In an investigation of impetigo among troops, carried out in 1941, nearly half of the strains of Staphylococcus aureus isolated from the lesions had the ability to inhibit the growth of corynebacteria on solid media. A much smaller proportion of strains from other superficial lesions and from nose and throat swabs had this ability, and strains from deep suppurative lesions were uniformly negative.
Three-quarters of Staph. aureus strains isolated from schoolchildren with impetigo in Lancashire in 1953 and early 1954 were of one variety, which could be denned by its susceptibility to typing phages (‘type 71’).
Nearly 90 % of ‘type 71’ staphylococci, and very few others, produced a narrow, sharp zone of inhibition of Corynebacterium diphtheriae mitis on solid media.
A small number of other staphylococci, mainly non-typable or unclassifiable strains, produced a wider, hazy zone of inhibition.
The majority of the impetigo staphylococci were penicillin-resistant, and most of the resistant strains were members of ‘type 71’. However, ‘type 71’ gave rise to only a small proportion of the penicillin-resistant hospital infections occurring in the same district at the same time.
Three-quarters of the Str. pyogenes strains from impetigo lesions belonged to one of two groups of closely related serological types, one of which was rarely encountered in other situations.