The rapid emergence and spread of multi-resistant bacteria have created an urgent need for new antimicrobial agents. We report here a series of amphipathic α,α-disubstituted β-amino amide derivatives with activity against 30 multi-resistant clinical isolates of Gram-positive and Gram-negative bacteria, including isolates with extended spectrum β-lactamase - carbapenemase (ESBL-CARBA) production. A variety of halogenated aromatic side-chains were investigated to improve antimicrobial potency and minimize formation of Phase I metabolites. Net positive charge and cationic character of the derivatives had an important effect on toxicity against human cell lines. The most potent and selective derivative was the diguanidine derivative 4e with 3,5-di-brominated benzylic side-chains. Derivative 4e displayed minimum inhibitory concentrations (MIC) of 0.25-8 μg/mL against Gram-positive and Gram-negative reference strains, and 2-32 μg/mL against multi-resistant clinical isolates. Derivative 4e showed also low toxicity against human red blood cells (EC > 200 μg/mL), human hepatocyte carcinoma cells (HepG2: EC > 64 μg/mL), and human lung fibroblast cells (MRC-5: EC > 64 μg/mL). The broad-spectrum antimicrobial activity and low toxicity of diguanylated derivatives such as 4e make them attractive as lead compounds for development of novel antimicrobial drugs.