Susceptibility testing of Streptococcus mitis group isolates.

BACKGROUND & OBJECTIVES Suppurative oral and maxillofacial infections are usually mixed infections due to aerobic and anaerobic bacteria, most frequently by oral streptococci and antimicrobial treatment is necessary for such infections. The aim of this study was to investigate the antimicrobial susceptibility of Streptococcus mitis group strains isolated from Romanian patients with different oral and maxillofacial infections. METHODS Eighty-five isolates belonging to S. mitis group isolated from pus samples were identified at species level by the Rapid ID 32 STREP system. The E test was used to determine the susceptibilities of the isolates to penicillin, ampicillin, cefotaxime, erythromycin, clindamycin, chloramphenicol and tetracycline. RESULTS Of the 151 samples studied, 85 isolates belonged to S. mitis group. The minimum inhibitory concentration (MIC) values (mg/l) ranged from 0.016-0.75 for penicillin, 0.016-2 for ampicillin, 0.016- 1 for cefotaxime, 0.016-4 for erythromycin, 0.016-0.047 for clindamycin, 0.5-4 for chloramphenicol and 0.047-256 for tetracycline. INTERPRETATION & CONCLUSION The low susceptibility and the resistance to some commonly used antibiotics found in this study indicated a need for a careful surveillance of the susceptibility pattern of oral streptococci isolates of clinical significance. Clindamycin and chloramphenicol might be suitable alternative agents in treatment of oral and maxillofacial infections involving penicillin-resistant bacteria and in case of patients with hypersensitivity to beta-lactam antibiotics.