Our defense against bacterial infections has been put at significant risk by a decline in the discovery of new classes of antibiotics and a concurrent increase in the emergence and spread of antibiotic resistance. No class of antibiotics discovered since 1962 has yielded an approved drug for the most dangerous types of bacteria called Gram-negatives.
The first antibiotic was discovered in 1928 when Alexander Fleming found that a type of mold, Penicillium notatum, could kill bacteria. Many other antibiotics were isolated from a variety of natural sources following this breakthrough, but since these compounds are found in nature it is not surprising that bacteria have also had a chance to evolve resistance mechanisms to combat them.
Most current antibiotics target bacteria through just a few common mechanisms of action such as disrupting the cell wall, blocking production of new proteins, or inhibiting DNA replication. As a result, resistance to a single antibiotic can often have a detrimental impact on the efficacy of entire classes; this is why finding novel classes is extremely important.