Preclinical evaluation of novel antibacterial agents by microbiological and molecular techniques

Repurposing cinacalcet suppresses multidrug-resistant Staphylococcus aureus by disruption of cell membrane and inhibits biofilm by targeting IcaR

BACKGROUND

MDR Staphylococcus aureus infections, along with the severity of biofilm-associated infections, continue to threaten human health to a great extent. It necessitates the urgent development of novel antimicrobial and antibiofilm agents.

OBJECTIVES

To reveal the mechanism and target of cinacalcet as an antibacterial and antimicrobial agent for S. aureus.

METHODS

Screening of non-antibiotic drugs for antibacterial and antibiofilm properties was conducted using a small-molecule drug library. In vivo efficacy was assessed through animal models, and the antibacterial mechanism was studied using quantitative proteomics, biochemical assays, LiP-SMap, BLI detection and gene knockout techniques.

RESULTS

Cinacalcet, an FDA-approved drug, demonstrated antibacterial and antibiofilm activity against S. aureus, with less observed development of bacterial resistance. Importantly, cinacalcet significantly improved survival in a pneumonia model and bacterial clearance in a biofilm infection model. Moreover, the antibacterial mechanism of cinacalcet mainly involves the destruction of membrane-targeted structures, alteration of energy metabolism, and production of reactive oxygen species (ROS). Cinacalcet was found to target IcaR, inhibiting biofilm formation through the negative regulation of IcaADBC.

CONCLUSIONS

The findings suggest that cinacalcet has potential for repurposing as a therapeutic agent for MDR S. aureus infections and associated biofilms, warranting further investigation.

Initial culture media pH influences the antibacterial activity and metabolic footprint of Lactobacillus acidophilus BIOTECH 1900

This study investigated the impact of initial culture media pH on the antibacterial properties and metabolic profile of cell-free supernatants (CFSs) from Lactobacillus acidophilus BIOTECH 1900 (LAB1900). The CFSs harvested from LAB1900 grown in de Man, Rogosa, Sharpe broth with initial pH of 5.5 (CFS5.5) and 6.6 (CFS6.6) were tested. The two CFSs elicited varying degrees of activity against three gram-negative bacteria. In the agar-well diffusion against Pseudomonas aeruginosa, CFS5.5 and CFS6.6 recorded 14.36 ± 1.34 and 13.06 ± 1.29 mm inhibition, respectively. Interestingly, against Klebsiella pneumoniae, CFS5.5 showed 14.36 ± 1.56 mm inhibition which was significantly higher than the 12.22 ± 1.31 mm inhibition of CFS6.6 (p = 0.0464). While against Acinetobacter baumannii, significantly higher inhibition of 10.66 ± 0.51 mm was observed in CFS6.6 compared to the 7.58 ± 1.93 mm inhibition of CFS5.5 (p = 0.0087). Nonetheless, both CFSs were bactericidal, with a minimum inhibitory and bactericidal concentration range of 3.90625-7.8125 mg/mL. The varied antibacterial activities may be attributed to the metabolite compositions of CFSs. A total of 152 metabolites driving the separation between CFSs were noted, with the majority upregulated in CFS5.5. Furthermore, 15 were putatively identified belonging to acylcarnities, vitamins, gibberellins, glycerophospholipids, and peptides. In summary, initial culture media pH affects the production of microbial metabolites with antibacterial properties.

Hit-to-Lead Identification and Validation of a Triaromatic Pleuromutilin Antibiotic Candidate

Herein, we report the hit-to-lead identification of a drug-like pleuromutilin conjugate 16, based on a triaromatic hit reported in 2020. The lead arose as the clear candidate from a hit-optimization campaign in which Gram-positive antibacterial activity, solubility, and P-gp affinity were optimized. Conjugate 16 was extensively evaluated for its in vitro ADMET performance which, apart from solubility, was overall on par with lefamulin. This evaluation included Caco-2 cell permeability, plasma protein binding, hERG inhibition, cytotoxicity, metabolism in microsomes and CYP3A4, resistance induction, and time-kill kinetics. Intravenous pharmacokinetics of 16 proved satisfactory in both mice and pigs; however, oral bioavailability was limited likely due to insufficient solubility. The in vivo efficacy was evaluated in mice, systemically infected with Staphylococcus aureus, where 16 showed rapid reduction in blood bacteriaemia. Through our comprehensive studies, lead 16 has emerged as a highly promising and safe antibiotic candidate for the treatment of Gram-positive bacterial infections.

Investigation of 60Co Irradiation on the Volatile Organic Compounds from Finger Citron (Citri Sarcodactylis Fructus) Using GC-IMS

In recent years, as the desire for a healthy lifestyle has become more widespread, consumers are gaining an increasing appreciation for safe, high-quality food. Researchers are constantly seeking new ways to protect foods from insect pests and fungi. This study used GC-IMS to analyze the volatile organic compounds and flavor characteristics of Finger Citron in response to different doses of 60Co irradiation. The principal component analysis method was used to explore the overall differences in flavor spectra, and a total of 60 compounds were identified. The fingerprints of volatile organic compounds in the samples showed that the volatile organic compounds with doses of 60Co irradiation in about 0 kGy and 5 kGy are similar, while the 10 kGy samples are quite different. The PCA results showed that the similarity between 0 kGy and 5 kGy was slightly higher, and the difference between 10 kGy and other samples was greater. Therefore, it was determined that 60Co irradiation with a 10 kGy intensity has a significant influence on the content of volatile oils components, while 60Co irradiation with a 5 kGy intensity has little effect. Irradiation technology is demonstrated as a promising method of food sterilization, but the irradiation dose and chemical composition must be taken into consideration.

Intelligent De Novo Design of Novel Antimicrobial Peptides against Antibiotic-Resistant Bacteria Strains

Because of the growing number of clinical antibiotic resistance cases in recent years, novel antimicrobial peptides (AMPs) may be ideal for next-generation antibiotics. This study trained a Wasserstein generative adversarial network with gradient penalty (WGAN-GP) based on known AMPs to generate novel AMP candidates. The quality of the GAN-designed peptides was evaluated in silico, and eight of them, named GAN-pep 1–8, were selected by an AMP Artificial Intelligence (AI) classifier and synthesized for further experiments. Disc diffusion testing and minimum inhibitory concentration (MIC) determinations were used to identify the antibacterial effects of the synthesized GAN-designed peptides. Seven of the eight synthesized GAN-designed peptides displayed antibacterial activity. Additionally, GAN-pep 3 and GAN-pep 8 presented a broad spectrum of antibacterial effects and were effective against antibiotic-resistant bacteria strains, such as methicillin-resistant Staphylococcus aureus and carbapenem-resistant Pseudomonas aeruginosa. GAN-pep 3, the most promising GAN-designed peptide candidate, had low MICs against all the tested bacteria. In brief, our approach shows an efficient way to discover AMPs effective against general and antibiotic-resistant bacteria strains. In addition, such a strategy also allows other novel functional peptides to be quickly designed, identified, and synthesized for validation on the wet bench.

An extensively validated whole-cell biosensor for specific, sensitive and high-throughput detection of antibacterial inhibitors targeting cell-wall biosynthesis

BACKGROUND

Whole-cell biosensor strains are powerful tools for antibacterial drug discovery, in principle allowing the identification of inhibitors acting on specific, high-value target pathways. Whilst a variety of biosensors have been described for detecting cell-wall biosynthesis inhibitors (CWBIs), these strains typically lack specificity and/or sensitivity, and have for the most part not been rigorously evaluated as primary screening tools. Here, we describe several Staphylococcus aureus CWBI biosensors and show that specific and sensitive biosensor-based discovery of CWBIs is achievable.

METHODS

Biosensors comprised lacZ reporter fusions with S. aureus promoters (PgltB, PilvD, PmurZ, PoppB, PORF2768, PsgtB) that are subject to up-regulation following inhibition of cell-wall biosynthesis. Induction of biosensors was detected by measuring expression of β-galactosidase using fluorogenic or luminogenic substrates.

RESULTS

Three of the six biosensors tested (those based on PgltB, PmurZ, PsgtB) exhibited apparently specific induction of β-galactosidase expression in the presence of CWBIs. Further validation of one of these (PmurZ) using an extensive array of positive and negative control compounds and conditional mutants established that it responded appropriately and uniquely to inhibition of cell-wall biosynthesis. Using this biosensor, we established, validated and deployed a high-throughput assay that identified a potentially novel CWBI from a screen of >9000 natural product extracts.

CONCLUSIONS

Our extensively validated PmurZ biosensor strain offers specific and sensitive detection of CWBIs, and is well-suited for high-throughput screening; it therefore represents a valuable tool for antibacterial drug discovery.

A lipoglycopeptide antibiotic for Gram-positive biofilm-related infections

Drug-resistant Gram-positive bacterial infections are still a substantial burden on the public health system, with two bacteria ( Staphylococcus aureus and Streptococcus pneumoniae ) accounting for over 1.5 million drug-resistant infections in the United States alone in 2017. In 2019, 250,000 deaths were attributed to these pathogens globally. We have developed a preclinical glycopeptide antibiotic, MCC5145, that has excellent potency (MIC 90 ≤ 0.06 μg/ml) against hundreds of isolates of methicillin-resistant S. aureus (MRSA) and other Gram-positive bacteria, with a greater than 1000-fold margin over mammalian cell cytotoxicity values. The antibiotic has therapeutic in vivo efficacy when dosed subcutaneously in multiple murine models of established bacterial infections, including thigh infection with MRSA and blood septicemia with S. pneumoniae , as well as when dosed orally in an antibiotic-induced Clostridioides difficile infection model. MCC5145 exhibited reduced nephrotoxicity at microbiologically active doses in mice compared to vancomycin. MCC5145 also showed improved activity against biofilms compared to vancomycin, both in vitro and in vivo, and a low propensity to select for drug resistance. Characterization of drug action using a transposon library bioinformatic platform showed a mechanistic distinction from other glycopeptide antibiotics.

Combination with a FtsZ inhibitor potentiates the in vivo efficacy of oxacillin against methicillin-resistant Staphylococcus aureus

Oxacillin is a first-line antibiotic for the treatment of methicillin-sensitive Staphylococcus aureus (MSSA) infections but is ineffective against methicillin-resistant S. aureus (MRSA) due to resistance. Here we present results showing that co-administering oxacillin with the FtsZ-targeting prodrug TXA709 renders oxacillin efficacious against MRSA. The combination of oxacillin and the active product of TXA709 (TXA707) is associated with synergistic bactericidal activity against clinical isolates of MRSA that are resistant to current standard-of-care antibiotics. We show that MRSA cells treated with oxacillin in combination with TXA707 exhibit morphological characteristics and PBP2 mislocalization behavior similar to that exhibited by MSSA cells treated with oxacillin alone. Co-administration with TXA709 renders oxacillin efficacious in mouse models of both systemic and tissue infection with MRSA, with this efficacy being observed at human-equivalent doses of oxacillin well below that recommended for daily adult use. Pharmacokinetic evaluations in mice reveal that co-administration with TXA709 also increases total exposure to oxacillin. Viewed as a whole, our results highlight the clinical potential of repurposing oxacillin to treat MRSA infections through combination with a FtsZ inhibitor.

Tetramate Derivatives by Chemoselective Dieckmann Ring Closure of threo-Phenylserines and Their Antibacterial Activity

A general route, which provides direct access to substituted bicyclic tetramates, making use of Dieckmann cyclization of oxazolidines derived from threo-arylserines, is reported; the latter were found to be available by an efficient aldol-like reaction of glycine with some substituted benzaldehydes under alkaline conditions. The tetramates were found to release chelated metal cations acquired during chromatographic purification by mild acid wash. Some compounds in the library showed good antibacterial activity against Gram-positive bacteria. Cheminformatic analysis demonstrates that the most active compounds were Ro5-compliant and occupy a narrow region of chemical space, distinct from that occupied by other known antibiotics, with the most potent compounds having 399 < M_w < 530 Da; 3.5 < cLogP < 6.6; 594 < MSA <818 Ų; 9.6 < rel. PSA <13.3%. MIC values were shifted to higher concentrations when tested in the presence of HSA or blood, but was not completely abolished, consistent with a plasma protein binding (PPB) effect.

Dysregulation of Cell Envelope Homeostasis in Staphylococcus aureus Exposed to Solvated Lignin

Lignin is an aromatic plant cell wall polymer that facilitates water transport through the vasculature of plants and is generated in large quantities as an inexpensive by-product of pulp and paper manufacturing and biorefineries. Although lignin's ability to reduce bacterial growth has been reported previously, its hydrophobicity complicates the ability to examine its biological effects on living cells in aqueous growth media. We recently described the ability to solvate lignin in Good's buffers with neutral pH, a breakthrough that allowed examination of lignin's antimicrobial effects against the human pathogen Staphylococcus aureus. These analyses showed that lignin damages the S. aureus cell membrane, causes increased cell clustering, and inhibits growth synergistically with tunicamycin, a teichoic acid synthesis inhibitor. In the present study, we examined the physiological and transcriptomic responses of S. aureus to lignin. Intriguingly, lignin restored the susceptibility of genetically resistant S. aureus isolates to penicillin and oxacillin, decreased intracellular pH, impaired normal cell division, and rendered cells more resistant to detergent-induced lysis. Additionally, transcriptome sequencing (RNA-Seq) differential expression (DE) analysis of lignin-treated cultures revealed significant gene expression changes (P < 0.05 with 5% false discovery rate [FDR]) related to the cell envelope, cell wall physiology, fatty acid metabolism, and stress resistance. Moreover, a pattern of concurrent up- and downregulation of genes within biochemical pathways involved in transmembrane transport and cell wall physiology was observed, which likely reflects an attempt to tolerate or compensate for lignin-induced damage. Together, these results represent the first comprehensive analysis of lignin's antibacterial activity against S. aureus. IMPORTANCE S. aureus is a leading cause of skin and soft tissue infections. The ability of S. aureus to acquire genetic resistance to antibiotics further compounds its ability to cause life-threatening infections. While the historical response to antibiotic resistance has been to develop new antibiotics, bacterial pathogens are notorious for rapidly acquiring genetic resistance mechanisms. As such, the development of adjuvants represents a viable way of extending the life span of current antibiotics to which pathogens may already be resistant. Here, we describe the phenotypic and transcriptomic response of S. aureus to treatment with lignin. Our results demonstrate that lignin extracted from sugarcane and sorghum bagasse restores S. aureus susceptibility to β-lactams, providing a premise for repurposing these antibiotics in treatment of resistant S. aureus strains, possibly in the form of topical lignin/β-lactam formulations.

relBE Toxin-antitoxin System as a Reliable Anti-biofilm Target in Pseudomonas aeruginosa

AIMS

The ability of the pathogenic bacterium Pseudomonas aeruginosa to produce biofilms has made it more difficult to treat its infections with current antibiotics. Several genes are involved in biofilm production, and toxin-antitoxin (TA) loci have been reported to be responsible for the regulation of biofilm-associated genes. This study was aimed at evaluating various TA loci in P. aeruginosa to find a reliable target in order to disrupt biofilm formation.

METHODS AND RESULTS

Thirty clinical isolates of P. aeruginosa were assessed for biofilm production as well as the presence of various TA loci in their genomes. The relBETA locus was present in all 30 P. aeruginosa isolates but its expression was not detectable in isolates that did not show biofilm production. Quantitative real-time -PCR (q-PCR) also demonstrated that the expression of relBE was higher in isolates with stronger biofilm-producing capability. Knocking out the relBE locus in one biofilm-producing P. aeruginosa isolate led to the cessation of biofilm-producing capacity in that isolate and eliminated the expression of ndvB, which is among the genes involved in biofilm production.

CONCLUSIONS

These results inferred the involvement of relBE TA locus in the regulation of biofilm production in P. aeruginosa and indicated the possibility of relBE as an anti-biofilm target for this pathogen.

Biotechnology of the Tree Fern Cyathea smithii (J.D. Hooker; Soft Tree Fern, Katote) II Cell Suspension Culture: Focusing on Structure and Physiology in the Presence of 2,4-D and BAP

The aim of our research was to describe the structure and growth potential of a cell suspension of the tree fern Cyathea smithii. Experiments were performed on an established cell suspension with ½ MS medium supplemented with 9.05 µM 2,4-D + 0.88 µM BAP. In the experiments, attention was paid to the microscopic description of cell suspension, evaluation of cell growth dependent on the initial mass of cells and organic carbon source in the medium, the length of the passage, the content of one selected flavonoid in the post-culture medium, nuclear DNA content, ethylene production, and the antimicrobial value of the extract. For a better understanding of the cell changes that occurred during the culture of the suspension, the following structures of the cell were observed: nucleus, lipid bodies, tannin deposits, starch grains, cell walls, primary lamina, and the filaments of metabolites released into the medium. The nuclear DNA content (acriflavine-Feulgen staining) of cell aggregates distinctly indicated a lack of changes in the sporophytic origin of the cultured cell suspension. The physiological activity of the suspension was found to be high because of kinetics, intensive production of ethylene, and quercetin production. The microbiological studies suggested that the cell suspension possessed a bactericidal character against microaerobic Gram-positive bacteria. A sample of the cell suspension showed bacteriostatic activity against aerobic bacteria.

Mediation of metal chelation in cysteine-derived tetramate systems

A study of bicyclic tetramates modified with a bulky ester, which leads to steric hindrance of distal chelating atoms as a route for the alteration of metal binding ability is reported. This approach required the development of a direct method for the synthesis of different esters of cysteine from cystine, which then provided access to bicyclic tetramates by Dieckmann cyclisation. Further derivation to ketones and carboxamides by Grignard addition and transamination reactions respectively provided rapid access to a chemical library of tetramates with diverse substitution. Of interest is that bicyclic tetramate ketones and carboxamides showed different tautomeric and metal binding behaviour in solution. Significantly, in both systems, the incorporation of bulky C-5 esters at the bridging position not only reduced metal binding, but also enhanced antibacterial potencies against Gram-positive MRSA bacteria. Those tetramates with antibacterial activity which was not metal dependent showed physiochemical properties of MSA of 559-737 Ų, MW of 427-577 Da, clogP of 1.8-6.1, clogD_7.4 of -1.7 to 3.7, PSA of 83-109 Ų and relative PSA of 12-15% and were generally Lipinski rule compliant. A subset of tetramates exhibited good selectivity towards prokaryotic bacterial cells. Given that the work reported herein is synthesis-led, without the underpinning detailed mechanistic understanding of biological/biochemical mechanism, that the most active compounds occupy a small region of chemical space as defined by MW, clogP, PSA and %PSA is of interest. Overall, the bicyclic tetramate template is a promising structural motif for the development of novel antibacterial drugs, with good anti-MRSA potencies and appropriate drug-like physiochemical properties, coupled with a potential for multi-targeting mechanisms and low eukaryotic cytotoxicity.

Potency of commonly retailed antibiotics in pharmacies found in Adama, Oromia regional state, Ethiopia

Introduction

Antibiotics are commonly used for the treatment and prevention of bacterial infections. The potency of antibiotics can be affected by factors such as temperature, light, moisture, and storage conditions. Inappropriate storage and transportation of antibiotics may lead to loss of potency earlier than the expiry date. The aim of this study was to determine the potency and associated factors of commonly retailed antibiotics.

Method

Institution-based cross-sectional study was conducted on commonly retailed antibiotics in pharmacies that are available in Adama, Ethiopia from March 2018 to June 2018. This study focused on commonly ordered antibiotics such as amoxicillin, azithromycin, ciprofloxacin, and ceftriaxone. Antibiotics to be tested were selected by using a simple random sampling technique. Socio-demographic and related data were collected using a semi-structured questionnaire. Antibiotic susceptibility testing was performed using the disc diffusion method as described in the Clinical Laboratory Standard Institute guideline.

Results

Mean inhibition zones of amoxicillin, ciprofloxacin, azithromycin, and ceftriaxone were 14.2 ± 4 mm, 30.9 ± 4.2 mm, 17.47 ± 3.83 mm, and 32.7±1.8 respectively. Out of 164 antibiotics tested, 61% passed the potency test. The potency of antibiotics varies across different countries in which 53.7% and 54.6 of antibiotics from India and Ethiopia passed the potency test. All ceftriaxone tested in this study passed the potency test. Factors such as air condition of pharmacy (X² = 4.27; p = 0.039), source of all antibiotics (X² = 5.41; p = 0.02), and source of amoxicillin (X² = 4.73; p = 0.03) were significantly associated with potency of antibiotics.

Conclusions

About 40% of antibiotics tested in the current study did not pass the potency test; this warrants further investigation to identify the magnitude of the problem and its causes at a large scale.

Flavonoid and Phenolic Acids Content and In Vitro Study of the Potential Anti-Aging Properties of Eutrema japonicum (Miq.) Koidz Cultivated in Wasabi Farm Poland

Skin aging is a natural, unavoidable, and complex process caused by oxidative stress. As a consequence, it leads to an increase in the activation of extracellular matrix disruption enzymes and DNA damage. The search for natural sources that inhibit these mechanisms can be a good approach to prevent skin aging. The purpose of our study was to evaluate the composition of flavonoids and phenolic acids in the extracts obtained from the flowers, roots, and leaves of Eutrema japonicum cultivated in Poland. Then, the resultant extracts were subjected to an assessment of antioxidant, anti-collagenase, anti-elastase, anti-hyaluronidase, antibacterial, and cytotoxic properties. It was demonstrated that the extract from the flowers had the highest content of flavonoid glycosides (17.15 mg/g DE). This extract showed the greatest antioxidant, anti-collagenase, anti-elastase, and anti-hyaluronidase activities compared to the other samples. Importantly, the collagenase inhibitory activity of this extract (93.34% ± 0.77%) was better than that of positive control epigallocatechin gallate (88.49% ± 0.45%). An undeniable advantage of this extract was also to possess moderate antibacterial properties and no cytotoxicity towards normal human skin fibroblasts. Our results suggest that extracts from E. japonicum flowers may be considered as a promising antiaging compound for applications in cosmetic formulations.

A platform for detecting cross-resistance in antibacterial drug discovery

Background

To address the growing antibiotic resistance problem, new antibacterial drugs must exert activity against pathogens resistant to agents already in use. With a view to providing a rapid means for deselecting antibacterial drug candidates that fail to meet this requirement, we report here the generation and application of a platform for detecting cross-resistance between established and novel antibacterial agents.

Methods

This first iteration of the cross-resistance platform (CRP) consists of 28 strains of defined resistance genotype, established in a uniform genetic background (the SH1000 strain of the clinically significant pathogen Staphylococcus aureus). Most CRP members were engineered through introduction of constitutively expressed resistance determinants on a low copy-number plasmid, with a smaller number selected as spontaneous resistant mutants.

Results

Members of the CRP collectively exhibit resistance to many of the major classes of antibacterial agent in use. We employed the CRP to test two antibiotics that have been proposed in the literature as potential drug candidates: γ-actinorhodin and batumin. No cross-resistance was detected for γ-actinorhodin, whilst a CRP member resistant to triclosan exhibited a 32-fold reduction in susceptibility to batumin. Thus, a resistance phenotype that already exists in clinical strains mediates profound resistance to batumin, implying that this compound is not a promising antibacterial drug candidate.

Conclusions

By detecting cross-resistance between established and novel antibacterial agents, the CRP offers the ability to deselect compounds whose activity is substantially impaired by existing resistance mechanisms. The CRP therefore represents a useful addition to the antibacterial drug discovery toolbox.

The Food Anti-Microbials β-Phenylethylamine (-HCl) and Ethyl Acetoacetate Do Not Change during the Heating Process

β-Phenylethylamine hydrochloride (PEA-HCl) and ethyl acetoacetate (EAA) are anti-microbials with applications in food processing. As food anti-microbials, the compounds will have to withstand the cooking process without changing to toxic compounds. With this Communication, we address the question of whether PEA and EAA are altered when heated to 73.9 °C or 93.3 °C. A combination of gas chromatography and mass spectrometry was used to analyze solutions of PEA(-HCl) or EAA in beef broth or water. In addition, the anti-microbial activity of PEA-HCl and EAA was compared between heated and unheated samples at a range of concentrations. The gas chromatograms of PEA(-HCl) and EAA showed one peak at early retention times that did not differ between the heated and unheated samples. The mass spectra for PEA and EAA were near identical to those from a spectral database and did not show any differences between the heated and unheated samples. We conclude that PEA(-HCl) and EAA formed pure solutions and were not altered during the heating process. In addition, the anti-microbial activity of PEA-HCl and EAA did not change after the heating of the compounds. Regardless of temperature, the minimal inhibitory concentrations (MICs) for PEA-HCl were 20.75 mmol mL⁻¹ for Escherichia coli and Salmonella enterica serotype Typhimurium. For EAA, the MICs were 23.4 mmol mL⁻¹ for E. coli and 15.6 mmol mL⁻¹ for S. enterica.

1,3-Oxazine-2-one derived dual-targeted molecules against replicating and non-replicating forms of Mycobacterium tuberculosis

The high mortality rate and increasing prevalence of resistant Mtb are the major concerns for the Tuberculosis (TB) treatment in this century. To curtail the prevalence of resistant Mtb, we have prepared 1,3-oxazine-2-one based dual targeted molecules. Compound 67 and 68 were found to be equally active against replicating and non-replicatiing form of Mtb (MIC_MABA 3.48 and 2.97 μg/ml; MIC_LORA 2.94 and 2.15 μg/ml respectively). They had found to suppress the biosynthesis of alfa, methoxy and keto-mycolate completely, as well as inhibit enzymatic activity of MenG (IC₅₀ = 9.11 and 6.25 μg/ml respectively for H37Ra; IC₅₀ = 11.76 and 10.88 μg/ml respectively for M smegmatis).

Perspective on Antibacterial Lead Identification Challenges and the Role of Hypothesis-Driven Strategies

For the past three decades, the pharmaceutical industry has undertaken many diverse approaches to discover novel antibiotics, with limited success. We have witnessed and personally experienced many mistakes, hurdles, and dead ends that have derailed projects and discouraged scientists and business leaders. Of the many factors that affect the outcomes of screening campaigns, a lack of understanding of the properties that drive efflux and permeability requirements across species has been a major barrier for advancing hits to leads. Hits that possess bacterial spectrum have seldom also possessed druglike properties required for developability and safety. Persistence in solving these two key barriers is necessary for the reinvestment into discovering antibacterial agents. This perspective narrates our experience in antibacterial discovery-our lessons learned about antibacterial challenges as well as best practices for screening strategies. One of the tenets that guides us is that drug discovery is a hypothesis-driven science. Application of this principle, at all steps in the antibacterial discovery process, should improve decision making and possibly the odds of what has become, in recent decades, an increasingly challenging endeavor with dwindling success rates.

Thiazoles, Their Benzofused Systems, and Thiazolidinone Derivatives: Versatile and Promising Tools to Combat Antibiotic Resistance

Thiazoles, their benzofused systems, and thiazolidinone derivatives are widely recognized as nuclei of great value for obtaining molecules with various biological activities, including analgesic, anti-inflammatory, anti-HIV, antidiabetic, antitumor, and antimicrobial. In particular, in the past decade, many compounds bearing these heterocycles have been studied for their promising antibacterial properties due to their action on different microbial targets. Here we assess the recent development of this class of compounds to address mechanisms underlying antibiotic resistance at both bacterial-cell and community levels (biofilms). We also explore the SAR and the prospective clinical application of thiazole and its benzofused derivatives, which act as inhibitors of mechanisms underlying antibiotic resistance in the treatment of severe drug-resistant infections. In addition, we examined all bacterial targets involved in their antimicrobial activity reporting, when described, their spontaneous frequencies of resistance.

Pegylated triarylmethanes: Synthesis, antimicrobial activity, anti-proliferative behavior and in silico studies

We describe herein the synthesis, characterization and biological studies of novel PEGylated triarylmethanes. Non-symmetrical and symmetrical triarylmethanes series have been synthesized by Friedel-Crafts hydroxyalkylation or directly from bisacodyl respectively followed by a functionalization with PEG fragments in order to increase bioavailability and biological effectiveness. The antimicrobial activity was investigated against Gram-positive and Gram-negative foodborne pathogens and against Candida albicans, an opportunistic pathogenic yeast. The anti-biocidal activity was also studied using Staphylococcus aureus as a reference bacterium. Almost all PEGylated molecules displayed an antifungal activity comparable with fusidic acid with MIC values ranging from 6.25 to 50 μg/mL. Compounds also revealed a promising antibiofilm activity with biofilm eradication percentages values above 80% for the best molecules (compounds 4d and 7). Compounds 7 and 8b showed a modest antiproliferative activity against human colorectal cancer cell lines HT-29. Finally, in silico molecular docking studies revealed DHFR and DNA gyrase B as potential anti-bacterial targets and in silico predictions of ADME suggested adequate drug-likeness profiles for the synthetized triarylmethanes.

Profiling antimicrobial peptides from the medical maggot Lucilia sericata as potential antibiotics for MDR Gram-negative bacteria

Background

The ability of MDR Gram-negative bacteria to evade even antibiotics of last resort is a severe global challenge. The development pipeline for conventional antibiotics cannot address this issue, but antimicrobial peptides (AMPs) offer an alternative solution.

Objectives

Two insect-derived AMPs (LS-sarcotoxin and LS-stomoxyn) were profiled to assess their suitability for systemic application in humans.

Methods

The peptides were tested against an extended panel of 114 clinical MDR Gram-negative bacterial isolates followed by time–kill analysis, interaction studies and assays to determine the likelihood of emerging resistance. In further in vitro studies we addressed cytotoxicity, cardiotoxicity and off-target interactions. In addition, an in vivo tolerability and pharmacokinetic study in mice was performed.

Results

LS-sarcotoxin and LS-stomoxyn showed potent and selective activity against Gram-negative bacteria and no cross-resistance with carbapenems, fluoroquinolones or aminoglycosides. Peptide concentrations of 4 or 8 mg/L inhibited 90% of the clinical MDR isolates of Escherichia coli, Enterobacter cloacae, Acinetobacter baumannii and Salmonella enterica isolates tested. The ‘all-d’ homologues of the peptides displayed markedly reduced activity, indicating a chiral target. Pharmacological profiling revealed a good in vitro therapeutic index, no cytotoxicity or cardiotoxicity, an inconspicuous broad-panel off-target profile, and no acute toxicity in mice at 10 mg/kg. In mouse pharmacokinetic experiments LS-sarcotoxin and LS-stomoxyn plasma levels above the lower limit of quantification (1 and 0.25 mg/mL, respectively) were detected after 5 and 15 min, respectively.

Conclusions

LS-sarcotoxin and LS-stomoxyn are suitable as lead candidates for the development of novel antibiotics; however, their pharmacokinetic properties need to be improved for systemic administration.

Glycyrrhizin Use for Multi-Drug Resistant Pseudomonas aeruginosa: In Vitro and In Vivo Studies

Purpose

Our purpose was to test glycyrrhizin (GLY) effects and ciprofloxacin interactions on multidrug resistant (MDR) isolates of Pseudomonas aeruginosa in vitro and in vivo in a mouse model of keratitis.

Methods

A Hardy-disk tested antibiotic sensitivity of isolates MDR9 (nonocular) and B1045 (ocular). GLY MIC (both isolates) and ciprofloxacin was determined spectrophotometrically. A live/dead assay using confocal microscopy and plate count, tested GLY effects on bacterial permeabilization/viability. Proteomics profiled bacterial efflux pumps (MDR9 vs. PAO1); RT-PCR comparatively tested GLY effects on their mRNA expression levels. The activity of efflux pumps was tested using ethidium bromide (EB); and scanning electron microscopy (SEM) visualized the effects of GLY treatment of bacteria. A combination of GLY and ciprofloxacin was tested in C57BL/6 mice (begun 18 hours after infection) and disease scored, photographed and MPO and plate counts done.

Results

MDR9 was resistant to 6/12 and B1045 to 7/12 antibiotics (both to ciprofloxacin). MIC GLY for MDR9 was 40 mg/mL and 15 mg/mL for B1045. Ciprofloxacin MIC (32 μg/mL) was reduced 2-fold to 16 μg/mL when ciprofloxacin and GLY were combined. GLY altered bacterial membrane permeability and reduced viability. Proteomics revealed increased efflux pumps in MDR9 versus PAO1; GLY reduced their mRNA expression levels and EB suggested decreased activity. In C57BL/6 mice, treatment with GLY and ciprofloxacin versus ciprofloxacin, significantly reduced clinical scores, plate count, and MPO.

Conclusions

GLY decreases MDR by: altering bacterial parameters, including viability and efflux pump activity. In vivo, it increases the effectiveness of ciprofloxacin, reducing ocular disease, plate count, and MPO activity.

Metallohelices that kill Gram-negative pathogens using intracellular antimicrobial peptide pathways

A range of new water-compatible optically pure metallohelices - made by self-assembly of simple non-peptidic organic components around Fe ions - exhibit similar architecture to some natural cationic antimicrobial peptides (CAMPs) and are found to have high, structure-dependent activity against bacteria, including clinically problematic Gram-negative pathogens. A key compound is shown to freely enter rapidly dividing E. coli cells without significant membrane disruption, and localise in distinct foci near the poles. Several related observations of CAMP-like mechanisms are made via biophysical measurements, whole genome sequencing of tolerance mutants and transcriptomic analysis. These include: high selectivity for binding of G-quadruplex DNA over double stranded DNA; inhibition of both DNA gyrase and topoisomerase I in vitro; curing of a plasmid that contributes to the very high virulence of the E. coli strain used; activation of various two-component sensor/regulator and acid response pathways; and subsequent attempts by the cell to lower the net negative charge of the surface. This impact of the compound on multiple structures and pathways corresponds with our inability to isolate fully resistant mutant strains, and supports the idea that CAMP-inspired chemical scaffolds are a realistic approach for antimicrobial drug discovery, without the practical barriers to development that are associated with natural CAMPS.

Transient Silencing of Antibiotic Resistance by Mutation Represents a Significant Potential Source of Unanticipated Therapeutic Failure

Sporadic literature reports describe isolates of pathogenic bacteria that harbor an antibiotic resistance determinant but remain susceptible to the corresponding antibiotic as a consequence of a genetic defect. Such strains represent a source from which antibiotic resistance may reemerge to cause treatment failure in patients. Here, we report a systematic investigation into the prevalence and nature of this phenomenon, which we term silencing of antibiotic resistance by mutation (SARM). Instances of SARM were detected among 1,470 Staphylococcus aureus isolates through side-by-side comparison of antibiotic resistance genotype (as determined by whole-genome sequencing) versus phenotype (as assessed through susceptibility testing). Of the isolates analyzed, 152 (10.3%) harbored a silenced resistance gene, including 46 (3.1%) that exhibited SARM to currently deployed antistaphylococcal drugs. SARM resulted from diverse mutational events but most commonly through frameshift mutation of resistance determinants as a result of point deletion in poly(A) tracts. The majority (∼90%) of SARM strains reverted to antibiotic resistance at frequencies of ≥10^-9; thus, while appearing antibiotic sensitive in the clinical microbiology laboratory, most S. aureus isolates exhibiting SARM will revert to antibiotic resistance at frequencies achievable in patients. In view of its prevalence in a major pathogen, SARM represents a significant potential threat to the therapeutic efficacy of antibiotics.IMPORTANCE Antibiotic resistance hinders the treatment of bacterial infection. To guide effective therapy, clinical microbiology laboratories routinely perform susceptibility testing to determine the antibiotic sensitivity of an infecting pathogen. This approach relies on the assumption that it can reliably distinguish bacteria capable of expressing antibiotic resistance in patients, an idea challenged by the present study. We report that the important human pathogen Staphylococcus aureus frequently carries antibiotic resistance genes that have become inactivated ("silenced") by mutation, leading strains to appear antibiotic sensitive. However, resistance can rapidly reemerge in most such cases, at frequencies readily achievable in infected patients. Silent antibiotic resistance is therefore prevalent, transient, and evades routine detection, rendering it a significant potential threat to antibacterial chemotherapy.

Chemical Composition and Mechanism of Vibriocidal Action of Essential Oil from Resin of Protium heptaphyllum

Protium heptaphyllum is a plant widely distributed in Brazilian ecosystems that produce a resin which has pharmacological activities. In this study, the chemical composition, antimicrobial and antibiofilm activity, and the possible mechanism of action against the bacterium V. parahaemolyticus of essential oil from P. heptaphyllum (EOPH) were investigated. Twenty-two components were detected in EOPH, and β-phellandrene (60.68%) had the majority. The inhibition halo, MIC, and MBC values were 11 mm, 2 mg/mL, and 8 mg/mL, respectively. Biofilm biomass inhibition and biomass reduction of the preformed biofilm were detected at 4 mg/mL EOPH concentration. The assays of cell constituent release and membrane permeability indicated that EOPH may disrupt the cell membrane, leading to leakage of intracellular constituent as reducing sugars and materials with an absorbance of 260 nm.

Functionalised bicyclic tetramates derived from cysteine as antibacterial agents

Routes to bicyclic tetramates derived from cysteine permitting ready incorporation of functionality at two different points around the periphery of a heterocyclic skeleton are reported. This has enabled the identification of systems active against Gram-positive bacteria, some of which show gyrase and RNA polymerase inhibitory activity. In particular, tetramates substituted with glycosyl side chains, chosen to impart polarity and aqueous solubility, show high antibacterial activity coupled with modest gyrase/polymerase activity in two cases. An analysis of physicochemical properties indicates that the antibacterially active tetramates generally occupy physicochemical space with MW of 300-600, clog D7.4 of -2.5 to 4 and rel. PSA of 11-22%. This work demonstrates that biologically active 3D libraries are readily available by manipulation of a tetramate skeleton.

Bio-Orthogonal Chemistry and Reloadable Biomaterial Enable Local Activation of Antibiotic Prodrugs and Enhance Treatments against Staphylococcus aureus Infections

Systemic administration of antibiotics can cause severe side-effects such as liver and kidney toxicity, destruction of healthy gut bacteria, as well as multidrug resistance. Here, we present a bio-orthogonal chemistry-based strategy toward local prodrug concentration and activation. The strategy is based on the inverse electron-demand Diels-Alder chemistry between trans-cyclooctene and tetrazine and involves a biomaterial that can concentrate and activate multiple doses of systemic antibiotic therapy prodrugs at a local site. We demonstrate that a biomaterial, consisting of alginate hydrogel modified with tetrazine, is efficient at activating multiple doses of prodrugs of vancomycin and daptomycin in vitro as well as in vivo. These results support a drug delivery process that is independent of endogenous environmental markers. This approach is expected to improve therapeutic efficacy with decreased side-effects of antibiotics against bacterial infections. The platform has a wide scope of possible applications such as wound healing, and cancer and immunotherapy.

Thinking Outside the Box-Novel Antibacterials To Tackle the Resistance Crisis

The public view on antibiotics as reliable medicines changed when reports about "resistant superbugs" appeared in the news. While reasons for this resistance development are easily spotted, solutions for re-establishing effective antibiotics are still in their infancy. This Review encompasses several aspects of the antibiotic development pipeline from very early strategies to mature drugs. An interdisciplinary overview is given of methods suitable for mining novel antibiotics and strategies discussed to unravel their modes of action. Select examples of antibiotics recently identified by using these platforms not only illustrate the efficiency of these measures, but also highlight promising clinical candidates with therapeutic potential. Furthermore, the concept of molecules that disarm pathogens by addressing gatekeepers of virulence will be covered. The Review concludes with an evaluation of antibacterials currently in clinical development. Overall, this Review aims to connect select innovative antimicrobial approaches to stimulate interdisciplinary partnerships between chemists from academia and industry.

Interfacial Emulsification: An Emerging Monodisperse Droplet Generation Method for Microreactors and Bioanalysis

The generation of uniform droplets has been extensively investigated owing to its profound potentials both in scientific research and engineering applications. Although various methods have been put forward to expand this area, new innovations are still needed to improve the technical convenience and save instrumental cost. In this feature article, we highlight an interfacial emulsification technique that we developed in the past several years. This technique serves as a platform for preparing uniform droplets that are formed on the air-liquid interface of the continuous phase based on interfacial shearing. Three specific aspects of interfacial emulsification are reviewed, including its basic design and principle, the preparation of droplets with controllable size and adjustable components, and practical applications of the method in bioanalysis, microreactors, and particle synthesis. Compared to other droplet generation methods, several attractive advantages and perspectives for further development have been summarized.

Mixing two different propolis samples potentiates their antimicrobial activity and wound healing property: A novel approach in wound healing and infection

Aim:

The study aimed to investigate whether mixing two different propolis samples can potentiate their biological activity. This hypothesis was tested by studying the effect of mixed propolis on microbial growth and wound healing and compared with the effect of each propolis individually.

Materials and Methods:

The effect of mixing two different propolis extracts (A and B) collected from different locations in Iraq on Escherichia coli, Staphylococcus aureus, and Candida albicans was studied by minimum inhibitory concentration assessment and compared with the effect of each propolis. Wound healing effect of the mixed propolis was studied. Twenty-four rabbits were used for the experiment, and they were assigned to four groups. Wounds were created on the dorsum of each rabbit and treated by topical application of 1 mL of either mixed propolis, propolis A, or propolis B extracts or were kept without treatment as a control. Macroscopic wound evaluation was performed with an assessment of wound size, wound recovery, redness, edema, discharge, granulation tissue, and epithelialization.

Results:

Propolis A was more potent than propolis B extracts to inhibit the growth of E. coli, S. aureus, and C. albicans (p<0.05). However, mixed propolis showed a higher antimicrobial activity toward all the pathogens than propolis A or propolis B extract individually (p<0.05). Furthermore, propolis A and propolis B extracts showed favorable effects on wound healing which was more pronounced with propolis A extract. Interestingly, mixed propolis accelerated wound healing faster than propolis A or propolis B extracts, and it shortened the time of reepithelialization (p<0.05).

Conclusion:

This study demonstrates for the first time that mixing different propolis samples possesses a higher antimicrobial activity and higher wound healing property than individual propolis. This approach could pave the way for the development of more effective antimicrobials and wound healing agents.

Membrane activity profiling of small molecule B. subtilis growth inhibitors utilizing novel duel-dye fluorescence assay

Small molecule disruption of the bacterial membrane is both a challenge and interest for drug development. While some avoid membrane activity due to toxicity issues, others are interested in leveraging the effects for new treatments. Existing assays are available for measuring disruption of membrane potential or membrane permeability, two key characteristics of the bacterial membrane, however they are limited in their ability to distinguish between these properties. Here, we demonstrate a high throughput assay for detection and characterization of membrane active compounds. The assay distinguishes the effect of small molecules on either the membrane potential or membrane permeability using the fluorescent dyes TO-PRO-3 iodide and DiOC2(3) without the need for secondary assays. We then applied this assay to a library of 3520 synthetic molecules previously shown to inhibit growth of B. subtilis in order to determine the frequency of membrane activity within such a biologically active library. From the library, we found 249 compounds that demonstrated significant membrane activity, suggesting that synthetic libraries of this kind do not contain a plurality of membrane active molecules.

Revisiting unexploited antibiotics in search of new antibacterial drug candidates: the case of γ-actinorhodin

Of the thousands of natural product antibiotics discovered to date, only a handful have been developed for the treatment of bacterial infection. The clinically unexploited majority likely include compounds with untapped potential as antibacterial drugs, and in view of the ever-growing unmet medical need for such agents, warrant systematic re-evaluation. Here we revisit the actinorhodins, a class that was first reported 70 years ago, but which remains poorly characterized. We show that γ-actinorhodin possesses many of the requisite properties of an antibacterial drug, displaying potent and selective bactericidal activity against key Gram-positive pathogens (including Staphylococcus aureus and enterococci), a mode of action distinct from that of other agents in clinical use, an extremely low potential for the development of resistance, and a degree of in vivo efficacy in an invertebrate model of infection. Our findings underscore the utility of revisiting unexploited antibiotics as a source of novel antibacterial drug candidates.

Development of Methionyl-tRNA Synthetase Inhibitors as Antibiotics for Gram-Positive Bacterial Infections

Antibiotic-resistant bacteria are widespread and pose a growing threat to human health. New antibiotics acting by novel mechanisms of action are needed to address this challenge. The bacterial methionyl-tRNA synthetase (MetRS) enzyme is essential for protein synthesis, and the type found in Gram-positive bacteria is substantially different from its counterpart found in the mammalian cytoplasm. Both previously published and new selective inhibitors were shown to be highly active against Gram-positive bacteria with MICs of ≤1.3 μg/ml against Staphylococcus, Enterococcus, and Streptococcus strains. Incorporation of radioactive precursors demonstrated that the mechanism of activity was due to the inhibition of protein synthesis. Little activity against Gram-negative bacteria was observed, consistent with the fact that Gram-negative bacterial species contain a different type of MetRS enzyme. The ratio of the MIC to the minimum bactericidal concentration (MBC) was consistent with a bacteriostatic mechanism. The level of protein binding of the compounds was high (>95%), and this translated to a substantial increase in MICs when the compounds were tested in the presence of serum. Despite this, the compounds were very active when they were tested in a Staphylococcus aureus murine thigh infection model. Compounds 1717 and 2144, given by oral gavage, resulted in 3- to 4-log decreases in the bacterial load compared to that in vehicle-treated mice, which was comparable to the results observed with the comparator drugs, vancomycin and linezolid. In summary, the research describes MetRS inhibitors with oral bioavailability that represent a class of compounds acting by a novel mechanism with excellent potential for clinical development.

Characterization of Three Ocular Clinical Isolates of P. aeruginosa: Viability, Biofilm Formation, Adherence, Infectivity, and Effects of Glycyrrhizin

We selectively characterized three isolates from Pseudomonas aeruginosa keratitis patients and how glycyrrhizin (GLY) affected them. Type III toxins were determined using polymerase chain reaction (PCR). Minimum Inhibitory Concentration (MIC) of GLY and assays for its effects on: time kill, bacterial permeability, and biofilm/adhesion were done. In vivo, C57BL/6 (B6) mice were treated topically with GLY after G81007 infection. Clinical score, photography with a slit lamp and RT-PCR were used to assess treatment effects. Isolates expressed exoS and exoT, but not exoU. MIC for all isolates was 40 mg/mL GLY and bacteriostatic effects were seen for G81007 after treatment using time kill assays. From viability testing, GLY treatment significantly increased the number of permeabilized bacteria (live/dead assay). Isolates 070490 and G81007 formed more biofilms compared with R59733 and PAO1 (control). GLY-treated bacteria had diminished biofilm compared with controls for all isolates. GLY reduced adherence of the G81007 isolate to cultured cells and affected specific biofilm associated systems tested by reverse transcription PCR (RT-PCR). In vivo, after G81007 infection, GLY treatment reduced clinical score and messenger RNA (mRNA) expression of IL-1β, TNF-α, CXCL2 and HMGB1. This study provides evidence that GLY is bacteriostatic for G81007. It also affects biofilm production, adherence to cultured cells, and an improved keratitis outcome.

Antibacterial, tyrosinase, and DNA photocleavage studies of some triazolylnucleosides

In order to explore the biological potential, some synthesized triazolylnucleosides were evaluated for their antibacterial, tyrosinase and DNA photocleavage activities. Triazolylnucleosides (5-12) were screened against Staphylococcus aureus (ATCC 6538), gram-positive and Escherichia coli (ATCC 10536), gram-negative bacterial strains. Among the series, compound 9 exhibited a significant level of antibacterial activity against both strains at higher concentration in reference to the standard drug, Levofloxacin. Tyrosinase activity and inhibition of these compounds were also studied, and it has been found that compounds 8 and 11 displayed more than 50% inhibitory activity. In addition, six compounds (7-12) were evaluated for their DNA photocleavage activity. The compounds 8 and 12 exhibited excellent DNA photocleavage activity at a concentration of 10 μg and may be used as template for antitumor drugs in the future.

Phenolic Compounds and In Vitro Antibacterial and Antioxidant Activities of Three Tropic Fruits: Persimmon, Guava, and Sweetsop

In our previous study, we have found that persimmon, guava, and sweetsop owned considerably high antioxidant activity and contained high total phenolic contents as well. In order to further supply information on the antibacterial and antioxidant activity of these three tropic fruits, they were extracted by 80% methanol. We then examined the extractions about their phenolic compounds and also studied the extractions and phenolic contents about their minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against twelve targeted pathogens including 8 standard strains (Staphylococcus aureus, Bacillus cereus, Staphylococcus epidermidis, Monilia albican, Escherichia coli, Salmonella typhimurium, Shigella flexneri, and Pseudomonas aeruginosa) and 4 multidrug-resistant strains (methicillin-resistant Staphylococcus aureus, ESBLs-producing Escherichia coli, carbapenems-resistant Pseudomonas aeruginosa, and multidrug-resistant Acinetobacter baumannii), which are common and comprehensive in clinic. We also employed two ways, that is, FRAP and TEAC, to evaluate their antioxidant activities, using ultraviolet and visible spectrophotometer. Our study indicated that the three tropical fruits possessed obvious antioxidant and antibacterial activity, which supported the possibility of developing the fruits into new natural resource food and functional food as well as new natural antimicrobial agent and food preservatives. Moreover, phenolic compounds detected in the fruits could be used as a potential natural antibacterial agent and antioxidant.

Genetic diversity and antimicrobial susceptibility of Nocardia species among patients with nocardiosis

The aim of this multicenter study was to determine the genetic diversity and antibiotic susceptibility of clinically isolated Nocardia species. One hundred twenty-seven patients with nocardiosis were randomly selected from 5 provinces of Iran. Molecular diagnosis of Nocardia species was performed using multilocus sequence analysis of gyrase B of the β subunit of DNA topoisomerase (gyrB), and 16S rRNA and subunit A of SecA preproteintranslocase (secA1). Antimicrobial susceptibility testing was performed following the Clinical and Laboratory Standards Institute recommendations. Thirty-five N. cyriacigeorgica, 30 N. asteroides, 26 N. farcinica, 12 N. otitidiscaviarum, and 10 N. abscessus cultures were studied. All isolates were susceptible to linezolid. All isolates of N. cyriacigeorgica, N. asteroides, N. abscessus, and N. otitidiscaviarum were susceptible to trimethoprim-sulfamethoxazole, while 8% of N. farcinica isolates were resistant to this drug. All N. otitidiscaviarum isolates were highly resistant to imipenem, but N. cyriacigeorgica, N. asteroides, N. farcinica, and N. abscessus were only moderate resistant. The susceptibility patterns vary with different species of Nocardia. Resistance to trimethoprim-sulfamethoxazole in Iran is low and this drug should be first line therapy, unless drug susceptibility testing shows resistance. Linezolid also covers Nocardia well and could be a second line agent.

Equisetin, reutericyclin and streptolodygin as natural product lead structures for novel antibiotic libraries

The emergence of antimicrobial resistance has created a need for the development of novel antibacterial therapies to treat infection. Natural products that exhibit antibacterial activity offer validated starting points for library generation, and the authors report here that small molecule mimics of tetramate-containing natural products may show antibacterial activity and offer the potential for further optimization.