Antibiotics tend to lose their efficacy over time due to the emergence and dissemination of resistance among bacterial pathogens. Strains with resistance to multiple antibiotic classes have emerged among major Gram-positive and Gram-negative species including Staphylococcus aureus, Enterococcus spp., Pseudomonas aeruginosa, Acinetobacter spp. Enterobacteriaceae, and Neisseria gonorrhoeae. With some Gram-negatives, resistance may involve most or even all the available antimicrobial options, resulting in extremely drug-resistant or totally drug-resistant phenotypes. This so-called 'antibiotic resistance crisis' has been compounded by the lagging in antibiotic discovery and development programs occurred in recent years, and is jeopardizing the essential role played by antibiotics in current medical practices. Copyright © 2014 Elsevier Ltd. All rights reserved.