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 mug/mL) and 9.3% high-level (greater than or equal to2 mug/mL)], cefotaxime insusceptibility (greater than or equal to1 mug/mL) 12.7 %, ciprofloxacine insusceptibilty (greater than or equal to2 mug/mL) 15.6 % with 1.5 % of high level resistance (greater than or equal to4 mug/mL), erythromycin insusceptibility (greater than or equal to0.5 mug/mL) 36.1 % and tetracycline insusceptibility (greater than or equal to4 mug/mL) 22.9 %. Decreased susceptibility to cefotaxime was found in 78.8 % of the penicillin-insusceptible isolates. No decreased susceptibility was found for gemifloxacin (greater than or equal to0.5 mug/mL) and trovafloxacin (greater than or equal to1 mug/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 beta -lactams rose with those of penicillin for penicillin-insusceptible isolates. Amoxicillin +/- cravulanate, 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 less than or equal to 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.