Pseudomonas aeruginosa: new insights into pathogenesis and host defenses

Sepsis-induced inflammasome impairment facilitates development of secondary A. baumannii pneumonia

BACKGROUND

Acinetobacter baumannii has become one of the most critical pathogens causing nosocomial pneumonia. Existing animal models of A. baumannii pneumonia are not relevant to the majority of critical care patients. We aimed to develop a novel model of secondary A. baumannii pneumonia in post-sepsis mice.

METHODS

A two-hit model of sepsis induced by cecal ligation and puncture followed by A. baumannii pneumonia on day 5 was established. In addition, the two-hit model was established in humanized mice. A period of 2 h of mechanical ventilation followed by observation was used in additional experiments. Lung histopathology, bacterial cultures, and cellular infiltration were analysed as well as markers of the inflammasome activity in vivo and ex vivo.

RESULTS

A. baumannii infection caused mortality and loss of body weight and temperature in post-sepsis mice. Increased lung bacterial burden and dissemination together with signs of enhanced inflammatory injury were observed in post-sepsis mice but not control mice that were challenged with A. baumannii. Post-sepsis mice were unable to mount inflammasome activation in response to secondary pneumonia to the level of control mice. Transfer of wild-type but not capsase-1 KO alveolar macrophages was able to restore the pulmonary protection against A. baumannii. Mechanical ventilation exacerbated the pathological response to pneumonia in post-sepsis mice but enhanced inflammasome signalling in non-sepsis mice with pneumonia.

CONCLUSIONS

We established a novel model of A. baumannii pneumonia that revealed sepsis-induced impairment of inflammasome activation in alveolar macrophages is critical for the control of secondary A. baumannii pneumonia.

Diffuse panbronchiolitis in children misdiagnosed as asthma: A case report

BACKGROUND

Diffuse panbronchiolitis (DPB) is a rare, chronic inflammatory lung disease marked by chronic cough, breathlessness, and preceding sinusitis. Symptoms often persist for years and can be misdiagnosed as asthma, particularly in children. This report describes a DPB case resolved with long-term azithromycin therapy, emphasizing the need for a timely and accurate diagnosis.

CASE SUMMARY

A 12-year-old girl, diagnosed with asthma at age five and managed with inhaled corticosteroids and long-acting beta-2 agonists, developed a history of chronic productive cough and chronic sinusitis for a year. On examination, she exhibited wheezing and coarse crackles. Despite receiving treatment for an asthma exacerbation, her symptoms did not improve. A chest X-ray revealed reticulonodular infiltration in both lower lungs, prompting further evaluation with high-resolution computed tomography (HRCT). The HRCT confirmed centrilobular nodule opacities, a 'tree-in-bud' pattern, and non-tapering bronchi, suggesting DPB. Elevated cold hemagglutinin titers at 128 further supported the diagnosis. Her cough and sinusitis resolved within a month after starting azithromycin therapy, chosen for its anti-inflammatory and immunomodulatory effects. Follow-up HRCT scans after 1 year of continuous treatment showed complete normalization.

CONCLUSION

This case highlights the importance of early diagnosis and prompt treatment in achieving favorable outcomes for DPB.

Edaravone alleviates Pseudomonas aeruginosa associated-acute lung injury by inhibiting inflammation and promoting anti-microbial peptide production

Acute respiratory distress syndrome (ARDS) is the most common respiratory emergency and one of the most severe clinical syndromes. Bacterial and viral infections are the frequent etiological factors. Pseudomonas aeruginosa (PA) is the most significant gram-negative pathogen associated with pneumonia and ARDS in critically ill patients with respiratory diseases. However, multi-drug resistance and biofilm formation pose significant challenges to the clinical treatment of PA-associated pulmonary infections. In this study, we focused on edaravone (EDA), a brain-protective agent and free-radical scavenger commonly used in neurology, and examined its role in PA-ALI. We found EDA significantly mitigated pulmonary pathological damage, inflammatory responses and Reactive Oxygen Species (ROS) generation induced by PA in vivo. The in-vitro assays revealed EDA inhibited the transcription and secretion of pro-inflammatory factors induced by PA in RAW264.7 cells by targeting the TLR4/MyD88/NF-κB signaling pathways. Additionally, EDA reduced the production of intracellular ROS and cell death. EDA treatment enhanced the transcription of antimicrobial peptides, including defensin beta 1 (Defb1), defensin beta 2 (Defb2), CC motif chemokine ligand 20 (Ccl20), secretory leukocyte peptidase inhibitor (Slpi), and lactotransferrin (Ltf), with a significant upregulation of Defb1 expression. We also explored the role of EDA in lung endogenous stem cells using Sftpc-DreER; Scgb1a1-CreER; R26-TLR mice. Our findings indicated that EDA promoted the regeneration of club cells in response to PA stimulation by promoting their proliferation. And also, EDA inhibited PA infection induced cell apoptosis in lung tissues. In conclusion, EDA acts as a protective agent in PA-ALI. It not only inhibits inflammatory responses induced by PA but also enhances the expression of antimicrobial peptides and promotes club cell regeneration. Therefore, EDA may serve as an adjunctive treatment for PA-ARDS.

Pathogen Partnerships or Power Struggles? Pseudomonas aeruginosa, and Staphylococcus aureus Dynamics in Cystic Fibrosis

Cystic fibrosis (CF) is a polymicrobial infection characterized by interactions among various bacterial species that affect one another's cohabitation. The investigation of interspecies interactions in dual infections is essential to understand their reaction in the environment better and assist in the development of treatment regimens and innovative disease control approaches. Our hypothesis posits that co-infection interactions promote the adaptation of Staphylococcus aureus and Pseudomonas aeruginosa, potentially leading to synergistic action. To explore this, we examined dual-species interactions in co-isolated pairs of these organisms from Egyptian CF patients using laboratory media and artificial sputum media (ASM). Based on demographic data, 82 collected bacterial isolates from single, dual, and triple cultures were identified from 50 enrolled patients. In the interaction of the pairs in mimic media, P. aeruginosa exo-products significantly enhanced the biofilm formation and growth of S. aureus. Conversely, S. aureus did not inhibit P. aeruginosa biofilm formation. Furthermore, the biofilm mode of dual-organism growth provides protection in the CF context, as bacterial biofilms can withstand much higher antimicrobial levels compared to planktonically grown bacteria. Additionally, key biofilm genes regulated by quorum sensing were differentially expressed in both species in an isolate-dependent manner, highlighting their significant role in coexistence dual-species biofilm coexistence. In conclusion, our study illuminates the competitive and cooperative interactions between these two pathogens, which impact their coexistence and encourage biofilm production. This, in turn, accelerates disease progression and compromises patient health.

Molecular characterization of virulent genes in Pseudomonas aeruginosa based on componential usage divergence

Genetic characteristics of virulent genes in Pseudomonas aeruginosa attracted significant attention for they could govern their drug-resistances. Studies on the componential usage divergences in the virulent genes are beneficial for further explicating their molecular characteristics. In present study, one thousand complete genomes of Pseudomonas aeruginosa were considered to study the molecular characteristics of 21 typical virulent genes. The important componential usage patterns (i.e., the base usage pattern, the codon usage pattern and their divergences) of 21 specific virulent genes were counted and calculated. The results show that (1) most virulent genes concerned in the present study are high GC sequences (overall GC ratio > 50%), especially from the codon usage perspective, the virulent genes are obviously GC3-abundant sequences (GC3 ratio > 70%); (2) the relative synonymous codon usage of all concerned virulent genes are uneven, especially in the anvM and the lptA, there is no codon for some certain amino acids, which could reveal their obvious codon usage bias; (3) some genes (i.e., the oprF and the fadD1) with lower divergence have steady effective number of codons. The findings of the present work would improve novel insights on the genetic characteristics of virulent genes in Pseudomonas aeruginosa.

Co-regulation of cooperative and private traits by PsdR in Pseudomonas aeruginosa

Social interactions profoundly shape the dynamics and functionality of microbial populations. However, mechanisms governing the regulation of cooperative or individual traits have remained elusive. Here, we investigated the regulatory mechanisms of social behaviors by characterizing the fitness of transcriptional regulator PsdR mutants in cooperating Pseudomonas aeruginosa populations. In a canonical model described previously, PsdR was shown to solely have a nonsocial role in adaptation of these populations by controlling the intracellular uptake and processing of dipeptides. In addition to these known private traits, we found that PsdR mutants also enhanced cooperation by increasing the production of quorum sensing (QS)-regulated public goods. Although private dipeptide utilization promotes individual absolute fitness, it only partially accounts for the growth advantage of PsdR mutants. The absence of the QS master regulator LasR delayed the appearance of PsdR variants in an evolution experiment. We also demonstrated that the growth fitness of PsdR mutants is determined by a combination of the QS-mediated cooperative trait and the dipeptide metabolism-related private trait. This dual trait is co-regulated by PsdR, leading to the rapid spread of PsdR variants throughout the population. In conclusion, we identified a new social model of co-regulating cooperative and private traits in PsdR variants, uncovering the social and nonsocial roles of this transcriptional regulator in cooperating bacterial populations. Our findings advance the fundamental understanding of bacterial social interactions and provide insights into population evolution, pathogen infection control and synthetic biotechnology.

Evaluation of the safety and probiotic properties of Limosilactobacillus fermentum BGI-AF16, a uric acid-lowering probiotic strain

Some beneficial microorganisms in the intestine have the potential to degrade uric acid, offering a novel strategy for the prevention of hyperuricemia. In this study, the safety and probiotic potentials of Limosilactobacillus fermentum BGI-AF16 were evaluated by whole genome sequence analysis and in vitro experiments. Based on the gene analysis of antibiotic resistance and virulence factors, L. fermentum BGI-AF16 has been shown to be safe. We identified probiotic-related genes by genome annotation tools and conducted in vitro experiments to evaluate the ability of L. fermentum BGI-AF16 to inhibit pathogenic bacteria, tolerate a simulated gastrointestinal environment, and degrade uric acid. The results from in vitro experiments showed that L. fermentum BGI-AF16 had inhibitory effects on four clinically relevant pathogens and was highly tolerant to the gastrointestinal environment. In addition, L. fermentum BGI-AF16 was able to rapidly degrade uric acid within the first hour, and the strain could degrade 56.36 ± 2.32 % of uric acid by the third hour. The genome of the strain contains genes encoding flavin adenine dinucleotide (FAD)-dependent urate hydroxylase (EC.1.14.13.113), an enzyme that directly metabolizes uric acid. And the strain has a complete uric acid metabolic pathway. These results suggest that L. fermentum BGI-AF16 is a probiotic candidate with significant potential for reducing uric acid level.

Identification of the Pseudomonas aeruginosa AgtR-CspC-RsaL pathway that controls Las quorum sensing in response to metabolic perturbation and Staphylococcus aureus

Environmental metabolites and metabolic pathways significantly influence bacterial pathogenesis and interspecies competition. We previously discovered that a mutation in the triosephosphate isomerase gene, tpiA, in Pseudomonas aeruginosa led to defective type III secretion and increased susceptibility to aminoglycoside antibiotics. In this study, we found that the tpiA mutation enhances the Las quorum sensing system due to reduced translation of the negative regulator RsaL. Further investigations demonstrated an upregulation of CspC, a CspA family protein that represses rsaL translation. DNA pull-down assay, along with genetic studies, revealed the role of AgtR in regulating cspC transcription. AgtR is known to regulate pyocyanin production in response to N-acetylglucosamine (GlcNAc), contributing to competition against Staphylococcus aureus. We demonstrated that CspC activates the Las quorum sensing system and subsequent pyocyanin production in response to GlcNAc and S. aureus. Overall, our results elucidate the AgtR-CspC-RsaL-LasI pathway that regulates bacterial virulence factors and its role in competition against S. aureus.

Luteolin inhibits inflammation and M1 macrophage polarization in the treatment of Pseudomonas aeruginosa-induced acute pneumonia through suppressing EGFR/PI3K/AKT/NF-κB and EGFR/ERK/AP-1 signaling pathways

BACKGROUND

The opportunistic pathogen Pseudomonas aeruginosa primarily causes infections in immunocompromised individuals. Luteolin, a natural flavonoid, is widely present in plants, which exerts various pharmacological activities, including anti-inflammatory and antimicrobial activities.

PURPOSE

This study aimed to explore the therapeutic efficacy of luteolin and the underlying molecular mechanisms in treating the P. aeruginosa-induced acute pneumonia.

METHODS

Network pharmacology was utilized to identify the core targets of luteolin for treating acute P. aeruginosa pneumonia. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis were performed to dissect the potential effects of luteolin and the involved signaling pathways. Surface plasmon resonance (SPR) assay and molecular docking were employed for studying the binding affinities of luteolin with the key targets. Furthermore, we applied a mouse model of bacterial pneumonia for assessing the therapeutic effects of luteolin in vivo, and an in vitro infection model for specifically investigating the effects of luteolin on macrophages as well as the underlying mechanisms upon P. aeruginosa infection.

RESULTS

Network pharmacology identified TNF, IL-6, EGFR and AKT1 as the key targets of luteolin for treating acute P. aeruginosa pneumonia. Moreover, as revealed by GO and KEGG enrichment analysis, EGFR, MAPK and PI3K/AKT pathways were the potential pathways regulated the P. aeruginosa-induced inflammatory response. According to the in vivo results, luteolin effectively mitigated the P. aeruginosa-induced acute lung injury through reducing the pulmonary permeability, neutrophil infiltration, proinflammatory cytokine production (IL-1β, IL-6, TNF and MIP-2) and bacterial burden in lung tissues, which led to increased survival rate of mice. Furthermore, the luteolin-treated mice had diminished EGFR, PI3K, AKT, IκBα, NF-κB p65, ERK, c-Jun and c-Fos phosphorylation, down-regulated M1 macrophage marker levels (iNOS, CD86 and IL-1β) but up-regulated M2 macrophage marker levels (Ym1, CD206 and Arg1) in lung tissues. Consistently, the luteolin-pretreated macrophages exhibited reduced phosphorylation of these regulatory proteins, diminished proinflammatory cytokine production, and down-regulated expression of M1 macrophage markers, but up-regulated expression of IL-10 and M2 macrophage markers.

CONCLUSION

luteolin effectively suppressed the inflammatory responses and M1 macrophage polarization through inhibiting EGFR/PI3K/AKT/NF-κB and EGFR/ERK/AP-1 signaling pathways in the treatment of acute P. aeruginosa pneumonia. This study suggests that luteolin could be a promising candidate for development as a therapeutic agent for acute bacterial pneumonia.

Pediococcus pentosaceus MZF16 Probiotic Strain Prevents In Vitro Cytotoxic Effects of Pseudomonas aeruginosa H103 and Prolongs the Lifespan of Caenorhabditis elegans

Pseudomonas aeruginosa is an opportunistic pathogenic bacterium, responsible for several life-threatening infections due to its multiple virulence factors and problematic multi-drug resistance, hence the necessity to find alternatives such as competitive probiotics. Pediococcus pentosaceus MZF16 is an LAB strain, isolated from traditional dried meat "Ossban", with high probiotic potential. Our study investigated the capacity of P. pentosaceus MZF16 to counteract P. aeruginosa H103 using several tests on intestinal cells (analysis of cytotoxicity, inflammation, adhesion/invasion) and on the in vivo Caenorhabditis elegans model. The effect of MZF16 on the quorum sensing of the pathogen was also examined. We found that P. pentosaceus MZF16 was able to reduce H103 cytotoxicity and inflammatory activity and prevented pathogen colonization and translocation across Caco-2/TC7 cells. MZF16 also exerted an anti-virulence effect by attenuating quorum-sensing (QS) molecules and pyoverdine production and extended C. elegans lifespan. The obtained results highlight the potential of P. pentosaceus MZF16 probiotic strain as an anti-Pseudomonas aeruginosa alternative and establish a basis for elucidating the mechanisms of P. pentosaceus MZF16 involved in countering P. aeruginosa virulence.

Is Pseudomonas aeruginosa a possible aetiological agent of periodontitis in dogs?

Introduction

Periodontal diseases are the most frequently diagnosed problem in small animal veterinary medicine. Although their exact cause is not fully understood, bacteria play an important role in their development. Pseudomonas aeruginosa is a Gram-negative, rod-shaped, non-spore-forming bacterium. The living environment of this bacterium may be soil and water; however, it can also be found in humans and animals. Antibiotic treatment of periodontitis may be complicated by the carbapenem resistance of some P. aeruginosa strains, if these bacteria are found to be an aetiological agent. The aim of the study was to identify all bacterial strains isolated from dog with periodontitis.

Material and Methods

After a clinical examination of a Schnauzer dog in the Department and Clinic of Animal Surgery in the University of Life Sciences in Lublin Faculty of Veterinary Medicine, periodontitis was diagnosed. A swab was taken from the diseased tissue and submitted for microbiological tests. Microorganisms were initially identified by colony morphology, haemolytic pattern and Gram staining, and subsequently by sensitivity tests, VITEK 2 and matrix-assisted laser desorption/ionisation-time-of-flight.

Results

Pseudomonas aeruginosa was isolated and identified as a probable aetiological factor of periodontitis in dogs.

Conclusion

In our opinion, attention should be paid to Pseudomonas aeruginosa as a possible aetiological factor of periodontal diseases in dogs.

Pseudomonas aeruginosa in Chronic Suppurative Otitis Media

BACKGROUND

Chronic suppurative otitis media (CSOM) has caused many hearing disorder cases in developing countries. Inappropriate antibiotic use resulted in a shift of bacterial resistance. The biofilm-forming bacteria, like Pseudomonas aeruginosa, was a common germ detected in CSOM that contributed to a poor prognosis. This study aimed to investigate the bacterial pattern from samples taken from CSOM patients regarding its antibiotic susceptibility and the antibiofilm activity of acetic acid against P. aeruginosa.

MATERIALS AND METHODS

Sterile swabs of forty-five patients with CSOM were collected, followed by isolation of bacterial pathogens, identification, and evaluation of antibiotic sensitivity using modified Kirby Bauer disc diffusion protocol. In vitro testing was done by adding acetic acid to P. aeruginosa culture to gauge the minimum concentration of biofilm inhibition and eradication. They were conducted using the microtiter plate assay method and quantified with an ELISA reader. The data were analyzed statistically using One-Way ANOVA and Tukey Honestly Significant Difference post hoc test.

RESULTS

The samples obtained from 31 of 45 CSOM patients showed positive microbial growth; 26 (57.78%) had a monomicrobial pattern, and 5 (11.11%) had a polymicrobial pattern. The researcher ascertained that 24 isolates, representing 66.67%, were gram-negative bacteria, with P.-aeruginosa identified as the predominant species. P. aeruginosa isolates were sensitive to several antibiotics, including meropenem, amikacin, piperacillin-tazobactam, ceftazidime, and cefoperazone-sulbactam with a rate of 93.33%. The minimum concentration of acetic acid required to qualify as the minimum biofilm inhibitory concentration (MBIC) was determined to be 0.16%, yielding an inhibition rate of 26.79%. A concentration of 0.31% was identified as the minimum biofilm eradication concentration (MBEC), achieving an eradication rate of 77.27%.

CONCLUSION

P. aeruginosa, the most common bacteria found in CSOM samples, was sensitive to imipenem, amikacin, piperacillin-tazobactam, ceftazidime, and cefoperazone-sulbactam. Acetic acid suppresses P. aeruginosa bacterial biofilm formation at MBIC of 0.16% and MBEC of 0.31%.

Reprofiling lamivudine as an antibiofilm and anti-pathogenic agent against Pseudomonas aeruginosa

Resistance to antibiotics is a critical growing public health problem that needs urgent action to combat. To avoid the stress on bacterial growth that evokes the development of resistance, anti-virulence agents can be an attractive strategy as they do not target bacterial growth. There are FDA approved drugs have been screened for their anti-virulence activities. Lamivudine (LAM) is a synthetic nucleoside analogue used as an antiretroviral in treatment of HIV and can be used in treatment of HBV. The present study aimed to assess the anti-virulence activities of LAM against a clinically important pathogen Pseudomonas aeruginosa. The LAM's antibiofilm and anti-virulence activities were evaluated. The impact of LAM on the quorum sensing (QS) systems which control the production of these virulence factors was assessed virtually and by quantification of the expression of QS-encoding genes. Furthermore, in vivo mice protection assay was conducted to attest the LAM's anti-pathogenic activity. The current findings elaborated the promising anti-pathogenic and anti-QS activities of LAM. LAM interfered with biofilm formation in P. aeruginosa PAO1 strain. Moreover, swarming motility and production of pyocyanin and protease were significantly diminished. At the molecular level, LAM downregulated the QS-encoding genes LasI, LasR, RhlR, PqsA and PqsR. Additionally, the detailed in silico docking and molecular simulation studies showed the considered high LAM's ability to bind and hinder the QS receptors in the P. aeruginosa. In an agreement with in vitro and in silico, the in vivo results showed the LAM full protection of mice against P. aeruginosa. In conclusion, LAM could be repurposed to be employed as adjunct therapy with traditional antibiotics for treating serious pseudomonal infections.

Virulence factors of Pseudomonas aeruginosa and immune response during exacerbations and stable phase in bronchiectasis

The study of key Pseudomonas aeruginosa (PA) virulence factors, the molecular basis of pathogenicity, as well as their correlation with the immune response during exacerbations in patients with non-cystic fibrosis bronchiectasis can help to identify novel targets and biomarkers for clinical management. The objective was to compare P. aeruginosa virulence and the patient's immune response during stable phases and exacerbations of bronchiectasis. We used polymerase chain reaction (PCR) and real-time quantitative PCR (qRT-PCR) to perform molecular characterization of the genomic islands and virulence genes present in 42 P. aeruginosa strains obtained from the sputum of patients with bronchiectasis during stability and exacerbations. Immunoglobulin (Ig) and interleukin (IL) levels in 32 serum samples were analyze by ELISA and Luminex assay. A greater presence of the conjugative element pKLC102, specific virulence genes (exoS, exoY) and pyoverdine production characterize the P. aeruginosa strains obtained during exacerbations. The expression levels of type III secretion system (exoS, exoY) showed an important role in the humoral immune response during exacerbations. Exacerbations were associated with high levels of IL-6. The presence of specific genomic islands, virulence genes, and increased IL-6 levels provide an accurate characterization on bronchiectasis exacerbations. These targets could be useful in the prevention, management and treatment of these exacerbations.

Regulatory role of PA3299.1 small RNA in Pseudomonas aeruginosa biofilm formation via modulation of algU and mucA expression

Small RNAs (sRNAs) have emerged as key regulators of transcriptional factors and components within regulatory networks that govern bacterial biofilm formation. This study aimed to explore the regulatory role of the PA3299.1 sRNA in controlling biofilm formation in P. aeruginosa. Results showed that PA3299.1 expression was significantly elevated in both substratum-attached and colony biofilms compared to planktonic growth. Further investigation revealed that strains overexpressing PA3299.1 exhibited enhanced biofilm formation, while its deletion resulted in a substantial reduction in biofilm development. PA3299.1 was found to regulate the expression of AlgU and MucA, the sigma and anti-sigma factors, integral to the biofilm developmental network. In summary, this research identifies PA3299.1 as a critical regulator of biofilm formation and potentially a contributor to the pathogenicity of P. aeruginosa, that could help to develop new therapeutic strategies to manage biofilm-associated infections.

Quorum Quenching of P. aeruginosa by Portulaca oleracea Methanolic Extract and Its Phytochemical Profile

Quorum sensing (QS) is a molecular communication mechanism among bacterial cells. It is critical in regulating virulence factors, motility, antibiotic resistance, and biofilm formation. Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen linked to healthcare-associated infections, food poisoning, and biofilm formation. Treating infections caused by pathogenic bacteria has become a challenge due to the development of multi-antibiotic resistance upon continuous exposure of bacteria to antibiotics. An alternative strategy to conventional antimicrobials to decrease the bacterial pathogenicity is QS inhibition, also known as quorum quenching. Using plant-derived compounds is an environmentally friendly strategy to block the bacterial QS and inhibit bacterial growth. Portulaca oleracea is a popular plant in different countries and is also used in traditional medicine. It is widely consumed raw in salads and as garnishes, though it can be cooked as a vegetarian dish. This study evaluates the antimicrobial activity of the methanolic extract of P. oleracea and its effectiveness in blocking or attenuating the QS of P. aeruginosa. The agar well diffusion method used for screening the antibacterial activity showed a significant growth inhibition of P. aeruginosa by the extract at 500 mg/mL with a minimum inhibitory concentration of 31.25 mg/mL. A bioindicator bacterium, Chromobacterium violaceum CV026, was used to determine the effect of the methanolic extract on the QS of P. aeruginosa. The results indicated a significant reduction in biofilm formation, pyocyanin production, and LasA staphylolytic activity. The phytochemical analysis by Gas Chromatography-Mass Spectrometry showed that the methanolic extract contained several phenols, alkaloids, esters, and other compounds previously reported to have antibacterial and antioxidant effects. These findings highlight the effectiveness of P. oleracea methanolic extract in attenuating the QS and virulence factors of P. aeruginosa. This study suggests that P. oleracea is an important source of natural antimicrobials and its use would be beneficial in food and pharmaceutical applications.

Efficacy of bacteriophages with Aloe vera extract in formulated cosmetics to combat multidrug-resistant bacteria in skin diseases

Phage therapy offers a promising alternative to antibiotic treatment for combating illnesses caused by multidrug-resistant bacteria. In this study, pathogenic bacteria Staphylococcus aureus and Pseudomonas aeruginosa were isolated from pus and skin infected fluidsusing selective media. These bacterial isolates were biochemically identified as S. aureus and P. aeruginosa with probabilities of 98% and 99%, respectively, through VITEK2 system, and were confirmed as multidrug-resistant based on minimum inhibitory concentration test using colorimetric reagent cards. Lytic phages specific to these isolates were isolated, identified through plaque assays, transmission electron microscopy and classified morphologically according to the new International Committee on Taxonomy of Viruses classification as members of the Straboviridae, Drexlerviridae, and Autographiviridae families. A cosmetic gel formulation combining Aloe vera extract and the phage cocktail was prepared and tested. This gel significantly enhanced phage longevity and reduced bacterial growth by 95.5% compared to the reductions of 90.5% with Aloe Vera extract alone and 45.7% with the basic cosmetic gel. The phage remained effective for 4 to over 12 weeks after being preserved in the cosmetic formula, maintaining populations ranging from 5 × 103 to 25 × 104 PFU/mL in vitro. These findings highlight the potential of phage-based formulations, such as Vena Skin Gel, as innovative biotherapeutic tools for managing skin infections.

In-vitro activity of newly-developed β-lactamase inhibitors avibactam, relebactam and vaborbactam in combination with anti-pseudomonal β-lactam antibiotics against AmpC-overproducing clinical Pseudomonas aeruginosa isolates

PURPOSE

Overproduction of the intrinsic chromosomally-encoded AmpC β-lactamase is one of the main mechanisms responsible for broad-spectrum β-lactam resistance in Pseudomonas aeruginosa. Our study aimed to evaluate the in-vitro activity of anti-pseudomonal β-lactam molecules associated with the recently-developed and commercially-available β-lactamase inhibitors, namely avibactam, relebactam and vaborbactam, against P. aeruginosa isolates overproducing their AmpC.

METHODS

MIC values of ceftazidime, cefepime, meropenem, imipenem and ceftolozane with or without β-lactam inhibitor were determined for 50 AmpC-overproducing P. aeruginosa clinical isolates. MIC breakpoints for resistance were retained at 8 mg/L for β-lactams and β-lactam/β-lactamase inhibitor combinations containing ceftazidime, cefepime and meropenem, while 4 mg/L was used for those containing imipenem and ceftolozane. The concentration of all β-lactamases inhibitors was fixed at 4 mg/L, except for vaborbactam (8 mg/L).

RESULTS

The rates of isolates not being resistant to ceftazidime, cefepime, meropenem, imipenem and ceftolozane were found at 12%, 22%, 34%, 8% and 74%, respectively. When combined with avibactam, those rates increased to 60%, 62%, 60%, 46%, and 80%, respectively. The highest rates were found with relebactam-based combinations, being 76%, 64%, 66%, 76% and 84%, respectively. By contrast, associations with vaborbactam did not lead to significantly increased "non-resistance" rates.

CONCLUSION

Our results showed that all combinations including relebactam led to higher "non-resistance" rates against AmpC-overproducing P. aeruginosa clinical isolates. The best activity was achieved by combining ceftolozane and relebactam, that might therefore be considered as an excellent clinical alternative against AmpC overproducers.

Molecular Analysis of Pseudomonas aeruginosa Isolates with Mutant gyrA Gene and Development of a New Ciprofloxacin Derivative for Antimicrobial Therapy

This study focuses on the prevalence of Pseudomonas aeruginosa in various medical specimens. In addition, the investigates of this research shows the genetic analysis of pathogen-resistant isolates and chemical modifications to ciprofloxacin. A total of 225 specimens from men and women aged 30 to 60 were carefully collected and examined, including samples from wound, burn, urine, sputum, and ear samples. The data were obtained from AL Muthanna hospitals. PCR-RFLP and gene expression analysis were used to identify resistant strains and explore the genetic basis of antibiotic resistance. A ciprofloxacin derivative was synthesized and confirmed through FT-IR, 1H-NMR, and mass spectroscopy techniques then it was tested as antibacterial agent. Also, molecular docking study was conducted to predict the mechanism of action for the synthesized derivative. The results demonstrated that wound samples had the highest positive rate (33.7%) of P. aeruginosa isolates. The PCR-RFLP testing correlated ciprofloxacin resistance with gyrA gene mutation. Gene expression analysis revealed significant changes in the gyrA gene expression in comparison to the reference rpsL gene subsequent to exposure to the synthesized derivative. Furthermore, the molecular docking investigation illustrated the strategic positioning of the ciprofloxacin derivative within the DNA-binding site of the gyrA enzyme. The examination of genetic expression patterns manifested diverse effects attributed to the CIP derivative on P. aeruginosa, thus portraying it as a viable candidate in the quest for the development of novel antimicrobial agents. Ciprofloxacin derivative may offer new antimicrobial therapeutic options for treating Pseudomonas aeruginosa infections in wound specimens, addressing resistance and gyrA gene mutations.

Genotypic and phenotypic analyses of two distinct sets of Pseudomonas aeruginosa urinary tract isolates

Introduction. Urinary tract infections (UTIs) are associated with a high burden of morbidity, mortality and cost. Pseudomonas aeruginosa employs a myriad of virulence factors, including biofilm formation and motility mechanisms, to cause infections including persistent UTIs. P. aeruginosa is highly resistant to antibiotics, and the World Health Organization has identified it as a pathogen for which novel antimicrobials are urgently required.Gap statement. Genotypic and phenotypic characterization of P. aeruginosa from UTIs is underreported. In addition, the rise of antimicrobial resistance (AMR) is a cause for concern, particularly in many countries where surveillance is severely lacking.Aim. To identify genotypic and phenotypic characteristics of P. aeruginosa UTI isolates sourced from the UK and the state of Kuwait, with an emphasis on genotypic diversity and AMR.Methods. Twenty-three P. aeruginosa UTI isolates were sourced from the UK and Kuwait. To establish the phenotypes of UK isolates, growth analysis, biofilm formation assays, motility assays and antibiotic disc diffusion assays were performed. Whole-genome sequencing, antimicrobial susceptibility assays and in silico detection of AMR-associated genes were conducted on both sets of isolates.Results. In terms of their phenotypic characteristics and genomic composition, the UTI isolates varied. Multiple resistance genes are associated with resistance to various classes of antibiotics, such as aminoglycosides, fluoroquinolones and β-lactams, particularly in isolates from Kuwait. Extreme antibiotic resistance was detected in the isolates obtained from Kuwait, indicating that the country may be an antibiotic resistance hotspot.Conclusion. This study highlights that isolates from UTIs are diverse and can display extremely high resistance. Surveillance in countries such as Kuwait is currently limited, and this study suggests the need for greater surveillance.

Resilience and charge-dependent fibrillation of functional amyloid: Interactions of Pseudomonas biofilm-associated FapB and FapC amyloids

FapC and FapB are biofilm-associated amyloids involved in the virulence of Pseudomonas and other bacteria. We herein demonstrate their exceptional thermal and chemical resilience, suggesting that their biofilm structures might withstand standard sterilization, thereby contributing to the persistence of Pseudomonas aeruginosa infections. Our findings also underscore the impact of environmental factors on functional amyloid in Pseudomonas (Fap) proteins, suggesting that orthologs in different Pseudomonas strains adapt to specific environments and roles. Challenging previous assumptions about a simple nucleation role for FapB in promoting FapC aggregation, the study shows a significant influence of FapC on FapB aggregation. The interaction between these FapB and FapC is intricate: FapB stabilizes FapC fibrils, while FapC slows down FapB fibrillation but can still serve as a cross-seeding template. This complex interplay is the key to understanding their roles in bacterial biofilms. Furthermore, the study highlights distinct differences between Fap and Escherichia coli's CsgA (curli) amyloid, where CsgB assumes a simple unidirectional role in nucleating CsgA fibrillation, emphasizing the importance of a comprehensive understanding of various amyloid systems. This knowledge is vital for developing effective intervention strategies against bacterial infections and leveraging the unique properties of these amyloids in technological applications such as novel bionanomaterials or protective coatings.

Multi-strain phage induced clearance of bacterial infections

Bacteriophage (or 'phage' - viruses that infect and kill bacteria) are increasingly considered as a therapeutic alternative to treat antibiotic-resistant bacterial infections. However, bacteria can evolve resistance to phage, presenting a significant challenge to the near- and long-term success of phage therapeutics. Application of mixtures of multiple phages (i.e., 'cocktails') has been proposed to limit the emergence of phage-resistant bacterial mutants that could lead to therapeutic failure. Here, we combine theory and computational models of in vivo phage therapy to study the efficacy of a phage cocktail, composed of two complementary phages motivated by the example of Pseudomonas aeruginosa facing two phages that exploit different surface receptors, LUZ19v and PAK_P1. As confirmed in a Luria-Delbrück fluctuation test, this motivating example serves as a model for instances where bacteria are extremely unlikely to develop simultaneous resistance mutations against both phages. We then quantify therapeutic outcomes given single- or double-phage treatment models, as a function of phage traits and host immune strength. Building upon prior work showing monophage therapy efficacy in immunocompetent hosts, here we show that phage cocktails comprised of phage targeting independent bacterial receptors can improve treatment outcome in immunocompromised hosts and reduce the chance that pathogens simultaneously evolve resistance against phage combinations. The finding of phage cocktail efficacy is qualitatively robust to differences in virus-bacteria interactions and host immune dynamics. Altogether, the combined use of theory and computational analysis highlights the influence of viral life history traits and receptor complementarity when designing and deploying phage cocktails in immunocompetent and immunocompromised hosts.

Moxifloxacin-Loaded Polymeric Nanoparticles for Overcoming Multidrug Resistance in Chronic Pulmonary Infections Caused by Pseudomonas aeruginosa

Pseudomonas aeruginosa (P. aeruginosa) infections are increasingly challenging due to their propensity to form biofilms and low outer membrane permeability, especially in chronically infected patients with thick mucus. P. aeruginosa exhibits multiple drug resistance mechanisms, making it one of the most significant global public health threats. In this study, we found that moxifloxacin (MXC) and antibacterial peptides (ε-poly-l-lysine, ε-PLL) exhibited a synergistic effect against multidrug-resistant P. aeruginosa (MDR-P. aeruginosa). MXC was combined with ε-PLL to prepare lipase-responsive nanoparticles (MCIP/(PEG-PCL)/PLL NPs) with a weakly negative charge. The weakly negatively charged MCIP/(PEG-PCL)/PLL NPs demonstrated remarkable mucus and biofilm penetration capabilities, thereby overcoming one of the adaptive drug resistance mechanisms. MCIP/(PEG-PCL)/PLL NPs improved the outer and inner membrane permeability and inhibited the expression of the efflux pump MexAB-OprM gene in MDR-P. aeruginosa, thereby overcoming mechanisms of both intrinsic and acquired drug resistance. Meanwhile, the nanoparticles demonstrated an ability to reduce repeated infections with MDR-P. aeruginosa. Additionally, the bacterial burden in the lungs of mice treated with MCIP/(PEG-PCL)/PLL NPs was significantly lower than that in the MXC group, resulting in a 99% clearance rate. Notably, MCIP/(PEG-PCL)/PLL NPs showed no toxicity toward BEAS-2B cells or RAW 267.4 cells, nor did they adversely affect pulmonary function or major organs. This study demonstrated the potential of the nanodrug delivery system composed of the antibiotic moxifloxacin and the antibacterial peptide ε-PLL in addressing the clinical challenges of treating chronic pulmonary infections caused by MDR-P. aeruginosa.

Modeling and simulation of distribution and drug resistance of major pathogens in patients with respiratory system infections

BACKGROUND

Respiratory tract infections (RTIs) are one of the leading causes of morbidity and mortality worldwide. The increase in antimicrobial resistance in respiratory pathogens poses a major challenge to the effective management of these infections.

OBJECTIVE

To investigate the distribution of major pathogens of RTIs and their antimicrobial resistance patterns in a tertiary care hospital and to develop a mathematical model to explore the relationship between pathogen distribution and antimicrobial resistance.

METHODS

Five hundred patients with RTIs were included in the study and 475 bacterial strains were isolated from their respiratory specimens. Antimicrobial susceptibility testing and analysis of influencing factors were performed. A mathematical model was developed to simulate the relationship between pathogen distribution and drug resistance.

RESULTS

The most common pathogens were Streptococcus pneumoniae (30%), Haemophilus influenzae (20%), Pseudomonas aeruginosa (15%), Staphylococcus aureus (10%) and Klebsiella pneumoniae (10%). The distribution of pathogens varied according to age group and type of RTIs, with higher proportions of Pseudomonas aeruginosa and Staphylococcus aureus in hospital-acquired and ventilator-associated pneumonia. Isolated pathogens showed high and increasing rates of resistance to commonly used antibiotics. Model simulations suggest that a shift in the distribution of pathogens toward more resistant strains may lead to a significant increase in overall resistance rates, even if antibiotic use patterns remain unchanged.

CONCLUSION

This study emphasizes the importance of regular monitoring of respiratory pathogen distribution and antimicrobial resistance patterns and the need for a comprehensive approach to managing RTIs, including implementation of antibiotic stewardship programs, infection control measures, and development of new therapies.

New Bacteriophage Pseudomonas Phage Ka2 from a Tributary Stream of Lake Baikal

Pseudomonas aeruginosa, an opportunistic pathogen, causes various biofilm-associated infections like pneumonia, infections in cystic fibrosis patients, and urinary tract and burn infections with high morbidity and mortality, as well as low treatment efficacy due to the extremely wide spread of isolates with multidrug resistance. Here, we report the new bacteriophage Pseudomonas phage Ka2 isolated from a tributary stream of Lake Baikal and belonging to the Pbunavirus genus. Transmission electron microscopy resolved that Pseudomonas phage Ka2 has a capsid of 57 ± 9 nm and a contractile and inflexible tail of 115 ± 10 nm in the non-contracted state. The genome consists of 66,310 bp with a GC content of 55% and contains 96 coding sequences. Among them, 52 encode proteins have known functions, and none of them are potentially associated with lysogeny. The bacteriophage lyses 21 of 30 P. aeruginosa clinical isolates and decreases the MIC of amikacin, gentamicin, and cefepime up to 16-fold and the MIC of colistin up to 32-fold. When treating the biofilms with Ka2, the biomass was reduced by twice, and up to a 32-fold decrease in the antibiotics MBC against biofilm-embedded cells was achieved by the combination of Ka2 with cefepime for the PAO1 strain, along with a decrease of up to 16-fold with either amikacin or colistin for clinical isolates. Taken together, these data characterize the new Pseudomonas phage Ka2 as a promising tool for the combined treatment of infections associated with P. aeruginosa biofilms.

Prophages are Infrequently Associated With Antibiotic Resistance in Pseudomonas aeruginosa Clinical Isolates

Lysogenic bacteriophages can integrate their genome into the bacterial chromosome in the form of a prophage and can promote genetic transfer between bacterial strains in vitro . However, the contribution of lysogenic phages to the incidence of antimicrobial resistance (AMR) in clinical settings is poorly understood. Here, in a set of 186 clinical isolates of Pseudomonas aeruginosa collected from respiratory cultures from 82 patients with cystic fibrosis (CF), we evaluate the links between prophage counts and both genomic and phenotypic resistance to six anti-pseudomonal antibiotics: tobramycin, colistin, ciprofloxacin, meropenem, aztreonam, and piperacillin-tazobactam. We identified 239 different prophages in total. We find that P. aeruginosa isolates contain on average 3.06 +/- 1.84 (SD) predicted prophages. We find no significant association between the number of prophages per isolate and the minimum inhibitory concentration (MIC) for any of these antibiotics. We then investigate the relationship between particular prophages and AMR. We identify a single lysogenic phage associated with phenotypic resistance to the antibiotic tobramycin and, consistent with this association, we observe that AMR genes associated with resistance to tobramycin are more likely to be found when this prophage is present. However we find that they are not encoded directly on prophage sequences. Additionally, we identify a single prophage statistically associated with ciprofloxacin resistance but do not identify any genes associated with ciprofloxacin phenotypic resistance. These findings suggest that prophages are only infrequently associated with the AMR genes in clinical isolates of P. aeruginosa .

Importance

Antibiotic-resistant infections of Pseudomonas aeruginosa , a leading pathogen in patients with Cystic Fibrosis (CF) are a global health threat. While lysogenic bacteriophages are known to facilitate horizontal gene transfer, their role in promoting antibiotic resistance in clinical settings remains poorly understood. In our analysis of 186 clinical isolates of P. aeruginosa from CF patients, we find that prophage abundance does not predict phenotypic resistance to key antibiotics but that specific prophages are infrequently associated with tobramycin resistance genes. In addition, we do not find antimicrobial resistance (AMR) genes encoded directly on prophages. These results highlight that while phages can be associated with AMR, phage-mediated AMR transfer may be rare in clinical isolates and difficult to identify. This work is important for future efforts on mitigating AMR in Cystic Fibrosis and other vulnerable populations affected by Pseudomonas aeruginosa infections and advances our understanding of bacterial-phage dynamics in clinical infections.

Synergistic efficacy of ceftazidime/avibactam and aztreonam against carbapenemase-producing Pseudomonas aeruginosa: insights from the hollow-fiber infection model

BACKGROUND

Combination therapy is an attractive therapeutic option for extensively drug-resistant (XDR) Pseudomonas aeruginosa infections. Existing data support the combination of aztreonam and ceftazidime/avibactam (CZA) against class serine-β-lactamase (SBL)- and metallo-β-lactamase (MBL) - producing Enterobacterales. However, data about that combination against SBL- and MBL-producing P. aeruginosa are scarce. The objective of the study was to assess the in vitro activity of CZA and aztreonam alone and in combination against SBL- and MBL-producing XDR P. aeruginosa isolates.

METHODS

The combination was analyzed by means of the hollow-fiber infection model in three selected carbapenemase-producing P. aeruginosa isolates that were representative of the three most common XDRP. aeruginosa high-risk clones (ST175, ST111, ST235) responsible for global nosocomial infection outbreaks.

RESULTS

The three isolates were nonsusceptible to CZA and nonsusceptible to aztreonam. In the dynamic hollow-fiber infection model, the combination of CZA plus aztreonam exerts a bactericidal effect on the isolates, regardless of their resistance mechanism and demonstrates synergistic interactions against three isolates, achieving a bacterial reduction of 5.07 log10 CFU/ml, 5.2 log10 CFU/ml and 4 log10 CFU/ml, respectively.

CONCLUSION

The combination of CZA and aztreonam significantly enhanced the in vitro efficacy against XDR P. aeruginosa isolates compared to each monotherapy. This improvement suggests that the combination could serve as a feasible treatment alternative for infections caused by carbapenemase-producing XDR P. aeruginosa, especially in scenarios where no other treatment options are available.

Analysis of the potentially pathogenic bacteria of lower respiratory tract infections in children per-, during and post-COVID-19: a retrospective study

BACKGROUND

The coronavirus disease 2019 (COVID-19) pandemic has caused significant changes in lower respiratory tract infections (LRTIs). This study aimed to characterize potentially pathogenic bacterial infections in paediatric patients hospitalized for LRTIs per-, during and post-COVID-19.

METHODS

Sputum culture data from 85,659 children with LRTIs at the Children's Hospital of Soochow University from January 2016 to May 2024 were analyzed for eight bacteria: Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, Moraxella catarrhalis, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Acinetobacter baumannii. The data during the pandemic (2020-2022, during COVID-19) and after the pandemic (January 2023-May 2024, post-COVID-19) were compared with those before the pandemic (2016-2019).

RESULTS

Overall, 85,659 children with LRTIs were enrolled. Of these, 42,567 cases (49.7%) were diagnosed in the pre-COVID-19 period, 22,531 cases (26.3%) during the COVID-19 period and 20,561 cases (24.0%) in the post-COVID-19 period. The overall positive rate for pathogenic bacteria was 37.1%, with the top three being S. pneumoniae (14.5%), H. influenzae (12.1%) and S. aureus (6.5%). Compared to the average pre-COVID-19 levels, the bacterial pathogen positive rate decreased by 3.5% during the COVID-19 period (OR: 0.94, 95% CI: 0.91-0.98) and by 23.4% in the post-COVID-19 period (OR: 0.66, 95% CI: 0.64-0.69). During the COVID-19 period, the positive rates for S. pneumoniae, H. influenzae, E. coli, K. pneumoniae and mixed infections decreased by 11.7%, 35.3%, 22.2%, 33.3% and 45.7% respectively, while the positive rates for S. aureus, M. catarrhalis and P. aeruginosa increased by 21.7%, 44.7% and 25% respectively. In the post-COVID-19 period, the positive rates for S. pneumoniae, H. influenzae, E. coli, P. aeruginosa, K. pneumoniae, A. baumannii and mixed infections decreased by 50.0%, 7.4%, 22.2%, 50.0%, 44.4%, 60.0% and 32.6% respectively, while there was no statistical change in the positive rates for S. aureus and M. catarrhalis. Bacteria case detection decreases in 2020 (67.0%), 2021 (60.5%), 2022 (76.3%) and 2023 (72.7%) compared to predicted cases.

CONCLUSIONS

Measures to restrict COVID-19 as a driver of declining bacterial positive rates. Respiratory bacteria in children are change across COVID-19 phases, age groups and seasons. After COVID-19, clinicians should continue to increase surveillance for pathogenic bacteria, especially drug-resistant flora.

High-Affinity Lectin Ligands Enable the Detection of Pathogenic Pseudomonas aeruginosa Biofilms: Implications for Diagnostics and Therapy

Pseudomonas aeruginosa is a critical priority pathogen and causes life-threatening acute and biofilm-associated chronic infections. The choice of suitable treatment for complicated infections requires lengthy culturing for species identification from swabs or an invasive biopsy. To date, no fast, pathogen-specific diagnostic tools for P. aeruginosa infections are available. Here, we present the noninvasive pathogen-specific detection of P. aeruginosa using novel fluorescent probes that target the bacterial biofilm-associated lectins LecA and LecB. Several glycomimetic probes were developed to target these extracellular lectins and demonstrated to stain P. aeruginosa biofilms in vitro. Importantly, for the targeting of LecA an activity boost to low-nanomolar affinity could be achieved, which is essential for in vivo application. In vitro, the nanomolar divalent LecA-targeted imaging probe accumulated effectively in biofilms under flow conditions, independent of the fluorophore identity. Investigation of these glycomimetic imaging probes in a murine lung infection model and fluorescence imaging revealed accumulation at the infection site. These findings demonstrate the use of LecA- and LecB-targeting probes for the imaging of P. aeruginosa infections and suggest their potential as pathogen-specific diagnostics to accelerate the start of the appropriate treatment.

Substrate-Based Ligand Design for Phenazine Biosynthesis Enzyme PhzF

The phenazine pyocyanin is an important virulence factor of the pathogen Pseudomonas aeruginosa, which is on the WHO list of antibiotic resistant "priority pathogens". In this study the isomerase PhzF, a key bacterial enzyme of the pyocyanin biosynthetic pathway, was investigated as a pathoblocker target. The aim of the pathoblocker strategy is to reduce the virulence of the pathogen without killing it, thus preventing the rapid development of resistance. Based on crystal structures of PhzF, derivatives of the inhibitor 3-hydroxyanthranilic acid were designed. Co-crystal structures of the synthesized derivatives with PhzF revealed spacial limitations of the binding pocket of PhzF in the closed conformation. In contrast, ligands aligned to the open conformation of PhzF provided more room for structural modifications. The intrinsic fluorescence of small 3-hydroxyanthranilic acid derivatives enabled direct affinity determinations using FRET assays. The analysis of structure-activity relationships showed that the carboxylic acid moiety is essential for binding to the target enzyme. The results of this study provide fundamental structural insights that will be useful for the design of PhzF-inhibitors.

Prevalence and antibiotic resistance patterns of Pseudomonas aeruginosa and Acinetobacter baumannii strains isolated from chicken droppings on poultry farms in Gondar city, Northwest Ethiopia

Background

Pseudomonas aeruginosa and Acinetobacter baumannii are common nosocomial pathogens in hospital settings. Recently, they have also been found in non-hospital environments, such as poultry farms. While most studies in Ethiopia have focused on these bacteria's antibiotic resistance patterns in hospitals, information regarding their prevalence and resistance in veterinary settings, particularly poultry farms, is limited. This study aimed to assess the prevalence and antibiotic resistance patterns of P. aeruginosa and A. baumannii isolated from chicken droppings on poultry farms.

Methods

A cross-sectional study was conducted from March 2022 to June 2022. A total of 87 poultry farms were included in this study, and pooled chicken dropping samples were collected. The samples were subsequently transferred to buffered peptone water and cultured on MacConkey agar. Species of the isolates were identified via routine biochemical tests, including oxidase, catalase, urease, Simon's citrate, sulfide indole motility medium, triple sugar iron agar and growth at temperatures of 37 °C and 42 °C. The Kirby-Bauer disk diffusion technique was used for antibiotic susceptibility testing. The data were entered into EpiData version 4.6 and then exported to SPSS version 26 for analysis. Fisher's exact test was used to observe an appropriate association between independent variables and the occurrence of isolates. The results are presented in the text, figures and tables.

Results

Among the 87 poultry farms, 41 (47.1 %) were positive for Pseudomonas and Acinetobacter. Among these strains, 24 (27.6 %) P. aeruginosa strains and 13 (14.9 %) A. baumannii strains were recovered. P. aeruginosa showed complete resistance to tetracycline (24, 100.0 %) and trimethoprim-sulfamethoxazole (24, 100.0 %). Additionally, there was a high rate of resistance to ciprofloxacin (13, 54.2 %) and amikacin (12, 50.0 %). Similarly, 13 (100.0 %) A. baumannii isolates were resistant to tetracycline, and 12 (92.3 %) were resistant to trimethoprim-sulfamethoxazole. However, both isolates presented lower resistance rates to piperacillin-tazobactam (4, 9.8 %) and cefepime (7, 17.1 %). Both A. baumannii and P. aeruginosa exhibited multidrug resistance in 10/13 (76.9 %) and 16/24 (66.7 %) of the strains, respectively. The overall prevalence of multidrug resistance in this study was 28/41 (68.3 %).

Conclusion

This study demonstrated that poultry farms may be potential reservoirs for P. aeruginosa and A. baumannii, including antibiotic-resistant strains. This is a significant concern to public health because poultry farmers may be contaminated, increasing their dissemination to the community. Therefore, poultry farmers should improve sanitation and reduce the misuse and overuse of antibiotics at poultry farms.

The frequency of AmpC overproduction, OprD downregulation and OprM efflux pump expression in Pseudomonas aeruginosa: A comprehensive meta-analysis

OBJECTIVES

Pseudomonas aeruginosa is a major opportunistic pathogen responsible for a wide range of infections. The emergence of antibiotic resistance in this pathogen poses a significant public health challenge. This study aims to conduct a comprehensive meta-analysis of studies conducted in Iran to determine the frequency of key antibiotic resistance mechanisms in Pseudomonas aeruginosa and their association with multidrug-resistant and extensively drug-resistant strains or pandrug-resistant strains.

METHODS

Systematic database searches encompassing literature up to June 2023 were undertaken. The selected studies centered on OprD downregulation, efflux pump (mexAB-OprM, mexXY-OprM) expression, and AmpC overproduction. Extracted data were synthesised in a meta-analysis for pooled frequency determination of each resistance mechanism.

RESULTS

In total, 24 studies were included. OprD downregulation exhibited a pooled frequency of 61%. Efflux pump component frequency ranged from 48% to 77.5%. AmpC overproduction was identified in 29.1% of isolates. Polymyxin B and colistin demonstrated lower antibiotic resistance rates, with pooled frequency of 1% and 1.6%, respectively. Conversely, resistance to other antibiotics ranged widely, with pooled frequency spanning 38.4% to 98.2%.

CONCLUSIONS

This study underscores the concerning frequency of diverse antibiotic resistance mechanisms in Pseudomonas aeruginosa strains from Iran. Concurrent OprD downregulation, mexAB, mexXY, OprM expression, and AmpC overproduction highlight the urgent need for stringent infection control and prudent antibiotic usage to curb the dissemination of these resistant strains.

PROSPERO

CRD42022379311.

Phenotypic and molecular characterization of extended spectrum- and metallo- beta lactamase producing Pseudomonas aeruginosa clinical isolates from Egypt

BACKGROUND

Antimicrobial resistance among Pseudomonas aeruginosa (P. aeruginosa), a leading cause of nosocomial infections worldwide, is escalating. This study investigated the prevalence of extended-spectrum β-lactamases (ESBLs) and metallo-β-lactamases (MBLs) among 104 P. aeruginosa clinical isolates from Alexandria Main University Hospital, Alexandria, Egypt.

METHODS

Antimicrobial susceptibility testing was performed using agar dilution technique, or broth microdilution method in case of colistin. ESBL and MBL prevalence was assessed phenotypically and genotypically using polymerase chain reaction (PCR). The role of plasmids in mediating resistance to extended-spectrum β-lactams was studied via transformation technique using plasmids isolated from ceftazidime-resistant isolates.

RESULTS

Antimicrobial susceptibility testing revealed alarming resistance rates to carbapenems, cephalosporins, and fluoroquinolones. Using PCR as the gold standard, phenotypic methods underestimated ESBL production while overestimating MBL production. Eighty-five isolates (81.7%) possessed only ESBL encoding genes, among which 69 isolates harbored a single ESBL gene [blaOXA-10 (n = 67) and blaPER (n = 2)]. Four ESBL-genotype combinations were detected: blaPER + blaOXA-10 (n = 8), blaVEB-1 + blaOXA-10 (n = 6), blaPSE + blaOXA-10 (n = 1), and blaPER + blaVEB-1 + blaOXA-10 (n = 1). Three isolates (2.9%) possessed only the MBL encoding gene blaVIM. Three ESBL + MBL- genotype combinations: blaOXA-10 + blaAIM, blaOXA-10 + blaVIM, and blaPER + blaOXA-10 + blaAIM were detected in 2, 1 and 1 isolate(s), respectively. Five plasmid preparations harboring blaVEB-1 and blaOXA-10 were successfully transformed into chemically competent Escherichia coli DH5α with transformation efficiencies ranging between 6.8 × 10 3 and 3.7 × 10 4    CFU/μg DNA plasmid. Selected tested transformants were ceftazidime-resistant and harbored plasmids carrying blaOXA-10.

CONCLUSIONS

The study highlights the importance of the expeditious characterization of ESBLs and MBLs using genotypic methods among P. aeruginosa clinical isolates to hinder the development and dissemination of multidrug resistant strains.

Ser/Thr protein kinase Stk1 phosphorylates the key transcriptional regulator AlgR to modulate virulence and resistance in Pseudomonas aeruginosa

Pseudomonas aeruginosa is one of the leading causes of nosocomial infections worldwide and has emerged as a serious public health threat, due in large part to its multiple virulence factors and remarkable resistance capabilities. Stk1, a eukaryotic-type Ser/Thr protein kinase, has been shown in our previous work to be involved in the regulation of several signalling pathways and biological processes. Here, we demonstrate that deletion of stk1 leads to alterations in several virulence- and resistance-related physiological functions, including reduced pyocyanin and pyoverdine production, attenuated twitching motility, and enhanced biofilm production, extracellular polysaccharide secretion, and antibiotic resistance. Moreover, we identified AlgR, an important transcriptional regulator, as a substrate for Stk1, with its phosphorylation at the Ser143 site catalysed by Stk1. Intriguingly, both the deletion of stk1 and the mutation of Ser143 of AlgR to Ala result in similar changes in the above-mentioned physiological functions. Furthermore, assays of algR expression in these strains suggest that changes in the phosphorylation state of AlgR, rather than its expression level, underlie changes in these physiological functions. These findings uncover Stk1-mediated phosphorylation of AlgR as an important mechanism for regulating virulence and resistance in P. aeruginosa.

Loop-Mediated Isothermal Amplification Coupled with Reverse Line Blot Hybridization for the Detection of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a pathogen of critical priority importance according to the WHO. Due to its multi-resistance and expression of various virulence factors, it is the causal agent of severe healthcare-acquired infections (HAIs). Effective strategies to control infections caused by P. aeruginosa must include early and specific detection of the pathogen for early and timely antibiotic prescription. The need to develop a specific and reproducible diagnostic technique is urgent, which must often be more sensitive and faster than current clinical diagnostic methods. In this study, we implement and standardize the loop-mediated isothermal amplification (LAMP) technique, coupled with the reverse line blot hybridization (RLBH) technique for the detection of P. aeruginosa. A set of primers and probes was designed to amplify a specific region of the P. aeruginosa 16s rRNA gene. The sensitivity of the LAMP-RLBH method was 3 × 10-4 ng/μL, 1000 times more sensitive than the PCR and LAMP technique (this work), with a sensitivity of 3 × 10-3 ng/μL. The LAMP-RLBH and LAMP techniques showed specific amplification and no cross-reaction with members of the ESKAPE group and other Pseudomonas species. The present investigation provides a technique that can be easily performed in less time, achieving a faster and more reliable alternative compared to traditional microbial diagnostic methods for the detection of P. aeruginosa.

Highly Effective Biocides against Pseudomonas aeruginosa Reveal New Mechanistic Insights Across Gram-Negative Bacteria

Pseudomonas aeruginosa is a major nosocomial pathogen that persists in healthcare settings despite rigorous disinfection protocols due to intrinsic mechanisms conferring resistance. We sought to systematically assess cationic biocide efficacy against this pathogen using a panel of multidrug-resistant P. aeruginosa clinical isolates. Our studies revealed widespread resistance to commercial cationic disinfectants that are the current standard of care, raising concerns about their efficacy. To address this shortcoming, we highlight a new class of quaternary phosphonium compounds that are highly effective against all members of the panel. To understand the difference in efficacy, mechanism of action studies were carried out, which identified a discrete inner-membrane selective target. Resistance selection studies implicated the SmvRA efflux system (a transcriptionally regulated, inner membrane-associated efflux system) as a major determinant of resistance. This system is also implicated in resistance to two commercial bolaamphiphile antiseptics, octenidine and chlorhexidine, which was further validated herein. In sum, this work highlights, for the first time, a discrete inner-membrane specific mechanism for the bolaamphiphile class of disinfectants that contrasts with the prevailing model of indiscriminate membrane interactions of commercial amphiphiles paving the way for future innovations in disinfectant research.

Non-antibiotic pharmaceutical phenylbutazone binding to MexR reduces the antibiotic susceptibility of Pseudomonas aeruginosa

Antimicrobial resistance has been an increasingly serious threat to global public health. The contribution of non-antibiotic pharmaceuticals to the development of antibiotic resistance has been overlooked. Our study found that the anti-inflammatory drug phenylbutazone could protect P. aeruginosa against antibiotic mediated killing by binding to the efflux pump regulator MexR. In this study, antibiotic activity against P. aeruginosa alone or in combination with phenylbutazone was evaluated in vitro and in vivo. Resazurin accumulation assay, transcriptomic sequencing, and PISA assay were conducted to explore the underlying mechanism for the reduced antibiotic susceptibility caused by phenylbutazone. Then EMSA, ITC, molecular dynamic simulations, and amino acid substitutions were used to investigate the interactions between phenylbutazone and MexR. We found that phenylbutazone could reduce the susceptibility of P. aeruginosa to multiple antibiotics, including parts of β-lactams, fluoroquinolones, tetracyclines, and macrolides. Phenylbutazone could directly bind to MexR, then promote MexR dissociating from the mexA-mexR intergenic region and de-repress the expression of MexAB-OprM efflux pump. The overexpressed MexAB-OprM pump resulted in the reduced antibiotic susceptibility. And the His41 and Arg21 residues of MexR were involved in the phenylbutazone-MexR interaction. We hope this study would imply the potential risk of antibiotic resistance caused by non-antibiotic pharmaceuticals.

Curcumin-mediated photodynamic disinfection strategy with specific spectral range for mucoid Pseudomonas Aeruginosa from hospital water

BACKGROUND

Hospital water systems represent critical environments for the transmission of pathogens, including multidrug-resistant strains like mucoid Pseudomonas aeruginosa (M-PA). Conventional disinfection methods often struggle to eradicate these pathogens effectively, highlighting the need for innovative approaches.

OBJECTIVE

This study aimed to develop an enhanced photodynamic disinfection strategy targeting M-PA from hospital water systems, using curcumin-mediated photodynamic inactivation (PDI) with specific spectral range.

METHODS

An M-PA strain isolated from hospital water was subjected to photodynamic treatment using curcumin as the photosensitizer. The efficacy of different wavelengths of light and varying concentrations of curcumin, with and without Tris-EDTA adjuvants, was evaluated through bacterial enumeration, ROS level measurements, transcriptome analysis, and assessment of virulence factors and biofilm formation. In vivo experiments utilizing a DSS-induced colitis mouse model assessed the protective effects of the photodynamic treatment against M-PA infection.

RESULTS

Our findings demonstrated that the combination of curcumin-mediated PDI with specific spectral range effectively reduced M-PA counts in water, particularly when supplemented with Tris-EDTA. Transcriptome analysis revealed significant downregulation of virulence-related genes under sublethal photodynamic conditions. Furthermore, photodynamic treatment inhibited pyocyanin production and biofilm formation in M-PA, highlighting its potential to disrupt pathogenicity mechanisms. In vivo experiments showed that PDI attenuated M-PA-induced colitis in mice, indicating its protective efficacy.

CONCLUSION

This study presents a promising photodynamic disinfection strategy for combating M-PA from hospital water. By optimizing curcumin-mediated PDI with specific spectral range and adjuvants, our approach demonstrates substantial efficacy in reducing bacterial counts, inhibiting virulence factors, and preventing M-PA-associated colitis.

Metapopulation model of phage therapy of an acute Pseudomonas aeruginosa lung infection

Infections caused by multidrug resistant (MDR) pathogenic bacteria are a global health threat. Bacteriophages ("phage") are increasingly used as alternative or last-resort therapeutics to treat patients infected by MDR bacteria. However, the therapeutic outcomes of phage therapy may be limited by the emergence of phage resistance during treatment and/or by physical constraints that impede phage-bacteria interactions in vivo. In this work, we evaluate the role of lung spatial structure on the efficacy of phage therapy for Pseudomonas aeruginosa infections. To do so, we developed a spatially structured metapopulation network model based on the geometry of the bronchial tree, including host innate immune responses and the emergence of phage-resistant bacterial mutants. We model the ecological interactions between bacteria, phage, and the host innate immune system at the airway (node) level. The model predicts the synergistic elimination of a P. aeruginosa infection due to the combined effects of phage and neutrophils, given the sufficient innate immune activity and efficient phage-induced lysis. The metapopulation model simulations also predict that MDR bacteria are cleared faster at distal nodes of the bronchial tree. Notably, image analysis of lung tissue time series from wild-type and lymphocyte-depleted mice revealed a concordant, statistically significant pattern: infection intensity cleared in the bottom before the top of the lungs. Overall, the combined use of simulations and image analysis of in vivo experiments further supports the use of phage therapy for treating acute lung infections caused by P. aeruginosa, while highlighting potential limits to therapy in a spatially structured environment given impaired innate immune responses and/or inefficient phage-induced lysis.

IMPORTANCE

Phage therapy is increasingly employed as a compassionate treatment for severe infections caused by multidrug-resistant (MDR) bacteria. However, the mixed outcomes observed in larger clinical studies highlight a gap in understanding when phage therapy succeeds or fails. Previous research from our team, using in vivo experiments and single-compartment mathematical models, demonstrated the synergistic clearance of acute P. aeruginosa pneumonia by phage and neutrophils despite the emergence of phage-resistant bacteria. In fact, the lung environment is highly structured, prompting the question of whether immunophage synergy explains the curative treatment of P. aeruginosa when incorporating realistic physical connectivity. To address this, we developed a metapopulation network model mimicking the lung branching structure to assess phage therapy efficacy for MDR P. aeruginosa pneumonia. The model predicts the synergistic elimination of P. aeruginosa by phage and neutrophils but emphasizes potential challenges in spatially structured environments, suggesting that higher innate immune levels may be required for successful bacterial clearance. Model simulations reveal a spatial pattern in pathogen clearance where P. aeruginosa are cleared faster at distal nodes of the bronchial tree than in primary nodes. Interestingly, image analysis of infected mice reveals a concordant and statistically significant pattern: infection intensity clears in the bottom before the top of the lungs. The combined use of modeling and image analysis supports the application of phage therapy for acute P. aeruginosa pneumonia while emphasizing potential challenges to curative success in spatially structured in vivo environments, including impaired innate immune responses and reduced phage efficacy.

Molecular Epidemiology of Pseudomonas aeruginosa in Brazil: A Systematic Review and Meta-Analysis

BACKGROUND

Globally, Pseudomonas aeruginosa is a high-priority opportunistic pathogen which displays several intrinsic and acquired antimicrobial resistance (AMR) mechanisms, leading to challenging treatments and mortality of patients. Moreover, its wide virulence arsenal, particularly the type III secretion system (T3SS) exoU+ virulotype, plays a crucial role in pathogenicity and poor outcome of infections. In depth insights into the molecular epidemiology of P. aeruginosa, especially the prevalence of high-risk clones (HRCs), are crucial for the comprehension of virulence and AMR features and their dissemination among distinct strains. This study aims to evaluate the prevalence and distribution of HRCs and non-HRCs among Brazilian isolates of P. aeruginosa.

METHODS

A systematic review and meta-analysis were conducted on studies published between 2011 and 2023, focusing on the prevalence of P. aeruginosa clones determined by multilocus sequence typing (MLST) in Brazil. Data were extracted from retrospective cross-sectional and case-control studies, encompassing clinical and non-clinical samples. The analysis included calculating the prevalence rates of various sequence types (STs) and assessing the regional variability in the distribution of HRCs and non-HRCs.

RESULTS

A total of 872 samples were analyzed within all studies, of which 298 (34.17%) were MLST typed, identifying 78 unique STs. HRCs accounted for 48.90% of the MLST-typed isolates, with ST277 being the most prevalent (100/298-33.55%), followed by ST244 (29/298-9.73%), ST235 (13/298-4.36%), ST111 (2/298-0.67%), and ST357 (2/298-0.67%). Significant regional variability was observed, with the Southeast region showing a high prevalence of ST277, while the North region shows a high prevalence of MLST-typed samples and HRCs.

CONCLUSIONS

Finally, this systematic review and meta-analysis highlight the role of P. aeruginosa clones in critical issue of AMR in P. aeruginosa in Brazil and the need of integration of comprehensive data from individual studies.

Multifaceted strategies for alleviating Pseudomonas aeruginosa infection by targeting protease activity: Natural and synthetic molecules

Pseudomonas aeruginosa has become a top-priority pathogen in the health sector because it is ubiquitous, has high metabolic/genetic versatility, and is identified as an opportunistic pathogen. The production of numerous virulence factors by P. aeruginosa was reported to act individually or cooperatively to make them robots invasion, adherences, persistence, proliferation, and protection against host immune systems. P. aeruginosa produces various kinds of extracellular proteases such as alkaline protease, protease IV, elastase A, elastase B, large protease A, Pseudomonas small protease, P. aeruginosa aminopeptidase, and MucD. These proteases effectively allow the cells to invade and destroy host cells. Thus, inhibiting these protease activities has been recognized as a promising approach to controlling the infection caused by P. aeruginosa. The present review discussed in detail the characteristics of these proteases and their role in infection to the host system. The second part of the review discussed the recent updates on the multiple strategies for attenuating or inhibiting protease activity. These strategies include the application of natural and synthetic molecules, as well as metallic/polymeric nanomaterials. It has also been reported that a propeptide present in the middle domain of protease IV also attenuates the virulence properties and infection ability of P. aeruginosa.

Multi-strain phage induced clearance of bacterial infections

Bacteriophage (or 'phage' - viruses that infect and kill bacteria) are increasingly considered as a therapeutic alternative to treat antibiotic-resistant bacterial infections. However, bacteria can evolve resistance to phage, presenting a significant challenge to the near- and long-term success of phage therapeutics. Application of mixtures of multiple phage (i.e., 'cocktails') have been proposed to limit the emergence of phage-resistant bacterial mutants that could lead to therapeutic failure. Here, we combine theory and computational models of in vivo phage therapy to study the efficacy of a phage cocktail, composed of two complementary phages motivated by the example of Pseudomonas aeruginosa facing two phages that exploit different surface receptors, LUZ19v and PAK_P1. As confirmed in a Luria-Delbrück fluctuation test, this motivating example serves as a model for instances where bacteria are extremely unlikely to develop simultaneous resistance mutations against both phages. We then quantify therapeutic outcomes given single- or double-phage treatment models, as a function of phage traits and host immune strength. Building upon prior work showing monophage therapy efficacy in immunocompetent hosts, here we show that phage cocktails comprised of phage targeting independent bacterial receptors can improve treatment outcome in immunocompromised hosts and reduce the chance that pathogens simultaneously evolve resistance against phage combinations. The finding of phage cocktail efficacy is qualitatively robust to differences in virus-bacteria interactions and host immune dynamics. Altogether, the combined use of theory and computational analysis highlights the influence of viral life history traits and receptor complementarity when designing and deploying phage cocktails in immunocompetent and immunocompromised hosts.

Pseudomonas aeruginosa: metabolic allies and adversaries in the world of polymicrobial infections

Pseudomonas aeruginosa (PA), an opportunistic human pathogen that is frequently linked with chronic infections in immunocompromised individuals, is also metabolically versatile, and thrives in diverse environments. Additionally, studies report that PA can interact with other microorganisms, such as bacteria, and fungi, producing unique metabolites that can modulate the host immune response, and contribute to disease pathogenesis. This review summarizes the current knowledge related to the metabolic interactions of PA with other microorganisms (Staphylococcus, Acinetobacter, Klebsiella, Enterococcus, and Candida) and human hosts, and the importance of these interactions in a polymicrobial context. Further, we highlight the potential applications of studying these metabolic interactions toward designing better diagnostic tools, and therapeutic strategies to prevent, and treat infections caused by this pathogen.

Methyl gallate attenuates virulence and decreases antibiotic resistance in extensively drug-resistant Pseudomonasaeruginosa

Pseudomonas aeruginosa infections have become a serious threat to public health due to the increasing emergence of extensively antibiotic-resistant strains and high mortality rates. Therefore, the search for new therapeutic alternatives has become crucial. In this study, the antivirulence and antibacterial activity of methyl gallate was evaluated against six clinical isolates of extensively antibiotic-resistant P. aeruginosa. Methyl gallate exhibited minimal inhibitory concentrations of 256-384 μg/mL; moreover, the use of subinhibitory concentrations of the compound inhibited biofilm formation, swimming, swarming, proteolytic activity, and pyocyanin production. Methyl gallate plus antipseudomonal antibiotics showed a synergistic effect by reduced the MICs of ceftazidime, gentamicin and meropenem. Furthermore, the potential therapeutic effect of methyl gallate was demonstrated in an infection model. This study evidenced the antivirulence and antimicrobial activity of methyl gallate as a therapeutic alternative against P. aeruginosa.

A microbiological survey approach to understanding the virulence factors of Pseudomonas species in healthcare sinks

BACKGROUND

Hospital water is involved in both the prevention and spread of healthcare-associated infections (HCAIs). Handwashing is key to reducing the transmission of pathogens, yet numerous outbreaks have been found to be caused by organisms within sinks, taps and showers. Pseudomonas aeruginosa and increasingly non-aeruginosa Pseudomonas cause waterborne HCAI, however, little is known about the virulence potential of Pseudomonas species found within hospital environments.

METHODS

Swabs were taken from 62 sinks within two newly opened wards at Great Ormond Street Hospital, samples were taken before and after the wards opened to understand the impact of patient occupancy on sink micro-organisms. Culturable bacteria were identified by MALDI-TOF and virulence factors assessed through phenotypic methods.

RESULTS

A total of 106 bacterial isolates were recovered including 24 Pseudomonas isolates. Of these 25% were identified as P. oleovorans, 21% P. aeruginosa, 17% P. composti, 13% P. alicalipha, 8% P. monteilii, 4% P. putida, 4% P. stutzeri and 8% could only be identified to genus level by MALDI-TOF. Differences were seen in both the number of Pseudomonas isolates and virulence production between the two wards, overall 25% of the Pseudomonas isolates produced pigment, 58% were capable of haemolysis, 87.5% were able to swim, 83.3% were capable of twitching motility, 33.3% produced alkaline protease and 8.3% produced gelatinase.

CONCLUSIONS

Results suggest that patients may be back-contaminating sinks with colonizing organisms which has ongoing implications for infection prevention and control. Additionally, this work highlights the ability of non-aeruginosa Pseudomonas to produce virulence factors traditionally associated with P. aeruginosa.

Control of phosphodiesterase activity in the regulator of biofilm dispersal RbdA from Pseudomonas aeruginosa

The switch between planktonic and biofilm lifestyle correlates with intracellular concentration of the second messenger bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP). While bacteria possess cyclase and phosphodiesterase enzymes to catalyse formation or hydrolysis of c-di-GMP, both enzymatic domains often occur in a single protein. It is tacitly assumed that one of the two enzymatic activities is dominant, and that additional domains and protein interactions enable responses to environmental conditions and control activity. Here we report the structure of the phosphodiesterase domain of the membrane protein RbdA (regulator of biofilm dispersal) in a dimeric, activated state and show that phosphodiesterase activity is controlled by the linked cyclase. The phosphodiesterase region around helices α5/α6 forms the dimer interface, providing a rationale for activation, as this region was seen in contact with the cyclase domain in an auto-inhibited structure previously described. Kinetic analysis supports this model, as the activity of the phosphodiesterase alone is lower when linked to the cyclase. Analysis of a computed model of the RbdA periplasmatic domain reveals an all-helical architecture with a large binding pocket that could accommodate putative ligands. Unravelling the regulatory circuits in multi-domain phosphodiesterases like RbdA is important to develop strategies to manipulate or disperse bacterial biofilms.

The quorum sensing regulator RhlR positively controls the expression of the type III secretion system in Pseudomonas aeruginosa PAO1

Pseudomonas aeruginosa is an opportunist bacterium that causes acute and chronic infections. During acute infections, the type III secretion system (T3SS) plays a pivotal role in allowing the bacteria to translocate effectors such as ExoS, ExoT, and ExoY into host cells for colonization. Previous research on the involvement of quorum sensing systems Las and Rhl in controlling the T3SS gene expression produced ambiguous results. In this study, we determined the role of the Las and Rhl systems and the PqsE protein on T3SS expression. Our results show that in the wild-type PAO1 strain, the deletion of lasR or pqsE do not affect the secretion of ExoS. However, rhlI inactivation increases the expression of T3SS genes. In contrast to the rhlI deletion, rhlR inactivation decreases both T3SS genes expression and ExoS secreted protein levels, and this phenotype is restored when this mutant is complemented with the exsA gene, which codes for the master regulator of the T3SS. Additionally, cytotoxicity is affected in the rhlR mutant strain compared with its PAO1 parental strain. Overall, our results indicate that neither the Las system nor PqsE are involved in regulating the T3SS. Moreover, the Rhl system components have opposite effects, RhlI participates in negatively controlling the T3SS expression, while RhlR does it in a positive way, and this regulation is independent of C4 or PqsE. Finally, we show that rhlR, rhlI, or pqsE inactivation abolished pyocyanin production in T3SS-induction conditions. The ability of RhlR to act as a positive T3SS regulator in the absence of its cognate autoinducer and PqsE shows that it is a versatile regulator that controls different virulence traits allowing P. aeruginosa to compete for a niche.

Amoebae as training grounds for microbial pathogens

Grazing of amoebae on microorganisms represents one of the oldest predator-prey dynamic relationships in nature. It represents a genetic "melting pot" for an ancient and continuous multi-directional inter- and intra-kingdom horizontal gene transfer between amoebae and its preys, intracellular microbial residents, endosymbionts, and giant viruses, which has shaped the evolution, selection, and adaptation of microbes that evade degradation by predatory amoeba. Unicellular phagocytic amoebae are thought to be the ancient ancestors of macrophages with highly conserved eukaryotic processes. Selection and evolution of microbes within amoeba through their evolution to target highly conserved eukaryotic processes have facilitated the expansion of their host range to mammals, causing various infectious diseases. Legionella and environmental Chlamydia harbor an immense number of eukaryotic-like proteins that are involved in ubiquitin-related processes or are tandem repeats-containing proteins involved in protein-protein and protein-chromatin interactions. Some of these eukaryotic-like proteins exhibit novel domain architecture and novel enzymatic functions absent in mammalian cells, such as ubiquitin ligases, likely acquired from amoebae. Mammalian cells and amoebae may respond similarly to microbial factors that target highly conserved eukaryotic processes, but mammalian cells may undergo an accidental response to amoeba-adapted microbial factors. We discuss specific examples of microbes that have evolved to evade amoeba predation, including the bacterial pathogens- Legionella, Chlamydia, Coxiella, Rickettssia, Francisella, Mycobacteria, Salmonella, Bartonella, Rhodococcus, Pseudomonas, Vibrio, Helicobacter, Campylobacter, and Aliarcobacter. We also discuss the fungi Cryptococcus, and Asperigillus, as well as amoebae mimiviruses/giant viruses. We propose that amoeba-microbe interactions will continue to be a major "training ground" for the evolution, selection, adaptation, and emergence of microbial pathogens equipped with unique pathogenic tools to infect mammalian hosts. However, our progress will continue to be highly dependent on additional genomic, biochemical, and cellular data of unicellular eukaryotes.

The uncharacterized PA3040-3042 operon is part of the cell envelope stress response and a tobramycin resistance determinant in a clinical isolate of Pseudomonas aeruginosa

Bacteriophages (hereafter "phages") are ubiquitous predators of bacteria in the natural world, but interest is growing in their development into antibacterial therapy as complement or replacement for antibiotics. However, bacteria have evolved a huge variety of antiphage defense systems allowing them to resist phage lysis to a greater or lesser extent. In addition to dedicated phage defense systems, some aspects of the general stress response also impact phage susceptibility, but the details of this are not well known. In order to elucidate these factors in the opportunistic pathogen Pseudomonas aeruginosa, we used the laboratory-conditioned strain PAO1 as host for phage infection experiments as it is naturally poor in dedicated phage defense systems. Screening by transposon insertion sequencing indicated that the uncharacterized operon PA3040-PA3042 was potentially associated with resistance to lytic phages. However, we found that its primary role appeared to be in regulating biofilm formation, particularly in a clinical isolate of P. aeruginosa in which it also altered tobramycin resistance. Its expression was highly growth-phase dependent and responsive to phage infection and cell envelope stress. Our results suggest that this operon may be a cryptic but important locus for P. aeruginosa stress tolerance.

IMPORTANCE

An important category of bacterial stress response systems is bacteriophage defense, where systems are triggered by bacteriophage infection and activate a response which may either destroy the phage genome or destroy the infected cell so that the rest of the population survives. In some bacteria, the cell envelope stress response is activated by bacteriophage infection, but it is unknown whether this contributes to the survival of the infection. We have found that a conserved uncharacterized operon (PA3040-PA3042) of the cell envelope stress regulon in Pseudomonas aeruginosa, which has very few dedicated phage defense systems, responds to phage infection and stationary phase as well as envelope stress and is important for growth and biofilm formation in a clinical isolate of P. aeruginosa, even in the absence of phages. As homologs of these genes are found in other bacteria, they may be a novel component of the general stress response.

Impact of multidrug resistance on the virulence and fitness of Pseudomonas aeruginosa: a microbiological and clinical perspective

Pseudomonas aeruginosa is one of the most common nosocomial pathogens and part of the top emergent species associated with antimicrobial resistance that has become one of the greatest threat to public health in the twenty-first century. This bacterium is provided with a wide set of virulence factors that contribute to pathogenesis in acute and chronic infections. This review aims to summarize the impact of multidrug resistance on the virulence and fitness of P. aeruginosa. Although it is generally assumed that acquisition of resistant determinants is associated with a fitness cost, several studies support that resistance mutations may not be associated with a decrease in virulence and/or that certain compensatory mutations may allow multidrug resistance strains to recover their initial fitness. We discuss the interplay between resistance profiles and virulence from a microbiological perspective but also the clinical consequences in outcomes and the economic impact.