Peptides identified as natural antibiotic

Researchers have shown for the first time in living mammals that specific peptides with known anti-microbial properties, also act as natural antibiotics.

These small portions of a protein provide the body's first line of defence against invading bacteria and keep fast-moving infections in check until the immune system can mount a full-blown attack.

The study, published by researchers at the University of California, San Diego (UCSD), School of Medicine and the VA San Diego Healthcare System, focused on peptides called cathelicidins which are found in various tissue in all mammals, including skin, lungs, intestines and circulating white blood cells. The research was conducted in mice and experimental culture systems.

Able to inhibit microbe growth in culture dishes, cathelicidins have never been shown, until now, to be natural antibiotics that play a part in mammalian innate immunity, the body's immediate, first defence against invading pathogens.

"Although we have suspected that certain anti-microbial peptides contribute to the immune system's first response in fighting infection, we have never had proof of the precise mechanism in living animals until now," said Richard Gallo, chief of the dermatology section at the VA. "Our findings show that humans and other mammals have the ability to make our own natural antibiotics."

Gallo added that a potential application of the research is development of a blood test to identify mutated versions of the gene. This might allow doctors to design specific treatment for individuals more susceptible to bacterial infections than others. Another potential application, Gallo said, is use of cathelicidins as a model to develop safer drugs to fight infections.

Victor Nizet, UCSD assistant professor of paediatrics, added that the discovery also gives researchers a new line of investigation regarding bacterial resistance.

"Overuse of pharmaceutical antibiotics often leads to bacterial resistance," he said. "The natural antibiotic we studied, however, has continued to be effective in killing certain bacteria for tens of thousands of years. With further studies of its properties and the bacterial genes that determine sensitivity or resistance, we hope to gain insight into why and how some bacteria develop resistance to antibiotics while others do not."