Conclusion: Younger children tend to harbor more resistant strains because they are exposed to these pathogens more often through contacts with siblings or attendance at day-care centers and are frequently treated with antibiotics. The high prevalence of BLNAR strains should be taken into account in the treatment of AOM in young children.
Objective: Non-beta-lactamase-producing ampicillin-resistant (BLNAR) strains with mutations in penicillin-binding protein (PBP) genes of Haemophilus influenzae have been prevalent recently among younger children.
Material and methods: We investigated mutations in the ftsI gene encoding PBP-3 of H. influenzae isolated from the nasopharynx of children with acute otitis media (AOM) using polymerase chain reaction (PCR).
Results: Strains containing the bla gene (beta-lactamase-producing ampicillin-resistant) were identified in 4.7% of cases. Strains with mutations in the ftsI gene (BLNAR) were identified in 23.3% of cases. Strains without mutations in the ftsI gene and that did not contain the bla gene (non-beta-lactamase-producing ampicillin-susceptible) were identified in 70.7% of cases. Strains with both expression of the bla gene and mutations in the ftsI gene (beta-lactamase-producing amoxicillin clavulanate-resistant) were identified in 1.3% of cases. The MICs of ampicillin against the strains evaluated in this study were 0.5-2.0 microg/ml. Cefditoren-pivoxil had the lowest MIC90 against the strains (0.06 microg/ml). Strains with mutations in the ftsI gene (BLNAR) were broadly identified among young children.