IN-VITRO SUSCEPTIBILITIES OF 176 CLINICAL ISOLATES OF STREPTOCOCCUS-PNEUMONIAE TO 11 BETA-LACTAMS, ERYTHROMYCIN, AND TETRACYCLINE

One hundred seventy six consecutive, non-duplicate pneumococcal isolat es from clinical specimens collected from November 1994 through Februa ry 1995 in nine general hospitals throughout Belgium were tested for t heir in vitro susceptibilities to penicillin, ampicillin, amoxycillin with and without clavulanate, cefaclor, cefuroxime, cefonicid, cefproz il, cefpodoxime, cefotaxime, imipenem, tetracycline, and erythromycin by means of the NCCLS microdilution test. The overall rate of decrease d susceptibility to penicillin was 12.5%, including 6.3% of intermedia tely and 6.3% of fully resistant isolates. Penicillin, ampicillin amox ycillin, amoxycillin/clavulanate, cefuroxime, cefotaxime and imipenem had the highest activity on a weight basis (MIC(50) less than or equal to 0.008 mu g/ml), followed by cefpodoxime and erythromycin (MIC(50) of 0.015 mu g/ml), cefprozil and tetracycline (MIC(50) of 0.12 mu g/ml ), and eventually, cefaclor and cefonicid (MIC(50) of 0.5 mu g/ml). Ag gregate rates of susceptible plus intermediately resistant isolates at NCCLS-recommended breakpoints, i.e. overall percentages of isolates l ikely to respond to increased antibiotic doses in vivo (except for men ingitis), were 100.0% for imipenem and cefotaxime, 98.9% for amoxycill in with and without clavulanate, 93.8% for penicillin, and 90.9% for c efuroxime. Overall rates of susceptibility to erythromycin and tetracy cline amounted to 78.4% and 72.7%, respectively. MIC values of all bet a-lactams increased with those of penicillin. Ampicillin was equally a ctive as penicillin against isolates with reduced susceptibility to th e latter (MIC(90) of 2 mu g/ml); imipenem, cefotaxime, and amoxycillin with and without clavulanate however, were more active (MIC(90) 3, 1, and 1 doubling dilution, respectively, below that of penicillin), whi le cefpodoxime, cefuroxime, cefprozil, cefonicid, and cefaclor on the other hand, were less active (MIC(90), 1, 1, 2, 5, and 5 doubling dilu tions, respectively, above that of penicillin). In conclusion, the pre sent data confirm that pneumococcal resistance to penicillin has incre ased in Belgium, suggest that resistance to erythromycin may have stab ilised, and reveal an unexpectedly high rate of resistance to tetracyc line. Imipenem was the most active antibiotic tested overall, and amox ycillin with or without clavulanate the most active oral antibiotic, w ith activity almost similar to that of cefotaxime.