The successful use of probiotics against animal diseases suggests the bacteria could be used to prevent and even treat human diseases, according to scientists from Ireland.

Presenting the work at a Society for General Microbiology meeting in the UK on 2 April, Colin Hill of University College Cork described how his team had used three animal models of disease that had human counterparts — bovine mastitis, porcine salmonellosis (a gastrointestinal disease) and listeriosis in mice (an often fatal form of food poisoning) — to demonstrate the protective effects of probiotics.

The researchers used their own probiotic preparations containing safe bacteria such as Lactobacillus species newly isolated from human volunteers. Hill said that in all three animal diseases, they research group observed a positive effect, in that the animals were "significantly protected" against infection.

The team also used probiotics to control disease in animals that were already infected. The results of these tests, said Hill, showed that administering these safe bacteria to an infected animal was as effective as the best available antibiotic therapies in eliminating the infectious agent and resolving the symptoms.

In each instance the protection was linked to a particular bacterial species, and the mechanism of action varied from direct antagonism, where the probiotic directly kills the pathogenic bacteria, to effects mediated by the host immune system.

For example, Lactobacillus salivarius UCC118 protected mice against listeriosis (a disease which can affect pregnant women) by producing an antimicrobial peptide that eliminates Listeria monocytogenes in the gut of the animal.

In another mechanism, Lactococcus lactis could be used to treat mastitis by eliciting an immune response that overwhelmed the infectious bacteria.

"We have shown that we can protect and even treat animals against pathogenic bacteria by introducing harmless bacteria at the site of the infection," said Hill. "In order to use similar strategies in preventing or treating human disease we must understand the molecular basis of their efficacy. This understanding will provide the basis for intelligent screening and selection of the most appropriate protective bacterial cultures to go forward into human trials."

He added: "It is likely that using probiotics rather than antibiotics will appeal to at-risk individuals since they are safe, non-invasive, do not create resistant bacteria and can even be administered in the form of tasty foods or beverages."