Evaluation of targeting schemes for complement-modulating, strain-selective antimicrobial microparticles

Abstract

Here we present bifunctional microparticles that bind Escherichia coli (E. coli) bacteria via a cell membrane constituent while also activating the classical complement pathway. Carboxylated polystyrene microparticles 1 µm in diameter were functionalized through several means with nonspecific polyclonal IgG and/or a monoclonal E. coli-binding antibody to compare different targeting schemes to localize complement to a particular bacterial strain. The complement-prompting polyclonal antibody was either adsorbed to saturate the particle nonspecifically (Untargeted, UT), adsorbed nonspecifically at half-saturation in combination with the targeting antibody (Mixed Untargeted, MUT), or interspersed amongst crosslinker-monoclonal antibody pairs formed such that the antibody Fab regions project outward (MT, Mixed Targeted). Cytotoxicity of each particle type to its cognate, either complement-sensitive non-pathogenic mutant E. coli J5 and wild-type pathogenic E. coli O157:H7 was evaluated, as was targeting affinity for anti-J5 particles and J5 bacteria. Although no type provided clinically-relevant cytotoxicity, notably the MUT particles were somewhat effective against the virulent and otherwise complement-resistant O157. Orienting the targeting moiety with the MT provided no benefit against either strain, and binding frequencies were attenuated relative to the MUT for J5 bacteria. Complement-sensitive J5 was most vulnerable to UT particles. In most cases, there was a correlation between increased cytotoxicity and the extent of IgG coverage, but this effect was generally not pronounced. Additional modifications to the MUT platform to more potently stimulate complement activation and a new base material for biocompatibility could enable its use as a sensitizer to be paired with antibiotics for systemic diseases such as sepsis or candidiasis.