(168a) Enzyme-Based Antimicrobial Nanoconjugates

Bacterial infections remain a major public health concern. However, broad­spectrum antibiotics largely target redundant mechanisms of bacterial survival and lead to gained resistance owing to microbial evolution. An effective weapon to fight bacterial pathogens is the naturally present lytic enzymes, which selectively target particular structures of bacterial cell wall and cause rapid cell lysis likely without triggering common resistance. Lytic enzymes, usually consisting of a catalytic domain and a cell wall binding domain (CBD), can be engineered by domain swapping for the generation of new functions. In addition, these enzymes, when immobilized onto or incorporated into nanomaterials, retain excellent bactericidal activity and stability either in solution phase or on solid surfaces. These properties make lytic enzymes promising candidates in supplementing or replacing traditional antibiotics for environmental disinfection/decontamination or as therapeutics. In this talk, three specific topics will be covered. First, various enzyme-nanoconjugates with excellent antibacterial activities against several common food-borne or hospital-acquired bacterial pathogens will be showcased, with a focus on silver nanoparticle-CBD conjugates, which selectively kill Bacillus anthracis in a mixture with B. subtilis or Staphylococcus aureus, while silver nanoparticles alone are less active and non-selective. In the second part, engineering of lytic enzymes for sensitive detection of a single bacterial species in a multi-species mixture will be described. Biotin-CBDs, streptavidin (SA), and biotinylated reporters are self-assembled into CBD-SA-reporter complexes, which enable simultaneous spectrophotometric detection of S. aureus, B. anthracis, and Listeria innocua cells in salt solution with a detection limit of >100 CFU/mL. Further modification of this system results in self-assembled CBD-SA-DNA complexes, which achieve a 1-10 CFU/mL detection limit without cross-reactivity when combined with qPCR. In the third part of this talk, the basic understanding of the functionalities of lytic enzymes in complex, non-ideal environment will be discussed. The lytic enzyme CD11, being highly active in buffer but inactive in rich growth media, efficiently kills Clostridium difficile with a decreased level of the wall teichoic acid (WTA), a bacterial cell surface glycopolymer. The low activity of lysostaphin against S. aureus in unprotonated amines is also regulated by the WTA. A possible mechanism of WTA-mediated cell resistance is proposed.