[Resistance to penicillin and other antimicrobials in 301 clinical isolates of Streptococcus pneumoniae]

Abstract

Background: The aim of this study was to assess the susceptibility to penicillin of Streptococcus pneumoniae clinical strains and to analyze the association between penicillin resistance and cefotaxime and cefixime activity in S. pneumoniae isolates with decreased sensitivity to penicillin.

Methods: 301 S. pneumoniae clinical strains were isolated from patients during 1995-1996. Susceptibility to penicillin, cefotaxime, cefepime, erythromycin, chloramphenicol, tetracycline, cotrimoxazole and ciprofloxacin were studied.

Results: 38.2% isolates were penicillin-susceptible and 61.8% were penicillin-resistant; 20.6% showed high-level resistance. Resistance rates to erythromycin, chloramphenicol, tetracycline, cotrimoxazole and ciprofloxacin were, respectively, 30.9, 30.2, 40.9, 66.4, and 13.3% overall, and 54.8, 54.8, 61.3, and 93.5% in the 62 strains with high-level resistance to penicillin. Strains resistant to cefotaxime and cefepime were 13.9 and 14.9%, respectively. MIC50 and MIC90 for cefotaxime and cefepime in penicillin-resistant strains were 0.5 and 1 mg/ml.

Conclusions: A high proportion of S. pneumoniae isolates showed resistance to penicillin, in agreement with other Spanish reports. Moreover, resistance to penicillin was significantly associated (p < 0.001) with resistance to erythromycin, chloramphenicol, tetracycline and cotrimoxazole, but not with ciprofloxacin. MIC50 and MIC90 for cefotaxime and cefepime were similar, and lower than those for penicillin in penicillin-resistant pneumococci strains.