IN-VITRO ACTIVITIES OF 8 MACROLIDE ANTIBIOTICS AND RP-59500 (QUINUPRISTIN-DALFOPRISTIN) AGAINST VIRIDANS GROUP STREPTOCOCCI ISOLATED FROM BLOOD OF NEUTROPENIC CANCER-PATIENTS

From January 1988 to December 1994, 66 consecutive blood culture isola tes of viridans group streptococci collected from febrile neutropenic cancer patients were tested for antimicrobial susceptibilities by the agar dilution method, The antibiotics studied were erythromycin, clari thromycin, roxithromycin, dirithromycin, azithromycin, josamycin, diac etyl-midecamycin, spiramycin, and quinupristin-dalfopristin. A total o f 26 (39.4%) strains were resistant to erythromycin with an MIC range of 0.5 to >128 mu g/ml. The strains were classified into three groups according to their penicillin susceptibility: 42 (63.6%) were suscepti ble, 8 (12.1%) were intermediately resistant, and 16 (24.3%) were high ly resistant, The percentages of erythromycin-resistant strains in eac h group were 23.8, 62.5, and 68.8%, respectively. Streptococcus mitis was the species most frequently isolated (83.3%) and showed the highes t rates of penicillin (40%) and erythromycin (13.6%) resistance, MICs of all macrolide antibiotics tested and of quinupristin-dalfopristin w ere higher for penicillin-resistant strains than for penicillin-suscep tible strains. All macrolide antibiotics tested had cross resistance t o erythromycin, which was not observed with quinupristin-dalfopristin. Our study shows a high rate of macrolide resistance among viridans gr oup streptococci isolated from blood samples of neutropenic cancer pat ients, especially those infected with penicillin-resistant strains. Th ese findings make macrolides unsuitable prophylactic agents against vi ridans group streptococcal bacteremia in this patient population.