Antimicrobial susceptibility of 278 streptococcal blood isolates to seven antimicrobial agents.

A total of 278 streptococci isolated from blood (including 66 strains of Streptococcus pneumoniae) were tested for their MIC to penicillin G, gentamicin, rifampicin, clindamycin, erythromycin, vancomycin and teicoplanin to determine the current state of resistance among streptococci isolated from blood at a University Hospital in Copenhagen, Denmark, and thereby to assess alternative treatment for patients who are infected with a penicillin-resistant streptococcal strain or allergic to penicillin. Danish Blood Sensitivity Agar and the Etest were used. Overall, resistance to penicillin among Streptococcus mitis strains was 44.4% (37% intermediately susceptible and 7.4% resistant). As penicillin resistance in S. mitis may be an early indication of emerging penicillin resistance among other streptococcal species, this finding is a matter of concern. Except for this observation, penicillin remains the best and a safe choice for treatment of streptococcal infection. For alternative treatment when the patient is allergic to penicillin and for prophylaxis, the usual recommendation is macrolide antibiotics or clindamycin. The majority of non-enterococcal groups of streptococci remain sensitive to erthromycin and clindamycin, but the antibiotic susceptibility pattern is unpredictable without testing the isolates, so empirical therapy or prophylaxis may fail.