Nontypeable Haemophilus influenzae isolated from intractable acute otitis media internalized into cultured human epithelial cells

Abstract

Objectives The aim of this study is to examine the internalization of nontypeable Haemophilus influenzae (NTHi) into human epithelial cells. Methods Bactericidal assay was applied to examine the effects of antibiotics against cell-adherent NTHi using HEp-2 cells. A trans-well chamber assay was applied to examine the internalization and penetration of NTHi using Detroit562 cells. Results The adherence of NTHi to HEp-2 cells was noted after 2 h of incubation. Azithromycin had a strong bactericidal effect against both cell-associated and non-adherent NTHi, while ceftriaxone did not show bactericidal effects on NTHi adhered to the HEp-2 cells. Three (60.0%) out of five NTHi isolates from the nasopharynx of children with intractable acute otitis media (AOM) internalized into and subsequently penetrated through the epithelial cells at various degrees. Azithromycin had a strong bactericidal effect against the cell-internalized NTHi, while ceftriaxone was bactericidal only against extracellular NTHi. Conclusion The potential of NTHi as the intracellular pathogen may contribute to the persistent existence of this pathogen that result in the prolonged and intractable clinical course of AOM. Azithromycin may be a therapeutically significant antibiotic for patients with prolonged respiratory tract infections due to NTHi.