Paolo Rossi Castelli 2 July 2020 3 min read

An irresistible antibiotic from Princeton researchers | IBSA Foundation

After many years of studies and unsuccessful attempts, the fight against the bacteria resistant to normal drugs may be at a turning point. The merit is due to a new antibiotic, SCH-79797, developed by researchers from Princeton University (USA), who described the innovative qualities of this substance in an article published in the scientific journal Cell. SCH-79797 is, in fact, capable of simultaneously attacking bacteria using two mechanisms: externally, by perforating the bacterial wall, and internally, by blocking the production of folates, essential molecules for bacteria (as well as for humans). An even more powerful and safe version was then obtained from SCH-79797 and immediately renamed Irresistin-16, which proved to be highly efficient at eradicating the family of the so-called Gram-negative bacteria. At present there are very few effective drugs to fight these microorganisms, because they are protected by a kind of armour (no new classes of Gram-negative-killing drugs have been approved in nearly 30 years). Tests with Irresistin were conducted against one of the most difficult bacteria to fight – a particular strain of Neisseria gonorrhoeae (the bacteria that causes gonorrhoea), impossible to beat with the antibiotics currently on the market (it is on the top 5 list of most dangerous bacteria that pose an urgent threat published by the Center for Disease Control and Prevention). Tested on laboratory animals, Irresistin-16 has produced excellent results.

To check if this new molecule created resistance, which is often the case unfortunately with other antibiotics (when bacteria quickly develop genetic variants that render them unresponsive to drugs), the US researchers used various methods. They attempted to measure the incidence of possible mutations, and then, as a final test, they exposed the Neisseria gonorrhoeae bacteria to Irresistin, in the lab, for 25 days. This was an enormous feat, since bacteria take about 20 minutes to generate and therefore, over such a long period of time, they had millions of chances to develop resistance – but they didn’t. This is also why the drug was named Irresistin.

“This is the first antibiotic that can target Gram-positives and Gram-negatives without resistance,” said Zemer Gitai, Professor of Biology at Princeton University and the senior author on the paper, “We are hoping it is generalizable, leading to better antibiotics — and new types of antibiotics — in the future”.

Compared to the “initial” molecule (SCH-79797), Irresistin-16 is nearly 1000 times more potent against bacteria than human cells: this is necessary, of course, for avoiding dangerous consequences (i.e. for completely reducing the risk of killing the patient before killing the infection to zero…).


Paolo Rossi Castelli

Journalist since 1983, Paolo has been dealing with scientific divulgation for years, especially in the fields of medicine and biology. He is the creator of Sportello Cancro, the site created by on oncology in collaboration with the Umberto Veronesi Foundation. He collaborated with the pages of the Science of Corriere della Sera for several years. He is the founder and director of PRC-Comunicare la scienza.