Microbiological characterisation of southern African medicinal and cosmetic clays

Metatranscriptomic insight into the possible role of clay microbiome in skin disease management

Even though the scientific documentation is limited, microbiome of healing clay is gradually gaining attention of the scientific community, as a therapeutic force playing an indispensable role in skin disease management. The present study explores the metatranscriptome profile of the Chamliyal clay, widely known for its efficacy in managing various skin problems, using Illumina NextSeq sequencing technology. The gene expression profile of the clay microbial community was analyzed through SEED subsystems of the MG-RAST server. Due to the unavailability of metatranscriptomic data on other therapeutic clays, Chamliyal's profile was compared to non-therapeutic soils, as well as healthy and diseased human skin microbiomes. The study identified Firmicutes, Proteobacteria, and Actinobacteria as the primary active microbial phyla in Chamliyal clay. These resemble those abundant in a healthy human skin microbiome. This is significant as lower levels of these phyla in the skin are linked to inflammatory skin conditions like psoriasis. Interestingly, pathogenic microbes actively metabolizing in the clay were absent. Importantly, 6% of the transcripts annotated to sulfur and iron metabolism, which are known to play a major role in skin disease management. This study provides the most comprehensive and a novel overview of the metatranscriptome of any of the healing clay available worldwide. The findings offer valuable insights into the clay microbiome's potential in managing skin disorders, inspiring future endeavors to harness these insights for medical applications.

Effect of natural antibacterial clays against single biofilm formation by Staphylococcus aureus and Salmonella Typhimurium bacteria on a stainless-steel surface

Staphylococcus aureus and Salmonella Typhimurium have a propensity to develop biofilms on food contact surfaces, such as stainless-steel, that persist despite rigorous cleaning and sanitizing procedures. Since both bacterial species pose a significant public health risk within the food chain, improved anti-biofilm measures are needed. This study examined the potential of clays as antibacterial and anti-biofilm agents against these two pathogens on appropriate contact surfaces. Natural soil was processed to yield leachates and suspensions of both untreated and treated clays. Soil particle size, pH, cation-exchange capacity, and metal ions were characterized to assess their importance in bacterial killing. Initial antibacterial screening was performed on nine distinct types of natural Malaysian soil using a disk diffusion assay. Untreated leachate from Kuala Gula and Kuala Kangsar clays were found to inhibit S. aureus (7.75 ± 0.25 mm) and Salmonella Typhimurium (11.85 ± 1.63 mm), respectively. The treated Kuala Gula suspension (50.0 and 25.0 %) reduced S. aureus biofilms by 4.4 and 4.2 log at 24 and 6 h, respectively, while treated Kuala Kangsar suspension (12.5 %) by a 4.16 log reduction at 6 h. Although less effective, the treated Kuala Gula leachate (50.0 %) was effective in removing Salmonella Typhimurium biofilm with a decrease of >3 log in 24 h. In contrast to Kuala Kangsar clays, the treated Kuala Gula clays contained a much higher soluble metal content, especially Al (301.05 ± 0.45 ppm), Fe (691.83 ± 4.80 ppm) and Mg (88.44 ± 0.47 ppm). Elimination of S. aureus biofilms correlated with the presence of Fe, Cu, Pb, Ni, Mn and Zn irrespective of the pH of the leachate. Our findings demonstrate that a treated suspension is the most effective for eradication of S. aureus biofilms with a potential as a sanitizer-tolerant, natural antibacterial against biofilms for applications in the food industry.

A Review of Pickering Emulsions: Perspectives and Applications

Pickering emulsions are systems composed of two immiscible fluids stabilized by organic or inorganic solid particles. These solid particles of certain dimensions (micro- or nano-particles), and desired wettability, have been shown to be an alternative to conventional emulsifiers. The use of biodegradable and biocompatible stabilizers of natural origin, such as clay minerals, presents a promising future for the development of Pickering emulsions and, with this, they deliver some advantages, especially in the area of biomedicine. In this review, the effects and characteristics of microparticles in the preparation and properties of Pickering emulsions are presented. The objective of this review is to provide a theoretical basis for a broader type of emulsion, in addition to reviewing the main aspects related to the mechanisms and applications to promote its stability. Through this review, we highlight the use of this type of emulsion and its excellent properties as permeability promoters of solid particles, providing ideal results for local drug delivery and use in Pickering emulsions.

Broad-Spectrum Antimicrobial and Antibiofilm Activity of a Natural Clay Mineral from British Columbia, Canada

Worldwide increases in antibiotic resistance and the dearth of new antibiotics have created a global crisis in the treatment of infectious diseases. These concerns highlight the pressing need for novel antimicrobial agents. Natural clay minerals have a long history of therapeutic and biomedical applications and have lately received specific attention for their potent antimicrobial properties. In particular, Kisameet clay (KC) has strong antibacterial activity against a variety of multidrug-resistant (MDR) bacterial pathogens in vitro Here, we have extended the known spectrum of activity of KC by demonstrating its efficacy against two major fungal pathogens, Candida albicans and Cryptococcus neoformans In addition, KC also exhibits potent activity against the opportunistic bacterial pathogen Mycobacterium marinum, a model organism for M. ulcerans infection. Moreover, aqueous KC leachates (KC-L) exhibited broad-spectrum antibacterial activity, eradicated Gram-negative and Gram-positive biofilms, and prevented their formation. The mechanism(s) underlying KC antibacterial activity appears to be complex. Adjusting KC-L to neutral pH rendered it inactive, indicating a contribution of pH, although low pH alone was insufficient for its antibacterial activity. Treatment of KC minerals with cation-chelating agents such as EDTA, 2,2'-bipyridyl, and deferoxamine reduced the antibacterial activity, while supplementation of KC-L with these chelating agents eliminated the inhibitory activity. Together, the data suggest a positive role for divalent and trivalent cations, including iron and aluminum, in bacterial inhibition by KC. Collectively, these studies demonstrate the range of KC bioactivity and provide a better understanding of the mechanism underlying its antibacterial effects.IMPORTANCE The escalating emergence of multidrug-resistant (MDR) bacteria, together with the paucity of novel antimicrobial agents in antibiotic development, is recognized as a worldwide public health crisis. Kisameet clay (KC), found in British Columbia (BC), Canada, is a clay mineral with a long history of therapeutic applications among people of the First Nations. We previously reported the antibacterial activity of KC against a group of MDR clinical pathogens. Here, we demonstrate its activity against two major human-pathogenic fungal species, as well as against bacterial biofilms, which underlie many recalcitrant bacterial infections. In these studies, we also identified several geochemical characteristics of KC, such as metal ions and low pH, which are involved in its antibacterial activity. These findings provide a better understanding of the components of KC antibacterial activity and a basis for developing defined preparations of this clay mineral for therapeutic applications.

Lake Zeiļu Clay Application Induced Changes in Human Skin Hydration, Elasticity, Transepidermal Water Loss and PH in Healthy Individuals

Clay has a great biomedical application potential, however there are just a few instrumental studies and the impact of lake clay on the skin has not yet been studied. The DermaLab skin analysis system (Cortex Technology) was used for hydration, elasticity, transepidermal water loss (TEWL) and pH measurements after lake clay facial applications. Research included short-term tests (measurements 20 and 60 min after clay application) and long-term tests (application every 4th day for 3 weeks with measurements 20–24 h post-application). Control measurements and application tests to exclude contact allergy were made beforehand. No volunteer (n = 30) had positive allergic reaction. The matched-pairs design was applied: the right and left parts of forehead were used for the test and control groups. The Wilcoxon signed-rank test (significance level p = 0.001) was applied for statistical analysis. There were statistically significant pH changes demonstrated during the short-term measurements. The long-term measurements provided data that clay significantly improves skin hydration and elasticity.

Healing and edible clays: a review of basic concepts, benefits and risks

The use of clay by humans for medicinal and wellness purposes is most probably as old as mankind. Within minerals, due to its ubiquitous occurrence in nature and easy availability, clay was the first to be used and is still used worldwide. Healing clays have been traditionally used by man for therapeutic, nutritional and skin care purposes, but they could impart some important health and skin care risks. For instance, clay particles could adsorb and make available for elimination or excretion any potential toxic elements or toxins being ingested or produced, but they could adsorb and make available for incorporation, through ingestion or through dermal absorption, toxic elements, e.g. heavy metals. Edible clays, a particular case of healing clays, have been traditionally used by man for nutritional and therapeutic purposes. Geophagy, the deliberate soil eating, earth eating, clay eating and pica (medical condition or eating disorder shown by individuals addicted to eat earth substances), has been observed in all parts of the world since antiquity, reflecting cultural practice, religious belief and physiological needs, be they nutritional (dietary supplementation) or as a remedy for disease. This paper pretends to review historical data, basic concepts and functions, as well as benefits and risks of the use of healing clays, in general, for therapeutic and cosmetic purposes, and of edible clays, in particular, for therapeutic purposes.

FDA 2014 survey of eye area cosmetics for microbiological safety

In an attempt to assess cosmetics containing 'nontraditional' preservatives, 93 eye area cosmetic products were selected based on labelled or marketed claims that these products were 'green', 'natural', 'paraben-free', 'preservative-free' or contained nontraditional preservatives (e.g. botanical extracts). Products were analysed for water activity, pH and microbiological content, which included enumeration of aerobic micro-organisms, detection of microbial growth after a 7-day enrichment and identification of microbial isolates. The survey found that 60% (56/93) of the eye area cosmetics were free of microbiological growth under test conditions, 32% (30/93) showed the presence of micro-organisms at low levels (<100 CFU per ml or g) and 8% (7/93) showed microbiological growth at higher levels (> 100 CFU per ml or g). Gram-positive bacteria such as Bacillus and Staphylococcus were the dominant genera identified in these cosmetic products, whereas Gram-negative species were relatively uncommon. The survey found a positive association between lower water activity cosmetics and the presence of micro-organisms in these products. Similarly, colour cosmetics were more likely to contain micro-organisms than noncolour cosmetics. The most represented micro-organisms in the survey were from genus Bacillus, suggesting that the natural raw materials are the likely source of observed microbial loads.

SIGNIFICANCE AND IMPACT OF THE STUDY

In the United States, cosmetic products are regulated postmarket; therefore, surveillance programmes are one of FDA's most important tools for monitoring microbiological safety of cosmetics. 'Traditional' preservatives, such as parabens and formaldehyde releasers, are perceived unfavourably by some consumers, resulting in cosmetic manufacturers increasingly using 'nontraditional' preservatives. FDA conducted an analytical survey of eye area cosmetics that claimed to be free of traditional preservatives and determined microbiological loads in tested products. This study explores the association of microbial loads with the physical and chemical characteristics of the cosmetic products, and points to the limits of preservative activity in cosmetics.

Bacillus cereus in personal care products: risk to consumers

Bacillus cereus is ubiquitous in nature and thus occurs naturally in a wide range of raw materials and foodstuffs. B. cereus spores are resistant to desiccation and heat and able to survive dry storage and cooking. Vegetative cells produce several toxins which on ingestion in sufficient numbers can cause vomiting and/or diarrhoea depending on the toxins produced. Gastrointestinal disease is commonly associated with reheated or inadequately cooked foods. In addition to being a rare cause of several acute infections (e.g. pneumonia and septicaemia), B. cereus can also cause localized infection of post-surgical or trauma wounds and is a rare but significant pathogen of the eye where it may result in severe endophthalmitis often leading to loss of vision. Key risk factors in such cases are trauma to the eye and retained contaminated intraocular foreign bodies. In addition, rare cases of B. cereus-associated keratitis (inflammation of the cornea) have been linked to contact lens use. Bacillus cereus is therefore a microbial contaminant that could adversely affect product safety of cosmetic and facial toiletries and pose a threat to the user if other key risk factors are also present. The infective dose in the human eye is unknown, but as few as 100 cfu has been reported to initiate infection in a susceptible animal model. However, we are not aware of any reports in the literature of B. cereus infections in any body site linked with use of personal care products. Low levels of B. cereus spores may on occasion be present in near-eye cosmetics, and these products have been used by consumers for many years. In addition, exposure to B. cereus is more likely to occur through other routes (e.g. dustborne contamination) due to its ubiquity and resistance properties of spores. The organism has been recovered from the eyes of healthy individuals. Therefore, although there may be a perceived hazard, the risk of severe eye infections as a consequence of exposure through contaminated near-eye cosmetics is judged to be vanishingly small. It is unlikely that more stringent microbiological standards for near-eye cosmetics will have any impact on the risk of severe eye infections caused by B. cereus, as these are not linked to use of personal care products.

Bacterial diversity in soil from geophagic mining sites in the Qwa-Qwa region of South Africa

Geophagia is practised in many parts of the world and can be associated with medicinal treatments, ceremonial events and spiritual behaviours/practices. This is the first report on a systematic investigation and description of the bacterial diversity in soil regularly ingested by geophagic individuals using a culture-independent method. Diversity in 17 different mining sites was investigated using denaturing gradient gel electrophoresis. Genetic material from Pantoea, Stenotrophomonas, Listeria, Rhodococcus and Sphingomonads was present in most of the soil samples. Species from these genera are recognised, potential or immerging human pathogens, and are of special interest in immune-compromised individuals. Other genera able to produce a variety of bacteriocins and antimicrobial/antifungal substances inhibitory towards food borne pathogens (Dactylosporangium and Bacillus) and able to degrade a range of environmental pollutants and toxins (Duganella and Massilia) were also present. These essential insights provide the platform for adjusting culturing strategies to isolate specific bacteria, further phylogenetic studies and microbial mining prospect for bacterial species of possible economic importance.

Antimicrobial clay-based materials for wound care

The historical use of clay minerals for the treatment of wounds and other skin ailments is well documented and continues within numerous human cultures the world over. However, a more scientific inquiry into the chemistry and properties of clay minerals emerged in the 19th century with work investigating their role within health gathering pace since the second half of the 20th century. This review gives an overview of clay minerals and how their properties can be manipulated to facilitate the treatment of infected wounds. Evidence of the antimicrobial and healing effects of some natural clay minerals is presented alongside a range of chemical modifications including metal-ion exchange, the formation of clay–drug composites and the development of various polymer–clay systems. While the evidence for applying these materials to infected wounds is limited, we contextualize and discuss the future of this research.

Effects of antibacterial mineral leachates on the cellular ultrastructure, morphology, and membrane integrity of Escherichia coli and methicillin-resistant Staphylococcus aureus

Background

We have previously identified two mineral mixtures, CB07 and BY07, and their respective aqueous leachates that exhibit in vitro antibacterial activity against a broad spectrum of pathogens. The present study assesses cellular ultrastructure and membrane integrity of methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli after exposure to CB07 and BY07 aqueous leachates.

Methods

We used scanning and transmission electron microscopy to evaluate E. coli and MRSA ultrastructure and morphology following exposure to antibacterial leachates. Additionally, we employed Baclight LIVE/DEAD staining and flow cytometry to investigate the cellular membrane as a possible target for antibacterial activity.

Results

Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) imaging of E. coli and MRSA revealed intact cells following exposure to antibacterial mineral leachates. TEM images of MRSA showed disruption of the cytoplasmic contents, distorted cell shape, irregular membranes, and distorted septa of dividing cells. TEM images of E. coli exposed to leachates exhibited different patterns of cytoplasmic condensation with respect to the controls and no apparent change in cell envelope structure. Although bactericidal activity of the leachates occurs more rapidly in E. coli than in MRSA, LIVE/DEAD staining demonstrated that the membrane of E. coli remains intact, while the MRSA membrane is permeabilized following exposure to the leachates.

Conclusions

These data suggest that the leachate antibacterial mechanism of action differs for Gram-positive and Gram-negative organisms. Upon antibacterial mineral leachate exposure, structural integrity is retained, however, compromised membrane integrity accounts for bactericidal activity in Gram-positive, but not in Gram-negative cells.