SKINIPEDIA - Skin Encyclopedia: Skin Bacteria & Disinfection
Skin Bacteria and Skin Disinfection
Epochal Study by Sydney Selwyn and Harold Ellis, Published by the British Medical Journal
SUMMARY
Large discrepancies in the available data on skin microbiology
stimulated investigations of the number, interactions,
and location of commensals and the true efficiency
of disinfection by using skin biopsy, culture of
frozen sections, and other methods.
Most current procedures were less than 0 5% as sensitive
as the biopsy method described. This gave mean
bacterial counts ranging from 4,400/cm2 on the breast to
400,000/cm2 in the axillae. An iodine preparation removed
95% of accessible organisms, but about 20% of bacteria
were protected by follicles, crevices, and lipids. Commensals
in over 20% of people produced antibiotics against
a wide range of pathogens. Conversely, "satellitism" was
demonstrable in 12% of people.
Introduction
Though the human skin is uniquely accessible to investigation
there is, paradoxically, less well established information
about its bacteriology than is the case with the urogenital,
respiratory, or alimentary tract. A general review of the
subject by Russell (1962) encompassed an apparently sound
body of facts. However, the work of the succeeding decade
has changed complacency into uncertainty, and the modem
literature on skin microbiology contains alarming contradictions
about the size and exact nature of the normal microbial
population and its precise location in the skin (Marples, 1969).
Moreover, in studies on skin disinfection a notable fallacy
has been to regard those bacteria that are accessible to standard
sampling methods as the total resident flora.
Materials and Methods
The medium used throughout was conventional nutrient
agar with the addition of 0-5% Tween 80 and 0-5°O glucose
at pH 6-5. Duplicate aerobic and anaerobic cultures were
incubated at 33°C for 72 hours.
SKIN SAMPLING METHODS
Paired specimens of unprepared and disinfected skin were
excised in approximately 1-cm squares both at the start of
routine surgical procedures and also from a series of cadavers (mainly cases of sudden death stored under refrigeration for
less than 24 hours). The full-thickness specimens were placed
in sterile Petri dishes and measured. They were then, without
delay, transferred to sterile bottles for a two-minute mechanical
shake in 10 ml of a sterile solution of 0-10 Triton X-100 in
0 075 M phosphate buffer at pH 7 9-a solution which gives
optimal dispersal of bacteria from skin and yet is free from
antibacterial action (Williamson, 1965). Poured plates were
made with the resultant bacterial suspensions by mixing
0O02-, 0-2-, and 1-ml volumes, in triplicate, with molten agar
in standard Petri dishes. Specimens after disinfection were
examined by filtering 1- and 8-ml volumes (with neutralizers)
through Millipore filter discs (0 45-ptm pore size), which were
then cultured on the agar medium.
Microscopical studies were performed on coverslip preparations
of 10-ptm-thick frozen sections made from excised
skin that had been snap-frozen over carbon dioxide. Some
sections were examined direct, but most were first incubated
for six hours or more on agar before Gram-staining.
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