Viridans group streptococci in blood culture isolates, antibiotic susceptibility and identification of resistance genes

Abstract number: p1271

Westling  K., Julander  I., Ljungman  P., Jalal  S., Nord  C.E., Wretlind  B.

Objectives: 

Viridans group streptococci (VGS) cause severe infections, in immunocompromised patients antibiotic resistance is reported.

Methods: 

Patients with VGS isolated in blood cultures from four clinics 1998–2003, Karolinska University Hospital were included in this study. Clinical data as septicaemia, haematological diseases, infective endocarditis (using Dukes criteria) were registered. Identification of the VGS species by using RNase P RNA gene (rnpB). Antibiotic susceptibility testing against ciprofloxacin, clindamycin, dalbavancin, erythromycin, linezolid, penicillin, tigecycline, TMP-SMX, vancomycin and daptomycin was performed using agar dilution method, reference values according to NCCLS 2003. Identification of ermB and mefA genes was performed in strains with a reduced susceptibility to erythromycin (MIC >= 0.5 mg/ml).

Results: 

Antibiotic susceptibility testing results from 129 VGS blood cultures isolates (except for daptomycin). A reduced susceptibility to penicillin was documented in 18% (MIC >= 0.25 mg/ml) of the isolates while resistance to penicillin (MIC >= 4.0 mg/ml) was found in 4%, all patients with haematological diseases. 6% of the strains from patients with definite or possible endocarditis had a reduced susceptibility to penicillin. A reduced susceptibility to erythromycin was found in 25/129 (19%) of the isolates, nearly all patients with haematological diseases. ErmB and mef A gene were identified in 48% (12/25) and 80% (20/25) of the isolates respectively. The strains sequenced as Streptococcus mitis had a higher degree of non-susceptibility to penicillin and erythromycin. All the isolates were susceptible to vancomycin and linezolid.

Conclusion: 

Penicillin and erythromycin resistance in VGS is primarily a problem in neutropenic haematological patients but a reduced susceptibility to penicillin exists in immunocompetent patients.