Scientists from China and the UK have discovered that a leaf-cutting ant, Acromyrmex octospinosus, uses a cocktail of antibiotics to keep its fungus gardens neat. Among these antibiotics, which are produced by bacteria living on the ants, is a novel compound that could be used to treat fungal infections. The study, published in the journal Biomed Central (BMC) Biology, is the first to demonstrate that a single ant colony uses multiple antibiotics.

Attine ants cultivate the fungus Leucoagaricus gongylophorus, creating a rich growth medium out of chewed-up leaves and keeping it free of weeds. In return, the fungus serves as the ants' main food source. The well-studied attine ant Acromyrmex octospinosus, native to South and Central America, enjoys a mutually beneficial relationship with a variety of bacteria that produce antibiotics, which they use as weed killer.

In the current study, the researchers asked whether the ants have co-evolved with weed-killing bacteria, or whether they actually sample bacteria from the soil and select those species that make the most useful antibiotics.

The team of the University of East Anglia in the UK found that a species of Streptomyces which produces the well-known fungicide candicidin is most probably collected by the ants. But in the same colony they found that a species of Pseudonocardia, which produces a novel antifungal, most probably co-evolved with the ant. The combination of co-evolved and collected bacteria provides the ants with a powerful collection of weed killers, allowing them to keep their food source safe from invaders.

The findings, published in the journal Biomed Central (BMC) Biology, are particularly important in light of the rising number of multi-drug-resistant infections in humans. The use of multiple antibiotics by the ants shows that these tiny creatures, which appeared on the scene between 8 and 12 million years ago, evolved both agriculture and natural antibiotic 'combination therapy' well before humans.