Characterization of Staphylococcus aureus enterotoxin L

Abstract

Staphylococcus aureus causes a wide variety of diseases. Major virulence factors of this organism include enterotoxins (SEs) that cause both food poisoning and toxic shock syndrome. Recently, a novel SE, tentatively designated SEL, was identified in a pathogenicity island from a bovine mastitis isolate. The toxin had a molecular weight of 26,000 and an isoelectric point of 8.5. Recombinant SEL shared many biological activities with SEs, including superantigenicity, pyrogenicity, enhancement of endotoxin shock, and lethality in rabbits when administered in subcutaneous miniosmotic pumps, but the protein lacked emetic activity. T cells bearing the T-cell receptor beta chain variable regions 5.1, 5.2, 6.7, 16, and 22 were significantly stimulated by recombinant SEL.

FIG. 1.

Rabbit splenocyte mitogenicity of rSEL compared to that of TSST-1. Splenocytes (2 × 10⁵/well) in quadruplicate wells of a microtiter plate were stimulated for 3 days with the indicated amounts of rSEL or TSST-1, and then 1 μCi of [³H]thymidine was added to each well. Cells were then reincubated for another day, and DNA was harvested onto glass fiber filters. Counts per minute were determined by scintillation counting. Negative-control wells (neg control) contained splenocytes only.

FIG. 2.

TRBV profile of rSEL. Peripheral blood mononuclear cells from five study subjects were stimulated with either anti-CD3 (white bars), which stimulates all T cells, or rSEL (black bars), which selectively stimulates T cells dependent on the TRBVs. Cells were stained with monoclonal antibodies against listed TRBVs, and the results were evaluated by flow cytometry. The percentages of T cells expressing the listed TRBVs are shown. Results from all five study subjects are reflected in each case, except for those for TRBV 6.7, which are the averages of four of five study subjects (results for the fifth study subject were not obtained). P values were determined by using the paired Student t test (∗, P = 0.046; ∗∗, P = 0.009; ∗∗∗, P < 0.003). Error bars represent the standard errors for each data set.