Tobramycin reduces key virulence determinants in the proteome of Pseudomonas aeruginosa outer membrane vesicles.

Tobramycin is commonly used to treat Pseudomonas aeruginosa lung infections in patients with Cystic Fibrosis (CF). Tobramycin treatment leads to increased lung function and fewer clinical exacerbations in CF patients, and modestly reduces the density of P. aeruginosa in the lungs. P. aeruginosa resides primarily in the mucus overlying lung epithelial cells and secretes outer membrane vesicles (OMVs) that diffuse through the mucus and fuse with airway epithelial cells, thus delivering virulence factors into the cytoplasm that modify the innate immune response. The goal of this study was to test the hypothesis that Tobramycin reduces the abundance of virulence factors in OMVs secreted by P. aeruginosa. Characterization of the proteome of OMVs isolated from control or Tobramycin-exposed P. aeruginosa strain PAO1 revealed that Tobramycin reduced several OMV-associated virulence determinants, including AprA, an alkaline protease that enhances P. aeruginosa survival in the lung, and is predicted to contribute to the inhibitory effect of P. aeruginosa on Phe508del-CFTR Cl- secretion by primary human bronchial epithelial cells. Deletion of the gene encoding AprA reduced the inhibitory effect of P. aeruginosa on Phe508del-CFTR Cl- secretion. Moreover, as predicted by our proteomic analysis, OMVs isolated from Tobramycin treated P. aeruginosa had a diminished inhibitory effect on Phe508del-CFTR Cl- secretion compared to OMVs isolated from control P. aeruginosa. Taken together, our proteomic analysis of OMVs and biological validation suggest that Tobramycin may improve lung function in CF patients infected with P. aeruginosa by reducing several key virulence factors in OMVs that reduce CFTR Cl- secretion, which is essential for bacterial clearance from the lungs.

Development of Engineered Bacteriophages for Escherichia coli Detection and High-Throughput Antibiotic Resistance Determination.

T7 bacteriophages (phages) have been genetically engineered to carry the lacZ operon, enabling the overexpression of beta-galactosidase (ß-gal) during phage infection and allowing for the enhanced colorimetric detection of Escherichia coli (E. coli). Following the phage infection of E. coli, the enzymatic activity of the released ß-gal was monitored using a colorimetric substrate. Compared with a control T7 phage, our T7lacZ phage generated significantly higher levels of ß-gal expression following phage infection, enabling a lower limit of detection for E. coli cells. Using this engineered T7lacZ phage, we were able to detect E. coli cells at 10 CFU·mL-1 within 7 h. Furthermore, we demonstrated the potential for phage-based sensing of bacteria antibiotic resistance profiling using our T7lacZ phage, and subsequent ß-gal expression to detect antibiotic resistant profile of E. coli strains.

Genetic optimization of a bacteriophage-delivered alkaline phosphatase reporter to detect Escherichia coli.

A large fraction of foodborne illnesses are linked to (∼46%) leafy green vegetables contaminated by pathogens harbored in agricultural water. To prevent this, accurate point-of-production detection tools are required to identify and quantify bacterial contaminants in produce before consumers are impacted. In this study, a proof-of-concept model was engineered for a phage-based Escherichia coli detection system. We engineered the coliphage T7 to express alkaline phosphatase (ALP) to serve as the signal for E. coli detection. Wild type phoA (T7ALP) and a dominant-active allele, phoA D153G D330N (T7ALP*) was inserted into the T7 genome, with engineered constructs selected by CRISPR-mediated cleavage of unaltered chromosomes and confirmed by PCR. Engineered phages and E. coli target cells were co-incubated for 16 hours to produce lysates with liberated ALP correlated with input cell concentrations. A colorimetric assay used p-nitrophenyl phosphate (pNPP) to demonstrate significant ALP production by T7ALP and T7ALP* compared to the vector control (T7EV) (p≤ 0.05). Furthermore, T7ALP* produced 2.5-fold more signal than T7ALP (p≤ 0.05) at pH 10. Due to the increase in signal for the modified ALP* allele, we assessed T7ALP* sensitivity in a dose-responsive manner. We observed 3-fold higher signal for target cell populations as low as ∼2 × 10(5) CFU mL(-1) (p≤ 0.05 vs. no-phage control).

Colorimetric Detection of Escherichia coli Based on the Enzyme-Induced Metallization of Gold Nanorods.

A novel enzyme-induced metallization colorimetric assay is developed to monitor and measure beta-galactosidase (ß-gal) activity, and is further employed for colorimetric bacteriophage (phage)-enabled detection of Escherichia coli (E. coli). This assay relies on enzymatic reaction-induced silver deposition on the surface of gold nanorods (AuNRs). In the presence of ß-gal, the substrate p-aminophenyl ß-d-galactopyranoside is hydrolyzed to produce p-aminophenol (PAP). Reduction of silver ions by PAP generates a silver shell on the surface of AuNRs, resulting in the blue shift of the longitudinal localized surface plasmon resonance peak and multicolor changes of the detection solution from light green to orange-red. Under optimized conditions, the detection limit for ß-gal is 128 pM, which is lower than the conventional colorimetric assay. Additionally, the assay has a broader dynamic range for ß-gal detection. The specificity of this assay for the detection of ß-gal is demonstrated against several protein competitors. Additionally, this technique is successfully applied to detect E. coli bacteria cells in combination with bacteriophage infection. Due to the simplicity and short incubation time of this enzyme-induced metallization colorimetric method, the assay is well suited for the detection of bacteria in low-resource settings.

Global regulator Anr represses PlcH phospholipase activity in Pseudomonas aeruginosa when oxygen is limiting.

Haemolytic phospholipase C (PlcH) is a potent virulence and colonization factor that is expressed at high levels by Pseudomonas aeruginosa within the mammalian host. The phosphorylcholine liberated from phosphatidylcholine and sphingomyelin by PlcH is further catabolized into molecules that both support growth and further induce plcH expression. We have shown previously that the catabolism of PlcH-released choline leads to increased activity of Anr, a global transcriptional regulator that promotes biofilm formation and virulence. Here, we demonstrated the presence of a negative feedback loop in which Anr repressed plcH transcription and we proposed that this regulation allowed for PlcH levels to be maintained in a way that promotes productive host-pathogen interactions. Evidence for Anr-mediated regulation of PlcH came from data showing that growth at low oxygen (1%) repressed PlcH abundance and plcH transcription in the WT, and that plcH transcription was enhanced in an Δanr mutant. The plcH promoter featured an Anr consensus sequence that was conserved across all P. aeruginosa genomes and mutation of conserved nucleotides within the Anr consensus sequence increased plcH expression under hypoxic conditions. The Anr-regulated transcription factor Dnr was not required for this effect. The loss of Anr was not sufficient to completely derepress plcH transcription as GbdR, a positive regulator of plcH, was required for expression. Overexpression of Anr was sufficient to repress plcH transcription even at 21 % oxygen. Anr repressed plcH expression and phospholipase C activity in a cell culture model for P. aeruginosa-epithelial cell interactions.

Anr and its activation by PlcH activity in Pseudomonas aeruginosa host colonization and virulence.

Pseudomonas aeruginosa hemolytic phospholipase C (PlcH) degrades phosphatidylcholine (PC), an abundant lipid in cell membranes and lung surfactant. A ΔplcHR mutant, known to be defective in virulence in animal models, was less able to colonize epithelial cell monolayers and was defective in biofilm formation on plastic when grown in lung surfactant. Microarray analyses found that strains defective in PlcH production had lower levels of Anr-regulated transcripts than the wild type. PC degradation stimulated the Anr regulon in an Anr-dependent manner under conditions where Anr activity was submaximal because of the presence of oxygen. Two PC catabolites, choline and glycine betaine (GB), were sufficient to stimulate Anr activity, and their catabolism was required for Anr activation. The addition of choline or GB to glucose-containing medium did not alter Anr protein levels, growth rates, or respiratory activity, and Anr activation could not be attributed to the osmoprotectant functions of GB. The Δanr mutant was defective in virulence in a mouse pneumonia model. Several lines of evidence indicate that Anr is important for the colonization of biotic and abiotic surfaces in both P. aeruginosa PAO1 and PA14 and that increases in Anr activity resulted in enhanced biofilm formation. Our data suggest that PlcH activity promotes Anr activity in oxic environments and that Anr activity contributes to virulence, even in the acute infection phase, where low oxygen tensions are not expected. This finding highlights the relationships among in vivo bacterial metabolism, the activity of the oxygen-sensitive regulator Anr, and virulence.

Farnesol induces hydrogen peroxide resistance in Candida albicans yeast by inhibiting the Ras-cyclic AMP signaling pathway.

Farnesol, a Candida albicans cell-cell signaling molecule that participates in the control of morphology, has an additional role in protection of the fungus against oxidative stress. In this report, we show that although farnesol induces the accumulation of intracellular reactive oxygen species (ROS), ROS generation is not necessary for the induction of catalase (Cat1)-mediated oxidative-stress resistance. Two antioxidants, alpha-tocopherol and, to a lesser extent, ascorbic acid effectively reduced intracellular ROS generation by farnesol but did not alter farnesol-induced oxidative-stress resistance. Farnesol inhibits the Ras1-adenylate cyclase (Cyr1) signaling pathway to achieve its effects on morphology under hypha-inducing conditions, and we demonstrate that farnesol induces oxidative-stress resistance by a similar mechanism. Strains lacking either Ras1 or Cyr1 no longer exhibited increased protection against hydrogen peroxide upon preincubation with farnesol. While we also observed the previously reported increase in the phosphorylation level of Hog1, a known regulator of oxidative-stress resistance, in the presence of farnesol, the hog1/hog1 mutant did not differ from wild-type strains in terms of farnesol-induced oxidative-stress resistance. Analysis of Hog1 levels and its phosphorylation states in different mutant backgrounds indicated that mutation of the components of the Ras1-adenylate cyclase pathway was sufficient to cause an increase of Hog1 phosphorylation even in the absence of farnesol or other exogenous sources of oxidative stress. This finding indicates the presence of unknown links between these signaling pathways. Our results suggest that farnesol effects on the Ras-adenylate cyclase cascade are responsible for many of the observed activities of this fungal signaling molecule.