Scientists have identified a new antibiotic candidate in the human body, paving the way for developing new drugs that could be used against drug-resistant bacteria.
 

In the study, researchers from the MIT and the University of Naples Federico II in Italy found that fragments of the protein pepsinogen -- an enzyme used to digest food in the stomach, can kill bacteria such as Salmonella and E. coli. Pepsinogen breaks down proteins in food. 

After being secreted by cells that line the stomach, hydrochloric acid in the stomach mixes with pepsinogen, converting it into pepsin A, which digests proteins, and into several other small fragments. Those fragments, which previously had no known functions, work as antimicrobial candidates, the researchers explained.

For the study, detailed in the journal ACS Synthetic Biology, the team developed a search algorithm that analyses databases of human protein sequences in search of similarities to known antimicrobial peptides. In a screen of nearly 2,000 human proteins, the algorithm identified about 800 with possible antimicrobial activity. 

Once the researchers identified Pepsinogen candidates, they tested them against bacteria grown in lab dishes and found that they could kill a variety of microbes, including foodborne pathogens, such as Salmonella and E. coli, as well as others, including Pseudomonas aeruginosa, which often infects the lungs of cystic fibrosis patients. 

This effect was seen at both acidic pH, similar to that of the stomach, and neutral pH. "The human stomach is attacked by many pathogenic bacteria, so it makes sense that we would have a host defense mechanism to defend ourselves from such attacks," said Cesar de la Fuente-Nunez, postdoctoral student at the MIT. 

The researchers also tested the three pepsinogen fragments against a Pseudomonas aeruginosa skin infection in mice, and found that the peptides significantly reduced the infections. They now hope to modify these peptides to make them more effective, so that they could be potentially used as antibiotics.