unassigned: is a category A infective agent that causes bubonic, septicemic, and pneumonic plague. Notably, the acquisition of antimicrobial or multidrug resistance through natural or purposed means qualifies as a potential biothreat agent. Therefore, high-quality antibodies designed for accurate and sensitive diagnostics, and therapeutics potentiating or replacing traditional antibiotics are of utmost need for national security and public health preparedness. unassigned: Here, we describe a set of human monoclonal immunoglobulins (IgG1s) targeting fraction 1 (F1) antigen, previously derived from in vitro evolution of a phage-display library of single-chain antibodies (scFv). We extensively characterized these antibodies and their effect on bacterial and mammalian cells via: ELISA, flow cytometry, mass spectrometry, spectroscopy, and various metabolic assays. unassigned: Two of our anti-F1 IgG (αF1Ig 2 and αF1Ig 8) stood out for high production yield, specificity, and stability. These two antibodies were additionally attractive in that they displayed picomolar affinity, did not compete when binding , and retained immunoreactivity upon chemical derivatization. Most importantly, these antibodies detected <1,000 cells in sandwich ELISA, did not harm respiratory epithelial cells, induced agglutination at low concentration (350 nM), and caused apparent reduction in cell growth when radiolabeled at a nonagglutinating concentration (34 nM). unassigned: These antibodies are amenable to the development of accurate and sensitive diagnostics and immuno/radioimmunotherapeutics.