Prevalence rate and antibiotic susceptibility of oral viridans group streptococci (VGS) in healthy children population

The aim of this study was to evaluated the prevalence rate of oral viridans group streptococci (VGS) and their susceptibilities to some antibiotics in healthy children. Samples of pharyngeal swabs and supragingival dental plaques for microbiological studies were collected from 206 healthy children, aged 4-18 years. Additionally, 75 samples of carious lesions from children with dental caries were included. The streptococci were isolated and identified using standard methods and commercial identification kits. For performance of antibacterial susceptibility testing of VGS strains disk diffusion and/or breakpoints procedures were used according to NCCLS standards and criteria. A total of 425 VGS strains were tested against penicillin, ampicillin, erythromycin, clindamycin, tetracycline, doxycycline, ciprofloxacin and vancomycin. A total of 239 VGS strains belonging to 8 species from pharyngeal swabs of 192 (93.2%) children were isolated. VGS strains from supragingival plaques were isolated in 149 (72.3%) healthy children (p < 0.05), and from carious lesions in 37 (49.3%) children with dental caries. VGS strains of S. mitis species were isolated most frequently from 4-5 year old as compared to 12 and 18 year old children (p < 0.05), while S. vestibularis strains isolated most often in 12 year old ones (p < 0.05). Among 425 VGS strains, high level of penicillin resistance (MIC > or = 2.0 mg/L) was shown in 71 (16.7%) strains, 33 (46.5%) of them belonged to S. mitis species. VGS strains were also resistant to erythromycin (23.5%), clindamycin (23.1%), tetracyclines (T-52%, DOX-16%), gentamycin (25.9%) and ciprofloxacin (55.2%). All VGS strains were vancomycin - susceptible. 1. In the oral cavities of healthy children, approximately 98% of streptococci belonged to two VGS groups, i.e. mitis and salivarius groups. Streptococci of mutans and anginosus groups were isolated sporadically (2%). 2. We observed difference in susceptibility to penicillin and other antibiotics between the various species of viridans groups streptococci. Mitis group strains (except S. pneumoniae) were more frequently penicillin-resistant (23%) in comparison to salivarius group of VGS strains (9%) (p = 0.0001).