E-035. Antibodies against Enterococcal LTA Are Broadly Cross-Reactive and Opsonic to many Gram-Positive Bacteria
Objectives: Antibiotic treatment options against gram-positive pathogens like enteroccci and staphylocci are limited and immunotherapy may be a valuable addition to antimicrobial treatment. We have shown previously that LTA is the target of opsonic antibodies against Enterococcus faecalis 12030. Since LTA from different gram-positive bacteria share structural similarities we wanted to evaluate the serodiversity of antibodies specific to LTA against different enterococcal strains and other gram-positive bacteria. Methods: Lipoteichoic acid from gram-positive bacteria was prepared using hydrophobic interaction chromatography. LTA-specific antibodies were quantified by ELISA. An opsonophagocytic assay was used to assess killing mediated by rabbit anti-LTA. Protection of rabbit anti-LTA antiserum was evaluated in a mouse bacteremia model after passive immunization by comparison of quantitative bacterial counts in the peripheral blood 48 h after i.v. challenge. Results: Anti-LTA was cross-reactive with LTA isolated from heterologous E. faecalis serotypes, E. faecium and LTA from S. aureus, S. epidermidis and group B streptococci (GBS) as assessed by ELISA. Rabbit anti-LTA promoted opsonophagocytic killing of E. faecalis strains of the CPS-A and CPS-B (serotyping system of Hufnagel et al.) and some E. faeciums strains. Anti-LTA serum was also opsonic to S. aureus SA113, S. epidermidis M187 and GBS NEM316. Opsonophagocytic killing was inhibited by preincubation of anti-LTA serum with LTA isolated from E. faecalis 12030. Mice passively immunized with rabbit anti-LTA and challenged i.v. with E. faecalis 12030 had significantly lower bacterial counts. Passive immunisation with anti-LTA also protected against some of the non-enterococcal gram-positive bacteria tested. Conclusions: Antibodies specific to LTA bind not only to enterococcal LTA, but also to LTA from other gram-positive bacteria and mediate opsonophagocytic killing of many enterococcal strains as well as other gram-positive bacteria including S. aureus. This cell wall polymer may be a promising vaccine candidate.