New antibiotic candidate identified in human body

Scientists have found compounds in the human body with potent antimicrobial effects, that may lead to the development of new drugs and help leverage mankind's fight against superbugs.

The human body produces many antimicrobial peptides that help the immune system fend off infection. Scientists are hoping to harness these peptides as potential antibiotics.

Researchers from Massachusetts Institute of Technology (MIT) in the US 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.

They believe that by modifying these peptides to enhance their antimicrobial activity, they may be able to develop synthetic peptides that could be used as antibiotics against drug-resistant bacteria.

"These peptides really constitute a great template for engineering. The idea now is to use synthetic biology to modify them further and make them more potent," said Cesar de la Fuente-Nunez, from MIT.

Antimicrobial peptides, which are found in nearly all living organisms, can kill many microbes, but they are typically not powerful enough to act as antibiotic drugs on their own.

Many scientists have been exploring ways to create more potent versions of these peptides, in hopes of finding new weapons to combat the growing problem posed by antibiotic-resistant bacteria.

In the study published in the journal ACS Synthetic Biology, the researchers wanted to explore whether other proteins found in the human body, outside of the previously known antimicrobial peptides, might also be able to kill bacteria.

They developed a search algorithm that analyzes databases of human protein sequences in search of similarities to known antimicrobial peptides.

"It's a data-mining approach to very easily find peptides that were previously unexplored," de la Fuente-Nunez said.

"We have patterns that we know are associated with classical antimicrobial peptides, and the search engine goes through the database and finds patterns that look similar to what we know makes up a peptide that kills bacteria," he said.

In a screen of nearly 2,000 human proteins, the algorithm identified about 800 with possible antimicrobial activity.

Researchers focused on the peptide pepsinogen, whose role is to break down proteins in food.

After pepsinogen is 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, showed up as candidates in the antimicrobial screen.

Once the researchers identified those 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.