FIG. 5.

Virulence of the rsr mutant. (A) A group of six C57BL/6 mice were each injected subcutaneously with 10⁸ CFU of parent SH1000 or the rsr mutant and monitored daily. Eight days postinfection, the mice were sacrificed, and punch biopsies of the skin were done to determine bacterial load (*, P < 0.01, as determined by the Student t test) and to examine any histological differences between the mice from the parental SH1000 group (left) and the rsr mutant group (right). (B) Top, low magnification (100×) of the dermal and subdermal layers. Note the absence of the dermal layer and subcellular structures (*) in the biopsy specimen taken from a mouse infected with the rsr mutant and the presence of clusters of bacteria (arrows). Bottom, higher magnification (1,000×) of a representative bacterial cluster (right, arrow) present in the rsr mutant-infected tissue (right) and an equivalent region from the SH1000-infected tissue (left).