A scheme for the “fingerprinting” of streptococci according to their production of (P typing) and sensitivity to (S typing) bacteriocine-like inhibitory substances has been developed.

P typing of 450 β-haemolytic streptococci by their action on a set of nine standard indicator strains revealed that 80% of strains produced one or more detectable inhibitors, and that 17 different P types could be recognised. Production of some inhibitors seemed to be a property of strains of a particular serological group or type. Bacteriocine-like substances were produced by streptococci of serological groups, A, B, C, D, E, F and G.

Nine strains were selected as standard producers for S typing. These strains differed in their spectra of inhibition, but all seemed to be active only against gram-positive bacteria. One producer, a group-F streptococcus, specifically inhibited group-A streptococci.

The conditions of incubation were critical for demonstration of inhibitor production. A requirement for blood and for incubation at 32°C were important factors. None of the inhibitors was induced by ultraviolet irradiation. The observed inhibitory effects were not attributable to either hydrogen peroxide or low/H, but to the production of a variety of substances having diverse physicochemical properties and production requirements. Most of the inhibitors do not seem to be produced in liquid media.

The “fingerprinting” procedure is simple and inexpensive, and provides a reliable means of subdividing streptococcal strains that may find application as a supplement to the existing serological typing schemes.


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