Bile Acid Oligomers and Their Combination with Antibiotics To Combat Bacterial Infections

Xanthone Derivatives Enhance the Therapeutic Potential of Neomycin against Polymicrobial Gram-Negative Bacterial Infections

Gram-negative bacterial infections are difficult to manage as many antibiotics are ineffective owing to the presence of impermeable bacterial membranes. Polymicrobial infections pose a serious threat due to the inadequate efficacy of available antibiotics, thereby necessitating the administration of antibiotics at higher doses. Antibiotic adjuvants have emerged as a boon as they can augment the therapeutic potential of available antibiotics. However, the toxicity profile of antibiotic adjuvants is a major hurdle in clinical translation. Here, we report the design, synthesis, and biological activities of xanthone-derived molecules as potential antibiotic adjuvants. Our SAR studies witnessed that the p-dimethylamino pyridine-derivative of xanthone (X8) enhances the efficacy of neomycin (NEO) against Escherichia coli and Pseudomonas aeruginosa and causes a synergistic antimicrobial effect without any toxicity against mammalian cells. Biochemical studies suggest that the combination of X8 and NEO, apart from inhibiting protein synthesis, enhances the membrane permeability by binding to lipopolysaccharide. Notably, the combination of X8 and NEO can disrupt the monomicrobial and polymicrobial biofilms and show promising therapeutic potential against a murine wound infection model. Collectively, our results unveil the combination of X8 and NEO as a suitable adjuvant therapy for the inhibition of the Gram-negative bacterial infections.

Cholic Acid-Derived Gemini Amphiphile Can Eradicate Interkingdom Polymicrobial Biofilms and Wound Infections

Biofilm infections are mainly caused by Gram-positive bacteria (GPB) like Staphylococcus aureus, Gram-negative bacteria (GNB) like Pseudomonas aeruginosa, and fungi like Candida albicans. These infections are responsible for antimicrobial tolerance, and commensal interactions of these microbes pose a severe threat to chronic infections. Treatment therapies against biofilm infections are limited to eradicating only 20-30% of infections. Here, we present the synthesis of a series of bile acid-derived molecules using lithocholic acid, deoxycholic acid, and cholic acid where two bile acid molecules are tethered through 3'-hydroxyl or 24'-carboxyl terminals with varying spacer length (trimethylene, pentamethylene, octamethylene, and dodecamethylene). Our structure-activity relationship investigations revealed that G21, a cholic acid-derived gemini amphiphile having trimethylene spacer tethered through the C24 position, is a broad-spectrum antimicrobial agent. Biochemical studies witnessed that G21 interacts with negatively charged lipoteichoic acid, lipopolysaccharide, and phosphatidylcholine moieties of GPB, GNB, and fungi and disrupts the microbial cell membranes. We further demonstrated that G21 can eradicate polymicrobial biofilms and wound infections and prevent bacteria and fungi from developing drug resistance. Therefore, our findings revealed the potential of G21 as a versatile antimicrobial agent capable of effectively targeting polymicrobial biofilms and wound infections, suggesting that it is a promising antimicrobial agent for future applications.

Facial amphiphilic naphthoic acid-derived antimicrobial polymers against multi-drug resistant gram-negative bacteria and biofilms

Inspired by the facial amphiphilic nature and antimicrobial efficacy of many antimicrobial peptides, this work reported facial amphiphilic bicyclic naphthoic acid derivatives with different ratios of charges to rings that were installed onto side chains of poly(glycidyl methacrylate). Six quaternary ammonium-charged (QAC) polymers were prepared to investigate the structure-activity relationship. These QAC polymers displayed potent antibacterial activity against various multi-drug resistant (MDR) gram-negative pathogens such as Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Acinetobacter baumannii. Polymers demonstrated low hemolysis and high antimicrobial selectivity. Additionally, they were able to eradicate established biofilms and kill metabolically inactive dormant cells. The membrane permeabilization and depolarization results indicated a mechanism of action through membrane disruption. Two lead polymers showed no resistance from MDR-P. aeruginosa and MDR-K. pneumoniae. These facial amphiphiles are potentially a new class of potent antimicrobial agents to tackle the antimicrobial resistance for both planktonic and biofilm-related infections.

Prophylactic vs. Therapeutic Effect of Probiotics on the Inflammation Mediated by the NF-κB Pathway in Inflammatory Bowel Conditions

Probiotic supplements consumed adequately at the proper time can affect health by modulating inflammatory pathways in gastrointestinal epithelial cells and modifying the resultant inflammatory response. The current study applied in vitro models to investigate the effectiveness of probiotics in modulating inflammatory pathways and altering inflammatory gene expression in gastrointestinal epithelial cells, with the ultimate goal of promoting probiotic consumption as a therapeutic and preventive measure for chronic inflammatory bowel conditions. HT-29 cells were treated with Gram-negative bacteria to evaluate the changes in pathways related to inflammation activities before and after treatment with a Lactobacillus spp. cocktail (L. plantarum, L. rhamnosus, L. brevis, and L. ruteri) and a Bifidobacterium spp. cocktail (B. bifidum, B. langum, and B. breve) using the real-time PCR method and ELISA for IL-1β and IL-6 as pro-inflammatory cytokines. The results showed that the expression of NF-κB signaling pathway genes and IL-1β and IL-6 cytokines increased after exposure to Gram-negative components. In contrast, all probiotic combinations significantly decreased the expression of genes and the secretion of cytokines. However, this decrease was significantly smaller in cells that underwent probiotic treatment after inflammation induction. In addition, cocktails containing combined Lactobacillus and Bifidobacterium demonstrated robust anti-inflammatory activity relative to solo cocktails. Our observations confirm that probiotic consumption could positively impact inflammatory conditions and alleviate inflammatory symptoms; they can be particularly effective as a preventive measure. Our study provides preliminary evidence to support the lifetime consumption of probiotics.

Investigation of α,ω-Disubstituted Polyamine-Cholic Acid Conjugates Identifies Hyodeoxycholic and Chenodeoxycholic Scaffolds as Non-Toxic, Potent Antimicrobials

With the increased incidence of antibiotic resistance, the discovery and development of new antibacterials is of increasing importance and urgency. The report of the natural product antibiotic squalamine in 1993 has stimulated a lot of interest in the study of structurally simplified cholic acid-polyamine derivatives. We report the synthesis of a focused set of deoxycholic acid-polyamine conjugates and the identification of hyodeoxycholic acid derivatives as being potently active towards S. aureus MRSA and some fungal strains, but with no attendant cytotoxicity or hemolytic properties. Analogue 7e exhibited bactericidal activity towards a range of Gram-positive bacteria, while preliminary investigation of its mechanism of action ruled out the bacterial membrane as being a primary cellular target as determined using an ATP-release bioluminescence assay.

Facial amphiphilicity index correlating chemical structures with antimicrobial efficacy

Facial amphiphilicity is an extraordinary chemical structure feature of a variety of antimicrobial peptides and polymers. Vast efforts have been dedicated to small molecular, macromolecular and dendrimer-like systems to mimic this highly preferred structure or conformation, including local facial amphiphilicity and global amphiphilicity. This work conceptualizes Facial Amphiphilicity Index (FAI) as a numerical value to quantitatively characterize the measure of chemical compositions and structural features in dictating antimicrobial efficacy. FAI is a ratio of numbers of charges to rings, representing both compositions of hydrophilicity and hydrophobicity. Cationic derivatives of multicyclic compounds were evaluated as model systems for testing antimicrobial selectivity against Gram-negative and Gram-positive bacteria. Both monocyclic and bicyclic compounds are non-antimicrobial regardless of FAIs. Antimicrobial efficacy was observed with systems having larger cross-sectional areas including tricyclic abietic acid and tetracyclic bile acid. While low and high FAIs respectively lead to higher and lower antimicrobial efficacy, in consideration of cytotoxicity, the sweet spot is typically suited with intermediate FAIs for each specific system. This can be well explained by the synergistic hydrophobic-hydrophobic and electrostatic interactions with bacterial cell membranes and the difference between bacterial and mammalian cell membranes. The adoption of FAI would pave a new avenue toward the design of next-generation antimicrobial macromolecules and peptides.

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Established a numerical index to quantify the effect of facial amphiphilicity on antimicrobial efficacy.

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Evaluated the facial amphiphilicity index of multicyclic compounds possessing various rings and cationic charges.

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Provided this index a new tool toward more quantitative designs of AMP mimics.

In vitro and in vivo evaluation of DNase I in reinstating antibiotic efficacy against Klebsiella pneumoniae biofilms

Klebsiella pneumoniae is an opportunistic pathogen associated with biofilm-based infections, which are intrinsically antibiotic resistant. Extracellular DNA plays a crucial role in biofilm formation and self-defence, with nucleases being proposed as promising agents for biofilm disruption. This study evaluated the in vitro and in vivo efficacy of DNase I in improving the activity of cefotaxime, amikacin, and ciprofloxacin against K. pneumoniae biofilms. K. pneumoniae ATCC 700603 and a clinical isolate from catheter-related bloodstream infection were cultured for biofilm formation on microtiter plates, and the antibiofilm activity of the antibiotics (0.03-64 mg/L), with or without bovine pancreatic DNase I (1-32 mg/L) was determined by XTT dye reduction test and viable counting. The effect of ciprofloxacin (2 mg/L) and DNase I (16 mg/L) was further evaluated in vitro on 1-cm-long silicon catheter segments, and in a mouse model of subcutaneous catheter-associated infection. Combination with DNase I did not improve the biofilm-preventive capacity of the three antibiotics or the biofilm-eradicating capacity of cefotaxime and amikacin. The biofilm-eradicating capacity of ciprofloxacin was increased by 8-fold and 4-fold in K. pneumoniae ATCC 700603 and clinical isolate, respectively, with DNase I. The combination therapy caused 99% reduction in biofilm biomass in the mouse model.

Noncovalent Bile Acid Oligomers as Facial Amphiphilic Antimicrobials

New antimicrobial agents are needed to address the ever-growing risk of bacterial resistance, particularly for methicillin- and vancomycin-resistant Staphylococcus aureus (S. aureus). Here, we report a class of bile acid oligomers as facial amphiphilic antimicrobials, which are noncovalently fabricated by cholic acid (CA) and deoxycholic acid (DCA) with polyamines (e.g., diamines, diethylenetriamine, spermidine, and spermine). The antibacterial activities of these bile acid oligomers (CA/polyamines and DCA/polyamines) against S. aureus become stronger with increasing the amine group numbers of polyamines without obviously enhanced cytotoxicity and skin irritation. DCA/spermine, entirely composed of natural products, exhibits the best antibacterial activity but the lowest cytotoxicity and the weakest skin irritation. All CA/polyamines and DCA/polyamines form well-ordered ribbon-like aggregates, collecting numerous facial amphiphilic structures to significantly enhance the interactions with bacterial membranes. In particular, the biogenic polyamines with more than two amine groups provide extra positively charged sites, hence facilitating the binding of bile acid oligomers to the negatively charged outer membrane of the bacteria via electrostatic interaction. This in turn promotes more oligomeric bile acid units that can be inserted into the membrane through hydrophobic interaction between bile acids and lipid domains. The noncovalently constructed and separable amphiphilic antimicrobials can avoid the long-term coexistence of microorganisms and antibacterial molecules in different acting modes. Therefore, the noncovalent bile acid oligomers, especially those with higher oligomerization degrees, can be a potential approach to effectively enhance antibacterial activity, improve environmental friendliness, and reduce bacterial drug resistance.

Facially Amphiphilic Skeleton-Derived Antibacterial Cationic Dendrimers

It is urgent to develop biocompatible and high-efficiency antimicrobial agents since microbial infections have always posed serious challenges to human health. Herein, through the marriage of facially amphiphilic skeletons and cationic dendrimers, high-density positively charged dendrimers D-CA₆-N⁺ (G2) and D-CA₂-N⁺ (G1) were designed and synthesized using the "branch" of facially amphiphilic bile acids, followed by their modification with quaternary ammonium charges. Both dendrimers could self-assemble into nanostructured micelles in aqueous solution. D-CA₆-N⁺ displays potent antibacterial activity against Staphylococcus aureus and Escherichia coli, with minimum inhibitory concentrations (MICs) as low as 7.50 and 7.79 μM, respectively, and has an evidently stronger antibacterial activity than D-CA₂-N⁺. Moreover, D-CA₆-N⁺ can kill S. aureus faster than E. coli. The facial amphiphilicity of the bile acid skeleton facilitates the selective destruction of bacterial membranes and endows dendrimers with negligible hemolysis and cytotoxicity even under a high concentration of 16× MIC. In vivo studies show that D-CA₆-N⁺ is much more effective and safer than penicillin G in treating S. aureus infection and promoting wound healing, which suggests facially amphiphilic skeleton-derived cationic dendrimers can be a promising approach to effectively enhance antibacterial activity and biocompatibility of antibacterial agent, simultaneously.

N-methyl Benzimidazole Tethered Cholic Acid Amphiphiles Can Eradicate S. aureus-Mediated Biofilms and Wound Infections

Infections associated with Gram-positive bacteria like S. aureus pose a major threat as these bacteria can develop resistance and thereby limit the applications of antibiotics. Therefore, there is a need for new antibacterials to mitigate these infections. Bacterial membranes present an attractive therapeutic target as these membranes are anionic in nature and have a low chance of developing modifications in their physicochemical features. Antimicrobial peptides (AMPs) can disrupt the microbial membranes via electrostatic interactions, but the poor stability of AMPs halts their clinical translation. Here, we present the synthesis of eight N-methyl benzimidazole substituted cholic acid amphiphiles as antibacterial agents. We screened these novel heterocyclic cholic acid amphiphiles against different pathogens. Among the series, CABI-6 outperformed the other amphiphiles in terms of bactericidal activity against S. aureus. The membrane disruptive property of CABI-6 using a fluorescence-based assay has also been investigated, and it was inferred that CABI-6 can enhance the production of reactive oxygen species. We further demonstrated that CABI-6 can clear the pre-formed biofilms and can mitigate wound infection in murine models.

The Indigenous Volatile Inhibitor 2-Methyl-2-butene Impacts Biofilm Formation and Interspecies Interaction of the Pathogenic Mucorale Rhizopus arrhizus

2-Methyl-2-butene has recently been reported to be a quorum-based volatile self-inhibitor of spore germination and growth in pathogenic Mucorale Rhizopus arrhizus. The present study aimed to elucidate if this compound can influence R. arrhizus biofilm formation and interspecies interaction. The compound was found to significantly decrease R. arrhizus biofilm formation (p < 0.001), with nearly 25% and 50% lesser biomass in the biofilms cultured with exposure to 4 and 32 µg/ml of 2-methyl-2-butene, respectively. The growth of pre-formed biofilms was also impacted, albeit to a lesser extent. Additionally, 2-methyl-2-butene was found to self-limit R. arrhizus growth during interspecies interaction with Staphylococcus aureus and was detected at a substantially greater concentration in the headspace of co-cultures (2338.75 µg/ml) compared with monocultures (69.52 µg/ml). Some of the C5 derivatives of this compound (3-methyl-1-butanol, 2-methyl-2-butanol, and 3-methyl-1-butyne) were also observed to partially mimic its action, such as inhibition of spore germination, but did not impact R. arrhizus biofilm formation. Finally, the treated R. arrhizus displayed changes in fungal morphology suggestive of cytoskeletal alterations, such as filopodia formation, blebs, increased longitudinal folds and/or corrugations, and finger-like and sheet-like surface protrusions, depending upon the concentration of the compound(s) and the planktonic or biofilm growth mode.

Bile Acid Regulates the Colonization and Dissemination of Candida albicans from the Gastrointestinal Tract by Controlling Host Defense System and Microbiota

Candida albicans (CA), a commensal and opportunistic eukaryotic organism, frequently inhabits the gastrointestinal (GI) tract and causes life-threatening infections. Antibiotic-induced gut dysbiosis is a major risk factor for increased CA colonization and dissemination from the GI tract. We identified a significant increase of taurocholic acid (TCA), a major bile acid in antibiotic-treated mice susceptible to CA infection. In vivo findings indicate that administration of TCA through drinking water is sufficient to induce colonization and dissemination of CA in wild-type and immunosuppressed mice. Treatment with TCA significantly reduced mRNA expression of immune genes ang4 and Cxcr3 in the colon. In addition, TCA significantly decreased the relative abundance of three culturable species of commensal bacteria, Turicibacter sanguinis, Lactobacillus johnsonii, and Clostridium celatum, in both cecal contents and mucosal scrapings from the colon. Taken together, our results indicate that TCA promotes fungal colonization and dissemination of CA from the GI tract by controlling the host defense system and intestinal microbiota that play a critical role in regulating CA in the intestine.

Unlocking the bacterial membrane as a therapeutic target for next-generation antimicrobial amphiphiles

Gram-positive bacteria like Enterococcus faecium and Staphylococcus aureus, and Gram-negative bacteria like Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter Spp. are responsible for most of fatal bacterial infections. Bacteria present a handful of targets like ribosome, RNA polymerase, cell wall biosynthesis, and dihydrofolate reductase. Antibiotics targeting the protein synthesis like aminoglycosides and tetracyclines, inhibitors of RNA/DNA synthesis like fluoroquinolones, inhibitors of cell wall biosynthesis like glycopeptides and β-lactams, and membrane-targeting polymyxins and lipopeptides have shown very good success in combating the bacterial infections. Ability of the bacteria to develop drug resistance is a serious public health challenge as bacteria can develop antimicrobial resistance against newly introduced antibiotics that enhances the challenge for antibiotic drug discovery. Therefore, bacterial membranes present a suitable therapeutic target for development of antimicrobials as bacteria can find it difficult to develop resistance against membrane-targeting antimicrobials. In this review, we present the recent advances in engineering of membrane-targeting antimicrobial amphiphiles that can be effective alternatives to existing antibiotics in combating bacterial infections.

Self-assembled supramolecular nanomicelles from a bile acid-docetaxel conjugate are highly tolerable with improved therapeutic efficacy

Herein, we present the engineering of a supramolecular nanomicellar system that is composed of self-assembled units of the PEGylated lithocholic acid (LCA)-docetaxel (DTX) conjugate (LCA-DTX-PEG). We tethered a short polyethylene glycol unit to LCA and used an esterase-sensitive ester linkage between DTX and LCA. The LCA-DTX-PEG conjugate formed nanomicelles (LCA-DTX-PEG NMs) with ∼160 nm hydrodynamic diameter that are sensitive to cellular esterases and maximized the release of DTX under high esterase exposure. LCA-DTX-PEG NMs were found to be effective as the parent drug in breast cancer cells by stabilizing tubulin and arresting the cells in the G₂/M phase. We determined the maximum tolerated dose (MTD) and systemic and vital organ toxicity of LCA-DTX-PEG NMs in mice, rats, and rabbits. LCA-DTX-PEG NMs showed a MTD of >160 mg kg^-1 and are found to be safe in comparison with their parent FDA-approved drug formulation (Taxotere® or DTX-TS) that is highly toxic. LCA-DTX-PEG NMs effectively reduced the tumor volume and increased the survival of 4T1 tumor-bearing mice with improved blood circulation time of the drug and its higher accumulation in tumor tissues. Therefore, this study highlights the potential of PEGylated bile acid-drug conjugate based nanomicelles for the development of next generation cancer therapeutics.

Untargeted Metabolomics Reveals Intestinal Pathogenesis and Self-Repair in Rabbits Fed an Antibiotic-Free Diet

Simple Summary

In recent years, China imposed a total ban on the use of antibiotics in animal husbandry. This caused huge economic losses, one of the main reasons being an increase in the incidence of diseases. In this study, rabbits were used as a model to study the pathogenesis of intestinal diseases in rabbits on an antibiotic-free diet, through non-targeted metabolomics methods. The results showed that 1969 different metabolites were identified. These differential metabolites were involved in five metabolic pathways associated with intestinal inflammation (tryptophan metabolism, pyrimidine metabolism, phenylalanine, tyrosine and tryptophan biosynthesis, lysine degradation, and bile secretion). In summary, the use of non-antibiotic feed might cause intestinal inflammation in rabbits and activate intestinal repair.

Abstract

The prohibition of the use of growth-promoting drug additives in feeds was implemented in China in 2020. However, rabbits can experience symptoms of intestinal disease, such as diarrhea and flatulence, when switching from standard normal diets with antibiotics to antibiotic-free diets. The molecular mechanisms related to the occurrence of these diseases as well as associated physiological and metabolic changes in the intestine are unclear. Thus, the objectives of this study were to study the pathogenesis of intestinal inflammation using untargeted metabolomics. This was done to identify differential metabolites between a group of antibiotic-free feed Hyplus rabbits (Dia) whose diet was abruptly changed from a standard normal diet with antibiotics to an antibiotic-free diet, and an antibiotic diet group Hyplus rabbits (Con) that was fed a standard normal diet with antibiotics. Morphological damage to the three intestinal tissues was determined through visual microscopic examination of intestinal Dia and Con tissue samples stained with hematoxylin and eosin (HE). A total of 1969 different metabolites were identified in the three intestinal tissues from Dia and Con rabbits. The level of 1280 metabolites was significantly higher and the level of 761 metabolites was significantly lower in the Dia than in the Con group. These differential metabolites were involved in five metabolic pathways associated with intestinal inflammation (tryptophan metabolism, pyrimidine metabolism, phenylalanine, tyrosine and tryptophan biosynthesis, lysine degradation, and bile secretion). Rabbits in the Dia group developed metabolic disorders that affected the intestinal microbiota and changed the permeability of the intestinal tract, thereby triggering intestinal inflammation, affecting feed utilization, reducing production performance, and activating the intestinal tract self-repair mechanism. Thus, the abrupt transition from a diet with antibiotics to an antibiotic-free diet affected the structure and metabolism of the intestinal tract in Hyplus rabbits. Consequently, to avoid these problems, the antibiotic content in a rabbit diet should be changed gradually or alternative antibiotics should be found.

Recent Progress in Bile Acid-Based Antimicrobials

With the emergence of drug-resistant bacteria and the formation of biofilms by bacteria and fungi, microbial infections gradually threaten global health. Natural antimicrobial peptides (AMPs) have low susceptibility for developing resistance due to the membrane targeted mechanism, but instability and high manufacturing cost limit their applications in clinic. Bile acids, a group of steroids in the human body, with high stability, biocompatibility, and inherent facial amphiphilic structure similar to the characteristics of AMPs, have been applied to the biological field, such as drug delivery systems, self-healing hydrogels, antimicrobials, and so on. In this review, we mainly focus on the different classes of bile acid-based antimicrobials in recent years. Various designs and methods for the preparation of unimolecular antimicrobials with bile acid skeletons are first introduced, including coupling of primary amine, quaternary ammonium, and amino acid units with bile acid skeletons. Some representative oligomeric antimicrobials, including dimers of bile acids, are summarized. Finally, macromolecular antimicrobials bearing some positive charges at the main chain or side chain and interaction mechanisms of these bile acid-based antimicrobials are discussed.

A copper-catalyzed synthesis of aryloxy-tethered symmetrical 1,2,3-triazoles as potential antifungal agents targeting 14 α-demethylase

The search for potent therapeutic agents has prompted the design and synthesis of a library of twenty-six aryloxy-tethered and amide-linked symmetrical 1,2,3-triazoles (8a–z) using a copper(i)-catalyzed click chemistry approach.

Current Trends in Experimental and Computational Approaches to Combat Antimicrobial Resistance

A multitude of factors, such as drug misuse, lack of strong regulatory measures, improper sewage disposal, and low-quality medicine and medications, have been attributed to the emergence of drug resistant microbes. The emergence and outbreaks of multidrug resistance to last-line antibiotics has become quite common. This is further fueled by the slow rate of drug development and the lack of effective resistome surveillance systems. In this review, we provide insights into the recent advances made in computational approaches for the surveillance of antibiotic resistomes, as well as experimental formulation of combinatorial drugs. We explore the multiple roles of antibiotics in nature and the current status of combinatorial and adjuvant-based antibiotic treatments with nanoparticles, phytochemical, and other non-antibiotics based on synergetic effects. Furthermore, advancements in machine learning algorithms could also be applied to combat the spread of antibiotic resistance. Development of resistance to new antibiotics is quite rapid. Hence, we review the recent literature on discoveries of novel antibiotic resistant genes though shotgun and expression-based metagenomics. To decelerate the spread of antibiotic resistant genes, surveillance of the resistome is of utmost importance. Therefore, we discuss integrative applications of whole-genome sequencing and metagenomics together with machine learning models as a means for state-of-the-art surveillance of the antibiotic resistome. We further explore the interactions and negative effects between antibiotics and microbiomes upon drug administration.

The Great ESKAPE: Exploring the Crossroads of Bile and Antibiotic Resistance in Bacterial Pathogens

Throughout the course of infection, many pathogens encounter bactericidal conditions that threaten the viability of the bacteria and impede the establishment of infection. Bile is one of the most innately bactericidal compounds present in humans, functioning to reduce the bacterial burden in the gastrointestinal tract while also aiding in digestion. It is becoming increasingly apparent that pathogens successfully resist the bactericidal conditions of bile, including bacteria that do not normally cause gastrointestinal infections. This review highlights the ability of Enterococcus, Staphylococcus, Klebsiella, Acinetobacter, Pseudomonas, Enterobacter (ESKAPE), and other enteric pathogens to resist bile and how these interactions can impact the sensitivity of bacteria to various antimicrobial agents. Given that pathogen exposure to bile is an essential component to gastrointestinal transit that cannot be avoided, understanding how bile resistance mechanisms align with antimicrobial resistance is vital to our ability to develop new, successful therapeutics in an age of widespread and increasing antimicrobial resistance.

Facially Amphiphilic Cholic Acid-Lysine Conjugates as Promising Antimicrobials

The emergence of multidrug-resistant microbes is a significant health concern posing a constant need for new antimicrobials. Membrane-targeting antibiotics are promising candidates with reduced ability of microbes to develop resistance. In the present investigation, the principal reason behind choosing cholic acid as the crucial scaffold lies in the fact that it has a facially amphiphilic nature, which provides ample opportunity to refine the amphiphilicity by linking the amino acid lysine. A total of 16 novel amphipathic cholic acid derivatives were synthesized by sequentially linking lysine to C3-β-amino cholic acid methyl ester to maintain the hydrophobic/hydrophilic balance, which could be the essential requirement for the antimicrobial activity. Among the synthesized conjugates, a series with fluorenyl-9-methoxycarbonyl moiety attached to cholic acid via lysine linker showed promising antimicrobial activity against Staphylococcus aureus, Escherichia coli, and Candida albicans. A pronounced effect of increase in lysine residues was noted on the observed activity. The lead compounds were found to be active against drug-resistant bacterial and fungal clinical isolates and also improved the efficacy of antifungal agents amphotericin B and voriconazole. Membrane-permeability studies demonstrated the ability of these compounds to induce membrane damage in the tested microbes. The active conjugates did not show any hemolytic activity and were also found to be nontoxic to the normal cells as well as the examined cancer cell lines. The observed antimicrobial activity was attributed to the facial amphiphilic conformations, hydrophobic/hydrophilic balance, and the overall charge on the molecules.

Inhibitory effects of Lactobacilli cocktail on HT-29 colon carcinoma cells growth and modulation of the Notch and Wnt/β-catenin signaling pathways

Probiotics could be considered as attractive candidates for preventing tumor growth through maintaining homeostasis. The aim of this study was to evaluate the inhibitory effect of a cocktail of five Lactobacillus species on human colorectal carcinoma cell line HT-29. The anti-proliferative and apoptotic effects of Lactobacilli cocktail were evaluated using MTT and flow cytometry tests, respectively. Quantitative real-time polymerase chain reaction (qPCR) was used to analyze the expression of several genes in the Notch (notch, hes1, msi1, and numb) and Wnt/β-catenin (CTNNB1 and CCND1) pathways, following the treatment of HT-29 cells with Lactobacilli cocktail. The treatment by Lactobacilli cocktail induced a significant anti-proliferative effect and late stage apoptosis among the cancer cells (p < 0.05). Compared to the untreated cells, Lactobacilli cocktail induced the down-regulation of notch, hes1, and msi1 genes and up-regulation of numb gene in the Notch pathway as well as the down-regulation of CTNNB1 and CCND1 genes in the Wnt/β-catenin pathway in a time-dependent manner (p < 0.05). CONCLUSION: Lactobacilli cocktail was shown to have beneficial anti-tumor effects on HT-29 cells by modulating the Notch and Wnt/β-catenin pathways; therefore, the use of Lactobacilli probiotics as nutritional supplements may prevent the incidence of colon cancer.

Antagonistic Interaction of Staphylococcus aureus and Staphylococcus epidermidis with Rhizopus arrhizus Mediated by Phenol Soluble Modulins and Organic Acids

Rhizopus arrhizus (R. arrhizus) is a common causative agent of mucormycosis that usually enters the human body through the respiratory tract and skin. Both these sites harbor staphylococci as a part of the normal microflora, indicating the possibility of interspecies interactions. We aimed to elucidate this interaction and identify the molecular mechanisms involved. Both Staphylococcus aureus (S. aureus) and Staphylococcus epidermidis (S. epidermidis) substantially hindered R. arrhizus radial growth, spore germination, and liquid culture biomass. Secreted components in the stationary-phase supernatant were responsible for this activity. The active components, based on molecular weight-based fractionation, mass spectrometry, and ion exclusion chromatography, were identified as a truncated version of phenol soluble modulin α2 (Δ1Δ2PSMα2) and PSMα3 in S. aureus, PSMδ in S. epidermidis, and organic acids in both the species. Exposure to the phenol soluble modulins (PSMs) extensively damaged the fungal spores and pre-existing hyphae, leading to bleb formation, shriveling, hyphal shrinkage, and cell distortion.

Cholic Acid-Peptide Conjugates as Potent Antimicrobials against Interkingdom Polymicrobial Biofilms

Interkingdom polymicrobial biofilms formed by Gram-positive Staphylococcus aureus and Candida albicans pose serious threats of chronic systemic infections due to the absence of any common therapeutic target for their elimination. Herein, we present the structure-activity relationship (SAR) of membrane-targeting cholic acid-peptide conjugates (CAPs) against Gram-positive bacterial and fungal strains. Structure-activity investigations validated by mechanistic studies revealed that valine-glycine dipeptide-derived CAP 3 was the most effective broad-spectrum antimicrobial against S. aureus and C. albicans CAP 3 was able to degrade the preformed single-species and polymicrobial biofilms formed by S. aureus and C. albicans, and CAP 3-coated materials prevented the formation of biofilms. Murine wound and catheter infection models further confirmed the equally potent bactericidal and fungicidal effect of CAP 3 against bacterial, fungal, and polymicrobial infections. Taken together, these results demonstrate that CAPs, as potential broad-spectrum antimicrobials, can effectively clear the frequently encountered polymicrobial infections and can be fine-tuned further for future applications.

Cholic Acid-Derived Amphiphile which Combats Gram-Positive Bacteria-Mediated Infections via Disintegration of Lipid Clusters

Inappropriate and uncontrolled use of antibiotics results in the emergence of antibiotic resistance, thereby threatening the present clinical regimens to treat infectious diseases. Therefore, new antimicrobial agents that can prevent bacteria from developing drug resistance are urgently needed. Selective disruption of bacterial membranes is the most effective strategy for combating microbial infections as accumulation of genetic mutations will not allow for the emergence of drug resistance against these antimicrobials. In this work, we tested cholic acid (CA) derived amphiphiles tethered with different alkyl chains for their ability to combat Gram-positive bacterial infections. In-depth biophysical and biomolecular simulation studies suggested that the amphiphile with a hexyl chain (6) executes more effective interactions with Gram-positive bacterial membranes as compared to other hydrophobic counterparts. Amphiphile 6 is effective against multidrug resistant Gram-positive bacterial strains as well and does not allow the adherence of S. aureus on amphiphile 6 coated catheters implanted in mice. Further, treatment of wound infections with amphiphile 6 clears the bacterial infections. Therefore, the current study presents strategic guidelines in design and development of CA-derived membrane-targeting antimicrobials for Gram-positive bacterial infections.