Detection of Staphylococcal protein A (SpA) in culture medium for developing sortase inhibitor screening method

Staphylococcus aureus (S.aureus) is a bacteria that can cause infections disease in both of humans and animals. It has several virulence factors, most of which are toxins or enzymes that secrete to extracellular or exotoxin and can cause the disease to host. One of the virulence factors is a Staphylococcal SpA (SpA) that can be expressed at the cell wall and secreted into the culture medium by using enzyme Sortase (Srt) activity. This work studied the optimum condition for measuring the SpA in culture medium of S. aureus with anti-SpA antibody by Direct enzyme-linked immunosorbent assay (ELISA). In this study we used Methicillin-resistant S. aureus (MRSA)ATCC 43300 strain and Methicillin-sensitive S. aureus (MSSA) ATCC 25923strain which already examined that they have srtA gene by Polymerase chain reaction (PCR). The results showed that the highest SpA concentration in MRSA and MSSA were 41.79 and 63 ng/ml after 5-6 h cultivation, respectively. Moreover, MSSA treat with sortase A inhibitor show the reduction of SpA in the culture medium compare with non treatment (p< 0.05) The result may be developed as a sortase A inhibitor screening method further.