In order to compare and evaluate three animal models for studying the pathogenicity of Staphylococcus epidermidis strains, three experimental animal models, namely, murine intra2venous LD50, mouse foreign body infection and rat central venous catheter (CVC) infection models were used to assess the relative virulence of two S. epidermidis strains, ATCC 12228 and 972337. The results from three animal models were comparable, indicating S. epidermidis 972337 was more viru-lent than strain ATCC 12228. The rat CVC infection model best mimicked the conditions of clinical patients with intra2venous catheters, and more information could be obtained from this model. We conclude that different in vivo models serve for dif-ferent purposes, and the rat CVC infection model is most suitable for studying specific characteristics of catheter related in-fections caused by S. epidermidis strains.

Sixteen pairs of two-component regulatory systems are identified in the genome of Staphylococcus epidermidis ATCC12228 strain, which is newly sequenced by our laboratory for Medical Molecular Virology and Chinese National Human Genome Center at Shanghai, by using bio-informatics analysis. Comparative analysis of the two-component regulatory systems in S. epidermidis and that of S. aureus and Bacillus subtilis shows that these systems may regulate some important biological functions, e.g. growth, biofilm formation, and expression of virulence factors in S. epidermidis. Two conserved domains, i.e. HATPase-c and REC domains, are found in all 16 pairs of two-component proteins. Homologous modelling analysis indicates that there are 4 similar HATPase-c domain structures of histidine kinases and 13 similar REC domain structures of response regulators, and there is one AMP-PNP binding pocket in the HATPase-c domain and three active aspartate residues in the REC domain. Preliminary experiment reveals that the bioinfor-matics analysis of the conserved domain structures in the two-component regulatory systems in S. epidermidis may provide useful information for discovery of potential drug target.