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Researches on Novel Antibacterial Agents

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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Medicinal Chemistry".

Deadline for manuscript submissions: closed (31 August 2022) | Viewed by 31492

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Prof. Dr. Hristo Najdenski

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Department of Infectious Microbiology, The Stephan Angeloff Institute of Microbiology, Bulgarian Academy of Sciences, 26 Acad. G. Bonchev Str., 1113 Sofia, Bulgaria
Interests: pathogenic bacteria; zoonoses; factors and mechanisms of bacterial virulence,; bacterial-host relationships; medical and veterinary microbiology; infectious immunology; molecular biology; ecology of pathogenic bacteria; new antibacterial agents; antimicrobial resistance
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Dear Colleagues,

The natural products of plant, animal, microbial origin, etc., are rich sources of bioactive compounds with diverse structures and functional groups. This could make bacteria and other microorganisms sensitive to them and contribute to the overcoming of global health problems like antimicrobial resistance (AMR). Each year, the WHO is alerted to crisis levels of AMR in various communities and hospitals all over the world due to the overuse of antibiotics and the genetic evolution of bacteria. This increase in the resistance emphasizes the importance of the continued development of new candidates of natural origin. According to the economist Jim O’Neill, deaths caused by AMR could increase from 700,000 in 2014 to 10 million by 2050. It is known that the bacteria have natural resistance and acquired resistance, as a result of genetic changes. The first includes efflux pumps, an impermeable cell wall, biofilm formation, and quorum sensing, while the second includes genetic changes. This requires searching for and developing novel antibacterial agents with the potential for pleiotropic effects, whihc are different from the current ones. Hence, in this Special Issue we welcome the submission of publications of research and review articles on the development of new compounds or mixtures with antibacterial activities, and studies clarifying their mechanisms and modes of action, including the inhibition of biofilm formation, quorum sensing, membrane interactions, the suppression of virulence/metabolite gene expression, the in vitro and in vivo evaluation of antibacterial effect, antimicrobial targets, and molecular approaches.

Prof. Dr. Hristo Najdenski
Guest Editor

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Keywords

drug discovery
antibacterial compounds
structure activity relationship (SAR)
in vitro and in vivo biological activity
antimicrobial resistance
antimicrobial resistance mechanisms
molecular mechanisms of antibacterial activity
novel targets of antibacterial agents

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Published Papers (10 papers)

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Research

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19 pages, 2202 KiB

Open AccessArticle

Study of the Physicochemical and Biological Properties of the Lipid Complex of Marine Microalgae Isolated from the Coastal Areas of the Eastern Water Area of the Baltic Sea

by Vyacheslav Dolganyuk, Anna Andreeva, Stanislav Sukhikh, Egor Kashirskikh, Alexander Prosekov, Svetlana Ivanova, Philippe Michaud and Olga Babich

Molecules 2022, 27(18), 5871; https://doi.org/10.3390/molecules27185871 - 10 Sep 2022

Cited by 3 | Viewed by 1888

Abstract

The Baltic Sea algae species composition includes marine euryhaline, freshwater euryhaline, and true brackish water forms. This study aimed to isolate a lipid–pigment complex from microalgae of the Baltic Sea (Kaliningrad region) and investigate its antimicrobial activity against Gram-positive and Gram-negative bacteria. Microalgae were sampled using a box-shaped bottom sampler. Sequencing was used for identification. Spectroscopy and chromatography with mass spectroscopy were used to study the properties of microalgae. Antibiotic activity was determined by the disc diffusion test. Lipids were extracted using the Folch method. Analysis of the results demonstrated the presence of antimicrobial activity of the lipid–pigment complex of microalgae against E. coli (the zone diameter was 17.0 ± 0.47 mm and 17.0 ± 0.21 mm in Chlorella vulgaris and Arthrospira platensis, respectively) and Bacillus pumilus (maximum inhibition diameter 16.0 ± 0.27 mm in C. vulgaris and 16.0 ± 0.22 mm in A. platensis). The cytotoxic and antioxidant activities of the lipid complexes of microalgae C. vulgaris and A. platensis were established and their physicochemical properties and fatty acid composition were studied. The results demonstrated that the lipid–pigment complex under experimental conditions was the most effective against P. pentosaceus among Gram-positive bacteria. Antimicrobial activity is directly related to the concentration of the lipid–pigment complex. The presence of antibacterial activity in microalgae lipid–pigment complexes opens the door to the development of alternative natural preparations for the prevention of microbial contamination of feed. Because of their biological activity, Baltic Sea microalgae can be used as an alternative to banned antibiotics in a variety of fields, including agriculture, medicine, cosmetology, and food preservation. Full article

(This article belongs to the Special Issue Researches on Novel Antibacterial Agents)

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23 pages, 6475 KiB

Open AccessArticle

The Healing Capability of Clove Flower Extract (CFE) in Streptozotocin-Induced (STZ-Induced) Diabetic Rat Wounds Infected with Multidrug Resistant Bacteria

by Rewaa Ali, Tarek Khamis, Gamal Enan, Gamal El-Didamony, Basel Sitohy and Gamal Abdel-Fattah

Molecules 2022, 27(7), 2270; https://doi.org/10.3390/molecules27072270 - 31 Mar 2022

Cited by 11 | Viewed by 5262

Abstract

Treatment of diabetic foot ulcer (DFU) is of great challenge as it is shown to be infected by multidrug resistant bacteria (MDR bacteria). Sixty four bacterial isolates were isolated from DFU cases; antibiotic susceptibility tests were carried out for all of them. One bacterial isolate (number 11) was shown to resist the action of 8 out of 12 antibiotics used and was identified by both a Vitek-2 system and 16S rRNA fingerprints as belonging to Proteus mirabilis, and was designated Proteus mirabilis LC587231 (P. mirabilis). Clove flower extract (CFE) inhibited distinctively the P. mirabilis bacterium obtained. GC-MS spectroscopy showed that this CFE contained nine bioactive compounds. The effect of CFE on wound healing of Type 1 diabetic albino rats (Rattus norvegicus) was studied. The results indicated that topical application of CFE hydrogel improved wound size, wound index, mRNA expression of the wound healing markers (Coli1, MMP9, Fibronectin, PCNA, and TGFβ), growth factor signaling pathways (PPAR-α, PGC1-α, GLP-1, GLPr-1, EGF-β, EGF-βr, VEGF-β, and FGF-β), inflammatory cytokine expression (IL8, TNFα, NFKβ, IL1β, and MCP1), as well as anti-inflammatory cytokines (IL4 & IL10), pro-apoptotic markers (FAS, FAS-L, BAX, BAX/BCL-2, Caspase-3, P53, P38), as well as an antiapoptotic one (BCL2). Furthermore, it improved the wound oxidative state and reduced the wound microbial load, as the cefepime therapy improved the wound healing parameters. Based on the previous notions, it could be concluded that CFE represents a valid antibiotics alternative for DFU therapy since it improves diabetic wound healing and exerts antibacterial activity either in vitro or in vivo. Full article

(This article belongs to the Special Issue Researches on Novel Antibacterial Agents)

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13 pages, 986 KiB

Open AccessArticle

Bioprospecting the Antibiofilm and Antimicrobial Activity of Soil and Insect Gut Bacteria

by Sofía Raffaelli, Eduardo Abreo, Nora Altier, Álvaro Vázquez and Silvana Alborés

Molecules 2022, 27(6), 2002; https://doi.org/10.3390/molecules27062002 - 21 Mar 2022

Cited by 5 | Viewed by 2941

Abstract

Antimicrobial resistance is a growing concern in public health and current research shows an important role for bacterial biofilms in recurrent or chronic infections. New strategies, therefore, are necessary to overcome antimicrobial resistance, through the development of new therapies that could alter or inhibit biofilm formation. In this sense, antibiofilm natural products are very promising. In this work, a bioprospection of antimicrobial and antibiofilm extracts from Uruguayan soil bacteria and insect gut bacteria was carried out. Extracts from extracellular broths were tested for their ability to inhibit planktonic cell growth and biofilm formation. Genomic analysis of Bacillus cereus ILBB55 was carried out. All extracts were able to inhibit the growth of, at least, one microorganism and several extracts showed MICs lower than 500 µg mL⁻¹ against microorganisms of clinical relevance (Staphylococcus aureus, Pseudomonas aeruginosa, and Enterobacter cloacae). Among the extracts evaluated for biofilm inhibition only ILBB55, from B. cereus, was able to inhibit, S. aureus (99%) and P. aeruginosa (62%) biofilms. Genomic analysis of this strain showed gene clusters similar to other clusters that code for known antimicrobial compounds. Our study revealed that extracts from soil bacteria and insect gut bacteria, especially from B. cereus ILBB55, could be potential candidates for drug discovery to treat infectious diseases and inhibit S. aureus and P. aeruginosa biofilms. Full article

(This article belongs to the Special Issue Researches on Novel Antibacterial Agents)

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28 pages, 5857 KiB

Open AccessArticle

Identification of Antibacterial Components in the Methanol-Phase Extract from Edible Herbaceous Plant Rumex madaio Makino and Their Antibacterial Action Modes

by Yue Liu, Lianzhi Yang, Pingping Liu, Yinzhe Jin, Si Qin and Lanming Chen

Molecules 2022, 27(3), 660; https://doi.org/10.3390/molecules27030660 - 20 Jan 2022

Cited by 6 | Viewed by 2409

Abstract

Outbreaks and prevalence of infectious diseases worldwide are some of the major contributors to morbidity and morbidity in humans. Pharmacophageous plants are the best source for searching antibacterial compounds with low toxicity to humans. In this study, we identified, for the first time, antibacterial components and action modes of methanol-phase extract from such one edible herbaceous plant Rumex madaio Makino. The bacteriostatic rate of the extract was 75% against 23 species of common pathogenic bacteria. The extract was further purified using the preparative high-performance liquid chromatography (Prep-HPLC) technique, and five separated componential complexes (CC) were obtained. Among these, the CC 1 significantly increased cell surface hydrophobicity and membrane permeability and decreased membrane fluidity, which damaged cell structure integrity of Gram-positive and -negative pathogens tested. A total of 58 different compounds in the extract were identified using ultra-HPLC and mass spectrometry (UHPLC-MS) techniques. Comparative transcriptomic analyses revealed a number of differentially expressed genes and various changed metabolic pathways mediated by the CC1 action, such as down-regulated carbohydrate transport and/or utilization and energy metabolism in four pathogenic strains tested. Overall, the results in this study demonstrated that the CC1 from R. madaio Makino are promising candidates for antibacterial medicine and human health care products. Full article

(This article belongs to the Special Issue Researches on Novel Antibacterial Agents)

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25 pages, 1458 KiB

Open AccessArticle

Antimicrobial and Antioxidant Potential of Scenedesmus obliquus Microalgae in the Context of Integral Biorefinery Concept

by Maya Margaritova Zaharieva, Dimitrina Zheleva-Dimitrova, Snezhana Rusinova-Videva, Yana Ilieva, Anna Brachkova, Vessela Balabanova, Reneta Gevrenova, Tanya Chan Kim, Mila Kaleva, Almira Georgieva, Milka Mileva, Krassimira Yoncheva, Niko Benbassat, Hristo Najdenski and Alexander Dimitrov Kroumov

Molecules 2022, 27(2), 519; https://doi.org/10.3390/molecules27020519 - 14 Jan 2022

Cited by 18 | Viewed by 3326

Abstract

Small-scale photobioreactors (PBRs) in the inoculum stage were designed with internal (red or green) and external white LED light as an initial step of a larger-scale installation aimed at fulfilling the integral biorefinery concept for maximum utilization of microalgal biomass in a multifunctional laboratory. The specific growth rate of Scenedesmus obliquus (Turpin) Kützing biomass for given cultural conditions was analyzed by using MAPLE software. For the determination of total polyphenols, flavonoids, chlorophyll “a” and “b”, carotenoids and lipids, UHPLC-HRMS, ISO-20776/1, ISO-10993-5 and CUPRAC tests were carried out. Under red light growing, a higher content of polyphenols was found, while the green light favoured the flavonoid accumulation in the biomass. Chlorophylls, carotenoids and lipids were in the same order of magnitude in both samples. The dichloromethane extracts obtained from the biomass of each PBR synergistically potentiated at low concentrations (0.01–0.05 mg/mL) the antibacterial activity of penicillin, fluoroquinolones or oregano essential oil against the selected food-borne pathogens (Staphylococcus aureus, Escherichia coli and Salmonella typhimurium) without showing any in vitro cytotoxicity. Both extracts exhibited good cupric ion-reducing antioxidant capacity at concentrations above 0.042–0.08 mg/mL. The UHPLC-HRMS analysis revealed that both extracts contained long chain fatty acids and carotenoids thus explaining their antibacterial and antioxidant potential. The applied engineering approach showed a great potential to modify microalgae metabolism for the synthesis of target compounds by S. obliquus with capacity for the development of health-promoting nutraceuticals for poultry farming. Full article

(This article belongs to the Special Issue Researches on Novel Antibacterial Agents)

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25 pages, 3918 KiB

Open AccessArticle

In Vitro Antineoplastic and Antiviral Activity and In Vivo Toxicity of Geum urbanum L. Extracts

by Maya M. Zaharieva, Lyudmila L. Dimitrova, Stanislav Philipov, Ivanka Nikolova, Neli Vilhelmova, Petar Grozdanov, Nadya Nikolova, Milena Popova, Vassya Bankova, Spiro M. Konstantinov, Dimitrina Zheleva-Dimitrova and Hristo M. Najdenski

Molecules 2022, 27(1), 245; https://doi.org/10.3390/molecules27010245 - 31 Dec 2021

Cited by 6 | Viewed by 2655

Abstract

This study evaluated the in vitro antineoplastic and antiviral potential and in vivo toxicity of twelve extracts with different polarity obtained from the herbaceous perennial plant Geum urbanum L. (Rosaceae). In vitro cytotoxicity was determined by ISO 10993-5/2009 on bladder cancer, (T-24 and BC-3C), liver carcinoma (HEP-G2) and normal embryonic kidney (HEK-293) cell lines. The antineoplastic activity was elucidated through assays of cell clonogenicity, apoptosis induction, nuclear factor kappa B p65 (NFκB p65) activation and total glutathione levels. Neutral red uptake study was applied for antiviral activity. The most promising G. urbanum extract was analyzed by UHPLC–HRMS. The acute in vivo toxicity analysis was carried out following OEDC 423. The ethyl acetate extract of aerial parts (EtOAc-AP) exhibited the strongest antineoplastic activity on bladder cancer cell lines (IC₅₀ = 21.33–25.28 µg/mL) by inducing apoptosis and inhibiting NFκB p65 and cell clonogenicity. EtOAc and n-butanol extracts showed moderate antiviral activity against human adenovirus type 5 and human simplex virus type I. Seventy four secondary metabolites (gallic and ellagic acid derivatives, phenolic acids, flavonoids, etc.) were identified in EtOAc-AP by UHPLC–HRMS. This extract induced no signs of acute toxicity in liver and kidney specimens of H-albino mice in doses up to 210 mg/kg. In conclusion, our study contributes substantially to the detailed pharmacological characterization of G. urbanum, thus helping the development of health-promoting phytopreparations. Full article

(This article belongs to the Special Issue Researches on Novel Antibacterial Agents)

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16 pages, 2983 KiB

Open AccessArticle

Non-Thermal Plasma Sources Based on Cometary and Point-to-Ring Discharges

by Josef Khun, Anna Machková, Petra Kašparová, Myron Klenivskyi, Eva Vaňková, Pavel Galář, Jaroslav Julák and Vladimír Scholtz

Molecules 2022, 27(1), 238; https://doi.org/10.3390/molecules27010238 - 31 Dec 2021

Cited by 8 | Viewed by 2439

Abstract

A non-thermal plasma (NTP) is a promising tool against the development of bacterial, viral, and fungal diseases. The recently revealed development of microbial resistance to traditional drugs has increased interest in the use of NTPs. We have studied and compared the physical and microbicidal properties of two types of NTP sources based on a cometary discharge in the point-to-point electrode configuration and a corona discharge in the point-to-ring electrode configuration. The electrical and emission properties of both discharges are reported. The microbicidal effect of NTP sources was tested on three strains of the bacterium Staphylococcus aureus (including the methicillin-resistant strain), the bacterium Pseudomonas aeruginosa, the yeast Candida albicans, and the micromycete Trichophyton interdigitale. In general, the cometary discharge is a less stable source of NTP and mostly forms smaller but more rapidly emerging inhibition zones on agar plates. Due to the point-to-ring electrode configuration, the second type of discharge has higher stability and provides larger affected but often not completely inhibited zones. However, after 60 min of exposure, the NTP sources based on the cometary and point-to-ring discharges showed a similar microbicidal effect for bacteria and an individual effect for microscopic fungi. Full article

(This article belongs to the Special Issue Researches on Novel Antibacterial Agents)

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13 pages, 416 KiB

Open AccessCommunication

Novel Small-Molecule Hybrid-Antibacterial Agents against S. aureus and MRSA Strains

by Robin Gehrmann, Tobias Hertlein, Elisa Hopke, Knut Ohlsen, Michael Lalk and Andreas Hilgeroth

Molecules 2022, 27(1), 61; https://doi.org/10.3390/molecules27010061 - 23 Dec 2021

Cited by 6 | Viewed by 2688

Abstract

Ongoing resistance developments against antibiotics that also affect last-resort antibiotics require novel antibacterial compounds. Strategies to discover such novel structures have been dimerization or hybridization of known antibacterial agents. We found novel antibacterial agents by dimerization of indols and hybridization with carbazoles. They were obtained in a simple one-pot reaction as bisindole tetrahydrocarbazoles. Further oxidation led to bisindole carbazoles with varied substitutions of both the indole and the carbazole scaffold. Both the tetrahydrocarbazoles and the carbazoles have been evaluated in various S. aureus strains, including MRSA strains. Those 5-cyano substituted derivatives showed best activities as determined by MIC values. The tetrahydrocarbazoles partly exceed the activity of the carbazole compounds and thus the activity of the used standard antibiotics. Thus, promising lead compounds could be identified for further studies. Full article

(This article belongs to the Special Issue Researches on Novel Antibacterial Agents)

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9 pages, 1155 KiB

Open AccessArticle

Enhancement of Antibiotic Activity by 1,8-Naphthyridine Derivatives against Multi-Resistant Bacterial Strains

by José B. de Araújo-Neto, Maria M. C. da Silva, Cícera D. de M. Oliveira-Tintino, Iêda M. Begnini, Ricardo A. Rebelo, Luiz E. da Silva, Sandro L. Mireski, Michele C. Nasato, Maria I. L. Krautler, Jaime Ribeiro-Filho, Abolghasem Siyadatpanah, Polrat Wilairatana, Henrique D. M. Coutinho and Saulo R. Tintino

Molecules 2021, 26(23), 7400; https://doi.org/10.3390/molecules26237400 - 6 Dec 2021

Cited by 8 | Viewed by 2327

Abstract

The search for new antibacterial agents has become urgent due to the exponential growth of bacterial resistance to antibiotics. Nitrogen-containing heterocycles such as 1,8-naphthyridine derivatives have been shown to have excellent antimicrobial properties. Therefore, the purpose of this study was to evaluate the antibacterial and antibiotic-modulating activities of 1,8-naphthyridine derivatives against multi-resistant bacterial strains. The broth microdilution method was used to determine the minimum inhibitory concentration (MIC) of the following compounds: 7-acetamido-1,8-naphthyridin-4(1H)-one and 3-trifluoromethyl-N-(5-chloro-1,8-naphthyridin-2-yl)-benzenesulfonamide. The antibiotic-modulating activity was analyzed using subinhibitory concentrations (MIC/8) of these compounds in combination with norfloxacin, ofloxacin, and lomefloxacin. Multi-resistant strains of Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus were used in both tests. Although the compounds had no direct antibacterial activity (MIC ≥ 1.024 µg/mL), they could decrease the MIC of these fluoroquinolones, indicating synergism was obtained from the association of the compounds. These results suggest the existence of a structure–activity relationship in this group of compounds with regard to the modulation of antibiotic activity. Therefore, we conclude that 1,8-naphthyridine derivatives potentiate the activity of fluoroquinolone antibiotics against multi-resistant bacterial strains, and thereby interesting candidates for the development of drugs against bacterial infections caused by multidrug resistant strains. Full article

(This article belongs to the Special Issue Researches on Novel Antibacterial Agents)

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Review

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12 pages, 1507 KiB

Open AccessReview

Contribution of Aldehydes and Their Derivatives to Antimicrobial and Immunomodulatory Activities

by Mariam Nasser Aljaafari, Maryam Abdulraheem Alkhoori, Mohammed Hag-Ali, Wan-Hee Cheng, Swee-Hua-Erin Lim, Jiun-Yan Loh and Kok-Song Lai

Molecules 2022, 27(11), 3589; https://doi.org/10.3390/molecules27113589 - 2 Jun 2022

Cited by 24 | Viewed by 4533

Abstract

Essential oils (EOs) are intricate combinations of evaporative compounds produced by aromatic plants and extracted by distillation or expression. EOs are natural secondary metabolites derived from plants and have been found to be useful in food and nutraceutical manufacturing, perfumery and cosmetics; they have also been found to alleviate the phenomenon of antimicrobial resistance (AMR) in addition to functioning as antibacterial and antifungal agents, balancing menstrual cycles and being efficacious as an immune system booster. Several main aldehyde constituents can be found in different types of EOs, and thus, aldehydes and their derivatives will be the main focus of this study with regard to their antimicrobial, antioxidative, anti-inflammatory and immunomodulatory effects. This brief study also explores the activity of aldehydes and their derivatives against pathogenic bacteria for future use in the clinical setting. Full article

(This article belongs to the Special Issue Researches on Novel Antibacterial Agents)

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