Identification and antimicrobial susceptibility of viridans group streptoccoci isolated from blood cultures

Viridans group streptococci (VGS) are a frequent cause of endocarditis and bacteremia that need antimicrobial therapy. The emergence of antimicrobial resistant VGS was recently reported depending on the species. The aim of the present study was to determine the antimicrobial susceptibility among VGS isolated from blood samples and to identify the species level. Seventy five isolates of VGS were identified to species level according to Facklam and Washington scheme; susceptibility test was done by agar dilution according with the NCCLS guidelines. Strains were identified as S. mitis (n = 26), S. milleri group (n = 16), S. salivarius (n = 14), S. mutans (n = 13), and S, sanguis (n = 6). Twenty-four percent of the isolates had reduced susceptibility to penicillin (MIC greater than or equal to 0,25 mug/ml). Resistance rates to other drugs were as follows: 28% erythromycin and 12% cefotaxime. Increased resistance to gentamicin and streptomycin was found in 10 (14,6%) and 9 (12%) isolates, and high-level resistance in 4 and 3 isolates respectively. Eight isolates showed simultaneous resistance to penicillin and erythromycin, and five to penicillin and gentamicin, The results of this study indicate the importance of continuous surveillance of antibiotic resistance trends in VGS.