Viridans group streptococci in blood culture isolates in a Swedish university hospital: antibiotic susceptibility and identification of erythromycin resistance genes

One hundred and twenty-nine isolates of viridans group streptococci in blood cultures from patients with septicaemia or endocarditis isolated between 1998 and 2003 were tested for antibiotic susceptibility to penicillin, ciprofloxacin, clindamycin, dalbavancin, daptomycin, erythromycin, linezolid, tigecycline, trimethoprim/sulphamethoxazole and vancomycin. Reduced susceptibility to penicillin (minimum inhibitory concentration (MIC) ≥0.25 μg/mL) was found in 18% of the isolates, and 4% of the strains were resistant to penicillin (MIC ≥ 4.0 μg/mL). Nineteen percent of the isolates had reduced susceptibility to erythromycin (MIC ≥ 0.5 μg/mL), among which ermB and mefA were found in 40% and 80%, respectively. Strains sequenced as Streptococcus mitis by rnpB had a high degree of non-susceptibility to erythromycin (32%) and penicillin (21%). The level of penicillin resistance in this Swedish study was lower compared with studies from other countries where the antibiotic pressure might be higher than in Sweden. Susceptibility to newer antibiotics was high; all strains were susceptible to dalbavancin, daptomycin, linezolid and vancomycin.