Resident Bacterial Flora in the Skin of C57BL/6 Mice Housed under SPF Conditions

Research in cutaneous biology frequently involves models that use mice housed in SPF conditions. Little information is available concerning the species of bacteria that normally inhabit the skin of these mice. The aim of this study was to characterize the bacterial skin flora of mice housed under SPF conditions. Skin biopsies from C57BL/6 mice under normal and surgically prepped conditions were both cultured and analyzed by using DNA extraction and sequencing. The species isolated most commonly from culture were staphylococci. Coagulase-negative staphylococci were isolated more frequently than was Staphylococcus aureus. Molecular sequencing yielded several additional organisms not found by culture. Overall, culturing of isolates yielded 14 species of bacteria, and molecular sequencing identified another 6 species. Investigators conducting cutaneous research in mouse models should aware of the cutaneous bacterial flora present on these mice.Abbreviation: CNS, coagulase-negative staphylococci; DGGE, density gradient gel electrophoresisMice are used frequently in cutaneous biology and wound healing research. Most mice studied in skin biology are housed in SPF facilities. However, many investigators are unclear about the functional definition of SPF. SPF conditions ensure that a predefined group of known pathogenic organisms are excluded from the environment where the animals are housed. Little is known about the bacterial species inhabiting the skin of normal mice housed under SPF conditions. Because bacterial colonization or infection by microorganisms can affect the outcome of studies,¹ identifying the bacterial flora colonizing murine skin under SPF conditions is important in understanding the effect of these organisms on cutaneous research in mice.We use a mouse implant model to study skin interaction with biomaterials, with the goal of decreasing bacterial infections by restoring cutaneous barrier function.⁷ Characterizing the bacterial flora of murine skin housed under SPF conditions establishes a critical baseline for studies such as ours, in which bacterial infection plays a key role.