4.7. Spa Typing

Protein A, which is encoded by spa gene, is a surface protein originally found in the cell wall of S. aureus and it has been used in biochemical research because of its ability to bind immunoglobulins. According to the number, characteristics, and arrangement of repeated sequences in X region, which is a highly repeated sequence in protein A, the spa typing can reliably and accurately present the polymorphism of S. aureus [52]. PCR amplification targeting spa gene with primers spa-Up and spa-Dn (Table 5) was performed for spa typing. The PCR was programmed as follows: the first denaturation at 94 °C for 5 min, denaturation at 94 °C for 30 s, annealing at 60 °C for 45 s, and an extension at 72 °C for 90 s for 30 cycles, and at last the final extension at 72 °C for 10 min. PCR products were analyzed by electrophoresis on 1.5% agarose gel. Purified amplicons were sequenced with ABI Prism 377 DNA Sequencer (PE Applied Biosystems, Foster City, CA, USA) and repetitive sequences were collected to align to Ridom spa-server (https://spaserver.ridom.de/) (accessed on 4 October 2017) in which 16150 spa types, 709 repeats, and 350761 strains are available.