BackgroundSymbiotic bacteria in house dust mites pose a risk of immunological side effects in the clinical use of immunotherapeutic agents. In this study, we investigated the duration for which the bacterial concentration inDermatophagoides farinaecould be kept low with antibiotic treatment, and whether the allergenic properties of the mite changed under ampicillin treatment.MethodsD. farinaewas cultivated in the presence of ampicillin powder in an autoclaved medium for 6 weeks. After subsequent subcultures without ampicillin, the mites were harvested, and the extract was prepared. The amounts of bacteria, lipopolysaccharides (LPS), and two major allergens (Der f 1 and Der f 2) were measured. Human bronchial epithelial cells and mice were treated with theD. farinaeextract to assess the allergic airway inflammation.ResultsThe number of bacteria and level of LPS were reduced by 150-fold and 33-fold, respectively, at least 18 weeks after ampicillin treatment. The concentration of Der f 1 and Der f 2 remained unchanged by ampicillin treatment. The secretion of interleukin (IL)-6 and IL-8 from the human airway epithelial cells decreased when treated with the extract of ampicillin-treatedD. farinaecompared with that of ampicillin-untreatedD. farinae. A mouse asthma model was developed using ampicillin-treatedD. farinae. We observed that the level of lung function, airway inflammation, and serum-specific immunoglobulin were not different for the mouse asthma model developed using ampicillin-treatedD. farinaethan the model developed using ampicillin-untreatedD. farinae.ConclusionsWe showed that bacterial content inD. farinaewas reduced by ampicillin treatment, which was sufficient to induce allergic sensitization and an immune response. This method will be used to develop more controlled allergy immunotherapeutic agents.