Cockroach gut microbiota is a significant source of endotoxin, a risk factor for asthma in cockroach-infested homes

The German cockroach, an obligate indoor pest, produces potent aeroallergens whose presence, along with endotoxins, are often reported as important indoor predictors of increased risk of morbidity in sensitized asthmatic children. In our recent analysis, we found significantly higher endotoxin concentrations in household dust from cockroach-infested homes than from uninfested homes in the same communities. We also found that both female and male cockroaches excreted large amounts of endotoxin in their feces. In this study, we hypothesized that if the cockroach gut microbiota is the major source of endotoxin, then all life stages would be expected to excrete endotoxin in relation to their gut microbial abundance. Using the kinetic Limulus amebocyte lysate assay, we found high levels of endotoxin in the feces of all life stages of the cockroach. In both laboratory-maintained and recently field-collected cockroaches, adult females produced 2.5- to 3-fold more endotoxin than males, consistent with their larger body mass and greater food consumption. Nymphs produced less endotoxin than adults, but the endotoxin concentration (endotoxin per mg) was higher in nymph feces than in adult feces. We found trace amounts of endotoxin in the feces of adults with axenic guts lacking microbiota. Lastly, endotoxin in fecal residues remained stable for at least 30 days at ambient room temperature. These results reveal that cockroaches expose sensitized people to a mix of allergens that are potent asthma triggers and endotoxins that can exacerbate the allergic response. Further research is warranted to understand their combined effects on asthma sensitization and exacerbation.