The saliva protein could help fight a range of infections
It raises hopes for people with diseases like HIV and cystic fibrosis, who regularly develop infections that are difficult to treat with conventional drugs.
Dr Libuse Bobek, who carried out research at the University at Buffalo School of Dental Medicine in New York, said: "There is an increasing need for new antimicrobial agents, especially antifungals.
"This is a particular problem for immuno-compromised patients, such as those with HIV/AIDS, organ transplant patients and chemotherapy patients."
So far, the work has been conducted in the laboratory and has yet to be tested on animals or humans.
The saliva chemical has been shown to kill fungal agents like candidiasis, cryptococcosis and aspergillosis that can threaten people whose immune systems are compromised.
It has also destroyed several bacteria, including E.coli and P. gingivalis, which respectively cause serious intestinal and oral infections, and S. mutans, which causes dental decay.
Welcome development
Scientists also found the chemical is active at very low concentrations and 10 micrograms per millilitre show little or no toxicity to mammalian cells.
The discovery has been welcomed by the Cystic Fibrosis Trust.
The organisation's director of research and clinical care, Dr Lorna Layward, said: "It would be good if it could lead to the production of new antimicrobial agents.
"However, this is very early research and we need to know if these new molecules are safe to use in patients.
"In cystic fibrosis, the lungs get infected with a range of different micro organisms and anything that can be found to be effective and safe to eradicate lung infections would make a significant difference to people's lives."
The Public Health Laboratory Service (PHLS) is also interested in this development.
Dr Alan Johnson from the PHLS said: "Given the increasing prevalence of strains of bacteria resistant to current antibiotics, any new drugs that show antibacterial activity are to be welcomed.
"An added attraction of the compound reported by Bobek and colleagues is that it also attacks fungi, which commonly cause infections in patients with malfunctioning immune systems."