Adaptation and diversification in virulence factors among urinary catheter-associated Pseudomonas aeruginosa isolates

Novel surface biochemical modifications of urinary catheters to prevent catheter-associated urinary tract infections

More than 70% of hospital-acquired urinary tract infections are related to urinary catheters, which are commonly used for the treatment of about 20% of hospitalized patients. Urinary catheters are used to drain the bladder if there is an obstruction in the tube that carries urine out of the bladder (urethra). During catheter-associated urinary tract infections, microorganisms rise up in the urinary tract and reach the bladder, and cause infections. Various materials are used to fabricate urinary catheters such as silicone, polyurethane, and latex. These materials allow bacteria and fungi to develop colonies on their inner and outer surfaces, leading to bacteriuria or other infections. Urinary catheters could be modified to exert antibacterial and antifungal effects. Although so many research have been conducted over the past years on the fabrication of antibacterial and antifouling catheters, an ideal catheter needs to be developed for long-term catheterization of more than a month. In this review, we are going to introduce the recent advances in fabricating antibacterial materials to prevent catheter-associated urinary tract infections, such as nanoparticles, antibiotics, chemical compounds, antimicrobial peptides, bacteriophages, and plant extracts.

Differential expression of urease genes and ureolytic activity of uropathogenic Escherichia coli and Pseudomonas aeruginosa isolates in different nutritional conditions

Uropathogens have adaptation strategies to survive in the host urinary tract by efficiently utilizing and tolerating the urinary metabolites. Many uropathogens harbour the enzyme urease for the breakdown of urea and the enzymatic breakdown of urea increases the pH and facilitate the struvite crystallization. In this study, the differential urease activity of uropathogenic Escherichia coli and Pseudomonas aeruginosa strains was investigated under different nutritional conditions. The experiments included measurement of growth, pH, urease activity, NH4-N generation and urease gene (ureC) expression among the bacterial strains under different conditions. Further, the implications of urea breakdown on the struvite crystallization in vitro and biofilm formation were also assessed. The study included urease positive isolates and for comparison urease negative isolates were included. Compared to the urease negative strains the urease positive strains formed higher biofilms and motility. The urease positive P. aeruginosa showed significantly higher (p < 0.01) pH and urease activity (A557-A630) compared to E. coli under experimental conditions. Further, supplementation of glucose to the growth media significantly increased the urease activity in P. aeruginosa and in contrast, it was significantly lower in E. coli. The expression profile of urease gene (ureC) was significantly higher (p < 0.001) in P. aeruginosa compared to E. coli and was consistent with the biochemical results of the urease activity under the nutritional conditions. The differential urease activity under two nutritional conditions influenced the biogenic struvite crystallization. It correlated with the urease activity showing higher crystallization rate in P. aeruginosa compared to E. coli. The results highlight the differential urease activity in two common uropathogens under different nutritional conditions that may have significant role on the regulation of virulence, pathogenicity and in the kidney stone disease.

Resistance Is Not Futile: The Role of Quorum Sensing Plasticity in Pseudomonas aeruginosa Infections and Its Link to Intrinsic Mechanisms of Antibiotic Resistance

Bacteria use a cell-cell communication process called quorum sensing (QS) to orchestrate collective behaviors. QS relies on the group-wide detection of extracellular signal molecules called autoinducers (AI). Quorum sensing is required for virulence and biofilm formation in the human pathogen Pseudomonas aeruginosa. In P. aeruginosa, LasR and RhlR are homologous LuxR-type soluble transcription factor receptors that bind their cognate AIs and activate the expression of genes encoding functions required for virulence and biofilm formation. While some bacterial signal transduction pathways follow a linear circuit, as phosphoryl groups are passed from one carrier protein to another ultimately resulting in up- or down-regulation of target genes, the QS system in P. aeruginosa is a dense network of receptors and regulators with interconnecting regulatory systems and outputs. Once activated, it is not understood how LasR and RhlR establish their signaling hierarchy, nor is it clear how these pathway connections are regulated, resulting in chronic infection. Here, we reviewed the mechanisms of QS progression as it relates to bacterial pathogenesis and antimicrobial resistance and tolerance.

Cell adhesion and twitching motility influence strong biofilm formation in Pseudomonas aeruginosa

In the present study, biofilm formation was quantified in UTI isolates of Pseudomonas aeruginosa (n = 22) using the crystal violet assay and was categorized into; strong (n = 16), weak (n = 4), and moderate (n = 2) biofilm producers. Further experiments were done using strong (n = 4) and weak (n = 4) biofilm producers. Biofilm formation was greater in Luria broth followed by natural urine and artificial urine on silicone and silicone-coated latex. Cell adhesion and twitching motility were greater in strong biofilm producers. The presence of thick biofilm with an increased number of dead and total number of cells of strong biofilm producers was observed using CLSM. The concentrations of exopolymeric substances (eDNA, protein, and pel polysaccharide) were high in strong biofilm producers. FEG-SEM visualization of biofilm produced by strong biofilm producers showed more cells encased in thick biofilm matrix than weak ones. Overall results provide evidence for increased cell adhesion and twitching motility in strong biofilm producers.

Carvone - a quorum sensing inhibitor blocks biofilm formation in Chromobacterium violaceum

Carvone is a natural monoterpenoid and in this study it was tested for its role in attenuating quorum sensing (QS) controlled biofilm formation in Chromobacterium violaceum. It showed significant QS inhibition in terms of reduction in violacein at a concentration range of 60 to 70 µg/mL against C. violaceum ATCC 12472. At the same concentration, carvone also inhibited biofilm formation by more than 80%. The biofilm morphology of C. violaceum is unique with a well organised pattern of cell arrangement in a tight matrix. The same was evident in Scanning electron microscopy, however, carvone treatment not only showed reduction in biofilm density but also disruption of biofilm matrix. Interruption of biofilm formation was attributed to reduction in the exopolysaccharide production and swarming motility. Molecular investigations (RT-PCR) showed that the important genes involved in biofilm regulation such as pilS, pilR, pilB and pilT were downregulated significantly in the treatment groups.

Revisiting the virulence hallmarks of Pseudomonas aeruginosa: a chronicle through the perspective of quorum sensing

Pseudomonas aeruginosa is an opportunistic pathogen and the leading cause of mortality among immunocompromised patients in clinical setups. The hallmarks of virulence in P. aeruginosa encompass six biologically competent attributes that cumulatively drive disease progression in a multistep manner. These multifaceted hallmarks lay the principal foundation for rationalizing the complexities of pseudomonal infections. They include factors for host colonization and bacterial motility, biofilm formation, production of destructive enzymes, toxic secondary metabolites, iron-chelating siderophores and toxins. This arsenal of virulence hallmarks is fostered and stringently regulated by the bacterial signalling system called quorum sensing (QS). The central regulatory functions of QS in controlling the timely expression of these virulence hallmarks for adaptation and survival drive the disease outcome. This review describes the intricate mechanisms of QS in P. aeruginosa and its role in shaping bacterial responses, boosting bacterial fitness. We summarize the virulence hallmarks of P. aeruginosa, relating them with the QS circuitry in clinical infections. We also examine the role of QS in the development of drug resistance and propose a novel antivirulence therapy to combat P. aeruginosa infections. This can prove to be a next-generation therapy that may eventually become refractory to the use of conventional antimicrobial treatments.

Reduced Crystalline Biofilm Formation on Superhydrophobic Silicone Urinary Catheter Materials

Crystalline biofilm formation in indwelling urinary catheters is a serious health problem as it creates a barrier for antibacterial coatings. This emphasizes the failure of antibacterial coatings that do not have a mechanism to reduce crystal deposition on catheter surfaces. In this study, trifluoropropyl spray-coated polydimethylsiloxane (TFP-PDMS) has been employed as an antibiofilm forming surface without any antibacterial agent. Here, TFP was coated on half-cured PDMS using the spray coating technique to obtain a durable superhydrophobic coating for a minimum five cycles of different sterilization methods. The crystalline biofilm-forming ability of Proteus mirabilis in artificial urine, under static and flow conditions, was assessed on a TFP-PDMS surface. In comparison to the commercially available silver-coated latex and silicone catheter surfaces, TFP-PDMS displayed reduced bacterial attachment over 14 days. Moreover, the elemental analysis determined by atomic absorption spectroscopy and energy-dispersive X-ray analysis revealed that the enhanced antibiofilm forming ability of TFP-PDMS was due to the self-cleaning activity of the surface. We believe that this modified surface will significantly reduce biofilm formation in indwelling urinary catheters and further warrant future clinical studies.

Pseudomonas aeruginosa biofilms and their partners in crime

Pseudomonas aeruginosa biofilms and the capacity of the bacterium to coexist and interact with a broad range of microorganisms have a substantial clinical impact. This review focuses on the main traits of P. aeruginosa biofilms, such as the structural composition and regulatory networks involved, placing particular emphasis on the clinical challenges they represent in terms of antimicrobial susceptibility and biofilm infection clearance. Furthermore, the ability of P. aeruginosa to grow together with other microorganisms is a significant pathogenic attribute with clinical relevance; hence, the main microbial interactions of Pseudomonas are especially highlighted and detailed throughout this review. This article also explores the infections caused by single and polymicrobial biofilms of P. aeruginosa and the current models used to recreate them under laboratory conditions. Finally, the antimicrobial and antibiofilm strategies developed against P. aeruginosa mono and multispecies biofilms are detailed at the end of this review.

In vitro Interaction of Pseudomonas aeruginosa Biofilms With Human Peripheral Blood Mononuclear Cells

The human immune cell response against bacterial biofilms is a crucial, but still poorly investigated area of research. Herein, we aim to establish an in vitro host cell-biofilm interaction model suitable to investigate the peripheral blood mononuclear cell (PBMC) response to Pseudomonas aeruginosa biofilms. P. aeruginosa biofilms were obtained by incubating bacteria in complete RPMI 1640 medium with 10% human plasma for 24 h. PBMC obtained from healthy donors were added to preformed P. aeruginosa biofilms. Following a further 24 h incubation, we assessed (i) PBMC viability and activation; (ii) cytokine profiles in the supernatants; and (iii) CFU counts of biofilm forming bacteria. Cell-death was <10% upon 24 h incubation of PBMC with P. aeruginosa biofilms. PBMC incubated for 24 h with preformed P. aeruginosa biofilms were significantly more activated compared to PBMC incubated alone. Interestingly, a marked activation of CD56⁺CD3⁻ natural killer (NK) cells was observed that reached 60% of NK cells as an average of different donors. In the culture supernatants of PBMC co-cultured with P. aeruginosa biofilms, not only pro-inflammatory (IL-1β, IFN-γ, IL-6, and TNF-α) but also anti-inflammatory (IL-10) cytokines were significantly increased as compared to PBMC incubated alone. Furthermore, incubation of biofilms with PBMC, caused a statistically significant increase in the CFU number of P. aeruginosa, as compared to biofilms incubated without PBMC. In order to assess whether PBMC products could stimulate the growth of P. aeruginosa biofilms, we incubated preformed P. aeruginosa biofilms with or without supernatants obtained from the co-cultures of PBMC with biofilms. In the presence of the supernatants, the CFU count of biofilm-derived P. aeruginosa, was two to seven times higher than those of biofilms incubated without supernatants (P < 0.01). Overall, the results obtained shed light on the reciprocal interaction between human PBMC and P. aeruginosa biofilms. P. aeruginosa biofilms induced PBMC activation and cytokine secretion but, in turn, the presence of PBMC and/or PBMC-derived components enhanced the number of P. aeruginosa biofilm associated bacteria. This may indicate a successful bacterial defensive/persistence strategy against immune response.

Synthesis and characterization of chitosan oligosaccharide-capped gold nanoparticles as an effective antibiofilm drug against the Pseudomonas aeruginosa PAO1

The infection caused by Pseudomonas aeruginosa is a serious concern in human health. The bacterium is an opportunistic pathogen which has been reported to cause nosocomial and chronic infections through biofilm formation and synthesis of several toxins and virulence factors. Furthermore, the formation of biofilm by P. aeruginosa is known as one of the resistance mechanisms against conventional antibiotics. Natural compounds from marine resources have become one of the simple, cost-effective, biocompatible and non-toxicity for treating P. aeruginosa biofilm-related infections. Furthermore, hybrid formulation with nanomaterials such as nanoparticles becomes an effective alternative strategy to minimize the drug toxicity problem and cytotoxicity properties. For this reason, the present study has employed chitosan oligosaccharide for the synthesis of chitosan oligosaccharide-capped gold nanoparticles (COS-AuNPs). The synthesized COS-AuNPs were then characterized by using UV-Visible spectroscopy, Dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR), Field emission transmission electron microscopy (FE-TEM), and Energy dispersive X-ray diffraction (EDX). The synthesized COS-AuNPs were applied for inhibiting P. aeruginosa biofilm formation. Results have shown that COS-AuNPs exhibited inhibition to biofilm as well as eradication to pre-existing mature biofilm. Simultaneously, COS-AuNPs were also able to reduce bacterial hemolysis and different virulence factors produced by P. aeruginosa. Overall, the present study concluded that the hybrid nanoformulation such as COS-AuNPs could act as a potential agent to exhibit inhibitory properties against the P. aeruginosa pathogenesis arisen from biofilm formation.

Anti-biofilm and cytoprotective activities of quercetin against Pseudomonas aeruginosa isolates

Increase in infection with multidrug resistant Pseudomonas aeruginosa is a serious global challenge in healthcare. Pseudomonas aeruginosa is capable of causing human infection in various sites and complicates the infection due to its virulence factors. This study was aimed to investigate the effect of quercetin, a dietary flavonoid against the virulence factors of P. aeruginosa and its cell protective effects on epithelial cells. Bactericidal activity, anti-biofilm activity and effect on different virulence factors were carried out using standard methods by using five P. aeruginosa isolates. Cytotoxicity and cell protective effect of quercetin was evaluated by trypan blue dye exclusion assay. All the tested isolates were completely inhibited (100%) by quercetin at a concentration of 500 μg ml^-1 . It showed significant (P < 0·05) inhibitory effect on virulence factors including biofilm formation and showed significant protective effect on HEK 293T cells infected with P. aeruginosa strains. This study supports the role of quercetin against P. aeruginosa, by inhibiting virulence factors as well as its cytoprotective activity during bacterial infection either by attenuating the virulence or providing direct protective effect to the host cells. SIGNIFICANCE AND IMPACT OF THE STUDY: The increase in infections caused by opportunistic pathogen Pseudomonas aeruginosa is a serious concern in the health care system. This study describes the beneficial effects of a dietary flavonoid, quercetin against pathogenic P. aeruginosa strains and its protective effect against the P. aeruginosa infection in HEK 293T cells in vitro.