A Significant Role of Nontypeable Haemophilus influenzae in Acute Otitis Media in Bulgarian Children

Abstract Objective  We conducted a study on Haemophilus influenzae isolates recovered from children with acute otitis media (AOM). We aimed to establish the distribution of noncapsulated (also known as nontypeable Haemophilus influenzae [NTHi]) and encapsulated H. influenzae in the study population, and the antimicrobial susceptibilities of the isolates. Methods  We collected 113 nasopharyngeal swabs and 91 middle ear fluids/otorrhea specimens from patients up to 9 years of age with AOM. Of these, 26.1% ( n  = 53) were culture-positive for H. influenzae . Only one episode of AOM was included per patient. Conventional tests and rapid panel Neisseria/Haemophilus panel were used for the identification of the isolates. Detection of encapsulated and noncapsulated strains was done by polymerase chain reaction (PCR) for bexA gene. PCR-serotyping was performed for capsule types: “a” and “f.” Biotypes were assigned based on the indole, urease, and ornithine decarboxylase activity. Susceptibility testing was performed according to the criteria of European Committee on Antimicrobial Susceptibility Testing (EUCAST). Results  Capsule determination showed that 96.2% of H. influenzae isolates responsible for “mild” and “severe” AOM cases in children were NTHi. Biotype I was predominantly associated with AOM isolates. Capsule types “a” and “c” were found in two isolates. Antibiotic resistance was found in 39.6% of the isolates. The highest resistance rate was for trimethoprim-sulfamethoxazole (37.7%). About 20.7% of isolates were ampicillin-resistant: 5.6% expressed a β-lactamase, and 15.1% had a β–lactamase-negative ampicillin-resistant phenotype. Conclusion  The current prevalence rates of nonsusceptible H. influenzae to ampicillin appear to be low among AOM. NTHi is an emergent pathogen in AOM cases. Ongoing observations are needed about how NTHi colonizes, survives, and evolves into a leading causative agent of H. influenzae diseases.