Microorganisms

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Open AccessComment

Comment on: “Melanisation of Aspergillus terreus—Is Butyrolactone I Involved in the Regulation of Both DOPA and DHN Types of Pigments in Submerged Culture? Microorganisms 2017, 5, 22”

by Elena Geib and Matthias Brock

Microorganisms 2017, 5(2), 34; https://doi.org/10.3390/microorganisms5020034 - 21 Jun 2017

Cited by 6 | Viewed by 6818

Abstract

A recent article by Palonen et al. describes the effect of butyrolactone I on the expression of a secondary metabolite biosynthesis gene cluster from Aspergillus terreus that shows similarities to fusarubin biosynthesis gene clusters from Fusarium species. The authors claim that two different [...] Read more.

A recent article by Palonen et al. describes the effect of butyrolactone I on the expression of a secondary metabolite biosynthesis gene cluster from Aspergillus terreus that shows similarities to fusarubin biosynthesis gene clusters from Fusarium species. The authors claim that two different types of pigments are formed in Aspergillus terreus conidia, whereby one pigment is termed a DOPA-type melanin and the second a DHN-type melanin. Unfortunately, the terminology of the classification of melanin-types requires revision as Asp-melanin present in A. terreus conidia is clearly distinct from DOPA-melanins. In addition, some hypotheses in this manuscript are based on questionable data published previously, resulting in incorrect conclusions. Finally, as biochemical data are lacking and metabolite production is only deduced from bioinformatics and transcriptomic data, the production of a second pigment type in A. terreus conidia appears highly speculative. Full article

(This article belongs to the Special Issue Filamentous Fungi in White Biotechnology)

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Open AccessReview

Purine Acquisition and Synthesis by Human Fungal Pathogens

by Jessica L. Chitty and James A. Fraser

Microorganisms 2017, 5(2), 33; https://doi.org/10.3390/microorganisms5020033 - 8 Jun 2017

Cited by 28 | Viewed by 6779

Abstract

While members of the Kingdom Fungi are found across many of the world’s most hostile environments, only a limited number of species can thrive within the human host. The causative agents of the most common invasive fungal infections are Candida albicans, Aspergillus [...] Read more.

While members of the Kingdom Fungi are found across many of the world’s most hostile environments, only a limited number of species can thrive within the human host. The causative agents of the most common invasive fungal infections are Candida albicans, Aspergillus fumigatus, and Cryptococcus neoformans. During the infection process, these fungi must not only combat the host immune system while adapting to dramatic changes in temperature and pH, but also acquire sufficient nutrients to enable growth and dissemination in the host. One class of nutrients required by fungi, which is found in varying concentrations in their environmental niches and the human host, is the purines. These nitrogen-containing heterocycles are one of the most abundant organic molecules in nature and are required for roles as diverse as signal transduction, energy metabolism and DNA synthesis. The most common life-threatening fungal pathogens can degrade, salvage and synthesize de novo purines through a number of enzymatic steps that are conserved. While these enable them to adapt to the changing purine availability in the environment, only de novo purine biosynthesis is essential during infection and therefore an attractive antimycotic target. Full article

(This article belongs to the Special Issue Fungal Nutrition Assimilation Strategies and Pathogenicity)

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Open AccessReview

Interaction of Candida Species with the Skin

by Andreas Kühbacher, Anke Burger-Kentischer and Steffen Rupp

Microorganisms 2017, 5(2), 32; https://doi.org/10.3390/microorganisms5020032 - 7 Jun 2017

Cited by 115 | Viewed by 13121

Abstract

The human skin is commonly colonized by diverse fungal species. Some Candida species, especially C. albicans, do not only reside on the skin surface as commensals, but also cause infections by growing into the colonized tissue. However, defense mechanisms at the skin [...] Read more.

The human skin is commonly colonized by diverse fungal species. Some Candida species, especially C. albicans, do not only reside on the skin surface as commensals, but also cause infections by growing into the colonized tissue. However, defense mechanisms at the skin barrier level are very efficient, involving residential non-immune and immune cells as well as immune cells specifically recruited to the site of infection. Therefore, the skin is an effective barrier against fungal infection. While most studies about commensal and pathogenic interaction of Candida species with host epithelia focus on the interaction with mucosal surfaces such as the vaginal and gastrointestinal epithelia, less is known about the mechanisms underlying Candida interaction with the skin. In this review, we focus on the ecology and molecular pathogenesis of Candida species on the skin and give an overview of defense mechanisms against C. albicans in this context. We also discuss new research avenues in dermal infection, including the involvement of neurons, fibroblasts, and commensal bacteria in both mouse and human model systems. Full article

(This article belongs to the Special Issue Fungal Pathogenesis and Immune Defense)

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Open AccessArticle

Changes in Microbial (Bacteria and Archaea) Plankton Community Structure after Artificial Dispersal in Grazer-Free Microcosms

by Hera Karayanni, Alexandra Meziti, Sofie Spatharis, Savvas Genitsaris, Claude Courties and Konstantinos A. Kormas

Microorganisms 2017, 5(2), 31; https://doi.org/10.3390/microorganisms5020031 - 3 Jun 2017

Cited by 4 | Viewed by 5116

Abstract

Microbes are considered to have a global distribution due to their high dispersal capabilities. However, our knowledge of the way geographically distant microbial communities assemble after dispersal in a new environment is limited. In this study, we examined whether communities would converge because [...] Read more.

Microbes are considered to have a global distribution due to their high dispersal capabilities. However, our knowledge of the way geographically distant microbial communities assemble after dispersal in a new environment is limited. In this study, we examined whether communities would converge because similar taxa would be selected under the same environmental conditions, or would diverge because of initial community composition, after artificial dispersal. To this aim, a microcosm experiment was performed, in which the temporal changes in the composition and diversity of different prokaryoplankton assemblages from three distant geographic coastal areas (Banyuls-sur-Mer in northwest Mediterranean Sea, Pagasitikos Gulf in northeast Mediterranean and Woods Hole, MA, USA in the northwest Atlantic), were studied. Diversity was investigated using amplicon pyrosequencing of the V1–V3 hypervariable regions of the 16S rRNA. The three assemblages were grown separately in particle free and autoclaved Banyuls-sur-mer seawater at 18 °C in the dark. We found that the variability of prokaryoplankton community diversity (expressed as richness, evenness and dominance) as well as the composition were driven by patterns observed in Bacteria. Regarding community composition, similarities were found between treatments at family level. However, at the OTU level microbial communities from the three different original locations diverge rather than converge during incubation. It is suggested that slight differences in the composition of the initial prokaryoplankton communities, resulted in separate clusters the following days even when growth took place under identical abiotic conditions. Full article

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Open AccessReview

Table Olive Fermentation Using Starter Cultures with Multifunctional Potential

by Stamatoula Bonatsou, Chrysoula C. Tassou, Efstathios Z. Panagou and George-John E. Nychas

Microorganisms 2017, 5(2), 30; https://doi.org/10.3390/microorganisms5020030 - 28 May 2017

Cited by 74 | Viewed by 9107

Abstract

Table olives are one of the most popular plant-derived fermented products. Their enhanced nutritional value due to the presence of phenolic compounds and monounsaturated fatty acids makes olives an important food commodity of the Mediterranean diet. However, despite its economic significance, table olive [...] Read more.

Table olives are one of the most popular plant-derived fermented products. Their enhanced nutritional value due to the presence of phenolic compounds and monounsaturated fatty acids makes olives an important food commodity of the Mediterranean diet. However, despite its economic significance, table olive fermentation is mainly craft-based and empirically driven by the autochthonous microbiota of the olives depending on various intrinsic and extrinsic factors, leading to a spontaneous process and a final product of variable quality. The use of microorganisms previously isolated from olive fermentations and studied for their probiotic potential and technological characteristics as starter cultures may contribute to the reduction of spoilage risk resulting in a controlled fermentation process. This review focuses on the importance of the development and implementation of multifunctional starter cultures related to olives with desirable probiotic and technological characteristics for possible application on table olive fermentation with the main purpose being the production of a health promoting and sensory improved functional food. Full article

(This article belongs to the Special Issue Beneficial Microorganisms for Food Manufacturing—Fermented and Biopreserved Foods and Beverages)

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Open AccessArticle

Toxin Variability Estimations of 68 Alexandrium ostenfeldii (Dinophyceae) Strains from The Netherlands Reveal a Novel Abundant Gymnodimine

by Helge Martens, Urban Tillmann, Kirsi Harju, Carmela Dell’Aversano, Luciana Tartaglione and Bernd Krock

Microorganisms 2017, 5(2), 29; https://doi.org/10.3390/microorganisms5020029 - 26 May 2017

Cited by 27 | Viewed by 5238

Abstract

Alexandrium ostenfeldii is a toxic dinoflagellate that has recently bloomed in Ouwerkerkse Kreek, The Netherlands, and which is able to cause a serious threat to shellfish consumers and aquacultures. We used a large set of 68 strains to the aim of fully characterizing [...] Read more.

Alexandrium ostenfeldii is a toxic dinoflagellate that has recently bloomed in Ouwerkerkse Kreek, The Netherlands, and which is able to cause a serious threat to shellfish consumers and aquacultures. We used a large set of 68 strains to the aim of fully characterizing the toxin profiles of the Dutch A. ostenfeldii in consideration of recent reports of novel toxins. Alexandrium ostenfeldii is known as a causative species of paralytic shellfish poisoning, and consistently in the Dutch population we determined the presence of several paralytic shellfish toxins (PST) including saxitoxin (STX), GTX2/3 (gonyautoxins), B1 and C1/C2. We also examined the production of spiroimine toxins by the Dutch A. ostenfeldii strains. An extensive liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis revealed a high intraspecific variability of spirolides (SPX) and gymnodimines (GYM). Spirolides included 13-desMethyl-spirolide C generally as the major compound and several other mostly unknown SPX-like compounds that were detected and characterized. Besides spirolides, the presence of gymnodimine A and 12-Methyl-gymnodimine A was confirmed, together with two new gymnodimines. One of these was tentatively identified as an analogue of gymnodimine D and was the most abundant gymnodimine (calculated cell quota up to 274 pg cell⁻¹, expressed as GYM A equivalents). Our multi-clonal approach adds new analogues to the increasing number of compounds in these toxin classes and revealed a high strain variability in cell quota and in toxin profile of toxic compounds within a single population. Full article

(This article belongs to the Special Issue Toxic Cyanobacteria and Toxic Dinoflagellates)

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Open AccessReview

Regulatory and Safety Requirements for Food Cultures

by Svend Laulund, Anette Wind, Patrick M. F. Derkx and Véronique Zuliani

Microorganisms 2017, 5(2), 28; https://doi.org/10.3390/microorganisms5020028 - 23 May 2017

Cited by 81 | Viewed by 13054

Abstract

The increased use of food cultures to ferment perishable raw materials has potentiated the need for regulations to assess and assure the safety of food cultures and their uses. These regulations differ from country to country, all aimed at assuring the safe use [...] Read more.

The increased use of food cultures to ferment perishable raw materials has potentiated the need for regulations to assess and assure the safety of food cultures and their uses. These regulations differ from country to country, all aimed at assuring the safe use of food cultures which has to be guaranteed by the food culture supplier. Here we highlight national differences in regulations and review a list of methods and methodologies to assess the safety of food cultures at strain level, at production, and in the final product. Full article

(This article belongs to the Special Issue Beneficial Microorganisms for Food Manufacturing—Fermented and Biopreserved Foods and Beverages)

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Open AccessReview

From Genome to Phenotype: An Integrative Approach to Evaluate the Biodiversity of Lactococcus lactis

by Valérie Laroute, Hélène Tormo, Christel Couderc, Muriel Mercier-Bonin, Pascal Le Bourgeois, Muriel Cocaign-Bousquet and Marie-Line Daveran-Mingot

Microorganisms 2017, 5(2), 27; https://doi.org/10.3390/microorganisms5020027 - 19 May 2017

Cited by 54 | Viewed by 9385

Abstract

Lactococcus lactis is one of the most extensively used lactic acid bacteria for the manufacture of dairy products. Exploring the biodiversity of L. lactis is extremely promising both to acquire new knowledge and for food and health-driven applications. L. lactis is divided into [...] Read more.

Lactococcus lactis is one of the most extensively used lactic acid bacteria for the manufacture of dairy products. Exploring the biodiversity of L. lactis is extremely promising both to acquire new knowledge and for food and health-driven applications. L. lactis is divided into four subspecies: lactis, cremoris, hordniae and tructae, but only subsp. lactis and subsp. cremoris are of industrial interest. Due to its various biotopes, Lactococcus subsp. lactis is considered the most diverse. The diversity of L. lactis subsp. lactis has been assessed at genetic, genomic and phenotypic levels. Multi-Locus Sequence Type (MLST) analysis of strains from different origins revealed that the subsp. lactis can be classified in two groups: “domesticated” strains with low genetic diversity, and “environmental” strains that are the main contributors of the genetic diversity of the subsp. lactis. As expected, the phenotype investigation of L. lactis strains reported here revealed highly diverse carbohydrate metabolism, especially in plant- and gut-derived carbohydrates, diacetyl production and stress survival. The integration of genotypic and phenotypic studies could improve the relevance of screening culture collections for the selection of strains dedicated to specific functions and applications. Full article

(This article belongs to the Special Issue Beneficial Microorganisms for Food Manufacturing—Fermented and Biopreserved Foods and Beverages)

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Open AccessArticle

Adding Value to Goat Meat: Biochemical and Technological Characterization of Autochthonous Lactic Acid Bacteria to Achieve High-Quality Fermented Sausages

by Miriam T. Nediani, Luis García, Lucila Saavedra, Sandra Martínez, Soledad López Alzogaray and Silvina Fadda

Microorganisms 2017, 5(2), 26; https://doi.org/10.3390/microorganisms5020026 - 17 May 2017

Cited by 16 | Viewed by 7739

Abstract

Quality and safety are important challenges in traditional fermented sausage technology. Consequently, the development of a tailored starter culture based on indigenous microbiota constitutes an interesting alternative. In the present study, spontaneously fermented goat meat sausages were created and analyzed using a physicochemical [...] Read more.

Quality and safety are important challenges in traditional fermented sausage technology. Consequently, the development of a tailored starter culture based on indigenous microbiota constitutes an interesting alternative. In the present study, spontaneously fermented goat meat sausages were created and analyzed using a physicochemical and microbiological approach. Thereafter 170 lactic acid bacteria (LAB) strains were isolated and preliminary characterized by phenotypic assays. The hygienic and technological properties, and growth and fermentative potential of isolates using a goat-meat-based culture medium were evaluated. All strains proved to have bioprotective features due to their acidogenic metabolism. Almost all grew optimally in meat environments. LAB isolates presented proteolytic activity against meat proteins and enriched amino acid contents of the goat-meat-based model. The most efficient strains were four different Lactobacillus sakei isolates, as identified by genotyping and RAPD analysis. L. sakei strains are proposed as optimal candidates to improve the production of fermented goat meat sausages, creating a new added-value fermented product. Full article

(This article belongs to the Special Issue Beneficial Microorganisms for Food Manufacturing—Fermented and Biopreserved Foods and Beverages)

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Open AccessReview

Microbial Diversity in Extreme Marine Habitats and Their Biomolecules

by Annarita Poli, Ilaria Finore, Ida Romano, Alessia Gioiello, Licia Lama and Barbara Nicolaus

Microorganisms 2017, 5(2), 25; https://doi.org/10.3390/microorganisms5020025 - 16 May 2017

Cited by 146 | Viewed by 18109

Abstract

Extreme marine environments have been the subject of many studies and scientific publications. For many years, these environmental niches, which are characterized by high or low temperatures, high-pressure, low pH, high salt concentrations and also two or more extreme parameters in combination, have [...] Read more.

Extreme marine environments have been the subject of many studies and scientific publications. For many years, these environmental niches, which are characterized by high or low temperatures, high-pressure, low pH, high salt concentrations and also two or more extreme parameters in combination, have been thought to be incompatible to any life forms. Thanks to new technologies such as metagenomics, it is now possible to detect life in most extreme environments. Starting from the discovery of deep sea hydrothermal vents up to the study of marine biodiversity, new microorganisms have been identified, and their potential uses in several applied fields have been outlined. Thermophile, halophile, alkalophile, psychrophile, piezophile and polyextremophile microorganisms have been isolated from these marine environments; they proliferate thanks to adaptation strategies involving diverse cellular metabolic mechanisms. Therefore, a vast number of new biomolecules such as enzymes, polymers and osmolytes from the inhabitant microbial community of the sea have been studied, and there is a growing interest in the potential returns of several industrial production processes concerning the pharmaceutical, medical, environmental and food fields. Full article

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Open AccessReview

Dairy Propionibacteria: Versatile Probiotics

by Houem Rabah, Fillipe Luiz Rosa do Carmo and Gwénaël Jan

Microorganisms 2017, 5(2), 24; https://doi.org/10.3390/microorganisms5020024 - 13 May 2017

Cited by 85 | Viewed by 11618

Abstract

Dairy propionibacteria are used as cheese ripening starters, as biopreservative and as beneficial additives, in the food industry. The main species, Propionibacterium freudenreichii, is known as GRAS (Generally Recognized As Safe, USA, FDA). In addition to another dairy species, Propionibacterium acidipropionici, they are [...] Read more.

Dairy propionibacteria are used as cheese ripening starters, as biopreservative and as beneficial additives, in the food industry. The main species, Propionibacterium freudenreichii, is known as GRAS (Generally Recognized As Safe, USA, FDA). In addition to another dairy species, Propionibacterium acidipropionici, they are included in QPS (Qualified Presumption of Safety) list. Additional to their well-known technological application, dairy propionibacteria increasingly attract attention for their promising probiotic properties. The purpose of this review is to summarize the probiotic characteristics of dairy propionibacteria reported by the updated literature. Indeed, they meet the selection criteria for probiotic bacteria, such as the ability to endure digestive stressing conditions and to adhere to intestinal epithelial cells. This is a prerequisite to bacterial persistence within the gut. The reported beneficial effects are ranked according to property’s type: microbiota modulation, immunomodulation, and cancer modulation. The proposed molecular mechanisms are discussed. Dairy propionibacteria are described as producers of nutraceuticals and beneficial metabolites that are responsible for their versatile probiotic attributes include short chain fatty acids (SCFAs), conjugated fatty acids, surface proteins, and 1,4-dihydroxy-2-naphtoic acid (DHNA). These metabolites possess beneficial properties and their production depends on the strain and on the growth medium. The choice of the fermented food matrix may thus determine the probiotic properties of the ingested product. This review approaches dairy propionibacteria, with an interest in both technological abilities and probiotic attributes. Full article

(This article belongs to the Special Issue Beneficial Microorganisms for Food Manufacturing—Fermented and Biopreserved Foods and Beverages)

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Open AccessArticle

Lactic Fermentation as an Efficient Tool to Enhance the Antioxidant Activity of Tropical Fruit Juices and Teas

by Amandine Fessard, Ashish Kapoor, Jessica Patche, Sophie Assemat, Mathilde Hoarau, Emmanuel Bourdon, Theeshan Bahorun and Fabienne Remize

Microorganisms 2017, 5(2), 23; https://doi.org/10.3390/microorganisms5020023 - 10 May 2017

Cited by 64 | Viewed by 9354

Abstract

Tropical fruits like pineapple, papaya, mango, and beverages such as green or black teas, represent an underestimated source of antioxidants that could exert health-promoting properties. Most food processing technologies applied to fruit beverages or teas result in an impairment of inherent nutritional properties. [...] Read more.

Tropical fruits like pineapple, papaya, mango, and beverages such as green or black teas, represent an underestimated source of antioxidants that could exert health-promoting properties. Most food processing technologies applied to fruit beverages or teas result in an impairment of inherent nutritional properties. Conversely, we hypothesise that lactic acid fermentation may constitute a promising route to maintain and even improve the nutritional qualities of processed fruits. Using specific growth media, lactic acid bacteria were selected from the fruit phyllosphere diversity and fruit juice, with the latter undergoing acidification kinetics analyses and characterised for exopolysaccharide production. Strains able to ferment tropical fruit juices or teas into pleasant beverages, within a short time, were of particular interest. Strains Weissella cibaria 64 and Leuconostoc mesenteroides 12b, able to increase antioxidant activity, were specifically studied as potential starters for lactic fermented pineapple juice. Full article

(This article belongs to the Special Issue Beneficial Microorganisms for Food Manufacturing—Fermented and Biopreserved Foods and Beverages)

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Open AccessArticle

Melanisation of Aspergillus terreus—Is Butyrolactone I Involved in the Regulation of Both DOPA and DHN Types of Pigments in Submerged Culture?

by Elina K. Palonen, Sheetal Raina, Annika Brandt, Jussi Meriluoto, Tajalli Keshavarz and Juhani T. Soini

Microorganisms 2017, 5(2), 22; https://doi.org/10.3390/microorganisms5020022 - 4 May 2017

Cited by 12 | Viewed by 5452

Abstract

Pigments and melanins of fungal spores have been investigated for decades, revealing important roles in the survival of the fungus in hostile environments. The key genes and the encoded enzymes for pigment and melanin biosynthesis have recently been found in Ascomycota, including Aspergillus [...] Read more.

Pigments and melanins of fungal spores have been investigated for decades, revealing important roles in the survival of the fungus in hostile environments. The key genes and the encoded enzymes for pigment and melanin biosynthesis have recently been found in Ascomycota, including Aspergillus spp. In Aspergillus terreus, the pigmentation has remained mysterious with only one class of melanin biogenesis being found. In this study, we examined an intriguing, partially annotated gene cluster of A. terreus strain NIH2624, utilizing previously sequenced transcriptome and improved gene expression data of strain MUCL 38669, under the influence of a suggested quorum sensing inducing metabolite, butyrolactone I. The core polyketide synthase (PKS) gene of the cluster was predicted to be significantly longer on the basis of the obtained transcriptional data, and the surrounding cluster was positively regulated by butyrolactone I at the late growth phase of submerged culture, presumably during sporulation. Phylogenetic analysis of the extended PKS revealed remarkable similarity with a group of known pigments of Fusarium spp., indicating a similar function for this PKS. We present a hypothesis of this PKS cluster to biosynthesise a 1,8-dihydroxynaphthalene (DHN)-type of pigment during sporulation with the influence of butyrolactone I under submerged culture. Full article

(This article belongs to the Special Issue Filamentous Fungi in White Biotechnology)

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Open AccessArticle

Hyperbaric Oxygen Therapy is Ineffective as an Adjuvant to Daptomycin with Rifampicin Treatment in a Murine Model of Staphylococcus aureus in Implant-Associated Osteomyelitis

by Nis Pedersen Jørgensen, Kasper Hansen, Caroline Marie Andreasen, Michael Pedersen, Kurt Fuursted, Rikke L. Meyer and Eskild Petersen

Microorganisms 2017, 5(2), 21; https://doi.org/10.3390/microorganisms5020021 - 25 Apr 2017

Cited by 13 | Viewed by 6975

Abstract

Implant-associated infections caused by bacterial biofilms are difficult to treat. Surgical intervention is often necessary to cure the patient, as the antibiotic recalcitrance of biofilms renders them untreatable with conventional antibiotics. Intermittent hyperbaric oxygen treatment (HBOT) has been proposed as an adjuvant to [...] Read more.

Implant-associated infections caused by bacterial biofilms are difficult to treat. Surgical intervention is often necessary to cure the patient, as the antibiotic recalcitrance of biofilms renders them untreatable with conventional antibiotics. Intermittent hyperbaric oxygen treatment (HBOT) has been proposed as an adjuvant to conventional antibiotic treatment and it has been speculated that combining HBOT with antibiotics could improve treatment outcomes for biofilm infections. In this study we addressed whether HBOT could improve treatment outcomes of daptomycin and rifampicin combination therapy. The effect of HBOT on the treatment outcomes of daptomycin and rifampicin against implant-associated osteomyelitis was quantified in a murine model. In total, 80 mice were randomized into two groups receiving antibiotics, either alone or in combination with daily intermittent HBOT (304 kPa for 60 min) following injection of antibiotics. Treatment was initiated 11 days after animals were infected with Staphylococcus aureus and treatment duration was 14 days. We found that HBOT did not improve the cure rate and did not reduce the bacterial load on the implant surface or in the surrounding tissue. Cure rates of daptomycin + rifampicin were 40% in infected tibias and 75% for implants while cure rates for HBOT-daptomycin + rifampicin were 50% and 85%, respectively, which were not significantly higher (Fisher’s exact test). While it is encouraging that the combination of daptomycin and rifampicin is very effective, our study demonstrates that this efficacy cannot be improved by adjuvant HBOT. Full article

(This article belongs to the Special Issue Microbial Biofilms and Human Infections)

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Open AccessArticle

Tellurite and Tellurate Reduction by the Aerobic Anoxygenic Phototroph Erythromonas ursincola, Strain KR99 Is Carried out by a Novel Membrane Associated Enzyme

by Chris Maltman, Lynda J. Donald and Vladimir Yurkov

Microorganisms 2017, 5(2), 20; https://doi.org/10.3390/microorganisms5020020 - 19 Apr 2017

Cited by 20 | Viewed by 4730

Abstract

Erythromonas ursincola, strain KR99 isolated from a freshwater thermal spring of Kamchatka Island in Russia, resists and reduces very high levels of toxic tellurite under aerobic conditions. Reduction is carried out by a constitutively expressed membrane associated enzyme, which was purified and [...] Read more.

Erythromonas ursincola, strain KR99 isolated from a freshwater thermal spring of Kamchatka Island in Russia, resists and reduces very high levels of toxic tellurite under aerobic conditions. Reduction is carried out by a constitutively expressed membrane associated enzyme, which was purified and characterized. The tellurite reductase has a molecular weight of 117 kDa, and is comprised of two subunits (62 and 55 kDa) in a 1:1 ratio. Optimal activity occurs at pH 7.0 and 28 °C. Tellurite reduction has a V_max of 5.15 µmol/min/mg protein and a K_m of 3.36 mM. The enzyme can also reduce tellurate with a V_max and K_m of 1.08 µmol/min/mg protein and 1.44 mM, respectively. This is the first purified membrane associated Te oxyanion reductase. Full article

(This article belongs to the Special Issue Microorganisms for Environmental and Industrial Applications)

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Open AccessReview

The Status of Biofilms in Penile Implants

by Matthew Faller and Tobias Kohler

Microorganisms 2017, 5(2), 19; https://doi.org/10.3390/microorganisms5020019 - 18 Apr 2017

Cited by 10 | Viewed by 5052

Abstract

Erectile dysfunction is prevalent among men and will continue to become more so with the aging population. Of the available treatment options, implantable prosthetic devices are typically thought of as a third line treatment even though they have the highest satisfaction rate and [...] Read more.

Erectile dysfunction is prevalent among men and will continue to become more so with the aging population. Of the available treatment options, implantable prosthetic devices are typically thought of as a third line treatment even though they have the highest satisfaction rate and continually improving success rates. Infection and mechanical failure are the most common reasons for implant revision in the past. Since the development of more reliable devices, bacterial biofilms are coming to the forefront of discussion as causes of required revision. Biofilms are problematic as they are ubiquitous and exceedingly difficult to prevent or treat. Full article

(This article belongs to the Special Issue Microbial Biofilms and Human Infections)

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Open AccessArticle

High Prevalence of bla_NDM-1, bla_VIM, qacE, and qacEΔ1 Genes and Their Association with Decreased Susceptibility to Antibiotics and Common Hospital Biocides in Clinical Isolates of Acinetobacter baumannii

by Fatma Alzahraa M. Gomaa, Zeinab H. Helal and Mazhar I. Khan

Microorganisms 2017, 5(2), 18; https://doi.org/10.3390/microorganisms5020018 - 12 Apr 2017

Cited by 52 | Viewed by 5747

Abstract

The objective of this study was to evaluate the susceptibility of metallo-β-lactamase (MBL)-producing Acinetobacter baumannii (A. baumannii) clinical isolates to biocides. We also determined the prevalence and correlation of efflux pump genes, class 1 integron and MBL encoding genes. In addition, [...] Read more.

The objective of this study was to evaluate the susceptibility of metallo-β-lactamase (MBL)-producing Acinetobacter baumannii (A. baumannii) clinical isolates to biocides. We also determined the prevalence and correlation of efflux pump genes, class 1 integron and MBL encoding genes. In addition, bla_VIM, bla_NDM-1, qacE and qacEΔ1 nucleotide sequence analysis was performed and compared to sequences retrieved from GenBank at the National Center for Biotechnology Information database. A. baumannii had a resistance rate to carbapenem of 71.4% and 39.3% and was found to be a MBL producer. The minimum inhibitory concentrations (MICs) of chlorhexidine and cetrimide were higher than the recommended concentrations for disinfection in 54.5% and 77.3% of MBL-positive isolates respectively and their MICs were significantly higher among qac gene-positive isolates. Coexistence of qac genes was detected in 68.1% and 50% of the isolates with bla_VIM and bla_NDM-1 respectively. There was a significant correlation between the presence of qac genes and MBL-encoding bla_VIM and bla_NDM-1 genes. Each of the bla_NDM-1, bla_VIM, qacE and qacEΔ1 DNA sequences showed homology with each other and with similar sequences reported from other countries. The high incidence of Verona integron-encoded metallo-β-lactamases (VIM) and New-Delhi-metallo-β-lactamase (NDM) and qac genes in A. baumannii highlights emerging therapeutic challenges for being readily transferable between clinically relevant bacteria. In addition reduced susceptibility to chlorhexidine and cetrimide and the potential for cross resistance to some antibiotics necessitates the urgent need for healthcare facilities to periodically evaluate biocides efficacy, to address the issue of antiseptic resistance and to initiate a “biocidal stewardship”. Full article

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Open AccessEditorial

Probiotic Microorganisms: A Closer Look

by Julio Villena and Haruki Kitazawa

Microorganisms 2017, 5(2), 17; https://doi.org/10.3390/microorganisms5020017 - 8 Apr 2017

Cited by 13 | Viewed by 4950

Abstract

In recent decades; scientists have provided encouraging evidence that probiotic microorganisms are valuable in the prevention and treatment of a variety of diseases.[...] Full article

(This article belongs to the Special Issue Probiotic Microorganisms: An Intimate Gaze)

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Open AccessArticle

Insights on Klebsiella pneumoniae Biofilms Assembled on Different Surfaces Using Phenotypic and Genotypic Approaches

by Maria Bandeira, Vítor Borges, João P. Gomes, Aida Duarte and Luisa Jordao

Microorganisms 2017, 5(2), 16; https://doi.org/10.3390/microorganisms5020016 - 3 Apr 2017

Cited by 22 | Viewed by 6925

Abstract

Klebsiella pneumoniae is a prominent etiological agent of healthcare associated infections (HAIs). In this context, multidrug-resistant and biofilm-producing bacteria are of special public health concern due to the difficulties associated with treatment of human infections and eradication from hospital environments. Here, in order [...] Read more.

Klebsiella pneumoniae is a prominent etiological agent of healthcare associated infections (HAIs). In this context, multidrug-resistant and biofilm-producing bacteria are of special public health concern due to the difficulties associated with treatment of human infections and eradication from hospital environments. Here, in order to study the impact of medical devices-associated materials on the biofilm dynamics, we performed biofilm phenotypic analyses through a classic and a new scanning electron microscopy (SEM) technique for three multidrug-resistant K. pneumoniae isolates growing on polystyrene and silicone. We also applied whole-genome sequencing (WGS) to search for genetic clues underlying biofilm phenotypic differences. We found major differences in the extracellular polymeric substances (EPS) content among the three strains, which were further corroborated by in-depth EPS composition analysis. WGS analysis revealed a high nucleotide similarity within the core-genome, but relevant differences in the accessory genome that may account for the detected biofilm phenotypic dissimilarities, such as genes already associated with biofilm formation in other pathogenic bacteria (e.g., genes coding haemogglutinins and haemolysins). These data reinforce that the research efforts to defeat bacterial biofilms should take into account that their dynamics may be contingent on the medical devices-associated materials. Full article

(This article belongs to the Special Issue The Biofilm Matrix)

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Open AccessReview

Approaches to Dispersing Medical Biofilms

by Derek Fleming and Kendra P. Rumbaugh

Microorganisms 2017, 5(2), 15; https://doi.org/10.3390/microorganisms5020015 - 1 Apr 2017

Cited by 231 | Viewed by 15423

Abstract

Biofilm-associated infections pose a complex problem to the medical community, in that residence within the protection of a biofilm affords pathogens greatly increased tolerances to antibiotics and antimicrobials, as well as protection from the host immune response. This results in highly recalcitrant, chronic [...] Read more.

Biofilm-associated infections pose a complex problem to the medical community, in that residence within the protection of a biofilm affords pathogens greatly increased tolerances to antibiotics and antimicrobials, as well as protection from the host immune response. This results in highly recalcitrant, chronic infections and high rates of morbidity and mortality. Since as much as 80% of human bacterial infections are biofilm-associated, many researchers have begun investigating therapies that specifically target the biofilm architecture, thereby dispersing the microbial cells into their more vulnerable, planktonic mode of life. This review addresses the current state of research into medical biofilm dispersal. We focus on three major classes of dispersal agents: enzymes (including proteases, deoxyribonucleases, and glycoside hydrolases), antibiofilm peptides, and dispersal molecules (including dispersal signals, anti-matrix molecules, and sequestration molecules). Throughout our discussion, we provide detailed lists and summaries of some of the most prominent and extensively researched dispersal agents that have shown promise against the biofilms of clinically relevant pathogens, and we catalog which specific microorganisms they have been shown to be effective against. Lastly, we discuss some of the main hurdles to development of biofilm dispersal agents, and contemplate what needs to be done to overcome them. Full article

(This article belongs to the Special Issue Microbial Biofilms and Human Infections)

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Open AccessArticle

Identification and Characterization of Spontaneous Auxotrophic Mutants in Fusarium langsethiae

by Olga Gavrilova, Anna Skritnika and Tatiana Gagkaeva

Microorganisms 2017, 5(2), 14; https://doi.org/10.3390/microorganisms5020014 - 31 Mar 2017

Cited by 13 | Viewed by 7367

Abstract

Analysis of 49 strains of Fusarium langsethiae originating from northern Europe (Russia, Finland, Sweden, UK, Norway, and Latvia) revealed the presence of spontaneous auxotrophic mutants that reflect natural intraspecific diversity. Our investigations detected that 49.0% of F. langsethiae strains were auxotrophic mutants for [...] Read more.

Analysis of 49 strains of Fusarium langsethiae originating from northern Europe (Russia, Finland, Sweden, UK, Norway, and Latvia) revealed the presence of spontaneous auxotrophic mutants that reflect natural intraspecific diversity. Our investigations detected that 49.0% of F. langsethiae strains were auxotrophic mutants for biotin, and 8.2% of the strains required thiamine as a growth factor. They failed to grow on vitamin-free media. For both prototrophic and auxotrophic strains, no growth defect was observed in rich organic media. Without essential vitamins, a significant reduction in the growth of the auxotrophic strains results in a decrease of the formation of T-2 toxin and diacetoxyscirpenol. In addition, all analysed F. langsethiae strains were distinguished into two subgroups based on PCR product sizes. According to our results, 26 and 23 strains of F. langsethiae belong to subgroups I and II respectively. We determined that the deletion in the intergenic spacer (IGS) region of the rDNA of F. langsethiae belonging to subgroup II is linked with temperature sensitivity and causes a decrease in strain growth at 30 °C. Four thiamine auxotrophic strains were found in subgroup I, while 21 biotin auxotrophic strains were detected in subgroups II. To the best of our knowledge, the spontaneous mutations in F. langsethiae observed in the present work have not been previously reported. Full article

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Microorganisms, Volume 5, Issue 2 (June 2017) – 21 articles

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