FIG. 1.

Abscess formation and growth of bacteria in mice intradermally infected with MRSA. (A) Abscess formation. One to 10 days after intradermal infection of MRSA at a dose of 10⁸ CFU/mouse, abscess formation in normal mice (n = 3; open circles) and burned mice (n = 3; filled circles) was tested. The abscess volume was expressed in mm³ (length by width by height). Data are means ± standard errors of the means (SEM) of results from three different experiments. *, P < 0.01; **, P < 0.001; †, dead. (B) Numbers of MRSA in the infection site tissues. Following the same MRSA infection shown in panel A, the MRSA infection site tissues (15 by 15 mm) were excised from normal mice (n = 3; open circles) and burned mice (n = 3; filled circles) 1 to 5 days after infection. Tissues removed were homogenized, and the numbers of bacteria in these homogenates were determined using a standard colony-counting assay. Data are means ± SEM of results from three different experiments. *, P < 0.01; †,died. (C) Growth of MRSA in blood. Blood specimens were obtained from normal (n = 3; open circles) and burned (n = 3; filled circles) mice 1 to 3 days after MRSA infection. The numbers of bacteria in blood samples were determined using a standard colony-forming assay. Data are means ± SEM of results from three different experiments. *, P < 0.01; †, dead. (D, E) Amounts of TNF-α and IL-1β in the sera of normal and burned mice infected with MRSA. Serum specimens were obtained from normal (n = 3) and burned (n = 3) mice 3 days after intradermal infection with 10⁸ CFU/mouse of MRSA. Amounts of TNF-α (D) and IL-1β (E) were measured using ELISA. Data are means ± SEM of results from three different experiments. *, P < 0.01. (F) Abscess formation in mice infected with 3 different strains of Staphylococcus aureus. Normal mice were intradermally infected with 10⁸ CFU/mouse of the BAA-44 strain of MRSA (n = 3; open circles), the 33591 strain of MRSA (n = 3; filled circles), or the 29213 strain of MSSA (n = 3; open squares). The volumes of abscesses formed in these mice were measured. Data are means ± SEM of results from three different experiments.