Bacterial members displayed a high degree of resistance to multiple antibiotics. The virulence potential of the 2-member communities was examined in C. elegansduring nutrient deprivation and exposure to opioids in order to mimic local conditions in the gut during critical illness. Under conditions of nutrient deprivation, the bacterial members attenuated the virulence of fungal members, leading to a “commensal lifestyle.” However, exposure to opioids led to a breakdown in this commensalism in 2 of the ultra-low-diversity communities.