Surface proteins in the transduction of groups A and G streptococci.

Abstract

Four pairs of M+SOR+ and M-SOR- variants of group-A type-49 streptococci were compared as receptor strains in transduction of a streptomycin-resistance marker. The yield of transductants was 5-9-fold greater with the M-SOR- variants than with the corresponding M+SOR+ variants. Treatment of M+SOR+ variants of type-49 streptococci with trypsin enhanced the rate of transduction by 16-35-fold whereas trypsin treatment of corresponding M-SOR- variants resulted in minimal enhancement (5-fold or less). With trypsin treatment the numbers of transductants were approximately equal in pairs of M+SOR+ and M-SOR- variants. Enhanced transduction (10-26-fold) of streptomycin resistance was obtained by trypsin treatment of another seven M+SOR+ type-49 strains, of diverse phage subtypes and from various geographical locations. A wide range of enhancement (5-46-fold) was found in eight of nine M+ strains of group-A type-6 streptococci. With trypsin treatment, three of 10 transducible group-G strains showed enhanced transduction (10-13-fold) of a plasmid containing a determinant for erythromycin resistance. Transductional enhancement is proteolytic in nature, being enhanced by trypsin, chymotrypsin, papain, pronase and streptococcal proteinase. Although interference with phage adsorption by surface proteins would appear to be the most obvious explanation for these findings, further studies are required to define more clearly the mechanism of trypsin enhancement.