Special Issue "Natural Antimicrobials and Alternatives to Antimicrobials"

A special issue of Antibiotics (ISSN 2079-6382). This special issue belongs to the section "Novel Antimicrobial Agents".

Deadline for manuscript submissions: closed (31 December 2021) | Viewed by 13137

Special Issue Editors

Prof. Dr. David Martin
E-Mail Website
Guest Editor
Institute of Integrative Medicine, University of Witten/Herdecke , Herdecke, Germany
Interests: pediatrics; pediatric oncology; integrative medicine; fever
Dr. Merlin Willcox
E-Mail Website
Guest Editor
School of Primary Care, Population Sciences and Medical Education, University of Southampton, Southampton, UK
Interests: herbal medicine; primary care; common infections; antibiotic stewardship; global health
Dr. Xiao-Yang (Mio) Hu
E-Mail Website
Guest Editor
Primary Care, Population Science, and Medical Education, Faculty of Medicine, University of Southampton, Southampton, UK
Interests: antimicrobial stewardship; common infections; integrative medicine
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Michael Moore
E-Mail Website
Guest Editor
School of Primary Care, Population Sciences and Medical Education, University of Southampton, Southampton, UK
Interests: primary care; antibiotic stewardship; acute infections

Special Issue Information

Dear Colleagues,

Following on from the two Special Issues “Natural Compounds as Antimicrobial Agents”, we would like to produce a clinically oriented Special Issue on “Natural Alternatives to Antimicrobials”.

The focus is on natural and complementary medicine in humans as a tool for antibiotic stewardship.

Thus, this Special Issue will cover, but is not limited to, the following topics:

  • Herbal preparations
  • Complementary and alternative treatments for fever
  • New natural antimicrobial compounds
  • Antimicrobial effects
  • Clinical applications
  • Antifungal properties
  • Antiviral properties
  • Antibacterial mechanisms
  • Antifungal mechanisms
  • New formulations
  • Anthroposophic Medicine,
  • Ayurvedic Medicine
  • Traditional Chinese Medicine
  • Activity as disinfectants
  • Combination with other antimicrobials
  • Global microbiome changes
  • Acupuncture and moxibustion
  • Probiotics

Prof. Dr. David Martin
Dr. Merlin Willcox
Dr. Xiao-Yang (Mio) Hu
Prof. Dr. Mike Moore
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Antibiotics is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (9 papers)

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Research

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Article
The Efficacy of Moina micrura Enriched with Probiotic Bacillus pocheonensis in Enhancing Survival and Disease Resistance of Red Hybrid Tilapia (Oreochromis spp.) Larvae
Antibiotics 2021, 10(8), 989; https://doi.org/10.3390/antibiotics10080989 - 16 Aug 2021
Cited by 2 | Viewed by 1126
Abstract
The administration of probiotics via live feeds, such as Artemia and rotifers, has gained significant attention. Moreover, indiscriminate use of antibiotics in conventional aquaculture practices in order to prevent or control disease outbreaks has resulted in the occurrence of residues and antimicrobial resistance. [...] Read more.
The administration of probiotics via live feeds, such as Artemia and rotifers, has gained significant attention. Moreover, indiscriminate use of antibiotics in conventional aquaculture practices in order to prevent or control disease outbreaks has resulted in the occurrence of residues and antimicrobial resistance. Thus, the application of eco-friendly feed additives, such as probiotics, as a safer alternative has received increasing attention in recent years. However, only minimal information on the administration of probiotics via freshwater cladoceran Moina micrura is available despite being commonly used for larval and post-larval feeding of freshwater crustaceans and fish. Thus, this study aimed to evaluate the application of Bacillus pocheonensis strain S2 administered via M. micrura to red hybrid tilapia (Oreochromis spp.) larvae. Bacillus pocheonensis that has been previously isolated from Spirulina sp. was subjected to preliminary in vitro evaluation of antagonistic properties. The agar well-diffusion assay revealed that this probiont could inhibit the growth of Streptococcus agalactiae and Aeromonas hydrophila. The size of inhibition zones ranged from 8.8 ± 0.2 to 18.2 ± 0.4 mm. Moina micrura was later used as a biological model in preliminary in vivo bacterial challenge assays to evaluate the efficacy of B. pocheonensis in protecting the host from diseases. Moina micrura was pre-enriched with B. pocheonensis at 104 and 106 CFU mL1 before S. agalactiae and A. hydrophila were introduced into the culture. The study revealed that B. pocheonensis at 104 CFU mL1 was able to significantly enhance the survival of M. micrura after being challenged with both pathogens (63 ± 3%) in comparison to the control group. The relative percentage survival (RPS) of M. micrura was highest (p < 0.05) when treated with B. pocheonensis at both concentrations 104 and 106 CFU mL1 (38.33) after being challenged against S. agalactiae. To assess the efficacy of B. pocheonensis in protecting red hybrid tilapia against streptococcosis, the larvae were fed with either unenriched (control) Moina or probiont-enriched Moina daily for 10 days. A significantly (p < 0.05) higher survival rate (77 ± 3%) was observed in larvae fed with probiont-enriched M. micrura compared to other treatments, and the RPS was recorded at 62.90. In addition, the S. agalactiae load was suppressed in larvae fed probiont-enriched M. micrura (6.84±0.39 CFU mL1) in comparison to the control group (7.78±0.09 CFU mL1), indicating that the probiont might have contributed to the improvement of tilapia health and survival. This study illustrated that M. micrura was suitable to be used as a vector for probiotics in freshwater fish larvae as an alternative to hazardous antibiotics for disease control. Full article
(This article belongs to the Special Issue Natural Antimicrobials and Alternatives to Antimicrobials)
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Article
Influence of Alternative Lifestyles on Antibiotic Use during Pregnancy, Lactation and in Children
Antibiotics 2021, 10(7), 837; https://doi.org/10.3390/antibiotics10070837 - 09 Jul 2021
Viewed by 993
Abstract
Alternative lifestyles are likely to be associated with distinct usage of specific medicinal products. Our goal was to find out whether the intake of antibiotics during pregnancy and by children differs according to whether the mothers have alternative or conventional lifestyles. Therefore, we [...] Read more.
Alternative lifestyles are likely to be associated with distinct usage of specific medicinal products. Our goal was to find out whether the intake of antibiotics during pregnancy and by children differs according to whether the mothers have alternative or conventional lifestyles. Therefore, we investigated the use of antibiotics by pregnant women and by children up to 11 years of age participating in the KOALA Birth Cohort Study. This cohort comprises two recruitment groups of mother–infant pairs, one with alternative lifestyles (selected via organic food shops, anthroposophic clinicians and midwives, anthroposophic under-five clinics, Rudolf Steiner schools and relevant magazines, n = 491) the other with conventional lifestyles (no selection based on lifestyle, n = 2343). Mothers in the alternative lifestyle group more frequently adhered to specific living rules and identified themselves with anthroposophy more than mothers in the conventional lifestyle group. The results revealed significant differences in antibiotic use during pregnancy and in children from 3 months to 10 years of age between the two groups. The rate of antibiotic use in children was consistently lower in the alternative lifestyle group than in the conventional lifestyle group. Antibiotic use in pregnancy was higher in low educated women, and maternal antibiotic use during lactation was higher after an instrumented delivery in hospital. Antibiotic use in the infant was higher when they had older sibs or were born in hospital, and lower in those who had been longer breastfed. After adjustment for these factors, the differences in antibiotic use between the alternative and conventional groups remained. The results suggest that an alternative lifestyle is associated with cautious antibiotic use during pregnancy, lactation and in children. Full article
(This article belongs to the Special Issue Natural Antimicrobials and Alternatives to Antimicrobials)
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Article
Anti-Candida Activity of Hyaluronic Acid Combined with Lactobacillus crispatus Lyophilised Supernatant: A New Antifungal Strategy
Antibiotics 2021, 10(6), 628; https://doi.org/10.3390/antibiotics10060628 - 25 May 2021
Cited by 4 | Viewed by 933
Abstract
Vulvovaginal candidiasis (VVC) and recurrencies are common in reproductive-aged women. The emergence of Candida strains resistant to conventional antimycotic drugs prompted the search for alternative therapies. Hyaluronic acid (HA), a uniform and linear glycosaminoglycan, has been proposed as an anti-Candida agent. Vaginal [...] Read more.
Vulvovaginal candidiasis (VVC) and recurrencies are common in reproductive-aged women. The emergence of Candida strains resistant to conventional antimycotic drugs prompted the search for alternative therapies. Hyaluronic acid (HA), a uniform and linear glycosaminoglycan, has been proposed as an anti-Candida agent. Vaginal lactobacilli and their derivatives, including cell free culture supernatants (CFS), represent potential strategies for the treatment of Candida infections. In the present paper, the anti-Candida potential of HA and lyophilised CFS (LCFS), obtained from the vaginal strain Lactobacillus crispatus BC5, was investigated. HA and LCFS proved to be active towards a panel of clinical Candida isolates belonging to different species in a dose dependent manner and their association maintained the antifungal activity. Notably, also Candida species generally resistant to conventional antifungals resulted sensitive. A vaginal matrix based on microcrystalline cellulose and containing effective doses of both agents was developed and characterised. This vaginal formulation showed mucoadhesive ability and almost abrogated Candida albicans growth. In conclusion, HA and LCFS from L. crispatus BC5 are thus good candidates to design a new therapeutic strategy to counteract VVC, and the proposed vaginal matrix represents a promising prototype. Full article
(This article belongs to the Special Issue Natural Antimicrobials and Alternatives to Antimicrobials)
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Article
Antimicrobial Effect and the Mechanism of Diallyl Trisulfide against Campylobacter jejuni
Antibiotics 2021, 10(3), 246; https://doi.org/10.3390/antibiotics10030246 - 02 Mar 2021
Cited by 3 | Viewed by 754
Abstract
Campylobacter jejuni is an important foodborne pathogen causing campylobacteriosis. It can infect humans through the consumption of contaminated chicken products or via the direct handling of animals. Diallyl trisulfide (DATS) is a trisulfide compound from garlic extracts that has a potential antimicrobial effect [...] Read more.
Campylobacter jejuni is an important foodborne pathogen causing campylobacteriosis. It can infect humans through the consumption of contaminated chicken products or via the direct handling of animals. Diallyl trisulfide (DATS) is a trisulfide compound from garlic extracts that has a potential antimicrobial effect on foodborne pathogens. This study investigated the antimicrobial activity of DATS on C. jejuni by evaluating the minimal inhibitory concentrations (MICs) of C. jejuni 81-168, and fourteen C. jejuni isolates from chicken carcasses. Thirteen of 14 C. jejuni isolates and 81-176 had MICs ≤ 32 μg/mL, while one isolate had MIC of 64 μg/mL. Scanning electron microscopy (SEM) analysis showed the disruption and shrink of C. jejuni bacterial cell membrane after the DATS treatment. A time-killing analysis further showed that DATS had a dose-dependent in vitro antimicrobial effect on C. jejuni during the 24 h treatment period. In addition, DATS also showed an antimicrobial effect in chicken through the decrease of C. jejuni colony count by 1.5 log CFU/g (cloacal sample) during the seven-day DATS treatment period. The transcriptional analysis of C. jejuni with 16 μg/mL (0.5× MIC) showed 210 differentially expression genes (DEGs), which were mainly related to the metabolism, bacterial membrane transporter system and the secretion system. Fourteen ABC transporter-related genes responsible for bacterial cell homeostasis and oxidative stress were downregulated, indicating that DATS could decrease the bacterial ability to against environmental stress. We further constructed five ABC transporter deletion mutants according to the RNA-seq analysis, and all five mutants proved less tolerant to the DATS treatment compared to the wild type by MIC test. This study elucidated the antimicrobial activity of DATS on C. jejuni and suggested that DATS could be used as a potential antimicrobial compound in the feed and food industry. Full article
(This article belongs to the Special Issue Natural Antimicrobials and Alternatives to Antimicrobials)
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Article
The P.E.A.N.U.T. Method: Update on an Integrative System Approach for the Treatment of Chronic Otitis Media with Effusion and Adenoid Hypertrophy in Children
Antibiotics 2021, 10(2), 134; https://doi.org/10.3390/antibiotics10020134 - 30 Jan 2021
Cited by 3 | Viewed by 1510
Abstract
Background and objectives: Based on our previous single-center study on optimization of treatment of chronic otitis media with effusion (COME) and adenoid hypertrophy (AH) in children using a noninvasive system approach to lower the necessity of antibiotics, analgesic use, and surgical interventions, we [...] Read more.
Background and objectives: Based on our previous single-center study on optimization of treatment of chronic otitis media with effusion (COME) and adenoid hypertrophy (AH) in children using a noninvasive system approach to lower the necessity of antibiotics, analgesic use, and surgical interventions, we proceeded to perform a multicenter investigation in an outpatient setting. The purpose of the previous prospective study in 2013–2015 was to compare outcomes in the treatment of COME and AH using the noninvasive multimodal integrative method (IM) versus conventional treatment practice (COM). Materials and Methods: In this paper, we retrospectively analyze the data of patients treated with the integrative method between 2017 and 2020 in a multicenter setting and compared the outcomes with data from 2013–2015 in order to evaluate generalizability. In both periods, all eligible and willing participants were included and treated with the IM protocol under real-life conditions. The treatment involved pneumatization exercises, education, an antiallergic diet, nasal hygiene, useful constitutional therapy, and thermal interventions (P.E.A.N.U.T.). A total of 48 versus 28 patients, aged 1–8, were assessed, presenting with COME and AH, with moderate to severe hearing impairment at entry. Results: The significant improvement found in both audiometric measures (intact hearing) and tympanometric measures (normal A-type curve) was similar in both datasets with respect to conventional treatment. The new data confirms that the P.E.A.N.U.T. method results in a significant reduction of antibiotics, analgesic use, and surgical interventions. Conclusion: In this multicenter trial, we confirm the effectiveness of the noninvasive system approach for the treatment of COME in lowering the need for antibiotics and analgesic use and elective surgery. This could be especially important with respect to a generally observed increase in antibiotic resistance. The method is easy to perform in different clinical settings and is effective, safe, and well-tolerated. Full article
(This article belongs to the Special Issue Natural Antimicrobials and Alternatives to Antimicrobials)
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Article
Inhibition of Biofilm Formation by the Synergistic Action of EGCG-S and Antibiotics
Antibiotics 2021, 10(2), 102; https://doi.org/10.3390/antibiotics10020102 - 21 Jan 2021
Cited by 5 | Viewed by 1451
Abstract
Biofilm, a stress-induced physiological state, is an established means of antimicrobial tolerance. A perpetual increase in multidrug resistant (MDR) infections associated with high mortality and morbidity have been observed in healthcare settings. Multiple studies have indicated that the use of natural products can [...] Read more.
Biofilm, a stress-induced physiological state, is an established means of antimicrobial tolerance. A perpetual increase in multidrug resistant (MDR) infections associated with high mortality and morbidity have been observed in healthcare settings. Multiple studies have indicated that the use of natural products can prevent bacterial growth. Recent studies in the field have identified that epigallocatechin gallate (EGCG), a green tea polyphenol, could disrupt bacterial biofilms. A modified lipid-soluble EGCG, epigallocatechin-3-gallate-stearate (EGCG-S), has enhanced the beneficial properties of green tea. This study focuses on utilizing EGCG-S as a novel synergistic agent with antibiotics to prevent or control biofilm. Different formulations of EGCG-S and selected antibiotics were used to study their combinatorial effects on biofilms produced by five potential pathogenic bacteria, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcusepidermidis, and Mycobacterium smegmatis. The crystal violet (CV) assay and the sensitive fluorescence-based resazurin biofilm viability assay were used to assess the biofilm production. Our results identified optimal formulation for each bacterium, effectively inhibiting biofilm formation to an extent of 95–99%. Colony-forming unit (CFU) and cell viability analyses showed a decrease of viable bacteria. These results depict the potential of EGCG-S as a synergistic agent with antibiotics and as an anti-biofilm agent. Full article
(This article belongs to the Special Issue Natural Antimicrobials and Alternatives to Antimicrobials)
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Article
Thymol Nanoemulsion: A New Therapeutic Option for Extensively Drug Resistant Foodborne Pathogens
Antibiotics 2021, 10(1), 25; https://doi.org/10.3390/antibiotics10010025 - 30 Dec 2020
Cited by 27 | Viewed by 1741
Abstract
Foodborne pathogens have been associated with severe and complicated diseases. Therefore, these types of infections are a concern for public health officials and food and dairy industries. Regarding the wide-spread multidrug resistant (MDR) and extensively drug resistant (XDR) foodborne pathogens such as Salmonella [...] Read more.
Foodborne pathogens have been associated with severe and complicated diseases. Therefore, these types of infections are a concern for public health officials and food and dairy industries. Regarding the wide-spread multidrug resistant (MDR) and extensively drug resistant (XDR) foodborne pathogens such as Salmonella Enteritidis (S. Enteritidis), new and alternative therapeutic approaches are urgently needed. Therefore, we investigated the antimicrobial, anti-virulence, and immunostimulant activities of a stable formulation of thymol as thymol nanoemulsion in an in vivo approach. Notably, treatment with 2.25% thymol nanoemulsion led to a pronounced improvement in the body weight gain and feed conversion ratio in addition to decreases in the severity of clinical findings and mortality percentages of challenged chickens with XDR S. Enteritidis confirming its pronounced antimicrobial activities. Moreover, thymol nanoemulsion, at this dose, had protective effects through up-regulation of the protective cytokines and down-regulation of XDR S. Enteritidis sopB virulence gene and interleukins (IL)-4 and IL-10 cytokines as those hinder the host defenses. Furthermore, it enhanced the growth of gut Bifidobacteria species, which increases the strength of the immune system. For that, we suggested the therapeutic use of thymol nanoemulsion against resistant foodborne pathogens. Finally, we recommended the use of 2.25% thymol nanoemulsion as a feed additive for immunocompromised individuals as well as in the veterinary fields. Full article
(This article belongs to the Special Issue Natural Antimicrobials and Alternatives to Antimicrobials)
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Article
Antimicrobial Effects of Essential Oils on Oral Microbiota Biofilms: The Toothbrush In Vitro Model
Antibiotics 2021, 10(1), 21; https://doi.org/10.3390/antibiotics10010021 - 29 Dec 2020
Cited by 8 | Viewed by 1438
Abstract
The present investigation intended to evaluate the bacteriostatic and bactericidal abilities of clove, oregano and thyme essential oils against oral bacteria in planktonic and biofilm states. Furthermore, aiming to mimic everyday conditions, a toothbrush in vitro model was developed. Determination of the minimum [...] Read more.
The present investigation intended to evaluate the bacteriostatic and bactericidal abilities of clove, oregano and thyme essential oils against oral bacteria in planktonic and biofilm states. Furthermore, aiming to mimic everyday conditions, a toothbrush in vitro model was developed. Determination of the minimum inhibitory concentration, minimum bactericidal concentration, minimum biofilm inhibitory concentration and minimum biofilm eradication concentration were achieved using the microdilution procedure. To simulate the toothbrush environment, nylon fibers were inoculated with oral bacteria, which, after incubation to allow biofilm development, were submitted to contact with the essential oils under study. Thyme and oregano essential oils revealed promising antimicrobial effects, both in growth inhibition and the destruction of cells in planktonic and biofilm states, while clove essential oil showed a weaker potential. Regarding the toothbrush in vitro model, observation of the nylon fibers under a magnifying glass proved the essential oil anti-biofilm properties. Considering the effects observed using the in vitro toothbrush model, a realistic approximation to oral biofilm establishment in an everyday use object, a putative application of essential oils as toothbrush sanitizers to help prevent the establishment of bacterial biofilm can be verified. Full article
(This article belongs to the Special Issue Natural Antimicrobials and Alternatives to Antimicrobials)
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Review

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Review
Staphylococcal Biofilms: Challenges and Novel Therapeutic Perspectives
Antibiotics 2021, 10(2), 131; https://doi.org/10.3390/antibiotics10020131 - 29 Jan 2021
Cited by 21 | Viewed by 2444
Abstract
Staphylococci, like Staphylococcus aureus and S. epidermidis, are common colonizers of the human microbiota. While being harmless in many cases, many virulence factors result in them being opportunistic pathogens and one of the major causes of hospital-acquired infections worldwide. One of these [...] Read more.
Staphylococci, like Staphylococcus aureus and S. epidermidis, are common colonizers of the human microbiota. While being harmless in many cases, many virulence factors result in them being opportunistic pathogens and one of the major causes of hospital-acquired infections worldwide. One of these virulence factors is the ability to form biofilms—three-dimensional communities of microorganisms embedded in an extracellular polymeric matrix (EPS). The EPS is composed of polysaccharides, proteins and extracellular DNA, and is finely regulated in response to environmental conditions. This structured environment protects the embedded bacteria from the human immune system and decreases their susceptibility to antimicrobials, making infections caused by staphylococci particularly difficult to treat. With the rise of antibiotic-resistant staphylococci, together with difficulty in removing biofilms, there is a great need for new treatment strategies. The purpose of this review is to provide an overview of our current knowledge of the stages of biofilm development and what difficulties may arise when trying to eradicate staphylococcal biofilms. Furthermore, we look into promising targets and therapeutic methods, including bacteriocins and phage-derived antibiofilm approaches. Full article
(This article belongs to the Special Issue Natural Antimicrobials and Alternatives to Antimicrobials)
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