Comparison of Two Nonculture Techniques for Detection of Hemophilus influenzae in Sputum: In situ Hybridization and Immunoperoxidase Staining with Monoclonal Antibodies

Abstract

Two nonculture methods, in situ hybridization and immunoperoxidase staining with monoclonal antibodies, were compared for the detection of Hemophilus influenzae in 184 sputa. For in situ hybridization, a biotin-labeled probe of total genomic DNA of H influenzae type b was prepared that hybridizes specifically with H influenzae, H parainfluenzae, H hemolyticus, and H parahemolyticus DNA. Immunoperoxidase staining was done with monoclonal antibody 8BD9 directed against outer membrane protein P6 of H influenzae. Both techniques detected Hemophilus in sputum equally well and were superior to culture: all 30 sputum samples culture-positive for H influenzae were positive on both nonculture tests, and 13 additional positive sputum samples were detected from which Hemophilus was not cultured. The higher sensitivity of the nonculture tests was mainly attributed to culture failure because of overgrowth of H influenzae by other bacteria, especially in patients with cystic fibrosis. The immunoperoxidase staining technique appeared slightly easier and quicker to perform than the in situ hybridization test. For the in situ DNA hybridization probe, DNA can be prepared from any strain of H influenzae. The immunoperoxidase test requires monoclonal antibody 8BD9 but has a higher specificity than the hybridization technique. Both techniques can be reliably applied, especially for the detection of Hemophilus in sputum of patients with cystic fibrosis.