth, e.g. phospholipases, adhesion factors, as well as those of the GacAS Two-Component System (TCS) and Type 6 Secretion System (T6SS). We also highlighted that Bam and Tam systems, both related to the OM insertion machinery, play a critical role during pellicle biogenesis. Moreover, sessile bacteria activate several pathways, e.g. iron, magnesium, phosphate pathways, which allows for increasing the panel of nutrient sources.
Highlights
Acinetobacter baumannii is a member of the ESKAPE group of bacterial pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, A. baumannii, Pseudomonas aeruginosa, and Enterobacter sp.) [1], responsible for a majority of hospital-acquired infections
The mechanism of bacterial biofilm resistance to antibiotics is still under investigation but several explanations have been proposed: [1] the biofilm extracellular polymeric substances (EPS) matrix acts as penetration barriers to antibiotics, [2] the biofilm bacteria up-regulate efflux pumps decreasing intracellular antibiotic concentration, and [3] the presence of a nondividing dormant bacterial subpopulation that is protected from antibiotics [18, 19]
This study provides the widest proteomic investigation devoted to the dynamic protein expression of A. baumannii cells grown as pellicle
Summary
Acinetobacter baumannii is a member of the ESKAPE group of bacterial pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, A. baumannii, Pseudomonas aeruginosa, and Enterobacter sp.) [1], responsible for a majority of hospital-acquired infections This Gram-negative pathogenic bacterium has become an important human pathogen owing to both an increasing number of infections and an emergence of multidrug-resistant (MDR) strains [2]. Biofilms are structured communities of bacteria encapsulated within a polymeric matrix formed by extracellular polymeric substances (EPS), e.g. exopolysaccharides, proteins, nucleic acids, and other substances [14]. This matrix acts as a protective layer and creates an optimal environment for genetic material exchange between the microorganisms [15]. A recent study in our laboratory [8] showed that the Acinetobacter species forming pellicles
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