Diversity of Staphylococcus Species Strains Based on Partial kat (Catalase) Gene Sequences and Design of a PCR-Restriction Fragment Length Polymorphism Assay for Identification and Differentiation of Coagulase-Positive Species ( S. aureus , S. delphini , S. hyicus , S. intermedius , S. pseudintermedius , and S. schleiferi subsp. coagulans )