WEDNESDAY, Dec. 14 (HealthDay News) -- House dust mite DNA contains evidence of Bartonella and other Gram-negative species, which are the likely sources of endotoxin found in mite allergenic extracts, according to a study published in the December issue of the Journal of Allergy and Clinical Immunology.

Jay Slater, M.D., of the U.S. Food and Drug Administration, Center for Biologics Evaluation and Research in Rockville, Md., and colleagues extracted DNA from two mite species -- Dermatophagoides farinae and Dermatophagoides pteronyssinus -- and amplified the DNA encoding bacterial 16S ribosomal RNA.

The researchers found that the D. farinae DNA contained 11- to 24-fold more 16S ribosomal gene copies than the D. pteronyssinus DNA. A sequence analysis indicated the dominant presence of at least three phylogenetic clusters of Bartonella species (henselae, quintana, vinsonii, and grahamii), as well as an uncharacterized alpha-proteobacteria, from both D. farinae and D. pteronyssinus.

The authors called for further research to answer questions raised by their study. "Is there a difference in the efficacy of D. farinae and D. pteronyssinus allergenic extracts used in allergen immunotherapy?" they ask. "If so, what role does the greater amount of endotoxin in D. farinae extracts play in this difference?"

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