601 SKIN MICROBIOME INNOVATIONS
this opportunity, it is crucial to explore the current methods of microbiome analysis and
presentation, and to further examine the current effectiveness of communication.
METAGENOMIC SEQUENCING
Metagenomics is a sequencing technique that analyzes an entire genomic material present
in a sample.10 The two primary methodologies for studying microbial communities with
this high-throughput sequencing are marker gene studies and whole-genome shotgun
(WGS) metagenomics. WGS metagenomics sequences all genomes in an environmental
sample, allowing for the examination of biodiversity and functional capabilities of the
microbial community. The habitat sampled can go through comprehensive characterization,
identifying archaea, bacteria, eukaryotes, viruses, plasmids, as well as their gene content.10
This is an advantage of metagenomic sequencing, as traditional approaches relied on key
gene markers, such as 16S ribonucleic acid (RNA) gene amplification, to identify bacteria.11
Currently, the only downfall to metagenomic sequencing is the dependence on references
available in the database.12
Vermicomposting decomposes organic waste by utilizing the synergistic effects of worms
and microorganisms. Specifically, vermicomposting of grape marc produces organic
fertilizer that is incredibly microbially diverse and a high source of bioactive polyphenols.12
To review what metagenomic sequencing results look like, Figure 1 displays the results
taken from a third-party study that applied this technique to characterize the bacterial and
fungal communities present with vermicomposting.12
Metagenomic sequencing has traditionally been employed for soil genome analysis.
However, the remarkable efficacy of this technique, coupled with the rising interest in the
skin microbiome, has sparked its application across diverse industries. This groundbreaking
science holds immense potential, but will it resonate with everyday beauty consumers?
How can brands leverage these insights? Perhaps delving into another prevalent method for
characterizing the skin’s microbiome could provide further clarity.
Figure 1. Redrawn from Pérez-Losada M.12 Bar plots of the mean relative abundance of the predominant
bacteria by phylum. Bacterial alpha-diversity control (CT) and earthworm (EW) treatment samples were
measured. The source shows full phylum, class, family, and genus using shotgun reads and 16S amplicon
sequence variants in 12 microcosms. The white section of the bar plots represents the less abundant taxa
aggregated.12 The researcher compared mean relative microbial abundances between both high throughput
(HTP) sequencing approaches to establish rankings for each taxonomic category.12

602 JOURNAL OF COSMETIC SCIENCE
MINIMUM INHIBITORY CONCENTRATION ANALYSIS
Minimum inhibitory concentration (MIC) is another effective tool used to access a
microbiome environment. This method was developed in response to issues pertaining to
the inefficiency of medical therapies to cure bacterial infections. MIC measures the in vitro
susceptibility or resistance of bacteria strains to an antibiotic, which is crucial for selecting
a therapeutic strategy to directly influence the success of infection treatment.13 MICs go a
step further than the above metagenomic sequencing. While metagenomic sequencing is
valuable for assessing the entire microbial environment, MIC testing provides a solution to
the infectious problem. With the current research of correlating certain bacteria overgrowth
on the skin to certain skin conditions, an MIC reading will provide an effective treatment
plan to restore the skin’s microbiome.
There are a few different MIC methods, including dilution (in agar or in a liquid medium)
or gradient methods (strips impregnated with a predetermined concentration gradient of
an antibiotic).13 Whichever media is chosen, within 30 minutes of preparation, the bacteria
should be added in a way that cell density is maintained. The incubation is conducted in
aerobic conditions between 18 to 24 hours. After this time, the medium is observed for any
growth of bacterial colonies. The report then states the lowest concentration of an antibiotic
in which there is no bacterial growth, the MIC.13 Figure 2 below displays an example of the
agar dilution method, one of the most used and accepted.14
Usually, multiple antibiotics are evaluated on the same bacteria to gather data at which
would be the most effective. The data is split into quantitative data (the MIC value) and
qualitative data (susceptible, intermediate, or resistant). Table I below is an example of MIC
data collected to assess the susceptibility against Klebsiella pneumoniae, a type of Gram-
negative bacteria that typically causes nosocomial infections, or infections commonly
acquired in a hospital setting.13
It is important to highlight that an alternative model was recently required due to the
growing body of evidence indicating that problematic bacterial species on the skin
frequently form biofilms. To address this, antimicrobial efficacy must be evaluated within
the context of biofilm formation, necessitating the use of a Minimum Biofilm Eradication
Figure 2. Redrawn from Giuliano.14 A quantified concentration of microorganisms on an agar plate. The
MIC is determined by identifying the lowest concentration of antibiotic that inhibits bacterial growth. This
example shows an MIC of 32 mcg/mL.14