Longitudinal study of the scalp microbiome suggests coconut oil to enrich healthy scalp commensals

Rituja Saxena, Parul Mittal, Cecile Clavaud, Darshan B Dhakan, Nita Roy, Lionel Breton, Namita Misra, Vineet K Sharma, Rituja Saxena, Parul Mittal, Cecile Clavaud, Darshan B Dhakan, Nita Roy, Lionel Breton, Namita Misra, Vineet K Sharma

Abstract

Dandruff is a recurrent chronic scalp disorder, affecting majority of the population worldwide. Recently a metagenomic study of the Indian scalp microbiome described an imperative role of bacterial commensals in providing essential vitamins and amino acids to the scalp. Coconut oil and its formulations are commonly applied on the scalp in several parts of the world to maintain scalp health. Thus, in this study we examined the effect of topical application of coconut oil on the scalp microbiome (bacterial and fungal) at the taxonomic and functional levels and their correlation with scalp physiological parameters. A 16-weeks-long time-course study was performed including 12-weeks of treatment and 4-weeks of relapse phase on a cohort of 140 (70 healthy and 70 dandruff) Indian women, resulting in ~ 900 metagenomic samples. After the treatment phase, an increase in the abundance of Cutibacterium acnes and Malassezia globosa in dandruff scalp was observed, which were negatively correlated to dandruff parameters. At the functional level, an enrichment of healthy scalp-related bacterial pathways, such as biotin metabolism and decrease in the fungal pathogenesis pathways was observed. The study provides novel insights on the effect of coconut oil in maintaining a healthy scalp and in modulating the scalp microbiome.

Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Study Design. Swab samples were collected at three phases, baseline (t = 1), treatment phase (t = 2) and relapse phase (t = 3) from healthy and dandruff scalps. Bacterial and fungal DNA was extracted from the collected swab samples, and amplicon (bacterial 16S rRNA V3 and fungal ITS1 region) and shotgun metagenomic sequencing were performed to carry out the taxonomic and functional analysis. In the figure, H = healthy scalp, D = dandruff scalp, O = oil-treatment, S = shampoo-treatment, and B, T and R = the three phases or time-points i.e. Baseline, Treatment and Relapse phase, and n = number of subjects in each group.
Figure 2
Figure 2
Comparison of fungal population at the three phases. (a) Bubble plots representing the top five fungal species across all the groups. The bubble size indicates mean relative abundance of species within each group. Square brackets indicate the groups between which a significant difference in the species abundance was observed (p ≤ 0.05, Wilcoxon test, + indicates the group with the higher abundance among the two). (b) Core fungal species showing significant variations across the three phases (FDR adjusted p ≤ 0.05, repeated measures ANOVA).
Figure 3
Figure 3
Comparison of bacterial population at the three phases. (a) Bubble plots representing the top five bacterial species across all the groups. The bubble size indicates mean relative abundance of species within each group. Square brackets indicate the groups between which a significant difference in the species abundance was observed (p ≤ 0.05, Wilcoxon test, + indicates the group with the higher abundance among the two). (b) Significant fold-change differences (p ≤ 0.05) observed in bacterial species abundance between oil-treatment and shampoo-application. No significant difference was observed in the fungal species between the two treatment groups. (c) Core bacterial species showing significant variations across the three phases (FDR adjusted p ≤ 0.05, repeated measures ANOVA).
Figure 4
Figure 4
Spearman’s correlation between microbial taxa and host physiological parameters. (a) Fungal and (b) bacterial taxa showing significant correlations (+ , FDR adjusted p ≤ 0.05) with any of the parameters are plotted as a heatmap.
Figure 5
Figure 5
Functional analysis of fungal microbiome. The proportions of fungal pathways showing significant variations across all the three phases in the following groups (FDR adjusted p ≤ 0.05, repeated measures ANOVA) are shown in the box plots: (a) Healthy oil-treated group, (b) dandruff oil-treated group, (c) healthy shampoo-treated group and (d) dandruff shampoo-treated group.
Figure 6
Figure 6
Functional analysis of bacterial microbiome. Differentially abundant bacterial KEGG pathways after (a) oil-treatment and (b) shampoo application in the dandruff group (which showed p ≤ 0.05, Wilcoxon test) are shown in the bar graphs. None of the pathways showed significant differences in the healthy group.
Figure 7
Figure 7
Schematic representation of biotin metabolism pathway describing the significantly enriched KOs (p ≤ 0.05) in the dataset.

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