The gut microbiota confers resistance against Salmonella Typhimurium in cockroaches by modulating innate immunity

Cockroaches exhibit unexplained intra- and interpopulation variation in susceptibility to <i>Salmonella enterica</i> serovar Typhimurium (<i>S.</i> Typhimurium) infection. Here, we show that the gut microbiota has a protective effect against colonization by ingested <i>S.</i> Typhimurium in cockroaches. We further examine two potential mechanisms for this effect, showing that commensal bacteria present in the gut do not compete with <i>S.</i> Typhimurium during growth in cockroach feces, but rather prime expression of host antimicrobial peptide genes that suppress <i>S.</i> Typhimurium infection. Lastly, we determine that neither absolute abundance of the microbiota nor its overall diversity is linked to infection susceptibility. Instead, we identify several minority bacterial taxa that exhibit interindividual variation in abundance as key indicators of infection susceptibility among genetically similar individuals. These findings illuminate the potential of cockroaches as an invertebrate model for interspecies microbial interactions and provide insight into vector-borne <i>Salmonella</i> transmission, suggesting that the microbiota of cockroaches could be targeted to reduce pathogen transmission.