The human skin microbiome is diverse and plays important roles in human health. Different regions of the skin harbor distinct bacterial communities that are influenced by environmental and host factors. While some bacteria can cause infection, many resident skin bacteria participate in mutually beneficial relationships or protect the host from pathogens. Maintaining a balanced skin microbiome is important for both immune function and preventing infectious diseases.

2. OVERVIEW
1. Introduction
2. Identification
3. Presence
4. Function
5. Conclusion

3. 1. INTRODUCTION
SKIN AS ECOSYSTEM
• Life on human skin is like life on planet earth.
• The plants and trees are like the hair follicles.
• Birds and animals are like the skin microbial flora.
• Deserts and rain forests are like the trunk and axillae of man.
• Different populations are seen in different regions in both cases.

4. TYPES OF SYMBIOSIS
• Definition: Interaction between two different organisms living in close
physical association with that of its environment.

5. TYPES OF SYMBIOSIS
• Definition: Interaction between two different organisms living in close
physical association with that of its environment.
• 3 main types:
Parasitism – One organism benefits while the other is harmed.
Commensalism – One benefits while the other is unharmed.
Mutualism – Both benefit from each other.
• In skin, organisms can exhibit more than one behavior in different
circumstances.

6. TYPES OF SKIN FLORA
• Stable residents
• Transcients
• Temporary residents
• Frank pathogens

7. CHALLENGES IN LAB
• Mere presence is not pathogenic.
• Organism characteristics: Number, strain difference.
• Host characteristics: Immunocompromise, breach in skin barrier, etc.

8. CLASSIFICATION
BACTERIA FUNGI VIRUS MITE
1. Actinobacteria
- Propionibacteria
- Corynebacteria
2. Firmicutes
- Staphylococci
3. Bacteroides
4. Proteobacteria
Malassezia spp. Demodex folliculorum---

10. QUICK FACTS
• Taking bacteria alone, estimated 1 million bacteria, with hundreds of
distinct species, inhabit each square centimeter of skin1.
1. Rook’s Textbook of Dermatology, 9th Edition, pp 2.13.

11. QUICK FACTS
• The composition of these communities depend on skin characteristics,
host and environmental factors.
1. Rook’s Textbook of Dermatology, 9th Edition, pp 2.13.

12. QUICK FACTS
• Skin microbes may contribute even to noninfectious pathologies, such
as atopic dermatitis, psoriasis, rosacea, and acne.
1. Rook’s Textbook of Dermatology, 9th Edition, pp 2.13.

13. QUICK FACTS
• Skin microbes tend to maintain a state of equilibrium, thereby
protecting the host from microbial pathogens by excluding them from
the cutaneous ecosystem.
1. Rook’s Textbook of Dermatology, 9th Edition, pp 2.13.

14. QUICK FACTS
• Activities that seem trivial to us, such as taking a shower, may be the
equivalent of a hurricane to the microbes inhabiting the skin, with
changes in landscape and population structure.
1. Rook’s Textbook of Dermatology, 9th Edition, pp 2.13.

15. 2. IDENTIFICATION
METHODS OF SAMPLING
• Conventional method: Swabbing.
• Semi-quantitative methods:
- Sticky tape sampling
- Roll tubes
- Replica plating
• Quantitative methods:
- Cylinder, liquid vehicle & scrubbing.
- Air sampling technique (with settle plates / impaction sampler)
• Skin biopsy: HPE examination.

16. 2. IDENTIFICATION
ISOLATION MEDIA (for culture-dependent method)
• Blood / serum agar – for aerobic organisms.
• Brewer’s Thioglycolate medium with 1% Tween 80® - for P. acnes.

17. 2. IDENTIFICATION
ISOLATION MEDIA (for culture-dependent method)
• Blood / serum agar – for aerobic organisms.
• Brewer’s Thioglycolate medium with 1% Tween 80® - for P. acnes.
ISOLATION METHOD (for culture independent method)
• PCR – to amplify rRNA gene sequences.

18. 2. IDENTIFICATION
CULTURE GENOMICS METAGENOMICS
• Historically, characterizing cutaneous microbes involved culturing skin
swabs or biopsies.
• However, less than 1% of bacterial species can be cultivated with standard
lab conditions.
• Recent advances in DNA amplification and sequencing technology can now
bypass the culture steps and allow for more complete, unbiased views.

19. METAGENETICS
1. A culture-free, sequence-based method of analyzing any collection of
microorganisms.

20. METAGENETICS
2. It involves amplifying the 16S ribosomal RNA (16S rRNA) gene – which exists in
all bacteria – by PCR directly from skin samples.

21. METAGENETICS
3. 16S rRNA gene has:
- Conserved regions – for binding of PCR primers
- Variable regions – for taxonomic classification (after sequencing)

22. METAGENETICS
4. Sequences that are more than 97% identical can be classified within 1 species.

23. METAGENETICS
5. The number of sequences counted within one species represents the relative
abundance of that species in the original skin sample.

24. METAGENETICS
6. Thus, this metagenomic approach gives a comprehensive picture of the
bacterial community by providing both identification and relative abundances of all
present species.

25. 3. PRESENCE
• In utero, fetal skin is sterile, but minutes after birth, colonization begins
to occur.
• Newborns are first homogenously colonized with a similar, low-
diversity microbiome all over the body.
• As infants contact environmental microbiota and as different areas of
the skin develop distinct moisture, temperature, and glandular
characteristics, the microbial population begins to vary.
• Likely to have, as temporary residents, Streptococci and Micrococcus.

26. REASONS FOR VARIATION

27. REASONS FOR VARIATION
OILY SITES - Propionibacterium spp. and Malassezia spp.
MOIST SITES - Coryneforms and S. aureus.
DRY SITES - Variable; Gram negative bacilli, Proteobacteria, Micrococcus.
HAIR FOLLICLES - Deep – Anaerobic Propionibacterium;
Superficial – Aerobic cocci, Malassezia spp.

28. Source: Yasmine Belkaid et al., Dialogue between skin microbiota and
immunity, Science 21 Nov 2014: Vol. 346, Issue 6212, pp. 954-959.

29. STABLE BACTERIAL RESIDENTS
GRAM + GRAM -
1. Cocci: Firmicutes (eg. Staph)
2. Rods
3. Coryneforms / diptheroids
1. Acinetobacter spp.
ANAEROBES
1. Propionibacteria
2. Staphylococcus saccharolyticus

30. VARIATIONS
DIVERSITY
Alpha Diversity – Diversity of microbial skin flora between individuals.
Beta Diversity – Diversity within one habitat compared to other sites of
same individual.
• Skin microbial flora has less alpha diversity and more beta diversity.

31. VARIATIONS
TEMPORAL VOLATILITY
• Partially occluded sites (eg. inguinal crease) have more stable
bacterial communities over time, while dryer and more exposed
skin sites (eg. palms) have more temporal fluctuations.

32. VARIATIONS
CLIMATE CHANGES
• In humid tropical climate, P. aeruginosa is common in moist areas.

33. VARIATIONS
CLIMATE CHANGES
• In humid tropical climate, P. aeruginosa is common in moist areas.
SERIOUSLY ILL PATIENTS
• Gram negative organisms are common residents.

34. VARIATIONS
CLIMATE CHANGES
• In humid tropical climate, P. aeruginosa is common in moist areas.
SERIOUSLY ILL PATIENTS
• Gram negative organisms are common residents.
TOPICAL ANTISEPTIC APPLICATION
• Removes transcient flora and reduces resident flora.

35. SPECIAL RESIDENTS
• CONS, Micrococci, Coryneforms, S. aureus (35% of healthy people)
NASAL VESTIBULE

36. SPECIAL RESIDENTS
• CONS, Micrococci, Coryneforms, S. aureus (35% of healthy people)
NASAL VESTIBULE
EXTERNAL AUDITORY MEATUS
• CONS, Coryneforms, Proteus sp., E. coli, N. catarrhalis, N. flora.

37. SPECIAL RESIDENTS
• CONS, Micrococci, Coryneforms, S. aureus (35% of healthy people)
NASAL VESTIBULE
EXTERNAL AUDITORY MEATUS
• CONS, Coryneforms, Proteus sp., E. coli, N. catarrhalis, N. flora.
AXILLA
• Staphylococci, Coryneforms.

38. SPECIAL RESIDENTS
• CONS, Micrococci, Coryneforms, S. aureus (35% of healthy people)
NASAL VESTIBULE
EXTERNAL AUDITORY MEATUS
• CONS, Coryneforms, Proteus sp., E. coli, N. catarrhalis, N. flora.
AXILLA
• Staphylococci, Coryneforms.
TOE CLEFTS
• Brevibacterium, Acinebacter, Alkaligenes spp., Coliforms.

39. SPECIAL RESIDENTS
• CONS, micrococci, coryneforms, coliforms, enterococci, Group B Strep.
VULVA

40. SPECIAL RESIDENTS
• CONS, micrococci, coryneforms, coliforms, enterococci, Group B Strep.
VULVA
PERENIUM AND GROIN
• CONS, micrococci, coryneforms, Acinetobacter.

41. SPECIAL RESIDENTS
• CONS, micrococci, coryneforms, coliforms, enterococci, Group B Strep.
VULVA
PERENIUM AND GROIN
• CONS, micrococci, coryneforms, Acinetobacter.
UMBILICUS
• Staph aureus, Strep pyogenes.

42. SPECIAL RESIDENTS
• CONS, micrococci, coryneforms, coliforms, enterococci, Group B Strep.
VULVA
PERENIUM AND GROIN
• CONS, micrococci, coryneforms, Acinetobacter.
UMBILICUS
• Staph aureus, Strep pyogenes.
VAGINA
• Bacteria and fungi (Candida albicans). There is an inverse
relationship between bacterial and yeast floras with respect to
prevalence and numerical abundance.

43. SPECIAL RESIDENTS
VAGINAL FLORA
AEROBES ANAEROBES

44. 4. FUNCTIONS
1. Pathogenesis of non-infectious disease: Atopic Dermatitis
• Implicated in “flares.”
• S. aureus and S. epidermidis are seen in abundance.
• S. epidermidis increases as an antagonistic response to an increasing
S. aureus population.
• Novel treatments of AD flares thus needs to rebalance and re-
diversify the skin microbiome rather than eliminating S. aureus
burden on skin.
• The clinical significance of studies of microbiome in psoriasis, acne
vulgaris and chronic wounds are yet to be elucidated.

45. 4. FUNCTIONS
2. Microbiome in immune development
• Educates and assists the immune system and alerts immune system
to pathogenicity.
• AMPs production is upregulated by the presence of
Propionibacterium species and other Gram-positive bacteria.
• S. epidermidis' Pheno Soluble Modulins have bacteria-killing activity
but no effect on neutrophils.

46. 4. FUNCTIONS
3. Cancer Immunology and microbiome
• Workers, such as farmers and waste incinerator workers, who were
exposed heavily to environmental microbiota, had lower cancer
rates1.
• Evidence has now been provided that certain microbial components
actually do have antitumor activity against bladder and colon
cancers, at least in part by heightening immunosurveillance2.
1. Rylander R. Environmental exposures with decreased risks for lung cancer? Int J Epidemiol. 1990;
19(Suppl 1):S67–S72.
2. Grange JM, Bottasso O, Stanford CA, Stanford JL. The use of mycobacterial adjuvant-based agents for
immunotherapy of cancer. Vaccine. 2008; 26:4984–4990.

47. • They compete against pathogenic strains and interfere with their presence.
• They make the environment acidic & thereby inhibits growth of organisms.
Example, P. acnes converts lipid to FFA and Lactobacilli produce lactic acid.
Both thereby create an acidic environment and inhibits organisms such as
Streptococcus pyogenes (eg. P. acnes) and G. vaginalis (eg. Lactobacilli).
4. Preventing infectious diseases
4. FUNCTIONS

48. 4. Preventing infectious diseases

49. Staphylococci are pathogenic and mutualistic. (a) Virulence factors and molecules
produced by staphylococci that aid in pathogenesis. (b) Staphylococci act mutually by
inhibiting pathogens and priming the immune response. (c) Molecules from
staphylococci that have dual functions.

50. 5. CONCLUSION
• Current research related to infectious diseases of the skin targets
microbial virulence factors and aims to eliminate harmful
organisms.
• Some of these same microbes potentially also play an opposite
role by protecting the host.
• An overuse of antibiotics, for instance, may disrupt the delicate
balance of the cutaneous microflora leaving the skin susceptible
to pathogens previously kept at bay by the existing resident and
mutual microbiota.
• Further advances in our understanding of microbial pathogens
promise to lead to novel diagnostic and therapeutic approaches
to dermatological disease.