Species-Specific Difference in Antimicrobial Susceptibility Among Viridans Group Streptococci

Background: Viridans group streptococci (VGS) are both commensal microbes and potential pathogens. Increasing resistance to penicillin in VGS is an ongoing issue in the clinical environment. We investigated the difference in susceptibility and resistance to penicillin among various VGS species. Methods: In total 1,448 VGS isolated from various clinical specimens were analyzed over a two-yr period. Identification and antimicrobial susceptibility test was performed by the automated VITEK 2 system (bioMerieux, France) or the Micro Scan MICroSTREP system (Siemens, Germany). Results: Among the 1,448 isolates, 412 were isolated from blood (28.4%). Streptococcus mitis group was the most frequently isolated (589 isolates, 40.7%), followed by the Streptococcus anginosus group (290 isolates, 20.0%), Streptococcus sanguinis group (179 isolates, 12.4%) and Streptococcus salivarius group (57 isolates, 3.9%). In total, 314 isolates could not be identified up to the species level. The overall non-susceptibility to penicillin was observed to be 40.0% (resistant, 11.2% and intermediately resistant, 28.8%) with uneven distribution among groups; 40.2% in Streptococcus sanguinis group (resistant, 5.0% and intermediately resistant, 35.2%), 60.3% in Streptococcus mitis group (resistant, 20.9% and intermediately resistant, 39.4%), 78.9% in Streptococcus salivarius group (resistant, 8.8% and intermediately resistant, 70.1%), and 6.2% in Streptococcus anginosus group (resistant, 1.7% and intermediately resistant, 4.5%). Conclusions: Antimicrobial resistance patterns towards penicillin show differences among various VGS; this should be considered while devising an effective antimicrobial treatment against VGS.