Assay of Blood and Synovial Fluid of Patients With Rheumatoid Arthritis for Staphylococcus aureus Enterotoxin D: Absence of Bacteria But Presence of Its Toxin

BACKGROUND Rheumatoid arthritis (RA) is the most common chronic inflammatory disease. The staphylococcal superantigens are considered as the causative agent of RA disease. OBJECTIVES This study aimed to assess the presence of staphylococcal enterotoxin D in synovial fluid and blood of patients with RA. PATIENTS AND METHODS A total of 120 blood and SF samples of patients with RA were studied. Bacterial culture, primer pairs design, polymerase chain reaction (PCR), and enzyme-linked immunosorbent assay (ELISA) methods have been used to assess of the staphylococcal enterotoxin D. The data were analyzed through descriptive statistics. RESULTS During this study and after sequential subcultures, only 5 bacterial strains were isolated. The results of PCR showed the presence of staphylococcal enterotoxin D gene in almost 50% of SF and also in 48.4% of blood samples of patients with RA. Similarly, the ELISA method detected staphylococcal enterotoxin D in 36.16% of SF and in 33.33% of blood of patients with RA. CONCLUSIONS The result of this study showed that a high percentage of patients with RA have shown staphylococcal enterotoxin D (superantigen D) or entD gene in SF and in blood. However, the origin of this superantigen was not clarified and no Staphylococcus aureus enterotoxin D producer was isolated. This finding indicates other role of this superantigen besides its intoxication. Therefore, staphylococcal enterotoxin D as a biomarker may provide a good model for the diagnosis and treatment of patients with RA.