In-vitro susceptibility of group A beta-haemolytic streptococci (GABHS) to penicillin, erythromycin, clarithromycin and azithromycin in Styria, Austria

248 Strains of group A beta-haemolytic streptococci (GABHS) were tested against penicillin and the macrolide antibiotics, erythromycin, clarithromycin and azithromycin. 213 (85.9%) GABHS isolates were taken from throat swabs from patients with pharyngotonsillitis, 35 isolates (14.1%) were from other body sites or from invasive infections. The age of the patients ranged from 9 months to 89 years, 155 of the patients (62.5%) were below 10 years of age. The results of the E-test method and a disk diffusion assay were compared; to classify the phenotype of the erythromycin-resistant strains, a disk induction test was carried out. None of the 248 GABHS strains showed resistance to penicillin, whereas 53 GABHS isolates (21.4%) were resistant to the macrolide antibiotics included in the test. There were only minor discrepancies between the two testing methods. The MIC data obtained with the E-test method suggested that among the macrolides, erythromycin and clarithromycin had slightly higher antistreptococcal activity than azithromycin in vitro. 50 (94.3%) of the erythromycin-resistant GABHS showed the pattern of novel resistance (M phenotype), 2 (3.8%) strains showed inducible resistance (IR) and 1 (1.9%) strain exhibited consecutive resistance (CR).