Oral streptococcal strains isolated from odontogenic infections and their susceptibility to antibiotics

The aim of this study was to identify at species level and to investigate the antibiotic susceptibility of oral streptococcal strains isolated from 100 pus samples collected from Romanian patients with different odontogenic infections. The isolates were identified at species level using the Rapid ID 32 STREP system and their susceptibility was testing by the Etest, against: penicillin G, ampicillin, erythromycin, clindamycin and tetracycline. For the investigation of erythromycin resistance phenotype the disk diffusion test was used. The isolates belonged to several species, with Streptococcus anginosus and Streptococcus oralis predominating. Reduced susceptibility to beta-lactam antibiotics was found only among the isolates belonging to S. mitis and S. sanguinis groups. Resistance to erythromycin was detected among all species, except for: S. constellatus, S. intermedius and S. gordonii, and the M phenotype was established, while resistance to tetracycline was detected within all species but S. gordonii. In contrast, clindamycin was fully active. As most odontogenic infections are mixed infections, often involving strictly anaerobic bacteria, which are frequently beta-lactamase producers, the association of a penicillin and a beta-lactamase inhibitor, like Amoxiclav, is recommended when the antimicrobial treatment is necessary.