Bactericidal and Anti-biofilm Activity of the Retinoid Compound CD437 Against Enterococcus faecalis

Analysis on the change of gut microbiota and metabolome in lung transplant patients

Previous studies have shown that the gut microbiota and its metabolites are associated with the success of organ transplantation. However, the specific changes in the gut microbiota of lung transplant patients remain unclear. Hence, this study aimed to elucidate the interplay between the gut microbiota, metabolome, and lung transplantation outcomes. Using 16S metagenomics sequencing and untargeted metabolic profiling, we conducted a comprehensive analysis of gut microbial and metabolic alterations in lung transplant recipients relative to non-transplant group. Our findings revealed the predominance of Enterococcus and Streptococcus genera within the lung transplant cohort, accompanied by the significant reduction in Bacteroides, Epulopiscium, Faecalibacterium, and Prevotella abundance. In addition, a significant reduction in ATRA (all-trans retinoic acid) levels and suppression of IgA production were observed in lung transplant recipients, which were found to be closely associated with the Enterococcus genus. It was speculated that the association might have implications for the prognosis of lung transplant patients. Notably, the differences in gut microbial composition and metabolomic profiles between successful transplant recipients and those experiencing chronic rejection were not statistically significant. These novel insights shed light on the putative implications of the gut microbiota and metabolome in shaping lung transplantation outcomes, and provide a foundation for future investigations and targeted therapeutic interventions.

IMPORTANCE

This study has profound implications for lung transplantation as it uncovers the important role of gut microbiota and metabolome in shaping transplantation outcomes. The identification of dominant bacterial genera, such as Enterococcus and Streptococcus, within the lung transplant cohort, along with the significant decrease in Bacteroides, Epulopiscium, Faecalibacterium, and Prevotella abundance, reveals potential microbial imbalances associated with lung transplantation. In addition, a significant reduction in ATRA (all-trans retinoic acid) levels and suppression of IgA production were observed in lung transplant recipients, which were found to be closely associated with the Enterococcus genus. It was speculated that the association might have implications for the prognosis of lung transplant patients. These findings hold immense clinical significance as they lay the groundwork for future research and targeted therapeutic interventions. Understanding the impact of the gut microbiota and metabolome on lung transplantation outcomes offers promising avenues for improving transplantation patient prognosis.

In vitro inhibition of Pseudomonas aeruginosa PAO1 biofilm formation by DZ2002 through regulation of extracellular DNA and alginate production

Introduction

Pseudomonas aeruginosa (P. aeruginosa) is a common pathogen associated with biofilm infections, which can lead to persistent infections. Therefore, there is an urgent need to develop new anti-biofilm drugs. DZ2002 is a reversible inhibitor that targets S-adenosylhomocysteine hydrolase and possesses anti-inflammatory and immune-regulatory activities. However, its anti-biofilm activity has not been reported yet.

Methods and results

Therefore, we investigated the effect of DZ2002 on P. aeruginosa PAO1 biofilm formation by crystal violet staining (CV), real-time quantitative polymerase chain reaction (RT-qPCR) and confocal laser scanning microscopy (CLSM). The results indicated that although DZ2002 didn't affect the growth of planktonic PAO1, it could significantly inhibit the formation of mature biofilms. During the inhibition of biofilm formation by DZ2002, there was a parallel decrease in the synthesis of alginate and the expression level of alginate genes, along with a weakening of swarming motility. However, these results were unrelated to the expression of lasI, lasR, rhII, rhIR. Additionally, we also found that after treatment with DZ2002, the biofilms and extracellular DNA content of PAO1 were significantly reduced. Molecular docking results further confirmed that DZ2002 had a strong binding affinity with the active site of S-adenosylhomocysteine hydrolase (SahH) of PAO1.

Discussion

In summary, our results indicated that DZ2002 may interact with SahH in PAO1, inhibiting the formation of mature biofilms by downregulating alginate synthesis, extracellular DNA production and swarming motility. These findings demonstrate the potential value of DZ2002 in treating biofilm infections associated with P. aeruginosa.

Drug repurposing: insights into the antimicrobial effects of AKBA against MRSA

Staphylococcus aureus is a major threat in infectious diseases due to its varied infection types and increased resistance. S. aureus could form persister cells under certain condition and could also attach on medical apparatus to form biofilms, which exhibited extremely high resistance to antibiotics. 3-Acetyl-11-keto-beta-boswellic acid (AKBA) is a well-studied anti-tumor and antioxidant drug. This study is aimed to determine the antimicrobial effects of AKBA against S. aureus and its persister cells and biofilms. The in vitro antimicrobial susceptibility of AKBA was assessed by micro-dilution assay, disc diffusion assay and time-killing assay. Drug combination between AKBA and conventional antibiotics was detected by checkerboard assay. And the antibiofilm effects of AKBA against S. aureus were explored by crystal violet staining combined with SYTO/PI probes staining. Next, RBC lysis activity and CCK-8 kit were used to determine the cytotoxicity of AKBA. In addition, murine subcutaneous abscess model was used to assess the antimicrobial effects of AKBA in vivo. Our results revealed that AKBA was found to show effective antimicrobial activity against methicillin-resistant S. aureus (MRSA) with the minimal inhibitory concentration of 4-8 µg/mL with undetectable cytotoxicity. And no resistant mutation was induced by AKBA after 20 days of consecutive passage. Further, we found that AKBA could be synergy with gentamycin or amikacin against S. aureus and its clinical isolates. By crystal violet and SYTO9/PI staining, AKBA exhibited strong biofilm inhibitory and eradication effects at the concentration of 1 ~ 4 µg/mL. In addition, the effective antimicrobial effect was verified in vivo in a mouse model. And no detectable in vivo toxicity was found. These results indicated that AKBA has great potential to development as an alternative treatment for the refractory S. aureus infections.

Quorum Quenching with a Diffusible Signal Factor Analog in Stenotrophomonas maltophilia

Stenotrophomonas maltophilia is a multidrug-resistant Gram-negative bacillus associated with nosocomial infections in intensive care units, and nowadays, its acquired resistance to trimethoprim-sulfamethoxazole (SXT) by sul genes within class 1 integrons is a worldwide health problem. Biofilm and motility are two of the major virulence factors in this bacterium and are auto-induced by the diffusible signal factor (DSF). In recent studies, retinoids have been used to inhibit (Quorum Quenching) these virulence factors and for their antimicrobial effect. The aim was to reduce biofilm formation and motility with retinoic acid (RA) in S. maltophilia SXT-resistant strains. Eleven SXT-resistant strains and two SXT-susceptible strains were tested for biofilm formation/reduction and planktonic/sessile cell viability with RA and SXT-MIC50/RA; motility (twitching, swimming, swarming) was measured with/without RA; and MLST typing was determined. The biofilm formation of the strains was classified as follows: 15.38% (2/13) as low, 61.54% (8/13) as moderate, and 23.08% (3/13) as high. It was significantly reduced with RA and SXT-MIC50/RA (p < 0.05); cell viability was not significantly reduced with RA (p > 0.05), but it was with SXT-MIC50/RA (p < 0.05); and swimming (p < 0.05) and swarming (p < 0.05) decreased significantly. MLST typing showed the first and novel strains of Mexican S. maltophilia registered in PubMLST (ST479-485, ST497, ST23, ST122, ST175, ST212, and ST300). In conclusion, RA reduced biofilm formation and motility without affecting cell viability; furthermore, antimicrobial synergism with SXT-MIC50/RA in different and novel STs of S. maltophilia was observed.

Poultices as biofilms of titanium dioxide nanoparticles/carboxymethyl cellulose/Phytagel for cleaning of infected cotton paper by Aspergillus sydowii and Nevskia terrae

In this study, TiO2 nanoparticle (TiO2NP)-coated film was produced to protect manuscripts against microorganisms using ecofriendly benign materials. As a result, a simple method was created that uses poultice biofilm made of carboxymethyl cellulose (CMC) and Phytagel plant cell (PGP) loaded with TiO2NPs to preserve manuscripts against microbes in an environmentally responsible way. Three volumes (1, 2, 4 mL) of TiO2NPs were put into a biofilm combination to produce the poultices known as CMC/PGP/TiO2-1, CMC/PGP/TiO2-2, and CMC/PGP/TiO2-3. The synthesized TiO2NPs were nearly spherical in shape, small in size (98 nm), and stable (zeta potential value - 33 mV). The results showed that the unique deposition of TiO2NPs on the biofilm surface gave the produced films loaded with TiO2NPs a rough structure. The highest values of mechanical characteristics were determined to be in CMC/PGP/TiO2-1 with values of 25.4 g, 6.6 MPa, and 11.4%, for tensile strength, elongation at break, and tear strength, respectively. Based on molecular identification, the fungus Aspergillus sydowii and the bacterium Nevskia terrae, with accession numbers MG991624 and AB806800, respectively, were isolated and identified from an antiquated manuscript formed from cellulosic fibers. Before the experiments, the produced cotton paper samples were aged, and then, one group was infected for 6 months by A. sydowii and the second group with N. terrae. Following the preparation of a CMC/PGP biofilm loaded with various volumes of TiO2NPs, poultices were applied to infected cotton paper in order to clean it. The infected cotton paper was placed inside the sandwich-like poultices that were created. The poultice CMC/PGP/TiO2-2 demonstrated potential for preventing the growth of A. sydowii and N. terrae-infected cotton paper, when the fibers were saved, cleaned, and coated with CMC/PGP/TiO2-2 after absorbing the fungus and the bacterium and exhibiting exceptional antimicrobial activities. Finally, the novel biofilms have demonstrated their capacity to lessen microbial contamination of cotton paper. In order to generalize the usage of these poultices, it is also advised that they be produced on a large scale and tested on a variety of organic materials in the future.

Non-Antibiotic Compounds Synergistically Kill Chronic Wound-Associated Bacteria and Disrupt Their Biofilms

Chronic wounds and their treatment present a significant burden to patients and healthcare systems alike, with their management further complicated by bacterial infection. Historically, antibiotics have been deployed to prevent and treat infections, but the emergence of bacterial antimicrobial resistance and the frequent development of biofilms within the wound area necessitates the identification of novel treatment strategies for use within infected chronic wounds. Here, several non-antibiotic compounds, polyhexamethylene biguanide (PHMB), curcumin, retinol, polysorbate 40, ethanol, and D-α-tocopheryl polyethylene glycol succinate 1000 (TPGS) were screened for their antibacterial and antibiofilm capabilities. The minimum inhibitory concentration (MIC) and crystal violet (CV) biofilm clearance against two bacteria frequently associated with infected chronic wounds, Staphylococcus aureus and Pseudomonas aeruginosa, were determined. PHMB was observed to have highly effective antibacterial activity against both bacteria, but its ability to disperse biofilms at MIC levels was variable. Meanwhile, TPGS had limited inhibitory activity but demonstrated potent antibiofilm properties. The subsequent combination of these two compounds in a formulation resulted in a synergistic enhancement of their capability to kill both S. aureus and P. aeruginosa and disperse their biofilms. Collectively, this work highlights the utility of combinatory approaches to the treatment of infected chronic wounds where bacterial colonization and biofilm formation remains significant issues.

Repurposing CD5789 as an Antimicrobial Agent Against MRSA and Its High Resistant Phonotypes

Methicillin-resistant Staphylococcus aureus (MRSA) poses a great threat to human health, and the formation of biofilm and persister cells make the situation even worse. Drug repurposing is an effective way to solve this problem by shortening the drug development times and reducing the research costs. In this study, CD5789 (trifarotene), a fourth-generation retinoid to be approved by the FDA in 2019 for the topical acne vulgaris regimens, was exhibited antimicrobial activity against MRSA type strains and its clinical isolates with the minimal concentration (MIC) of 2-4 μg/mL and 4-16 μg/mL, respectively, in a dose-dependent manner. By crystal violet staining, we found that CD5789 could inhibit the biofilm formation by MRSA and could further eradicate the pre-formed biofilm at the concentration of 8 μg/mL. By checkerboard dilution assay, sub-MIC of CD5789 showed synergistic antimicrobial effects with sub-MIC of gentamycin against MRSA type strains as well as clinical isolates. In addition, CD5789 also exhibited effective bactericidal activity against MRSA persister cells at the concentration of 8 ~ 16 μg/mL. Extremely low cytotoxicity of CD5789 was observed by CCK-8 assay indicated the well tolerability to human body. In all, CD5789 has the potential to be an alternative for the treatment of refractory MRSA-related infections.

The small RNA PrrH of Pseudomonas aeruginosa regulates hemolysis and oxidative resistance in bloodstream infection

Small regulatory RNAs (sRNAs) regulate multiple physiological functions in bacteria, and sRNA PrrH can regulate iron homeostasis and virulence. However, the function of PrrH in Pseudomonas aeruginosa (P. aeruginosa) bloodstream infection (BSI) is largely unknown. The aim of this study was to investigate the role of PrrH in P. aeruginosa BSI model. First, P. aeruginosa PAO1 was co-cultured with peripheral blood cells for 6 h qRT-PCR results showed a transient up-regulation of PrrH expression at 1 h. Simultaneously, the expression of iron uptake genes fpvA, pvdS and phuR was upregulated. In addition, the use of iron chelator 2,2'-dipyridyl to create low-iron conditions caused up-regulation of PrrH expression, a result similar to the BSI model. Furthermore, the addition of FeCl3 was found to decrease PrrH expression. These results support the hypothesis that the expression of PrrH is regulated by iron in BSI model. Then, to clarify the effect of PrrH on major cells in the blood, we used PrrH mutant, overexpressing and wild-type strains to act separately on erythrocytes and neutrophils. On one hand, the hemolysis assay revealed that PrrH contributes to the hemolytic activity of PAO1, and its effect was dependent on the T3SS system master regulator gene exsA, yet had no association with the hemolytic phospholipase C (plcH), pldA, and lasB elastase genes. On the other hand, PrrH mutant enhanced the oxidative resistance of PAO1 in the neutrophils co-culture assay, H2O2-treated growth curve and conventional plate spotting assays. Furthermore, the katA was predicted to be a target gene of PrrH by bioinformatics software, and then verified by qPCR and GFP reporter system. In summary, dynamic changes in the expression of prrH are iron-regulated during PAO1 bloodstream infection. In addition, PrrH promotes the hemolytic activity of P. aeruginosa in an exsA-dependent manner and negatively regulates katA to reduce the oxidative tolerance of P. aeruginosa.

Biological Evaluation of the Antibacterial Retinoid CD437 in Cutibacterium acnes Infection

Acne vulgaris is a complex skin disease involving infection by Cutibacterium acnes, inflammation, and hyperkeratinization. We evaluated the activity of the retinoid 6-[3-(adamantyl)-4-hydroxyphenyl]-2-naphthalene carboxylic acid (CD437) and 16 other retinoid analogs as potential anti-C. acnes compounds and found that CD437 displayed the highest antimicrobial activity with an MIC against C. acnes (ATCC 6919 and HM-513) of 1 μg/mL. CD437 demonstrated an MBC of 2 μg/mL compared to up to 64 μg/mL for the retinoid adapalene and up to 16 μg/mL for tetracycline, which are commonly used clinically to treat acne. Membrane permeability assays demonstrated that exposure of C. acnes ATCC 6919 to CD437 damaged the integrity of C. acnes ATCC 6919 bacterial membranes, and this finding was confirmed with scanning electron microscopy. Additionally, CD437 downregulated the expression of C. acnes ATCC 6919 virulence factors, including the genes encoding Christie-Atkins-Munch-Petersen factor 1 (CAMP1), CAMP2, glycerol-ester hydrolase B (GehB), sialidase B, and neuraminidase. In a mouse skin infection model of C. acnes ATCC 6919, topical treatment with CD437 ameliorated skin lesions and reduced the bacterial burden in situ (P < 0.001). In human NHEK primary cells, CD437 reduced the transcriptional levels of the coding genes for inflammatory cytokines (interleukin-1α, ~10-fold; interleukin-6, ~20-fold; interleukin-8, ~30-fold; and tumor necrosis factor-alpha, ~6-fold) and downregulated the transcriptional levels of KRT10 (~10-fold), FLG (~4-fold), and TGM1 (~2-fold), indicating that CD437 can diminish inflammation and hyperkeratinization. In summary, CD437 deserves further attention for its dual function as a potential acne therapeutic that potentially acts on both the pathogen and the host.

Bactericidal synergism between phage endolysin Ply2660 and cathelicidin LL-37 against vancomycin-resistant Enterococcus faecalis biofilms

Antibiotic resistance and the ability to form biofilms of Enterococcus faecalis have compromised the choice of therapeutic options, which triggered the search for new therapeutic strategies, such as the use of phage endolysins and antimicrobial peptides. However, few studies have addressed the synergistic relationship between these two promising options. Here, we investigated the combination of the phage endolysin Ply2660 and the antimicrobial peptide LL-37 to target drug-resistant biofilm-producing E. faecalis. In vitro bactericidal assays were used to demonstrate the efficacy of the Ply2660-LL-37 combination against E. faecalis. Larger reductions in viable cell counts were observed when Ply2660 and LL-37 were applied together than after individual treatment with either substance. Transmission electron microscopy revealed that the Ply2660-LL-37 combination could lead to severe cell lysis of E. faecalis. The mode of action of the Ply2660-LL-37 combination against E. faecalis was that Ply2660 degrades cell wall peptidoglycan, and subsequently, LL-37 destroys the cytoplasmic membrane. Furthermore, Ply2660 and LL-37 act synergistically to inhibit the biofilm formation of E. faecalis. The Ply2660-LL-37 combination also showed a synergistic effect for the treatment of established biofilm, as biofilm killing with this combination was superior to each substance alone. In a murine peritoneal septicemia model, the Ply2660-LL-37 combination distinctly suppressed the dissemination of E. faecalis isolates and attenuated organ injury, being more effective than each treatment alone. Altogether, our findings indicate that the combination of a phage endolysin and an antimicrobial peptide may be a potential antimicrobial strategy for combating E. faecalis.

Identification of a small molecule 0390 as a potent antimicrobial agent to combat antibiotic-resistant Escherichia coli

Introduction

Antibiotic resistance has posed a serious challenge to global public health. With the increasing resistance emergence of E. coli and mortality caused by drug-resistant E. coli infections, it is urgent to develop novel antibiotics.

Methods

By high-throughput screening assay, we found a bioactive molecule, 0390 (6056-0390), which demonstrated antimicrobial effects against E. coli. The antimicrobial effects of 0390 alone or in combination with conventional antibiotics were assessed by scanning electron microscopy, transmission electron microscopy, drug combination assay, and growth inhibition assay. In addition, we investigated the antimicrobial efficacy in subcutaneous infection model in vivo.

Results

0390 showed significant synergistic antimicrobial effects in combination with SPR741, a polymyxin B derivative, against E. coli standard strain and extensively drug-resistant (XDR) clinical isolates, and the combination exhibited good safety property in vitro. In addition, we demonstrated that the combinational treatment of 0390 and SPR741 exhibited a considerable antibacterial activity in vivo, and no tissue damage or other toxicity was observed after the therapeutic dose treatment.

Discussion

To confront the issue of the infectious diseases related to E. coli and its multidrug resistant strains, potential approaches, such as new antibacterial agents with different structures from conventional antibiotics and drug combinations, are urgently needed. In this study, we have determined the in vitro and in vivo antimicrobial potential of 0390 alone or in combination with SPR741, which might be used as a treatment option for E. coli related infections.

Insights into the antimicrobial effects of ceritinib against Staphylococcus aureus in vitro and in vivo by cell membrane disruption

According to a 2019 report from the Centers of Disease Control and Prevention (CDC), methicillin-resistant Staphylococcus aureus (MRSA) was listed as one of the “serious threats” that had become a global public challenge in hospitals and community. Biofilm-associated infections and refractory persisters of S. aureus also impede the effectiveness of conventional antibiotics that have greatly increased difficulty in clinical therapy. There is an urgent need to develop new antimicrobials with antibiofilm and anti-persister capacities, and drug repurposing is the most effective and most economical solution to the problem. The present study profiles the antimicrobial activity of ceritinib, a tyrosine kinase inhibitor, against S. aureus in vitro and in vivo. We investigated the antimicrobial efficacy of ceritinib against planktonic and persistent S. aureus by a time-killing kinetics assay. Then, antibiofilm effect of ceritinib was assessed by crystal violet staining and laser confocal microscope observation. Ceritinib showed biofilm inhibition and mature biofilm eradication, and possesses robust bactericidal activity against S. aureus persisters. We also evaluated antimicrobial efficacy in vivo using a subcutaneous abscess infection model. Ceritinib ameliorated infection in a subcutaneous abscess mouse model and only showed negligible systemic toxicity in vivo. Mechanism exploration was conducted by transmission electron microscopy, fluorescently labeled giant unilamellar vesicle assays, and a series of fluorescent dyes. In conclusion, we find ceritinib represents potential bactericidal activity against MRSA by disrupting cell membrane integrity and inducing reactive oxygen species production, suggesting ceritinib has the potential to treat MRSA-related infections.

Antimicrobial activity of CT-K3K7, a modified peptide by lysine substitutions from ctry2459 - A Chaerilus tryznai scorpion venom peptide

Antimicrobial peptides (AMPs) have started to garner more interest as novel antimicrobial agents. The scorpion venom peptide ctry2459 was modified to CT-K3K7 by lysine substitutions at the 3rd and 7th positions to increase the cationic properties. We discovered that the modified peptides CT-K3K7 had improved antibacterial activity, higher thermal stability, as well as lower hemolytic activity. It can kill S. aureus and P. aeruginosa rapidly, and reduce the production of biofilm and live bacterial residues in biofilm in vitro. CT-K3K7 has also been demonstrated to decrease bacterial counts, abscess area, and inflammatory cell infiltration in the mouse subcutaneous abscess models that were duplicated by S. aureus and P. aeruginosa. CT-K3K7 has difficulty in inducing S. aureus and P. aeruginosa to develop drug resistance, which may be related to the bactericidal properties. CT-K3K7 increases cationic properties by lysine substitutions can increase the electrostatic force between the peptides and the bacterial surface, which can lead to an increase in bacterial membrane permeability and DNA binding. In conclusion, the modified peptide CT-K3K7 enhances the antimicrobial activity and can be a novel antimicrobial agent candidate for the treatment of infections by S. aureus and P. aeruginosa.

SPR741, Double- or Triple-Combined With Erythromycin and Clarithromycin, Combats Drug-Resistant Klebsiella pneumoniae, Its Biofilms, and Persister Cells

Klebsiella pneumoniae has emerged as a major clinical and public health threat owing to the increasing prevalence of healthcare-associated infections caused by multidrug-resistant or extensively drug-resistant strains. However, increasing antibiotic resistance and the absence of clinically effective antimicrobial agents make combination therapy an urgent need. This study investigated the anti-microbial activity of SPR741, a polymyxin B derivative, in combination with macrolide antibiotics (erythromycin and clarithromycin), against extensively drug-resistant and pandrug-resistant K. pneumoniae. Monotherapy, double, and triple combination therapies were performed to identify the most effective treatment combination using in vitro checkerboard, time-killing kinetics. Furthermore, we evaluated the biofilm eradication and persister cell-killing activity of these combinations using laser confocal microscopy and colony forming unit counting. In addition, a neutropenic mouse thigh infection model was used to assess the therapeutic efficacy and toxicity of the triple antibiotic combination against pandrug-resistant K. pneumoniae in vivo. Our results suggested that SPR741 combined with macrolides exhibited strong synergistic antibacterial activity against extensively drug-resistant and pandrug-resistant K. pneumoniae. These antibiotic combinations could also effectively eradicate highly resistant bacterial biofilms and persister cells in vitro and demonstrate considerable efficacy and low toxicity in vivo. In summary, our findings indicated that SPR741, in combination with macrolide antibiotics (double or triple combination), has the potential to serve as a novel treatment option against drug-resistant K. pneumoniae -related infections.

A novel bactericidal small molecule, STK-35, and its derivative, STK-66, as antibacterial agents against Gram-negative pathogenic bacteria in vitro and in vivo

Due to the increasing rate of antibiotic resistance and the emergence of persister cells of Gram-negative pathogenic bacteria, the development of new antibacterial agents is urgently needed to deal with this problem. Our results indicated that both newly identified small molecule STK-35 and its derivative STK-66 exhibited effective antibacterial properties against a variety of Gram-negative pathogens including A. baumannii, E. coli, K. pneumoniae and P. aeruginosa. The minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) ranges were 0.0625-8 μg mL^-1 and 0.125-16 μg mL^-1 respectively, while no hemolytic activity and mammalian cell cytotoxicity were observed. The time-killing assays showed STK-35/66 had strong bactericidal activity against Gram-negative pathogens. STK-35/66 also showed different degrees of synergistic antibacterial activity with conventional antibiotics and exhibited persister cells killing activity. Moreover, STK-35/66 effectively eradicated the pre-formed biofilms of P. aeruginosa and A. baumannii. In addition, STK-35/66 significantly increased the survival rate of E. coli infected mice and induced a decrease in bacterial load of the peritonitis model. In nutshell, these results suggested that STK-35/66 possessed antimicrobial activity against Gram-negative pathogenic bacteria in vitro and in vivo, which could be considered as potential substitutes for the treatment of Gram-negative pathogenic infections after further structure optimization.

Evaluation of the antibacterial effect of tea tree oil on Enterococcus faecalis and biofilm in vitro

ETHNOPHARMACOLOGICAL RELEVANCE

Tea tree essential oil (TTO) is extracted from the leaves of Melaleuca alternifolia by steam distillation. It is well known for its traditional medicinal uses, particularly for the treatment of bruises, insect bites, skin infections, vertigo, convulsions, toothache, and rheumatism. Earlier research has shown that TTO can effectively inhibit oral microorganisms in the root canals. Enterococcus faecalis (E. faecalis) has been considered to be associated with persistent root canal infections and root canal treatment failure. The biofilm of E. faecalis makes it more vigorous, toxic, and resistant to antibiotics.

AIM OF THE STUDY

In this study, our aim was to evaluate the antimicrobial effects of TTO on planktonic E. faecalis and biofilms compared with 0.2% CHX.

MATERIALS AND METHODS

We explored the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC), the bacteriostatic rate by MTT assay, the antimicrobial time by time-kill assay, and the effects on cell integrity, the biomass, and bacterial activity of E. faecalis biofilms. Finally, we investigated the microstructure changes of E. faecalis biofilms using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM).

RESULTS

The MIC and MBC values were 0.25% and 0.5%, the bacterial inhibition rate, time-kill was dosage dependent, and TTO can effectively destroy membrane integrity. SEM CLSM images revealed that TTO could reduce bacterial aggregation, biofilm thickness and inhibited biofilm formation. The effect of TTO was the same as that of 0.2% CHX at some specific concentrations. In summary, TTO has the potential to be effective against E. faecalis infections.

CONCLUSIONS

TTO was able to inhibit E. faecalis by destroying cell membrane, inhibiting the formation of E. faecalis biofilms, and eliminating mature formed biofilms. In this study, TTO has the potential to be further developed as a novel antibacterial drug.

Inhibitory effects of 1,3-diaminopropane on the biofilm formation of Pseudomonas aeruginosa via interaction with quorum sensing system

OBJECTIVES

To study the inhibitory effects of 1,3-diaminopropane on the biofilm formation of Pseudomonas aeruginosa and the underlying mechanisms.

METHODS

The experiment was divided into an experimental group and a control group. Crystal violet staining was used to examine the inhibitory effects of 1,3-diaminopropane on the biofilm formation of Pseudomonas aeruginosa, and the biofilm formation was compared between the 2 groups.Initial adherence inhibition assay and swimming plate assay were used to determine the inhibitory effects of 1,3-diaminopropane on the initial adherence and swimming motility of Pseudomonas aeruginosa,and the quantification of adhered cells and swimming diameter were compared between the 2 groups. Meanwhile, Western blotting was used to detect the Flagellin production of Pseudomonas aeruginosa; real-time RT-PCR was used to detect the quorum sensing system relative genes and flagellum regulative related genes expression in the 2 groups. Finally, molecular docking assay was used to calculate the interaction between 1,3-diaminopropane and LasI.

RESULTS

Compared with the control group, the biofilm formation of Pseudomonas aeruginosa was significantly inhibited in the experimental group in a dose-dependent manner (t=6.07, P<0.01).Compared with the control group, the initial adherence of Pseudomonas aeruginosa could significantly inhibit from (0.890±0.389)×106 to (0.245±0.076)×106 CFU/mL (t=3.257, P<0.05) in the experimental group (2.0 mmol/L).Compared with the control group, the swimming motility of Pseudomonas aeruginosa flagellar mediation could also inhibit in the experimental group (2.0 mmol/L). The swimming motility diameter was from (1.840±0.144) to (0.756±0.222) cm (t=7.099, P<0.01). Compared with the control group, the Flagellin production was inhibited in the experimental group. Finally, the molecular docking assay showed that the potential target of 1,3-diaminopropane was LasI.

CONCLUSIONS

1,3-diaminopropane can significantly inhibit the biofilm formation of Pseudomonas aeruginosa, which potentially targets LasI protein.

Repurposing Candesartan Cilexetil as Antibacterial Agent for MRSA Infection

Staphylococcus aureus is an important pathogen causing hospital-acquired infections. Methicillin-resistant S. aureus (MRSA), biofilms, and persisters are highly tolerant to traditional antibiotics and make it difficult to treat. Therefore, new antimicrobial agents are urgently needed to treat hard-to-eradicate diseases caused by this bacterium. In this study, candesartan cilexetil (CC), an angiotensin hypertension drug, had strong antimicrobial activity against S. aureus with minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) of 8-16 μg/ml and 16-32 μg/ml. CC exhibited limited cytotoxicity and low potential to induce drug resistance. In addition, it showed a synergistic antibacterial effect when combined with gentamicin and tobramycin. The effective concentrations to inhibit MRSA biofilm formation were 16-64 μg/ml, and intractable persisters were killed at 4-8 × MIC. Through the analysis of its mechanism of action, it was evident that the membrane permeability was disrupted as well as the cell structure was damaged. Furthermore, we demonstrated that CC had antibacterial effects in vivo in MRSA-infected murine skin abscess models. In conclusion, these results imply that CC might be a potential antibacterial agent for the treatment of S. aureus-associated infections.

Retinoids in Fungal Infections: From Bench to Bedside

Retinoids-a class of chemical compounds derived from vitamin A or chemically related to it-are used especially in dermatology, oncohematology and infectious diseases. It has been shown that retinoids-from their first generation-exert a potent antimicrobial activity against a wide range of pathogens, including bacteria, fungi and viruses. In this review, we summarize current evidence on retinoids' efficacy as antifungal agents. Studies were identified by searching electronic databases (MEDLINE, EMBASE, PubMed, Cochrane, Trials.gov) and reference lists of respective articles from 1946 to today. Only articles published in the English language were included. A total of thirty-nine articles were found according to the criteria. In this regard, to date, In vitro and In vivo studies have demonstrated the efficacy of retinoids against a broad-spectrum of human opportunistic fungal pathogens, including yeast fungi that normally colonize the skin and mucosal surfaces of humans such as Candida spp., Rhodotorula mucilaginosa and Malassezia furfur, as well as environmental moulds such as Aspergillus spp., Fonsecae monofora and many species of dermatophytes associated with fungal infections both in humans and animals. Notwithstanding a lack of double-blind clinical trials, the efficacy, tolerability and safety profile of retinoids have been demonstrated against localized and systemic fungal infections.

Antimicrobial, Antibiofilm, and Anti-persister Activities of Penfluridol Against Staphylococcus aureus

Staphylococcus aureus has increasingly attracted global attention as a major opportunistic human pathogen owing to the emergence of biofilms (BFs) and persisters that are known to increase its antibiotic resistance. However, there are still no effective antimicrobial agents in clinical settings. This study investigated the antimicrobial activity of penfluridol (PF), a long-acting antipsychotic drug, against S. aureus and its clinical isolates via drug repurposing. PF exhibited strong bactericidal activity against S. aureus, with a minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 4–8 and 16–32 μg/ml, respectively. PF could significantly inhibit biofilm formation and eradicate 24 h preformed biofilms of S. aureus in a dose-dependent manner. Furthermore, PF could effectively kill methicillin-resistant S. aureus (MRSA) persister cells and demonstrated considerable efficacy in a mouse model of subcutaneous abscess, skin wound infection, and acute peritonitis caused by MRSA. Notably, PF exerted almost no hemolysis activity on human erythrocytes, with limited cytotoxicity and low tendency to cause resistance. Additionally, PF induced bacterial membrane permeability and ATP release and further caused membrane disruption, which may be the underlying antibacterial mechanism of PF. In summary, our findings suggest that PF has the potential to serve as a novel antimicrobial agent against S. aureus biofilm- or persister-related infections.

Review on the Antibacterial Mechanism of Plant-Derived Compounds against Multidrug-Resistant Bacteria (MDR)

Microbial resistance has progressed rapidly and is becoming the leading cause of death globally. The spread of antibiotic-resistant microorganisms has been a significant threat to the successful therapy against microbial infections. Scientists have become more concerned about the possibility of a return to the pre-antibiotic era. Thus, searching for alternatives to fight microorganisms has become a necessity. Some bacteria are naturally resistant to antibiotics, while others acquire resistance mainly by the misuse of antibiotics and the emergence of new resistant variants through mutation. Since ancient times, plants represent the leading source of drugs and alternative medicine for fighting against diseases. Plants are rich sources of valuable secondary metabolites, such as alkaloids, quinones, tannins, terpenoids, flavonoids, and polyphenols. Many studies focus on plant secondary metabolites as a potential source for antibiotic discovery. They have the required structural properties and can act by different mechanisms. This review analyses the antibiotic resistance strategies produced by multidrug-resistant bacteria and explores the phytochemicals from different classes with documented antimicrobial action against resistant bacteria, either alone or in combination with traditional antibiotics.

Antibacterial activity of noscapine analogs

The antibacterial properties of close noscapine analogs have not been previously reported. We used our pDualrep2 double-reporter High Throughput Screening (HTS) platform to identify a series of noscapine derivatives with promising antibacterial activity. The platform is based on RPF (SOS-response/DNA damage) and Katushka2S (inhibition of translation) proteins and simultaneously provides information on antibacterial activity and the mechanism of action of small-molecule compounds against E. coli. The most potent compound exhibited an MIC of 13.5 µM(6.25 µg/ml) and a relatively low cytotoxicity against HEK293 cells (CC₅₀ = 71 µM, selectivity index: ~5.5). Some compounds from this series induced average Katushka2S reporter signals, indicating inhibition of translation machinery in the bacteria; however, these compounds did not attenuate translation in vitro in a luciferase-based translation assay. The most effective compounds did not significantly arrest the mitotic cycle in HEK293 cells, in contrast to the parent compound in a flow cytometry assay. Several molecules showed activity against clinically relevant gram-negative and gram-positive bacterial strains. Compounds from the discovered series can be reasonably regarded as good templates for further development and evaluation.

Drug repurposing: Antimicrobial and antibiofilm effects of penfluridol against Enterococcus faecalis

The bacterium Enterococcus faecalis has increasingly attracted global attention as an important opportunistic pathogen due to its ability to form biofilms that are known to increase drug resistance. However, there are still no effective antibiofilm drugs in clinical settings. Here, by drug repurposing, we investigated the antibacterial activity of penfluridol (PF), an oral long‐acting antipsychotic approved by the FDA, against E. faecalis type strain and its clinical isolates. It was found that PF inhibited the growth of E. faecalis planktonic cells with the MIC and MBC of 7.81 µg/ml and 15.63 ~ 62.50 µg/ml, respectively. Moreover, PF could significantly prevent the biofilm formation of E. faecalis at the concentration of 1 × MIC. Furthermore, PF significantly eradicated 24 h pre‐formed biofilms of E. faecalis in a dose‐dependent manner, with a concentration range of 1 × MIC to 8 × MIC. Here, through the checkerboard method with other tested conventional antibiotics, we also determined that gentamycin, penicillin G, and amikacin showed partial synergistic antibacterial effects with PF. Also, PF showed almost no hemolysis on human erythrocytes. In a mouse peritonitis model, a single dose of 20 mg/kg of PF treatment could significantly reduce the bacterial colonization in the liver (~5‐fold reduction) and spleen (~3‐fold reduction). In conclusion, these findings indicated that after structural optimization, PF has the potential as a new antibacterial agent against E. faecalis.

Recent Advances Regarding the Therapeutic Potential of Adapalene

Adapalene (ADP) is a representative of the third retinoids generation and successfully used in first-line acne treatment. ADP binds to retinoic acid nuclear receptors. The comedolytic, anti-inflammatory, antiproliferative, and immunomodulatory are the known ADP effects. Its safety profile is an advantage over other retinoids. ADP recently was found to be effective in the treatment of several dermatological diseases and photoaging besides the utility in the treatment of acne vulgaris. New biological effects of adapalene with therapeutic potential are highlighted in this review paper. Thus, adapalene could be a valuable therapeutic drug into the treatment of several types of cancer. Additionally, some neurodegenerative diseases could be treated with a suitable formulation for intravenous administration. The antibacterial activity against methicillin-resistant Staphylococcus aureus of an analogue of ADP has been proven. In different therapeutic schemes, ADP is more effective in combination with other active substances. New topical combinations with adapalene include ketoconazole (antifungal), mometasone furoate (anti-inflammatory corticosteroid), nadifloxacin (fluoroquinolone), and alfa and beta hydroxy acids. Combination with oral drugs is a new trend that enhances the properties of topical formulations with adapalene. Several studies have investigated the effects of ADP in co-administration with azithromycin, doxycycline, faropenem, isotretinoin, and valganciclovir. Innovative formulations of ADP also aim to achieve a better bioavailability, increased efficacy, and reduced side effects. In this review, we have highlighted the current studies on adapalene regarding biological effects useful in various treatment types. Adapalene has not been exploited yet to its full biological potential.

Repurposing Antispasmodic Agent Otilonium Bromide for Treatment of Staphylococcus aureus Infections

Recently, the problem of bacterial resistance has been brought into focus, which makes the development of new antibiotics become a necessity. Compared with traditional development approaches, drug repurposing provides a faster and more effective approach to find new antimicrobial agents. In this study, we found that antispasmodic agent otilonium bromide had strong antibacterial ability and bactericidal activity against Staphylococcus aureus, with minimal inhibitory concentrations (MICs) of 4-8 μg/ml, and bacteria could be killed completely after treatment with 2× MIC of otilonium bromide for 5 h. Furthermore, it had a potent effect on eradicating biofilm at concentrations ranging from 16 to 64 μg/ml. At the same time, it had low tendency to develop resistance and possessed limited cytotoxicity. In the methicillin-resistant S. aureus-infected mouse peritonitis model, it was also effective to cure mice and improve their survival rate. In addition, we observed that otilonium bromide changed the permeability of bacterial membrane and caused membrane damage, and it is probably the antibacterial mechanism of otilonium bromide. Taken together, our results indicated that otilonium bromide could be a new antimicrobial agent to treat S. aureus infections more safely and efficiently.