Identification of bacterial antigens and super antigens in synovial fluid of patients with arthritis: a cross sectional study

ABSTRACT

An accurate and prompt diagnosis of bacterial arthritis is essential for earlier treatment and a good outcome. Superantigens produced by Staph. Aureus are among the most lethal toxins. The paper objective was Identification of common bacterial antigens and S. aureus superantigens in synovial fluid [SF] of children with negative culture and direct smear for other bacteria except for S. aureus. In this cross-sectional study a total of 62 patients with a mean age of 11 +/- 3.8 years [range 5 months-16 years] with acute arthritis in pediatric and orthopedic wards of Rasoul Hospital [2008-2010] were studied. Three common bacterial antigens [e.g. S.pneumonia, H.influenza, N. meningitis] using LPA [latex particle antigen] and Staphylococcal superantigens [TSSTl; Enterotoxin A; B; C] using ELISA method [ABcam; USA] were identified in 60 adequate SF samples with negative culture and negative direct smears [for other bacteria except for S. aureus. Staphylococcal superantigens were compared with S. aureus infection [positive culture or direct smear]. Positive bacterial antigens [LPA test] were found in 4 cases including two S. Pneumonia, one N. meningitis, and one H.influenza. S.aureus was diagnosed in 7 cases including 4 positive cultures and 3 positive smears. Staphylococcal superantigens [toxins] were found in 73% of SF samples. Some cases had 2 or 3 types of toxins. S. aureus toxins were reported in 47% of culture negative SF samples. Positive TSSTl, Enterotoxin B, Enterotoxin A, and Enterotoxin C were found in 47% [n= 28], 18% [n= 10], 39% [n= 22], and 39% [n=21] of cases respectively. The most common type of superantigens was TSSTl; and Enterotoxin A was the less common type. Except for Enterotoxin A, no relation between positive S. aureus culture and positive tests for superantigens in SF was found. S. aureus has a prominent role in septic arthritis. S.aureus toxins might have a prominent role in arthritis with negative SF culture. Rapid identification of bacterial antigens [LPA] or S.aureus superantigens [toxins] are valuable for diagnosis in cases with negative cultures. We recommend usage of complementary methods [e.g. antigen detection tests] in children. Those tests are cheaper and easier in comparison with PCR as a complex and time-taking method. Identification of S. aureus superantigens in SF of all cases with negative culture, or treatment with antagonist drugs needs further clinical trial studies