Comparison of skin changes induced on mice by either group A type 12 or group G streptococci

Adult Swiss webster mice were injected with 3 x 10(6) colony-forming units (cfu) of group G or 2.5 x 10(6) cfu of group A streptococci at intradermal injection sites on the right and left paralumbar areas of the back. The mice were sacrificed at intervals between 4 hours and 14 days post-injection (p.i.) and full thickness biopsies of skin 10 mm in diameter encompassing the sites of injection were taken. One tissue specimen was homogenized in PBS and plated to determine the number of cfu, while another was used for histopathological studies. The number of viable group A and group G streptococci in the tissue increased to 3 x 10(9) cfu by 96 hours p.i.: after 192 hours p.i. the group A cells had declined to 2.7 x 10(6) cfu compared to 1.1 x 10(8) cfu for group G cells. No streptococci of either group were detected at 336 hours (14 days p.i.). Gross edematous lesions induced by either streptococcus group were evident on all animals at 24 hours (p.i.). Group G streptococci lesions were larger and persisted longer than lesions induced by group A. Histological examination consistently revealed more inflammation and necrosis in tissue sections from mice injected with group G streptococci.