Dual strategies in ant antimicrobial defences: evidence for chemical diversity and microbial specificity

The evolution of sociality provides many benefits but also increases the risk of disease transmission. In response, social insects have evolved social immune defences, including the production of antimicrobial compounds. The development of exocrine glands that secrete these antimicrobials is linked to the origins of sociality. However, it remains unclear how social insects prevent pathogens from evolving resistance to these compounds. We tested whether ants use chemically diverse and pathogen-specific antimicrobial compounds, both of which may combat antimicrobial resistance. Using solvents of varying polarity, we extracted compounds from six ant species and tested their inhibitory effects on Gram-positive bacteria, Gram-negative bacteria, and a fungal pathogen. Our results show that ants exhibit antimicrobial activity in both polar and non-polar extracts, consistent with the presence of compounds that differ in chemical properties. Inhibition also varied across microbial groups, with some species showing stronger effects against particular classes of microbes. Notably, five of the six ant species tested inhibited Candida auris, an emerging fungal pathogen of critical concern in human medicine due to its multidrug resistance. These findings suggest that social immunity in ants may be supported by both chemically diverse and microbe specific antimicrobials, which may combat antimicrobial resistance.