Normal Microflora of the Skin

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Normal human skin is colonized by a large variety of organisms that live as commensals on its surface. There are quantitative differences among different regions of the skin, related to temperature difference, moisture content, and the presence of various amounts of skin lipids that may be inhibitory or lethal for some microorganisms. These differences characterize three main regions of the skin: (1) axilla, perineum, and toe webs; (2) hands, face, and trunk; and (3) arms and legs [20]. The skin microflora reside on the skin surface and in the ducts of hair follicles and sebaceous glands [38].

Table 11.1. The most important genera and species of bacteria normally found on the skin



Most prevalent species

Coagulase-negative Staphylococcus

Aerobic, Gram-positive cocci

S. hominis, S. haemolyticus S. epidermidis


Aerobic, Gram-positive cocci

M. luteus, M. varians


Aerobic, Gram-positive pleomorphic rods

C. bovis, C. minutissimum


Anaerobic, Gram-positive rods

P. acnes, P. granulosum, P. avidum


Aerobic, Gram-negative coccobacilli

A .calcoaceticus var. lwoffi and var. anitratus

The sites affected by HS are, in order of frequency: axillary, inguinal, perianal and perine-al, mammary and inframammary, buttock, pubic region, chest, scalp, retroauricular, and the eyelid [50].

The major groups of microorganisms present on the skin are various genera of bacteria and yeasts. The predominant bacteria of the skin are as follows (Table 11.1) [20, 21]:

■ Coagulase-negative staphylococci

■ Micrococci

■ Saprophytic Corynebacterium species (diphtheroids)

■ Propionibacterium species

■ Acinetobacter species.

Various coagulase-negative staphylococci are found on the skin and some have special predilection for some areas, for example Staphylococcus hominis and Staphylococcus haemolyticus are found principally in areas where there are numerous apocrine glands, such as axillae and the pubic region [20, 32]. Staphylococcus epider-midis is also an important resident, colonizing moist areas of the skin [21]. It is found preferentially in the upper part of the body and represents over 50% of the resident staphylococci [47].

Micrococcus species are found on the skin, especially in women and children, and Micro-coccus luteus and Micrococcus varians are the prevailing species [20, 21]. These microorganisms often colonize axilla, perineum, and groin [21].

Different bacteria belonging to the genus Corynebacterium are associated, but not exclusively, with moist areas of the skin [21].

Propionibacteria are Gram-positive rod-shaped anaerobic bacteria. Propionibacterium acnes and Propionibacterium granulosum are associated with follicles that have large sebaceous glands on the face and upper trunk and they have a role in acne pathogenesis. Propioni-bacterium avidum is found in moist areas (axillae and groin) and it is not known if it has pathogenic potential [21].

Acinetobacter species are the only important Gram-negative residents of the skin and are found in the axillae and groin of 25% of the population [21].

In addition, any bacterial species that is found in nature or belongs to the normal flora on non-cutaneous areas may temporarily be found on the skin [47]. Staphylococcus aureus is not normally considered a resident of normal skin, but it can be found on perineal skin, axillae, and in the toe cleft. Hemolytic streptococci may be found as transients on different skin sites, more often in children [38]. Atypical mycobacteria may be found in genital and axillary regions and Bacillus species or different Gram-negative bacilli such as Proteus, Pseudomonas, Entero-bacter and Klebsiella are rarely found on the skin [20, 38].

In conclusion, a large variety of bacteria are able to colonize the most affected areas in HS: axilla, perineum, and the groin.

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