Molecular relationships and antimicrobial susceptibilities of viridans group streptococci isolated from blood of neutropenic cancer patients

From January 1995 to May 1998, 57 episodes of bacteremia due to viridans gr oup streptococci were identified in 50 febrile neutropenic patients with he matologic malignancies. Four patients experienced two separate episodes of streptococcal bacteremia, and one patient had four separate episodes of str eptococcal bacteremia. Strains were identified to species level as Streptoc occus mitis (n = 37), Streptococcus oralis (n = 19), and Streptococcus sali varius (n = 1). Epidemiologic relatedness of these strains was studied by u sing PCR-based fingerprinting with M13 and ERIC-2 primers and pulsed-field gel electrophoresis with restriction enzyme SmaI. All strains that were iso lated from different patients exhibited unique fingerprint patterns, thus s uggesting that viridans group streptococcal bacteremia usually derives from an endogenous source. Cross-transmission of strains between patients could not be established. Four S. mitis isolates recovered during four separate bacteremic episodes in a single patient had identical fingerprint patterns. Susceptibility testing was carried out by broth microdilution technique ac cording to National Committee for Clinical Laboratory Standards guidelines. The MICs at which 90% of the isolates are inhibited were (in milligrams pe r liter) as follows: 0.5 (penicillin), 0.5 (amoxicillin), 0.25 (cefotaxime) , 2 (chloramphenicol), 4 (erythromycin), 0.5 (clindamycin), greater than or equal to 32 (tetracycline), greater than or equal to 32 (trimethoprim-sulf amethoxazole), 4 (ciprofloxacin), 0.5 (sparfloxacin), 0.5 (vancomycin), 0.2 5 (teicoplanin), and 1 (quinupristin-dalfopristin). High-level penicillin r esistance (MIC, greater than or equal to 4 mg/liter) was found in one isola te only, but intermediate penicillin resistance was noted in 11 isolates (1 9%). Resistance rates to other drugs were as follows: 7% (amoxicillin), 4% (cefotaxime), 4% (chloramphenicol), 32% (erythromycin), 9% (clindamycin), 3 9% (tetracycline), 68% (trimethoprim-sulfamethoxazole),23% (ciprofloxacin), 0% (sparfloxacin), 0% (vancomycin), 0% (teicoplanin), and 0% (quinupristin -dalfopristin).