Surveillance of antibiotic resistance in clinical isolates of Streptococcus pneumoniae collected in Belgium during winter 2000-2001

Abstract

A total of 314 isolates of Streptococcus pneumoniae collected by 10 different laboratories were tested for their susceptibility by using a microdilution technique following NCCLS recommendations. The following antibiotics were included: penicillin, ampicillin, amoxicillin, amoxicillin/clavulanate, cefaclor, cefuroxime, cefotaxime, imipenem, ciprofloxacin, gemifloxacin, levofloxacin, erythromycin, clarithromycin, azithromycin, miocamycin, clindamycin and tetracycline. The insusceptibility rate (IR) to penicillin was 21.0% [10.8% intermediate (≥0.12 - 1μg/mL) and 10.2 % high-level (≥2 μg/mL)], to cefotaxime 7.3 % [3.5 % intermediate (μ 1μg/mL) and 3.8 % high-level (μ2 μg/ mL)], to imipenem 3.8 % [3.8 % intermediate (≥0.25 -0.5 μg/mL) and 0 % high-level (≥1μg/mL)], to ciprofloxacin 11.2 % [8.3 % intermediate (2 μg/mL) and 3.9 % high-level (≥4 μg/mL)], to erythromycin 30.3 % [3.5 % intermediate (0.5 μg/mL) and 26.8 % high-level (≥1μg/mL)] and to tetracycline 38.5 % [0.9 % intermediate (4μg/mL) and 37.6 % high-level (≥8 μg/mL)]. No decreased susceptibility was found for gemifloxacin (≥0.5 μg/mL). This compound was the most active with MIC50, MIC90 and an IR of 0.015 μg/mL, 0.03 μg/mL and 0 % respectively, followed by amoxicillin/ clavulanate, amoxicillin and imipenem (MIC50, MIC90 and IR: 0.015 μg/mL, 1 μg/mL, 1.6 %/0.015 μg/mL, 1 μg/mL, 1.9 %/0.008 μg/mL, 0.12 μg/mL, 3.8 % respectively). Compared to the 1999 surveillance, penicillin and tetracycline-insusceptibility increased with 4.9 % and 15.6% respectively, while cefotaxime, erythromycin and ciprofloxacin insusceptibility decreased with 5.4 %, 5.8 % and 4.4 % respectively. MICs of all β-lactams rose with those of penicillin for penicillin-insusceptible isolates. Imipenem, cefotaxime, amoxicillin and amoxicillin/clavulanate were generally 4, 2, 1 and 1 doubling dilutions respectively more potent than penicillin on these isolates while ampicillin, cefuroxime and cefaclor were generally 1, 2 and 4 dilutions respectively less potent. Most penicillin-insusceptible isolates remained fully susceptible to amoxicillin/clavulanate (92.4 %), amoxicillin (90.9 %) and imipenem (81.8 %). Erythromycin-tetracycline insusceptibility was the most common resistance phenotype (14.3 %). Three- and four-fold resistance was found in 12.4 %and 1.6 % respectively of the isolates. Most penicillin-insusceptible isolates were of capsular types 14 (22.7 %), 23 (21.2 %), 6 (18.2 %), 9 (13.6 %) and 19 (12.1%).