Remarkably high prevalence of fts I gene mutations in Haemophilus influenzae isolates from upper respiratory tract infections in children of the Sapporo district, Japan.

Recently, the frequency of isolation of beta-lactamase-negative ampicillin resistant (BLNAR) strains of Haemophilus influenzae in Japanese children has been increasing rapidly. Drug resistance in BLNAR strains is associated with mutations of the fts I gene, which encodes penicillin-binding protein 3. In the otolaryngological field, only a few reports have been available concerning fts I gene mutations in BLNAR. We investigated the prevalence of fts I gene mutations, by polymerase chain reaction (PCR) genotyping, in H. influenzae isolates from the upper respiratory tracts of children in the Sapporo district, Japan. When the isolates were classified according to PCR genotyping, 34 (44.2%) of 77 isolates were beta-lactamase-negative ampicillin-sensitive (g-BLNAS), 8 (10.4%) were g-low-BLNAR, 30 (39.0%) were g-high-BLNAR, 2 (2.6%) were beta-lactamase-positive ampicillin-resistant (g-BLPAR), and 3 (3.9%) were beta-lactamase-positive ampicillin/clavulanic acid-resistant (g-high-BLPACR). Mutations in the fts I gene were generally parallel to ampicillin susceptibility, and were frequently observed in children who were 7 years or younger. Of the beta-lactams tested, cefditoren showed the strongest inhibition of H. influenzae isolates, and it inhibited g-BLNAR and g-BLPACR. This study revealed a remarkably high prevalence of fts I gene mutations (g-BLNAR and g-BLPACR) in our district. Furthermore, a regional difference in the prevalence of fts I gene mutations was observed even at the district level.