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. 2022 Aug 30;10(9):1755.
doi: 10.3390/microorganisms10091755.

Effect of Biogenic Silver Nanoparticles on the Quorum-Sensing System of Pseudomonas aeruginosa PAO1 and PA14

Erika Kushikawa Saeki  1 , Heloísa Moreira Martins  2 , Larissa Ciappina de Camargo  2 , Laís Anversa  3 , Eliandro Reis Tavares  4 , Sueli Fumie Yamada-Ogatta  4 , Lucy Megumi Yamauchi Lioni  4 , Renata Katsuko Takayama Kobayashi  2 , Gerson Nakazato  2
Affiliations

Effect of Biogenic Silver Nanoparticles on the Quorum-Sensing System of Pseudomonas aeruginosa PAO1 and PA14

Erika Kushikawa Saeki et al. Microorganisms. .

Abstract

The increase in multidrug-resistant microorganisms represents a global threat requiring the development novel strategies to fight bacterial infection. This study aimed to assess the effect of silver nanoparticles (bio-AgNPs) on bacterial growth, biofilm formation, production of virulence factors, and expression of genes related to the quorum-sensing (QS) system of P. aeruginosa PAO1 and PA14. Biofilm formation and virulence assays were performed with bio-AgNPs. RT-qPCR was carried out to determine the effect of bio-AgNPs on the QS regulatory genes lasI, lasR, rhlI, rhlR, pqsA, and mvfR. Bio-AgNPs had an MIC value of 62.50 μM, for both strains. Phenotypic and genotypic assays were carried out using sub-MIC values. Experimental results showed that treatment with sub-MICs of bio-AgNPs reduced (p < 0.05) the motility and rhamnolipids and elastase production in P. aeruginosa PAO1. In PA14, bio-AgNPs stimulated swarming and twitching motilities as well as biofilm formation and elastase and pyocyanin production. Bio-AgNP treatment increased (p < 0.05) the expression of QS genes in PAO1 and PA14. Despite the different phenotypic behaviors in both strains, both showed an increase in the expression of QS genes. Demonstrating that the bio-AgNPs acted in the induction of regulation. The possible mechanism underlying the action of bio-AgNPs involves the induction of the rhl and/or pqs system of PAO1 and of the las and/or pqs system of PA14. These results suggest that exposure to low concentrations of bio-AgNPs may promote the expression of QS regulatory genes in P. aeruginosa, consequently inducing the production of virulence factors such as elastase, pyocyanin, and biofilms.

Keywords: AgNPs; antivirulence; gene regulation; quorum quenching.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Growth curve of Pseudomonas aeruginosa. (A) PAO1 and (B) PA14 in the presence or absence (control) of subinhibitory concentrations (31.25 µM, 15.62 µM, and 7.81 µM) of biogenic silver nanoparticles (Bio-AgNP). Bacteria were inoculated at a density of 5 × 105 CFU/mL. Results are expressed as mean ± standard deviation.
Figure 2
Figure 2
Effect of bio-AgNPs on swarming, swimming, and twitching motilities in Pseudomonas aeruginosa PAO1 and PA14. Swarming motility in (A1) PAO1 and (A2) PA14. Swimming motility in (B1) PAO1 and (B2) PA14. Twitching motility in (C1) PAO1 and (C2) PA14. Each data point represents the result of one treatment, and the mean of three replications is indicated by a black bar. Images below the graphs are representative photographs of PAO1 and PA14 motility halos. Asterisks indicate significant differences between means and the control at p < 0.05 by analysis of variance followed by Tukey’s test.
Figure 3
Figure 3
Effect of bio-AgNPs on virulence factors of Pseudomonas aeruginosa PAO1 and PA14. Rhamnolipid production in (A1) PAO1 and (A2) PA14. Alkaline protease production in (B1) PAO1 and (B2) PA14. Elastase B production in (C1) PAO1 and (C2) PA14. Pyocyanin production in (D1) PAO1 and (D2) PA14. Results are expressed as mean ± standard deviation (n = 3). a–c Tukey’s honestly significant difference test at p < 0.05.
Figure 4
Figure 4
Relative expression of quorum-sensing regulatory genes in Pseudomonas aeruginosa treated with bio-AgNPs. The mean relative gene expression was normalized to that of the reference gene proC. * p < 0.05.
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