Mécanismes physiologiques permettant à pseudomonas aeruginosa d'accéder aux composés organiques hydrophobes : rôle de l'adhérence et des biosurfactants, et implication dans la formation de biofilms

Hydrocarbures aromatiques polycycliques -- Hydrocarbures aliphatiques linéaires -- Restauration des sites contaminés -- Paramètres importants dans la biorestauration des sites contaminés aux hydrocarbures -- Biodisponibilité -- Mécanismes physiologiques microbiens d'accession aux substrats hydrophobes -- Biofilms bactériens -- Biosurfactants de P. Aeruginosa -- Bioréacteurs à deux phases liquides -- Modèle conceptuel de la fonction des rhamnolipides dans l'assimilation des hydrocarbures -- Hydrocarbures liquides

Pseudomonas aeruginosa in premise plumbing of large buildings

Pseudomonas aeruginosa is an opportunistic bacterial pathogen that is widely occurring in the environment and is recognized for its capacity to form or join biofilms. The present review consolidates current knowledge on P.aeruginosa ecology and its implication in healthcare facilities premise plumbing. The adaptability of P.aeruginosa and its capacity to integrate the biofilm from the faucet and the drain highlight the role premise plumbing devices can play in promoting growth and persistence. A meta-analysis of P.aeruginosa prevalence in faucets (manual and electronic) and drains reveals the large variation in device positivity reported and suggest the high variability in the sampling approach and context as the main reason for this variation. The effects of the operating conditions that prevail within water distribution systems (disinfection, temperature, and hydraulic regime) on the persistence of P.aeruginosa are summarized. As a result from the review, recommendations for proactive control measures of water contamination by P.aeruginosa are presented. A better understanding of the ecology of P.aeruginosa and key influencing factors in premise plumbing are essential to identify culprit areas and implement effective control measures

Biosurfactants: New Insights in Their Biosynthesis, Production and Applications

Editoria

Impact of stagnation and sampling volume on water microbial quality monitoring in large buildings

Microbial drinking water quality can be altered in large buildings, especially after stagnation. In this study, bacterial profiles were generated according to the stagnation time and the volume of water collected at the tap. Successive volumes of cold and hot water were sampled after controlled stagnation periods. Bacterial profiles revealed an important decline (> 2 log) in culturable cells in the first 500 mL sampled from the hot and cold water systems, with a steep decline in the first 15 mL. The strong exponential correlation (R2 >/= 0.97) between the culturable cell counts in water and the pipe surface-to-volume ratio suggests the biofilm as the main contributor to the rapid increase in suspended culturable cells measured after a short stagnation of one-hour. Results evidence the contribution of the high surface-to-volume ratio at the point of use and the impact of short stagnation times on the increased bacterial load observed. Simple faucets with minimal internal surface area should be preferred to minimize surface area. Sampling protocol, including sampling volume and prior stagnation, was also shown to impact the resulting culturable cell concentration by more than 1000-fold. Sampling a smaller volume on first draw after stagnation will help maximize recovery of bacteria

A Novel Glycolipid Biosurfactant Confers Grazing Resistance upon Pantoea ananatis BRT175 against the Social Amoeba Dictyostelium discoideum

Pantoea is a versatile genus of bacteria with both plant-and animal-pathogenic strains, some of which have been suggested to cause human infections. There is, however, limited knowledge on the potential determinants used for host association and pathogenesis in animal systems. In this study, we used the model host Dictyostelium discoideum to show that isolates of Pantoea ananatis exhibit differential grazing susceptibility, with some being resistant to grazing by the amoebae. We carried out a high-throughput genetic screen of one grazing-resistant isolate, P. ananatis BRT175, using the D. discoideum pathosystem to identify genes responsible for the resistance phenotype. Among the 26 candidate genes involved in grazing resistance, we identified rhlA and rhlB, which we show are involved in the biosynthesis of a biosurfactant that enables swarming motility in P. ananatis BRT175. Using liquid chromatography-mass spectrometry (LC-MS), the biosurfactant was shown to be a glycolipid with monohexose-C10-C10 as the primary congener. We show that this novel glycolipid biosurfactant is cytotoxic to the amoebae and is capable of compromising cellular integrity, leading to cell lysis. The production of this biosurfactant may be important for bacterial survival in the environment and could contribute to the establishment of opportunistic infections. IMPORTANCE The genetic factors used for host interaction by the opportunistic human pathogen Pantoea ananatis are largely unknown. We identified two genes that are important for the production of a biosurfactant that confers grazing resistance against the social amoeba Dictyostelium discoideum. We show that the biosurfactant, which exhibits cytotoxicity toward the amoebae, is a glycolipid that incorporates a hexose rather than rhamnose. The production of this biosurfactant may confer a competitive advantage in the environment and could potentially contribute to the establishment of opportunistic infections

Bactericidal Effect of Tomatidine-Tobramycin Combination against Methicillin-Resistant Staphylococcus aureus and Pseudomonas aeruginosa Is Enhanced by Interspecific Small-Molecule Interactions.

This study investigated the antibacterial activity of the plant alkaloid tomatidine (TO) against Staphylococcus aureus grown in presence of Pseudomonas aeruginosa. Since the P. aeruginosa exoproduct 4-hydroxy-2-heptylquinoline-N-oxide (HQNO) is known to cause respiratory deficiency in S. aureus and that respiratory-deficient S. aureus are known to be hypersensitive to TO, we performed kill kinetics of TO (8 mug/ml) against S. aureus in co-culture with P. aeruginosa. Kill kinetics were also carried out using P. aeruginosa mutants deficient in the production of different exoproducts and quorum sensing-related compounds. After 24h in co-culture, TO increased the killing of S. aureus by 3.4 log10 CFU/ml in comparison to that observed in a co-culture without TO. The effect of TO was abolished when S. aureus was in co-culture with the lasR-/rhlR-, pqsA-, pqsL- or lasA- mutant of P. aeruginosa. The bactericidal effect of TO against S. aureus in co-culture with the pqsL- mutant was restored by supplemental HQNO. In a S. aureus mono-culture, the combination of HQNO and TO was bacteriostatic, indicating that the pqsL- mutant produced an additional factor required for the bactericidal effect. The bactericidal activity of TO was also observed against a tobramycin-resistant methicillin-resistant S. aureus (MRSA) in co-culture with P. aeruginosa and addition of tobramycin significantly suppressed the growth of both microorganisms. TO shows a strong bactericidal effect against S. aureus when co-cultured with P. aeruginosa. The combination of TO and tobramycin may represent a new treatment approach for cystic fibrosis patients frequently co-colonized by MRSA and P. aeruginosa

Aspergillus Is Inhibited by Pseudomonas aeruginosa Volatiles

BACKGROUND: Pseudomonas aeruginosa (Pa) and Aspergillus fumigatus (Af) compete with each other for nutrients and survival in natural environments, and have been extensively studied because of their intermicrobial interactions in the human microbiome. These are the principal microbes infecting immunocompromised patients and persons with cystic fibrosis, particularly the airways. These intermicrobial studies have largely been conducted in liquid medium or on agar, and thus focus on soluble or diffusible microbial products. Several key inhibitory molecules were defined in such studies. METHODS: in the present report, we examine several methodologies which can be conveniently used to study the interaction of microbial volatiles, including capture methods and kinetics. RESULTS: Pa volatiles inhibit Af, and the inhibitory mechanism appears to be the incorporation of the inhibitory molecules into the substrate nourishing the Af, rather than directly onto Af structures. We define by mass spectroscopy some specific volatile Pa products that can inhibit Af. Some of these molecules are selected for interest by the study of gene deletion mutants, producing a few Pa strains that were impaired in inhibition. We presumed the volatiles of these latter strains could be excluded from the search for inhibitors. CONCLUSION: the Pa inhibition of Af via a gaseous phase could be critical components in their competition, particularly in airways, where more direct contact may not be extensive.</p

Proanthocyanidin Interferes with Intrinsic Antibiotic Resistance Mechanisms of Gram-Negative Bacteria

Antibiotic resistance is spreading at an alarming rate among pathogenic bacteria in both medicine and agriculture. Interfering with the intrinsic resistance mechanisms displayed by pathogenic bacteria has the potential to make antibiotics more effective and decrease the spread of acquired antibiotic resistance. Here, it is demonstrated that cranberry proanthocyanidin (cPAC) prevents the evolution of resistance to tetracycline in Escherichia coli and Pseudomonas aeruginosa, rescues antibiotic efficacy against antibiotic-exposed cells, and represses biofilm formation. It is shown that cPAC has a potentiating effect, both in vitro and in vivo, on a broad range of antibiotic classes against pathogenic E. coli, Proteus mirabilis, and P. aeruginosa. Evidence that cPAC acts by repressing two antibiotic resistance mechanisms, selective membrane permeability and multidrug efflux pumps, is presented. Failure of cPAC to potentiate antibiotics against efflux pump-defective mutants demonstrates that efflux interference is essential for potentiation. The use of cPAC to potentiate antibiotics and mitigate the development of resistance could improve treatment outcomes and help combat the growing threat of antibiotic resistance

Characterization of the biocontrol activity of three bacterial isolates against the phytopathogen Erwinia amylovora

Antibiotics are sprayed on apple and pear orchards to control, among other pathogens, the bacterium Erwinia amylovora, the causative agent of fire blight. As with many other pathogens, we observe the emergence of antibiotic-resistant strains of E. amylovora. Consequently, growers are looking for alternative solutions to combat fire blight. To find alternatives to antibiotics against this pathogen, we have previously isolated three bacterial strains with antagonistic and extracellular activity against E. amylovora, both in vitro and in planta, corresponding to three different bacterial genera: Here, we identified the inhibitory mode of action of each of the three isolates against E. amylovora. Isolate Bacillus amyloliquefaciens subsp. plantarum (now B. velezensis) FL50S produces several secondary metabolites including surfactins, iturins, and fengycins. Specifically, we identified oxydifficidin as the most active against E. amylovora S435. Pseudomonas poae FL10F produces an active extracellular compound against E. amylovora S435 that can be attributed to white-line-inducing principle (WLIP), a cyclic lipopeptide belonging to the viscosin subfamily (massetolide E, F, L, or viscosin). Pantoea agglomerans NY60 has a direct cell-to-cell antagonistic effect against E. amylovora S435. By screening mutants of this strain generated by random transposon insertion with decreased antagonist activity against strain S435, we identified several defective transposants. Of particular interest was a mutant in a gene coding for a Major Facilitator Superfamily (MFS) transporter corresponding to a transmembrane protein predicted to be involved in the extracytoplasmic localization of griseoluteic acid, an intermediate in the biosynthesis of the broad-spectrum phenazine antibiotic D-alanylgriseoluteic acid

La pompe à efflux MexEF-OprN de pseudomonas aeruginosa exporte la molécule de communication intercellulaires 4-hydroxy-2-heptyliquinoline (HHQ)

La bactérie pathogène opportuniste Pseudomonas aeruginosa est la cause d’infections chroniques chez les personnes atteintes de la fibrose kystique (FK). De plus, P. aeruginosa est naturellement très résistante aux antimicrobiens, ce qui rend l’antibiothérapie souvent inefficace. Les pompes à efflux sont des déterminants majeurs de la résistance aux antibiotiques chez cette bactérie. Elles permettent la résistance simultanée à différentes classes d'antibiotiques. La pompe à efflux MexEF-OprN promeut la résistance au chloramphénicol, au triméthoprime, au triclosan et aux fluoroquinolones. L’expression continue de l’opéron mexEF-oprN est observée chez des mutants de mexS, gène dont la fonction est inconnue. Une mutation dans mexS affecte aussi les mécanismes de quorum sensing (QS), c’est-à-dire de communication intercellulaire. Le QS contrôle l’expression de facteurs de virulence et la formation de biofilms, observées dans les voies respiratoires des personnes atteintes de FK. Le QS est contrôlé par des régulateurs transcriptionnels qui, pour être actifs, doivent être couplés à de petites molécules signales nommées auto-inducteurs. Alors que la population bactérienne se densifie, les auto-inducteurs s’accumulent dans le milieu extracellulaire jusqu’à atteindre une concentration-seuil, à laquelle le "quorum" est atteint. MvfR est un régulateur du QS et contrôle l’expression de plusieurs gènes importants pour la virulence, dont ceux de l’opéron pqsABCDE, impliqués dans la biosynthèse des 4-hydroxy-2-alkylquinolines (HAQ). Un auto-inducteur associé à MvfR est le 3,4-dihydroxy-2- heptylquinoline (PQS; Pseudomonas Quinolone Signal). L’enzyme PqsH est responsable de la synthèse du PQS et utilise un HAQ, le 4-hydroxy-2-heptylquinoline (HHQ), comme substrat. Étrangement, la quantité de PQS produit par les mutants mexS est substantiellement réduite. Afin de mieux comprendre l’influence de cette mutation sur les HAQ, nous avons quantifié leurs concentrations par LC-MS/MS chez la souche parentale PA14 et son mutant isogénique mexS. Cette expérience fut effectuée en absence ou présence d’inhibiteurs des pompes à efflux. De plus, le niveau d’expression de plusieurs gènes du QS fût déterminé grâce à des fusions transcriptionnelles entre les régions promotrices des gènes à l’étude et le gène rapporteur lacZ. Mis ensemble, nos résultats démontrent que c’est l’exportation du HHQ par MexEF-OprN qui cause le déficit en PQS. Puisque des souches qui surexpriment mexEF-oprN sont défectueuses pour le QS et moins virulentes, il serait intéressant d’identifier de nouvelles molécules à potentiel thérapeutique qui permettrait de moduler l’activité de la pompe MexEF-OprN. Cela pourrait faciliter le traitement des infections pulmonaires à P. aeruginosa