Frequent carriage of resistance mechanisms to b-lactams and biofilm formation in Haemophilus influenzae causing treatment failure and recurrent otitis media in young children

Abstract

Objectives: Non-typeable Haemophilus influenzae are a major cause of acute otitis media (AOM), including chronic and recurrent otitis in young children. The objective of this study was to determine whether non-typeable H. influenzae isolates causing these infections produce biofilms and carry resistance mechanisms to b-lactams.

Methods: A collection of 48 H. influenzae isolates was obtained by tympanocentesis or from otorrhoea samples from individual patients,3 years of age and diagnosed with recurrent or treatment failure AOM. Each isolatewas surveyed for the presence of blaTEM genes, amino acid substitutions in the transpeptidase domain of penicillinbinding protein 3 (PBP3) and biofilm formation in microtitre plates

Results: In 43 of the 48 isolates (89.6%), at least one of the three tested conditions was identified: biofilm formation (83.3%) and resistance mechanisms to b-lactams (33.3%), modifications in the transpeptidase domain of PBP3 being the most prevalent (22.9%), followed by b-lactamase production (10.4%). Additionally, 13 (27.1%) isolates had two or more of these three traits. In relation to biofilm formation, those isolates with an amoxicillin MIC ≤0.5 mg/L had higher optical density values than isolates with an amoxicillin MIC ≥1 mg/L (Mann–Whitney U-test, P¼0.048).

Conclusions: These findings suggest that the successful treatment of non-typeable H. influenzae causing chronic and recurrent AOM in young children may be compromised by the high biofilm-forming capacity of the isolates and the presence of b-lactam resistance mechanisms, particularly PBP3 mutations.