The Journal of Medical Microbiology, Vol 8, Issue 4 503-511, Copyright © 1975 by Society for General Microbiology
Enumeration of beta-haemolytic streptococci on normal skin by direct agar contact
J. Brown, L. W. Wannamaker and P. Ferrieri
Normal skin sites in children from a population in which streptococcal
impetigo is endemic were examined for the presence of beta-haemolytic
streptococci by a direct agar-contact technique. Ninety-eight of 554
samples (18%) were positive for these organisms. Penicillin prophylaxis
reduced the frequency of isolation of streptococci from the normal skin for
a period of 3 weeks, perhaps accounting in part for the lower isolation
rate in this than in earlier studies. Numbers of streptococcal
colony-forming units in positive samples were generally low, both in terms
of absolute numbers isolated from the surface area sampled and in
comparison with numbers of other aerobic flora recovered. The presence of
streptococcal pyoderma at the time of agar contact was not necessarily
associated with the presence of or with increased numbers of streptococci
on samples obtained from normal skin sites. Low counts were consistently
found in early summer and higher counts in some samples in late summer. In
a simultaneous comparison of paired samples taken from adjacent sites, the
frequency of detection of streptococci by direct agar contact compared
favourably with that obtained with a moist-swab method. The increased
frequency of detection by the agar-contact method appeared to be related to
an increased sensitivity for the detection of low numbers of streptococcal
colony-forming units on the normal skin.
