Antibody response to defined domains on enterobacterial outer membrane proteins in healthy persons and patients with bacteraemia

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Monoclonal antibody (MAb)-based competitive enzyme immunoassays (cELISAs) were elaborated to measure antibodies against MAb-defined domains on three different enterobacterial outer membrane (OM) proteins in sera from healthy individuals (n = 30) and in paired serum samples from patients (n = 45) with bacteraemia caused by enterobacteria or by various nonenteric bacteria (n = 15). The MAb-defined domains were Hm I and Hm II on the heat-modifiable (Hm) protein, PALp I and PALp II on the peptidoglycan-associated lipoprotein (PALp), and BLp I on Braun's lipoprotein (BLp). All MAbs have shown broad cross-reactivity with and specificity for enterobacteria. Sera from healthy individuals and from patients with infections caused by nonenteric bacteria contained low levels of MAb-blocking antibodies. Bacteraemia caused by enterobacteria resulted in generation of antibodies against the MAb-defined domains in many of the patients. Thus, 40% and 69% showed a positive BLp I cELISA with the first and second serum samples, respectively. Of the second serum samples, 20-38% showed positive Hm and PALp cELISAs. The BLp I cELISA showed higher diagnostic sensitivity than the previously described indirect ELISA for IgG antibodies against E. coli 055 OM protein antigens. Assays using the MAbs as competitors showed that the patients bacteraemic with enterobacteria, also generated antibodies against other domains on the OM proteins. The cELISAs may be useful in the diagnosis and management of patients with serious infections caused by enterobacteria. In this regard, the BLp I cELISA showed the most promising results.