FACTORS AFFECTING THE CHAIN LENGTH OF GROUP A STREPTOCOCCI

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Abstract
Long chains of group A. streptococci induced by growth in homologous anti serum broth media were shown to rapidly fragment into short chains upon addition of acid-heat extracts or purified M-protein antigen from homologous type organisms. The chain splitting reaction showed temperature at pH optima (37C, 7.5). It would not occur if the long chains were heat killed, inhibited by sublethal concentrations of mercuric chloride, or exposed to penicillin for 60-90 minutes prior to addition of the antigen. By study of variant strains it was shown that, in general, the most virulent strains grew with the shortest mean chain length in normal-serum enriched broth. Dissociation to less virulent strains, which involved a loss of the ability to synthesize M-protein and/or capsules, was accompanied by a marked increase in mean chain length. Enrichment of broth media with normal serum resulted in a shortening of the mean chain length of all strains studied. The chain shortening effect of serum enrichment was most apparent with encapsulated strains. Loss of capsules by mutation or by unfavorable growth conditions resulted in increased mean chain length. The physical presence of the capsule was not essential for short chaining, however, since enzymatic removal of the capsule with hyaluronidase during growth did not affect chain length. The results suggest that the scission of streptococcal chains occurs by an active metabolic process, presumably enzymatic, which is inhibited by the union of specific antibody with surface antigens.