Survey of the plasmid content of group A streptococci

Abstract Examination of 70 M-prototype group A streptococci showed small plasmids (2.0–2.5 MDa) to be present in strains representative of M-types 28, 57, 61, 63, 64 and 69. Identical results were obtained from M _r and restriction endonuclease analyses of a 2.2-MDa plasmid (pDN691) found in the M-type 69 strain and similar plasmids in the M57 prototype and two other independently isolated M-type 57 strains. In all four strains the presence of plasmid correlated with the production of bacteriocin-like inhibitory activity identifiable as P type 614. Similar analysis revealed a possible relationship between a 2.5-MDa plasmid in the prototype M61 and M64 strains and the production of P-type 216 inhibitory activity. A survey of 56 group A streptococci recovered in association with either rheumatic fever or nephritis failed to demonstrate plasmid DNA with the exception of 2.2-MDa plasmids in four nephritis-associated M-type 57 isolates.