The battle with the host over microbial size

Abstract

An eponymous feature of microbes is their small size, and size affects their pathogenesis. The recognition of microbes by host factors, for example, is often dependent on the density and number of molecular interactions occurring over a limited surface area. As a consequence, certain antimicrobial substances, such as complement, appear to target particles with a larger surface area more effectively. Although microbes may inhibit these antimicrobial activities by minimizing their effective size, the host uses defenses such as agglutination by immunoglobulin to counteract this microbial evasion strategy. Some successful pathogens in turn are able to prevent immune mediated clearance by expressing virulence factors that block agglutination. Thus, microbial size is one of the battlegrounds between microbial survival and host defense.

Fig. 1

Schematic representation of the relationship between microbial size and key aspects of pathogenesis. Increased microbial size, whether by natural changes in cellular morphology (above) or via antibody-mediated agglutination (below), promotes deposition of complement component 3 (C3), complement-dependent killing, and adherence to host cells and tissues. Adapted from Dalia and Weiser (8).