In vitro study on the antimicrobial activity of various antibiotics against clinical isolates of streptococcus pneumoniae from belgium collected during winter 1998-1999

A total of 205 isolates of Streptococcus pneumoniae obtained from 10 different centres were included in this study. The susceptibilities to penicillin, ampicillin, amoxicillin, amoxicillin/clavulanic acid, cefaclor, cefuroxime, cefotaxime, imipenem, ciprofloxacin, gemifloxacin, grepafloxacin, levofloxacin, trovafloxacin, erythromycin, clarithromycin, miocamycin, clindamycin and tetracycline were determined by a microdilution technique following NCCLS recommendations. Decreased susceptibility to penicillin was 16.1% [6.8% intermediate (0.12 - 1 μg/ mL) and 9.3% high-level (≥2 μg/mL)], cefotaxime insusceptibility (≥1 μg/mL) 12.7 %, ciprofloxacine insusceptibilty (≥2 μg/mL) 15.6% with 1.5 % of high level resistance (≥4 μg/mL), erythromycin insusceptibility (≥0.5 μg/mL) 36.1% and tetracycline insusceptibility (≥4 μg/mL) 22.9 %. Decreased susceptibility to cefotaxime was found in 78.8%) of the penicillin-insusceptible isolates. No decreased susceptibility was found for gemifloxacin (≥0.5 μg/mL) and trovafloxacin (≥1 μg/mL). Compared to the 1996-1997 surveillance, penicillin, cefotaxime and erythromycin insusceptibility rose by 3.8 %, 5.2 % and 5.0 % respectively, while tetracycline insusceptibility decreased with 8.2 %. MICs of all β-lactams rose with those of penicillin for penicillin-insusceptible isolates. Amoxicillin ± clavulanate, cefotaxime and imipenem were generally 1, 1 and 5 doubling dilutions respectively more potent than penicillin on these isolates. Penicillin, ampicillin and cefuroxime were equally active while cefaclor was generally 5 dilutions less potent. Most penicillin-insusceptible isolates remained fully susceptible to amoxicillin ± clavulanate and imipenem. The penicillin-insusceptible isolates were 36.4 %, 27.3 % and 3.0 % co-insusceptible to erythromycin, erythromycin plus tetracycline and tetracycline respectively. A subpopulation of 52 isolates obtained from children aged < 3 years was also studied. Compared to the other isolates we found a statistically significant increase in insusceptibility for penicillin, cefaclor, cefuroxime, erythromycin, clarithromycin and tetracycline while a significant decrease was found for ciprofloxacin.