Tissue remodeling by an opportunistic pathogen triggers allergic inflammation.

Different effector arms of the immune system are optimized to protect from different classes of pathogens. In some cases, pathogens manipulate the host immune system to promote the wrong type of effector response-a phenomenon known as immune deviation. Typically, immune deviation helps pathogens to avoid destructive immune responses. Here, we report on a type of immune deviation whereby an opportunistic pathogen, Pseudomonas aeruginosa (P. aeruginosa), induces the type 2 immune response resulting in mucin production that is used as an energy source by the pathogen. Specifically, P. aeruginosa-secreted toxin, LasB, processed and activated epithelial amphiregulin to induce type 2 inflammation and mucin production. This "niche remodeling" by P. aeruginosa promoted colonization and, as a by-product, allergic sensitization. Our study thus reveals a type of bacterial immune deviation by increasing nutrient supply. It also uncovers a mechanism of allergic sensitization by a bacterial virulence factor.

Quercetin: a promising virulence inhibitor of Pseudomonas aeruginosa LasB in vitro.

With the inappropriate use of antibiotics, antibiotic resistance has emerged as a major dilemma for patients infected with Pseudomonas aeruginosa. Elastase B (LasB), a crucial extracellular virulence factor secreted by P. aeruginosa, has been identified as a key target for antivirulence therapy. Quercetin, a natural flavonoid, exhibits promising potential as an antivirulence agent. We aim to evaluate the impact of quercetin on P. aeruginosa LasB and elucidate the underlying mechanism. Molecular docking and molecular dynamics simulation revealed a rather favorable intermolecular interaction between quercetin and LasB. At the sub-MICs of ≤256 µg/ml, quercetin was found to effectively inhibit the production and activity of LasB elastase, as well as downregulate the transcription level of the lasB gene in both PAO1 and clinical strains of P. aeruginosa. Through correlation analysis, significant positive correlations were shown between the virulence gene lasB and the QS system regulatory genes lasI, lasR, rhlI, and rhlR in clinical strains of P. aeruginosa. Then, we found the lasB gene expression and LasB activity were significantly deficient in PAO1 ΔlasI and ΔlasIΔrhlI mutants. In addition, quercetin significantly downregulated the expression levels of regulated genes lasI, lasR, rhlI, rhlR, pqsA, and pqsR as well as effectively attenuated the synthesis of signaling molecules 3-oxo-C12-HSL and C4-HSL in the QS system of PAO1. Quercetin was also able to compete with the natural ligands OdDHL, BHL, and PQS for binding to the receptor proteins LasR, RhlR, and PqsR, respectively, resulting in the formation of more stabilized complexes. Taken together, quercetin exhibits enormous potential in combating LasB production and activity by disrupting the QS system of P. aeruginosa in vitro, thereby offering an alternative approach for the antivirulence therapy of P. aeruginosa infections. KEY POINTS: • Quercetin diminished the content and activity of LasB elastase of P. aeruginosa. • Quercetin inhibited the QS system activity of P. aeruginosa. • Quercetin acted on LasB based on the QS system.

Facile Production of the Pseudomonas aeruginosa Virulence Factor LasB in Escherichia coli for Structure-Based Drug Design.

The human pathogen Pseudomonas aeruginosa has a number of virulence factors at its disposal that play crucial roles in the progression of infection. LasB is one of the major virulence factors and exerts its effects through elastolytic and proteolytic activities aimed at dissolving connective tissue and inactivating host defense proteins. LasB is of great interest for the development of novel pathoblockers to temper the virulence, but access has thus far largely been limited to protein isolated from Pseudomonas cultures. Here, we describe a new protocol for high-level production of native LasB in Escherichia coli. We demonstrate that this facile approach is suitable for the production of mutant, thus far inaccessible LasB variants, and characterize the proteins biochemically and structurally. We expect that easy access to LasB will accelerate the development of inhibitors for this important virulence factor.

Synthesis, biological evaluation, and molecular docking studies of aldotetronic acid-based LpxC inhibitors.

In order to develop novel inhibitors of the bacterial deacetylase LpxC bearing a substituent to target the UDP binding site of the enzyme, a series of aldotetronic acid-based hydroxamic acids was accessed in chiral pool syntheses starting from 4,6-O-benzylidene-d-glucose and l-arabinitol. The synthesized hydroxamic acids were tested for LpxC inhibitory activity in vitro, revealing benzyl ether 17a ((2S,3S)-4-(benzyloxy)-N,3-dihydroxy-2-[(4-{[4-(morpholinomethyl)phenyl]ethynyl}benzyl)oxy]butanamide) as the most potent LpxC inhibitor. This compound was additionally tested for antibacterial activity against a panel of clinically relevant Gram-negative bacteria, bacterial uptake, and susceptibility to efflux pumps. Molecular docking studies were performed to rationalize the observed structure-activity relationships.

A deep insight into the suppression mechanism of Sedum alfredii root exudates on Pseudomonas aeruginosa based on quorum sensing.

Quorum sensing (QS) plays an important role in the intensive communication between plants and microbes in the rhizosphere during the phytoremediation. This study explored the influence of the root exudates of hyperaccumulator Sedum alfredii on Pseudomonas aeruginosa based on QS. The effects of the components of root exudates, genes expression and transcription regulation of QS system (especially the las system) in Pseudomonas aeruginosa wild-type strain (WT) and rhl system mutant strain (ΔrhlI) were systematically analyzed and discussed. The WT and ΔrhlI exposed to gradient root exudates (0×, 1×, 2×, 5× and 10×) showed a concentration-corrective inhibition on protease production, with the inhibition rates of 51.4-74.5% and 31.2-50.0%, respectively. Among the components of the root exudates of Sedum alfredii, only thymol had an inhibition effects to the root exudates on the activity of protease and elastase. The inhibition rates of 50 µmol/L thymol on protease and elastase in WT were 44.7% and 24.3%, respectively, which was consistent with the variation in ΔrhlI. The gene expression of lasB declined 36.0% under the 1× root exudate treatment and 73.0% under the 50 µmol/L thymol treatment. Meanwhile, there was no significant impact on N-3-oxo-dodecanoyl-L-homoserine lactone signal production and the gene expression of lasI and lasR. Therefore, thymol from Sedum alfredii root exudates could inhibit the formation of protease and elastase in Pseudomonas aeruginosa by suppressing the expression of lasB, without any significant influence on the main las system as a potential natural QS inhibitor.

LasB and CbpD Virulence Factors of Pseudomonas aeruginosa Carry Multiple Post-Translational Modifications on Their Lysine Residues.

Pseudomonas aeruginosa is a multi-drug resistant human pathogen largely involved in nosocomial infections. Today, effective antibacterial agents are lacking. Exploring the bacterial physiology at the post-translational modifications (PTM) level may contribute to the renewal of fighting strategies. Indeed, some correlations between PTMs and the bacterial virulence, adaptation, and resistance have been shown. In a previous study performed in P. aeruginosa, we reported that many virulence factors like chitin-binding protein CbpD and elastase LasB were multiphosphorylated. Besides phosphorylation, other PTMs, like those occurring on lysine, seem to play key roles in bacteria. In the present study, we investigated for the first time the lysine succinylome and acetylome of the extracellular compartment of P. aeruginosa by using a two-dimensional immunoaffinity approach. Some virulence factors were identified as multimodified on lysine residues, among them, LasB and CbpD. Lysine can be modified by a wide range of chemical groups. In order to check the presence of other chemical groups on modified lysines identified on LasB and CbpD, we used 1- and 2- dimensional gel electrophoresis approaches to target lysine modified by 7 other modifications: butyrylation, crotonylation, dimethylation, malonylation, methylation, propionylation, and trimethylation. We showed that some lysines of these two virulence factors were modified by these 9 different PTMs. Interestingly, we found that the PTMs recovered on these two virulence factors were different than those previously reported in the intracellular compartment.

Real-time polymerase chain reaction assays for rapid detection and virulence evaluation of the environmental Pseudomonas aeruginosa isolates.

Rapid and species-specific detection, and virulence evaluation of opportunistic pathogens such as Pseudomonas aeruginosa, are issues that increasingly has attracted the attention of public health authorities. A set of primers and hydrolysis probe was designed based on one of the P. aeruginosa housekeeping genes, gyrB, and its specificity and sensitivity was evaluated by TaqMan qPCR methods. The end point PCR and SYBR Green qPCR were used as control methods. Furthermore, multiplex RT-qPCRs were developed for gyrB as reference and four virulence genes, including lasB, lasR, rhlR and toxA. Totally, 40 environmental samples, two clinical isolates from CF patients, two standard strains of P. aeruginosa, and 15 non-target reference strains were used to test the sensitivity and specificity of qPCR assays. In silico and in vitro cross-species testing confirmed the high specificity and low cross-species amplification of the designed gyrB418F/gyrB490R/gyrB444P. The sensitivity of both TaqMan and SYBR Green qPCRs was 100% for all target P. aeruginosa, and the detected count of bacteria was below ten genomic equivalents. The lowest M value obtained from gene-stability measurement was 0.19 that confirmed the suitability of gyrB as the reference gene for RT-qPCR. The developed qPCRs have enough detection power for identification of P. aeruginosa in environmental samples including clean and recreational water, treated and untreated sewage and soil. The short amplicon length of our designed primers and probes, alongside with a low M value, make it as a proper methodology for RT-qPCR in virulence genes expression assessment.

Acinetobacter baumannii virulence is enhanced by the combined presence of virulence factors genes phospholipase C (plcN) and elastase (lasB).

The ability of multidrug resistance Acinetobacter baumannii to persist in any circumstances regard to the acquisition of many virulence factors genes and antibiotic resistance genes is major concern in the hospitals environments. In this study, thirty A. baumannii isolates were collected from blood infections from hospitalized patients were subjected to screening for virulence factors genes plcN and lasB by conventional PCR. The pathogenicity of representative isolates bearing these gene were tested using galleria mellonella infection assay and adhesion-invasion assay on A549 cell line, and compared with other strain without this gene. Phylogenetic tree revealed that isolates were sorted in two major groups one of them contained two clusters (Group II and III), and another had the other group (Group I). All the 30 A. baumannii isolates were investigated for the presence of virulence factors genes (plc-N and lasB genes) and results showed that, 16 (53.33%) were harboring lasB genes while 7 (23.3%) isolates were harboring plcN gene The presence of any of these gene enhance the killing ability of A. baumannii strain and increased invasiveness in A549 cell line. Increase nosocomial infection with A. baumannii isolates is serious problem especially because of its potency to gain virulence factors genes and its ability to persist in hospital environments. So the shed light in finding which virulence factors these isolates which have is necessary to discover new antimicrobials that targeting the virulence factor of these powerful pathogens.

Quorum-sensing inhibition abrogates the deleterious impact of Pseudomonas aeruginosa on airway epithelial repair.

Chronic Pseudomonas aeruginosa lung infections are associated with progressive epithelial damage and lung function decline. In addition to its role in tissue injury, the persistent presence of P. aeruginosa-secreted products may also affect epithelial repair ability, raising the need for new antivirulence therapies. The purpose of our study was to better understand the outcomes of P. aeruginosa exoproducts exposure on airway epithelial repair processes to identify a strategy to counteract their deleterious effect. We found that P. aeruginosa exoproducts significantly decreased wound healing, migration, and proliferation rates, and impaired the ability of directional migration of primary non-cystic fibrosis (CF) human airway epithelial cells. Impact of exoproducts was inhibited after mutations in P. aeruginosa genes that encoded for the quorum-sensing (QS) transcriptional regulator, LasR, and the elastase, LasB, whereas impact was restored by LasB induction in ΔlasR mutants. P. aeruginosa purified elastase also induced a significant decrease in non-CF epithelial repair, whereas protease inhibition with phosphoramidon prevented the effect of P. aeruginosa exoproducts. Furthermore, treatment of P. aeruginosa cultures with 4-hydroxy-2,5-dimethyl-3(2H)-furanone, a QS inhibitor, abrogated the negative impact of P. aeruginosa exoproducts on airway epithelial repair. Finally, we confirmed our findings in human airway epithelial cells from patients with CF, a disease featuring P. aeruginosa chronic respiratory infection. These data demonstrate that secreted proteases under the control of the LasR QS system impair airway epithelial repair and that QS inhibitors could be of benefit to counteract the deleterious effect of P. aeruginosa in infected patients.-Ruffin, M., Bilodeau, C., Maillé, É., LaFayette, S. L., McKay, G. A., Trinh, N. T. N., Beaudoin, T., Desrosiers, M.-Y., Rousseau, S., Nguyen, D., Brochiero, E. Quorum-sensing inhibition abrogates the deleterious impact of Pseudomonas aeruginosa on airway epithelial repair.

Establishment of portable Pseudomonas aeruginosa detection platform based on one-tube CRISPR/Cas12a combined with recombinase polymerase amplification technology.

Pseudomonas aeruginosa, a common Gram-negative bacterium, is associated with diverse diseases. Its increasing resistance to antibiotics presents challenges in clinical treatment. The predominant diagnostic approach involves conventional biochemical cultures, known for their time and labor intensiveness. Despite progress in isothermal amplification studies, limitations persist, including reliance on specialized equipment, intricate primer design, and aerosol contamination. Therefore, there is a demand for enhanced clinical assays. This study successfully combined RPA and CRISPR/Cas12a techniques. Through a series of experiments involving the design and screening of lasB crRNA, the creation of lasB RPA primers, and the establishment of a streamlined RPA-CRISPR/Cas12a assay, the study developed a one-tube detection method targeting P. aeruginosa's lasB gene. The assay demonstrated inclusive behavior across standard and 21 isolates, while specifically discerning P. aeruginosa from diverse strains. Sensitivity reached 15.9 CFU/reaction. Clinical validation revealed a 97.62% concordance with traditional methods. The one-tube assay's protocol mitigated aerosol contamination. Offering precision, specificity, and sensitivity, this method shows promise for field applications in resource-scarce regions, enabling early detection and improved management of P. aeruginosa infections.

Chemical Optimization of Selective Pseudomonas aeruginosa LasB Elastase Inhibitors and Their Impact on LasB-Mediated Activation of IL-1ß in Cellular and Animal Infection Models.

LasB elastase is a broad-spectrum exoprotease and a key virulence factor of Pseudomonas aeruginosa, a major pathogen causing lung damage and inflammation in acute and chronic respiratory infections. Here, we describe the chemical optimization of specific LasB inhibitors with druglike properties and investigate their impact in cellular and animal models of P. aeruginosa infection. Competitive inhibition of LasB was demonstrated through structural and kinetic studies. In vitro LasB inhibition was confirmed with respect to several host target proteins, namely, elastin, IgG, and pro-IL-1ß. Furthermore, inhibition of LasB-mediated IL-1ß activation was demonstrated in macrophage and mouse lung infection models. In mice, intravenous administration of inhibitors also resulted in reduced bacterial numbers at 24 h. These highly potent, selective, and soluble LasB inhibitors constitute valuable tools to study the proinflammatory impact of LasB in P. aeruginosa infections and, most importantly, show clear potential for the clinical development of a novel therapy for life-threatening respiratory infections caused by this opportunistic pathogen.

Structure-Based Design of α-Substituted Mercaptoacetamides as Inhibitors of the Virulence Factor LasB from Pseudomonas aeruginosa.

Antivirulence therapy has become a widely applicable method for fighting infections caused by multidrug-resistant bacteria. Among the many virulence factors produced by the Gram-negative bacterium Pseudomonas aeruginosa, elastase (LasB) stands out as an important target as it plays a pivotal role in the invasion of the host tissue and evasion of the immune response. In this work, we explored the recently reported LasB inhibitor class of α-benzyl-N-aryl mercaptoacetamides by exploiting the crystal structure of one of the compounds. Our exploration yielded inhibitors that maintained inhibitory activity, selectivity, and increased hydrophilicity. These inhibitors were found to reduce the pathogenicity of the bacteria and to maintain the integrity of lung and skin cells in the diseased state. Furthermore, two most promising compounds increased the survival rate of Galleria mellonella larvae treated with P. aeruginosa culture supernatant.

Mutational analysis on stable expression and LasB inhibition of LasB propeptide in Pseudomonas aeruginosa.

Three major proteases, elastase B (LasB), protease IV (PIV), and elastase A (LasA) expressed in Pseudomonas aeruginosa play important roles in infections and pathogeneses. These are activated by a proteolytic cascade initiated by the activation of LasB. In this study, we investigated whether LasB could be inhibited using its propeptide (LasBpp). Although LasA and PIV were inhibited by their propeptides, LasB was not inhibited by purified LasBpp because LasB degraded LasBpp. To address this problem, mutant LasBpp variants were constructed to obtain a mutant LasBpp resistant to LasB degradation. A C-terminal deletion series of LasBpp was tested in vivo, and two positive candidates, T2 and T2-1, were selected. However, both caused growth retardation and were unstably expressed in vivo. Since deleting the C-terminal end of LasBpp significantly affected its stable expression, substitution mutations were introduced at the two amino acids near the truncation site of T2-1. The resulting mutants, LasBppE172D, LasBppG173A, and LasBppE172DG173A, significantly diminished LasB activity when overexpressed in vivo and were stably expressed in MW1, a quorum sensing mutant that does not produce LasB. In vitro analysis showed that purified LasBppE172DG173A inhibited LasB activity to a small extent. Summarizing, C-terminal modification of LasBpp profoundly affected the stable expression of LasBpp, and little enhanced the ability of LasBpp to resist degradation by LasB.

The Structures and Binding Modes of Small-Molecule Inhibitors of Pseudomonas aeruginosa Elastase LasB.

Elastase B (LasB) is a zinc metalloprotease and a crucial virulence factor of Pseudomonas aeruginosa. As the need for new strategies to fight antimicrobial resistance (AMR) constantly rises, this protein has become a key target in the development of novel antivirulence agents. The extensive knowledge of the structure of its active site, containing two subpockets and a zinc atom, led to various structure-based medicinal chemistry programs and the optimization of several chemical classes of inhibitors. This review provides a brief reminder of the structure of the active site and a summary of the disclosed P. aeruginosa LasB inhibitors. We specifically focused on the analysis of their binding modes with a detailed representation of them, hence giving an overview of the strategies aiming at targeting LasB by small molecules.

Clinical Strains of Pseudomonas aeruginosa Secrete LasB Elastase to Induce Hemorrhagic Diffuse Alveolar Damage in Mice.

BACKGROUND: Acute lung injury and acute respiratory distress syndrome (ALI/ARDS) are most often caused by bacterial pneumonia and characterized by severe dyspnea and high mortality. Knowledge about the lung injury effects of current clinical bacterial strains is lacking. The aim of this study was to investigate the ability of representative pathogenic bacteria isolated from patients to cause ALI/ARDS in mice and identify the major virulence factor. METHODS: Seven major bacterial species were isolated from clinical sputum and unilaterally instilled into the mouse airway. A histology study was performed to determine the lung injury effect. Virulence genes were examined by PCR. Sequence types of P. aeruginosa strains were identified by MLST. LC-MS/MS was used to analysis the bacterial exoproducts proteome. LasB was purified through a DEAE-cellulose column, and its toxicity was tested both in vitro and in vivo. RESULTS: Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus agalactiae, Acinetobacter baumannii, Klebsiella pneumoniae, Pseudomonas aeruginosa and Escherichia coli were randomly separated and tested 3 times. Among them, gram-negative bacteria have much more potential to cause acute lung injury than gram-positive bacteria. However, P. aeruginosa is the only pathogen that induces diffuse alveolar damage, hemorrhage and hyaline membranes in the lungs of mice. The lung injury effect is associated with the excreted LasB elastase. Purified LasB recapitulated lung injury similar to P. aeruginosa infection in vivo. We found that this was due to the powerful degradation effect of LasB on the extracellular matrix of the lung and key proteins in the coagulation cascade without inducing obvious cellular apoptosis. We also report for the first time that LasB could induce DIC-like coagulopathy in vitro. CONCLUSION: P. aeruginosa strains are most capable of inducing ALI/ARDS in mice among major clinical pathogenic bacteria tested, and this ability is specifically attributed to their LasB production.

Human Single-Chain Antibodies That Neutralize Elastolytic Activity of Pseudomonas aeruginosa LasB.

LasB (elastase/pseudolysin) is an injurious zinc-metalloprotease secreted by the infecting Pseudomonas aeruginosa. LasB is recognized as the bacterial key virulence factor for establishment of successful infection, acquisition of nutrients, dissemination, tissue invasion, and immune modulation and evasion. LasB digests a variety of the host tissue proteins, extracellular matrices, as well as components of both innate and adaptive immune systems, including immunoglobulins, complement proteins, and cytokines. Thus, this enzyme is an attractive target for disarming the P. aeruginosa. This study generated human single-chain antibodies (HuscFvs) that can neutralize the elastolytic activity of native LasB by using phage display technology. Gene sequences coding HuscFvs (huscfvs) isolated from HuscFv-displaying phage clones that bound to enzymatically active LasB were sub-cloned to expression plasmids for large scale production of the recombinant HuscFvs by the huscfv-plasmid transformed Escherichia coli. HuscFvs of two transformed E. coli clones, i.e., HuscFv-N42 and HuscFv-N45, neutralized the LasB elastolytic activities in vitro. Computer simulation by homology modeling and molecular docking demonstrated that antibodies presumptively formed contact interfaces with the LasB residues critical for the catalytic activity. Although the LasB neutralizing mechanisms await elucidation by laboratory experiments, the HuscFvs should be tested further towards the clinical application as a novel adjunctive therapeutics to mitigate severity of the diseases caused by P. aeruginosa.

Pseudomonas aeruginosa Elastase Contributes to the Establishment of Chronic Lung Colonization and Modulates the Immune Response in a Murine Model.

Chronic infection by Pseudomonas aeruginosa in cystic fibrosis (CF) patients is a major contributor to progressive lung damage and is poorly treated by available antibiotic therapy. An alternative approach to the development of additional antibiotic treatments is to identify complementary therapies which target bacterial virulence factors necessary for the establishment and/or maintenance of the chronic infection. The P. aeruginosa elastase (LasB) has been suggested as an attractive anti-virulence target due to its extracellular location, its harmful degradative effects on host tissues and the immune system, and the potential to inhibit its activity using small molecule inhibitors. However, while the relevance of LasB in acute P. aeruginosa infection has been demonstrated, it is still unclear whether this elastase might also play a role in the early phase of chronic lung colonization. By analyzing clinical P. aeruginosa clonal isolates from a CF patient, we found that the isolate RP45, collected in the early phase of persistence, produces large amounts of active LasB, while its clonal variant RP73, collected after years of colonization, does not produce it. When a mouse model of persistent pneumonia was used, deletion of the lasB gene in RP45 resulted in a significant reduction in mean bacterial numbers and incidence of chronic lung colonization at Day 7 post-challenge compared to those mice infected with wild-type (wt) RP45. Furthermore, deletion of lasB in strain RP45 also resulted in an increase in immunomodulators associated with innate and adaptive immune responses in infected animals. In contrast, deletion of the lasB gene in RP73 did not affect the establishment of chronic infection. Overall, these results indicate that LasB contributes to the adaptation of P. aeruginosa to a persistent lifestyle. In addition, these findings support pharmacological inhibition of LasB as a potentially useful therapeutic intervention for P. aeruginosa-infected CF patients prior to the establishment of a chronic infection.

Effect of Satureja khuzistanica essential oil (SKEO) extract on expression of lasA and lasB genes in Pseudomonas aeruginosa.

BACKGROUND AND OBJECTIVES: Expressions of lasA and lasB genes of Pseudomonas aeruginosa are associated with bacterium pathogenicity. The present study was aimed to assess the effect of Satureja khuzistanica essential oil (SKEO) extract on expression of lasA and lasB genes in P. aeruginosa. MATERIALS AND METHODS: Pseudomonas aeruginosa isolates were cultured in Mueller Hinton broth containing sub-inhibitory concentrations of SKEO and total RNA extracted using Trizol method. cDNA was synthesized using random Hexamer primer and finally the expression of lasA and lasB genes carried out by real-time PCR. RESULTS: The MICs of SKEO extract for PA9, PA10, PA11, PA13, PA41 and PA42 isolates were 8, 8, 8, 9, 7 and 12 µg/ml, respectively. Statistical analysis for 6 isolates revealed that the reduction in expression of lasA and lasB genes under SKEO treatment was significant (P<0.05). CONCLUSION: The insignificantly increasing of lasB gene expression may lead to low virulent strains, for probably reason that the strain's exotoxin A are destroyed in the high amount of protease. In conclusion, using of SKEO in burned patients infected with P. aeruginosa may be effective; however, it is better to assess the spectrum activity of SKEO, pharmacokinetics, potency and its toxicity in human cells.

Virulence determinants and biofilm formation of Acinetobacter baumannii isolated from hospitalized patients.

INTRODUCTION: Acinetobacter baumannii are nosocomial bacteria that are responsible for outbreaks and severe infections in hospitalized patients globally. The major target of this study was the characterization of virulence determinants and biofilm formation of A. baumannii isolates from hospitalized patients. METHODS: In total, 100 A. baumannii were collected from three hospitals in Tehran, Iran, 2017-2018. The isolates were assessed using phenotypic and genotypic methods and then screened for virulence factor encoding genes such as plcN and lasB using conventional polymerase chain reaction. Furthermore, bacterial biofilm formation, motility and hemolytic and proteolytic activities were assessed. RESULTS: Of 100 A. baumannii isolates, 20 isolates included plcN and four isolates included lasB using PCR assay. Overall, 21 isolates were negative for biofilm formation while 45, 20 and 14 of the total isolates were reported as weak, moderate and strong biofilm producers, respectively. All isolates were positive for bap genes using PCR. Moreover, 35 isolates were motile on Luria-Bertani media, 47 isolates were α-hemolytic on Brucella blood agar media and all isolates displayed proteolytic activity. CONCLUSIONS: Healthcare-associated infections with A. baumannii are a major concern, importantly due to their potency to acquire virulence factor genes. Therefore, shedding light in the discovery of new antimicrobial and/or therapeutic agents against virulent A. baumannii strains seem to be necessary.

The therapeutic potential of the insect metalloproteinase inhibitor against infections caused by Pseudomonas aeruginosa.

OBJECTIVES: The objective of this study was to investigate the therapeutic potential of the insect metalloproteinase inhibitor (IMPI) from Galleria mellonella, the only known specific inhibitor of M4 metalloproteinases. METHODS: The fusion protein IMPI-GST (glutathione-S-transferase) was produced by fermentation in Escherichia coli and was tested for its ability to inhibit the proteolytic activity of the M4 metalloproteinases thermolysin and Pseudomonas elastase (PE), the latter a key virulence factor of the wound-associated and antibiotic-resistant pathogen Pseudomonas aeruginosa. We also tested the ability of IMPI to inhibit the secretome (Sec) of a P. aeruginosa strain obtained from a wound. KEY FINDINGS: We found that IMPI-GST inhibited thermolysin and PE in vitro and increased the viability of human keratinocytes exposed to Sec by inhibiting detachment caused by changes in cytoskeletal morphology. IMPI-GST also improved the cell migration rate in an in vitro wound assay and reduced the severity of necrosis caused by Sec in an ex vivo porcine wound model. CONCLUSIONS: The inhibition of virulence factors is a novel therapeutic approach against antibiotic resistant bacteria. Our results indicate that IMPI is a promising drug candidate for the treatment of P. aeruginosa infections.