SERODIAGNOSIS OF LISTERIOSIS BASED UPON DETECTION OF ANTIBODIES AGAINST RECOMBINANT TRUNCATED FORMS OF LISTERIOLYSIN-O

Amino-terminal fragments of listeriolysin O (LLO) of 240 and 411 resid ues (fragments LLO240 and LLO411, respectively) were expressed in Esch erichia coli as fusion polypeptides with maltose-binding protein (MBP) with the aim of producing specific antigens for use in serological te sts. In Western blots (immunoblots) with crude bacterial extracts of t he fusion polypeptides, the reactivities of MBP-LLO240 and MBP-LLO411 with anti-LLO antibody (ALLO)- and anti-streptolysin O antibody (ASLO) -positive human sera were first compared with that of the entire LLO ( LLO530) also fused to MBP (MBP-LLO530). Sixteen of 17 (94.1%) ALLO-pos itive samples reacting with MBP-LLO530 also reacted with MBP-LLO411, w hereas this proportion dropped to 11 of 17 (63.7%) with MBP-LLO240. Al ternatively, 18 of 19 (94.7%) ASLO-positive samples giving an interpre table result reacted with MBP-LLO530, whereas 1 of 19 (5.3%) of these samples reacted with MBP-LLO240 or MBP-LLO411. The fusion polypeptide MBP-LLO411 was purified by maltose affinity chromatography and was fur ther evaluated as a diagnostic antigen in a Western blot assay. Twenty -one of 21 (100%) serum samples obtained from patients with listeriosi s and found to be positive for ALLO by a reference dot blot test react ed with MBP-LLO411, whereas 1 of 20 (5%) ASLO-positive serum samples a nd 1 of 100 (1%) serum samples from healthy adults were reactive. Thus , a polypeptide limited to the 411 amino-terminal residues of LLO is a specific and sensitive antigen for the detection of ALLO.