SKINIPEDIA - Skin Encyclopedia: Skin Bacteria & Disinfection

Skin Bacteria and Skin Disinfection - Part 5

Epochal Study by Sydney Selwyn and Harold Ellis, Published by the British Medical Journal

CASE FOR MINIMAL DISINFECTION (cont.)

Though the nihilistic approach of Dann (1969) seems unwise, relatively brief disinfection of the operation site will usually suffice. We have confirmed by our biopsy and other sensitive techniques that the patient's skin can be readily cleared of virtually all non-sporing contaminants-and accessible commensals-by swabbing with 0 5% chlorhexidine or 1'5% iodine in 70% ethanol which are allowed to act for 30 seconds. Two minutes is only marginally better (Lowbury et al., 1964) and even 15 seconds was found adequate by Gardner (1946). The iodophor, povidone-iodine, in spirit seems to be a satisfactory alternative to iodine in spirit (Lilly and Lowbury, 1971).

NATURAL ANTIMICROBIAL MECHANISMS

Though the skin is often contaminated with organisms from external and internal sources, it normally supports the growth
of only two kinds of bacteria. The most spectacular illustration of its "self-sterilizing" or "autodisinfecting" powers is in the perianal area, which is regularly anointed with enormous numbers of the richly varied intestinal flora following defaecation
and anal toilet, especially in the Occidental style; yet usually within an hour or so only the resident staphylococci and diphtheroids have survived (Holt and Leitch, 1970). A recent review of skin autodisinfection (Lancet, 1968) drew ttention to the importance of desiccation at the normal skin surface and also to the part played by fatty acids derived from skin lipids. However, no mention was made of the probable role of the resident flora itself in deterring visitors or invaders. Even the production of the moderately antimicrobial fatty acids is due to the lipolytic activities of the residentsa fact well known to the makers of deodorants. However, neither desiccation nor lipids can explain the relative rarity of Staph. aureus as a normal skin commensal, since the organism is at least as resistant to these factors as the normal flora. Other mechanisms are undoubtedly involved in the selfregulation of the skin microflora.

Interference among bacteria has already been studied in action following the inoculation of Staph. aureus (strain 502A)
on the skin and nostrils of neonates and others. Though this strain does not produce any detectable antibacterial substances (Anthony and Wannamaker, 1967) its use seemed to lead to a pronounced reduction in cross-infection (British Medical Journal, 1968). But the dangers of using even "a relatively avirulent strain" of Staph. aureus have become apparent (Blair and Tull, 1969). Far more attractive is the possibility of using coagulase-negative staphylococci and micrococci, many of which we have shown to be powerful producers of antibiotics.

We have recently demonstrated the possible value of these organisms when they occur naturally in surgical and skin patients (to be published). Bacterial "satellitism"-the converse of antagonism-has also been seen during our investigations.
The effect may be due to nutritional requirements of fastidious organisms, as with enhancement of Haemophilus influenzae by staphylococci, or to removal of toxic chemicals such as peroxides by growth enhancers, as first reported by Thompson
and Shibuya (1946). The possible role of satellitism in skin ecology and infection is as yet totally unexplored, but this
should be yet another fascinating area of study in skin microbiology.

Authors wish to acknowledge the skilled technical assistance of Mr. Derek Manson-Smith during the first part of this work. The illustrations were prepared by the department of medical photography, Westminster Medical School. These investigations were generously supported by the Research Committee, Westminster Hospital, and a grant towards expenses was provided by Leo Laboratories Ltd.

References

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