Background. Among strains of S. pneumoniae (pneumococci), isolated from blood or cerebrospinal fluid of 483 patients between January 2001 and October 2003 as many as 5.2 % strains were penicillin-non-susceptible. Methods and Results. Incidence of penicillin-non-susceptible S. pneumoniae (PNSP) strains was highest in children of the youngest age group (12.7 %). Cefotaxim-non-susceptibility was detected in 2.7 % of strains. Pneumococci tested were resistant to co-trimoxazol (9.9 %), tetracycline (8.9 %), chloramphenicol (4.6 %), erythromycin (2.3 %), clindamycin (1.4 %), levofloxacin (0.6 %) and rifampicin (0.2 %); none of the strains was resistant to linezolid. Comparison of the results from 1996–1999 shows a permanent occurrence of invasive PNSP strains ranging about 5 %. The PNSP strains were of 7 serotypes, with serotype 9V being the most frequent. The Czech collection of invasive pneumococcal strains is five times smaller than that of any other European country with comparable populations over the same period of time. Conclusions. Low incidence of invasive S. pneumoniae strains seems to be related to the underestimated significance of blood culturing. Valid data necessary for the safety of antibiotic therapy in terms of efficacy and prevention of resistance development cannot be obtained from some localities of the Czech Republic.

        Key words: invasive pneumococci, antibiotic resistance, serotypes.