Fig. 1.

Comparison of chronic, biofilm-mediated infection between C57BL/6 and BALB/c mice. (A) Percentages of C57BL/6 versus BALB/c mice still infected 7, 14, 21, 28, and 49 days after receiving an S. aureus-coated pin. The host immune response was unable to clear the infection in any C57BL/6 mice, as 100% of the mice were still infected at all time points. In contrast, 41.67%, 50.00%, and 25.00% of BALB/c mice were still infected at days 21, 28, and 49, respectively. Confocal laser scanning microscopic images are shown for pins removed at day 21 postimplantation from C57BL/6 mice receiving either sterile pins (B) or S. aureus-coated pins (C) or from BALB/c mice receiving S. aureus-coated pins (D). The pins were labeled using a FITC-labeled universal bacterial probe and a rhodamine-labeled universal eukaryotic cell probe, specific for bacterial and eukaryotic rRNAs, respectively. In contrast to the case for C57BL/6 mice, biofilm formation was not evident on the pins removed from infected BALB/c mice. Experiments were performed in triplicate (n = 5 to 8 mice per group). *, P < 0.05 for BALB/c compared to C57BL/6 mice (by Fisher's exact test).