Ined similar levels of SAK compared to lab strains and to clinical S. aureus strains from skin infection and from bacteremia with cutaneous origin. SAK expression by LS-1 spasak, which expresses SAK under the control of the protein A promoter, was about tenfold higher (Figure 1). Thus, S. aureus Xen36 is a relevant micro-organism to study the role of SAK in a skin infection model.Skin infection model Adenoviral-mediated human plasminogen expressionTo overcome the species-selectivity of SAK for huPlg, huPlg was expressed in mice through adenoviral gene transfer. Seven to 11 days after adenoviral injection, i.e. at the start of the subcutaneous infection experiment, huPlg plasma values in Adplasm injected mice were 31.6 ?15.5 g/ml in 2AP KO and 31.5 ?10.1 g/ml in 2AP WT mice. In mice injected with the control Adnull adenoviral vector, values of huPlg were below the detection level (3 g/ml). Human plasminogen remained present until the end of the experiment (27.3 ?10.0 g/ml at day 5 and 37.2 ?29.6 g/ml at day 10) (Figure 2). Hence, the expression of huPlg allowed for the selective interaction of SAK with huPlg throughout the course of the subcutaneous infection experiment.After subcutaneous inoculation with S. aureus Xen36, macroscopic lesion size was significantly larger in huPlg PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/12027669 expressing mice compared to control wild type mice (33.6 ?19.6 mm2 in WT/huPlg mice (n = 17) vs. 19.2 ?9.7 mm2 in WT/null mice (n = 12) at day 10, P < 0.01) (Figure 3A). The constitutive luciferase expression of S. aureus Xen36 also allowed for non-invasive monitoring of the spreading and density of the bacteria over time (illustrated in Figure 3C). Expression of huPlg increased both bacterial spreading (P < 0.05 on day 3, P < 0.01 on day 6 and 9) and bacterial load (P < 0.05 on day 3 and 9, P < 0.01 on day 6) 3-Bromo-2-methoxyaniline early in the course of infection (Figures 3B and 3D). Compared to wild type mice, bacterial spreading in 2AP KO mice was similar in the early stages of the infection, but was more pronounced at day 9 (P < 0.05) (Figure 3B), resulting in an increase in macroscopic lesion size at day 10 (31.8 ?20.9 mm2 in 2AP KO/null mice (n = 11) vs. 19.2 ?9.7 mm2 in WT/null mice (n = 12), P = 0.078) (Figure 3A). Bacterial density was higher in 2AP KO mice compared to wild type mice (P = 0.115 on day 6, P < 0.05 on day 9) (Figure 3D). In an additional experiment, 2AP KO or WT mice were infected with S. aureus LS-1 EP. We observed similar initial fibrin deposition in the abscess periphery in both groups at PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/21715270 day 1 (Additional file 1), consistent with a normal capacity for fibrin formation in 2AP KO plasma ex vivo (data not shown). However, at a later time point, less fibrin was observed in 2AP KO mice, as shown in Additional file 1.stra in sPeetermans et al. BMC Microbiology 2014, 14:310 http://www.biomedcentral.com/1471-2180/14/Page 3 ofhuPlg conc in murine plasma ( /ml)100 80 60 40 202AP KO mice 2AP WT micecontrolAdplasm vector S. aureus subcutaneous infection D0 D5 DFigure 4-tetrahydroisoquinoline 2-chloropyrimidine-4-carbonitrile Ethyl 3-amino-3-oxopropanoate 1-(Methylthio)butan-2-ol 2 Adenoviral-mediated human plasminogen expression. Human plasminogen (huPlg) expression in murine plasma after administration of 5 ?1010 viral particles of adenoviral vector Adplasm. Day 0 is the day of subcutaneous infection with S. aureus Xen36, 7 to 11 days after adenoviral injection. Values from Adnull injected mice 2-Amino-3-methoxypyridine are included as negative controls. The expression of huPlg during the whole course of the subcutaneous infection experiment allows the selective interaction of staphylokinase with huPlg.Th.