Summer Research Description: The number of individuals infected with Acinetobacter baumannii, a multidrug resistant bacterium, is increasing. 50% of patients with A. baumannii blood infection (sepsis) will die. Other than the antibiotic colistin, there are no current treatments for septic patients infected with A. baumannii. We aim to develop an adjuvant therapy where fluorescent polystyrene iron oxide composite microspheres decorated with colistin enable magnet extraction of A. baumannii from fluid. A facile protocol was developed to conjugate colistin, or other aminated molecules, to the surface of the polystyrene microspheres. Through carbodiimide chemistry, an EDC reaction was carried out to crosslink the carboxylic acids on the surface of the microspheres to the primary amines associated with the colistin. Fourier transform infrared spectroscopy (FT-IR), dynamic light scattering (DLS) and transmission electron microscopy (TEM) confirmed the conjugation of colistin to the microspheres. Varying concentrations of colistinated microspheres were used to both characterize bacterial toxicity and optimize the magnetic separation of A. baumannii. An alamarBlue® assay and flow cytometry were used to quantify the capture efficiency as a function of microsphere concentration. Capture efficiencies greater than 70% were achieved.