Bactericidal activities of parenteral antibiotics and genotype of penicillin-binding protein in Streptococcus pneumoniae and Haemophilus influenzae isolated from children's blood

A total of 16 isolates of Streptococcus pneumoniae and 18 isolates of Haemophilus influenzae were obtained from the blood of children admitted to the pediatric wards of hospitals in Hokkaido Kamikawa subprefecture between January 2003 and December 2005. The ages of the patients with S. pneumoniae or H. influenzae infection ranged from 2 months to 9 years and from 1 month to 4 years, respectively. The diagnoses of S. pneumoniae infection were as follows: pneumonia in 8 patients, occult bacteremia in 5 patients, and meningitis in 3 patients. The diagnoses of H. influenzae were: meningitis in 6 patients, pneumonia in 4 patients, occult bacteremia in 4 patients, epiglotitis in 2 patients, and facial cellulitis in 2 patients. Out of 16 S. pneumoniae isolates, penicillin-resistant strains with a mutation of 3 genes were observed in 7 children, and penicillin intermediate-resistant strains with a mutation of 1 or 2 genes were observed in 8 children. Out of 18 H. influenzae isolates, the β-lactamase-negative ampicillin-resistant strain with a substitution of 2 points in the ftsI gene was revealed in 2 children, the β-lactamase-negative ampicillin-resistant strain with a substitution of 1 point in the ftsI gene was observed in 4 children, the β-lactamase-positive amoxicillin/clavulanic acid-resistant strain with blaTEM-1 and ftsI with 2 substitutions in the ftsI gene was observed in 3 children, and the β-lactamase-positive ampicillin-resistant strain with blaTEM-1was not observed. The MBC90s of ampicillin, ceftriaxone, cefotaxime, meropenem, panipenem, and vancomycin against S. pneumoniae were 8 µg/ml, 1 µg/ml, 1 µg/ml 1 µg/ml, 0.25 µg/ml, and 0.5 µg/ml, respectively. Those of ampicillin, piperacillin, ceftriaxone, cefotaxime, meropenem, and panipenem against H. influenzae were >128 µg/ml, >128 µg/ml, 0.25 µg/mL, 1 µg/ml, 0.12 µg/ml, and 0.5 g/ml, respectively. It is suggest that the minimum bactricidal concentration (MBC) was dissociated from the minimum inhibitory concentration (MIC) in S. pneumoniae and H. influenzae with abnormal pbp genes.