Due to the massive use of antibiotics in agriculture, bacteria developed strategies to survive and this is causing the spread of Antibiotic Resistant Bacteria killing several hundred thousand people worldwide. In this paper, zinc oxide nanoparticles (ZnO NPs) synthesized by a sol-gel technique, are proposed as a potential solution against a variety of Gram-negative, Gram-positive and sensitive or multidrug-resistant (MDR) bacteria. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined. We found ZnO NPs were effective against Escherichia coli wild type, Escherichia coli producing carbapenemase (CRE), Klebsiella pneumoniae wild type, and Klebsiella pneumoniae producing Extended Spectrum Beta-lactamase (ESBL) wild type (SAT), Methicillin-resistant Staphylococcus aureus (MRSA) and Methicillin-sensitive Staphylococcus aureus (MSSA).