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Pseudomonas aeruginosa is a frequent causative agent of healthcare-associated diseases, but recently, other members of the Pseudomonas genus have been recognized to cause human colonization and infection. Since the aquatic environment could be an important source of contamination, we studied the drug resistance and virulence profiles in Pseudomonas species isolated from healthcare water systems. 17 Pseudomonas spp. out of 57 were randomly selected and their drug resistance and virulence profiles were later evaluated. Based on the positivity to the tests, the adhesion capability and biofilm formation on polystyrene and glass surfaces were studied in 6 strains, each belonging to different species. Six Pseudomonas strains (35%) were α-hemolytic, nine (53%) showed a positivity to the gelatinase test, and P. acidovorans 2R only was capable to degrade DNA. All Pseudomonas strains presented urease activity and the production of siderophores was widely observed (64,7%). Most of the strains showed one of the three types of motilities, 15 Pseudomonas (88.23%) resulted bacteriocin producers and all strains were resistant to one or more antibiotics. Lastly, among the six selected strains, P. aeruginosa 98.5 and P. fluorescens 97.4 were the best biofilm producers. Our study has highlighted how the majority of isolates shows biological characteristics that contribute to the pathogenicity of Pseudomonas. These features emphasize the virulence potentiality of other members of the Pseudomonas genus besides Pseudomonas aeruginosa, making them potentially pathogenic, especially against immunocompromised individuals.

Given the major threat of phytopathogenic bacteria to food production and ecosystem stability worldwide, novel alternatives to conventional chemicals-based agricultural practices are needed to combat these bacteria. The objective of this study is to evaluate the ability of Pseudomonas segetis strain P6, which was isolated from the Salicornia europaea rhizosphere, to act as a potential biocontrol agent given its plant growth-promoting (PGP) and quorum quenching (QQ) activities. Seed biopriming and in vivo assays of tomato plants inoculated with strain P6 resulted in an increase in seedling height and weight. We detected QQ activity, involving enzymatic degradation of signal molecules in quorum sensing communication systems, against a broad range of N -acylhomoserine lactones (AHLs). HPLC-MRM data and phylogenetic analysis indicated that the QQ enzyme was an acylase. The QQ activity of strain P6 reduced soft rot symptoms caused by Dickeya solani , Pectobacterium atrosepticum and P. carotovorum on potato and carrot. In vivo assays showed that the PGP and QQ activities of strain P6 protect tomato plants against Pseudomonas syringae pv. tomato, indicating that strain P6 could have biotechnological applications. To our knowledge, this is the first report to show PGP and QQ activities in an indigenous Pseudomonas strain from Salicornia plants.

Oil bioremediation may be achievable via Pseudomonas spp. leading to low-cost biosurfactant (BSF) production, but the environmental impact is unclear. Here, we studied P. aeruginosa PA14 and PAO1; P. putida mt-2 and F1; and P. citronellolis 620C, P3B5, and SJTE-3, for their ability to degrade oily wastewater (OW), produce BSFs, and impact the model insect, Drosophila melanogaster . Biodegradation was > 86% by day 1 and > 93% by day 7, while BSF production was > 200 mg/L by day 1 and > 400 mg/L by day 7 for all strains. P. aeruginosa PAO1 and PA14 produce rhamnolipids and glycolipopeptides, respectively. P. putida mt-2 and F1 formed glycolipopeptides and glycolipids, respectively . P. citronellolis P3B5 and SJTE-3 yielded glycolipids, whereas 620C produced lipopeptides. Strikingly, Drosophila was mostly attracted to food contaminated with any of the P. aeruginosa strains or P. putida mt-2, which were the most virulent. To the contrary, Drosophila was repelled from food containing the low in virulence P. putida F1 or any of the P. citronellolis strains. All strains exhibited high ability to colonize Drosophila and disperse from fly to fly, but the colonization and contagion extend by P. aeruginosa strains were slightly higher. Moreover, the virulence of Pseudomonas spp. aligned with the toxicity of their BSFs. BSFs produced by P. aeruginosa were the most toxic, followed by P. putida and P. citronellolis , indicating a correlation between BSF toxicity and microbial origin. We concluded that P. citronellolis strains and their BSFs are relatively innocuous to the fly populations, yet highly potent in biodegrading OW. Key points • >93% biodegradation of oily wastewater by all Pseudomonas spp. strains by day 7 • The virulence of Pseudomonas spp. aligns with the toxicity of their BSFs • P. citronellolis strains and their BSFs are more innocuous to Drosophila than those of P. putida and P. aeruginosa

Background Currently, no vaccine against Pseudomonas is available. IC43 is a new, recombinant, protein (OprF/I)-based vaccine against the opportunistic pathogen, Pseudomonas aeruginosa , a major cause of serious hospital-acquired infections. IC43 has proven immunogenicity and tolerability in healthy volunteers, patients with burns, and patients with chronic lung diseases. In order to assess the immunogenicity and safety of IC43 in patients who are most at risk of acquiring Pseudomonas infections, it was evaluated in mechanically ventilated ICU patients. Methods We conducted a randomized, placebo-controlled, partially blinded study in mechanically ventilated ICU patients. The immunogenicity of IC43 at day 14 was determined as the primary endpoint, and safety, efficacy against P. aeruginosa infections, and all-cause mortality were evaluated as secondary endpoints. Vaccinations (100 μg or 200 μg IC43 with adjuvant, or 100 μg IC43 without adjuvant, or placebo) were given twice in a 7-day interval and patients were followed up for 90 days. Results Higher OprF/I IgG antibody titers were seen at day 14 for all IC43 groups versus placebo ( P  < 0.0001). Seroconversion (≥4-fold increase in OprF/I IgG titer from days 0 to 14) was highest with 100 μg IC43 without adjuvant (80.6%). There were no significant differences in P. aeruginosa infection rates, with a low rate of invasive infections (pneumonia or bacteremia) in the IC43 groups (11.2-14.0%). Serious adverse events (SAEs) considered possibly related to therapy were reported by 2 patients (1.9%) in the group of 100 µg IC43 with adjuvant. Both SAEs resolved and no deaths were related to study treatment. Local tolerability symptoms were mild and rare (<5% of patients), a low rate of treatment-related treatment-emergent adverse events (3.1–10.6%) was observed in the IC43 groups. Conclusion This phase II study has shown that IC43 vaccination of ventilated ICU patients produced a significant immunogenic effect. P. aeruginosa infection rates did not differ significantly between groups. In the absence of any difference in immune response following administration of 100 μg IC43 without adjuvant compared with 200 μg IC43 with adjuvant, the 100 μg dose without adjuvant was considered for further testing of its possible benefit of improved outcomes. There were no safety or mortality concerns. Trial registration ClinicalTrials.gov, NCT00876252 . Registered on 3 April 2009.

We propose Pseudomonas coronafaciens sp. nov. as a new species in genus Pseudomonas, which is diverse from P. syringae. We also classified strains from onions which are responsible for yellow bud (YB) disease as P. coronafaciens. Sequencing of 16S rRNA gene and multi-locus sequence analysis (MLSA) of housekeeping genes (gyrB, rpoD, gltA and gap1 genes) for the P. syringae pv. coronafaciens strains along with other strains of P. syringae pathovars resulted in a distinct cluster separate from other P. syringae pathovars. Based on DNA-DNA relatedness, pathotype strain of P. syringae pv. coronafaciens (CFBP 2216PT) exhibited ≤35.5% similarity with the pathotype strains of P. syringae pv. syringae (CFBP 1392PT, 4702T) but exhibited ≥90.6% with the YB strains (YB 12–1, YB 12–4, YB 09–1). Also, the YB strains (YB 12–1, YB 12–4, YB 09–1) were able to infect only onion but not oat, rye and Italian ryegrass (common hosts for P. syrinage pv. coronafaciens). Contrastingly, P. syringae pv. coronafaciens strains (NCPPB 600PT, ATCC 19608, Pcf 83–300) produced typical halo blight symptoms on oat, rye and Italian rye grass but did not produce any symptoms on onion. These results provide evidence that P. syringae pv. coronafaciens should be elevated to a species level and the new YB strains may potentially be a novel pathovar of hereto proposed P. coronafaciens species.

Invasive species populations periodically collapse from high to low abundance, sometimes even to extinction. Pathogens and the burden they place on invader immune systems have been hypothesised as a mechanism for these collapses. We examined the association of the bacterial pathogen ( Pseudomonas spp.) and the viral community with immune gene expression in the globally invasive Argentine ant ( Linepithema humile (Mayr)). RNA-seq analysis found evidence for 17 different viruses in Argentine ants from New Zealand, including three bacteriophages with one ( Pseudomonas phage PS-1 ) likely to be attacking the bacterial host. Pathogen loads and prevalence varied immensely. Transcriptomic data showed that immune gene expression was consistent with respect to the viral classification of negative-sense, positive-sense and double-stranded RNA viruses. Genes that were the most strongly associated with the positive-sense RNA viruses such as the Linepithema humile virus 1 (LHUV-1) and the Deformed wing virus (DWV) were peptide recognition proteins assigned to the Toll and Imd pathways. We then used principal components analysis and regression modelling to determine how RT-qPCR derived immune gene expression levels were associated with viral and bacterial loads. Argentine ants mounted a substantial immune response to both Pseudomonas and LHUV-1 infections, involving almost all immune pathways. Other viruses including DWV and the Kashmir bee virus appeared to have much less immunological influence. Different pathogens were associated with varying immunological responses, which we hypothesize to interact with and influence the invasion dynamics of this species.

Adult bacterial meningitis (ABM) caused by non-Pseudomonas (Ps.) aeruginosa Pseudomonas (NPAP) species infection has rarely been reported. The clinical characteristics of 52 cases of Pseudomonas ABM (11 NPAP- and 41 Ps. aeruginosa-related meningitis) collected during a 30-year study period (1986–2015) were included. Eleven cases of NPAP ABM were identified in the literature, and their clinical data were also collected. Therefore, a total of 22 NPAP ABM cases were enrolled. The clinical characteristics of the NPAP ABM and Ps. aeruginosa ABM groups were compared. Of the implicated NPAP strains, Ps. putida and Ps. stutzeri were the most common (7 cases each), followed by Ps. mendocina in 4, Ps. fluorescens in 1, Ps. fulva in 1, Ps. alcaligenes in 1, and Ps. mosselii in 1. Of the 22 cases, 50% (11/22) had an underlying postneurosurgical state. Fever (77.3%, 17/22) and altered consciousness (45.5%, 10/22) were the most common clinical presentations. Antibiotic non-susceptibility was found in 3 strains of Ps. putida and 1 Ps. mosselii strain. Compared to the patients with Ps. aeruginosa ABM, those with NPAP ABM had a higher incidence of spontaneous infections and a better survival rate. In conclusion, although Ps. putida, Ps. stutzeri and Ps. mendocina were the major implicated strains of NPAP ABM, the clinical characteristics of this specific group of ABM demonstrated marked heterogeneity. Even though the cases with NPAP ABM had better therapeutic results than those with Ps. aeruginosa ABM, further large-scale studies are needed to better delineate this specific group of ABM.

With the rising development of bacterial resistance the search for new medical treatments beyond conventional antimicrobials has become a key aim of public health research. Possible innovative strategies include the inhibition of bacterial virulence. However, consideration must be given to the evolutionary and environmental consequences of such new interventions. Virulence and cooperative social behaviour of the bacterium Pseudomonas aeruginosa rely on the quorum-sensing (QS) controlled production of extracellular products (public goods). Hence QS is an attractive target for anti-virulence interventions. During colonization, non-cooperating (and hence less virulent) P. aeruginosa QS-mutants, benefiting from public goods provided by wild type isolates, naturally increase in frequency providing a relative protection from invasive infection. We hypothesized that inhibition of QS-mediated gene expression removes this growth advantage and selection of less virulent QS-mutants, and maintains the predominance of more virulent QS-wild type bacteria. We addressed this possibility in a placebo-controlled trial investigating the anti-QS properties of azithromycin, a macrolide antibiotic devoid of bactericidal activity on P. aeruginosa, but interfering with QS, in intubated patients colonized by P. aeruginosa. In the absence of azithromycin, non-cooperating (and hence less virulent) lasR (QS)-mutants increased in frequency over time. Azithromycin significantly reduced QS-gene expression measured directly in tracheal aspirates. Concomitantly the advantage of lasR-mutants was lost and virulent wild-type isolates predominated during azithromycin treatment. We confirmed these results in vitro with fitness and invasion experiments. Azithromycin reduced growth rate of the wild-type, but not of the lasR-mutant. Furthermore, the lasR-mutant efficiently invaded wild-type populations in the absence, but not in the presence of azithromycin. These in vivo and in vitro results demonstrate that anti-virulence interventions based on QS-blockade diminish natural selection towards reduced virulence and therefore may increase the prevalence of more virulent genotypes in the Hospital environment. More generally, the impact of intervention on the evolution of virulence of pathogenic bacteria should be assessed.

Purpose Anti-virulence strategies have not been evaluated for the prevention of bacterial infections. Prolonged colonization of intubated patients with Pseudomonas aeruginosa isolates producing high-levels of the quorum sensing (QS)-regulated virulence factor rhamnolipids has been associated with ventilator-associated pneumonia (VAP). In this pathogen, azithromycin reduces QS-regulated virulence. We aimed to assess whether azithromycin could prevent VAP in patients colonized by rhamnolipids producing isolates. Methods In a randomized, double-blind, multicenter trial, intubated colonized patients received either 300 mg/day azithromycin or placebo. Primary endpoint was the occurrence of P. aeruginosa VAP. We further identified those patients persistently colonized by isolates producing high-levels of rhamnolipids and therefore at the highest risk to develop VAP linked to this QS-dependent virulence factor. Results Ninety-two patients were enrolled; 43 azithromycin-treated and 42 placebo patients were eligible for the per-protocol analysis. In the per-protocol population, the occurrence of P. aeruginosa VAP was reduced in the azithromycin group but without reaching statistical significance (4.7 vs. 14.3 % VAP, p  = 0.156). QS-dependent virulence of colonizing isolates was similarly low in both study groups, and only five patients in each arm were persistently colonized by high-level rhamnolipids producing isolates. In this high-risk subgroup, the incidence of VAP was reduced fivefold in azithromycin versus placebo patients (1/5 vs. 5/5 VAP, p  = 0.048). Conclusions There was a trend towards reduced incidence of VAP in colonized azithromycin-treated patients . In addition, azithromycin significantly prevented VAP in those patients at high risk of rhamnolipid-dependent VAP, suggesting that virulence inhibition is a promising anti-microbial strategy.

Pf bacteriophages, lysogenic viruses that infect Pseudomonas aeruginosa (Pa), are implicated in the pathogenesis of chronic Pa infections; phage-infected (Pf+) strains are known to predominate in people with cystic fibrosis (pwCF) who are older and have more severe disease. However, the transmission patterns of Pf underlying the progressive dominance of Pf+ strains are unclear. In particular, it is unknown whether phage transmission commonly occurs horizontally between bacteria via viral particles within the airway or whether Pf+ bacteria are mostly acquired via de novo Pseudomonas infections. Here, we studied Pa genomic sequences from 3 patient cohorts totaling 662 clinical isolates from 105 pwCF. We identified Pf+ isolates and analyzed transmission patterns of Pf within patients between genetically similar groups of bacteria called \"clone types.\" We found that Pf was predominantly passed down vertically within Pa clone types and rarely via horizontal transfer between clone types within the airway. Conversely, we found extensive evidence of Pa de novo infection by a new, genetically distinct Pf+ Pa. Finally, we observed that clinical isolates showed reduced activity of type IV pili and reduced susceptibility to Pf in vitro. These results cast light on the transmission of virulence-associated phages in the clinical setting.