Prophylactic intravenous penicillin or ampicillin administration to carriers of Streptococcus agalactiae during childbirth reduces the incidence of early neonatal invasive infections caused by these bacteria by as much as 50%. In our group of isolates of S. agalactiae from 265 neonates and 204 pregnant women neither resistance nor reduced sensitivity to these antibiotics was proved. Alternative antibiotics in case of hypersensitivity of women to penicillin are erythromycin and in particular clindamycin because of more favourable pharmacokinetic parameters. Resistance to erythromycin was found in 4.4% isolates from pregnant women with an almost double frequency of non-invasive (7.0%) as compared with invasive strains (8.5%) isolated from neonates. Strains resistant to erythromycin were with the exception of one strain also resistant to clindamycin. The majority of isolates of S. agalactiae resistant to erythromycin (65.5%) belonged to serotype V. When selecting effective prophylaxis of infections caused by S. agalactiae in neonates always effective. Erroneous results of laboratory examination which describe a sensitive strain of S. agalactiae as penicillin resistant or omission of testing exaggerated data from pregnant women on their allergy to penicillin lead unnecessarily to selection of an alternative antibiotic. It must be however emphasized that the effectiveness of erythromycin and clindamycin is not certain because of the possible occurrence of resistant strains.

        Key words: neonatal infections - Streptococcus agalactiae - antibiotic resistance.