Group A streptococci express at least two surface-associated virulence factors, the antiphagocytic M protein and the antichemotactic streptococcal C5a peptidase (SCP). Preliminary evidence suggested that the biosynthesis of these two proteins is coordinately controlled and subject to simultaneous phase variation. To explore this possibility further, a series of phase-switching and phase-locked M-variants were assayed for SCP by enzyme-linked immunosorbent assay inhibition and for SCP-specific mRNA by dot blot hybridization. All Mcultures produced diminished amounts of SCP antigen and specific mRNA, whereas revertants produced quantities equivalent to those of the wild-type M' culture. A phase-locked strain that harbors a deletion in a region upstream of the M12 and SCP genes, termed the virR locus, failed to produce SCP antigen or SCP-specific transcripts. The SCP-specific transcript produced by M' bacteria was shown by Northern (RNA) blot hybridization to be 4 kilobases in size, distinguishing it from the transcript which encodes M protein. These data demonstrate that phase switching of both SCP and M12 proteins is at the transcriptional level and that expression is under the control of the upstream virR locus. We propose that the genetic determinants of these proteins and of colony morphology comprise a virulence regulon.The survival and multiplication of bacterial pathogens in a susceptible host depend on their abilities to acquire appropriate nutrients, interact with tissue receptors, and resist host defenses. A recent review (10) noted that the expression of multiple virulence determinants by gram-negative pathogens is a finely tuned process which is responsive to environmental changes and the general physiological state of the bacterial cell. It is now apparent that these virulence genes are globally controlled by a master gene which couples external stimuli to response pathways (10).The avoidance of human immunological defenses by group A streptococci is dependent on the following surface components: a diffuse hyaluronic capsule which mimics the ground substance of animal tissues (25); immunoglobulin G Fc receptors, which may disrupt recognition by antibodies (6b); a C5a peptidase which destroys chemotactic signals (23); and M protein, which interferes with the deposition of C3b opsonin to prevent phagocytic uptake (8, 9). M protein, thought to be the key determinant of virulence, has been the subject of intensive investigation. This dimeric coiled-coil molecule protrudes from the cell wall, where it both blocks the deposition of C3b opsonin and limits the interaction of bound C3b with receptors on polymorphonuclear leukocytes (8, 9). As a result, M+ streptococci are resistant to phagocytosis in the absence of type-specific M protein antibody and complement.Group A streptococcal cultures have long been recognized as genetically unstable (6,17,20). The expression of M protein on their surfaces, colony morphology, and virulence were reported to vary dramatically both in laboratory cultures (6, 17) and in st...

Specific proteolytic destruction of the human chemotaxin, C5a, is a property of group A and B streptococcal pathogens. Here we show that virulent group G streptococci from human sources also express C5a peptidase activity. The enzyme responsible for this activity is approximately the same size as and is antigenically similar to that produced by group A streptococci. On the basis of Southern hybridization analysis with an internal fragment of the group A C5a peptidase gene (scpA) as a probe, a copy of this gene was found in the genome of all group G human isolates tested. Comparison of partial restriction maps of scpA and scpG revealed significant similarity between the two genes. Group G strains isolated from dogs and cows were found to lack C5a peptidase activity and did not hybridize to the scpA-specific probe. The association of this activity with three streptococcal species suggests that elimination of phagocyte chemotactic attractants is a more universal virulence mechanism than originally anticipated.

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