[Sensitivity surveillance of Haemophilus influenzae isolates for several antibiotics in Gifu Prefecture (2006)].

We investigated the susceptibility to antibacterials of 194 strains of Haemophilus influenzae isolated from medical facilities in Gifu prefecture between 2005 and 2006, and compared these results with those of 280 strains of H. influenzae isolated between 1999 and 2000. Additionally, the strains that had been separated between 2005 and 2006 were examined for beta-lactamase (BL) production, the mutation of ftsI gene coding for PBP3, the bla gene coding for TEM type of BL and the serotype. Referring to the CLSI breakpoint, H. influenzae strains were classified into the following categories: (1) beta-lactamase-negative ampicillin-susceptible (BLNAS) strains, which showed BL negative, ampicillin (ABPC) and ampicillin/sulbactam (ABPC/SBT)-MIC < or = microg/ml, (2) beta-lactamase producing ampicillin-resistant (BLPAR) strains, which showed BL producing and ABPC/SBT-MIC < or =2 microg/ml, (3) beta-lactamase-negative ampicillin-resistant (BLNAR) strains, which showed BL negative, ABPC and ABPC/SBT-MIC > or =2 microg/ml, (4) beta-lactamase-producing amoxicillin/clavulanic acid-resistant (BLPACR) strains, which showed BL producing and ABPC/SBT-MIC > or =4 microg/ml. The prevalence of each resistance class were 71.8% for BLNAS, 7.9% for BLPAR, 19.6% for BLNAR and 0.7% for BLPACR in strains isolated between 1999 and 2000. But they were 38.1% for BLNAS, 4.6% for BLPAR, 54.6% for BLNAR and 2.6% for BLPACR in strains isolated between 2005 and 2006, indicating that the percentage of BLNAS and BLPAR decreased and that of BLNAR and BLPACR increased from 1999-2000 to 2005-2006. On the basis of ftsI substitutions and having bla gene, the strains isolated between 2005 and 2006 were classified into the following distribution: 24.2% for gBLNAS, 4.1% for gBLPAR, 10.8% for gLow-BLNAR, 57.7% for gBLNAR, and 3.1% for gBLPACR-II. Ratio of BLNAR belonging to gBLNAR and gLow-BLNAR based on the ftsI substitutions and having bla gene was higher than that based on the susceptibility pattern. The MIC50 and MIC90 for those strains isolated between 2005 and 2006 were as follows; 0.0039, 0.0156 microg/ml for garenoxacin, 0.0078, 0.0156 microg/ml for tosufloxacin and ciprofloxacin, 0.0156, 0.0313 microg/ml for levofloxacin, 0.0313, 0.0625 microg/ml for norfloxacin, 0.0625, 0.25 microg/ml for piperacillin/ tazobactam, 0.0625, 0.5 microg/ml for piperacillin, 0.125, 0.25 microg/ml for ceftriaxone and cefditoren, 0.5, 1 microg/ml for cefteram, chloramphenicol and tetracycline, 0.5, 2 microg/ml for cefotaxime, 2, 8 microg/ml for ampicillin, ampicillin/sulbactam and cefdinir. In comparison with the values for the strains isolated between 1999 and 2000, the MIC50s of beta-lactam for the strains isolated between 2005 and 2006 increased over 4 times.