Daily battle against body odor: towards the activity of the axillary microbiota

Microbial Colonization, Biofilm Formation, and Malodour of Washing Machine Surfaces and Fabrics and the Evolution of Detergents in Response to Consumer Demands and Environmental Concerns

Bacterial attachment and biofilm formation are associated with the contamination and fouling at several locations in a washing machine, which is a particularly complex environment made from a range of metal, polymer, and rubber components. Microorganisms also adhere to different types of clothing fibres during the laundering process as well as a range of sweat, skin particles, and other components. This can result in fouling of both washing machine surfaces and clothes and the production of malodours. This review gives an introduction into washing machine use and surfaces and discusses how biofilm production confers survival properties to the microorganisms. Microbial growth on washing machines and textiles is also discussed, as is their potential to produce volatiles. Changes in consumer attitudes with an emphasis on laundering and an overview regarding changes that have occurred in laundry habits are reviewed. Since it has been suggested that such changes have increased the risk of microorganisms surviving the laundering process, an understanding of the interactions of the microorganisms with the surface components alongside the production of sustainable detergents to meet consumer demands are needed to enhance the efficacy of new antimicrobial cleaning agents in these complex and dynamic environments.

Identification of a staphylococcal dipeptidase involved in the production of human body odor

The production of human body odor is the result of the action of commensal skin bacteria, including Staphylococcus hominis, acting to biotransform odorless apocrine gland secretions into volatile chemicals like thioalcohols such as 3-methyl-3-sulphanylhexan-1-ol (3M3SH). As the secreted odor precursor Cys-Gly-3M3SH contains a dipeptide, yet the final enzyme in the biotransformation pathway only functions on Cys-3M3SH, we sought to identify the remaining step in this human-adapted biochemical pathway using a novel coupled enzyme assay. Purification of this activity from S. hominis extracts led to the identification of the M20A-family PepV peptidase (ShPepV) as the primary Cys-Gly-3M3SH dipeptidase. To establish whether this was a primary substrate for PepV, the recombinant protein was purified and demonstrated broad activity against diverse dipeptides. The binding site for Cys-Gly-3M3SH was predicted using modeling, which suggested mutations that might accommodate this ligand more favorably. Indeed, a D437A resulted in an almost sixfold increase in the kcat/Km, whereas other introduced mutations reduced or abolished function. Together, these data identify an enzyme capable of catalyzing the missing step in an ancient human-specific biochemical transformation and suggest that the production of 3M3SH uses neither a dedicated transporter nor a peptidase for its breakdown, with only the final cleavage step, catalyzed by PatB cysteine-S-conjugate β-lyase, being a unique enzyme.

Using surface-enhanced Raman scattering for simultaneous multiplex detection and quantification of thiols associated to axillary malodour

Axillary malodour is caused by the microbial conversion of human-derived precursors to volatile organic compounds. Thiols strongly contribute to this odour but are hard to detect as they are present at low concentrations. Additionally, thiols are highly volatile and small making sampling and quantification difficult, including by gas chromatography-mass spectrometry. In this study, surface-enhanced Raman scattering (SERS), combined with chemometrics, was utilised to simultaneously quantify four malodourous thiols associated with axillary odour, both in individual and multiplex solutions. Univariate and multivariate methods of partial least squares regression (PLS-R) were used to calculate the limit of detection (LoD) and results compared. Both methods yielded comparable LoD values, with LoDs using PLS-R ranging from 0.0227 ppm to 0.0153 ppm for the thiols studied. These thiols were then examined and quantified simultaneously in 120 mixtures using PLS-R. The resultant models showed high linearity (Q2 values between 0.9712 and 0.9827 for both PLS-1 and PLS-2) and low values of root mean squared error of predictions (0.0359 ppm and 0.0459 ppm for PLS-1 and PLS-2, respectively). To test this approach further, these models were challenged with 15 new blind test samples, collected independently from the initial samples. This test demonstrated that SERS combined with PLS-R could be used to predict the unknown concentrations of these thiols in a mixture. These results display the ability of SERS for the simultaneous multiplex detection and quantification of analytes and its potential for future development for detecting gaseous thiols produced from skin and other body sites.

Human scent guides mosquito thermotaxis and host selection under naturalistic conditions

The African malaria mosquito Anopheles gambiae exhibits a strong innate drive to seek out humans in its sensory environment, classically entering homes to land on human skin in the hours flanking midnight. To gain insight into the role that olfactory cues emanating from the human body play in generating this epidemiologically important behavior, we developed a large-scale multi-choice preference assay in Zambia with infrared motion vision under semi-field conditions. We determined that An. gambiae prefers to land on arrayed visual targets warmed to human skin temperature during the nighttime when they are baited with carbon dioxide (CO2) emissions reflective of a large human over background air, body odor from one human over CO2, and the scent of one sleeping human over another. Applying integrative whole body volatilomics to multiple humans tested simultaneously in competition in a six-choice assay, we reveal high attractiveness is associated with whole body odor profiles from humans with increased relative abundances of the volatile carboxylic acids butyric acid, isobutryic acid, and isovaleric acid, and the skin microbe-generated methyl ketone acetoin. Conversely, those least preferred had whole body odor that was depleted of carboxylic acids among other compounds and enriched with the monoterpenoid eucalyptol. Across expansive spatial scales, heated targets without CO2 or whole body odor were minimally or not attractive at all to An. gambiae. These results indicate that human scent acts critically to guide thermotaxis and host selection by this prolific malaria vector as it navigates towards humans, yielding intrinsic heterogeneity in human biting risk.

Exploring the interrelationship between the skin microbiome and skin volatiles: A pilot study

Unravelling the interplay between a human’s microbiome and physiology is a relevant task for understanding the principles underlying human health and disease. With regard to human chemical communication, it is of interest to elucidate the role of the microbiome in shaping or generating volatiles emitted from the human body. In this study, we characterized the microbiome and volatile organic compounds (VOCs) sampled from the neck and axilla of ten participants (five male, five female) on two sampling days, by applying different methodological approaches. Volatiles emitted from the respective skin site were collected for 20 min using textile sampling material and analyzed on two analytical columns with varying polarity of the stationary phase. Microbiome samples were analyzed by a culture approach coupled with MALDI-TOF-MS analysis and a 16S ribosomal RNA gene (16S RNA) sequencing approach. Statistical and advanced data analysis methods revealed that classification of body sites was possible by using VOC and microbiome data sets. Higher classification accuracy was achieved by combination of both data pools. Cutibacterium, Staphylococcus, Micrococcus, Streptococcus, Lawsonella, Anaerococcus, and Corynebacterium species were found to contribute to classification of the body sites by the microbiome. Alkanes, esters, ethers, ketones, aldehydes and cyclic structures were used by the classifier when VOC data were considered. The interdisciplinary methodological platform developed here will enable further investigations of skin microbiome and skin VOCs alterations in physiological and pathological conditions.

Microbiota in Umbilical Dirt and Its Relationship with Odor

The umbilicus accumulates more dirt than other body surfaces and is difficult to clean. Hygiene in this area is vital, particularly for surgery, because of its proximity to the laparotomy site. Although microorganisms in the umbilicus have been extensively examined, those in umbilical dirt have not due to the lack of an efficient method of collection. We previously established a technique to extract umbilical dirt using the anchor effect of polymers, which are injected into the umbilicus. In the present study, we applied this technique for the first time to investigate umbilical dirt. The results obtained revealed an abundance of Corynebacterium among various bacteria, whereas Cutibacterium and Staphylococcus, which are abundant at other skin sites, were rare. The relationships between the microbiota and issues related to the umbilicus were investigated and some covariates, including the odor score and several bacteria, were identified. A detailed ana-lysis of the genera associated with odor revealed no correlation with Corynebacterium; however, some minor anaerobic bacteria, such as Mobiluncus, Arcanobacterium, and Peptoniphilus, were more abundant in the high odor score group. Therefore, this technique to collect umbilical dirt provided insights into the microbiota in umbilical dirt and suggested functions for minor anaerobes. Furthermore, since various pathogenic microorganisms were detected, their control may contribute to the prevention of both odor production and infectious diseases caused by these microorganisms.

Evolutionary consequences of vector-borne transmission: how using vectors shapes host, vector and pathogen evolution

Transmission mode is a key factor that influences host–parasite coevolution. Vector-borne pathogens are among the most important disease agents for humans and wildlife due to their broad distribution, high diversity, prevalence and lethality. They comprise some of the most important and widespread human pathogens, such as yellow fever, leishmania and malaria. Vector-borne parasites (in this review, those transmitted by blood-feeding Diptera) follow unique transmission routes towards their vertebrate hosts. Consequently, each part of this tri-partite (i.e. parasite, vector and host) interaction can influence co- and counter-evolutionary pressures among antagonists. This mode of transmission may favour the evolution of greater virulence to the vertebrate host; however, pathogen–vector interactions can also have a broad spectrum of fitness costs to the insect vector. To complete their life cycle, vector-borne pathogens must overcome immune responses from 2 unrelated organisms, since they can activate responses in both vertebrate and invertebrate hosts, possibly creating a trade-off between investments against both types of immunity. Here, we assess how dipteran vector-borne transmission shapes the evolution of hosts, vectors and the pathogens themselves. Hosts, vectors and pathogens co-evolve together in a constant antagonistic arms race with each participant's primary goal being to maximize its performance and fitness.

Rapid assembly of colorless antimicrobial and anti-odor coatings from polyphenols and silver

The development of antimicrobial fabrics and textiles that can sustainably inhibit a broad spectrum of microbes is crucial for protecting against pathogens in various environments. However, engineering antimicrobial textiles is challenging due to issues with discoloration and inhibited breathability, the use of harmful or harsh reagents and synthesis conditions, and complex and/or time-consuming processing. Herein, we develop a facile and rapid approach to deposit antimicrobial coatings using universally adherent plant polyphenols and antimicrobial silver ions. Importantly, the coatings are colorless, thin (< 10 nm), rapidly assembled (< 20 min), and can be deposited via immersion or spraying. We demonstrate that these metal-phenolic coatings on textiles can inhibit lipid-enveloped viruses over one thousand times more efficiently than coatings composed of other metal ions, while maintaining their efficacy even after 5 washes. Moreover, the coatings also inhibit Gram positive and negative bacteria, and fungi, and can prevent odors on clothes for at least 10 washes. Collectively, the ease of synthesis, use of simple and safe precursors, and amenability to at-home and industrial application suggests that the coatings will find practical application in various settings.

A headspace collection chamber for whole body volatilomics

The human body secretes a complex blend of volatile organic compounds (VOCs) via the skin, breath and bodily fluids. In this study, we have developed a headspace collection chamber for whole body volatilome profiling.

Aging Associated Changes in the Adult Human Skin Microbiome and the Host Factors That Affect Skin Microbiome Composition

Understanding changes in the skin microbiome and their relationship to host skin factors during aging remains largely unknown. To better understand this phenomenon, we collected samples for metagenomic and host skin factor analyses from forearm, buttock, and facial skin from 158 Caucasian females at 20-24, 30-34, 40-44, 50-54, 60-64, and 70-74 years of age. Metagenomics analysis was performed using 16S rRNA gene sequencing, while host sebocyte gland area, skin lipids, natural moisturizing factors (NMFs) and anti-microbial peptides (AMPs) measurements were also performed. These analyses demonstrated that skin bacterial diversity increased at all the skin sites with increasing age. Of the bacterial genera with average relative abundance of >1%, only Lactobacillus and Cutibacterium demonstrated a significant change (decrease) in abundance at all sampled skin sites with increasing age. Additional bacterial genera demonstrated significant age and site-specific changes in abundance. Analysis of sebocyte area, NMFs, lipids and AMPs demonstrated an age-related decrease in sebocyte area and increases in NMFs/AMPs/skin lipids, all which correlated with changes in specific bacterial genera. In conclusion, the human skin microbiome undergoes age-associated alterations that may reflect underlying age-related changes in cutaneous biology.

Thermoregulatory effects of guava leaf extract-menthol toner application for post-exercise use

CONTEXT

Psidium guajava L. (Myrtaceae) leaf contains a wide variety of bioactive compounds that contribute valuable effects on human well-being.

OBJECTIVE

This study investigates the influence of guava leaf extract-menthol toner on thermoregulation, including perspiration, skin temperature, and recovery heart rate.

MATERIALS AND METHODS

This randomised, placebo-controlled clinical trial assessed the effects of the guava leaf extract-menthol toner and placebo with a 1-week washout period. Sixty-four participants were enrolled. The participants exercised on a treadmill until a 75% heart rate reserve was achieved for 5 min, followed by a 5 min post-exercise rest period. The skin temperature and heart rate were then measured before 5 mL of the testing product was sprayed to specific areas of the body, left it for 30 sec before wiped off. Post-exercise perspiration and skin temperatures were collected by sweat patches and measured by the Skin-thermometer ST500, respectively. A 20 min heart rate monitoring period started 10 min after the exercise and measured every 2 min intervals.

RESULTS

Use of the toner significantly reduced post-exercise perspiration to approximately half of the baseline and placebo use values (p < 0.05). Furthermore, relative heart rate changes showed no significant differences among the tests (p > 0.05). Skin temperature was also unaffected (p > 0.05).

DISCUSSION AND CONCLUSION

Guava leaf extract-menthol toner reduced perspiration by astringent effects but did not influence heat dissipation and did not affect cardiovascular mechanism compared to the controls. Additional cleaning with guava leaf extract-menthol toner could offer better hygiene after a workout.

The Bacterial Life Cycle in Textiles is Governed by Fiber Hydrophobicity

Colonization of textiles and subsequent metabolic degradation of sweat and sebum components by axillary skin bacteria cause the characteristic sweat malodor and discoloring of dirty clothes. Once inside the textile, the bacteria can form biofilms that are hard to remove by conventional washing. When the biofilm persists after washing, the textiles retain the sweat odor. To design biofilm removal and prevention strategies, the bacterial behavior needs to be understood in depth. Here, we aim to study the bacterial behavior in each of the four stages of the bacterial life cycle in textiles: adhesion, growth, drying, and washing. To accomplish this, we designed a novel in vitro model to mimic physiological sweating in cotton and polyester textiles, in which many of the parameters that influence bacterial behavior could be controlled. Due to the higher hydrophobicity, polyester adhered more bacteria and absorbed more sebum, the bacteria's primary nutrient source. Bacteria were therefore also more active in polyester textiles. However, polyester did not bind water as well as cotton. The increased water content of cotton allowed some species to retain a higher activity after the textile had dried. However, none of the textiles retained enough water upon drying to prevent the bacteria from adhering irreversibly to the textile fibers. This work demonstrates that bacterial colonization of textiles depends partially on the hydrophobic and hygroscopic properties of the textile material, indicating that it might be possible to direct bacterial behavior in a more favorable direction by modifying these surface properties. IMPORTANCE During sweating, bacteria from the skin enter the worn textile along with the sweat. Once inside the clothes, the bacteria produce sweat malodor and form colonies that are extremely hard to remove by washing. Over time, this leads to a decreasing textile quality and consumer comfort. To design prevention and removal mechanisms, we investigated the behavior of bacteria during the four stages of their life cycle in textiles: adhesion, growth, drying, and washing. The bacterial behavior in textiles during all four stages is found to be affected by the textile's ability to bind water and fat. The study indicates that sweat malodor and bacterial accumulation in textiles over time can be reduced by making the textiles more repellant to water and fat.

Effect of a bioconverted product of Lotus corniculatus seed on the axillary microbiome and body odor

The skin microbiome, especially the axillary microbiome, consists of odor-causing bacteria that decompose odorless sweat into malodor compounds, which contributes to the formation of body odor. Plant-derived products are a cheap source of bioactive compounds that are common ingredients in cosmetics. Microbial bioconversion of natural products is an ecofriendly and economical method for production of new or improved biologically active compounds. Therefore, in this study, we tested the potential of a Lactobacillus acidophilus KNU-02-mediated bioconverted product (BLC) of Lotus corniculatus seed to reduce axillary malodor and its effect on the associated axillary microbiota. A chemical profile analysis revealed that benzoic acid was the most abundant chemical compound in BLC, which increased following bioconversion. Moreover, BLC treatment was found to reduce the intensity of axillary malodor. We tested the axillary microbiome of 18 study participants, divided equally into BLC and placebo groups, and revealed through 16S rRNA gene sequencing that Staphylococcus, Corynebacterium, and Anaerococcus were the dominant taxa, and some of these taxa were significantly associated with axillary malodor. After one week of BLC treatment, the abundance of Corynebacterium and Anaerococcus, which are associated with well-known odor-related genes that produce volatile fatty acids, had significantly reduced. Likewise, the identified odor-related genes decreased after the application of BLC. BLC treatment enhanced the richness and network density of the axillary microbial community. The placebo group, on the other hand, showed no difference in the microbial richness, odor associated taxa, and predicted functional genes after a week. The results demonstrated that BLC has the potential to reduce the axillary malodor and the associated odor-causing bacteria, which makes BLC a viable deodorant material in cosmetic products.

Smells Like Teen Spirit-A Model to Generate Laundry-Associated Malodour In Vitro

Although malodour formation on textiles and in washing machines has been reported to be a very relevant problem in domestic laundry, the processes leading to bad odours have not been studied intensively. In particular, the smell often described as "wet-and-dirty-dustcloth-like malodour" had not been reproduced previously. We developed a lab model based on a bacterial mixture of Micrococcus luteus, Staphylococcus hominis, and Corynebacterium jeikeium, which can produce this odour type and which might allow the detailed investigation of this problem and the development of counteractions. The model uses bacterial strains that have been isolated from malodourous textiles. We could also show that the three volatile compounds dimethyl disulfide, dimethyl trisulfide, and indole contribute considerably to the "wet-fabric-like" malodour. These substances were not only found to be formed in the malodour model but have already been identified in the literature as relevant malodourous substances.

Deodorants and antiperspirants: identification of new strategies and perspectives to prevent and control malodor and sweat of the body

Excessive sweating and body odors in many cultures can cause negative perceptions of an individual and in many cases is related to poor hygiene. Personal hygiene products have been developed with the intention of preventing these undesirable issues. The aim of this paper is to review the main active ingredients used in marketed deodorant and antiperspirant formulations as well as to identify new strategies and future methods to optimize such products and prevent malodor. PubMed and ScienceDirect databases were used to search for studies reporting the use of deodorants and antiperspirants, the compounds used in the formulations, their mechanisms of action and associated controversies, as well as new trends and approaches in the area. Even today, we are still using well-known and established actives such as triclosan and aluminum salts, and these are still the most used compounds in deodorants with bactericidal and antiperspirant properties. These substances have been on the market for more than 40 years, and still there are many questions concerning the safety of both actives. There is a general increased interest globally for lifestyles that focus on sustainability and more natural products such as plant sources and the use of, for example, essential oils. The research that focuses in the area of antiperspirants and deodorants is now more focused on studies of the armpit biochemistry and function and control of the microbiota present in this area. Other possible areas of interest are biotechnological solutions and finding new compounds that will interfere with the biochemistry of the process of sweat decomposition. Further approaches include formulations with probiotics which would maintain the balance of axillary microbiota.

SkinBug: an artificial intelligence approach to predict human skin microbiome-mediated metabolism of biotics and xenobiotics

In addition to being pivotal for the host health, the skin microbiome possesses a large reservoir of metabolic enzymes, which can metabolize molecules (cosmetics, medicines, pollutants, etc.) that form a major part of the skin exposome. Therefore, to predict the complete metabolism of any molecule by skin microbiome, a curated database of metabolic enzymes (1,094,153), reactions, and substrates from ∼900 bacterial species from 19 different skin sites were used to develop “SkinBug.” It integrates machine learning, neural networks, and chemoinformatics methods, and displays a multiclass multilabel accuracy of up to 82.4% and binary accuracy of up to 90.0%. SkinBug predicts all possible metabolic reactions and associated enzymes, reaction centers, skin microbiome species harboring the enzyme, and the respective skin sites. Thus, SkinBug will be an indispensable tool to predict xenobiotic/biotic metabolism by skin microbiome and will find applications in exposome and microbiome studies, dermatology, and skin cancer research.

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SkinBug is AI/ML-based tool to predict metabolism of molecules by Skin microbiome

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Database of 1,094,153 metabolic enzymes from 897 pangenomes of skin microbiome

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Predicts enzymes, bacterial species, and skin sites for the predicted reactions

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82.4% multilabel and 90.0% binary accuracy, and validated on 28 diverse real cases

Biological and Chemical Processes that Lead to Textile Malodour Development

The development of malodour on clothing is a well-known problem with social, economic and ecological consequences. Many people still think malodour is the result of a lack of hygiene, which causes social stigma and embarrassment. Clothing is washed more frequently due to odour formation or even discarded when permastink develops. The malodour formation process is impacted by many variables and processes throughout the textile lifecycle. The contact with the skin with consequent transfer of microorganisms, volatiles and odour precursors leads to the formation of a distinctive textile microbiome and volatilome. The washing and drying processes further shape the textile microbiome and impact malodour formation. These processes are impacted by interindividual differences and fabric type as well. This review describes the current knowledge on the volatilome and microbiome of the skin, textile and washing machine, the multiple factors that determine malodour formation on textiles and points out what information is still missing.

Microecological investigation and comparison of two clinical methods to evaluate axillary osmidrosis

Axillary osmidrosis (AO) is a common disease that causes patients to develop malodor and occurs worldwide. There is a lack of uniform standards to evaluate the severity of the odor and identify a sensitive and convenient method to determine the therapeutic effect of AO treatments in a clinical setting. In the present study, the association between pH value and disease severity was investigated and the potential pathogenic bacteria and probiotic pathogens of AO were further examined. A total of 32 patients with bilateral AO and 32 normal healthy controls were recruited for the present study. The odor was investigated using the traditional method (TM) and our groups newly developed Lu swab method (LSM) and according to the results, the cases were assigned a score on a 4-point scale. The patients' scores and pH value were recorded. The microbiological compositions of the affected sites were determined using 16S rDNA sequencing. The mean LSM score was higher compared with the mean TM score (P<0.05). Furthermore, the mean axillary pH value was higher in patients with AO compared with that in healthy subjects (P<0.0001), and the mean pH value of patients with high disease severity was higher compared with that in patients with moderate disease severity (P<0.001). In the microecological flora, the proportion of Staphylococcus species on patients with AO was significantly lower compared with that on normal controls (P<0.0001), while the proportion of Corynebacterium and Anaerococcus was significantly higher compared with that on normal controls (P<0.01 and P<0.001, respectively). In conclusion, LSM provided a higher sensitivity for evaluating odor severity than the TM and may be suitable for use in a clinical setting. The pH value was positively associated with AO severity. Staphylococcus may be an appropriate probiotic for the treatment of AO, while Corynebacterium and Anaerococcus may be causative pathogens of AO. The present study was registered in the Chinese Clinical Trial Registry (registration no. ChiCTR2000037275).

Detection of axillary perspiration metabolites using ion mobility spectrometry coupled to rapid gas chromatography

The composition of human sweat-and as a consequence the composition of volatiles released from human skin-strongly depends on genetic preconditions, diet, stress, personal hygiene but also on health status and medication. Accordingly, the composition is a carrier of information on the physical and mental states of a person. Therefore, rapid on-site analysis of the relevant substances may be used for medical diagnosis and medication control or even for psychological characterisation. Ion mobility spectrometry coupled to rapid gas chromatography (GC-IMS) was applied to the analysis of human axillary sweat as a sensitive, selective, rapid, and non-invasive method in a feasibility study. For this purpose, a sampling chamber was designed and manufactured. The design and the experimental setup were validated successfully. At least 179 human metabolites could be detected by GC-IMS from the skin of 7 volunteers. Fifteen metabolites were available in all samples from all volunteers and therefore can be characterised as basic sweat compounds which might enable the localisation of hidden persons. Furthermore, in a preliminary feasibility study, the potential of GC-IMS for differentiating the composition of sweat after physical exercises and in a stressful situation-even gender specific-could be demonstrated. Thus, with GC-IMS, a rapid and mobile analytical tool for the analysis of skin volatiles is available for a broad range of applications, e.g. with regard to axillary odour, human health, nutrition, consumption of remedies or drugs of abuse, the localisation of trapped or hidden persons, or even the characterisation of the reaction on stressful situations. Graphical abstract.

Skin microbiota: Friend or foe in pediatric skin health and skin disease

The human integument and gastrointestinal tract host unique microbial ecosystems. Within the last decade, research has focused on understanding the contributions of the microbiota to human health and disease. The majority of skin microbiome studies involve adults. This review focuses on key studies conducted within the pediatric population and provides a framework for future skin microbiome work in this ever-expanding field. This article begins by exploring the skin microbiome at birth and reviews the impact of delivery mode on infant skin colonization. How skin microbial colonization evolves from infancy to adulthood and normal development impacts the abundance of skin commensals such as Streptococcus, Staphylococcus, and Cutibacterium is also highlighted. Finally, several skin microbiome research studies in common pediatric skin conditions are reviewed, including body odor, atopic dermatitis (AD), and acne. The bacteria involved in metabolizing sweat, the impact on body odor, and how this process evolves from childhood to adulthood is outlined. In AD, different bacteria genera that predominate in children and adults and the impact of current AD therapies on skin microbiota are explored. Finally, in acne, the understanding of how Cutibacterium acnes contributes to acne pathogenesis and how acne therapies impact the skin microbial communities is reviewed.

5-methyl Furfural Reduces the Production of Malodors by Inhibiting Sodium l-lactate Fermentation of Staphylococcus epidermidis: Implication for Deodorants Targeting the Fermenting Skin Microbiome

Staphylococcus epidermidis (S. epidermidis) is a common bacterial colonizer on the surface of human skin. Lactate is a natural constituent of skin. Here, we reveal that S. epidermidis used sodium l-lactate as a carbon source to undergo fermentation and yield malodors detected by gas colorimetric tubes. Several furan compounds such as furfural originating from the fermentation metabolites play a role in the negative feedback regulation of the fermentation process. The 5-methyl furfural (5MF), a furfural analog, was selected as an inhibitor of sodium l-lactate fermentation of S. epidermidis via inhibition of acetolactate synthase (ALS). S. epidermidis treated with 5MF lost its ability to produce malodors, demonstrating the feasibility of using 5MF as an ingredient in deodorants targeting malodor-causing bacteria in the skin microbiome.

Developing a new device for continuously recording, in vivo, the excretion rate of sweat (perspiration) in humans

BACKGROUND

Some methodologies used for evaluating sweat production and antiperspirants are of a stationary aspect, that is, most often performed under warm (38°C) but resting conditions in a rather short period of time. The aim is to develop an electronic sensor apt at continuously recording sweat excretion, in vivo, during physical exercises, exposure to differently heated environments, or any other stimuli that may provoke sweat excretion.

MATERIAL AND METHODS

A sensor (20 cm² ) is wrapped under a double-layered textile pad. Fixed onto the armpits, these two arrays of electrodes are connected to electronic system through an analog multiplexer. A microcontroller is used to permanently record changes in the conductance between two electrodes during exposure of subjects to different sweat-inducing conditions or to assess the efficacy of applied aluminum hydrochloride (ACH)-based roll-ons at two concentrations (5% and 15%).

RESULTS

In vitro calibration, using a NaCl 0.5% solution, allows changes in mV to be related with progressively increased volumes. In vivo, results show that casual physical exercise leads to sweat excretions much higher than in warm environment (37 or 45°C). Only, an exposure to a 50°C environment induced comparable sweat excretion. In this condition, sweat excretions were found similar in both armpits and both genders. Decreased sweat excretions were recorded following applications of ACH, with a dose effect.

CONCLUSION

Developing phases of this new approach indicate that usual method or guidelines used to determine sweat excretions in vivo do not reflect true energy expenditure processes. As a consequence, they probably over-estimate the efficacy of antiperspirant agents or formulae.

Understanding the microbial basis of body odor in pre-pubescent children and teenagers

BACKGROUND

Even though human sweat is odorless, bacterial growth and decomposition of specific odor precursors in it is believed to give rise to body odor in humans. While mechanisms of odor generation have been widely studied in adults, little is known for teenagers and pre-pubescent children who have distinct sweat composition from immature apocrine and sebaceous glands, but are arguably more susceptible to the social and psychological impact of malodor.

RESULTS

We integrated information from whole microbiome analysis of multiple skin sites (underarm, neck, and head) and multiple time points (1 h and 8 h after bath), analyzing 180 samples in total to perform the largest metagenome-wide association study to date on malodor. Significant positive correlations were observed between odor intensity and the relative abundance of Staphylococcus hominis, Staphylococcus epidermidis, and Cutibacterium avidum, as well as negative correlation with Acinetobacter schindleri and Cutibacterium species. Metabolic pathway analysis highlighted the association of isovaleric and acetic acid production (sour odor) from enriched S. epidermidis (teen underarm) and S. hominis (child neck) enzymes and sulfur production from Staphylococcus species (teen underarm) with odor intensity, in good agreement with observed odor characteristics in pre-pubescent children and teenagers. Experiments with cultures on human and artificial sweat confirmed the ability of S. hominis and S. epidermidis to independently produce malodor with distinct odor characteristics.

CONCLUSIONS

These results showcase the power of skin metagenomics to study host-microbial co-metabolic interactions, identifying distinct pathways for odor generation from sweat in pre-pubescent children and teenagers and highlighting key enzymatic targets for intervention.

Individual- and Species-Specific Skin Microbiomes in Three Different Estrildid Finch Species Revealed by 16S Amplicon Sequencing

An animals' body is densely populated with bacteria. Although a large number of investigations on physiological microbial colonisation have emerged in recent years, our understanding of the composition, ecology and function of the microbiota remains incomplete. Here, we investigated whether songbirds have an individual-specific skin microbiome that is similar across different body regions. We collected skin microbe samples from three different bird species (Taeniopygia gutatta, Lonchura striata domestica and Stagonopleura gutatta) at two body locations (neck region, preen gland area). To characterise the skin microbes and compare the bacterial composition, we used high-throughput 16S rRNA amplicon sequencing. This method proved suitable for identifying the skin microbiome of birds, even though the bacterial load on the skin appeared to be relatively low. We found that across all species, the two evaluated skin areas of each individual harboured very similar microbial communities, indicative of an individual-specific skin microbiome. Despite experiencing the same environmental conditions and consuming the same diet, significant differences in the skin microbe composition were identified among the three species. The bird species differed both quantitatively and qualitatively regarding the observed bacterial taxa. Although each species harboured its own unique set of skin microbes, we identified a core skin microbiome among the studied species. As microbes are known to influence the host's body odour, our findings of an individual-specific skin microbiome might suggest that the skin microbiome in birds is involved in the odour production and could encode information on the host's genotype.

Olfactory Communication via Microbiota: What Is Known in Birds?

Animal bodies harbour a complex and diverse community of microorganisms and accumulating evidence has revealed that microbes can influence the hosts' behaviour, for example by altering body odours. Microbial communities produce odorant molecules as metabolic by-products and thereby modulate the biochemical signalling profiles of their animal hosts. As the diversity and the relative abundance of microbial species are influenced by several factors including host-specific factors, environmental factors and social interactions, there are substantial individual variations in the composition of microbial communities. In turn, the variations in microbial communities would consequently affect social and communicative behaviour by influencing recognition cues of the hosts. Therefore, microbiota studies have a great potential to expand our understanding of recognition of conspecifics, group members and kin. In this review, we aim to summarize existing knowledge of the factors influencing the microbial communities and the effect of microbiota on olfactory cue production and social and communicative behaviour. We concentrate on avian taxa, yet we also include recent research performed on non-avian species when necessary.

Population level evidence for seasonality of the human microbiome

The objective of this study is to determine whether human body odors undergo seasonal modulation. We utilized google trends search volume from the United States of America from January 1, 2010 to June 24, 2017 for a number of predetermined body odors. Regression modeling of time series data was completed. Our primary outcome was to determine the proportion of the variability in Internet searches for each unpleasant odor (about the mean) that is explained by a seasonal model. We determined that the seasonal (sinusoidal) model provided a significantly better fit than the null model (best straight line fit) for all searches relating to human body odors (P <.0001 for each). This effect was easily visible to the naked eye in the raw time series data. Seasonality explained 88% of the variability in search volume for flatulence (i.e. R2 = 0.88), 65% of the variability in search volume for axillary odor, 60% of the variability in search volume for foot odor, and 58% of the variability in search volume for bad breath. Flatulence and bad breath tended to peak in January, foot odor in February, and Axillary odor in July. We conclude that searching by the general public for information on unpleasant body odors undergoes substantial seasonal variation, with the timing of peaks and troughs varying with the body part involved. The symptom burden of such smells may have a similar seasonal variation, as might the composition of the commensal bacterial microflora that play a role in creating them.

Do apes smell like humans? The role of skin bacteria and volatiles of primates in mosquito host selection

Anthropophilic mosquitoes are effective vectors of human diseases because of their biting preference. To find their host, these mosquitoes are guided by human odours, primarily produced by human skin bacteria. By analysing the skin bacterial and skin volatile profiles of humans, bonobos, chimpanzees, gorillas, lemurs and cows, we investigated whether primates that are more closely related to humans have a skin bacterial community and odour profile that is similar to humans. We then investigated whether this affected discrimination between humans and closely related primates by anthropophilic and zoophilic mosquitoes that search for hosts. Humans had a lower skin bacterial diversity than the other animals and their skin bacterial composition was more similar to the other primates than to the skin bacterial composition of cows. Like the skin bacterial profiles, the volatile profiles of the animal groups were clearly different from each other. The cow and lemur volatile profiles were more closely related to the human profiles than expected. Human volatiles were indeed preferred above cow volatiles by anthropophilic mosquitoes and no preference was observed when tested against non-human primate odour, except for bonobo volatiles that were preferred over human volatiles. Unravelling the differences between mosquito hosts and their effect on host selection is important for a better understanding of cross-species transmission of vector-borne diseases.

The Association of the Skin Microbiota With Health, Immunity, and Disease

The human skin is densely colonized by a highly diverse microbiota comprising all three domains of life. Long believed to represent mainly a source of infection, the human skin microbiota is nowadays well accepted as an important driver of human (skin) health and well-being. This microbiota is influenced by many host and environmental factors and interacts closely with the skin immune system. Although cause and effect are usually difficult to discriminate, changes in the skin microbiota clearly play a role in the pathobiology of many types of skin disease and cosmetic disorders. Consequently, treatment and prevention strategies have to respect this role, rendering pre- and probiotic and even transplantation therapies an additional option to the use of antibiotics.

Composition of Asarum heterotropoides var. mandshuricum radix oil from different extraction methods and activities against human body odor-producing bacteria

In this study, oils from Asarum heterotropoides were extracted by traditional solvent extraction and supercritical CO₂ (SC-CO₂) extraction methods and their antioxidant activities along with antimicrobial and inhibitory activities against five human body odor-producing bacteria (Staphylococcus epidermidis, Propionibacterium freudenreichii, Micrococcus luteus, Corynebacterium jeikeium, and Corynebacterium xerosis) were evaluated. The oil was found to contain 15 components, among which the most abundant component was methyl eugenol (37.6%), which was identified at every condition studied in different extraction methods. The oil extracted with n-hexane and ethanol mixture exhibited a strong antioxidant activity (92% ± 2%) and the highest ABTS and 2,2-diphenyl-1-picrylhydrazyl scavenging activities (89% ± 0.2%). The highest amounts of total phenolic content and total flavonoid content were 23.1 ± 0.4 mg/g and 4.9 ± 0.1 mg/g, respectively, in the traditional method. In the SC-CO₂ method performed at 200 bar/50°C using ethanol as an entrainer, the highest inhibition zone was recorded against all the aforementioned bacteria. In particular, strong antibacterial activity (38 ± 2 mm) was found against M. luteus. The minimum inhibitory concentration (MIC) for the oil against bacteria ranged from 10.1 ± 0.1 μg/mL to 46 ± 2 μg/mL. The lowest MIC was found against M. luteus. Methyl eugenol was found to be one of the major compounds working against human body odor-producing bacteria.

The effect of habitual and experimental antiperspirant and deodorant product use on the armpit microbiome

An ever expanding body of research investigates the human microbiome in general and the skin microbiome in particular. Microbiomes vary greatly from individual to individual. Understanding the factors that account for this variation, however, has proven challenging, with many studies able to account statistically for just a small proportion of the inter-individual variation in the abundance, species richness or composition of bacteria. The human armpit has long been noted to host a high biomass bacterial community, and recent studies have highlighted substantial inter-individual variation in armpit bacteria, even relative to variation among individuals for other body habitats. One obvious potential explanation for this variation has to do with the use of personal hygiene products, particularly deodorants and antiperspirants. Here we experimentally manipulate product use to examine the abundance, species richness, and composition of bacterial communities that recolonize the armpits of people with different product use habits. In doing so, we find that when deodorant and antiperspirant use were stopped, culturable bacterial density increased and approached that found on individuals who regularly do not use any product. In addition, when antiperspirants were subsequently applied, bacterial density dramatically declined. These culture-based results are in line with sequence-based comparisons of the effects of long-term product use on bacterial species richness and composition. Sequence-based analyses suggested that individuals who habitually use antiperspirant tended to have a greater richness of bacterial OTUs in their armpits than those who use deodorant. In addition, individuals who used antiperspirants or deodorants long-term, but who stopped using product for two or more days as part of this study, had armpit communities dominated by Staphylococcaceae, whereas those of individuals in our study who habitually used no products were dominated by Corynebacterium. Collectively these results suggest a strong effect of product use on the bacterial composition of armpits. Although stopping the use of deodorant and antiperspirant similarly favors presence of Staphylococcaceae over Corynebacterium, their differential modes of action exert strikingly different effects on the richness of other bacteria living in armpit communities.

The Microbiota of the Human Skin

The aim of this chapter is to sum up important progress in the field of human skin microbiota research that was achieved over the last years.The human skin is one of the largest and most versatile organs of the human body. Owing to its function as a protective interface between the largely sterile interior of the human body and the highly microbially contaminated outer environment, it is densely colonized with a diverse and active microbiota. This skin microbiota is of high importance for human health and well-being. It is implicated in several severe skin diseases and plays a major role in wound infections. Many less severe, but negatively perceived cosmetic skin phenomena are linked with skin microbes, too. In addition, skin microorganisms, in particular on the human hands, are crucial for the field of hygiene research. Notably, apart from being only a potential source of disease and contamination, the skin microbiota also contributes to the protective functions of the human skin in many ways. Finally, the analysis of structure and function of the human skin microbiota is interesting from a basic, evolutionary perspective on human microbe interactions.Key questions in the field of skin microbiota research deal with (a) a deeper understanding of the structure (species inventory) and function (physiology) of the healthy human skin microbiota in space and time, (b) the distinction of resident and transient skin microbiota members,

Mapping axillary microbiota responsible for body odours using a culture-independent approach

BACKGROUND

Human axillary odour is commonly attributed to the bacterial degradation of precursors in sweat secretions. To assess the role of bacterial communities in the formation of body odours, we used a culture-independent approach to study axillary skin microbiota and correlated these data with olfactory analysis.

RESULTS

Twenty-four Caucasian male and female volunteers and four assessors showed that the underarms of non-antiperspirant (non-AP) users have significantly higher global sweat odour intensities and harboured on average about 50 times more bacteria than those of AP users. Global sweat odour and odour descriptors sulfury-cat urine and acid-spicy generally increased from the morning to the afternoon sessions. Among non-AP users, male underarm odours were judged higher in intensity with higher fatty and acid-spicy odours and higher bacterial loads. Although the content of odour precursors in underarm secretions varied widely among individuals, males had a higher acid: sulfur precursor ratio than females did. No direct correlations were found between measured precursor concentration and sweat odours. High-throughput sequencing targeting the 16S rRNA genes of underarm bacteria collected from 11 non-AP users (six females and five males) confirmed the strong dominance of the phyla Firmicutes and Actinobacteria, with 96% of sequences assigned to the genera Staphylococcus, Corynebacterium and Propionibacterium. The proportion of several bacterial taxa showed significant variation between males and females. The genera Anaerococcus and Peptoniphilus and the operational taxonomic units (OTUs) from Staphylococcus haemolyticus and the genus Corynebacterium were more represented in males than in females. The genera Corynebacterium and Propionibacterium were correlated and anti-correlated, respectively, with body odours. Within the genus Staphylococcus, different OTUs were either positively or negatively correlated with axillary odour. The relative abundance of five OTUs (three assigned to S. hominis and one each to Corynebacterium tuberculostearicum and Anaerococcus) were positively correlated with at least one underarm olfactory descriptor.

CONCLUSIONS

Positive and negative correlations between bacterial taxa found at the phylum, genus and OTU levels suggest the existence of mutualism and competition among skin bacteria. Such interactions, and the types and quantities of underarm bacteria, affect the formation of body odours. These findings open the possibility of developing new solutions for odour control.

Microbiome and skin diseases

PURPOSE OF REVIEW

This article reviews recent findings on the skin microbiome. It provides an update on the current understanding of the role of microbiota in healthy skin and in inflammatory and allergic skin diseases.

RECENT FINDINGS

Advances in computing and high-throughput sequencing technology have enabled in-depth analysis of microbiota composition and functionality of human skin. Most data generated to date are related to the skin microbiome of healthy volunteers, but recent studies have also addressed the dynamics of the microbiome in diseased and injured skin. Currently, reports are emerging that evaluate the strategies to manipulate the skin microbiome, intending to modulate diseases and/or their symptoms.

SUMMARY

The microbiome of normal human skin was found to have a high diversity and high interpersonal variation. Microbiota compositions of diseased lesional skin (in atopic dermatitis and psoriasis) showed distinct differences compared with healthy skin. The function of microbial colonization in establishing immune system homeostasis has been reported, whereas host-microbe interactions and genetically determined variation of stratum corneum properties might be linked to skin dysbiosis. Both are relevant for cutaneous disorders with aberrant immune responses and/or disturbed skin barrier function. Modulation of skin microbiota composition to restore host-microbiota homeostasis could be future strategies to treat or prevent disease.

Tomatoes cause under-arm odour

Under arm odour [axillary odour AO, bromidrosis] is a deeply unpleasant problem that can affect a person's self confidence and esteem and reduce social interaction. It is generally managed by good hygiene along with antiperspirants and deodorants, but the axillary apocrine glands may need surgical removal in severe cases of odour. The odour comes from microbial conversion of the apocrine secretions into short chain fatty acids like isovaleric acid and volatile sulphur compounds like 3-sulphanylhexan-1-ol. These can be detected at a few parts per billion to parts per trillion by the human nose so an unhygienic state is soon apparent. Recently genetics have been found to play an important role too as people with the AA variant of the ATP-binding cassette (ABC) transporter gene, ABCC11, do not secrete preodour substrates for bacterial conversion, while those with GA or GG variants do. Hygiene and genetics, are an incomplete explanation though, because the longitudinal ALSPAC study found that there is a mismatch between patients' secretory status, as determined by genetics, and their use of deodorants. This suggests that other metabolic pathways or compounds contribute to the odour. In this paper I propose that under arm odour is commonly caused by terpenes excreted via the axillary apocrine glands. I also show that these come from terpene and carotenoid-rich dietary sources including lycopene, tomatoes, orange peel and the glandular trichomes of tomato plants. These observations suggest that the axillary apocrine glands are a prominent excretory route for terpenes. Considering the quantities eaten, tomatoes are likely to be the main source of dietary terpenes, and under arm odour in turn. This study also shows that lycopene is probably metabolised by β-carotene 9 10 monooxygenase which cleaves β-carotene eccentrically at the 9 10 or 9'10' position of the chain. Direct evidence of lycopene metabolism by β-carotene 9 10 monooxygenase has hitherto been lacking. The study of terpene and carotenoid metabolism can be greatly advanced by analysing the content of axillary gland excretions.