Uncovering pathogens in the soil microbiome using the Galleria mellonella virulence model

Abstract

Environmental reservoirs of disease can harbour opportunistic pathogens that are harmful to human health. Anthropogenic effects such as climate change and antimicrobial resistance are likely to cause increase exposure to, and harm from, these pathogens. It is thus vital to study these environmental reservoirs in order to be prepared appropriately and prevent these diseases from emerging or re-emerging. Studies into the prevalence and diversity of opportunistic pathogens in the environment are largely focused on water sources. Microbial communities in soil are known to harbour a diverse range of species, yet are relatively poorly understood. Studies typically screen for specific ‘indicator pathogens’, or test the virulence of individual pathogens. These methods overlook a great deal of pathogenic species that can be present. Recent advances in the Galleria mellonella model system have shown that it can be used to screen for pathogens in microbial communities taken from environmental samples. We used the G. mellonella model to screen for potentially harmful pathogens in soil microbial communities. We frequently detected high levels of virulence, suggesting that soil often harbours pathogenic species. We were subsequently able to isolate pathogens from these soils and characterise their virulence, finding most of them to be highly virulent. 16s sequencing determined that the majority of pathogens found were either Serratia liquefaciens or Providencia alcalifaciens, both of which are known human pathogens. A highly virulent Aeromonas hydrophila was also identified. AMR profiling of these isolates found lower levels of antibiotic resistance than has typically been reported from clinical isolates. This study emphasises the importance of soil as a reservoir for pathogens, and provides a glimpse at the range of potentially harmful species that it contains.